BIRD 2.0 User's Guide

Ondrej Filip <feela@network.cz>, Pavel Machek <pavel@ucw.cz>, Martin Mares <mj@ucw.cz>, Maria Matejka <mq@jmq.cz>, Ondrej Zajicek <santiago@crfreenet.org>

1. Introduction<@@label>intro

1.1 What is BIRD <@@label>what-is-bird

The name `BIRD' is actually an acronym standing for `BIRD Internet Routing Daemon'. Let's take a closer look at the meaning of the name:

BIRD: Well, we think we have already explained that. It's an acronym standing for `BIRD Internet Routing Daemon', you remember, don't you? :-)

Internet Routing: It's a program (well, a daemon, as you are going to discover in a moment) which works as a dynamic router in an Internet type network (that is, in a network running either the IPv4 or the IPv6 protocol). Routers are devices which forward packets between interconnected networks in order to allow hosts not connected directly to the same local area network to communicate with each other. They also communicate with the other routers in the Internet to discover the topology of the network which allows them to find optimal (in terms of some metric) rules for forwarding of packets (which are called routing tables) and to adapt themselves to the changing conditions such as outages of network links, building of new connections and so on. Most of these routers are costly dedicated devices running obscure firmware which is hard to configure and not open to any changes (on the other hand, their special hardware design allows them to keep up with lots of high-speed network interfaces, better than general-purpose computer does). Fortunately, most operating systems of the UNIX family allow an ordinary computer to act as a router and forward packets belonging to the other hosts, but only according to a statically configured table.

A Routing Daemon is in UNIX terminology a non-interactive program running on background which does the dynamic part of Internet routing, that is it communicates with the other routers, calculates routing tables and sends them to the OS kernel which does the actual packet forwarding. There already exist other such routing daemons: routed (RIP only), GateD (non-free), Zebra and MRTD, but their capabilities are limited and they are relatively hard to configure and maintain.

BIRD is an Internet Routing Daemon designed to avoid all of these shortcomings, to support all the routing technology used in the today's Internet or planned to be used in near future and to have a clean extensible architecture allowing new routing protocols to be incorporated easily. Among other features, BIRD supports:

• both IPv4 and IPv6 protocols
• multiple routing tables
• the Border Gateway Protocol (BGPv4)
• the Routing Information Protocol (RIPv2, RIPng)
• the Open Shortest Path First protocol (OSPFv2, OSPFv3)
• the Babel Routing Protocol
• the Router Advertisements for IPv6 hosts
• a virtual protocol for exchange of routes between different routing tables on a single host
• a command-line interface allowing on-line control and inspection of status of the daemon
• soft reconfiguration (no need to use complex online commands to change the configuration, just edit the configuration file and notify BIRD to re-read it and it will smoothly switch itself to the new configuration, not disturbing routing protocols unless they are affected by the configuration changes)
• a powerful language for route filtering

BIRD has been developed at the Faculty of Math and Physics, Charles University, Prague, Czech Republic as a student project. It can be freely distributed under the terms of the GNU General Public License.

BIRD has been designed to work on all UNIX-like systems. It has been developed and tested under Linux 2.0 to 2.6, and then ported to FreeBSD, NetBSD and OpenBSD, porting to other systems (even non-UNIX ones) should be relatively easy due to its highly modular architecture.

BIRD 1.x supported either IPv4 or IPv6 protocol, but had to be compiled separately for each one. BIRD 2 supports both of them with a possibility of further extension. BIRD 2 supports Linux at least 3.16, FreeBSD 10, NetBSD 7.0, and OpenBSD 5.8. Anyway, it will probably work well also on older systems.

1.2 Installing BIRD <@@label>install

On a recent UNIX system with GNU development tools (GCC, binutils, m4, make) and Perl, installing BIRD should be as easy as:

        ./configure
        make
        make install
        vi /usr/local/etc/bird.conf
        bird

You can use ./configure --help to get a list of configure options. The most important ones are: --with-protocols= to produce a slightly smaller BIRD executable by configuring out routing protocols you don't use, and --prefix= to install BIRD to a place different from /usr/local.

1.3 Running BIRD <@@label>argv

You can pass several command-line options to bird:

<@@label>argv-config -c config name

use given configuration file instead of prefix/etc/bird.conf.

<@@label>argv-debug -d

enable debug messages to stderr, and run bird in foreground.

<@@label>argv-debug-file -D filename of debug log

enable debug messages to given file.

<@@label>argv-foreground -f

run bird in foreground.

<@@label>argv-group -g group

use that group ID, see the next section for details.

<@@label>argv-help -h, --help

display command-line options to bird.

<@@label>argv-local -l

look for a configuration file and a communication socket in the current working directory instead of in default system locations. However, paths specified by options -c, -s have higher priority.

<@@label>argv-parse -p

just parse the config file and exit. Return value is zero if the config file is valid, nonzero if there are some errors.

<@@label>argv-pid -P name of PID file

create a PID file with given filename.

<@@label>argv-recovery -R

apply graceful restart recovery after start.

<@@label>argv-socket -s name of communication socket

use given filename for a socket for communications with the client, default is prefix/var/run/bird.ctl.

<@@label>argv-user -u user

drop privileges and use that user ID, see the next section for details.

<@@label>argv-version --version

display bird version.

BIRD writes messages about its work to log files or syslog (according to config).

1.4 Privileges <@@label>privileges

BIRD, as a routing daemon, uses several privileged operations (like setting routing table and using raw sockets). Traditionally, BIRD is executed and runs with root privileges, which may be prone to security problems. The recommended way is to use a privilege restriction (options -u, -g). In that case BIRD is executed with root privileges, but it changes its user and group ID to an unprivileged ones, while using Linux capabilities to retain just required privileges (capabilities CAP_NET_*). Note that the control socket is created before the privileges are dropped, but the config file is read after that. The privilege restriction is not implemented in BSD port of BIRD.

An unprivileged user (as an argument to -u options) may be the user nobody, but it is suggested to use a new dedicated user account (like bird). The similar considerations apply for the group option, but there is one more condition -- the users in the same group can use birdc to control BIRD.

Finally, there is a possibility to use external tools to run BIRD in an environment with restricted privileges. This may need some configuration, but it is generally easy -- BIRD needs just the standard library, privileges to read the config file and create the control socket and the CAP_NET_* capabilities.

2. Architecture<@@label>architecture

2.1 Routing tables <@@label>routing-tables

The heart of BIRD is a routing table. BIRD has several independent routing tables; each of them contains routes of exactly one nettype (see below). There are two default tables -- master4 for IPv4 routes and master6 for IPv6 routes. Other tables must be explicitly configured.

These routing tables are not kernel forwarding tables. No forwarding is done by BIRD. If you want to forward packets using the routes in BIRD tables, you may use the Kernel protocol (see below) to synchronize them with kernel FIBs.

Every nettype defines a (kind of) primary key on routes. Every route source can supply one route for every possible primary key; new route announcement replaces the old route from the same source, keeping other routes intact. BIRD always chooses the best route for each primary key among the known routes and keeps the others as suboptimal. When the best route is retracted, BIRD re-runs the best route selection algorithm to find the current best route.

The global best route selection algorithm is (roughly) as follows:

• Preferences of the routes are compared.
• Source protocol instance preferences are compared.
• If source protocols are the same (e.g. BGP vs. BGP), the protocol's route selection algorithm is invoked.
• If source protocols are different (e.g. BGP vs. OSPF), result of the algorithm is undefined.

<@@label>dsc-table-sorted Usually, a routing table just chooses a selected route from a list of entries for one network. But if the sorted option is activated, these lists of entries are kept completely sorted (according to preference or some protocol-dependent metric). This is needed for some features of some protocols (e.g. secondary option of BGP protocol, which allows to accept not just a selected route, but the first route (in the sorted list) that is accepted by filters), but it is incompatible with some other features (e.g. deterministic med option of BGP protocol, which activates a way of choosing selected route that cannot be described using comparison and ordering). Minor advantage is that routes are shown sorted in show route, minor disadvantage is that it is slightly more computationally expensive.

2.2 Routes and network types <@@label>routes

BIRD works with several types of routes. Some of them are typical IP routes, others are better described as forwarding rules. We call them all routes, regardless of this difference.

Every route consists of several attributes (read more about them in the <@@ref>route-attributesRoute attributes section); the common for all routes are:

• IP address of router which told us about this route
• Source protocol instance
• Route preference
• Optional attributes defined by protocols

Other attributes depend on nettypes. Some of them are part of the primary key, these are marked (PK).

IPv4 and IPv6 routes<@@label>ip-routes

The traditional routes. Configuration keywords are ipv4 and ipv6.

• (PK) Route destination (IP prefix together with its length)
• Route next hops (see below)

IPv6 source-specific routes<@@label>ip-sadr-routes

The IPv6 routes containing both destination and source prefix. They are used for source-specific routing (SSR), also called source-address dependent routing (SADR), see RFC 8043. Currently limited mostly to the Babel protocol. Configuration keyword is ipv6 sadr.

• (PK) Route destination (IP prefix together with its length)
• (PK) Route source (IP prefix together with its length)
• Route next hops (see below)

VPN IPv4 and IPv6 routes<@@label>vpn-routes

Routes for IPv4 and IPv6 with VPN Route Distinguisher (RFC 4364). Configuration keywords are vpn4 and vpn6.

• (PK) Route destination (IP prefix together with its length)
• (PK) Route distinguisher (according to RFC 4364)
• Route next hops

Route Origin Authorization for IPv4 and IPv6<@@label>roa-routes

These entries can be used to validate route origination of BGP routes. A ROA entry specifies prefixes which could be originated by an AS number. Their keywords are roa4 and roa6.

• (PK) IP prefix together with its length
• (PK) Matching prefix maximal length
• (PK) AS number

Flowspec for IPv4 and IPv6<@@label>flow-routes

Flowspec rules are a form of firewall and traffic flow control rules distributed mostly via BGP. These rules may help the operators stop various network attacks in the beginning before eating up the whole bandwidth. Configuration keywords are flow4 and flow6.

• (PK) IP prefix together with its length
• (PK) Flow definition data
• Flow action (encoded internally as BGP communities according to RFC 5575)

MPLS switching rules<@@label>mpls-routes

This nettype is currently a stub before implementing more support of RFC 3031. BIRD currently does not support any label distribution protocol nor any label assignment method. Only the Kernel, Pipe and Static protocols can use MPLS tables. Configuration keyword is mpls.

• (PK) MPLS label
• Route next hops

Route next hops<@@label>route-next-hop

This is not a nettype. The route next hop is a complex attribute common for many nettypes as you can see before. Every next hop has its assigned device (either assumed from its IP address or set explicitly). It may have also an IP address and an MPLS stack (one or both independently). Maximal MPLS stack depth is set (in compile time) to 8 labels.

Every route (when eligible to have a next hop) can have more than one next hop. In that case, every next hop has also its weight.

2.3 Protocols and channels <@@label>protocols-concept

BIRD protocol is an abstract class of producers and consumers of the routes. Each protocol may run in multiple instances and bind on one side to route tables via channels, on the other side to specified listen sockets (BGP), interfaces (Babel, OSPF, RIP), APIs (Kernel, Direct), or nothing (Static, Pipe).

There are also two protocols that do not have any channels -- BFD and Device. Both of them are kind of service for other protocols.

Each protocol is connected to a routing table through a channel. Some protocols support only one channel (OSPF, RIP), some protocols support more channels (BGP, Direct). Each channel has two filters which can accept, reject and modify the routes. An export filter is applied to routes passed from the routing table to the protocol, an import filter is applied to routes in the opposite direction.

2.4 Graceful restart <@@label>graceful-restart

When BIRD is started after restart or crash, it repopulates routing tables in an uncoordinated manner, like after clean start. This may be impractical in some cases, because if the forwarding plane (i.e. kernel routing tables) remains intact, then its synchronization with BIRD would temporarily disrupt packet forwarding until protocols converge. Graceful restart is a mechanism that could help with this issue. Generally, it works by starting protocols and letting them repopulate routing tables while deferring route propagation until protocols acknowledge their convergence. Note that graceful restart behavior have to be configured for all relevant protocols and requires protocol-specific support (currently implemented for Kernel and BGP protocols), it is activated for particular boot by option -R.

Some protocols (e.g. BGP) could be restarted gracefully after both intentional outage and crash, while others (e.g. OSPF) after intentional outage only. For planned graceful restart, BIRD must be shut down by <@@ref>cli-graceful-restartgraceful restart command instead of regular <@@ref>cli-graceful-restartgraceful restart<@@ref>cli-downdown command. In this way routing neighbors are notified about planned graceful restart and routes are kept in kernel table after shutdown.

3. Configuration<@@label>config

3.1 Introduction <@@label>config-intro

BIRD is configured using a text configuration file. Upon startup, BIRD reads prefix/etc/bird.conf (unless the -c command line option is given). Configuration may be changed at user's request: if you modify the config file and then signal BIRD with SIGHUP, it will adjust to the new config. Then there's the client which allows you to talk with BIRD in an extensive way.

In the config, everything on a line after # or inside /* */ is a comment, whitespace characters are treated as a single space. If there's a variable number of options, they are grouped using the { } brackets. Each option is terminated by a ;. Configuration is case sensitive. There are two ways how to name symbols (like protocol names, filter names, constants etc.). You can either use a simple string starting with a letter (or underscore) followed by any combination of letters, numbers and underscores (e.g. R123, my_filter, bgp5) or you can enclose the name into apostrophes (') and than you can use any combination of numbers, letters, underscores, hyphens, dots and colons (e.g. '1:strange-name', '-NAME-', 'cool::name').

Here is an example of a simple config file. It enables synchronization of routing tables with OS kernel, learns network interfaces and runs RIP on all network interfaces found.

protocol kernel {
        ipv4 {
                export all;     # Default is export none
        };
        persist;                # Don't remove routes on BIRD shutdown
}

protocol device {
}

protocol rip {
        ipv4 {
                import all;
                export all;
        };
        interface "*";
}

3.2 Global options <@@label>global-opts

<@@label>opt-include include "filename";

This statement causes inclusion of a new file. The filename could also be a wildcard, in that case matching files are included in alphabetic order. The maximal depth is 8. Note that this statement can be used anywhere in the config file, even inside other options, but always on the beginning of line. In the following example, the first semicolon belongs to the include, the second to ipv6 table. If the tablename.conf contains exactly one token (the name of the table), this construction is correct:

---

ipv6 table
include "tablename.conf";;

---

<@@label>opt-log log "filename" [limit "backup"] | syslog [name name] | stderr all|{ list of classes }

Set logging of messages having the given class (either all or { error|trace [, ...] } etc.) into selected destination - a file specified as a filename string (with optional log rotation information), syslog (with optional name argument), or the stderr output.

Classes are: info, warning, error and fatal for messages about local problems, debug for debugging messages, trace when you want to know what happens in the network, remote for messages about misbehavior of remote machines, auth about authentication failures, bug for internal BIRD bugs.

Logging directly to file supports basic log rotation -- there is an optional log file limit and a backup filename, when log file reaches the limit, the current log file is renamed to the backup filename and a new log file is created.

You may specify more than one log line to establish logging to multiple destinations. Default: log everything to the system log, or to the debug output if debugging is enabled by -d/-D command-line option.

<@@label>opt-debug-protocols debug protocols all|off|{ states|routes|filters|interfaces|events|packets [, ...] }

Set global defaults of protocol debugging options. See debug in the following section. Default: off.

<@@label>opt-debug-commands debug commands number

Control logging of client connections (0 for no logging, 1 for logging of connects and disconnects, 2 and higher for logging of all client commands). Default: 0.

<@@label>opt-debug-latency debug latency switch

Activate tracking of elapsed time for internal events. Recent events could be examined using dump events command. Default: off.

<@@label>opt-debug-latency-limit debug latency limit time

If debug latency is enabled, this option allows to specify a limit for elapsed time. Events exceeding the limit are logged. Default: 1 s.

<@@label>opt-watchdog-warn watchdog warning time

Set time limit for I/O loop cycle. If one iteration took more time to complete, a warning is logged. Default: 5 s.

<@@label>opt-watchdog-timeout watchdog timeout time

Set time limit for I/O loop cycle. If the limit is breached, BIRD is killed by abort signal. The timeout has effective granularity of seconds, zero means disabled. Default: disabled (0).

<@@label>opt-mrtdump mrtdump "filename"

Set MRTdump file name. This option must be specified to allow MRTdump feature. Default: no dump file.

<@@label>opt-mrtdump-protocols mrtdump protocols all|off|{ states|messages [, ...] }

Set global defaults of MRTdump options. See mrtdump in the following section. Default: off.

<@@label>opt-filter filter name local variables{ commands }

Define a filter. You can learn more about filters in the following chapter.

<@@label>opt-function function name (parameters) local variables { commands }

Define a function. You can learn more about functions in the following chapter.

<@@label>opt-protocol protocol rip|ospf|bgp|... [name [from name2]] { protocol options }

Define a protocol instance called name (or with a name like "rip5" generated automatically if you don't specify any name). You can learn more about configuring protocols in their own chapters. When from name2 expression is used, initial protocol options are taken from protocol or template name2 You can run more than one instance of most protocols (like RIP or BGP). By default, no instances are configured.

<@@label>opt-template template rip|ospf|bgp|... [name [from name2]] { protocol options }

Define a protocol template instance called name (or with a name like "bgp1" generated automatically if you don't specify any name). Protocol templates can be used to group common options when many similarly configured protocol instances are to be defined. Protocol instances (and other templates) can use templates by using from expression and the name of the template. At the moment templates (and from expression) are not implemented for OSPF protocol.

<@@label>opt-define define constant = expression

Define a constant. You can use it later in every place you could use a value of the same type. Besides, there are some predefined numeric constants based on /etc/iproute2/rt_* files. A list of defined constants can be seen (together with other symbols) using 'show symbols' command.

<@@label>opt-attribute attribute type name

Declare a custom route attribute. You can set and get it in filters like any other route attribute. This feature is intended for marking routes in import filters for export filtering purposes instead of locally assigned BGP communities which have to be deleted in export filters.

<@@label>opt-router-id router id IPv4 address

Set BIRD's router ID. It's a world-wide unique identification of your router, usually one of router's IPv4 addresses. Default: the lowest IPv4 address of a non-loopback interface.

<@@label>opt-router-id-from router id from [-] [ "mask" ] [ prefix ] [, ...]

Set BIRD's router ID based on an IPv4 address of an interface specified by an interface pattern. See <@@ref>proto-ifaceinterface section for detailed description of interface patterns with extended clauses.

<@@label>opt-graceful-restart graceful restart wait number

During graceful restart recovery, BIRD waits for convergence of routing protocols. This option allows to specify a timeout for the recovery to prevent waiting indefinitely if some protocols cannot converge. Default: 240 seconds.

<@@label>opt-timeformat timeformat route|protocol|base|log "format1" [limit "format2"]

This option allows to specify a format of date/time used by BIRD. The first argument specifies for which purpose such format is used. route is a format used in 'show route' command output, protocol is used in 'show protocols' command output, base is used for other commands and log is used in a log file.

"format1" is a format string using strftime(3) notation (see man strftime for details). It is extended to support sub-second time part with variable precision (up to microseconds) using "%f" conversion code (e.g., "%T.%3f" is hh:mm:ss.sss time). limit and "format2" allow to specify the second format string for times in past deeper than limit seconds.

There are several shorthands: iso long is a ISO 8601 date/time format (YYYY-MM-DD hh:mm:ss) that can be also specified using "%F %T". Similarly, iso long ms and iso long us are ISO 8601 date/time formats with millisecond or microsecond precision. iso short is a variant of ISO 8601 that uses just the time format (hh:mm:ss) for near times (up to 20 hours in the past) and the date format (YYYY-MM-DD) for far times. This is a shorthand for "%T" 72000 "%F". And there are also iso short ms and iso short us high-precision variants of that.

By default, BIRD uses the iso short ms format for route and protocol times, and the iso long ms format for base and log times.

<@@label>opt-table nettype table name [sorted]

Create a new routing table. The default routing tables master4 and master6 are created implicitly, other routing tables have to be added by this command. Option sorted can be used to enable sorting of routes, see <@@ref>proto-ifaceinterface<@@ref>dsc-table-sortedsorted table description for details.

<@@label>opt-eval eval expr

Evaluates given filter expression. It is used by the developers for testing of filters.

3.3 Protocol options <@@label>protocol-opts

For each protocol instance, you can configure a bunch of options. Some of them (those described in this section) are generic, some are specific to the protocol (see sections talking about the protocols).

Several options use a switch argument. It can be either on, yes or a numeric expression with a non-zero value for the option to be enabled or off, no or a numeric expression evaluating to zero to disable it. An empty switch is equivalent to on ("silence means agreement").

<@@label>proto-disabled disabled switch

Disables the protocol. You can change the disable/enable status from the command line interface without needing to touch the configuration. Disabled protocols are not activated. Default: protocol is enabled.

<@@label>proto-debug debug all|off|{ states|routes|filters|interfaces|events|packets [, ...] }

Set protocol debugging options. If asked, each protocol is capable of writing trace messages about its work to the log (with category trace). You can either request printing of all trace messages or only of the types selected: states for protocol state changes (protocol going up, down, starting, stopping etc.), routes for routes exchanged with the routing table, filters for details on route filtering, interfaces for interface change events sent to the protocol, events for events internal to the protocol and packets for packets sent and received by the protocol. Default: off.

<@@label>proto-mrtdump mrtdump all|off|{ states|messages [, ...] }

Set protocol MRTdump flags. MRTdump is a standard binary format for logging information from routing protocols and daemons. These flags control what kind of information is logged from the protocol to the MRTdump file (which must be specified by global mrtdump option, see the previous section). Although these flags are similar to flags of debug option, their meaning is different and protocol-specific. For BGP protocol, states logs BGP state changes and messages logs received BGP messages. Other protocols does not support MRTdump yet.

<@@label>proto-router-id router id IPv4 address

This option can be used to override global router id for a given protocol. Default: uses global router id.

<@@label>proto-description description "text"

This is an optional description of the protocol. It is displayed as a part of the output of 'show protocols all' command.

<@@label>proto-vrf vrf "text"|default

Associate the protocol with specific VRF. The protocol will be restricted to interfaces assigned to the VRF and will use sockets bound to the VRF. A corresponding VRF interface must exist on OS level. For kernel protocol, an appropriate table still must be explicitly selected by table option.

By selecting default, the protocol is associated with the default VRF; i.e., it will be restricted to interfaces not assigned to any regular VRF. That is different from not specifying vrf at all, in which case the protocol may use any interface regardless of its VRF status.

Note that for proper VRF support it is necessary to use Linux kernel version at least 4.14, older versions have limited VRF implementation. Before Linux kernel 5.0, a socket bound to a port in default VRF collide with others in regular VRFs. In BGP, this can be avoided by using <@@ref>bgp-strict-bindstrict bind option.

<@@label>proto-channel channel name [{channel config}]

Every channel must be explicitly stated. See the protocol-specific configuration for the list of supported channel names. See the <@@ref>bgp-strict-bindstrict bind<@@ref>channel-optschannel configuration section for channel definition.

There are several options that give sense only with certain protocols:

<@@label>proto-iface interface [-] [ "mask" ] [ prefix ] [, ...] [ { option; [...] } ]

Specifies a set of interfaces on which the protocol is activated with given interface-specific options. A set of interfaces specified by one interface option is described using an interface pattern. The interface pattern consists of a sequence of clauses (separated by commas), each clause is a mask specified as a shell-like pattern. Interfaces are matched by their name.

An interface matches the pattern if it matches any of its clauses. If the clause begins with -, matching interfaces are excluded. Patterns are processed left-to-right, thus interface "eth0", -"eth*", "*"; means eth0 and all non-ethernets.

Some protocols (namely OSPFv2 and Direct) support extended clauses that may contain a mask, a prefix, or both of them. An interface matches such clause if its name matches the mask (if specified) and its address matches the prefix (if specified). Extended clauses are used when the protocol handles multiple addresses on an interface independently.

An interface option can be used more times with different interface-specific options, in that case for given interface the first matching interface option is used.

This option is allowed in Babel, BFD, Device, Direct, OSPF, RAdv and RIP protocols. In OSPF protocol it is used in the area subsection.

Default: none.

Examples:

interface "*" { type broadcast; }; - start the protocol on all interfaces with type broadcast option.

interface "eth1", "eth4", "eth5" { type ptp; }; - start the protocol on enumerated interfaces with type ptp option.

interface -192.168.1.0/24, 192.168.0.0/16; - start the protocol on all interfaces that have address from 192.168.0.0/16, but not from 192.168.1.0/24.

interface "eth*" 192.168.1.0/24; - start the protocol on all ethernet interfaces that have address from 192.168.1.0/24.

<@@label>proto-tx-class tx class|dscp num

This option specifies the value of ToS/DS/Class field in IP headers of the outgoing protocol packets. This may affect how the protocol packets are processed by the network relative to the other network traffic. With class keyword, the value (0-255) is used for the whole ToS/Class octet (but two bits reserved for ECN are ignored). With dscp keyword, the value (0-63) is used just for the DS field in the octet. Default value is 0xc0 (DSCP 0x30 - CS6).

<@@label>proto-tx-priority tx priority num

This option specifies the local packet priority. This may affect how the protocol packets are processed in the local TX queues. This option is Linux specific. Default value is 7 (highest priority, privileged traffic).

<@@label>proto-pass password "password" [ { password options } ]

Specifies a password that can be used by the protocol as a shared secret key. Password option can be used more times to specify more passwords. If more passwords are specified, it is a protocol-dependent decision which one is really used. Specifying passwords does not mean that authentication is enabled, authentication can be enabled by separate, protocol-dependent authentication option.

This option is allowed in BFD, OSPF and RIP protocols. BGP has also password option, but it is slightly different and described separately. Default: none.

Password option can contain section with some (not necessary all) password sub-options:

<@@label>proto-pass-id id num

ID of the password, (1-255). If it is not used, BIRD will choose ID based on an order of the password item in the interface. For example, second password item in one interface will have default ID 2. ID is used by some routing protocols to identify which password was used to authenticate protocol packets.

<@@label>proto-pass-gen-from generate from "time"

The start time of the usage of the password for packet signing. The format of time is dd-mm-yyyy HH:MM:SS.

<@@label>proto-pass-gen-to generate to "time"

The last time of the usage of the password for packet signing.

<@@label>proto-pass-accept-from accept from "time"

The start time of the usage of the password for packet verification.

<@@label>proto-pass-accept-to accept to "time"

The last time of the usage of the password for packet verification.

<@@label>proto-pass-from from "time"

Shorthand for setting both generate from and accept from.

<@@label>proto-pass-to to "time"

Shorthand for setting both generate to and accept to.

<@@label>proto-pass-algorithm algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 )

The message authentication algorithm for the password when cryptographic authentication is enabled. The default value depends on the protocol. For RIP and OSPFv2 it is Keyed-MD5 (for compatibility), for OSPFv3 protocol it is HMAC-SHA-256.

3.4 Channel options <@@label>channel-opts

Every channel belongs to a protocol and is configured inside its block. The minimal channel config is empty, then it uses default values. The name of the channel implies its nettype. Channel definitions can be inherited from protocol templates. Multiple definitions of the same channel are forbidden, but channels inherited from templates can be updated by new definitions.

<@@label>proto-table table name

Specify a table to which the channel is connected. Default: the first table of given nettype.

<@@label>proto-preference preference expr

Sets the preference of routes generated by the protocol and imported through this channel. Default: protocol dependent.

<@@label>proto-import import all | none | filter name | filter { filter commands } | where boolean filter expression

Specify a filter to be used for filtering routes coming from the protocol to the routing table. all is for keeping all routes, none is for dropping all routes. Default: all (except for EBGP).

<@@label>proto-export export filter

This is similar to the import keyword, except that it works in the direction from the routing table to the protocol. Default: none (except for EBGP).

<@@label>proto-import-keep-filtered import keep filtered switch

Usually, if an import filter rejects a route, the route is forgotten. When this option is active, these routes are kept in the routing table, but they are hidden and not propagated to other protocols. But it is possible to show them using show route filtered. Note that this option does not work for the pipe protocol. Default: off.

<@@label>proto-import-limit import limit [number | off ] [action warn | block | restart | disable]

Specify an import route limit (a maximum number of routes imported from the protocol) and optionally the action to be taken when the limit is hit. Warn action just prints warning log message. Block action discards new routes coming from the protocol. Restart and disable actions shut the protocol down like appropriate commands. Disable is the default action if an action is not explicitly specified. Note that limits are reset during protocol reconfigure, reload or restart. Default: off.

<@@label>proto-receive-limit receive limit [number | off ] [action warn | block | restart | disable]

Specify an receive route limit (a maximum number of routes received from the protocol and remembered). It works almost identically to import limit option, the only difference is that if import keep filtered option is active, filtered routes are counted towards the limit and blocked routes are forgotten, as the main purpose of the receive limit is to protect routing tables from overflow. Import limit, on the contrary, counts accepted routes only and routes blocked by the limit are handled like filtered routes. Default: off.

<@@label>proto-export-limit export limit [ number | off ] [action warn | block | restart | disable]

Specify an export route limit, works similarly to the import limit option, but for the routes exported to the protocol. This option is experimental, there are some problems in details of its behavior -- the number of exported routes can temporarily exceed the limit without triggering it during protocol reload, exported routes counter ignores route blocking and block action also blocks route updates of already accepted routes -- and these details will probably change in the future. Default: off.

This is a trivial example of RIP configured for IPv6 on all interfaces:

protocol rip ng {
        ipv6;
        interface "*";
}

This is a non-trivial example.

protocol rip ng {
        ipv6 {
                table mytable6;
                import filter { ... };
                export filter { ... };
                import limit 50;
        };
        interface "*";
}

And this is even more complicated example using templates.

template bgp {
        local 198.51.100.14 as 65000;

        ipv4 {
                table mytable4;
                import filter { ... };
                export none;
        };
        ipv6 {
                table mytable6;
                import filter { ... };
                export none;
        };
}

protocol bgp from  {
        neighbor 198.51.100.130 as 64496;

        # IPv4 channel is inherited as-is, while IPv6
        # channel is adjusted by export filter option
        ipv6 {
                export filter { ... };
        };
}

4. Remote control<@@label>remote-control

You can use the command-line client birdc to talk with a running BIRD. Communication is done using a bird.ctl UNIX domain socket (unless changed with the -s option given to both the server and the client). The commands can perform simple actions such as enabling/disabling of protocols, telling BIRD to show various information, telling it to show routing table filtered by filter, or asking BIRD to reconfigure. Press ? at any time to get online help. Option -r can be used to enable a restricted mode of BIRD client, which allows just read-only commands (show ...). Option -v can be passed to the client, to make it dump numeric return codes along with the messages. You do not necessarily need to use birdc to talk to BIRD, your own applications could do that, too -- the format of communication between BIRD and birdc is stable (see the programmer's documentation).

There is also lightweight variant of BIRD client called birdcl, which does not support command line editing and history and has minimal dependencies. This is useful for running BIRD in resource constrained environments, where Readline library (required for regular BIRD client) is not available.

Many commands have the name of the protocol instance as an argument. This argument can be omitted if there exists only a single instance.

Here is a brief list of supported functions:

<@@label>cli-show-status show status

Show router status, that is BIRD version, uptime and time from last reconfiguration.

<@@label>cli-show-interfaces show interfaces [summary]

Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned.

<@@label>cli-show-protocols show protocols [all]

Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if all is specified.

<@@label>cli-show-ospf-iface show ospf interface [name] ["interface"]

Show detailed information about OSPF interfaces.

<@@label>cli-show-ospf-neighbors show ospf neighbors [name] ["interface"]

Show a list of OSPF neighbors and a state of adjacency to them.

<@@label>cli-show-ospf-state show ospf state [all] [name]

Show detailed information about OSPF areas based on a content of the link-state database. It shows network topology, stub networks, aggregated networks and routers from other areas and external routes. The command shows information about reachable network nodes, use option all to show information about all network nodes in the link-state database.

<@@label>cli-show-ospf-topology show ospf topology [all] [name]

Show a topology of OSPF areas based on a content of the link-state database. It is just a stripped-down version of 'show ospf state'.

<@@label>cli-show-ospf-lsadb show ospf lsadb [global | area id | link] [type num] [lsid id] [self | router id] [name]

Show contents of an OSPF LSA database. Options could be used to filter entries.

<@@label>cli-show-rip-interfaces show rip interfaces [name] ["interface"]

Show detailed information about RIP interfaces.

<@@label>cli-show-rip-neighbors show rip neighbors [name] ["interface"]

Show a list of RIP neighbors and associated state.

<@@label>cli-show-static show static [name]

Show detailed information about static routes.

<@@label>cli-show-bfd-sessions show bfd sessions [name]

Show information about BFD sessions.

<@@label>cli-show-symbols show symbols [table|filter|function|protocol|template|roa|symbol]

Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).

<@@label>cli-show-route show route [[for] prefix|IP] [table (t | all)] [filter f|where c] [(export|preexport|noexport) p] [protocol p] [(stats|count)] [options]

Show contents of specified routing tables, that is routes, their metrics and (in case the all switch is given) all their attributes.

You can specify a prefix if you want to print routes for a specific network. If you use for prefix or IP, you'll get the entry which will be used for forwarding of packets to the given destination. By default, all routes for each network are printed with the selected one at the top, unless primary is given in which case only the selected route is shown.

The show route command can process one or multiple routing tables. The set of selected tables is determined on three levels: First, tables can be explicitly selected by table switch, which could be used multiple times, all tables are specified by table all. Second, tables can be implicitly selected by channels or protocols that are arguments of several other switches (e.g., export, protocol). Last, the set of default tables is used: master4, master6 and each first table of any other network type.

You can also ask for printing only routes processed and accepted by a given filter (filter name or filter { filter } or matching a given condition (where condition).

The export, preexport and noexport switches ask for printing of routes that are exported to the specified protocol or channel. With preexport, the export filter of the channel is skipped. With noexport, routes rejected by the export filter are printed instead. Note that routes not exported for other reasons (e.g. secondary routes or routes imported from that protocol) are not printed even with noexport. These switches also imply that associated routing tables are selected instead of default ones.

You can also select just routes added by a specific protocol. protocol p. This switch also implies that associated routing tables are selected instead of default ones.

If BIRD is configured to keep filtered routes (see import keep filtered option), you can show them instead of routes by using filtered switch.

The stats switch requests showing of route statistics (the number of networks, number of routes before and after filtering). If you use count instead, only the statistics will be printed.

<@@label>cli-mrt-dump mrt dump table name|"pattern" to "filename" [filter f|where c]

Dump content of a routing table to a specified file in MRT table dump format. See <@@ref>mrtMRT protocol for details.

<@@label>cli-configure configure [soft] ["config file"] [timeout [num]]

Reload configuration from a given file. BIRD will smoothly switch itself to the new configuration, protocols are reconfigured if possible, restarted otherwise. Changes in filters usually lead to restart of affected protocols.

If soft option is used, changes in filters does not cause BIRD to restart affected protocols, therefore already accepted routes (according to old filters) would be still propagated, but new routes would be processed according to the new filters.

If timeout option is used, config timer is activated. The new configuration could be either confirmed using configure confirm command, or it will be reverted to the old one when the config timer expires. This is useful for cases when reconfiguration breaks current routing and a router becomes inaccessible for an administrator. The config timeout expiration is equivalent to configure undo command. The timeout duration could be specified, default is 300 s.

<@@label>cli-configure-confirm configure confirm

Deactivate the config undo timer and therefore confirm the current configuration.

<@@label>cli-configure-undo configure undo

Undo the last configuration change and smoothly switch back to the previous (stored) configuration. If the last configuration change was soft, the undo change is also soft. There is only one level of undo, but in some specific cases when several reconfiguration requests are given immediately in a row and the intermediate ones are skipped then the undo also skips them back.

<@@label>cli-configure-check configure check ["config file"]

Read and parse given config file, but do not use it. useful for checking syntactic and some semantic validity of an config file.

<@@label>cli-enable-disable-restart enable|disable|restart name|"pattern"|all

Enable, disable or restart a given protocol instance, instances matching the pattern or all instances.

<@@label>cli-reload reload [in|out] name|"pattern"|all

Reload a given protocol instance, that means re-import routes from the protocol instance and re-export preferred routes to the instance. If in or out options are used, the command is restricted to one direction (re-import or re-export).

This command is useful if appropriate filters have changed but the protocol instance was not restarted (or reloaded), therefore it still propagates the old set of routes. For example when configure soft command was used to change filters.

Re-export always succeeds, but re-import is protocol-dependent and might fail (for example, if BGP neighbor does not support route-refresh extension). In that case, re-export is also skipped. Note that for the pipe protocol, both directions are always reloaded together (in or out options are ignored in that case).

<@@label>cli-down down

Shut BIRD down.

<@@label>cli-graceful-restart graceful restart

Shut BIRD down for graceful restart. See <@@ref>mrtMRT protocol<@@ref>graceful-restartgraceful restart section for details.

<@@label>cli-debug debug protocol|pattern|all all|off|{ states|routes|filters|events|packets [, ...] }

Control protocol debugging.

<@@label>cli-dump dump resources|sockets|interfaces|neighbors|attributes|routes|protocols

Dump contents of internal data structures to the debugging output.

<@@label>cli-echo echo all|off|{ list of log classes } [ buffer-size ]

Control echoing of log messages to the command-line output. See <@@ref>mrtMRT protocol<@@ref>graceful-restartgraceful restart<@@ref>opt-loglog option for a list of log classes.

<@@label>cli-eval eval expr

Evaluate given expression.

5. Filters<@@label>filters

5.1 Introduction <@@label>filters-intro

BIRD contains a simple programming language. (No, it can't yet read mail :-). There are two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is being passed between protocols and routing tables. The filter language contains control structures such as if's and switches, but it allows no loops. An example of a filter using many features can be found in filter/test.conf.

Filter gets the route, looks at its attributes and modifies some of them if it wishes. At the end, it decides whether to pass the changed route through (using accept) or whether to reject it. A simple filter looks like this:

filter not_too_far
int var;
{
        if defined( rip_metric ) then
                var = rip_metric;
        else {
                var = 1;
                rip_metric = 1;
        }
        if rip_metric > 10 then
                reject "RIP metric is too big";
        else
                accept "ok";
}

As you can see, a filter has a header, a list of local variables, and a body. The header consists of the filter keyword followed by a (unique) name of filter. The list of local variables consists of type name; pairs where each pair declares one local variable. The body consists of { statements }. Each statement is terminated by a ;. You can group several statements to a single compound statement by using braces ({ statements }) which is useful if you want to make a bigger block of code conditional.

BIRD supports functions, so that you don't have to repeat the same blocks of code over and over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions look like this:

function name ()
int local_variable;
{
        local_variable = 5;
}

function with_parameters (int parameter)
{
        print parameter;
}

Unlike in C, variables are declared after the function line, but before the first {. You can't declare variables in nested blocks. Functions are called like in C: name(); with_parameters(5);. Function may return values using the return [expr] command. Returning a value exits from current function (this is similar to C).

Filters are defined in a way similar to functions except they can't have explicit parameters. They get a route table entry as an implicit parameter, it is also passed automatically to any functions called. The filter must terminate with either accept or reject statement. If there's a runtime error in filter, the route is rejected.

A nice trick to debug filters is to use show route filter name from the command line client. An example session might look like:

pavel@bug:~/bird$ ./birdc -s bird.ctl
BIRD 0.0.0 ready.
bird> show route
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
127.0.0.0/8        dev lo [direct1 23:21] (240)
bird> show route ?
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
bird> show route filter { if 127.0.0.5 ~ net then accept; }
127.0.0.0/8        dev lo [direct1 23:21] (240)
bird>

5.2 Data types <@@label>data-types

Each variable and each value has certain type. Booleans, integers and enums are incompatible with each other (that is to prevent you from shooting oneself in the foot).

<@@label>type-bool bool

This is a boolean type, it can have only two values, true and false. Boolean is the only type you can use in if statements.

<@@label>type-int int

This is a general integer type. It is an unsigned 32bit type; i.e., you can expect it to store values from 0 to 4294967295. Overflows are not checked. You can use 0x1234 syntax to write hexadecimal values.

<@@label>type-pair pair

This is a pair of two short integers. Each component can have values from 0 to 65535. Literals of this type are written as (1234,5678). The same syntax can also be used to construct a pair from two arbitrary integer expressions (for example (1+2,a)).

<@@label>type-quad quad

This is a dotted quad of numbers used to represent router IDs (and others). Each component can have a value from 0 to 255. Literals of this type are written like IPv4 addresses.

<@@label>type-string string

This is a string of characters. There are no ways to modify strings in filters. You can pass them between functions, assign them to variables of type string, print such variables, use standard string comparison operations (e.g. =, !=, <, >, <=, >=), but you can't concatenate two strings. String literals are written as "This is a string constant". Additionally matching (~, !~) operators could be used to match a string value against a shell pattern (represented also as a string).

<@@label>type-ip ip

This type can hold a single IP address. The IPv4 addresses are stored as IPv4-Mapped IPv6 addresses so one data type for both of them is used. Whether the address is IPv4 or not may be checked by .is_ip4 which returns a bool. IP addresses are written in the standard notation (10.20.30.40 or fec0:3:4::1). You can apply special operator .mask(num) on values of type ip. It masks out all but first num bits from the IP address. So 1.2.3.4.mask(8) = 1.0.0.0 is true.

<@@label>type-prefix prefix

This type can hold a network prefix consisting of IP address, prefix length and several other values. This is the key in route tables.

Prefixes may be of several types, which can be determined by the special operator .type. The type may be:

NET_IP4 and NET_IP6 prefixes hold an IP prefix. The literals are written as ipaddress/pxlen. There are two special operators on these: .ip which extracts the IP address from the pair, and .len, which separates prefix length from the pair. So 1.2.0.0/16.len = 16 is true.

NET_IP6_SADR nettype holds both destination and source IPv6 prefix. The literals are written as ipaddress/pxlen from ipaddress/pxlen, where the first part is the destination prefix and the second art is the source prefix. They support the same operators as IP prefixes, but just for the destination part.

NET_VPN4 and NET_VPN6 prefixes hold an IP prefix with VPN Route Distinguisher (RFC 4364). They support the same special operators as IP prefixes, and also .rd which extracts the Route Distinguisher. Their literals are written as vpnrd ipprefix

NET_ROA4 and NET_ROA6 prefixes hold an IP prefix range together with an ASN. They support the same special operators as IP prefixes, and also .maxlen which extracts maximal prefix length, and .asn which extracts the ASN.

NET_FLOW4 and NET_FLOW6 hold an IP prefix together with a flowspec rule. Filters currently don't support flowspec parsing.

NET_MPLS holds a single MPLS label and its handling is currently not implemented.

<@@label>type-vpnrd vpnrd

This is a route distinguisher according to RFC 4364. There are three kinds of RD's: asn:32bit int, asn4:16bit int and IPv4 address:32bit int

<@@label>type-ec ec

This is a specialized type used to represent BGP extended community values. It is essentially a 64bit value, literals of this type are usually written as (kind, key, value), where kind is a kind of extended community (e.g. rt / ro for a route target / route origin communities), the format and possible values of key and value are usually integers, but it depends on the used kind. Similarly to pairs, ECs can be constructed using expressions for key and value parts, (e.g. (ro, myas, 3*10), where myas is an integer variable).

<@@label>type-lc lc

This is a specialized type used to represent BGP large community values. It is essentially a triplet of 32bit values, where the first value is reserved for the AS number of the issuer, while meaning of remaining parts is defined by the issuer. Literals of this type are written as (123, 456, 789), with any integer values. Similarly to pairs, LCs can be constructed using expressions for its parts, (e.g. (myas, 10+20, 3*10), where myas is an integer variable).

<@@label>type-set int|pair|quad|ip|prefix|ec|lc|enum set

Filters recognize four types of sets. Sets are similar to strings: you can pass them around but you can't modify them. Literals of type int set look like [ 1, 2, 5..7 ]. As you can see, both simple values and ranges are permitted in sets.

For pair sets, expressions like (123,*) can be used to denote ranges (in that case (123,0)..(123,65535)). You can also use (123,5..100) for range (123,5)..(123,100). You can also use * and a..b expressions in the first part of a pair, note that such expressions are translated to a set of intervals, which may be memory intensive. E.g. (*,4..20) is translated to (0,4..20), (1,4..20), (2,4..20), ... (65535, 4..20).

EC sets use similar expressions like pair sets, e.g. (rt, 123, 10..20) or (ro, 123, *). Expressions requiring the translation (like (rt, *, 3)) are not allowed (as they usually have 4B range for ASNs).

Also LC sets use similar expressions like pair sets. You can use ranges and wildcards, but if one field uses that, more specific (later) fields must be wildcards. E.g., (10, 20..30, *) or (10, 20, 30..40) is valid, while (10, *, 20..30) or (10, 20..30, 40) is not valid.

You can also use expressions for int, pair, EC and LC set values. However, it must be possible to evaluate these expressions before daemon boots. So you can use only constants inside them. E.g.

---

         define one=1;
         define myas=64500;
         int set odds;
         pair set ps;
         ec set es;

         odds = [ one, 2+1, 6-one, 2*2*2-1, 9, 11 ];
         ps = [ (1,one+one), (3,4)..(4,8), (5,*), (6,3..6), (7..9,*) ];
         es = [ (rt, myas, 3*10), (rt, myas+one, 0..16*16*16-1), (ro, myas+2, *) ];
        

---

Sets of prefixes are special: their literals does not allow ranges, but allows prefix patterns that are written as ipaddress/pxlen{low,high}. Prefix ip1/len1 matches prefix pattern ip2/len2{l,h} if the first min(len1, len2) bits of ip1 and ip2 are identical and len1 <= ip1 <= len2. A valid prefix pattern has to satisfy low <= high, but pxlen is not constrained by low or high. Obviously, a prefix matches a prefix set literal if it matches any prefix pattern in the prefix set literal.

There are also two shorthands for prefix patterns: address/len+ is a shorthand for address/len{len,maxlen} (where maxlen is 32 for IPv4 and 128 for IPv6), that means network prefix address/len and all its subnets. address/len- is a shorthand for address/len{0,len}, that means network prefix address/len and all its supernets (network prefixes that contain it).

For example, [ 1.0.0.0/8, 2.0.0.0/8+, 3.0.0.0/8-, 4.0.0.0/8{16,24} ] matches prefix 1.0.0.0/8, all subprefixes of 2.0.0.0/8, all superprefixes of 3.0.0.0/8 and prefixes 4.X.X.X whose prefix length is 16 to 24. [ 0.0.0.0/0{20,24} ] matches all prefixes (regardless of IP address) whose prefix length is 20 to 24, [ 1.2.3.4/32- ] matches any prefix that contains IP address 1.2.3.4. 1.2.0.0/16 ~ [ 1.0.0.0/8{15,17} ] is true, but 1.0.0.0/16 ~ [ 1.0.0.0/8- ] is false.

Cisco-style patterns like 10.0.0.0/8 ge 16 le 24 can be expressed in BIRD as 10.0.0.0/8{16,24}, 192.168.0.0/16 le 24 as 192.168.0.0/16{16,24} and 192.168.0.0/16 ge 24 as 192.168.0.0/16{24,32}.

It is possible to mix IPv4 and IPv6 prefixes/addresses in a prefix/ip set but its behavior may change between versions without any warning; don't do it unless you are more than sure what you are doing. (Really, don't do it.)

<@@label>type-enum enum

Enumeration types are fixed sets of possibilities. You can't define your own variables of such type, but some route attributes are of enumeration type. Enumeration types are incompatible with each other.

<@@label>type-bgppath bgppath

BGP path is a list of autonomous system numbers. You can't write literals of this type. There are several special operators on bgppaths:

P.first returns the first ASN (the neighbor ASN) in path P.

P.last returns the last ASN (the source ASN) in path P.

P.last_nonaggregated returns the last ASN in the non-aggregated part of the path P.

Both first and last return zero if there is no appropriate ASN, for example if the path contains an AS set element as the first (or the last) part. If the path ends with an AS set, last_nonaggregated may be used to get last ASN before any AS set.

P.len returns the length of path P.

P.empty makes the path P empty.

prepend(P,A) prepends ASN A to path P and returns the result.

delete(P,A) deletes all instances of ASN A from from path P and returns the result. A may also be an integer set, in that case the operator deletes all ASNs from path P that are also members of set A.

filter(P,A) deletes all ASNs from path P that are not members of integer set A. I.e., filter do the same as delete with inverted set A.

Statement P = prepend(P, A); can be shortened to P.prepend(A); if P is appropriate route attribute (for example bgp_path). Similarly for delete and filter.

<@@label>type-bgpmask bgpmask

BGP masks are patterns used for BGP path matching (using path ~ [= 2 3 5 * =] syntax). The masks resemble wildcard patterns as used by UNIX shells. Autonomous system numbers match themselves, * matches any (even empty) sequence of arbitrary AS numbers and ? matches one arbitrary AS number. For example, if bgp_path is 4 3 2 1, then: bgp_path ~ [= * 4 3 * =] is true, but bgp_path ~ [= * 4 5 * =] is false. BGP mask expressions can also contain integer expressions enclosed in parenthesis and integer variables, for example [= * 4 (1+2) a =]. You can also use ranges (e.g. [= * 3..5 2 100..200 * =]) and sets (e.g. [= 1 2 [3, 5, 7] * =]).

<@@label>type-clist clist

Clist is similar to a set, except that unlike other sets, it can be modified. The type is used for community list (a set of pairs) and for cluster list (a set of quads). There exist no literals of this type. There are three special operators on clists:

C.len returns the length of clist C.

C.empty makes the list C empty.

add(C,P) adds pair (or quad) P to clist C and returns the result. If item P is already in clist C, it does nothing. P may also be a clist, in that case all its members are added; i.e., it works as clist union.

delete(C,P) deletes pair (or quad) P from clist C and returns the result. If clist C does not contain item P, it does nothing. P may also be a pair (or quad) set, in that case the operator deletes all items from clist C that are also members of set P. Moreover, P may also be a clist, which works analogously; i.e., it works as clist difference.

filter(C,P) deletes all items from clist C that are not members of pair (or quad) set P. I.e., filter do the same as delete with inverted set P. P may also be a clist, which works analogously; i.e., it works as clist intersection.

Statement C = add(C, P); can be shortened to C.add(P); if C is appropriate route attribute (for example bgp_community). Similarly for delete and filter.

<@@label>type-eclist eclist

Eclist is a data type used for BGP extended community lists. Eclists are very similar to clists, but they are sets of ECs instead of pairs. The same operations (like add, delete or ~ and !~ membership operators) can be used to modify or test eclists, with ECs instead of pairs as arguments.

<@@label>type-lclist lclist

Lclist is a data type used for BGP large community lists. Like eclists, lclists are very similar to clists, but they are sets of LCs instead of pairs. The same operations (like add, delete or ~ and !~ membership operators) can be used to modify or test lclists, with LCs instead of pairs as arguments.

5.3 Operators <@@label>operators

The filter language supports common integer operators (+,-,*,/), parentheses (a*(b+c)), comparison (a=b, a!=b, a<b, a>=b). Logical operations include unary not (!), and (&&), and or (||). Special operators include (~, !~) for "is (not) element of a set" operation - it can be used on element and set of elements of the same type (returning true if element is contained in the given set), or on two strings (returning true if first string matches a shell-like pattern stored in second string) or on IP and prefix (returning true if IP is within the range defined by that prefix), or on prefix and prefix (returning true if first prefix is more specific than second one) or on bgppath and bgpmask (returning true if the path matches the mask) or on number and bgppath (returning true if the number is in the path) or on bgppath and int (number) set (returning true if any ASN from the path is in the set) or on pair/quad and clist (returning true if the pair/quad is element of the clist) or on clist and pair/quad set (returning true if there is an element of the clist that is also a member of the pair/quad set).

There is one operator related to ROA infrastructure - roa_check(). It examines a ROA table and does RFC 6483 route origin validation for a given network prefix. The basic usage is roa_check(table), which checks the current route (which should be from BGP to have AS_PATH argument) in the specified ROA table and returns ROA_UNKNOWN if there is no relevant ROA, ROA_VALID if there is a matching ROA, or ROA_INVALID if there are some relevant ROAs but none of them match. There is also an extended variant roa_check(table, prefix, asn), which allows to specify a prefix and an ASN as arguments.

5.4 Control structures <@@label>control-structures

Filters support two control structures: conditions and case switches.

Syntax of a condition is: if boolean expression then commandT; else commandF; and you can use { command1; command2; ... } instead of either command. The else clause may be omitted. If the boolean expression is true, commandT is executed, otherwise commandF is executed.

The case is similar to case from Pascal. Syntax is case expr { else: | num_or_prefix [ .. num_or_prefix]: statement ; [ ... ] }. The expression after case can be of any type which can be on the left side of the ~ operator and anything that could be a member of a set is allowed before :. Multiple commands are allowed without {} grouping. If expr matches one of the : clauses, statements between it and next : statement are executed. If expr matches neither of the : clauses, the statements after else: are executed.

Here is example that uses if and case structures:

case arg1 {
        2: print "two"; print "I can do more commands without {}";
        3 .. 5: print "three to five";
        else: print "something else";
}

if 1234 = i then printn "."; else {
  print "not 1234";
  print "You need {} around multiple commands";
}

5.5 Route attributes <@@label>route-attributes

A filter is implicitly passed a route, and it can access its attributes just like it accesses variables. There are common route attributes, protocol-specific route attributes and custom route attributes. Most common attributes are mandatory (always defined), while remaining are optional. Attempts to access undefined attribute result in a runtime error; you can check if an attribute is defined by using the defined( attribute ) operator. One notable exception to this rule are attributes of bgppath and *clist types, where undefined value is regarded as empty bgppath/*clist for most purposes.

Attributes can be defined by just setting them in filters. Custom attributes have to be first declared by <@@ref>opt-attributeattribute global option. You can also undefine optional attribute back to non-existence by using the unset( attribute ) operator.

Common route attributes are:

<@@label>rta-net prefix net

The network prefix or anything else the route is talking about. The primary key of the routing table. Read-only. (See the <@@ref>opt-attributeattribute<@@ref>routeschapter about routes.)

<@@label>rta-scope enum scope

The scope of the route. Possible values: SCOPE_HOST for routes local to this host, SCOPE_LINK for those specific for a physical link, SCOPE_SITE and SCOPE_ORGANIZATION for private routes and SCOPE_UNIVERSE for globally visible routes. This attribute is not interpreted by BIRD and can be used to mark routes in filters. The default value for new routes is SCOPE_UNIVERSE.

<@@label>rta-preference int preference

Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.)

<@@label>rta-from ip from

The router which the route has originated from.

<@@label>rta-gw ip gw

Next hop packets routed using this route should be forwarded to.

<@@label>rta-proto string proto

The name of the protocol which the route has been imported from. Read-only.

<@@label>rta-source enum source

what protocol has told me about this route. Possible values: RTS_DUMMY, RTS_STATIC, RTS_INHERIT, RTS_DEVICE, RTS_STATIC_DEVICE, RTS_REDIRECT, RTS_RIP, RTS_OSPF, RTS_OSPF_IA, RTS_OSPF_EXT1, RTS_OSPF_EXT2, RTS_BGP, RTS_PIPE, RTS_BABEL.

<@@label>rta-dest enum dest

Type of destination the packets should be sent to (RTD_ROUTER for forwarding to a neighboring router, RTD_DEVICE for routing to a directly-connected network, RTD_MULTIPATH for multipath destinations, RTD_BLACKHOLE for packets to be silently discarded, RTD_UNREACHABLE, RTD_PROHIBIT for packets that should be returned with ICMP host unreachable / ICMP administratively prohibited messages). Can be changed, but only to RTD_BLACKHOLE, RTD_UNREACHABLE or RTD_PROHIBIT.

<@@label>rta-ifname string ifname

Name of the outgoing interface. Sink routes (like blackhole, unreachable or prohibit) and multipath routes have no interface associated with them, so ifname returns an empty string for such routes. Setting it would also change route to a direct one (remove gateway).

<@@label>rta-ifindex int ifindex

Index of the outgoing interface. System wide index of the interface. May be used for interface matching, however indexes might change on interface creation/removal. Zero is returned for routes with undefined outgoing interfaces. Read-only.

<@@label>rta-igp-metric int igp_metric

The optional attribute that can be used to specify a distance to the network for routes that do not have a native protocol metric attribute (like ospf_metric1 for OSPF routes). It is used mainly by BGP to compare internal distances to boundary routers (see below).

Protocol-specific route attributes are described in the corresponding protocol sections.

5.6 Other statements <@@label>other-statements

The following statements are available:

<@@label>assignment variable = expr

Set variable (or route attribute) to a given value.

<@@label>filter-accept-reject accept|reject [ expr ]

Accept or reject the route, possibly printing expr.

<@@label>return return expr

Return expr from the current function, the function ends at this point.

<@@label>print print|printn expr [, expr...]

Prints given expressions; useful mainly while debugging filters. The printn variant does not terminate the line.

<@@label>quitbird quitbird

Terminates BIRD. Useful when debugging the filter interpreter.

6. Protocols<@@label>protocols

6.1 Babel <@@label>babel

Introduction<@@label>babel-intro

The Babel protocol (RFC 6126) is a loop-avoiding distance-vector routing protocol that is robust and efficient both in ordinary wired networks and in wireless mesh networks. Babel is conceptually very simple in its operation and "just works" in its default configuration, though some configuration is possible and in some cases desirable.

The Babel protocol is dual stack; i.e., it can carry both IPv4 and IPv6 routes over the same IPv6 transport. For sending and receiving Babel packets, only a link-local IPv6 address is needed.

BIRD implements an extension for IPv6 source-specific routing (SSR or SADR), but must be configured accordingly to use it. SADR-enabled Babel router can interoperate with non-SADR Babel router, but the later would ignore routes with specific (non-zero) source prefix.

Configuration<@@label>babel-config

The Babel protocol support both IPv4 and IPv6 channels; both can be configured simultaneously. It can also be configured with <@@ref>ip-sadr-routesIPv6 SADR channel instead of regular IPv6 channel, in such case SADR support is enabled. Babel supports no global configuration options apart from those common to all other protocols, but supports the following per-interface configuration options:

protocol babel [<name>] {
        ipv4 { <channel config> };
        ipv6 [sadr] { <channel config> };
        randomize router id <switch>;
        interface <interface pattern> {
                type <wired|wireless>;
                rxcost <number>;
                limit <number>;
                hello interval <time>;
                update interval <time>;
                port <number>;
                tx class|dscp <number>;
                tx priority <number>;
                rx buffer <number>;
                tx length <number>;
                check link <switch>;
                next hop ipv4 <address>;
                next hop ipv6 <address>;
        };
}

<@@label>babel-channel ipv4 | ipv6 [sadr] channel config

The supported channels are IPv4, IPv6, and IPv6 SADR.

<@@label>babel-random-router-id randomize router id switch

If enabled, Bird will randomize the top 32 bits of its router ID whenever the protocol instance starts up. If a Babel node restarts, it loses its sequence number, which can cause its routes to be rejected by peers until the state is cleared out by other nodes in the network (which can take on the order of minutes). Enabling this option causes Bird to pick a random router ID every time it starts up, which avoids this problem at the cost of not having stable router IDs in the network. Default: no.

<@@label>babel-type type wired|wireless

This option specifies the interface type: Wired or wireless. On wired interfaces a neighbor is considered unreachable after a small number of Hello packets are lost, as described by limit option. On wireless interfaces the ETX link quality estimation technique is used to compute the metrics of routes discovered over this interface. This technique will gradually degrade the metric of routes when packets are lost rather than the more binary up/down mechanism of wired type links. Default: wired.

<@@label>babel-rxcost rxcost num

This option specifies the nominal RX cost of the interface. The effective neighbor costs for route metrics will be computed from this value with a mechanism determined by the interface type. Note that in contrast to other routing protocols like RIP or OSPF, the rxcost specifies the cost of RX instead of TX, so it affects primarily neighbors' route selection and not local route selection. Default: 96 for wired interfaces, 256 for wireless.

<@@label>babel-limit limit num

BIRD keeps track of received Hello messages from each neighbor to establish neighbor reachability. For wired type interfaces, this option specifies how many of last 16 hellos have to be correctly received in order to neighbor is assumed to be up. The option is ignored on wireless type interfaces, where gradual cost degradation is used instead of sharp limit. Default: 12.

<@@label>babel-hello hello interval time s|ms

Interval at which periodic Hello messages are sent on this interface, with time units. Default: 4 seconds.

<@@label>babel-update update interval time s|ms

Interval at which periodic (full) updates are sent, with time units. Default: 4 times the hello interval.

<@@label>babel-port port number

This option selects an UDP port to operate on. The default is to operate on port 6696 as specified in the Babel RFC.

<@@label>babel-tx-class tx class|dscp|priority number

These options specify the ToS/DiffServ/Traffic class/Priority of the outgoing Babel packets. See <@@ref>ip-sadr-routesIPv6 SADR<@@ref>proto-tx-classtx class common option for detailed description.

<@@label>babel-rx-buffer rx buffer number

This option specifies the size of buffers used for packet processing. The buffer size should be bigger than maximal size of received packets. The default value is the interface MTU, and the value will be clamped to a minimum of 512 bytes + IP packet overhead.

<@@label>babel-tx-length tx length number

This option specifies the maximum length of generated Babel packets. To avoid IP fragmentation, it should not exceed the interface MTU value. The default value is the interface MTU value, and the value will be clamped to a minimum of 512 bytes + IP packet overhead.

<@@label>babel-check-link check link switch

If set, the hardware link state (as reported by OS) is taken into consideration. When the link disappears (e.g. an ethernet cable is unplugged), neighbors are immediately considered unreachable and all routes received from them are withdrawn. It is possible that some hardware drivers or platforms do not implement this feature. Default: yes.

<@@label>babel-next-hop-ipv4 next hop ipv4 address

Set the next hop address advertised for IPv4 routes advertised on this interface. Default: the preferred IPv4 address of the interface.

<@@label>babel-next-hop-ipv6 next hop ipv6 address

Set the next hop address advertised for IPv6 routes advertised on this interface. If not set, the same link-local address that is used as the source for Babel packets will be used. In normal operation, it should not be necessary to set this option.

Attributes<@@label>babel-attr

Babel defines just one attribute: the internal babel metric of the route. It is exposed as the babel_metric attribute and has range from 1 to infinity (65535).

Example<@@label>babel-exam

protocol babel {
        interface "eth*" {
                type wired;
        };
        interface "wlan0", "wlan1" {
                type wireless;
                hello interval 1;
                rxcost 512;
        };
        interface "tap0";

        # This matches the default of babeld: redistribute all addresses
        # configured on local interfaces, plus re-distribute all routes received
        # from other babel peers.

        ipv4 {
                export where (source = RTS_DEVICE) || (source = RTS_BABEL);
        };
        ipv6 {
                export where (source = RTS_DEVICE) || (source = RTS_BABEL);
        };
}

Known issues<@@label>babel-issues

When retracting a route, Babel generates an unreachable route for a little while (according to RFC). The interaction of this behavior with other protocols is not well tested and strange things may happen.

6.2 BFD <@@label>bfd

Introduction<@@label>bfd-intro

Bidirectional Forwarding Detection (BFD) is not a routing protocol itself, it is an independent tool providing liveness and failure detection. Routing protocols like OSPF and BGP use integrated periodic "hello" messages to monitor liveness of neighbors, but detection times of these mechanisms are high (e.g. 40 seconds by default in OSPF, could be set down to several seconds). BFD offers universal, fast and low-overhead mechanism for failure detection, which could be attached to any routing protocol in an advisory role.

BFD consists of mostly independent BFD sessions. Each session monitors an unicast bidirectional path between two BFD-enabled routers. This is done by periodically sending control packets in both directions. BFD does not handle neighbor discovery, BFD sessions are created on demand by request of other protocols (like OSPF or BGP), which supply appropriate information like IP addresses and associated interfaces. When a session changes its state, these protocols are notified and act accordingly (e.g. break an OSPF adjacency when the BFD session went down).

BIRD implements basic BFD behavior as defined in RFC 5880 (some advanced features like the echo mode or authentication are not implemented), IP transport for BFD as defined in RFC 5881 and RFC 5883 and interaction with client protocols as defined in RFC 5882.

BFD packets are sent with a dynamic source port number. Linux systems use by default a bit different dynamic port range than the IANA approved one (49152-65535). If you experience problems with compatibility, please adjust /proc/sys/net/ipv4/ip_local_port_range.

Configuration<@@label>bfd-config

BFD configuration consists mainly of multiple definitions of interfaces. Most BFD config options are session specific. When a new session is requested and dynamically created, it is configured from one of these definitions. For sessions to directly connected neighbors, interface definitions are chosen based on the interface associated with the session, while multihop definition is used for multihop sessions. If no definition is relevant, the session is just created with the default configuration. Therefore, an empty BFD configuration is often sufficient.

Note that to use BFD for other protocols like OSPF or BGP, these protocols also have to be configured to request BFD sessions, usually by bfd option.

A BFD instance not associated with any VRF handles session requests from all other protocols, even ones associated with a VRF. Such setup would work for single-hop BFD sessions if net.ipv4.udp_l3mdev_accept sysctl is enabled, but does not currently work for multihop sessions. Another approach is to configure multiple BFD instances, one for each VRF (including the default VRF). Each BFD instance associated with a VRF (regular or default) only handles session requests from protocols in the same VRF.

Some of BFD session options require time value, which has to be specified with the appropriate unit: num s|ms|us. Although microseconds are allowed as units, practical minimum values are usually in order of tens of milliseconds.

protocol bfd [<name>] {
        interface <interface pattern> {
                interval <time>;
                min rx interval <time>;
                min tx interval <time>;
                idle tx interval <time>;
                multiplier <num>;
                passive <switch>;
                authentication none;
                authentication simple;
                authentication [meticulous] keyed md5|sha1;
                password "<text>";
                password "<text>" {
                        id <num>;
                        generate from "<date>";
                        generate to "<date>";
                        accept from "<date>";
                        accept to "<date>";
                        from "<date>";
                        to "<date>";
                };
        };
        multihop {
                interval <time>;
                min rx interval <time>;
                min tx interval <time>;
                idle tx interval <time>;
                multiplier <num>;
                passive <switch>;
        };
        neighbor <ip> [dev "<interface>"] [local <ip>] [multihop <switch>];
}

<@@label>bfd-iface interface pattern [, ...] { options }

Interface definitions allow to specify options for sessions associated with such interfaces and also may contain interface specific options. See <@@ref>proto-ifaceinterface common option for a detailed description of interface patterns. Note that contrary to the behavior of interface definitions of other protocols, BFD protocol would accept sessions (in default configuration) even on interfaces not covered by such definitions.

<@@label>bfd-multihop multihop { options }

Multihop definitions allow to specify options for multihop BFD sessions, in the same manner as interface definitions are used for directly connected sessions. Currently only one such definition (for all multihop sessions) could be used.

<@@label>bfd-neighbor neighbor ip [dev "interface"] [local ip] [multihop switch]

BFD sessions are usually created on demand as requested by other protocols (like OSPF or BGP). This option allows to explicitly add a BFD session to the specified neighbor regardless of such requests.

The session is identified by the IP address of the neighbor, with optional specification of used interface and local IP. By default the neighbor must be directly connected, unless the session is configured as multihop. Note that local IP must be specified for multihop sessions.

Session specific options (part of interface and multihop definitions):

<@@label>bfd-interval interval time

BFD ensures availability of the forwarding path associated with the session by periodically sending BFD control packets in both directions. The rate of such packets is controlled by two options, min rx interval and min tx interval (see below). This option is just a shorthand to set both of these options together.

<@@label>bfd-min-rx-interval min rx interval time

This option specifies the minimum RX interval, which is announced to the neighbor and used there to limit the neighbor's rate of generated BFD control packets. Default: 10 ms.

<@@label>bfd-min-tx-interval min tx interval time

This option specifies the desired TX interval, which controls the rate of generated BFD control packets (together with min rx interval announced by the neighbor). Note that this value is used only if the BFD session is up, otherwise the value of idle tx interval is used instead. Default: 100 ms.

<@@label>bfd-idle-tx-interval idle tx interval time

In order to limit unnecessary traffic in cases where a neighbor is not available or not running BFD, the rate of generated BFD control packets is lower when the BFD session is not up. This option specifies the desired TX interval in such cases instead of min tx interval. Default: 1 s.

<@@label>bfd-multiplier multiplier num

Failure detection time for BFD sessions is based on established rate of BFD control packets (min rx/tx interval) multiplied by this multiplier, which is essentially (ignoring jitter) a number of missed packets after which the session is declared down. Note that rates and multipliers could be different in each direction of a BFD session. Default: 5.

<@@label>bfd-passive passive switch

Generally, both BFD session endpoints try to establish the session by sending control packets to the other side. This option allows to enable passive mode, which means that the router does not send BFD packets until it has received one from the other side. Default: disabled.

authentication none

No passwords are sent in BFD packets. This is the default value.

authentication simple

Every packet carries 16 bytes of password. Received packets lacking this password are ignored. This authentication mechanism is very weak.

authentication [meticulous] keyed md5|sha1

An authentication code is appended to each packet. The cryptographic algorithm is keyed MD5 or keyed SHA-1. Note that the algorithm is common for all keys (on one interface), in contrast to OSPF or RIP, where it is a per-key option. Passwords (keys) are not sent open via network.

The meticulous variant means that cryptographic sequence numbers are increased for each sent packet, while in the basic variant they are increased about once per second. Generally, the meticulous variant offers better resistance to replay attacks but may require more computation.

password "text"

Specifies a password used for authentication. See <@@ref>proto-ifaceinterface<@@ref>proto-passpassword common option for detailed description. Note that password option algorithm is not available in BFD protocol. The algorithm is selected by authentication option for all passwords.

Example<@@label>bfd-exam

protocol bfd {
        interface "eth*" {
                min rx interval 20 ms;
                min tx interval 50 ms;
                idle tx interval 300 ms;
        };
        interface "gre*" {
                interval 200 ms;
                multiplier 10;
                passive;
        };
        multihop {
                interval 200 ms;
                multiplier 10;
        };

        neighbor 192.168.1.10;
        neighbor 192.168.2.2 dev "eth2";
        neighbor 192.168.10.1 local 192.168.1.1 multihop;
}

6.3 BGP <@@label>bgp

The Border Gateway Protocol is the routing protocol used for backbone level routing in the today's Internet. Contrary to other protocols, its convergence does not rely on all routers following the same rules for route selection, making it possible to implement any routing policy at any router in the network, the only restriction being that if a router advertises a route, it must accept and forward packets according to it.

BGP works in terms of autonomous systems (often abbreviated as AS). Each AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number (ASN). Routers within each AS usually exchange AS-internal routing information with each other using an interior gateway protocol (IGP, such as OSPF or RIP). Boundary routers at the border of the AS communicate global (inter-AS) network reachability information with their neighbors in the neighboring AS'es via exterior BGP (eBGP) and redistribute received information to other routers in the AS via interior BGP (iBGP).

Each BGP router sends to its neighbors updates of the parts of its routing table it wishes to export along with complete path information (a list of AS'es the packet will travel through if it uses the particular route) in order to avoid routing loops.

Supported standards<@@label>bgp-standards

• RFC 4271 - Border Gateway Protocol 4 (BGP)
• RFC 1997 - BGP Communities Attribute
• RFC 2385 - Protection of BGP Sessions via TCP MD5 Signature
• RFC 2545 - Use of BGP Multiprotocol Extensions for IPv6
• RFC 2918 - Route Refresh Capability
• RFC 3107 - Carrying Label Information in BGP
• RFC 4360 - BGP Extended Communities Attribute
• RFC 4364 - BGP/MPLS IPv4 Virtual Private Networks
• RFC 4456 - BGP Route Reflection
• RFC 4486 - Subcodes for BGP Cease Notification Message
• RFC 4659 - BGP/MPLS IPv6 Virtual Private Networks
• RFC 4724 - Graceful Restart Mechanism for BGP
• RFC 4760 - Multiprotocol extensions for BGP
• RFC 4798 - Connecting IPv6 Islands over IPv4 MPLS
• RFC 5065 - AS confederations for BGP
• RFC 5082 - Generalized TTL Security Mechanism
• RFC 5492 - Capabilities Advertisement with BGP
• RFC 5549 - Advertising IPv4 NLRI with an IPv6 Next Hop
• RFC 5575 - Dissemination of Flow Specification Rules
• RFC 5668 - 4-Octet AS Specific BGP Extended Community
• RFC 6286 - AS-Wide Unique BGP Identifier
• RFC 6608 - Subcodes for BGP Finite State Machine Error
• RFC 6793 - BGP Support for 4-Octet AS Numbers
• RFC 7311 - Accumulated IGP Metric Attribute for BGP
• RFC 7313 - Enhanced Route Refresh Capability for BGP
• RFC 7606 - Revised Error Handling for BGP UPDATE Messages
• RFC 7911 - Advertisement of Multiple Paths in BGP
• RFC 7947 - Internet Exchange BGP Route Server
• RFC 8092 - BGP Large Communities Attribute
• RFC 8203 - BGP Administrative Shutdown Communication
• RFC 8212 - Default EBGP Route Propagation Behavior without Policies

Route selection rules<@@label>bgp-route-select-rules

BGP doesn't have any simple metric, so the rules for selection of an optimal route among multiple BGP routes with the same preference are a bit more complex and they are implemented according to the following algorithm. It starts the first rule, if there are more "best" routes, then it uses the second rule to choose among them and so on.

• Prefer route with the highest Local Preference attribute.
• Prefer route with the shortest AS path.
• Prefer IGP origin over EGP and EGP origin over incomplete.
• Prefer the lowest value of the Multiple Exit Discriminator.
• Prefer routes received via eBGP over ones received via iBGP.
• Prefer routes with lower internal distance to a boundary router.
• Prefer the route with the lowest value of router ID of the advertising router.

IGP routing table<@@label>bgp-igp-routing-table

BGP is mainly concerned with global network reachability and with routes to other autonomous systems. When such routes are redistributed to routers in the AS via BGP, they contain IP addresses of a boundary routers (in route attribute NEXT_HOP). BGP depends on existing IGP routing table with AS-internal routes to determine immediate next hops for routes and to know their internal distances to boundary routers for the purpose of BGP route selection. In BIRD, there is usually one routing table used for both IGP routes and BGP routes.

Protocol configuration<@@label>bgp-proto-config

Each instance of the BGP corresponds to one neighboring router. This allows to set routing policy and all the other parameters differently for each neighbor using the following configuration parameters:

<@@label>bgp-local local [ip] [port number] [as number]

Define which AS we are part of. (Note that contrary to other IP routers, BIRD is able to act as a router located in multiple AS'es simultaneously, but in such cases you need to tweak the BGP paths manually in the filters to get consistent behavior.) Optional ip argument specifies a source address, equivalent to the source address option (see below). Optional port argument specifies the local BGP port instead of standard port 179. The parameter may be used multiple times with different sub-options (e.g., both local 10.0.0.1 as 65000; and local 10.0.0.1; local as 65000; are valid). This parameter is mandatory.

<@@label>bgp-neighbor neighbor [ip | range prefix] [port number] [as number] [internal|external]

Define neighboring router this instance will be talking to and what AS it is located in. In case the neighbor is in the same AS as we are, we automatically switch to IBGP. Alternatively, it is possible to specify just internal or external instead of AS number, in that case either local AS number, or any external AS number is accepted. Optionally, the remote port may also be specified. Like local parameter, this parameter may also be used multiple times with different sub-options. This parameter is mandatory.

It is possible to specify network prefix (with range keyword) instead of explicit neighbor IP address. This enables dynamic BGP behavior, where the BGP instance listens on BGP port, but new BGP instances are spawned for incoming BGP connections (if source address matches the network prefix). It is possible to mix regular BGP instances with dynamic BGP instances and have multiple dynamic BGP instances with different ranges.

<@@label>bgp-iface interface string

Define interface we should use for link-local BGP IPv6 sessions. Interface can also be specified as a part of neighbor address (e.g., neighbor fe80::1234%eth0 as 65000;). The option may also be used for non link-local sessions when it is necessary to explicitly specify an interface, but only for direct (not multihop) sessions.

<@@label>bgp-direct direct

Specify that the neighbor is directly connected. The IP address of the neighbor must be from a directly reachable IP range (i.e. associated with one of your router's interfaces), otherwise the BGP session wouldn't start but it would wait for such interface to appear. The alternative is the multihop option. Default: enabled for eBGP.

<@@label>bgp-multihop multihop [number]

Configure multihop BGP session to a neighbor that isn't directly connected. Accurately, this option should be used if the configured neighbor IP address does not match with any local network subnets. Such IP address have to be reachable through system routing table. The alternative is the direct option. For multihop BGP it is recommended to explicitly configure the source address to have it stable. Optional number argument can be used to specify the number of hops (used for TTL). Note that the number of networks (edges) in a path is counted; i.e., if two BGP speakers are separated by one router, the number of hops is 2. Default: enabled for iBGP.

<@@label>bgp-source-address source address ip

Define local address we should use as a source address for the BGP session. Default: the address of the local end of the interface our neighbor is connected to.

<@@label>bgp-dynamic-name dynamic name "text"

Define common prefix of names used for new BGP instances spawned when dynamic BGP behavior is active. Actual names also contain numeric index to distinguish individual instances. Default: "dynbgp".

<@@label>bgp-dynamic-name-digits dynamic name digits number

Define minimum number of digits for index in names of spawned dynamic BGP instances. E.g., if set to 2, then the first name would be "dynbgp01". Default: 0.

<@@label>bgp-strict-bind strict bind switch

Specify whether BGP listening socket should be bound to a specific local address (the same as the source address) and associated interface, or to all addresses. Binding to a specific address could be useful in cases like running multiple BIRD instances on a machine, each using its IP address. Note that listening sockets bound to a specific address and to all addresses collide, therefore either all BGP protocols (of the same address family and using the same local port) should have set strict bind, or none of them. Default: disabled.

<@@label>bgp-check-link check link switch

BGP could use hardware link state into consideration. If enabled, BIRD tracks the link state of the associated interface and when link disappears (e.g. an ethernet cable is unplugged), the BGP session is immediately shut down. Note that this option cannot be used with multihop BGP. Default: enabled for direct BGP, disabled otherwise.

<@@label>bgp-bfd bfd switch|graceful

BGP could use BFD protocol as an advisory mechanism for neighbor liveness and failure detection. If enabled, BIRD setups a BFD session for the BGP neighbor and tracks its liveness by it. This has an advantage of an order of magnitude lower detection times in case of failure. When a neighbor failure is detected, the BGP session is restarted. Optionally, it can be configured (by graceful argument) to trigger graceful restart instead of regular restart. Note that BFD protocol also has to be configured, see <@@ref>bfdBFD section for details. Default: disabled.

<@@label>bgp-ttl-security ttl security switch

Use GTSM (RFC 5082 - the generalized TTL security mechanism). GTSM protects against spoofed packets by ignoring received packets with a smaller than expected TTL. To work properly, GTSM have to be enabled on both sides of a BGP session. If both ttl security and multihop options are enabled, multihop option should specify proper hop value to compute expected TTL. Kernel support required: Linux: 2.6.34+ (IPv4), 2.6.35+ (IPv6), BSD: since long ago, IPv4 only. Note that full (ICMP protection, for example) RFC 5082 support is provided by Linux only. Default: disabled.

<@@label>bgp-password password string

Use this password for MD5 authentication of BGP sessions (RFC 2385). When used on BSD systems, see also setkey option below. Default: no authentication.

<@@label>bgp-setkey setkey switch

On BSD systems, keys for TCP MD5 authentication are stored in the global SA/SP database, which can be accessed by external utilities (e.g. setkey(8)). BIRD configures security associations in the SA/SP database automatically based on password options (see above), this option allows to disable automatic updates by BIRD when manual configuration by external utilities is preferred. Note that automatic SA/SP database updates are currently implemented only for FreeBSD. Passwords have to be set manually by an external utility on NetBSD and OpenBSD. Default: enabled (ignored on non-FreeBSD).

<@@label>bgp-passive passive switch

Standard BGP behavior is both initiating outgoing connections and accepting incoming connections. In passive mode, outgoing connections are not initiated. Default: off.

<@@label>bgp-confederation confederation number

BGP confederations (RFC 5065) are collections of autonomous systems that act as one entity to external systems, represented by one confederation identifier (instead of AS numbers). This option allows to enable BGP confederation behavior and to specify the local confederation identifier. When BGP confederations are used, all BGP speakers that are members of the BGP confederation should have the same confederation identifier configured. Default: 0 (no confederation).

<@@label>bgp-confederation-member confederation member switch

When BGP confederations are used, this option allows to specify whether the BGP neighbor is a member of the same confederation as the local BGP speaker. The option is unnecessary (and ignored) for IBGP sessions, as the same AS number implies the same confederation. Default: no.

<@@label>bgp-rr-client rr client

Be a route reflector and treat the neighbor as a route reflection client. Default: disabled.

<@@label>bgp-rr-cluster-id rr cluster id IPv4 address

Route reflectors use cluster id to avoid route reflection loops. When there is one route reflector in a cluster it usually uses its router id as a cluster id, but when there are more route reflectors in a cluster, these need to be configured (using this option) to use a common cluster id. Clients in a cluster need not know their cluster id and this option is not allowed for them. Default: the same as router id.

<@@label>bgp-rs-client rs client

Be a route server and treat the neighbor as a route server client. A route server is used as a replacement for full mesh EBGP routing in Internet exchange points in a similar way to route reflectors used in IBGP routing. BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation, which behaves like plain EBGP but reduces modifications to advertised route attributes to be transparent (for example does not prepend its AS number to AS PATH attribute and keeps MED attribute). Default: disabled.

<@@label>bgp-allow-local-pref allow bgp_local_pref switch

A standard BGP implementation do not send the Local Preference attribute to eBGP neighbors and ignore this attribute if received from eBGP neighbors, as per RFC 4271. When this option is enabled on an eBGP session, this attribute will be sent to and accepted from the peer, which is useful for example if you have a setup like in RFC 7938. The option does not affect iBGP sessions. Default: off.

<@@label>bgp-allow-local-as allow local as [number]

BGP prevents routing loops by rejecting received routes with the local AS number in the AS path. This option allows to loose or disable the check. Optional number argument can be used to specify the maximum number of local ASNs in the AS path that is allowed for received routes. When the option is used without the argument, the check is completely disabled and you should ensure loop-free behavior by some other means. Default: 0 (no local AS number allowed).

<@@label>bgp-enable-route-refresh enable route refresh switch

After the initial route exchange, BGP protocol uses incremental updates to keep BGP speakers synchronized. Sometimes (e.g., if BGP speaker changes its import filter, or if there is suspicion of inconsistency) it is necessary to do a new complete route exchange. BGP protocol extension Route Refresh (RFC 2918) allows BGP speaker to request re-advertisement of all routes from its neighbor. BGP protocol extension Enhanced Route Refresh (RFC 7313) specifies explicit begin and end for such exchanges, therefore the receiver can remove stale routes that were not advertised during the exchange. This option specifies whether BIRD advertises these capabilities and supports related procedures. Note that even when disabled, BIRD can send route refresh requests. Default: on.

<@@label>bgp-graceful-restart graceful restart switch|aware

When a BGP speaker restarts or crashes, neighbors will discard all received paths from the speaker, which disrupts packet forwarding even when the forwarding plane of the speaker remains intact. RFC 4724 specifies an optional graceful restart mechanism to alleviate this issue. This option controls the mechanism. It has three states: Disabled, when no support is provided. Aware, when the graceful restart support is announced and the support for restarting neighbors is provided, but no local graceful restart is allowed (i.e. receiving-only role). Enabled, when the full graceful restart support is provided (i.e. both restarting and receiving role). Restarting role could be also configured per-channel. Note that proper support for local graceful restart requires also configuration of other protocols. Default: aware.

<@@label>bgp-graceful-restart-time graceful restart time number

The restart time is announced in the BGP graceful restart capability and specifies how long the neighbor would wait for the BGP session to re-establish after a restart before deleting stale routes. Default: 120 seconds.

<@@label>bgp-long-lived-graceful-restart long lived graceful restart switch|aware

The long-lived graceful restart is an extension of the traditional <@@ref>bfdBFD<@@ref>bgp-graceful-restartBGP graceful restart, where stale routes are kept even after the <@@ref>bfdBFD<@@ref>bgp-graceful-restartBGP graceful restart<@@ref>bgp-graceful-restart-timerestart time expires for additional long-lived stale time, but they are marked with the LLGR_STALE community, depreferenced, and withdrawn from routers not supporting LLGR. Like traditional BGP graceful restart, it has three states: disabled, aware (receiving-only), and enabled. Note that long-lived graceful restart requires at least aware level of traditional BGP graceful restart. Default: aware, unless graceful restart is disabled.

<@@label>bgp-long-lived-stale-time long lived stale time number

The long-lived stale time is announced in the BGP long-lived graceful restart capability and specifies how long the neighbor would keep stale routes depreferenced during long-lived graceful restart until either the session is re-stablished and synchronized or the stale time expires and routes are removed. Default: 3600 seconds.

<@@label>bgp-interpret-communities interpret communities switch

RFC 1997 demands that BGP speaker should process well-known communities like no-export (65535, 65281) or no-advertise (65535, 65282). For example, received route carrying a no-adverise community should not be advertised to any of its neighbors. If this option is enabled (which is by default), BIRD has such behavior automatically (it is evaluated when a route is exported to the BGP protocol just before the export filter). Otherwise, this integrated processing of well-known communities is disabled. In that case, similar behavior can be implemented in the export filter. Default: on.

<@@label>bgp-enable-as4 enable as4 switch

BGP protocol was designed to use 2B AS numbers and was extended later to allow 4B AS number. BIRD supports 4B AS extension, but by disabling this option it can be persuaded not to advertise it and to maintain old-style sessions with its neighbors. This might be useful for circumventing bugs in neighbor's implementation of 4B AS extension. Even when disabled (off), BIRD behaves internally as AS4-aware BGP router. Default: on.

<@@label>bgp-enable-extended-messages enable extended messages switch

The BGP protocol uses maximum message length of 4096 bytes. This option provides an extension to allow extended messages with length up to 65535 bytes. Default: off.

<@@label>bgp-capabilities capabilities switch

Use capability advertisement to advertise optional capabilities. This is standard behavior for newer BGP implementations, but there might be some older BGP implementations that reject such connection attempts. When disabled (off), features that request it (4B AS support) are also disabled. Default: on, with automatic fallback to off when received capability-related error.

<@@label>bgp-advertise-ipv4 advertise ipv4 switch

Advertise IPv4 multiprotocol capability. This is not a correct behavior according to the strict interpretation of RFC 4760, but it is widespread and required by some BGP implementations (Cisco and Quagga). This option is relevant to IPv4 mode with enabled capability advertisement only. Default: on.

<@@label>bgp-disable-after-error disable after error switch

When an error is encountered (either locally or by the other side), disable the instance automatically and wait for an administrator to fix the problem manually. Default: off.

<@@label>bgp-disable-after-cease disable after cease switch|set-of-flags

When a Cease notification is received, disable the instance automatically and wait for an administrator to fix the problem manually. When used with switch argument, it means handle every Cease subtype with the exception of connection collision. Default: off.

The set-of-flags allows to narrow down relevant Cease subtypes. The syntax is {flag [, ...] }, where flags are: cease, prefix limit hit, administrative shutdown, peer deconfigured, administrative reset, connection rejected, configuration change, connection collision, out of resources.

<@@label>bgp-hold-time hold time number

Time in seconds to wait for a Keepalive message from the other side before considering the connection stale. Default: depends on agreement with the neighboring router, we prefer 240 seconds if the other side is willing to accept it.

<@@label>bgp-startup-hold-time startup hold time number

Value of the hold timer used before the routers have a chance to exchange open messages and agree on the real value. Default: 240 seconds.

<@@label>bgp-keepalive-time keepalive time number

Delay in seconds between sending of two consecutive Keepalive messages. Default: One third of the hold time.

<@@label>bgp-connect-delay-time connect delay time number

Delay in seconds between protocol startup and the first attempt to connect. Default: 5 seconds.

<@@label>bgp-connect-retry-time connect retry time number

Time in seconds to wait before retrying a failed attempt to connect. Default: 120 seconds.

<@@label>bgp-error-wait-time error wait time number,number

Minimum and maximum delay in seconds between a protocol failure (either local or reported by the peer) and automatic restart. Doesn't apply when disable after error is configured. If consecutive errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.

<@@label>bgp-error-forget-time error forget time number

Maximum time in seconds between two protocol failures to treat them as a error sequence which makes error wait time increase exponentially. Default: 300 seconds.

<@@label>bgp-path-metric path metric switch

Enable comparison of path lengths when deciding which BGP route is the best one. Default: on.

<@@label>bgp-med-metric med metric switch

Enable comparison of MED attributes (during best route selection) even between routes received from different ASes. This may be useful if all MED attributes contain some consistent metric, perhaps enforced in import filters of AS boundary routers. If this option is disabled, MED attributes are compared only if routes are received from the same AS (which is the standard behavior). Default: off.

<@@label>bgp-deterministic-med deterministic med switch

BGP route selection algorithm is often viewed as a comparison between individual routes (e.g. if a new route appears and is better than the current best one, it is chosen as the new best one). But the proper route selection, as specified by RFC 4271, cannot be fully implemented in that way. The problem is mainly in handling the MED attribute. BIRD, by default, uses an simplification based on individual route comparison, which in some cases may lead to temporally dependent behavior (i.e. the selection is dependent on the order in which routes appeared). This option enables a different (and slower) algorithm implementing proper RFC 4271 route selection, which is deterministic. Alternative way how to get deterministic behavior is to use med metric option. This option is incompatible with <@@ref>bfdBFD<@@ref>bgp-graceful-restartBGP graceful restart<@@ref>bgp-graceful-restart-timerestart time<@@ref>dsc-table-sortedsorted tables. Default: off.

<@@label>bgp-igp-metric igp metric switch

Enable comparison of internal distances to boundary routers during best route selection. Default: on.

<@@label>bgp-prefer-older prefer older switch

Standard route selection algorithm breaks ties by comparing router IDs. This changes the behavior to prefer older routes (when both are external and from different peer). For details, see RFC 5004. Default: off.

<@@label>bgp-default-med default bgp_med number

Value of the Multiple Exit Discriminator to be used during route selection when the MED attribute is missing. Default: 0.

<@@label>bgp-default-local-pref default bgp_local_pref number

A default value for the Local Preference attribute. It is used when a new Local Preference attribute is attached to a route by the BGP protocol itself (for example, if a route is received through eBGP and therefore does not have such attribute). Default: 100 (0 in pre-1.2.0 versions of BIRD).

Channel configuration<@@label>bgp-channel-config

BGP supports several AFIs and SAFIs over one connection. Every AFI/SAFI announced to the peer corresponds to one channel. The table of supported AFI/SAFIs together with their appropriate channels follows.

Due to RFC 8212, external BGP protocol requires explicit configuration of import and export policies (in contrast to other protocols, where default policies of import all and export none are used in absence of explicit configuration). Note that blanket policies like all or none can still be used in explicit configuration.

BGP channels have additional config options (together with the common ones):

<@@label>bgp-mandatory mandatory switch

When local and neighbor sets of configured AFI/SAFI pairs differ, capability negotiation ensures that a common subset is used. For mandatory channels their associated AFI/SAFI must be negotiated (i.e., also announced by the neighbor), otherwise BGP session negotiation fails with 'Required capability missing' error. Regardless, at least one AFI/SAFI must be negotiated in order to BGP session be successfully established. Default: off.

<@@label>bgp-next-hop-keep next hop keep switch|ibgp|ebgp

Do not modify the Next Hop attribute and advertise the current one unchanged even in cases where our own local address should be used instead. This is necessary when the BGP speaker does not forward network traffic (route servers and some route reflectors) and also can be useful in some other cases (e.g. multihop EBGP sessions). Can be enabled for all routes, or just for routes received from IBGP / EBGP neighbors. Default: disabled for regular BGP, enabled for route servers, ibgp for route reflectors.

<@@label>bgp-next-hop-self next hop self switch|ibgp|ebgp

Always advertise our own local address as a next hop, even in cases where the current Next Hop attribute should be used unchanged. This is sometimes used for routes propagated from EBGP to IBGP when IGP routing does not cover inter-AS links, therefore IP addreses of EBGP neighbors are not resolvable through IGP. Can be enabled for all routes, or just for routes received from IBGP / EBGP neighbors. Default: disabled.

<@@label>bgp-next-hop-address next hop address ip

Specify which address to use when our own local address should be announced in the Next Hop attribute. Default: the source address of the BGP session (if acceptable), or the preferred address of an associated interface.

<@@label>bgp-missing-lladdr missing lladdr self|drop|ignore

Next Hop attribute in BGP-IPv6 sometimes contains just the global IPv6 address, but sometimes it has to contain both global and link-local IPv6 addresses. This option specifies what to do if BIRD have to send both addresses but does not know link-local address. This situation might happen when routes from other protocols are exported to BGP, or when improper updates are received from BGP peers. self means that BIRD advertises its own local address instead. drop means that BIRD skips that prefixes and logs error. ignore means that BIRD ignores the problem and sends just the global address (and therefore forms improper BGP update). Default: self, unless BIRD is configured as a route server (option rs client), in that case default is ignore, because route servers usually do not forward packets themselves.

<@@label>bgp-gateway gateway direct|recursive

For received routes, their gw (immediate next hop) attribute is computed from received bgp_next_hop attribute. This option specifies how it is computed. Direct mode means that the IP address from bgp_next_hop is used if it is directly reachable, otherwise the neighbor IP address is used. Recursive mode means that the gateway is computed by an IGP routing table lookup for the IP address from bgp_next_hop. Note that there is just one level of indirection in recursive mode - the route obtained by the lookup must not be recursive itself, to prevent mutually recursive routes.

Recursive mode is the behavior specified by the BGP standard. Direct mode is simpler, does not require any routes in a routing table, and was used in older versions of BIRD, but does not handle well nontrivial iBGP setups and multihop. Recursive mode is incompatible with <@@ref>dsc-table-sortedsorted tables. Default: direct for direct sessions, recursive for multihop sessions.

<@@label>bgp-igp-table igp table name

Specifies a table that is used as an IGP routing table. The type of this table must be as allowed in the table above. This option is allowed once for every allowed table type. Default: the same as the main table the channel is connected to (if eligible).

<@@label>bgp-import-table import table switch

A BGP import table contains all received routes from given BGP neighbor, before application of import filters. It is also called Adj-RIB-In in BGP terminology. BIRD BGP by default operates without import tables, in which case received routes are just processed by import filters, accepted ones are stored in the master table, and the rest is forgotten. Enabling import table allows to store unprocessed routes, which can be examined later by show route, and can be used to reconfigure import filters without full route refresh. Default: off.

<@@label>bgp-export-table export table switch

A BGP export table contains all routes sent to given BGP neighbor, after application of export filters. It is also called Adj-RIB-Out in BGP terminology. BIRD BGP by default operates without export tables, in which case routes from master table are just processed by export filters and then announced by BGP. Enabling export table allows to store routes after export filter processing, so they can be examined later by show route, and can be used to eliminate unnecessary updates or withdraws. Default: off.

<@@label>bgp-secondary secondary switch

Usually, if an export filter rejects a selected route, no other route is propagated for that network. This option allows to try the next route in order until one that is accepted is found or all routes for that network are rejected. This can be used for route servers that need to propagate different tables to each client but do not want to have these tables explicitly (to conserve memory). This option requires that the connected routing table is <@@ref>dsc-table-sortedsorted tables<@@ref>dsc-table-sortedsorted. Default: off.

<@@label>bgp-extended-next-hop extended next hop switch

BGP expects that announced next hops have the same address family as associated network prefixes. This option provides an extension to use IPv4 next hops with IPv6 prefixes and vice versa. For IPv4 / VPNv4 channels, the behavior is controlled by the Extended Next Hop Encoding capability, as described in RFC 5549. For IPv6 / VPNv6 channels, just IPv4-mapped IPv6 addresses are used, as described in RFC 4798 and RFC 4659. Default: off.

<@@label>bgp-add-paths add paths switch|rx|tx

Standard BGP can propagate only one path (route) per destination network (usually the selected one). This option controls the add-path protocol extension, which allows to advertise any number of paths to a destination. Note that to be active, add-path has to be enabled on both sides of the BGP session, but it could be enabled separately for RX and TX direction. When active, all available routes accepted by the export filter are advertised to the neighbor. Default: off.

<@@label>bgp-aigp aigp switch|originate

The BGP protocol does not use a common metric like other routing protocols, instead it uses a set of criteria for route selection consisting both overall AS path length and a distance to the nearest AS boundary router. Assuming that metrics of different autonomous systems are incomparable, once a route is propagated from an AS to a next one, the distance in the old AS does not matter.

The AIGP extension (RFC 7311) allows to propagate accumulated IGP metric (in the AIGP attribute) through both IBGP and EBGP links, computing total distance through multiple autonomous systems (assuming they use comparable IGP metric). The total AIGP metric is compared in the route selection process just after Local Preference comparison (and before AS path length comparison).

This option controls whether AIGP attribute propagation is allowed on the session. Optionally, it can be set to originate, which not only allows AIGP attribute propagation, but also new AIGP attributes are automatically attached to non-BGP routes with valid IGP metric (e.g. ospf_metric1) as they are exported to the BGP session. Default: enabled for IBGP (and intra-confederation EBGP), disabled for regular EBGP.

<@@label>bgp-cost cost number

When BGP <@@ref>dsc-table-sortedsorted tables<@@ref>dsc-table-sortedsorted<@@ref>bgp-gatewaygateway mode is recursive (mainly multihop IBGP sessions), then the distance to BGP next hop is based on underlying IGP metric. This option specifies the distance to BGP next hop for BGP sessions in direct gateway mode (mainly direct EBGP sessions).

<@@label>bgp-graceful-restart-c graceful restart switch

Although BGP graceful restart is configured mainly by protocol-wide <@@ref>dsc-table-sortedsorted tables<@@ref>dsc-table-sortedsorted<@@ref>bgp-gatewaygateway mode<@@ref>bgp-graceful-restartoptions, it is possible to configure restarting role per AFI/SAFI pair by this channel option. The option is ignored if graceful restart is disabled by protocol-wide option. Default: off in aware mode, on in full mode.

<@@label>bgp-long-lived-graceful-restart-c long lived graceful restart switch

BGP long-lived graceful restart is configured mainly by protocol-wide <@@ref>dsc-table-sortedsorted tables<@@ref>dsc-table-sortedsorted<@@ref>bgp-gatewaygateway mode<@@ref>bgp-graceful-restartoptions<@@ref>bgp-long-lived-graceful-restartoptions, but the restarting role can be set per AFI/SAFI pair by this channel option. The option is ignored if long-lived graceful restart is disabled by protocol-wide option. Default: off in aware mode, on in full mode.

<@@label>bgp-long-lived-stale-time-c long lived stale time number

Like previous graceful restart channel options, this option allows to set <@@ref>dsc-table-sortedsorted tables<@@ref>dsc-table-sortedsorted<@@ref>bgp-gatewaygateway mode<@@ref>bgp-graceful-restartoptions<@@ref>bgp-long-lived-graceful-restartoptions<@@ref>bgp-long-lived-stale-timelong lived stale time per AFI/SAFI pair instead of per protocol. Default: set by protocol-wide option.

Attributes<@@label>bgp-attr

BGP defines several route attributes. Some of them (those marked with `I' in the table below) are available on internal BGP connections only, some of them (marked with `O') are optional.

<@@label>rta-bgp-path bgppath bgp_path

Sequence of AS numbers describing the AS path the packet will travel through when forwarded according to the particular route. In case of internal BGP it doesn't contain the number of the local AS.

<@@label>rta-bgp-local-pref int bgp_local_pref [I]

Local preference value used for selection among multiple BGP routes (see the selection rules above). It's used as an additional metric which is propagated through the whole local AS.

<@@label>rta-bgp-med int bgp_med [O]

The Multiple Exit Discriminator of the route is an optional attribute which is used on external (inter-AS) links to convey to an adjacent AS the optimal entry point into the local AS. The received attribute is also propagated over internal BGP links. The attribute value is zeroed when a route is exported to an external BGP instance to ensure that the attribute received from a neighboring AS is not propagated to other neighboring ASes. A new value might be set in the export filter of an external BGP instance. See RFC 4451 for further discussion of BGP MED attribute.

<@@label>rta-bgp-origin enum bgp_origin

Origin of the route: either ORIGIN_IGP if the route has originated in an interior routing protocol or ORIGIN_EGP if it's been imported from the EGP protocol (nowadays it seems to be obsolete) or ORIGIN_INCOMPLETE if the origin is unknown.

<@@label>rta-bgp-next-hop ip bgp_next_hop

Next hop to be used for forwarding of packets to this destination. On internal BGP connections, it's an address of the originating router if it's inside the local AS or a boundary router the packet will leave the AS through if it's an exterior route, so each BGP speaker within the AS has a chance to use the shortest interior path possible to this point.

<@@label>rta-bgp-atomic-aggr void bgp_atomic_aggr [O]

This is an optional attribute which carries no value, but the sole presence of which indicates that the route has been aggregated from multiple routes by some router on the path from the originator.

<@@label>rta-bgp-aggregator void bgp_aggregator [O]

This is an optional attribute specifying AS number and IP address of the BGP router that created the route by aggregating multiple BGP routes. Currently, the attribute is not accessible from filters.

<@@label>rta-bgp-community clist bgp_community [O]

List of community values associated with the route. Each such value is a pair (represented as a pair data type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines the community and the second one being a per-AS identifier. There are lots of uses of the community mechanism, but generally they are used to carry policy information like "don't export to USA peers". As each AS can define its own routing policy, it also has a complete freedom about which community attributes it defines and what will their semantics be.

<@@label>rta-bgp-ext-community eclist bgp_ext_community [O]

List of extended community values associated with the route. Extended communities have similar usage as plain communities, but they have an extended range (to allow 4B ASNs) and a nontrivial structure with a type field. Individual community values are represented using an ec data type inside the filters.

<@@label>rta-bgp-large-community lclist bgp_large_community [O]

List of large community values associated with the route. Large BGP communities is another variant of communities, but contrary to extended communities they behave very much the same way as regular communities, just larger -- they are uniform untyped triplets of 32bit numbers. Individual community values are represented using an lc data type inside the filters.

<@@label>rta-bgp-originator-id quad bgp_originator_id [I, O]

This attribute is created by the route reflector when reflecting the route and contains the router ID of the originator of the route in the local AS.

<@@label>rta-bgp-cluster-list clist bgp_cluster_list [I, O]

This attribute contains a list of cluster IDs of route reflectors. Each route reflector prepends its cluster ID when reflecting the route.

<@@label>rta-bgp-aigp void bgp_aigp [O]

This attribute contains accumulated IGP metric, which is a total distance to the destination through multiple autonomous systems. Currently, the attribute is not accessible from filters.

Example<@@label>bgp-exam

protocol bgp {
        local 198.51.100.14 as 65000;        # Use a private AS number
        neighbor 198.51.100.130 as 64496;    # Our neighbor ...
        multihop;                            # ... which is connected indirectly
        ipv4 {
                export filter {                      # We use non-trivial export rules
                        if source = RTS_STATIC then { # Export only static routes
                                # Assign our community
                                bgp_community.add((65000,64501));
                                # Artificially increase path length
                                # by advertising local AS number twice
                                if bgp_path ~ [= 65000 =] then
                                        bgp_path.prepend(65000);
                                accept;
                        }
                        reject;
                };
                import all;
                next hop self; # advertise this router as next hop
                igp table myigptable4; # IGP table for routes with IPv4 nexthops
                igp table myigptable6; # IGP table for routes with IPv6 nexthops
        };
        ipv6 {
                export filter mylargefilter; # We use a named filter
                import all;
                missing lladdr self;
                igp table myigptable4; # IGP table for routes with IPv4 nexthops
                igp table myigptable6; # IGP table for routes with IPv6 nexthops
        };
        ipv4 multicast {
                import all;
                export filter someotherfilter;
                table mymulticasttable4; # Another IPv4 table, dedicated for multicast
                igp table myigptable4;
        };
}

6.4 Device <@@label>device

The Device protocol is not a real routing protocol. It doesn't generate any routes and it only serves as a module for getting information about network interfaces from the kernel. This protocol supports no channel.

Except for very unusual circumstances, you probably should include this protocol in the configuration since almost all other protocols require network interfaces to be defined for them to work with.

Configuration<@@label>device-config

<@@label>device-scan-time scan time number

Time in seconds between two scans of the network interface list. On systems where we are notified about interface status changes asynchronously (such as newer versions of Linux), we need to scan the list only in order to avoid confusion by lost notification messages, so the default time is set to a large value.

<@@label>device-iface interface pattern [, ...]

By default, the Device protocol handles all interfaces without any configuration. Interface definitions allow to specify optional parameters for specific interfaces. See <@@ref>proto-ifaceinterface common option for detailed description. Currently only one interface option is available:

<@@label>device-preferred preferred ip

If a network interface has more than one IP address, BIRD chooses one of them as a preferred one. Preferred IP address is used as source address for packets or announced next hop by routing protocols. Precisely, BIRD chooses one preferred IPv4 address, one preferred IPv6 address and one preferred link-local IPv6 address. By default, BIRD chooses the first found IP address as the preferred one.

This option allows to specify which IP address should be preferred. May be used multiple times for different address classes (IPv4, IPv6, IPv6 link-local). In all cases, an address marked by operating system as secondary cannot be chosen as the primary one.

As the Device protocol doesn't generate any routes, it cannot have any attributes. Example configuration looks like this:

protocol device {
        scan time 10;           # Scan the interfaces often
        interface "eth0" {
                preferred 192.168.1.1;
                preferred 2001:db8:1:10::1;
        };
}

6.5 Direct <@@label>direct

The Direct protocol is a simple generator of device routes for all the directly connected networks according to the list of interfaces provided by the kernel via the Device protocol. The Direct protocol supports both IPv4 and IPv6 channels; both can be configured simultaneously. It can also be configured with <@@ref>ip-sadr-routesIPv6 SADR channel instead of regular IPv6 channel in order to be used together with SADR-enabled Babel protocol.

The question is whether it is a good idea to have such device routes in BIRD routing table. OS kernel usually handles device routes for directly connected networks by itself so we don't need (and don't want) to export these routes to the kernel protocol. OSPF protocol creates device routes for its interfaces itself and BGP protocol is usually used for exporting aggregate routes. But the Direct protocol is necessary for distance-vector protocols like RIP or Babel to announce local networks.

There are just few configuration options for the Direct protocol:

<@@label>direct-iface interface pattern [, ...]

By default, the Direct protocol will generate device routes for all the interfaces available. If you want to restrict it to some subset of interfaces or addresses (e.g. if you're using multiple routing tables for policy routing and some of the policy domains don't contain all interfaces), just use this clause. See <@@ref>ip-sadr-routesIPv6 SADR<@@ref>proto-ifaceinterface common option for detailed description. The Direct protocol uses extended interface clauses.

<@@label>direct-check-link check link switch

If enabled, a hardware link state (reported by OS) is taken into consideration. Routes for directly connected networks are generated only if link up is reported and they are withdrawn when link disappears (e.g., an ethernet cable is unplugged). Default value is no.

Direct device routes don't contain any specific attributes.

Example config might look like this:

protocol direct {
        ipv4;
        ipv6;
        interface "-arc*", "*";         # Exclude the ARCnets
}

6.6 Kernel <@@label>krt

The Kernel protocol is not a real routing protocol. Instead of communicating with other routers in the network, it performs synchronization of BIRD's routing tables with the OS kernel. Basically, it sends all routing table updates to the kernel and from time to time it scans the kernel tables to see whether some routes have disappeared (for example due to unnoticed up/down transition of an interface) or whether an `alien' route has been added by someone else (depending on the learn switch, such routes are either ignored or accepted to our table).

Note that routes created by OS kernel itself, namely direct routes representing IP subnets of associated interfaces, are not imported even with learn enabled. You can use <@@ref>directDirect protocol to generate these direct routes.

If your OS supports only a single routing table, you can configure only one instance of the Kernel protocol. If it supports multiple tables (in order to allow policy routing; such an OS is for example Linux), you can run as many instances as you want, but each of them must be connected to a different BIRD routing table and to a different kernel table.

Because the kernel protocol is partially integrated with the connected routing table, there are two limitations - it is not possible to connect more kernel protocols to the same routing table and changing route destination (gateway) in an export filter of a kernel protocol does not work. Both limitations can be overcome using another routing table and the pipe protocol.

The Kernel protocol supports both IPv4 and IPv6 channels; only one channel can be configured in each protocol instance. On Linux, it also supports <@@ref>directDirect protocol<@@ref>ip-sadr-routesIPv6 SADR and <@@ref>directDirect protocol<@@ref>ip-sadr-routesIPv6 SADR<@@ref>mpls-routesMPLS channels.

Configuration<@@label>krt-config

<@@label>krt-persist persist switch

Tell BIRD to leave all its routes in the routing tables when it exits (instead of cleaning them up).

<@@label>krt-scan-time scan time number

Time in seconds between two consecutive scans of the kernel routing table.

<@@label>krt-learn learn switch

Enable learning of routes added to the kernel routing tables by other routing daemons or by the system administrator. This is possible only on systems which support identification of route authorship.

<@@label>krt-kernel-table kernel table number

Select which kernel table should this particular instance of the Kernel protocol work with. Available only on systems supporting multiple routing tables.

<@@label>krt-metric metric number

(Linux) Use specified value as a kernel metric (priority) for all routes sent to the kernel. When multiple routes for the same network are in the kernel routing table, the Linux kernel chooses one with lower metric. Also, routes with different metrics do not clash with each other, therefore using dedicated metric value is a reliable way to avoid overwriting routes from other sources (e.g. kernel device routes). Metric 0 has a special meaning of undefined metric, in which either OS default is used, or per-route metric can be set using krt_metric attribute. Default: 32.

<@@label>krt-graceful-restart graceful restart switch

Participate in graceful restart recovery. If this option is enabled and a graceful restart recovery is active, the Kernel protocol will defer synchronization of routing tables until the end of the recovery. Note that import of kernel routes to BIRD is not affected.

<@@label>krt-merge-paths merge paths switch [limit number]

Usually, only best routes are exported to the kernel protocol. With path merging enabled, both best routes and equivalent non-best routes are merged during export to generate one ECMP (equal-cost multipath) route for each network. This is useful e.g. for BGP multipath. Note that best routes are still pivotal for route export (responsible for most properties of resulting ECMP routes), while exported non-best routes are responsible just for additional multipath next hops. This option also allows to specify a limit on maximal number of nexthops in one route. By default, multipath merging is disabled. If enabled, default value of the limit is 16.

Attributes<@@label>krt-attr

The Kernel protocol defines several attributes. These attributes are translated to appropriate system (and OS-specific) route attributes. We support these attributes:

<@@label>rta-krt-source int krt_source

The original source of the imported kernel route. The value is system-dependent. On Linux, it is a value of the protocol field of the route. See /etc/iproute2/rt_protos for common values. On BSD, it is based on STATIC and PROTOx flags. The attribute is read-only.

<@@label>rta-krt-metric int krt_metric

(Linux) The kernel metric of the route. When multiple same routes are in a kernel routing table, the Linux kernel chooses one with lower metric. Note that preferred way to set kernel metric is to use protocol option metric, unless per-route metric values are needed.

<@@label>rta-krt-prefsrc ip krt_prefsrc

(Linux) The preferred source address. Used in source address selection for outgoing packets. Has to be one of the IP addresses of the router.

<@@label>rta-krt-realm int krt_realm

(Linux) The realm of the route. Can be used for traffic classification.

<@@label>rta-krt-scope int krt_scope

(Linux IPv4) The scope of the route. Valid values are 0-254, although Linux kernel may reject some values depending on route type and nexthop. It is supposed to represent `indirectness' of the route, where nexthops of routes are resolved through routes with a higher scope, but in current kernels anything below link (253) is treated as global (0). When not present, global scope is implied for all routes except device routes, where link scope is used by default.

In Linux, there is also a plenty of obscure route attributes mostly focused on tuning TCP performance of local connections. BIRD supports most of these attributes, see Linux or iproute2 documentation for their meaning. Attributes krt_lock_* and krt_feature_* have type bool, others have type int. Supported attributes are:

krt_mtu, krt_lock_mtu, krt_window, krt_lock_window, krt_rtt, krt_lock_rtt, krt_rttvar, krt_lock_rttvar, krt_sstresh, krt_lock_sstresh, krt_cwnd, krt_lock_cwnd, krt_advmss, krt_lock_advmss, krt_reordering, krt_lock_reordering, krt_hoplimit, krt_lock_hoplimit, krt_rto_min, krt_lock_rto_min, krt_initcwnd, krt_initrwnd, krt_quickack, krt_feature_ecn, krt_feature_allfrag

Example<@@label>krt-exam

A simple configuration can look this way:

protocol kernel {
        export all;
}

Or for a system with two routing tables:

protocol kernel {               # Primary routing table
        learn;                  # Learn alien routes from the kernel
        persist;                # Don't remove routes on bird shutdown
        scan time 10;           # Scan kernel routing table every 10 seconds
        ipv4 {
                import all;
                export all;
        };
}

protocol kernel {               # Secondary routing table
        kernel table 100;
        ipv4 {
                table auxtable;
                export all;
        };
}

6.7 MRT <@@label>mrt

Introduction<@@label>mrt-intro

The MRT protocol is a component responsible for handling the Multi-Threaded Routing Toolkit (MRT) routing information export format, which is mainly used for collecting and analyzing of routing information from BGP routers. The MRT protocol can be configured to do periodic dumps of routing tables, created MRT files can be analyzed later by other tools. Independent MRT table dumps can also be requested from BIRD client. There is also a feature to save incoming BGP messages in MRT files, but it is controlled by <@@ref>proto-mrtdumpmrtdump options independently of MRT protocol, although that might change in the future.

BIRD implements the main MRT format specification as defined in RFC 6396 and the ADD_PATH extension (RFC 8050).

Configuration<@@label>mrt-config

MRT configuration consists of several statements describing routing table dumps. Multiple independent periodic dumps can be done as multiple MRT protocol instances. The MRT protocol does not use channels. There are two mandatory statements: filename and period.

The behavior can be modified by following configuration parameters:

<@@label>mrt-table table name | "pattern"

Specify a routing table (or a set of routing tables described by a wildcard pattern) that are to be dumped by the MRT protocol instance. Default: the master table.

<@@label>mrt-filter filter { filter commands }

The MRT protocol allows to specify a filter that is applied to routes as they are dumped. Rejected routes are ignored and not saved to the MRT dump file. Default: no filter.

<@@label>mrt-where where filter expression

An alternative way to specify a filter for the MRT protocol.

<@@label>mrt-filename filename "filename"

Specify a filename for MRT dump files. The filename may contain time format sequences with strftime(3) notation (see man strftime for details), there is also a sequence "%N" that is expanded to the name of dumped table. Therefore, each periodic dump of each table can be saved to a different file. Mandatory, see example below.

<@@label>mrt-period period number

Specify the time interval (in seconds) between periodic dumps. Mandatory.

<@@label>mrt-always-add-path always add path switch

The MRT format uses special records (specified in RFC 8050) for routes received using BGP ADD_PATH extension to keep Path ID, while other routes use regular records. This has advantage of better compatibility with tools that do not know special records, but it loses information about which route is the best route. When this option is enabled, both ADD_PATH and non-ADD_PATH routes are stored in ADD_PATH records and order of routes for network is preserved. Default: disabled.

Example<@@label>mrt-exam

protocol mrt {
        table "tab*";
        where source = RTS_BGP;
        filename "/var/log/bird/%N_%F_%T.mrt";
        period 300;
}

6.8 OSPF <@@label>ospf

Introduction<@@label>ospf-intro

Open Shortest Path First (OSPF) is a quite complex interior gateway protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328 and the current IPv6 version (OSPFv3) is defined in RFC 5340 It's a link state (a.k.a. shortest path first) protocol -- each router maintains a database describing the autonomous system's topology. Each participating router has an identical copy of the database and all routers run the same algorithm calculating a shortest path tree with themselves as a root. OSPF chooses the least cost path as the best path.

In OSPF, the autonomous system can be split to several areas in order to reduce the amount of resources consumed for exchanging the routing information and to protect the other areas from incorrect routing data. Topology of the area is hidden to the rest of the autonomous system.

Another very important feature of OSPF is that it can keep routing information from other protocols (like Static or BGP) in its link state database as external routes. Each external route can be tagged by the advertising router, making it possible to pass additional information between routers on the boundary of the autonomous system.

OSPF quickly detects topological changes in the autonomous system (such as router interface failures) and calculates new loop-free routes after a short period of convergence. Only a minimal amount of routing traffic is involved.

Each router participating in OSPF routing periodically sends Hello messages to all its interfaces. This allows neighbors to be discovered dynamically. Then the neighbors exchange theirs parts of the link state database and keep it identical by flooding updates. The flooding process is reliable and ensures that each router detects all changes.

Configuration<@@label>ospf-config

First, the desired OSPF version can be specified by using ospf v2 or ospf v3 as a protocol type. By default, OSPFv2 is used. In the main part of configuration, there can be multiple definitions of OSPF areas, each with a different id. These definitions includes many other switches and multiple definitions of interfaces. Definition of interface may contain many switches and constant definitions and list of neighbors on nonbroadcast networks.

OSPFv2 needs one IPv4 channel. OSPFv3 needs either one IPv6 channel, or one IPv4 channel (RFC 5838). Therefore, it is possible to use OSPFv3 for both IPv4 and Pv6 routing, but it is necessary to have two protocol instances anyway. If no channel is configured, appropriate channel is defined with default parameters.

protocol ospf [v2|v3] <name> {
        rfc1583compat <switch>;
        rfc5838 <switch>;
        instance id <num>;
        stub router <switch>;
        tick <num>;
        ecmp <switch> [limit <num>];
        merge external <switch>;
        graceful restart <switch>|aware;
        graceful restart time <num>;
        area <id> {
                stub;
                nssa;
                summary <switch>;
                default nssa <switch>;
                default cost <num>;
                default cost2 <num>;
                translator <switch>;
                translator stability <num>;

                networks {
                        <prefix>;
                        <prefix> hidden;
                }
                external {
                        <prefix>;
                        <prefix> hidden;
                        <prefix> tag <num>;
                }
                stubnet <prefix>;
                stubnet <prefix> {
                        hidden <switch>;
                        summary <switch>;
                        cost <num>;
                }
                interface <interface pattern> [instance <num>] {
                        cost <num>;
                        stub <switch>;
                        hello <num>;
                        poll <num>;
                        retransmit <num>;
                        priority <num>;
                        wait <num>;
                        dead count <num>;
                        dead <num>;
                        secondary <switch>;
                        rx buffer [normal|large|<num>];
                        tx length <num>;
                        type [broadcast|bcast|pointopoint|ptp|
                                nonbroadcast|nbma|pointomultipoint|ptmp];
                        link lsa suppression <switch>;
                        strict nonbroadcast <switch>;
                        real broadcast <switch>;
                        ptp netmask <switch>;
                        check link <switch>;
                        bfd <switch>;
                        ecmp weight <num>;
                        ttl security [<switch>; | tx only]
                        tx class|dscp <num>;
                        tx priority <num>;
                        authentication none|simple|cryptographic;
                        password "<text>";
                        password "<text>" {
                                id <num>;
                                generate from "<date>";
                                generate to "<date>";
                                accept from "<date>";
                                accept to "<date>";
                                from "<date>";
                                to "<date>";
                                algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 );
                        };
                        neighbors {
                                <ip>;
                                <ip> eligible;
                        };
                };
                virtual link <id> [instance <num>] {
                        hello <num>;
                        retransmit <num>;
                        wait <num>;
                        dead count <num>;
                        dead <num>;
                        authentication none|simple|cryptographic;
                        password "<text>";
                        password "<text>" {
                                id <num>;
                                generate from "<date>";
                                generate to "<date>";
                                accept from "<date>";
                                accept to "<date>";
                                from "<date>";
                                to "<date>";
                                algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 );
                        };
                };
        };
}

<@@label>ospf-rfc1583compat rfc1583compat switch

This option controls compatibility of routing table calculation with RFC 1583. Default value is no.

<@@label>ospf-rfc5838 rfc5838 switch

Basic OSPFv3 is limited to IPv6 unicast routing. The RFC 5838 extension defines support for more address families (IPv4, IPv6, both unicast and multicast). The extension is enabled by default, but can be disabled if necessary, as it restricts the range of available instance IDs. Default value is yes.

<@@label>ospf-instance-id instance id num

When multiple OSPF protocol instances are active on the same links, they should use different instance IDs to distinguish their packets. Although it could be done on per-interface basis, it is often preferred to set one instance ID to whole OSPF domain/topology (e.g., when multiple instances are used to represent separate logical topologies on the same physical network). This option specifies the instance ID for all interfaces of the OSPF instance, but can be overridden by interface option. Default value is 0 unless OSPFv3-AF extended address families are used, see RFC 5838 for that case.

<@@label>ospf-stub-router stub router switch

This option configures the router to be a stub router, i.e., a router that participates in the OSPF topology but does not allow transit traffic. In OSPFv2, this is implemented by advertising maximum metric for outgoing links. In OSPFv3, the stub router behavior is announced by clearing the R-bit in the router LSA. See RFC 6987 for details. Default value is no.

<@@label>ospf-tick tick num

The routing table calculation and clean-up of areas' databases is not performed when a single link state change arrives. To lower the CPU utilization, it's processed later at periodical intervals of num seconds. The default value is 1.

<@@label>ospf-ecmp ecmp switch [limit number]

This option specifies whether OSPF is allowed to generate ECMP (equal-cost multipath) routes. Such routes are used when there are several directions to the destination, each with the same (computed) cost. This option also allows to specify a limit on maximum number of nexthops in one route. By default, ECMP is enabled if supported by Kernel. Default value of the limit is 16.

<@@label>ospf-merge-external merge external switch

This option specifies whether OSPF should merge external routes from different routers/LSAs for the same destination. When enabled together with ecmp, equal-cost external routes will be combined to multipath routes in the same way as regular routes. When disabled, external routes from different LSAs are treated as separate even if they represents the same destination. Default value is no.

<@@label>ospf-graceful-restart graceful restart switch|aware

When an OSPF instance is restarted, neighbors break adjacencies and recalculate their routing tables, which disrupts packet forwarding even when the forwarding plane of the restarting router remains intact. RFC 3623 specifies a graceful restart mechanism to alleviate this issue. For OSPF graceful restart, restarting router originates Grace-LSAs, announcing intent to do graceful restart. Neighbors receiving these LSAs enter helper mode, in which they ignore breakdown of adjacencies, behave as if nothing is happening and keep old routes. When adjacencies are reestablished, the restarting router flushes Grace-LSAs and graceful restart is ended.

This option controls the graceful restart mechanism. It has three states: Disabled, when no support is provided. Aware, when graceful restart helper mode is supported, but no local graceful restart is allowed (i.e. helper-only role). Enabled, when the full graceful restart support is provided (i.e. both restarting and helper role). Note that proper support for local graceful restart requires also configuration of other protocols. Default: aware.

<@@label>ospf-graceful-restart-time graceful restart time num

The restart time is announced in the Grace-LSA and specifies how long neighbors should wait for proper end of the graceful restart before exiting helper mode prematurely. Default: 120 seconds.

<@@label>ospf-area area id

This defines an OSPF area with given area ID (an integer or an IPv4 address, similarly to a router ID). The most important area is the backbone (ID 0) to which every other area must be connected.

<@@label>ospf-stub stub

This option configures the area to be a stub area. External routes are not flooded into stub areas. Also summary LSAs can be limited in stub areas (see option summary). By default, the area is not a stub area.

<@@label>ospf-nssa nssa

This option configures the area to be a NSSA (Not-So-Stubby Area). NSSA is a variant of a stub area which allows a limited way of external route propagation. Global external routes are not propagated into a NSSA, but an external route can be imported into NSSA as a (area-wide) NSSA-LSA (and possibly translated and/or aggregated on area boundary). By default, the area is not NSSA.

<@@label>ospf-summary summary switch

This option controls propagation of summary LSAs into stub or NSSA areas. If enabled, summary LSAs are propagated as usual, otherwise just the default summary route (0.0.0.0/0) is propagated (this is sometimes called totally stubby area). If a stub area has more area boundary routers, propagating summary LSAs could lead to more efficient routing at the cost of larger link state database. Default value is no.

<@@label>ospf-default-nssa default nssa switch

When summary option is enabled, default summary route is no longer propagated to the NSSA. In that case, this option allows to originate default route as NSSA-LSA to the NSSA. Default value is no.

<@@label>ospf-default-cost default cost num

This option controls the cost of a default route propagated to stub and NSSA areas. Default value is 1000.

<@@label>ospf-default-cost2 default cost2 num

When a default route is originated as NSSA-LSA, its cost can use either type 1 or type 2 metric. This option allows to specify the cost of a default route in type 2 metric. By default, type 1 metric (option default cost) is used.

<@@label>ospf-translator translator switch

This option controls translation of NSSA-LSAs into external LSAs. By default, one translator per NSSA is automatically elected from area boundary routers. If enabled, this area boundary router would unconditionally translate all NSSA-LSAs regardless of translator election. Default value is no.

<@@label>ospf-translator-stability translator stability num

This option controls the translator stability interval (in seconds). When the new translator is elected, the old one keeps translating until the interval is over. Default value is 40.

<@@label>ospf-networks networks { set }

Definition of area IP ranges. This is used in summary LSA origination. Hidden networks are not propagated into other areas.

<@@label>ospf-external external { set }

Definition of external area IP ranges for NSSAs. This is used for NSSA-LSA translation. Hidden networks are not translated into external LSAs. Networks can have configured route tag.

<@@label>ospf-stubnet stubnet prefix { options }

Stub networks are networks that are not transit networks between OSPF routers. They are also propagated through an OSPF area as a part of a link state database. By default, BIRD generates a stub network record for each primary network address on each OSPF interface that does not have any OSPF neighbors, and also for each non-primary network address on each OSPF interface. This option allows to alter a set of stub networks propagated by this router.

Each instance of this option adds a stub network with given network prefix to the set of propagated stub network, unless option hidden is used. It also suppresses default stub networks for given network prefix. When option summary is used, also default stub networks that are subnetworks of given stub network are suppressed. This might be used, for example, to aggregate generated stub networks.

<@@label>ospf-iface interface pattern [instance num]

Defines that the specified interfaces belong to the area being defined. See <@@ref>proto-ifaceinterface common option for detailed description. In OSPFv2, extended interface clauses are used, because each network prefix is handled as a separate virtual interface.

You can specify alternative instance ID for the interface definition, therefore it is possible to have several instances of that interface with different options or even in different areas. For OSPFv2, instance ID support is an extension (RFC 6549) and is supposed to be set per-protocol. For OSPFv3, it is an integral feature.

<@@label>ospf-virtual-link virtual link id [instance num]

Virtual link to router with the router id. Virtual link acts as a point-to-point interface belonging to backbone. The actual area is used as a transport area. This item cannot be in the backbone. Like with interface option, you could also use several virtual links to one destination with different instance IDs.

<@@label>ospf-cost cost num

Specifies output cost (metric) of an interface. Default value is 10.

<@@label>ospf-stub-iface stub switch

If set to interface it does not listen to any packet and does not send any hello. Default value is no.

<@@label>ospf-hello hello num

Specifies interval in seconds between sending of Hello messages. Beware, all routers on the same network need to have the same hello interval. Default value is 10.

<@@label>ospf-poll poll num

Specifies interval in seconds between sending of Hello messages for some neighbors on NBMA network. Default value is 20.

<@@label>ospf-retransmit retransmit num

Specifies interval in seconds between retransmissions of unacknowledged updates. Default value is 5.

<@@label>ospf-transmit-delay transmit delay num

Specifies estimated transmission delay of link state updates send over the interface. The value is added to LSA age of LSAs propagated through it. Default value is 1.

<@@label>ospf-priority priority num

On every multiple access network (e.g., the Ethernet) Designated Router and Backup Designated router are elected. These routers have some special functions in the flooding process. Higher priority increases preferences in this election. Routers with priority 0 are not eligible. Default value is 1.

<@@label>ospf-wait wait num

After start, router waits for the specified number of seconds between starting election and building adjacency. Default value is 4*hello.

<@@label>ospf-dead-count dead count num

When the router does not receive any messages from a neighbor in dead count*hello seconds, it will consider the neighbor down.

<@@label>ospf-dead dead num

When the router does not receive any messages from a neighbor in dead seconds, it will consider the neighbor down. If both directives dead count and dead are used, dead has precedence.

<@@label>ospf-rx-buffer rx buffer num

This option allows to specify the size of buffers used for packet processing. The buffer size should be bigger than maximal size of any packets. By default, buffers are dynamically resized as needed, but a fixed value could be specified. Value large means maximal allowed packet size - 65535.

<@@label>ospf-tx-length tx length num

Transmitted OSPF messages that contain large amount of information are segmented to separate OSPF packets to avoid IP fragmentation. This option specifies the soft ceiling for the length of generated OSPF packets. Default value is the MTU of the network interface. Note that larger OSPF packets may still be generated if underlying OSPF messages cannot be splitted (e.g. when one large LSA is propagated).

<@@label>ospf-type-bcast type broadcast|bcast

BIRD detects a type of a connected network automatically, but sometimes it's convenient to force use of a different type manually. On broadcast networks (like ethernet), flooding and Hello messages are sent using multicasts (a single packet for all the neighbors). A designated router is elected and it is responsible for synchronizing the link-state databases and originating network LSAs. This network type cannot be used on physically NBMA networks and on unnumbered networks (networks without proper IP prefix).

<@@label>ospf-type-ptp type pointopoint|ptp

Point-to-point networks connect just 2 routers together. No election is performed and no network LSA is originated, which makes it simpler and faster to establish. This network type is useful not only for physically PtP ifaces (like PPP or tunnels), but also for broadcast networks used as PtP links. This network type cannot be used on physically NBMA networks.

<@@label>ospf-type-nbma type nonbroadcast|nbma

On NBMA networks, the packets are sent to each neighbor separately because of lack of multicast capabilities. Like on broadcast networks, a designated router is elected, which plays a central role in propagation of LSAs. This network type cannot be used on unnumbered networks.

<@@label>ospf-type-ptmp type pointomultipoint|ptmp

This is another network type designed to handle NBMA networks. In this case the NBMA network is treated as a collection of PtP links. This is useful if not every pair of routers on the NBMA network has direct communication, or if the NBMA network is used as an (possibly unnumbered) PtP link.

<@@label>ospf-link-lsa-suppression link lsa suppression switch

In OSPFv3, link LSAs are generated for each link, announcing link-local IPv6 address of the router to its local neighbors. These are useless on PtP or PtMP networks and this option allows to suppress the link LSA origination for such interfaces. The option is ignored on other than PtP or PtMP interfaces. Default value is no.

<@@label>ospf-strict-nonbroadcast strict nonbroadcast switch

If set, don't send hello to any undefined neighbor. This switch is ignored on other than NBMA or PtMP interfaces. Default value is no.

<@@label>ospf-real-broadcast real broadcast switch

In type broadcast or type ptp network configuration, OSPF packets are sent as IP multicast packets. This option changes the behavior to using old-fashioned IP broadcast packets. This may be useful as a workaround if IP multicast for some reason does not work or does not work reliably. This is a non-standard option and probably is not interoperable with other OSPF implementations. Default value is no.

<@@label>ospf-ptp-netmask ptp netmask switch

In type ptp network configurations, OSPFv2 implementations should ignore received netmask field in hello packets and should send hello packets with zero netmask field on unnumbered PtP links. But some OSPFv2 implementations perform netmask checking even for PtP links. This option specifies whether real netmask will be used in hello packets on type ptp interfaces. You should ignore this option unless you meet some compatibility problems related to this issue. Default value is no for unnumbered PtP links, yes otherwise.

<@@label>ospf-check-link check link switch

If set, a hardware link state (reported by OS) is taken into consideration. When a link disappears (e.g. an ethernet cable is unplugged), neighbors are immediately considered unreachable and only the address of the iface (instead of whole network prefix) is propagated. It is possible that some hardware drivers or platforms do not implement this feature. Default value is yes.

<@@label>ospf-bfd bfd switch

OSPF could use BFD protocol as an advisory mechanism for neighbor liveness and failure detection. If enabled, BIRD setups a BFD session for each OSPF neighbor and tracks its liveness by it. This has an advantage of an order of magnitude lower detection times in case of failure. Note that BFD protocol also has to be configured, see <@@ref>proto-ifaceinterface<@@ref>bfdBFD section for details. Default value is no.

<@@label>ospf-ttl-security ttl security [switch | tx only]

TTL security is a feature that protects routing protocols from remote spoofed packets by using TTL 255 instead of TTL 1 for protocol packets destined to neighbors. Because TTL is decremented when packets are forwarded, it is non-trivial to spoof packets with TTL 255 from remote locations. Note that this option would interfere with OSPF virtual links.

If this option is enabled, the router will send OSPF packets with TTL 255 and drop received packets with TTL less than 255. If this option si set to tx only, TTL 255 is used for sent packets, but is not checked for received packets. Default value is no.

<@@label>ospf-tx-class tx class|dscp|priority num

These options specify the ToS/DiffServ/Traffic class/Priority of the outgoing OSPF packets. See <@@ref>proto-ifaceinterface<@@ref>bfdBFD<@@ref>proto-tx-classtx class common option for detailed description.

<@@label>ospf-ecmp-weight ecmp weight num

When ECMP (multipath) routes are allowed, this value specifies a relative weight used for nexthops going through the iface. Allowed values are 1-256. Default value is 1.

<@@label>ospf-auth-none authentication none

No passwords are sent in OSPF packets. This is the default value.

<@@label>ospf-auth-simple authentication simple

Every packet carries 8 bytes of password. Received packets lacking this password are ignored. This authentication mechanism is very weak. This option is not available in OSPFv3.

<@@label>ospf-auth-cryptographic authentication cryptographic

An authentication code is appended to every packet. The specific cryptographic algorithm is selected by option algorithm for each key. The default cryptographic algorithm for OSPFv2 keys is Keyed-MD5 and for OSPFv3 keys is HMAC-SHA-256. Passwords are not sent open via network, so this mechanism is quite secure. Packets can still be read by an attacker.

<@@label>ospf-pass password "text"

Specifies a password used for authentication. See <@@ref>proto-ifaceinterface<@@ref>bfdBFD<@@ref>proto-tx-classtx class<@@ref>proto-passpassword common option for detailed description.

<@@label>ospf-neighbors neighbors { set }

A set of neighbors to which Hello messages on NBMA or PtMP networks are to be sent. For NBMA networks, some of them could be marked as eligible. In OSPFv3, link-local addresses should be used, using global ones is possible, but it is nonstandard and might be problematic. And definitely, link-local and global addresses should not be mixed.

Attributes<@@label>ospf-attr

OSPF defines four route attributes. Each internal route has a metric.

Metric is ranging from 1 to infinity (65535). External routes use metric type 1 or metric type 2. A metric of type 1 is comparable with internal metric, a metric of type 2 is always longer than any metric of type 1 or any internal metric. Internal metric or metric of type 1 is stored in attribute ospf_metric1, metric type 2 is stored in attribute ospf_metric2.

When both metrics are specified then metric of type 2 is used. This is relevant e.g. when a type 2 external route is propagated from one OSPF domain to another and ospf_metric1 is an internal distance to the original ASBR, while ospf_metric2 stores the type 2 metric. Note that in such cases if ospf_metric1 is non-zero then ospf_metric2 is increased by one to ensure monotonicity of metric, as internal distance is reset to zero when an external route is announced.

Each external route can also carry attribute ospf_tag which is a 32-bit integer which is used when exporting routes to other protocols; otherwise, it doesn't affect routing inside the OSPF domain at all. The fourth attribute ospf_router_id is a router ID of the router advertising that route / network. This attribute is read-only. Default is ospf_metric2 = 10000 and ospf_tag = 0.

Example<@@label>ospf-exam

protocol ospf MyOSPF {
        ipv4 {
                export filter {
                        if source = RTS_BGP then {
                                ospf_metric1 = 100;
                                accept;
                        }
                        reject;
                };
        };
        area 0.0.0.0 {
                interface "eth*" {
                        cost 11;
                        hello 15;
                        priority 100;
                        retransmit 7;
                        authentication simple;
                        password "aaa";
                };
                interface "ppp*" {
                        cost 100;
                        authentication cryptographic;
                        password "abc" {
                                id 1;
                                generate to "22-04-2003 11:00:06";
                                accept from "17-01-2001 12:01:05";
                                algorithm hmac sha384;
                        };
                        password "def" {
                                id 2;
                                generate to "22-07-2005 17:03:21";
                                accept from "22-02-2001 11:34:06";
                                algorithm hmac sha512;
                        };
                };
                interface "arc0" {
                        cost 10;
                        stub yes;
                };
                interface "arc1";
        };
        area 120 {
                stub yes;
                networks {
                        172.16.1.0/24;
                        172.16.2.0/24 hidden;
                }
                interface "-arc0" , "arc*" {
                        type nonbroadcast;
                        authentication none;
                        strict nonbroadcast yes;
                        wait 120;
                        poll 40;
                        dead count 8;
                        neighbors {
                                192.168.120.1 eligible;
                                192.168.120.2;
                                192.168.120.10;
                        };
                };
        };
}

6.9 Perf <@@label>perf

Introduction<@@label>perf-intro

The Perf protocol is a generator of fake routes together with a time measurement framework. Its purpose is to check BIRD performance and to benchmark filters.

Import mode of this protocol runs in several steps. In each step, it generates 2^x routes, imports them into the appropriate table and withdraws them. The exponent x is configurable. It runs the benchmark several times for the same x, then it increases x by one until it gets too high, then it stops.

Export mode of this protocol repeats route refresh from table and measures how long it takes.

Output data is logged on info level. There is a Perl script proto/perf/parse.pl which may be handy to parse the data and draw some plots.

Implementation of this protocol is experimental. Use with caution and do not keep any instance of Perf in production configs for long time. The config interface is also unstable and may change in future versions without warning.

Configuration<@@label>perf-config

<@@label>perf-mode mode import|export

Set perf mode. Default: import

<@@label>perf-repeat repeat number

Run this amount of iterations of the benchmark for every amount step. Default: 4

<@@label>perf-from exp from number

Begin benchmarking on this exponent for number of generated routes in one step. Default: 10

<@@label>perf-to exp to number

Stop benchmarking on this exponent. Default: 20

<@@label>perf-threshold-min threshold min time

If a run for the given exponent took less than this time for route import, increase the exponent immediately. Default: 1 ms

<@@label>perf-threshold-max threshold max time

If every run for the given exponent took at least this time for route import, stop benchmarking. Default: 500 ms

6.10 Pipe <@@label>pipe

Introduction<@@label>pipe-intro

The Pipe protocol serves as a link between two routing tables, allowing routes to be passed from a table declared as primary (i.e., the one the pipe is connected to using the table configuration keyword) to the secondary one (declared using peer table) and vice versa, depending on what's allowed by the filters. Export filters control export of routes from the primary table to the secondary one, import filters control the opposite direction. Both tables must be of the same nettype.

The Pipe protocol retransmits all routes from one table to the other table, retaining their original source and attributes. If import and export filters are set to accept, then both tables would have the same content.

The primary use of multiple routing tables and the Pipe protocol is for policy routing, where handling of a single packet doesn't depend only on its destination address, but also on its source address, source interface, protocol type and other similar parameters. In many systems (Linux being a good example), the kernel allows to enforce routing policies by defining routing rules which choose one of several routing tables to be used for a packet according to its parameters. Setting of these rules is outside the scope of BIRD's work (on Linux, you can use the ip command), but you can create several routing tables in BIRD, connect them to the kernel ones, use filters to control which routes appear in which tables and also you can employ the Pipe protocol for exporting a selected subset of one table to another one.

Configuration<@@label>pipe-config

Essentially, the Pipe protocol is just a channel connected to a table on both sides. Therefore, the configuration block for protocol pipe shall directly include standard channel config options; see the example below.

<@@label>pipe-peer-table peer table table

Defines secondary routing table to connect to. The primary one is selected by the table keyword.

Attributes<@@label>pipe-attr

The Pipe protocol doesn't define any route attributes.

Example<@@label>pipe-exam

Let's consider a router which serves as a boundary router of two different autonomous systems, each of them connected to a subset of interfaces of the router, having its own exterior connectivity and wishing to use the other AS as a backup connectivity in case of outage of its own exterior line.

Probably the simplest solution to this situation is to use two routing tables (we'll call them as1 and as2) and set up kernel routing rules, so that packets having arrived from interfaces belonging to the first AS will be routed according to as1 and similarly for the second AS. Thus we have split our router to two logical routers, each one acting on its own routing table, having its own routing protocols on its own interfaces. In order to use the other AS's routes for backup purposes, we can pass the routes between the tables through a Pipe protocol while decreasing their preferences and correcting their BGP paths to reflect the AS boundary crossing.

ipv4 table as1;                         # Define the tables
ipv4 table as2;

protocol kernel kern1 {                 # Synchronize them with the kernel
        ipv4 { table as1; export all; };
        kernel table 1;
}

protocol kernel kern2 {
        ipv4 { table as2; export all; };
        kernel table 2;
}

protocol bgp bgp1 {                     # The outside connections
        ipv4 { table as1; import all; export all; };
        local as 1;
        neighbor 192.168.0.1 as 1001;
}

protocol bgp bgp2 {
        ipv4 { table as2; import all; export all; };
        local as 2;
        neighbor 10.0.0.1 as 1002;
}

protocol pipe {                         # The Pipe
        table as1;
        peer table as2;
        export filter {
                if net ~ [ 1.0.0.0/8+] then {   # Only AS1 networks
                        if preference>10 then preference = preference-10;
                        if source=RTS_BGP then bgp_path.prepend(1);
                        accept;
                }
                reject;
        };
        import filter {
                if net ~ [ 2.0.0.0/8+] then {   # Only AS2 networks
                        if preference>10 then preference = preference-10;
                        if source=RTS_BGP then bgp_path.prepend(2);
                        accept;
                }
                reject;
        };
}

6.11 RAdv <@@label>radv

Introduction<@@label>radv-intro

The RAdv protocol is an implementation of Router Advertisements, which are used in the IPv6 stateless autoconfiguration. IPv6 routers send (in irregular time intervals or as an answer to a request) advertisement packets to connected networks. These packets contain basic information about a local network (e.g. a list of network prefixes), which allows network hosts to autoconfigure network addresses and choose a default route. BIRD implements router behavior as defined in RFC 4861, router preferences and specific routes (RFC 4191), and DNS extensions (RFC 6106).

The RAdv protocols supports just IPv6 channel.

Configuration<@@label>radv-config

There are several classes of definitions in RAdv configuration -- interface definitions, prefix definitions and DNS definitions:

<@@label>radv-iface interface pattern [, ...] { options }

Interface definitions specify a set of interfaces on which the protocol is activated and contain interface specific options. See <@@ref>proto-ifaceinterface common options for detailed description.

<@@label>radv-prefix prefix prefix { options }

Prefix definitions allow to modify a list of advertised prefixes. By default, the advertised prefixes are the same as the network prefixes assigned to the interface. For each network prefix, the matching prefix definition is found and its options are used. If no matching prefix definition is found, the prefix is used with default options.

Prefix definitions can be either global or interface-specific. The second ones are part of interface options. The prefix definition matching is done in the first-match style, when interface-specific definitions are processed before global definitions. As expected, the prefix definition is matching if the network prefix is a subnet of the prefix in prefix definition.

<@@label>radv-rdnss rdnss { options }

RDNSS definitions allow to specify a list of advertised recursive DNS servers together with their options. As options are seldom necessary, there is also a short variant rdnss address that just specifies one DNS server. Multiple definitions are cumulative. RDNSS definitions may also be interface-specific when used inside interface options. By default, interface uses both global and interface-specific options, but that can be changed by rdnss local option.

<@@label>radv-dnssl dnssl { options }

DNSSL definitions allow to specify a list of advertised DNS search domains together with their options. Like rdnss above, multiple definitions are cumulative, they can be used also as interface-specific options and there is a short variant dnssl domain that just specifies one DNS search domain.

<@@label>radv-trigger trigger prefix

RAdv protocol could be configured to change its behavior based on availability of routes. When this option is used, the protocol waits in suppressed state until a trigger route (for the specified network) is exported to the protocol, the protocol also returns to suppressed state if the trigger route disappears. Note that route export depends on specified export filter, as usual. This option could be used, e.g., for handling failover in multihoming scenarios.

During suppressed state, router advertisements are generated, but with some fields zeroed. Exact behavior depends on which fields are zeroed, this can be configured by sensitive option for appropriate fields. By default, just default lifetime (also called router lifetime) is zeroed, which means hosts cannot use the router as a default router. preferred lifetime and valid lifetime could also be configured as sensitive for a prefix, which would cause autoconfigured IPs to be deprecated or even removed.

<@@label>radv-propagate-routes propagate routes switch

This option controls propagation of more specific routes, as defined in RFC 4191. If enabled, all routes exported to the RAdv protocol, with the exception of the trigger prefix, are added to advertisments as additional options. The lifetime and preference of advertised routes can be set individually by ra_lifetime and ra_preference route attributes, or per interface by route lifetime and route preference options. Default: disabled.

Note that the RFC discourages from sending more than 17 routes and recommends the routes to be configured manually.

Interface specific options:

<@@label>radv-iface-max-ra-interval max ra interval expr

Unsolicited router advertisements are sent in irregular time intervals. This option specifies the maximum length of these intervals, in seconds. Valid values are 4-1800. Default: 600

<@@label>radv-iface-min-ra-interval min ra interval expr

This option specifies the minimum length of that intervals, in seconds. Must be at least 3 and at most 3/4 * max ra interval. Default: about 1/3 * max ra interval.

<@@label>radv-iface-min-delay min delay expr

The minimum delay between two consecutive router advertisements, in seconds. Default: 3

<@@label>radv-solicited-ra-unicast solicited ra unicast switch

Solicited router advertisements are usually sent to all-nodes multicast group like unsolicited ones, but the router can be configured to send them as unicast directly to soliciting nodes instead. This is especially useful on wireless networks (see RFC 7772). Default: no

<@@label>radv-iface-managed managed switch

This option specifies whether hosts should use DHCPv6 for IP address configuration. Default: no

<@@label>radv-iface-other-config other config switch

This option specifies whether hosts should use DHCPv6 to receive other configuration information. Default: no

<@@label>radv-iface-link-mtu link mtu expr

This option specifies which value of MTU should be used by hosts. 0 means unspecified. Default: 0

<@@label>radv-iface-reachable-time reachable time expr

This option specifies the time (in milliseconds) how long hosts should assume a neighbor is reachable (from the last confirmation). Maximum is 3600000, 0 means unspecified. Default 0.

<@@label>radv-iface-retrans-timer retrans timer expr

This option specifies the time (in milliseconds) how long hosts should wait before retransmitting Neighbor Solicitation messages. 0 means unspecified. Default 0.

<@@label>radv-iface-current-hop-limit current hop limit expr

This option specifies which value of Hop Limit should be used by hosts. Valid values are 0-255, 0 means unspecified. Default: 64

<@@label>radv-iface-default-lifetime default lifetime expr [sensitive switch]

This option specifies the time (in seconds) how long (since the receipt of RA) hosts may use the router as a default router. 0 means do not use as a default router. For sensitive option, see <@@ref>proto-ifaceinterface<@@ref>radv-triggertrigger. Default: 3 * max ra interval, sensitive yes.

<@@label>radv-iface-default-preference default preference low|medium|high

This option specifies the Default Router Preference value to advertise to hosts. Default: medium.

<@@label>radv-iface-route-lifetime route lifetime expr [sensitive switch]

This option specifies the default value of advertised lifetime for specific routes; i.e., the time (in seconds) for how long (since the receipt of RA) hosts should consider these routes valid. A special value 0xffffffff represents infinity. The lifetime can be overriden on a per route basis by the <@@ref>proto-ifaceinterface<@@ref>radv-triggertrigger<@@ref>rta-ra-lifetimera_lifetime route attribute. Default: 3 * max ra interval, sensitive no.

For the sensitive option, see <@@ref>proto-ifaceinterface<@@ref>radv-triggertrigger<@@ref>rta-ra-lifetimera_lifetime<@@ref>radv-triggertrigger. If sensitive is enabled, even the routes with the ra_lifetime attribute become sensitive to the trigger.

<@@label>radv-iface-route-preference route preference low|medium|high

This option specifies the default value of advertised route preference for specific routes. The value can be overriden on a per route basis by the <@@ref>proto-ifaceinterface<@@ref>radv-triggertrigger<@@ref>rta-ra-lifetimera_lifetime<@@ref>radv-triggertrigger<@@ref>rta-ra-preferencera_preference route attribute. Default: medium.

<@@label>radv-prefix-linger-time prefix linger time expr

When a prefix or a route disappears, it is advertised for some time with zero lifetime, to inform clients it is no longer valid. This option specifies the time (in seconds) for how long prefixes are advertised that way. Default: 3 * max ra interval.

<@@label>radv-route-linger-time route linger time expr

When a prefix or a route disappears, it is advertised for some time with zero lifetime, to inform clients it is no longer valid. This option specifies the time (in seconds) for how long routes are advertised that way. Default: 3 * max ra interval.

<@@label>radv-iface-rdnss-local rdnss local switch

Use only local (interface-specific) RDNSS definitions for this interface. Otherwise, both global and local definitions are used. Could also be used to disable RDNSS for given interface if no local definitons are specified. Default: no.

<@@label>radv-iface-dnssl-local dnssl local switch

Use only local DNSSL definitions for this interface. See rdnss local option above. Default: no.

Prefix specific options

<@@label>radv-prefix-skip skip switch

This option allows to specify that given prefix should not be advertised. This is useful for making exceptions from a default policy of advertising all prefixes. Note that for withdrawing an already advertised prefix it is more useful to advertise it with zero valid lifetime. Default: no

<@@label>radv-prefix-onlink onlink switch

This option specifies whether hosts may use the advertised prefix for onlink determination. Default: yes

<@@label>radv-prefix-autonomous autonomous switch

This option specifies whether hosts may use the advertised prefix for stateless autoconfiguration. Default: yes

<@@label>radv-prefix-valid-lifetime valid lifetime expr [sensitive switch]

This option specifies the time (in seconds) how long (after the receipt of RA) the prefix information is valid, i.e., autoconfigured IP addresses can be assigned and hosts with that IP addresses are considered directly reachable. 0 means the prefix is no longer valid. For sensitive option, see <@@ref>proto-ifaceinterface<@@ref>radv-triggertrigger<@@ref>rta-ra-lifetimera_lifetime<@@ref>radv-triggertrigger<@@ref>rta-ra-preferencera_preference<@@ref>radv-triggertrigger. Default: 86400 (1 day), sensitive no.

<@@label>radv-prefix-preferred-lifetime preferred lifetime expr [sensitive switch]

This option specifies the time (in seconds) how long (after the receipt of RA) IP addresses generated from the prefix using stateless autoconfiguration remain preferred. For sensitive option, see <@@ref>proto-ifaceinterface<@@ref>radv-triggertrigger<@@ref>rta-ra-lifetimera_lifetime<@@ref>radv-triggertrigger<@@ref>rta-ra-preferencera_preference<@@ref>radv-triggertrigger<@@ref>radv-triggertrigger. Default: 14400 (4 hours), sensitive no.

RDNSS specific options:

<@@label>radv-rdnss-ns ns address

This option specifies one recursive DNS server. Can be used multiple times for multiple servers. It is mandatory to have at least one ns option in rdnss definition.

<@@label>radv-rdnss-lifetime lifetime [mult] expr

This option specifies the time how long the RDNSS information may be used by clients after the receipt of RA. It is expressed either in seconds or (when mult is used) in multiples of max ra interval. Note that RDNSS information is also invalidated when default lifetime expires. 0 means these addresses are no longer valid DNS servers. Default: 3 * max ra interval.

DNSSL specific options:

<@@label>radv-dnssl-domain domain address

This option specifies one DNS search domain. Can be used multiple times for multiple domains. It is mandatory to have at least one domain option in dnssl definition.

<@@label>radv-dnssl-lifetime lifetime [mult] expr

This option specifies the time how long the DNSSL information may be used by clients after the receipt of RA. Details are the same as for RDNSS lifetime option above. Default: 3 * max ra interval.

Attributes<@@label>radv-attr

RAdv defines two route attributes:

<@@label>rta-ra-preference enum ra_preference

The preference of the route. The value can be RA_PREF_LOW, RA_PREF_MEDIUM or RA_PREF_HIGH. If the attribute is not set, the <@@ref>radv-iface-route-preferenceroute preference option is used.

<@@label>rta-ra-lifetime int ra_lifetime

The advertised lifetime of the route, in seconds. The special value of 0xffffffff represents infinity. If the attribute is not set, the <@@ref>radv-iface-route-preferenceroute preference<@@ref>radv-iface-route-lifetimeroute lifetime option is used.

Example<@@label>radv-exam

ipv6 table radv_routes;                 # Manually configured routes go here

protocol static {
        ipv6 { table radv_routes; };

        route 2001:0DB8:4000::/48 unreachable;
        route 2001:0DB8:4010::/48 unreachable;

        route 2001:0DB8:4020::/48 unreachable {
                ra_preference = RA_PREF_HIGH;
                ra_lifetime = 3600;
        };
}

protocol radv {
        propagate routes yes;           # Propagate the routes from the radv_routes table
        ipv6 { table radv_routes; export all; };

        interface "eth2" {
                max ra interval 5;      # Fast failover with more routers
                managed yes;            # Using DHCPv6 on eth2
                prefix ::/0 {
                        autonomous off; # So do not autoconfigure any IP
                };
        };

        interface "eth*";               # No need for any other options

        prefix 2001:0DB8:1234::/48 {
                preferred lifetime 0;   # Deprecated address range
        };

        prefix 2001:0DB8:2000::/48 {
                autonomous off;         # Do not autoconfigure
        };

        rdnss 2001:0DB8:1234::10;       # Short form of RDNSS

        rdnss {
                lifetime mult 10;
                ns 2001:0DB8:1234::11;
                ns 2001:0DB8:1234::12;
        };

        dnssl {
                lifetime 3600;
                domain "abc.com";
                domain "xyz.com";
        };
}

6.12 RIP <@@label>rip

Introduction<@@label>rip-intro

The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors) distances to all networks it can reach. When a router hears distance to another network, it increments it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in RIP) and all routers know that network is unreachable. RIP tries to minimize situations where counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use RIP on networks where maximal distance is higher than 15 hosts.

BIRD supports RIPv1 (RFC 1058), RIPv2 (RFC 2453), RIPng (RFC 2080), and RIP cryptographic authentication (RFC 4822).

RIP is a very simple protocol, and it has a lot of shortcomings. Slow convergence, big network load and inability to handle larger networks makes it pretty much obsolete. It is still usable on very small networks.

Configuration<@@label>rip-config

RIP configuration consists mainly of common protocol options and interface definitions, most RIP options are interface specific. RIPng (RIP for IPv6) protocol instance can be configured by using rip ng instead of just rip as a protocol type.

RIP needs one IPv4 channel. RIPng needs one IPv6 channel. If no channel is configured, appropriate channel is defined with default parameters.

protocol rip [ng] [<name>] {
        infinity <number>;
        ecmp <switch> [limit <number>];
        interface <interface pattern> {
                metric <number>;
                mode multicast|broadcast;
                passive <switch>;
                address <ip>;
                port <number>;
                version 1|2;
                split horizon <switch>;
                poison reverse <switch>;
                check zero <switch>;
                update time <number>;
                timeout time <number>;
                garbage time <number>;
                ecmp weight <number>;
                ttl security <switch>; | tx only;
                tx class|dscp <number>;
                tx priority <number>;
                rx buffer <number>;
                tx length <number>;
                check link <switch>;
                authentication none|plaintext|cryptographic;
                password "<text>";
                password "<text>" {
                        id <num>;
                        generate from "<date>";
                        generate to "<date>";
                        accept from "<date>";
                        accept to "<date>";
                        from "<date>";
                        to "<date>";
                        algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 );
                };
        };
}

<@@label>rip-infinity infinity number

Selects the distance of infinity. Bigger values will make protocol convergence even slower. The default value is 16.

<@@label>rip-ecmp ecmp switch [limit number]

This option specifies whether RIP is allowed to generate ECMP (equal-cost multipath) routes. Such routes are used when there are several directions to the destination, each with the same (computed) cost. This option also allows to specify a limit on maximum number of nexthops in one route. By default, ECMP is enabled if supported by Kernel. Default value of the limit is 16.

<@@label>rip-iface interface pattern [, ...] { options }

Interface definitions specify a set of interfaces on which the protocol is activated and contain interface specific options. See <@@ref>proto-ifaceinterface common options for detailed description.

Interface specific options:

<@@label>rip-iface-metric metric num

This option specifies the metric of the interface. When a route is received from the interface, its metric is increased by this value before further processing. Valid values are 1-255, but values higher than infinity has no further meaning. Default: 1.

<@@label>rip-iface-mode mode multicast|broadcast

This option selects the mode for RIP to use on the interface. The default is multicast mode for RIPv2 and broadcast mode for RIPv1. RIPng always uses the multicast mode.

<@@label>rip-iface-passive passive switch

Passive interfaces receive routing updates but do not transmit any messages. Default: no.

<@@label>rip-iface-address address ip

This option specifies a destination address used for multicast or broadcast messages, the default is the official RIP (224.0.0.9) or RIPng (ff02::9) multicast address, or an appropriate broadcast address in the broadcast mode.

<@@label>rip-iface-port port number

This option selects an UDP port to operate on, the default is the official RIP (520) or RIPng (521) port.

<@@label>rip-iface-version version 1|2

This option selects the version of RIP used on the interface. For RIPv1, automatic subnet aggregation is not implemented, only classful network routes and host routes are propagated. Note that BIRD allows RIPv1 to be configured with features that are defined for RIPv2 only, like authentication or using multicast sockets. The default is RIPv2 for IPv4 RIP, the option is not supported for RIPng, as no further versions are defined.

<@@label>rip-iface-version-only version only switch

Regardless of RIP version configured for the interface, BIRD accepts incoming packets of any RIP version. This option restrict accepted packets to the configured version. Default: no.

<@@label>rip-iface-split-horizon split horizon switch

Split horizon is a scheme for preventing routing loops. When split horizon is active, routes are not regularly propagated back to the interface from which they were received. They are either not propagated back at all (plain split horizon) or propagated back with an infinity metric (split horizon with poisoned reverse). Therefore, other routers on the interface will not consider the router as a part of an independent path to the destination of the route. Default: yes.

<@@label>rip-iface-poison-reverse poison reverse switch

When split horizon is active, this option specifies whether the poisoned reverse variant (propagating routes back with an infinity metric) is used. The poisoned reverse has some advantages in faster convergence, but uses more network traffic. Default: yes.

<@@label>rip-iface-check-zero check zero switch

Received RIPv1 packets with non-zero values in reserved fields should be discarded. This option specifies whether the check is performed or such packets are just processed as usual. Default: yes.

<@@label>rip-iface-update-time update time number

Specifies the number of seconds between periodic updates. A lower number will mean faster convergence but bigger network load. Default: 30.

<@@label>rip-iface-timeout-time timeout time number

Specifies the time interval (in seconds) between the last received route announcement and the route expiration. After that, the network is considered unreachable, but still is propagated with infinity distance. Default: 180.

<@@label>rip-iface-garbage-time garbage time number

Specifies the time interval (in seconds) between the route expiration and the removal of the unreachable network entry. The garbage interval, when a route with infinity metric is propagated, is used for both internal (after expiration) and external (after withdrawal) routes. Default: 120.

<@@label>rip-iface-ecmp-weight ecmp weight number

When ECMP (multipath) routes are allowed, this value specifies a relative weight used for nexthops going through the iface. Valid values are 1-256. Default value is 1.

<@@label>rip-iface-auth authentication none|plaintext|cryptographic

Selects authentication method to be used. none means that packets are not authenticated at all, plaintext means that a plaintext password is embedded into each packet, and cryptographic means that packets are authenticated using some cryptographic hash function selected by option algorithm for each key. The default cryptographic algorithm for RIP keys is Keyed-MD5. If you set authentication to not-none, it is a good idea to add password section. Default: none.

<@@label>rip-iface-pass password "text"

Specifies a password used for authentication. See <@@ref>proto-ifaceinterface<@@ref>proto-passpassword common option for detailed description.

<@@label>rip-iface-ttl-security ttl security [switch | tx only]

TTL security is a feature that protects routing protocols from remote spoofed packets by using TTL 255 instead of TTL 1 for protocol packets destined to neighbors. Because TTL is decremented when packets are forwarded, it is non-trivial to spoof packets with TTL 255 from remote locations.

If this option is enabled, the router will send RIP packets with TTL 255 and drop received packets with TTL less than 255. If this option si set to tx only, TTL 255 is used for sent packets, but is not checked for received packets. Such setting does not offer protection, but offers compatibility with neighbors regardless of whether they use ttl security.

For RIPng, TTL security is a standard behavior (required by RFC 2080) and therefore default value is yes. For IPv4 RIP, default value is no.

<@@label>rip-iface-tx-class tx class|dscp|priority number

These options specify the ToS/DiffServ/Traffic class/Priority of the outgoing RIP packets. See <@@ref>proto-ifaceinterface<@@ref>proto-passpassword<@@ref>proto-tx-classtx class common option for detailed description.

<@@label>rip-iface-rx-buffer rx buffer number

This option specifies the size of buffers used for packet processing. The buffer size should be bigger than maximal size of received packets. The default value is 532 for IPv4 RIP and interface MTU value for RIPng.

<@@label>rip-iface-tx-length tx length number

This option specifies the maximum length of generated RIP packets. To avoid IP fragmentation, it should not exceed the interface MTU value. The default value is 532 for IPv4 RIP and interface MTU value for RIPng.

<@@label>rip-iface-check-link check link switch

If set, the hardware link state (as reported by OS) is taken into consideration. When the link disappears (e.g. an ethernet cable is unplugged), neighbors are immediately considered unreachable and all routes received from them are withdrawn. It is possible that some hardware drivers or platforms do not implement this feature. Default: yes.

Attributes<@@label>rip-attr

RIP defines two route attributes:

<@@label>rta-rip-metric int rip_metric

RIP metric of the route (ranging from 0 to infinity). When routes from different RIP instances are available and all of them have the same preference, BIRD prefers the route with lowest rip_metric. When a non-RIP route is exported to RIP, the default metric is 1.

<@@label>rta-rip-tag int rip_tag

RIP route tag: a 16-bit number which can be used to carry additional information with the route (for example, an originating AS number in case of external routes). When a non-RIP route is exported to RIP, the default tag is 0.

Example<@@label>rip-exam

protocol rip {
        ipv4 {
                import all;
                export all;
        };
        interface "eth*" {
                metric 2;
                port 1520;
                mode multicast;
                update time 12;
                timeout time 60;
                authentication cryptographic;
                password "secret" { algorithm hmac sha256; };
        };
}

6.13 RPKI <@@label>rpki

Introduction

The Resource Public Key Infrastructure (RPKI) is mechanism for origin validation of BGP routes (RFC 6480). BIRD supports only so-called RPKI-based origin validation. There is implemented RPKI to Router (RPKI-RTR) protocol (RFC 6810). It uses some of the RPKI data to allow a router to verify that the autonomous system announcing an IP address prefix is in fact authorized to do so. This is not crypto checked so can be violated. But it should prevent the vast majority of accidental hijackings on the Internet today, e.g. the famous Pakastani accidental announcement of YouTube's address space.

The RPKI-RTR protocol receives and maintains a set of ROAs from a cache server (also called validator). You can validate routes (RFC 6483) using function roa_check() in filter and set it as import filter at the BGP protocol. BIRD should re-validate all of affected routes after RPKI update by RFC 6811, but we don't support it yet! You can use a BIRD's client command reload in bgp_protocol_name for manual call of revalidation of all routes.

Supported transports

• Unprotected transport over TCP uses a port 323. The cache server and BIRD router should be on the same trusted and controlled network for security reasons.
• SSHv2 encrypted transport connection uses the normal SSH port 22.

Configuration

We currently support just one cache server per protocol. However you can define more RPKI protocols generally.

protocol rpki [<name>] {
        roa4 { table <tab>; };
        roa6 { table <tab>; };
        remote <ip> | "<domain>" [port <num>];
        port <num>;
        refresh [keep] <num>;
        retry [keep] <num>;
        expire [keep] <num>;
        transport tcp;
        transport ssh {
                bird private key "</path/to/id_rsa>";
                remote public key "</path/to/known_host>";
                user "<name>";
        };
}

Alse note that you have to specify the ROA channel. If you want to import only IPv4 prefixes you have to specify only roa4 channel. Similarly with IPv6 prefixes only. If you want to fetch both IPv4 and even IPv6 ROAs you have to specify both channels.

RPKI protocol options

remote ip | "hostname" [port num]

Specifies a destination address of the cache server. Can be specified by an IP address or by full domain name string. Only one cache can be specified per protocol. This option is required.

port num

Specifies the port number. The default port number is 323 for transport without any encryption and 22 for transport with SSH encryption.

refresh [keep] num

Time period in seconds. Tells how long to wait before next attempting to poll the cache using a Serial Query or a Reset Query packet. Must be lower than 86400 seconds (one day). Too low value can caused a false positive detection of network connection problems. A keyword keep suppresses updating this value by a cache server. Default: 3600 seconds

retry [keep] num

Time period in seconds between a failed Serial/Reset Query and a next attempt. Maximum allowed value is 7200 seconds (two hours). Too low value can caused a false positive detection of network connection problems. A keyword keep suppresses updating this value by a cache server. Default: 600 seconds

expire [keep] num

Time period in seconds. Received records are deleted if the client was unable to successfully refresh data for this time period. Must be in range from 600 seconds (ten minutes) to 172800 seconds (two days). A keyword keep suppresses updating this value by a cache server. Default: 7200 seconds

transport tcp

Unprotected transport over TCP. It's a default transport. Should be used only on secure private networks. Default: tcp

transport ssh { SSH transport options... }

It enables a SSHv2 transport encryption. Cannot be combined with a TCP transport. Default: off

SSH transport options

bird private key "/path/to/id_rsa"

A path to the BIRD's private SSH key for authentication. It can be a id_rsa file.

remote public key "/path/to/known_host"

A path to the cache's public SSH key for verification identity of the cache server. It could be a path to known_host file.

user "name"

A SSH user name for authentication. This option is a required.

Examples

BGP origin validation

Policy: Don't import ROA_INVALID routes.

roa4 table r4;
roa6 table r6;

protocol rpki {
        debug all;

        roa4 { table r4; };
        roa6 { table r6; };

        # Please, do not use rpki-validator.realmv6.org in production
        remote "rpki-validator.realmv6.org" port 8282;

        retry keep 5;
        refresh keep 30;
        expire 600;
}

filter peer_in_v4 {
        if (roa_check(r4, net, bgp_path.last) = ROA_INVALID) then
        {
                print "Ignore RPKI invalid ", net, " for ASN ", bgp_path.last;
                reject;
        }
        accept;
}

protocol bgp {
        debug all;
        local as 65000;
        neighbor 192.168.2.1 as 65001;
        ipv4 {
                import filter peer_in_v4;
                export none;
        };
}

SSHv2 transport encryption

roa4 table r4;
roa6 table r6;

protocol rpki {
        debug all;

        roa4 { table r4; };
        roa6 { table r6; };

        remote 127.0.0.1 port 2345;
        transport ssh {
                bird private key "/home/birdgeek/.ssh/id_rsa";
                remote public key "/home/birdgeek/.ssh/known_hosts";
                user "birdgeek";
        };

        # Default interval values
}

6.14 Static <@@label>static

The Static protocol doesn't communicate with other routers in the network, but instead it allows you to define routes manually. This is often used for specifying how to forward packets to parts of the network which don't use dynamic routing at all and also for defining sink routes (i.e., those telling to return packets as undeliverable if they are in your IP block, you don't have any specific destination for them and you don't want to send them out through the default route to prevent routing loops).

There are three classes of definitions in Static protocol configuration -- global options, static route definitions, and per-route options. Usually, the definition of the protocol contains mainly a list of static routes. Static routes have no specific attributes.

Global options:

<@@label>static-check-link check link switch

If set, hardware link states of network interfaces are taken into consideration. When link disappears (e.g. ethernet cable is unplugged), static routes directing to that interface are removed. It is possible that some hardware drivers or platforms do not implement this feature. Default: off.

<@@label>static-igp-table igp table name

Specifies a table that is used for route table lookups of recursive routes. Default: the same table as the protocol is connected to.

Route definitions (each may also contain a block of per-route options):

Regular routes; MPLS switching rules

There exist several types of routes; keep in mind that prefix syntax is <@@ref>type-prefixdependent on network type.

route prefix via ip|"interface" [mpls num[/num[/num[...]]]]

Next hop routes may bear one or more <@@ref>type-prefixdependent on network type<@@ref>route-next-hopnext hops. Every next hop is preceded by via and configured as shown.

route prefix recursive ip [mpls num[/num[/num[...]]]]

Recursive nexthop resolves the given IP in the configured IGP table and uses that route's next hop. The MPLS stacks are concatenated; on top is the IGP's nexthop stack and on bottom is this route's stack.

route prefix blackhole|unreachable|prohibit

Special routes specifying to silently drop the packet, return it as unreachable or return it as administratively prohibited. First two targets are also known as drop and reject.

When the particular destination is not available (the interface is down or the next hop of the route is not a neighbor at the moment), Static just uninstalls the route from the table it is connected to and adds it again as soon as the destination becomes adjacent again.

Route Origin Authorization

The ROA config is just route prefix max int as int with no nexthop.

Flowspec<@@label>flowspec-network-type

The flow specification are rules for routers and firewalls for filtering purpose. It is described by RFC 5575. There are 3 types of arguments: inet4 or inet6 prefixes, bitmasks matching expressions and numbers matching expressions.

Bitmasks matching is written using value/mask or !value/mask pairs. It means that (data & mask) is or is not equal to value.

Numbers matching is a matching sequence of numbers and ranges separeted by a commas (,) (e.g. 10,20,30). Ranges can be written using double dots .. notation (e.g. 80..90,120..124). An alternative notation are sequence of one or more pairs of relational operators and values separated by logical operators && or ||. Allowed relational operators are =, !=, <, <=, >, >=, true and false.

IPv4 Flowspec

<@@label>flow-dst dst inet4

Set a matching destination prefix (e.g. dst 192.168.0.0/16). Only this option is mandatory in IPv4 Flowspec.

<@@label>flow-src src inet4

Set a matching source prefix (e.g. src 10.0.0.0/8).

<@@label>flow-proto proto numbers-match

Set a matching IP protocol numbers (e.g. proto 6).

<@@label>flow-port port numbers-match

Set a matching source or destination TCP/UDP port numbers (e.g. port 1..1023,1194,3306).

<@@label>flow-dport dport numbers-match

Set a mating destination port numbers (e.g. dport 49151).

<@@label>flow-sport sport numbers-match

Set a matching source port numbers (e.g. sport = 0).

<@@label>flow-icmp-type icmp type numbers-match

Set a matching type field number of an ICMP packet (e.g. icmp type 3)

<@@label>flow-icmp-code icmp code numbers-match

Set a matching code field number of an ICMP packet (e.g. icmp code 1)

<@@label>flow-tcp-flags tcp flags bitmask-match

Set a matching bitmask for TCP header flags (aka control bits) (e.g. tcp flags 0x03/0x0f;). The maximum length of mask is 12 bits (0xfff).

<@@label>flow-length length numbers-match

Set a matching packet length (e.g. length > 1500;)

<@@label>flow-dscp dscp numbers-match

Set a matching DiffServ Code Point number (e.g. length > 1500;).

<@@label>flow-fragment fragment fragmentation-type

Set a matching type of packet fragmentation. Allowed fragmentation types are dont_fragment, is_fragment, first_fragment, last_fragment (e.g. fragment is_fragment && !dont_fragment).

protocol static {
        flow4;

        route flow4 {
                dst 10.0.0.0/8;
                port > 24 && < 30 || 40..50,60..70,80 && >= 90;
                tcp flags 0x03/0x0f;
                length > 1024;
                dscp = 63;
                fragment dont_fragment, is_fragment || !first_fragment;
        };
}

Differences for IPv6 Flowspec

Flowspec IPv6 are same as Flowspec IPv4 with a few exceptions.

• Prefixes inet6 can be specified not only with prefix length, but with prefix offset num too (e.g. ::1234:5678:9800:0000/101 offset 64). Offset means to don't care of num first bits.
• IPv6 Flowspec hasn't mandatory any flowspec component.
• In IPv6 packets, there is a matching the last next header value for a matching IP protocol number (e.g. next header 6).
• It is not possible to set dont_fragment as a type of packet fragmentation.

<@@label>flow6-dst dst inet6 [offset num]

Set a matching destination IPv6 prefix (e.g. dst ::1c77:3769:27ad:a11a/128 offset 64).

<@@label>flow6-src src inet6 [offset num]

Set a matching source IPv6 prefix (e.g. src fe80::/64).

<@@label>flow6-next-header next header numbers-match

Set a matching IP protocol numbers (e.g. next header != 6).

<@@label>flow6-label label bitmask-match

Set a 20-bit bitmask for matching Flow Label field in IPv6 packets (e.g. label 0x8e5/0x8e5).

protocol static {
        flow6 { table myflow6; };

        route flow6 {
                dst fec0:1122:3344:5566:7788:99aa:bbcc:ddee/128;
                src 0000:0000:0000:0001:1234:5678:9800:0000/101 offset 63;
                next header = 23;
                sport > 24 && < 30 || = 40 || 50,60,70..80;
                dport = 50;
                tcp flags 0x03/0x0f, !0/0xff || 0x33/0x33;
                fragment !is_fragment || !first_fragment;
                label 0xaaaa/0xaaaa && 0x33/0x33;
        };
}

Per-route options

<@@label>static-route-bfd bfd switch

The Static protocol could use BFD protocol for next hop liveness detection. If enabled, a BFD session to the route next hop is created and the static route is BFD-controlled -- the static route is announced only if the next hop liveness is confirmed by BFD. If the BFD session fails, the static route is removed. Note that this is a bit different compared to other protocols, which may use BFD as an advisory mechanism for fast failure detection but ignores it if a BFD session is not even established.

This option can be used for static routes with a direct next hop, or also for for individual next hops in a static multipath route (see above). Note that BFD protocol also has to be configured, see <@@ref>bfdBFD section for details. Default value is no.

<@@label>static-route-filter filter expression

This is a special option that allows filter expressions to be configured on per-route basis. Can be used multiple times. These expressions are evaluated when the route is originated, similarly to the import filter of the static protocol. This is especially useful for configuring route attributes, e.g., ospf_metric1 = 100; for a route that will be exported to the OSPF protocol.

Example static config

protocol static {
        ipv4 { table testable; };       # Connect to a non-default routing table
        check link;                     # Advertise routes only if link is up
        route 0.0.0.0/0 via 198.51.100.130; # Default route
        route 10.0.0.0/8                # Multipath route
                via 198.51.100.10 weight 2
                via 198.51.100.20 bfd   # BFD-controlled next hop
                via 192.0.2.1;
        route 203.0.113.0/24 unreachable; # Sink route
        route 10.2.0.0/24 via "arc0";   # Secondary network
        route 192.168.10.0/24 via 198.51.100.100 {
                ospf_metric1 = 20;      # Set extended attribute
        }
        route 192.168.10.0/24 via 198.51.100.100 {
                ospf_metric2 = 100;     # Set extended attribute
                ospf_tag = 2;           # Set extended attribute
                bfd;                    # BFD-controlled route
        }
}

7. Conclusions<@@label>conclusion

7.1 Future work <@@label>future-work

Although BIRD supports all the commonly used routing protocols, there are still some features which would surely deserve to be implemented in future versions of BIRD:

• Opaque LSA's
• Route aggregation and flap dampening
• Multicast routing protocols
• Ports to other systems

7.2 Getting more help <@@label>help

If you use BIRD, you're welcome to join the bird-users mailing list (bird-users@network.cz) where you can share your experiences with the other users and consult your problems with the authors. To subscribe to the list, visit http://bird.network.cz/?m_list. The home page of BIRD can be found at http://bird.network.cz/.

BIRD is a relatively young system and it probably contains some bugs. You can report any problems to the bird-users list and the authors will be glad to solve them, but before you do so, please make sure you have read the available documentation and that you are running the latest version (available at bird.network.cz:/pub/bird). (Of course, a patch which fixes the bug is always welcome as an attachment.)

If you want to understand what is going inside, Internet standards are a good and interesting reading. You can get them from ftp.rfc-editor.org (or a nicely sorted version from atrey.karlin.mff.cuni.cz:/pub/rfc).

Good luck!