1 <!doctype birddoc system>
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11 considered definition of configuration primitives, <cf> is fragment of
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17 Copyright 1999,2000 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later.
23 <title>BIRD User's Guide
25 Ondrej Filip <it/<feela@network.cz>/,
26 Pavel Machek <it/<pavel@ucw.cz>/,
27 Martin Mares <it/<mj@ucw.cz>/,
28 Ondrej Zajicek <it/<santiago@crfreenet.org>/
32 This document contains user documentation for the BIRD Internet Routing Daemon project.
35 <!-- Table of contents -->
38 <!-- Begin the document -->
45 <label id="what-is-bird">
47 <p>The name `BIRD' is actually an acronym standing for `BIRD Internet Routing
48 Daemon'. Let's take a closer look at the meaning of the name:
50 <p><em/BIRD/: Well, we think we have already explained that. It's an acronym
51 standing for `BIRD Internet Routing Daemon', you remember, don't you? :-)
53 <p><em/Internet Routing/: It's a program (well, a daemon, as you are going to
54 discover in a moment) which works as a dynamic router in an Internet type
55 network (that is, in a network running either the IPv4 or the IPv6 protocol).
56 Routers are devices which forward packets between interconnected networks in
57 order to allow hosts not connected directly to the same local area network to
58 communicate with each other. They also communicate with the other routers in the
59 Internet to discover the topology of the network which allows them to find
60 optimal (in terms of some metric) rules for forwarding of packets (which are
61 called routing tables) and to adapt themselves to the changing conditions such
62 as outages of network links, building of new connections and so on. Most of
63 these routers are costly dedicated devices running obscure firmware which is
64 hard to configure and not open to any changes (on the other hand, their special
65 hardware design allows them to keep up with lots of high-speed network
66 interfaces, better than general-purpose computer does). Fortunately, most
67 operating systems of the UNIX family allow an ordinary computer to act as a
68 router and forward packets belonging to the other hosts, but only according to a
69 statically configured table.
71 <p>A <em/Routing Daemon/ is in UNIX terminology a non-interactive program
72 running on background which does the dynamic part of Internet routing, that is
73 it communicates with the other routers, calculates routing tables and sends them
74 to the OS kernel which does the actual packet forwarding. There already exist
75 other such routing daemons: routed (RIP only), GateD (non-free),
76 <HTMLURL URL="http://www.zebra.org" name="Zebra"> and
77 <HTMLURL URL="http://sourceforge.net/projects/mrt" name="MRTD">,
78 but their capabilities are limited and they are relatively hard to configure
81 <p>BIRD is an Internet Routing Daemon designed to avoid all of these shortcomings,
82 to support all the routing technology used in the today's Internet or planned to
83 be used in near future and to have a clean extensible architecture allowing new
84 routing protocols to be incorporated easily. Among other features, BIRD
88 <item>both IPv4 and IPv6 protocols
89 <item>multiple routing tables
90 <item>the Border Gateway Protocol (BGPv4)
91 <item>the Routing Information Protocol (RIPv2)
92 <item>the Open Shortest Path First protocol (OSPFv2, OSPFv3)
93 <item>the Router Advertisements for IPv6 hosts
94 <item>a virtual protocol for exchange of routes between different
95 routing tables on a single host
96 <item>a command-line interface allowing on-line control and inspection
97 of status of the daemon
98 <item>soft reconfiguration (no need to use complex online commands to
99 change the configuration, just edit the configuration file and
100 notify BIRD to re-read it and it will smoothly switch itself to
101 the new configuration, not disturbing routing protocols unless
102 they are affected by the configuration changes)
103 <item>a powerful language for route filtering
106 <p>BIRD has been developed at the Faculty of Math and Physics, Charles
107 University, Prague, Czech Republic as a student project. It can be freely
108 distributed under the terms of the GNU General Public License.
110 <p>BIRD has been designed to work on all UNIX-like systems. It has been
111 developed and tested under Linux 2.0 to 2.6, and then ported to FreeBSD, NetBSD
112 and OpenBSD, porting to other systems (even non-UNIX ones) should be relatively
113 easy due to its highly modular architecture.
115 <p>BIRD supports either IPv4 or IPv6 protocol, but have to be compiled separately
116 for each one. Therefore, a dualstack router would run two instances of BIRD (one
117 for IPv4 and one for IPv6), with completely separate setups (configuration
121 <sect>Installing BIRD
124 <p>On a recent UNIX system with GNU development tools (GCC, binutils, m4, make)
125 and Perl, installing BIRD should be as easy as:
131 vi /usr/local/etc/bird.conf
135 <p>You can use <tt>./configure --help</tt> to get a list of configure
136 options. The most important ones are: <tt/--enable-ipv6/ which enables building
137 of an IPv6 version of BIRD, <tt/--with-protocols=/ to produce a slightly smaller
138 BIRD executable by configuring out routing protocols you don't use, and
139 <tt/--prefix=/ to install BIRD to a place different from <file>/usr/local</file>.
145 <p>You can pass several command-line options to bird:
148 <tag><label id="argv-config">-c <m/config name/</tag>
149 use given configuration file instead of <it/prefix/<file>/etc/bird.conf</file>.
151 <tag><label id="argv-debug">-d</tag>
152 enable debug messages and run bird in foreground.
154 <tag><label id="argv-log-file">-D <m/filename of debug log/</tag>
155 log debugging information to given file instead of stderr.
157 <tag><label id="argv-foreground">-f</tag>
158 run bird in foreground.
160 <tag><label id="argv-group">-g <m/group/</tag>
161 use that group ID, see the next section for details.
163 <tag><label id="argv-help">-h, --help</tag>
164 display command-line options to bird.
166 <tag><label id="argv-local">-l</tag>
167 look for a configuration file and a communication socket in the current
168 working directory instead of in default system locations. However, paths
169 specified by options <cf/-c/, <cf/-s/ have higher priority.
171 <tag><label id="argv-parse">-p</tag>
172 just parse the config file and exit. Return value is zero if the config
173 file is valid, nonzero if there are some errors.
175 <tag><label id="argv-pid">-P <m/name of PID file/</tag>
176 create a PID file with given filename.
178 <tag><label id="argv-recovery">-R</tag>
179 apply graceful restart recovery after start.
181 <tag><label id="argv-socket">-s <m/name of communication socket/</tag>
182 use given filename for a socket for communications with the client,
183 default is <it/prefix/<file>/var/run/bird.ctl</file>.
185 <tag><label id="argv-user">-u <m/user/</tag>
186 drop privileges and use that user ID, see the next section for details.
188 <tag><label id="argv-version">--version</tag>
189 display bird version.
192 <p>BIRD writes messages about its work to log files or syslog (according to config).
196 <label id="privileges">
198 <p>BIRD, as a routing daemon, uses several privileged operations (like setting
199 routing table and using raw sockets). Traditionally, BIRD is executed and runs
200 with root privileges, which may be prone to security problems. The recommended
201 way is to use a privilege restriction (options <cf/-u/, <cf/-g/). In that case
202 BIRD is executed with root privileges, but it changes its user and group ID to
203 an unprivileged ones, while using Linux capabilities to retain just required
204 privileges (capabilities CAP_NET_*). Note that the control socket is created
205 before the privileges are dropped, but the config file is read after that. The
206 privilege restriction is not implemented in BSD port of BIRD.
208 <p>An unprivileged user (as an argument to <cf/-u/ options) may be the user
209 <cf/nobody/, but it is suggested to use a new dedicated user account (like
210 <cf/bird/). The similar considerations apply for the group option, but there is
211 one more condition -- the users in the same group can use <file/birdc/ to
214 <p>Finally, there is a possibility to use external tools to run BIRD in an
215 environment with restricted privileges. This may need some configuration, but it
216 is generally easy -- BIRD needs just the standard library, privileges to read
217 the config file and create the control socket and the CAP_NET_* capabilities.
220 <chapt>About routing tables
221 <label id="routing-tables">
223 <p>BIRD has one or more routing tables which may or may not be synchronized with
224 OS kernel and which may or may not be synchronized with each other (see the Pipe
225 protocol). Each routing table contains a list of known routes. Each route
229 <item>network prefix this route is for (network address and prefix
230 length -- the number of bits forming the network part of the
231 address; also known as a netmask)
232 <item>preference of this route
233 <item>IP address of router which told us about this route
234 <item>IP address of router we should forward the packets to using this
236 <item>other attributes common to all routes
237 <item>dynamic attributes defined by protocols which may or may not be
238 present (typically protocol metrics)
241 Routing table maintains multiple entries for a network, but at most one entry
242 for one network and one protocol. The entry with the highest preference is used
243 for routing (we will call such an entry the <it/selected route/). If there are
244 more entries with the same preference and they are from the same protocol, the
245 protocol decides (typically according to metrics). If they aren't, an internal
246 ordering is used to break the tie. You can get the list of route attributes in
247 the Route attributes section.
249 <p>Each protocol is connected to a routing table through two filters which can
250 accept, reject and modify the routes. An <it/export/ filter checks routes passed
251 from the routing table to the protocol, an <it/import/ filter checks routes in
252 the opposite direction. When the routing table gets a route from a protocol, it
253 recalculates the selected route and broadcasts it to all protocols connected to
254 the table. The protocols typically send the update to other routers in the
255 network. Note that although most protocols are interested in receiving just
256 selected routes, some protocols (e.g. the <cf/Pipe/ protocol) receive and
257 process all entries in routing tables (accepted by filters).
259 <p><label id="dsc-table-sorted">Usually, a routing table just chooses a selected route
260 from a list of entries for one network. But if the <cf/sorted/ option is
261 activated, these lists of entries are kept completely sorted (according to
262 preference or some protocol-dependent metric). This is needed for some features
263 of some protocols (e.g. <cf/secondary/ option of BGP protocol, which allows to
264 accept not just a selected route, but the first route (in the sorted list) that
265 is accepted by filters), but it is incompatible with some other features (e.g.
266 <cf/deterministic med/ option of BGP protocol, which activates a way of choosing
267 selected route that cannot be described using comparison and ordering). Minor
268 advantage is that routes are shown sorted in <cf/show route/, minor disadvantage
269 is that it is slightly more computationally expensive.
272 <sect>Graceful restart
273 <label id="graceful-restart">
275 <p>When BIRD is started after restart or crash, it repopulates routing tables in
276 an uncoordinated manner, like after clean start. This may be impractical in some
277 cases, because if the forwarding plane (i.e. kernel routing tables) remains
278 intact, then its synchronization with BIRD would temporarily disrupt packet
279 forwarding until protocols converge. Graceful restart is a mechanism that could
280 help with this issue. Generally, it works by starting protocols and letting them
281 repopulate routing tables while deferring route propagation until protocols
282 acknowledge their convergence. Note that graceful restart behavior have to be
283 configured for all relevant protocols and requires protocol-specific support
284 (currently implemented for Kernel and BGP protocols), it is activated for
285 particular boot by option <cf/-R/.
292 <label id="config-intro">
294 <p>BIRD is configured using a text configuration file. Upon startup, BIRD reads
295 <it/prefix/<file>/etc/bird.conf</file> (unless the <tt/-c/ command line option
296 is given). Configuration may be changed at user's request: if you modify the
297 config file and then signal BIRD with <tt/SIGHUP/, it will adjust to the new
298 config. Then there's the client which allows you to talk with BIRD in an
301 <p>In the config, everything on a line after <cf/#/ or inside <cf>/* */</cf> is
302 a comment, whitespace characters are treated as a single space. If there's a
303 variable number of options, they are grouped using the <cf/{ }/ brackets. Each
304 option is terminated by a <cf/;/. Configuration is case sensitive. There are two
305 ways how to name symbols (like protocol names, filter names, constants etc.). You
306 can either use a simple string starting with a letter followed by any
307 combination of letters and numbers (e.g. "R123", "myfilter", "bgp5") or you can
308 enclose the name into apostrophes (<cf/'/) and than you can use any combination
309 of numbers, letters. hyphens, dots and colons (e.g. "'1:strange-name'",
310 "'-NAME-'", "'cool::name'").
312 <p>Here is an example of a simple config file. It enables synchronization of
313 routing tables with OS kernel, scans for new network interfaces every 10 seconds
314 and runs RIP on all network interfaces found.
318 persist; # Don't remove routes on BIRD shutdown
319 scan time 20; # Scan kernel routing table every 20 seconds
320 export all; # Default is export none
324 scan time 10; # Scan interfaces every 10 seconds
336 <label id="global-opts">
339 <tag><label id="opt-include">include "<m/filename/"</tag>
340 This statement causes inclusion of a new file. <m/Filename/ could also
341 be a wildcard, in that case matching files are included in alphabetic
342 order. The maximal depth is 8. Note that this statement could be used
343 anywhere in the config file, not just as a top-level option.
345 <tag><label id="opt-log">log "<m/filename/"|syslog [name <m/name/]|stderr all|{ <m/list of classes/ }</tag>
346 Set logging of messages having the given class (either <cf/all/ or
347 <cf/{ error|trace [, <m/.../] }/ etc.) into selected destination (a file specified
348 as a filename string, syslog with optional name argument, or the stderr
349 output). Classes are:
350 <cf/info/, <cf/warning/, <cf/error/ and <cf/fatal/ for messages about local problems,
351 <cf/debug/ for debugging messages,
352 <cf/trace/ when you want to know what happens in the network,
353 <cf/remote/ for messages about misbehavior of remote machines,
354 <cf/auth/ about authentication failures,
355 <cf/bug/ for internal BIRD bugs.
356 You may specify more than one <cf/log/ line to establish logging to
357 multiple destinations. Default: log everything to the system log.
359 <tag><label id="opt-debug-protocols">debug protocols all|off|{ states|routes|filters|interfaces|events|packets [, <m/.../] }</tag>
360 Set global defaults of protocol debugging options. See <cf/debug/ in the
361 following section. Default: off.
363 <tag><label id="opt-debug-commands">debug commands <m/number/</tag>
364 Control logging of client connections (0 for no logging, 1 for logging
365 of connects and disconnects, 2 and higher for logging of all client
366 commands). Default: 0.
368 <tag><label id="opt-debug-latency">debug latency <m/switch/</tag>
369 Activate tracking of elapsed time for internal events. Recent events
370 could be examined using <cf/dump events/ command. Default: off.
372 <tag><label id="opt-debug-latency-limit">debug latency limit <m/time/</tag>
373 If <cf/debug latency/ is enabled, this option allows to specify a limit
374 for elapsed time. Events exceeding the limit are logged. Default: 1 s.
376 <tag><label id="opt-watchdog-warn">watchdog warning <m/time/</tag>
377 Set time limit for I/O loop cycle. If one iteration took more time to
378 complete, a warning is logged. Default: 5 s.
380 <tag><label id="opt-watchdog-timeout">watchdog timeout <m/time/</tag>
381 Set time limit for I/O loop cycle. If the limit is breached, BIRD is
382 killed by abort signal. The timeout has effective granularity of
383 seconds, zero means disabled. Default: disabled (0).
385 <tag><label id="opt-mrtdump">mrtdump "<m/filename/"</tag>
386 Set MRTdump file name. This option must be specified to allow MRTdump
387 feature. Default: no dump file.
389 <tag><label id="opt-mrtdump-protocols">mrtdump protocols all|off|{ states|messages [, <m/.../] }</tag>
390 Set global defaults of MRTdump options. See <cf/mrtdump/ in the
391 following section. Default: off.
393 <tag><label id="opt-filter">filter <m/name local variables/{ <m/commands/ }</tag>
394 Define a filter. You can learn more about filters in the following
397 <tag><label id="opt-function">function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag>
398 Define a function. You can learn more about functions in the following chapter.
400 <tag><label id="opt-protocol">protocol rip|ospf|bgp|<m/.../ [<m/name/ [from <m/name2/]] { <m>protocol options</m> }</tag>
401 Define a protocol instance called <cf><m/name/</cf> (or with a name like
402 "rip5" generated automatically if you don't specify any
403 <cf><m/name/</cf>). You can learn more about configuring protocols in
404 their own chapters. When <cf>from <m/name2/</cf> expression is used,
405 initial protocol options are taken from protocol or template
406 <cf><m/name2/</cf> You can run more than one instance of most protocols
407 (like RIP or BGP). By default, no instances are configured.
409 <tag><label id="opt-template">template rip|bgp|<m/.../ [<m/name/ [from <m/name2/]] { <m>protocol options</m> }</tag>
410 Define a protocol template instance called <m/name/ (or with a name like
411 "bgp1" generated automatically if you don't specify any <m/name/).
412 Protocol templates can be used to group common options when many
413 similarly configured protocol instances are to be defined. Protocol
414 instances (and other templates) can use templates by using <cf/from/
415 expression and the name of the template. At the moment templates (and
416 <cf/from/ expression) are not implemented for OSPF protocol.
418 <tag><label id="opt-define">define <m/constant/ = <m/expression/</tag>
419 Define a constant. You can use it later in every place you could use a
420 value of the same type. Besides, there are some predefined numeric
421 constants based on /etc/iproute2/rt_* files. A list of defined constants
422 can be seen (together with other symbols) using 'show symbols' command.
424 <tag><label id="opt-router-id">router id <m/IPv4 address/</tag>
425 Set BIRD's router ID. It's a world-wide unique identification of your
426 router, usually one of router's IPv4 addresses. Default: in IPv4
427 version, the lowest IP address of a non-loopback interface. In IPv6
428 version, this option is mandatory.
430 <tag><label id="opt-router-id-from">router id from [-] [ "<m/mask/" ] [ <m/prefix/ ] [, <m/.../]</tag>
431 Set BIRD's router ID based on an IP address of an interface specified by
432 an interface pattern. The option is applicable for IPv4 version only.
433 See <ref id="proto-iface" name="interface"> section for detailed
434 description of interface patterns with extended clauses.
436 <tag><label id="opt-listen-bgp">listen bgp [address <m/address/] [port <m/port/] [dual]</tag>
437 This option allows to specify address and port where BGP protocol should
438 listen. It is global option as listening socket is common to all BGP
439 instances. Default is to listen on all addresses (0.0.0.0) and port 179.
440 In IPv6 mode, option <cf/dual/ can be used to specify that BGP socket
441 should accept both IPv4 and IPv6 connections (but even in that case,
442 BIRD would accept IPv6 routes only). Such behavior was default in older
445 <tag><label id="opt-graceful-restart">graceful restart wait <m/number/</tag>
446 During graceful restart recovery, BIRD waits for convergence of routing
447 protocols. This option allows to specify a timeout for the recovery to
448 prevent waiting indefinitely if some protocols cannot converge. Default:
451 <tag><label id="opt-timeformat">timeformat route|protocol|base|log "<m/format1/" [<m/limit/ "<m/format2/"]</tag>
452 This option allows to specify a format of date/time used by BIRD. The
453 first argument specifies for which purpose such format is used.
454 <cf/route/ is a format used in 'show route' command output,
455 <cf/protocol/ is used in 'show protocols' command output, <cf/base/ is
456 used for other commands and <cf/log/ is used in a log file.
458 "<m/format1/" is a format string using <it/strftime(3)/ notation (see
459 <it/man strftime/ for details). <m/limit> and "<m/format2/" allow to
460 specify the second format string for times in past deeper than <m/limit/
461 seconds. There are few shorthands: <cf/iso long/ is a ISO 8601 date/time
462 format (YYYY-MM-DD hh:mm:ss) that can be also specified using <cf/"%F %T"/.
463 <cf/iso short/ is a variant of ISO 8601 that uses just the time format
464 (hh:mm:ss) for near times (up to 20 hours in the past) and the date
465 format (YYYY-MM-DD) for far times. This is a shorthand for
466 <cf/"%T" 72000 "%F"/.
468 By default, BIRD uses the <cf/iso short/ format for <cf/route/ and
469 <cf/protocol/ times, and the <cf/iso long/ format for <cf/base/ and
472 In pre-1.4.0 versions, BIRD used an short, ad-hoc format for <cf/route/
473 and <cf/protocol/ times, and a <cf/iso long/ similar format (DD-MM-YYYY
474 hh:mm:ss) for <cf/base/ and <cf/log/. These timeformats could be set by
475 <cf/old short/ and <cf/old long/ compatibility shorthands.
477 <tag><label id="opt-table">table <m/name/ [sorted]</tag>
478 Create a new routing table. The default routing table is created
479 implicitly, other routing tables have to be added by this command.
480 Option <cf/sorted/ can be used to enable sorting of routes, see
481 <ref id="dsc-table-sorted" name="sorted table"> description for details.
483 <tag><label id="opt-roa-table">roa table <m/name/ [ { <m/roa table options .../ } ]</tag>
484 Create a new ROA (Route Origin Authorization) table. ROA tables can be
485 used to validate route origination of BGP routes. A ROA table contains
486 ROA entries, each consist of a network prefix, a max prefix length and
487 an AS number. A ROA entry specifies prefixes which could be originated
488 by that AS number. ROA tables could be filled with data from RPKI (<rfc
489 id="6480">) or from public databases like Whois. ROA tables are
490 examined by <cf/roa_check()/ operator in filters.
492 Currently, there is just one option, <cf>roa <m/prefix/ max <m/num/ as
493 <m/num/</cf>, which can be used to populate the ROA table with static
494 ROA entries. The option may be used multiple times. Other entries can be
495 added dynamically by <cf/add roa/ command.
497 <tag><label id="opt-eval">eval <m/expr/</tag>
498 Evaluates given filter expression. It is used by us for testing of filters.
502 <sect>Protocol options
503 <label id="protocol-opts">
505 <p>For each protocol instance, you can configure a bunch of options. Some of
506 them (those described in this section) are generic, some are specific to the
507 protocol (see sections talking about the protocols).
509 <p>Several options use a <m/switch/ argument. It can be either <cf/on/,
510 <cf/yes/ or a numeric expression with a non-zero value for the option to be
511 enabled or <cf/off/, <cf/no/ or a numeric expression evaluating to zero to
512 disable it. An empty <m/switch/ is equivalent to <cf/on/ ("silence means
516 <tag><label id="proto-preference">preference <m/expr/</tag>
517 Sets the preference of routes generated by this protocol. Default:
520 <tag><label id="proto-disabled">disabled <m/switch/</tag>
521 Disables the protocol. You can change the disable/enable status from the
522 command line interface without needing to touch the configuration.
523 Disabled protocols are not activated. Default: protocol is enabled.
525 <tag><label id="proto-debug">debug all|off|{ states|routes|filters|interfaces|events|packets [, <m/.../] }</tag>
526 Set protocol debugging options. If asked, each protocol is capable of
527 writing trace messages about its work to the log (with category
528 <cf/trace/). You can either request printing of <cf/all/ trace messages
529 or only of the types selected: <cf/states/ for protocol state changes
530 (protocol going up, down, starting, stopping etc.), <cf/routes/ for
531 routes exchanged with the routing table, <cf/filters/ for details on
532 route filtering, <cf/interfaces/ for interface change events sent to the
533 protocol, <cf/events/ for events internal to the protocol and <cf/packets/
534 for packets sent and received by the protocol. Default: off.
536 <tag><label id="proto-mrtdump">mrtdump all|off|{ states|messages [, <m/.../] }</tag>
537 Set protocol MRTdump flags. MRTdump is a standard binary format for
538 logging information from routing protocols and daemons. These flags
539 control what kind of information is logged from the protocol to the
540 MRTdump file (which must be specified by global <cf/mrtdump/ option, see
541 the previous section). Although these flags are similar to flags of
542 <cf/debug/ option, their meaning is different and protocol-specific. For
543 BGP protocol, <cf/states/ logs BGP state changes and <cf/messages/ logs
544 received BGP messages. Other protocols does not support MRTdump yet.
546 <tag><label id="proto-router-id">router id <m/IPv4 address/</tag>
547 This option can be used to override global router id for a given
548 protocol. Default: uses global router id.
550 <tag><label id="proto-import">import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag>
551 Specify a filter to be used for filtering routes coming from the
552 protocol to the routing table. <cf/all/ is shorthand for <cf/where true/
553 and <cf/none/ is shorthand for <cf/where false/. Default: <cf/all/.
555 <tag><label id="proto-export">export <m/filter/</tag>
556 This is similar to the <cf>import</cf> keyword, except that it works in
557 the direction from the routing table to the protocol. Default: <cf/none/.
559 <tag><label id="proto-import-keep-filtered">import keep filtered <m/switch/</tag>
560 Usually, if an import filter rejects a route, the route is forgotten.
561 When this option is active, these routes are kept in the routing table,
562 but they are hidden and not propagated to other protocols. But it is
563 possible to show them using <cf/show route filtered/. Note that this
564 option does not work for the pipe protocol. Default: off.
566 <tag><label id="proto-import-limit">import limit [<m/number/ | off ] [action warn | block | restart | disable]</tag>
567 Specify an import route limit (a maximum number of routes imported from
568 the protocol) and optionally the action to be taken when the limit is
569 hit. Warn action just prints warning log message. Block action discards
570 new routes coming from the protocol. Restart and disable actions shut
571 the protocol down like appropriate commands. Disable is the default
572 action if an action is not explicitly specified. Note that limits are
573 reset during protocol reconfigure, reload or restart. Default: <cf/off/.
575 <tag><label id="proto-receive-limit">receive limit [<m/number/ | off ] [action warn | block | restart | disable]</tag>
576 Specify an receive route limit (a maximum number of routes received from
577 the protocol and remembered). It works almost identically to <cf>import
578 limit</cf> option, the only difference is that if <cf/import keep
579 filtered/ option is active, filtered routes are counted towards the
580 limit and blocked routes are forgotten, as the main purpose of the
581 receive limit is to protect routing tables from overflow. Import limit,
582 on the contrary, counts accepted routes only and routes blocked by the
583 limit are handled like filtered routes. Default: <cf/off/.
585 <tag><label id="proto-export-limit">export limit [ <m/number/ | off ] [action warn | block | restart | disable]</tag>
586 Specify an export route limit, works similarly to the <cf>import
587 limit</cf> option, but for the routes exported to the protocol. This
588 option is experimental, there are some problems in details of its
589 behavior -- the number of exported routes can temporarily exceed the
590 limit without triggering it during protocol reload, exported routes
591 counter ignores route blocking and block action also blocks route
592 updates of already accepted routes -- and these details will probably
593 change in the future. Default: <cf/off/.
595 <tag><label id="proto-description">description "<m/text/"</tag>
596 This is an optional description of the protocol. It is displayed as a
597 part of the output of 'show route all' command.
599 <tag><label id="proto-table">table <m/name/</tag>
600 Connect this protocol to a non-default routing table.
603 <p>There are several options that give sense only with certain protocols:
606 <tag><label id="proto-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, <m/.../] [ { <m/option/; [<m/.../] } ]</tag>
607 Specifies a set of interfaces on which the protocol is activated with
608 given interface-specific options. A set of interfaces specified by one
609 interface option is described using an interface pattern. The interface
610 pattern consists of a sequence of clauses (separated by commas), each
611 clause is a mask specified as a shell-like pattern. Interfaces are
612 matched by their name.
614 An interface matches the pattern if it matches any of its clauses. If
615 the clause begins with <cf/-/, matching interfaces are excluded. Patterns
616 are processed left-to-right, thus <cf/interface "eth0", -"eth*", "*";/
617 means eth0 and all non-ethernets.
619 Some protocols (namely OSPFv2 and Direct) support extended clauses that
620 may contain a mask, a prefix, or both of them. An interface matches such
621 clause if its name matches the mask (if specified) and its address
622 matches the prefix (if specified). Extended clauses are used when the
623 protocol handles multiple addresses on an interface independently.
625 An interface option can be used more times with different interface-specific
626 options, in that case for given interface the first matching interface
629 This option is allowed in Babel, BFD, Direct, OSPF, RAdv and RIP
630 protocols, but in OSPF protocol it is used in the <cf/area/ subsection.
636 <cf>interface "*" { type broadcast; };</cf> - start the protocol on all
637 interfaces with <cf>type broadcast</cf> option.
639 <cf>interface "eth1", "eth4", "eth5" { type ptp; };</cf> - start the
640 protocol on enumerated interfaces with <cf>type ptp</cf> option.
642 <cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol
643 on all interfaces that have address from 192.168.0.0/16, but not from
646 <cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol
647 on all interfaces that have address from 192.168.0.0/16, but not from
650 <cf>interface "eth*" 192.168.1.0/24;</cf> - start the protocol on all
651 ethernet interfaces that have address from 192.168.1.0/24.
653 <tag><label id="proto-tx-class">tx class|dscp <m/num/</tag>
654 This option specifies the value of ToS/DS/Class field in IP headers of
655 the outgoing protocol packets. This may affect how the protocol packets
656 are processed by the network relative to the other network traffic. With
657 <cf/class/ keyword, the value (0-255) is used for the whole ToS/Class
658 octet (but two bits reserved for ECN are ignored). With <cf/dscp/
659 keyword, the value (0-63) is used just for the DS field in the octet.
660 Default value is 0xc0 (DSCP 0x30 - CS6).
662 <tag><label id="proto-tx-priority">tx priority <m/num/</tag>
663 This option specifies the local packet priority. This may affect how the
664 protocol packets are processed in the local TX queues. This option is
665 Linux specific. Default value is 7 (highest priority, privileged traffic).
667 <tag><label id="proto-pass">password "<m/password/" [ { <m>password options</m> } ]</tag>
668 Specifies a password that can be used by the protocol as a shared secret
669 key. Password option can be used more times to specify more passwords.
670 If more passwords are specified, it is a protocol-dependent decision
671 which one is really used. Specifying passwords does not mean that
672 authentication is enabled, authentication can be enabled by separate,
673 protocol-dependent <cf/authentication/ option.
675 This option is allowed in BFD, OSPF and RIP protocols. BGP has also
676 <cf/password/ option, but it is slightly different and described
681 <p>Password option can contain section with some (not necessary all) password sub-options:
684 <tag><label id="proto-pass-id">id <M>num</M></tag>
685 ID of the password, (1-255). If it is not used, BIRD will choose ID based
686 on an order of the password item in the interface. For example, second
687 password item in one interface will have default ID 2. ID is used by
688 some routing protocols to identify which password was used to
689 authenticate protocol packets.
691 <tag><label id="proto-pass-gen-from">generate from "<m/time/"</tag>
692 The start time of the usage of the password for packet signing.
693 The format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
695 <tag><label id="proto-pass-gen-to">generate to "<m/time/"</tag>
696 The last time of the usage of the password for packet signing.
698 <tag><label id="proto-pass-accept-from">accept from "<m/time/"</tag>
699 The start time of the usage of the password for packet verification.
701 <tag><label id="proto-pass-accept-to">accept to "<m/time/"</tag>
702 The last time of the usage of the password for packet verification.
704 <tag><label id="proto-pass-from">from "<m/time/"</tag>
705 Shorthand for setting both <cf/generate from/ and <cf/accept from/.
707 <tag><label id="proto-pass-to">to "<m/time/"</tag>
708 Shorthand for setting both <cf/generate to/ and <cf/accept to/.
710 <tag><label id="proto-pass-algorithm">algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 )</tag>
711 The message authentication algorithm for the password when cryptographic
712 authentication is enabled. The default value depends on the protocol.
713 For RIP and OSPFv2 it is Keyed-MD5 (for compatibility), for OSPFv3
714 protocol it is HMAC-SHA-256.
719 <sect>Flowspec network type
720 <label id="flowspec-network-type">
722 <p>The flow specification are rules for routers and firewalls for filtering
723 purpose. It is described by <rfc id="5575">. There are 3 types of arguments:
724 <m/inet4/ or <m/inet6/ prefixes, bitmasks matching expressions and numbers
725 matching expressions.
727 Bitmasks matching is written using <m/value/<cf>/</cf><m/mask/ or
728 <cf/!/<m/value/<cf>/</cf><m/mask/ pairs. It means that <cf/(/<m/data/ <cf/&/
729 <m/mask/<cf/)/ is or is not equal to <m/value/.
731 Numbers matching is a matching sequence of numbers and ranges separeted by a
732 commas (<cf/,/) (e.g. <cf/10,20,30/). Ranges can be written using double dots
733 <cf/../ notation (e.g. <cf/80..90,120..124/). An alternative notation are
734 sequence of one or more pairs of relational operators and values separated by
735 logical operators <cf/&&/ or <cf/||/. Allowed relational operators are <cf/=/,
736 <cf/!=/, <cf/</, <cf/<=/, <cf/>/, <cf/>=/, <cf/true/ and <cf/false/.
741 <tag><label id="flow-dst">dst <m/inet4/</tag>
742 Set a matching destination prefix (e.g. <cf>dst 192.168.0.0/16</cf>).
743 Only this option is mandatory in IPv4 Flowspec.
745 <tag><label id="flow-src">src <m/inet4/</tag>
746 Set a matching source prefix (e.g. <cf>src 10.0.0.0/8</cf>).
748 <tag><label id="flow-proto">proto <m/numbers-match/</tag>
749 Set a matching IP protocol numbers (e.g. <cf/proto 6/).
751 <tag><label id="flow-port">port <m/numbers-match/</tag>
752 Set a matching source or destination TCP/UDP port numbers (e.g.
753 <cf>port 1..1023,1194,3306</cf>).
755 <tag><label id="flow-dport">dport <m/numbers-match/</tag>
756 Set a mating destination port numbers (e.g. <cf>dport 49151</cf>).
758 <tag><label id="flow-sport">sport <m/numbers-match/</tag>
759 Set a matching source port numbers (e.g. <cf>sport = 0</cf>).
761 <tag><label id="flow-icmp-type">icmp type <m/numbers-match/</tag>
762 Set a matching type field number of an ICMP packet (e.g. <cf>icmp type
765 <tag><label id="flow-icmp-code">icmp code <m/numbers-match/</tag>
766 Set a matching code field number of an ICMP packet (e.g. <cf>icmp code
769 <tag><label id="flow-tcp-flags">tcp flags <m/bitmask-match/</tag>
770 Set a matching bitmask for TCP header flags (aka control bits) (e.g.
771 <cf>tcp flags 0x03/0x0f;</cf>).
773 <tag><label id="flow-length">length <m/numbers-match/</tag>
774 Set a matching packet length (e.g. <cf>length > 1500;</cf>)
776 <tag><label id="flow-dscp">dscp <m/numbers-match/</tag>
777 Set a matching DiffServ Code Point number (e.g. <cf>length > 1500;</cf>).
779 <tag><label id="flow-fragment">fragment <m/fragmentation-type/</tag>
780 Set a matching type of packet fragmentation. Allowed fragmentation
781 types are <cf/dont_fragment/, <cf/is_fragment/, <cf/first_fragment/,
782 <cf/last_fragment/ (e.g. <cf>fragment is_fragment &&
783 !dont_fragment</cf>).
792 port > 24 && < 30 || 40..50,60..70,80 && >= 90;
796 fragment dont_fragment, is_fragment || !first_fragment;
801 <sect1>Differences for IPv6 Flowspec
803 <p>Flowspec IPv6 are same as Flowspec IPv4 with a few exceptions.
805 <item>Prefixes <m/inet6/ can be specified not only with prefix length,
806 but with prefix <cf/offset/ <m/num/ too (e.g.
807 <cf>::1234:5678:9800:0000/101 offset 64</cf>). Offset means to don't
808 care of <m/num/ first bits.
809 <item>IPv6 Flowspec hasn't mandatory any flowspec component.
810 <item>In IPv6 packets, there is a matching the last next header value
811 for a matching IP protocol number (e.g. <cf>next header 6</cf>).
812 <item>It is not possible to set <cf>dont_fragment</cf> as a type of
813 packet fragmentation.
817 <tag><label id="flow6-dst">dst <m/inet6/ [offset <m/num/]</tag>
818 Set a matching destination IPv6 prefix (e.g. <cf>dst
819 ::1c77:3769:27ad:a11a/128 offset 64</cf>).
821 <tag><label id="flow6-src">src <m/inet6/ [offset <m/num/]</tag>
822 Set a matching source IPv6 prefix (e.g. <cf>src fe80::/64</cf>).
824 <tag><label id="flow6-next-header">next header <m/numbers-match/</tag>
825 Set a matching IP protocol numbers (e.g. <cf>next header != 6</cf>).
827 <tag><label id="flow6-label">label <m/bitmask-match/</tag>
828 Set a 20-bit bitmask for matching Flow Label field in IPv6 packets
829 (e.g. <cf>label 0x8e5/0x8e5</cf>).
837 dst fec0:1122:3344:5566:7788:99aa:bbcc:ddee/128;
838 src 0000:0000:0000:0001:1234:5678:9800:0000/101 offset 63;
840 sport > 24 && < 30 || = 40 || 50,60,70..80;
842 tcp flags 0x03/0x0f, !0/0xff || 0x33/0x33;
843 fragment !is_fragment || !first_fragment;
844 label 0xaaaa/0xaaaa && 0x33/0x33;
849 <chapt>Remote control
850 <label id="remote-control">
852 <p>You can use the command-line client <file>birdc</file> to talk with a running
853 BIRD. Communication is done using a <file/bird.ctl/ UNIX domain socket (unless
854 changed with the <tt/-s/ option given to both the server and the client). The
855 commands can perform simple actions such as enabling/disabling of protocols,
856 telling BIRD to show various information, telling it to show routing table
857 filtered by filter, or asking BIRD to reconfigure. Press <tt/?/ at any time to
858 get online help. Option <tt/-r/ can be used to enable a restricted mode of BIRD
859 client, which allows just read-only commands (<cf/show .../). Option <tt/-v/ can
860 be passed to the client, to make it dump numeric return codes along with the
861 messages. You do not necessarily need to use <file/birdc/ to talk to BIRD, your
862 own applications could do that, too -- the format of communication between BIRD
863 and <file/birdc/ is stable (see the programmer's documentation).
865 <p>There is also lightweight variant of BIRD client called <file/birdcl/, which
866 does not support command line editing and history and has minimal dependencies.
867 This is useful for running BIRD in resource constrained environments, where
868 Readline library (required for regular BIRD client) is not available.
870 <p>Many commands have the <m/name/ of the protocol instance as an argument.
871 This argument can be omitted if there exists only a single instance.
873 <p>Here is a brief list of supported functions:
876 <tag><label id="cli-show-status">show status</tag>
877 Show router status, that is BIRD version, uptime and time from last
880 <tag><label id="cli-show-interfaces">show interfaces [summary]</tag>
881 Show the list of interfaces. For each interface, print its type, state,
882 MTU and addresses assigned.
884 <tag><label id="cli-show-protocols">show protocols [all]</tag>
885 Show list of protocol instances along with tables they are connected to
886 and protocol status, possibly giving verbose information, if <cf/all/ is
889 <tag><label id="cli-show-ospf-iface">show ospf interface [<m/name/] ["<m/interface/"]</tag>
890 Show detailed information about OSPF interfaces.
892 <tag><label id="cli-show-ospf-neighbors">show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
893 Show a list of OSPF neighbors and a state of adjacency to them.
895 <tag><label id="cli-show-ospf-state">show ospf state [all] [<m/name/]</tag>
896 Show detailed information about OSPF areas based on a content of the
897 link-state database. It shows network topology, stub networks,
898 aggregated networks and routers from other areas and external routes.
899 The command shows information about reachable network nodes, use option
900 <cf/all/ to show information about all network nodes in the link-state
903 <tag><label id="cli-show-ospf-topology">show ospf topology [all] [<m/name/]</tag>
904 Show a topology of OSPF areas based on a content of the link-state
905 database. It is just a stripped-down version of 'show ospf state'.
907 <tag><label id="cli-show-ospf-lsadb">show ospf lsadb [global | area <m/id/ | link] [type <m/num/] [lsid <m/id/] [self | router <m/id/] [<m/name/] </tag>
908 Show contents of an OSPF LSA database. Options could be used to filter
911 <tag><label id="cli-show-rip-interfaces">show rip interfaces [<m/name/] ["<m/interface/"]</tag>
912 Show detailed information about RIP interfaces.
914 <tag><label id="cli-show-rip-neighbors">show rip neighbors [<m/name/] ["<m/interface/"]</tag>
915 Show a list of RIP neighbors and associated state.
917 <tag><label id="cli-show-static">show static [<m/name/]</tag>
918 Show detailed information about static routes.
920 <tag><label id="cli-show-bfd-sessions">show bfd sessions [<m/name/]</tag>
921 Show information about BFD sessions.
923 <tag><label id="cli-show-symbols">show symbols [table|filter|function|protocol|template|roa|<m/symbol/]</tag>
924 Show the list of symbols defined in the configuration (names of
925 protocols, routing tables etc.).
927 <tag><label id="cli-show-route">show route [[for] <m/prefix/|<m/IP/] [table <m/t/] [filter <m/f/|where <m/c/] [(export|preexport|noexport) <m/p/] [protocol <m/p/] [<m/options/]</tag>
928 Show contents of a routing table (by default of the main one or the
929 table attached to a respective protocol), that is routes, their metrics
930 and (in case the <cf/all/ switch is given) all their attributes.
932 <p>You can specify a <m/prefix/ if you want to print routes for a
933 specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
934 the entry which will be used for forwarding of packets to the given
935 destination. By default, all routes for each network are printed with
936 the selected one at the top, unless <cf/primary/ is given in which case
937 only the selected route is shown.
939 <p>You can also ask for printing only routes processed and accepted by
940 a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
941 </cf> or matching a given condition (<cf>where <m/condition/</cf>).
943 The <cf/export/, <cf/preexport/ and <cf/noexport/ switches ask for
944 printing of routes that are exported to the specified protocol.
945 With <cf/preexport/, the export filter of the protocol is skipped.
946 With <cf/noexport/, routes rejected by the export filter are printed
947 instead. Note that routes not exported to the protocol for other reasons
948 (e.g. secondary routes or routes imported from that protocol) are not
949 printed even with <cf/noexport/.
951 <p>You can also select just routes added by a specific protocol.
952 <cf>protocol <m/p/</cf>.
954 <p>If BIRD is configured to keep filtered routes (see <cf/import keep
955 filtered/ option), you can show them instead of routes by using
956 <cf/filtered/ switch.
958 <p>The <cf/stats/ switch requests showing of route statistics (the
959 number of networks, number of routes before and after filtering). If
960 you use <cf/count/ instead, only the statistics will be printed.
962 <tag><label id="cli-show-roa">show roa [<m/prefix/ | in <m/prefix/ | for <m/prefix/] [as <m/num/] [table <m/t/]</tag>
963 Show contents of a ROA table (by default of the first one). You can
964 specify a <m/prefix/ to print ROA entries for a specific network. If you
965 use <cf>for <m/prefix/</cf>, you'll get all entries relevant for route
966 validation of the network prefix; i.e., ROA entries whose prefixes cover
967 the network prefix. Or you can use <cf>in <m/prefix/</cf> to get ROA
968 entries covered by the network prefix. You could also use <cf/as/ option
969 to show just entries for given AS.
971 <tag><label id="cli-add-roa">add roa <m/prefix/ max <m/num/ as <m/num/ [table <m/t/]</tag>
972 Add a new ROA entry to a ROA table. Such entry is called <it/dynamic/
973 compared to <it/static/ entries specified in the config file. These
974 dynamic entries survive reconfiguration.
976 <tag><label id="cli-delete-roa">delete roa <m/prefix/ max <m/num/ as <m/num/ [table <m/t/]</tag>
977 Delete the specified ROA entry from a ROA table. Only dynamic ROA
978 entries (i.e., the ones added by <cf/add roa/ command) can be deleted.
980 <tag><label id="cli-flush-roa">flush roa [table <m/t/]</tag>
981 Remove all dynamic ROA entries from a ROA table.
983 <tag><label id="cli-configure">configure [soft] ["<m/config file/"] [timeout [<m/num/]]</tag>
984 Reload configuration from a given file. BIRD will smoothly switch itself
985 to the new configuration, protocols are reconfigured if possible,
986 restarted otherwise. Changes in filters usually lead to restart of
989 If <cf/soft/ option is used, changes in filters does not cause BIRD to
990 restart affected protocols, therefore already accepted routes (according
991 to old filters) would be still propagated, but new routes would be
992 processed according to the new filters.
994 If <cf/timeout/ option is used, config timer is activated. The new
995 configuration could be either confirmed using <cf/configure confirm/
996 command, or it will be reverted to the old one when the config timer
997 expires. This is useful for cases when reconfiguration breaks current
998 routing and a router becomes inaccessible for an administrator. The
999 config timeout expiration is equivalent to <cf/configure undo/
1000 command. The timeout duration could be specified, default is 300 s.
1002 <tag><label id="cli-configure-confirm">configure confirm</tag>
1003 Deactivate the config undo timer and therefore confirm the current
1006 <tag><label id="cli-configure-undo">configure undo</tag>
1007 Undo the last configuration change and smoothly switch back to the
1008 previous (stored) configuration. If the last configuration change was
1009 soft, the undo change is also soft. There is only one level of undo, but
1010 in some specific cases when several reconfiguration requests are given
1011 immediately in a row and the intermediate ones are skipped then the undo
1012 also skips them back.
1014 <tag><label id="cli-configure-check">configure check ["<m/config file/"]</tag>
1015 Read and parse given config file, but do not use it. useful for checking
1016 syntactic and some semantic validity of an config file.
1018 <tag><label id="cli-enable-disable-restart">enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
1019 Enable, disable or restart a given protocol instance, instances matching
1020 the <cf><m/pattern/</cf> or <cf/all/ instances.
1022 <tag><label id="cli-reload">reload [in|out] <m/name/|"<m/pattern/"|all</tag>
1023 Reload a given protocol instance, that means re-import routes from the
1024 protocol instance and re-export preferred routes to the instance. If
1025 <cf/in/ or <cf/out/ options are used, the command is restricted to one
1026 direction (re-import or re-export).
1028 This command is useful if appropriate filters have changed but the
1029 protocol instance was not restarted (or reloaded), therefore it still
1030 propagates the old set of routes. For example when <cf/configure soft/
1031 command was used to change filters.
1033 Re-export always succeeds, but re-import is protocol-dependent and might
1034 fail (for example, if BGP neighbor does not support route-refresh
1035 extension). In that case, re-export is also skipped. Note that for the
1036 pipe protocol, both directions are always reloaded together (<cf/in/ or
1037 <cf/out/ options are ignored in that case).
1039 <tag><label id="cli-down">down</tag>
1042 <tag><label id="cli-debug">debug <m/protocol/|<m/pattern/|all all|off|{ states|routes|filters|events|packets [, <m/.../] }</tag>
1043 Control protocol debugging.
1045 <tag><label id="cli-dump">dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
1046 Dump contents of internal data structures to the debugging output.
1048 <tag><label id="cli-echo">echo all|off|{ <m/list of log classes/ } [ <m/buffer-size/ ]</tag>
1049 Control echoing of log messages to the command-line output.
1050 See <ref id="opt-log" name="log option"> for a list of log classes.
1052 <tag><label id="cli-eval">eval <m/expr/</tag>
1053 Evaluate given expression.
1058 <label id="filters">
1061 <label id="filters-intro">
1063 <p>BIRD contains a simple programming language. (No, it can't yet read mail :-).
1064 There are two objects in this language: filters and functions. Filters are
1065 interpreted by BIRD core when a route is being passed between protocols and
1066 routing tables. The filter language contains control structures such as if's and
1067 switches, but it allows no loops. An example of a filter using many features can
1068 be found in <file>filter/test.conf</file>.
1070 <p>Filter gets the route, looks at its attributes and modifies some of them if
1071 it wishes. At the end, it decides whether to pass the changed route through
1072 (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks like
1079 if defined( rip_metric ) then
1085 if rip_metric > 10 then
1086 reject "RIP metric is too big";
1092 <p>As you can see, a filter has a header, a list of local variables, and a body.
1093 The header consists of the <cf/filter/ keyword followed by a (unique) name of
1094 filter. The list of local variables consists of <cf><M>type name</M>;</cf>
1095 pairs where each pair defines one local variable. The body consists of <cf>
1096 { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You
1097 can group several statements to a single compound statement by using braces
1098 (<cf>{ <M>statements</M> }</cf>) which is useful if you want to make a bigger
1099 block of code conditional.
1101 <p>BIRD supports functions, so that you don't have to repeat the same blocks of
1102 code over and over. Functions can have zero or more parameters and they can have
1103 local variables. Recursion is not allowed. Function definitions look like this:
1112 function with_parameters (int parameter)
1118 <p>Unlike in C, variables are declared after the <cf/function/ line, but before
1119 the first <cf/{/. You can't declare variables in nested blocks. Functions are
1120 called like in C: <cf>name(); with_parameters(5);</cf>. Function may return
1121 values using the <cf>return <m/[expr]/</cf> command. Returning a value exits
1122 from current function (this is similar to C).
1124 <p>Filters are declared in a way similar to functions except they can't have
1125 explicit parameters. They get a route table entry as an implicit parameter, it
1126 is also passed automatically to any functions called. The filter must terminate
1127 with either <cf/accept/ or <cf/reject/ statement. If there's a runtime error in
1128 filter, the route is rejected.
1130 <p>A nice trick to debug filters is to use <cf>show route filter <m/name/</cf>
1131 from the command line client. An example session might look like:
1134 pavel@bug:~/bird$ ./birdc -s bird.ctl
1137 10.0.0.0/8 dev eth0 [direct1 23:21] (240)
1138 195.113.30.2/32 dev tunl1 [direct1 23:21] (240)
1139 127.0.0.0/8 dev lo [direct1 23:21] (240)
1141 show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
1142 bird> show route filter { if 127.0.0.5 ˜ net then accept; }
1143 127.0.0.0/8 dev lo [direct1 23:21] (240)
1149 <label id="data-types">
1151 <p>Each variable and each value has certain type. Booleans, integers and enums
1152 are incompatible with each other (that is to prevent you from shooting in the
1156 <tag><label id="type-bool">bool</tag>
1157 This is a boolean type, it can have only two values, <cf/true/ and
1158 <cf/false/. Boolean is the only type you can use in <cf/if/ statements.
1160 <tag><label id="type-int">int</tag>
1161 This is a general integer type. It is an unsigned 32bit type; i.e., you
1162 can expect it to store values from 0 to 4294967295. Overflows are not
1163 checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
1165 <tag><label id="type-pair">pair</tag>
1166 This is a pair of two short integers. Each component can have values
1167 from 0 to 65535. Literals of this type are written as <cf/(1234,5678)/.
1168 The same syntax can also be used to construct a pair from two arbitrary
1169 integer expressions (for example <cf/(1+2,a)/).
1171 <tag><label id="type-quad">quad</tag>
1172 This is a dotted quad of numbers used to represent router IDs (and
1173 others). Each component can have a value from 0 to 255. Literals of
1174 this type are written like IPv4 addresses.
1176 <tag><label id="type-string">string</tag>
1177 This is a string of characters. There are no ways to modify strings in
1178 filters. You can pass them between functions, assign them to variables
1179 of type <cf/string/, print such variables, use standard string
1180 comparison operations (e.g. <cf/=, !=, <, >, <=, >=/), but
1181 you can't concatenate two strings. String literals are written as
1182 <cf/"This is a string constant"/. Additionally matching (<cf/˜,
1183 !˜/) operators could be used to match a string value against
1184 a shell pattern (represented also as a string).
1186 <tag><label id="type-ip">ip</tag>
1187 This type can hold a single IP address. Depending on the compile-time
1188 configuration of BIRD you are using, it is either an IPv4 or IPv6
1189 address; this may be checked by <cf>.is_ip4</cf> which returns <cf/bool/.
1190 IP addresses are written in the standard notation
1191 (<cf/10.20.30.40/ or <cf/fec0:3:4::1/). You can apply special operator
1192 <cf>.mask(<M>num</M>)</cf> on values of type ip. It masks out all but
1193 first <cf><M>num</M></cf> bits from the IP address. So
1194 <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
1196 <tag><label id="type-prefix">prefix</tag>
1197 This type can hold a network prefix consisting of IP address, prefix
1198 length and several other values. This is the key in route tables.
1200 Prefixes may be of several types, which can be determined by the special
1201 operator <cf/.type/. The type may be:
1203 <cf/NET_IP4/ and <cf/NET_IP6/ prefixes hold an IP prefix. The literals
1204 are written as <cf><m/ipaddress//<m/pxlen/</cf>,
1205 or <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
1206 operators on IP prefixes: <cf/.ip/ which extracts the IP address from
1207 the pair, and <cf/.len/, which separates prefix length from the pair.
1208 So <cf>1.2.0.0/16.len = 16</cf> is true.
1210 <cf/NET_VPN4/ and <cf/NET_VPN6/ prefixes hold an IP prefix with VPN
1211 Route Distinguisher (<rfc id="4364">). They support the same special
1212 operators as IP prefixes, and also <cf/.rd/ which extracts the Route
1213 Distinguisher. Their literals are written
1214 as <cf><m/vpnrd/ <m/ipprefix/</cf>
1216 <cf/NET_ROA4/ and <cf/NET_ROA6/ prefixes hold an IP prefix range
1217 together with an ASN. They support the same special operators as IP
1218 prefixes, and also <cf/.maxlen/ which extracts maximal prefix length,
1219 and <cf/.asn/ which extracts the ASN.
1221 <cf/NET_FLOW4/ and <cf/NET_FLOW6/ hold an IP prefix together with a
1222 flowspec rule. Filters currently don't support flowspec parsing.
1224 <tag><label id="type-ec">ec</tag>
1225 This is a specialized type used to represent BGP extended community
1226 values. It is essentially a 64bit value, literals of this type are
1227 usually written as <cf>(<m/kind/, <m/key/, <m/value/)</cf>, where
1228 <cf/kind/ is a kind of extended community (e.g. <cf/rt/ / <cf/ro/ for a
1229 route target / route origin communities), the format and possible values
1230 of <cf/key/ and <cf/value/ are usually integers, but it depends on the
1231 used kind. Similarly to pairs, ECs can be constructed using expressions
1232 for <cf/key/ and <cf/value/ parts, (e.g. <cf/(ro, myas, 3*10)/, where
1233 <cf/myas/ is an integer variable).
1235 <tag><label id="type-lc">lc</tag>
1236 This is a specialized type used to represent BGP large community
1237 values. It is essentially a triplet of 32bit values, where the first
1238 value is reserved for the AS number of the issuer, while meaning of
1239 remaining parts is defined by the issuer. Literals of this type are
1240 written as <cf/(123, 456, 789)/, with any integer values. Similarly to
1241 pairs, LCs can be constructed using expressions for its parts, (e.g.
1242 <cf/(myas, 10+20, 3*10)/, where <cf/myas/ is an integer variable).
1244 <tag><label id="type-set">int|pair|quad|ip|prefix|ec|lc|enum set</tag>
1245 Filters recognize four types of sets. Sets are similar to strings: you
1246 can pass them around but you can't modify them. Literals of type <cf>int
1247 set</cf> look like <cf> [ 1, 2, 5..7 ]</cf>. As you can see, both simple
1248 values and ranges are permitted in sets.
1250 For pair sets, expressions like <cf/(123,*)/ can be used to denote
1251 ranges (in that case <cf/(123,0)..(123,65535)/). You can also use
1252 <cf/(123,5..100)/ for range <cf/(123,5)..(123,100)/. You can also use
1253 <cf/*/ and <cf/a..b/ expressions in the first part of a pair, note that
1254 such expressions are translated to a set of intervals, which may be
1255 memory intensive. E.g. <cf/(*,4..20)/ is translated to <cf/(0,4..20),
1256 (1,4..20), (2,4..20), ... (65535, 4..20)/.
1258 EC sets use similar expressions like pair sets, e.g. <cf/(rt, 123,
1259 10..20)/ or <cf/(ro, 123, *)/. Expressions requiring the translation
1260 (like <cf/(rt, *, 3)/) are not allowed (as they usually have 4B range
1263 Also LC sets use similar expressions like pair sets. You can use ranges
1264 and wildcards, but if one field uses that, more specific (later) fields
1265 must be wildcards. E.g., <cf/(10, 20..30, *)/ or <cf/(10, 20, 30..40)/
1266 is valid, while <cf/(10, *, 20..30)/ or <cf/(10, 20..30, 40)/ is not
1269 You can also use expressions for int, pair, EC and LC set values.
1270 However, it must be possible to evaluate these expressions before daemon
1271 boots. So you can use only constants inside them. E.g.
1280 odds = [ one, 2+1, 6-one, 2*2*2-1, 9, 11 ];
1281 ps = [ (1,one+one), (3,4)..(4,8), (5,*), (6,3..6), (7..9,*) ];
1282 es = [ (rt, myas, 3*10), (rt, myas+one, 0..16*16*16-1), (ro, myas+2, *) ];
1285 Sets of prefixes are special: their literals does not allow ranges, but
1286 allows prefix patterns that are written
1287 as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
1288 Prefix <cf><m>ip1</m>/<m>len1</m></cf> matches prefix
1289 pattern <cf><m>ip2</m>/<m>len2</m>{<m>l</m>,<m>h</m>}</cf> if the
1290 first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are
1291 identical and <cf>len1 <= ip1 <= len2</cf>. A valid prefix pattern
1292 has to satisfy <cf>low <= high</cf>, but <cf/pxlen/ is not
1293 constrained by <cf/low/ or <cf/high/. Obviously, a prefix matches a
1294 prefix set literal if it matches any prefix pattern in the prefix set
1297 There are also two shorthands for prefix patterns: <cf><m/address//<m/len/+</cf>
1298 is a shorthand for <cf><m/address//<m/len/{<m/len/,<m/maxlen/}</cf>
1299 (where <cf><m/maxlen/</cf> is 32 for IPv4 and 128 for IPv6), that means
1300 network prefix <cf><m/address//<m/len/</cf> and all its subnets.
1301 <cf><m/address//<m/len/-</cf> is a shorthand for
1302 <cf><m/address//<m/len/{0,<m/len/}</cf>, that means network prefix
1303 <cf><m/address//<m/len/</cf> and all its supernets (network prefixes
1306 For example, <cf>[ 1.0.0.0/8, 2.0.0.0/8+, 3.0.0.0/8-, 4.0.0.0/8{16,24}
1307 ]</cf> matches prefix <cf>1.0.0.0/8</cf>, all subprefixes of
1308 <cf>2.0.0.0/8</cf>, all superprefixes of <cf>3.0.0.0/8</cf> and prefixes
1309 <cf/4.X.X.X/ whose prefix length is 16 to 24. <cf>[ 0.0.0.0/0{20,24} ]</cf>
1310 matches all prefixes (regardless of IP address) whose prefix length is
1311 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP
1312 address <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 ˜ [ 1.0.0.0/8{15,17} ]</cf>
1313 is true, but <cf>1.0.0.0/16 ˜ [ 1.0.0.0/8- ]</cf> is false.
1315 Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
1316 in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as
1317 <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
1318 <cf>192.168.0.0/16{24,32}</cf>.
1320 <tag><label id="type-enum">enum</tag>
1321 Enumeration types are fixed sets of possibilities. You can't define your
1322 own variables of such type, but some route attributes are of enumeration
1323 type. Enumeration types are incompatible with each other.
1325 <tag><label id="type-bgppath">bgppath</tag>
1326 BGP path is a list of autonomous system numbers. You can't write
1327 literals of this type. There are several special operators on bgppaths:
1329 <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
1331 <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
1333 <cf><m/P/.last_nonaggregated</cf> returns the last ASN in the non-aggregated part of the path <m/P/.
1335 Both <cf/first/ and <cf/last/ return zero if there is no appropriate
1336 ASN, for example if the path contains an AS set element as the first (or
1337 the last) part. If the path ends with an AS set, <cf/last_nonaggregated/
1338 may be used to get last ASN before any AS set.
1340 <cf><m/P/.len</cf> returns the length of path <m/P/.
1342 <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and
1345 <cf>delete(<m/P/,<m/A/)</cf> deletes all instances of ASN <m/A/ from
1346 from path <m/P/ and returns the result. <m/A/ may also be an integer
1347 set, in that case the operator deletes all ASNs from path <m/P/ that are
1348 also members of set <m/A/.
1350 <cf>filter(<m/P/,<m/A/)</cf> deletes all ASNs from path <m/P/ that are
1351 not members of integer set <m/A/. I.e., <cf/filter/ do the same as
1352 <cf/delete/ with inverted set <m/A/.
1354 Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
1355 <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
1356 (for example <cf/bgp_path/). Similarly for <cf/delete/ and <cf/filter/.
1358 <tag><label id="type-bgpmask">bgpmask</tag>
1359 BGP masks are patterns used for BGP path matching (using <cf>path
1360 ˜ [= 2 3 5 * =]</cf> syntax). The masks resemble wildcard patterns
1361 as used by UNIX shells. Autonomous system numbers match themselves,
1362 <cf/*/ matches any (even empty) sequence of arbitrary AS numbers and
1363 <cf/?/ matches one arbitrary AS number. For example, if <cf>bgp_path</cf>
1364 is 4 3 2 1, then: <tt>bgp_path ˜ [= * 4 3 * =]</tt> is true,
1365 but <tt>bgp_path ˜ [= * 4 5 * =]</tt> is false. BGP mask
1366 expressions can also contain integer expressions enclosed in parenthesis
1367 and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>. You can
1368 also use ranges, for example <tt>[= * 3..5 2 100..200 * =]</tt>.
1369 There is also old (deprecated) syntax that uses / .. / instead of [= .. =]
1372 <tag><label id="type-clist">clist</tag>
1373 Clist is similar to a set, except that unlike other sets, it can be
1374 modified. The type is used for community list (a set of pairs) and for
1375 cluster list (a set of quads). There exist no literals of this type.
1376 There are three special operators on clists:
1378 <cf><m/C/.len</cf> returns the length of clist <m/C/.
1380 <cf>add(<m/C/,<m/P/)</cf> adds pair (or quad) <m/P/ to clist <m/C/ and
1381 returns the result. If item <m/P/ is already in clist <m/C/, it does
1382 nothing. <m/P/ may also be a clist, in that case all its members are
1383 added; i.e., it works as clist union.
1385 <cf>delete(<m/C/,<m/P/)</cf> deletes pair (or quad) <m/P/ from clist
1386 <m/C/ and returns the result. If clist <m/C/ does not contain item
1387 <m/P/, it does nothing. <m/P/ may also be a pair (or quad) set, in that
1388 case the operator deletes all items from clist <m/C/ that are also
1389 members of set <m/P/. Moreover, <m/P/ may also be a clist, which works
1390 analogously; i.e., it works as clist difference.
1392 <cf>filter(<m/C/,<m/P/)</cf> deletes all items from clist <m/C/ that are
1393 not members of pair (or quad) set <m/P/. I.e., <cf/filter/ do the same
1394 as <cf/delete/ with inverted set <m/P/. <m/P/ may also be a clist, which
1395 works analogously; i.e., it works as clist intersection.
1397 Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
1398 <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute (for
1399 example <cf/bgp_community/). Similarly for <cf/delete/ and <cf/filter/.
1401 <tag><label id="type-eclist">eclist</tag>
1402 Eclist is a data type used for BGP extended community lists. Eclists
1403 are very similar to clists, but they are sets of ECs instead of pairs.
1404 The same operations (like <cf/add/, <cf/delete/ or <cf/˜/ and
1405 <cf/!˜/ membership operators) can be used to modify or test
1406 eclists, with ECs instead of pairs as arguments.
1408 <tag><label id="type-lclist">lclist/</tag>
1409 Lclist is a data type used for BGP large community lists. Like eclists,
1410 lclists are very similar to clists, but they are sets of LCs instead of
1411 pairs. The same operations (like <cf/add/, <cf/delete/ or <cf/˜/
1412 and <cf/!˜/ membership operators) can be used to modify or test
1413 lclists, with LCs instead of pairs as arguments.
1418 <label id="operators">
1420 <p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>,
1421 parentheses <cf/(a*(b+c))/, comparison <cf/(a=b, a!=b, a<b, a>=b)/.
1422 Logical operations include unary not (<cf/!/), and (<cf/&&/) and or
1423 (<cf/||/). Special operators include (<cf/˜/,
1424 <cf/!˜/) for "is (not) element of a set" operation - it can be used on
1425 element and set of elements of the same type (returning true if element is
1426 contained in the given set), or on two strings (returning true if first string
1427 matches a shell-like pattern stored in second string) or on IP and prefix
1428 (returning true if IP is within the range defined by that prefix), or on prefix
1429 and prefix (returning true if first prefix is more specific than second one) or
1430 on bgppath and bgpmask (returning true if the path matches the mask) or on
1431 number and bgppath (returning true if the number is in the path) or on bgppath
1432 and int (number) set (returning true if any ASN from the path is in the set) or
1433 on pair/quad and clist (returning true if the pair/quad is element of the
1434 clist) or on clist and pair/quad set (returning true if there is an element of
1435 the clist that is also a member of the pair/quad set).
1437 <p>There is one operator related to ROA infrastructure - <cf/roa_check()/. It
1438 examines a ROA table and does <rfc id="6483"> route origin validation for a
1439 given network prefix. The basic usage is <cf>roa_check(<m/table/)</cf>, which
1440 checks current route (which should be from BGP to have AS_PATH argument) in the
1441 specified ROA table and returns ROA_UNKNOWN if there is no relevant ROA,
1442 ROA_VALID if there is a matching ROA, or ROA_INVALID if there are some relevant
1443 ROAs but none of them match. There is also an extended variant
1444 <cf>roa_check(<m/table/, <m/prefix/, <m/asn/)</cf>, which allows to specify a
1445 prefix and an ASN as arguments.
1448 <sect>Control structures
1449 <label id="control-structures">
1451 <p>Filters support two control structures: conditions and case switches.
1453 <p>Syntax of a condition is: <cf>if <M>boolean expression</M> then <m/command1/;
1454 else <m/command2/;</cf> and you can use <cf>{ <m/command_1/; <m/command_2/;
1455 <M>...</M> }</cf> instead of either command. The <cf>else</cf> clause may be
1456 omitted. If the <cf><m>boolean expression</m></cf> is true, <m/command1/ is
1457 executed, otherwise <m/command2/ is executed.
1459 <p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case
1460 <m/expr/ { else: | <m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [
1461 ... ] }</cf>. The expression after <cf>case</cf> can be of any type which can be
1462 on the left side of the ˜ operator and anything that could be a member of
1463 a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/
1464 grouping. If <cf><m/expr/</cf> matches one of the <cf/:/ clauses, statements
1465 between it and next <cf/:/ statement are executed. If <cf><m/expr/</cf> matches
1466 neither of the <cf/:/ clauses, the statements after <cf/else:/ are executed.
1468 <p>Here is example that uses <cf/if/ and <cf/case/ structures:
1472 2: print "two"; print "I can do more commands without {}";
1473 3 .. 5: print "three to five";
1474 else: print "something else";
1477 if 1234 = i then printn "."; else {
1479 print "You need {} around multiple commands";
1484 <sect>Route attributes
1485 <label id="route-attributes">
1487 <p>A filter is implicitly passed a route, and it can access its attributes just
1488 like it accesses variables. Attempts to access undefined attribute result in a
1489 runtime error; you can check if an attribute is defined by using the
1490 <cf>defined( <m>attribute</m> )</cf> operator. One notable exception to this
1491 rule are attributes of clist type, where undefined value is regarded as empty
1492 clist for most purposes.
1495 <tag><label id="rta-net"><m/prefix/ net</tag>
1496 Network the route is talking about. Read-only. (See the chapter about
1499 <tag><label id="rta-scope"><m/enum/ scope</tag>
1500 The scope of the route. Possible values: <cf/SCOPE_HOST/ for routes
1501 local to this host, <cf/SCOPE_LINK/ for those specific for a physical
1502 link, <cf/SCOPE_SITE/ and <cf/SCOPE_ORGANIZATION/ for private routes and
1503 <cf/SCOPE_UNIVERSE/ for globally visible routes. This attribute is not
1504 interpreted by BIRD and can be used to mark routes in filters. The
1505 default value for new routes is <cf/SCOPE_UNIVERSE/.
1507 <tag><label id="rta-preference"><m/int/ preference</tag>
1508 Preference of the route. Valid values are 0-65535. (See the chapter
1509 about routing tables.)
1511 <tag><label id="rta-from"><m/ip/ from</tag>
1512 The router which the route has originated from.
1514 <tag><label id="rta-gw"><m/ip/ gw</tag>
1515 Next hop packets routed using this route should be forwarded to.
1517 <tag><label id="rta-proto"><m/string/ proto</tag>
1518 The name of the protocol which the route has been imported from.
1521 <tag><label id="rta-source"><m/enum/ source</tag>
1522 what protocol has told me about this route. Possible values:
1523 <cf/RTS_DUMMY/, <cf/RTS_STATIC/, <cf/RTS_INHERIT/, <cf/RTS_DEVICE/,
1524 <cf/RTS_STATIC_DEVICE/, <cf/RTS_REDIRECT/, <cf/RTS_RIP/, <cf/RTS_OSPF/,
1525 <cf/RTS_OSPF_IA/, <cf/RTS_OSPF_EXT1/, <cf/RTS_OSPF_EXT2/, <cf/RTS_BGP/,
1526 <cf/RTS_PIPE/, <cf/RTS_BABEL/.
1528 <tag><label id="rta-cast"><m/enum/ cast</tag>
1529 Route type (Currently <cf/RTC_UNICAST/ for normal routes,
1530 <cf/RTC_BROADCAST/, <cf/RTC_MULTICAST/, <cf/RTC_ANYCAST/ will be used in
1531 the future for broadcast, multicast and anycast routes). Read-only.
1533 <tag><label id="rta-dest"><m/enum/ dest</tag>
1534 Type of destination the packets should be sent to
1535 (<cf/RTD_ROUTER/ for forwarding to a neighboring router,
1536 <cf/RTD_DEVICE/ for routing to a directly-connected network,
1537 <cf/RTD_MULTIPATH/ for multipath destinations,
1538 <cf/RTD_BLACKHOLE/ for packets to be silently discarded,
1539 <cf/RTD_UNREACHABLE/, <cf/RTD_PROHIBIT/ for packets that should be
1540 returned with ICMP host unreachable / ICMP administratively prohibited
1541 messages). Can be changed, but only to <cf/RTD_BLACKHOLE/,
1542 <cf/RTD_UNREACHABLE/ or <cf/RTD_PROHIBIT/.
1544 <tag><label id="rta-ifname"><m/string/ ifname</tag>
1545 Name of the outgoing interface. Sink routes (like blackhole, unreachable
1546 or prohibit) and multipath routes have no interface associated with
1547 them, so <cf/ifname/ returns an empty string for such routes. Read-only.
1549 <tag><label id="rta-ifindex"><m/int/ ifindex</tag>
1550 Index of the outgoing interface. System wide index of the interface. May
1551 be used for interface matching, however indexes might change on interface
1552 creation/removal. Zero is returned for routes with undefined outgoing
1553 interfaces. Read-only.
1555 <tag><label id="rta-igp-metric"><m/int/ igp_metric</tag>
1556 The optional attribute that can be used to specify a distance to the
1557 network for routes that do not have a native protocol metric attribute
1558 (like <cf/ospf_metric1/ for OSPF routes). It is used mainly by BGP to
1559 compare internal distances to boundary routers (see below). It is also
1560 used when the route is exported to OSPF as a default value for OSPF type
1564 <p>There also exist some protocol-specific attributes which are described in the
1565 corresponding protocol sections.
1568 <sect>Other statements
1569 <label id="other-statements">
1571 <p>The following statements are available:
1574 <tag><label id="assignment"><m/variable/ = <m/expr/</tag>
1575 Set variable to a given value.
1577 <tag><label id="filter-accept-reject">accept|reject [ <m/expr/ ]</tag>
1578 Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
1580 <tag><label id="return">return <m/expr/</tag>
1581 Return <cf><m>expr</m></cf> from the current function, the function ends
1584 <tag><label id="print">print|printn <m/expr/ [<m/, expr.../]</tag>
1585 Prints given expressions; useful mainly while debugging filters. The
1586 <cf/printn/ variant does not terminate the line.
1588 <tag><label id="quitbird">quitbird</tag>
1589 Terminates BIRD. Useful when debugging the filter interpreter.
1594 <label id="protocols">
1600 <label id="babel-intro">
1602 <p>The Babel protocol
1603 (<rfc id="6126">) is a loop-avoiding distance-vector routing protocol that is
1604 robust and efficient both in ordinary wired networks and in wireless mesh
1605 networks. Babel is conceptually very simple in its operation and "just works"
1606 in its default configuration, though some configuration is possible and in some
1609 <p>While the Babel protocol is dual stack (i.e., can carry both IPv4 and IPv6
1610 routes over the same IPv6 transport), BIRD presently implements only the IPv6
1611 subset of the protocol. No Babel extensions are implemented, but the BIRD
1612 implementation can coexist with implementations using the extensions (and will
1613 just ignore extension messages).
1615 <p>The Babel protocol implementation in BIRD is currently in alpha stage.
1617 <sect1>Configuration
1618 <label id="babel-config">
1620 <p>Babel supports no global configuration options apart from those common to all
1621 other protocols, but supports the following per-interface configuration options:
1624 protocol babel [<name>] {
1625 interface <interface pattern> {
1626 type <wired|wireless>;
1628 hello interval <number>;
1629 update interval <number>;
1631 tx class|dscp <number>;
1632 tx priority <number>;
1635 check link <switch>;
1641 <tag><label id="babel-type">type wired|wireless </tag>
1642 This option specifies the interface type: Wired or wireless. Wired
1643 interfaces are considered more reliable, and so the default hello
1644 interval is higher, and a neighbour is considered unreachable after only
1645 a small number of "hello" packets are lost. On wireless interfaces,
1646 hello packets are sent more often, and the ETX link quality estimation
1647 technique is used to compute the metrics of routes discovered over this
1648 interface. This technique will gradually degrade the metric of routes
1649 when packets are lost rather than the more binary up/down mechanism of
1650 wired type links. Default: <cf/wired/.
1652 <tag><label id="babel-rxcost">rxcost <m/num/</tag>
1653 This specifies the RX cost of the interface. The route metrics will be
1654 computed from this value with a mechanism determined by the interface
1655 <cf/type/. Default: 96 for wired interfaces, 256 for wireless.
1657 <tag><label id="babel-hello">hello interval <m/num/</tag>
1658 Interval at which periodic "hello" messages are sent on this interface,
1659 in seconds. Default: 4 seconds.
1661 <tag><label id="babel-update">update interval <m/num/</tag>
1662 Interval at which periodic (full) updates are sent. Default: 4 times the
1665 <tag><label id="babel-port">port <m/number/</tag>
1666 This option selects an UDP port to operate on. The default is to operate
1667 on port 6696 as specified in the Babel RFC.
1669 <tag><label id="babel-tx-class">tx class|dscp|priority <m/number/</tag>
1670 These options specify the ToS/DiffServ/Traffic class/Priority of the
1671 outgoing Babel packets. See <ref id="proto-tx-class" name="tx class"> common
1672 option for detailed description.
1674 <tag><label id="babel-rx-buffer">rx buffer <m/number/</tag>
1675 This option specifies the size of buffers used for packet processing.
1676 The buffer size should be bigger than maximal size of received packets.
1677 The default value is the interface MTU, and the value will be clamped to a
1678 minimum of 512 bytes + IP packet overhead.
1680 <tag><label id="babel-tx-length">tx length <m/number/</tag>
1681 This option specifies the maximum length of generated Babel packets. To
1682 avoid IP fragmentation, it should not exceed the interface MTU value.
1683 The default value is the interface MTU value, and the value will be
1684 clamped to a minimum of 512 bytes + IP packet overhead.
1686 <tag><label id="babel-check-link">check link <m/switch/</tag>
1687 If set, the hardware link state (as reported by OS) is taken into
1688 consideration. When the link disappears (e.g. an ethernet cable is
1689 unplugged), neighbors are immediately considered unreachable and all
1690 routes received from them are withdrawn. It is possible that some
1691 hardware drivers or platforms do not implement this feature. Default:
1696 <label id="babel-attr">
1698 <p>Babel defines just one attribute: the internal babel metric of the route. It
1699 is exposed as the <cf/babel_metric/ attribute and has range from 1 to infinity
1703 <label id="babel-exam">
1710 interface "wlan0", "wlan1" {
1717 # This matches the default of babeld: redistribute all addresses
1718 # configured on local interfaces, plus re-distribute all routes received
1719 # from other babel peers.
1721 export where (source = RTS_DEVICE) || (source = RTS_BABEL);
1730 <label id="bfd-intro">
1732 <p>Bidirectional Forwarding Detection (BFD) is not a routing protocol itself, it
1733 is an independent tool providing liveness and failure detection. Routing
1734 protocols like OSPF and BGP use integrated periodic "hello" messages to monitor
1735 liveness of neighbors, but detection times of these mechanisms are high (e.g. 40
1736 seconds by default in OSPF, could be set down to several seconds). BFD offers
1737 universal, fast and low-overhead mechanism for failure detection, which could be
1738 attached to any routing protocol in an advisory role.
1740 <p>BFD consists of mostly independent BFD sessions. Each session monitors an
1741 unicast bidirectional path between two BFD-enabled routers. This is done by
1742 periodically sending control packets in both directions. BFD does not handle
1743 neighbor discovery, BFD sessions are created on demand by request of other
1744 protocols (like OSPF or BGP), which supply appropriate information like IP
1745 addresses and associated interfaces. When a session changes its state, these
1746 protocols are notified and act accordingly (e.g. break an OSPF adjacency when
1747 the BFD session went down).
1749 <p>BIRD implements basic BFD behavior as defined in <rfc id="5880"> (some
1750 advanced features like the echo mode or authentication are not implemented), IP
1751 transport for BFD as defined in <rfc id="5881"> and <rfc id="5883"> and
1752 interaction with client protocols as defined in <rfc id="5882">.
1754 <p>Note that BFD implementation in BIRD is currently a new feature in
1755 development, expect some rough edges and possible UI and configuration changes
1756 in the future. Also note that we currently support at most one protocol instance.
1758 <p>BFD packets are sent with a dynamic source port number. Linux systems use by
1759 default a bit different dynamic port range than the IANA approved one
1760 (49152-65535). If you experience problems with compatibility, please adjust
1761 <cf>/proc/sys/net/ipv4/ip_local_port_range</cf>
1763 <sect1>Configuration
1764 <label id="bfd-config">
1766 <p>BFD configuration consists mainly of multiple definitions of interfaces.
1767 Most BFD config options are session specific. When a new session is requested
1768 and dynamically created, it is configured from one of these definitions. For
1769 sessions to directly connected neighbors, <cf/interface/ definitions are chosen
1770 based on the interface associated with the session, while <cf/multihop/
1771 definition is used for multihop sessions. If no definition is relevant, the
1772 session is just created with the default configuration. Therefore, an empty BFD
1773 configuration is often sufficient.
1775 <p>Note that to use BFD for other protocols like OSPF or BGP, these protocols
1776 also have to be configured to request BFD sessions, usually by <cf/bfd/ option.
1778 <p>Some of BFD session options require <m/time/ value, which has to be specified
1779 with the appropriate unit: <m/num/ <cf/s/|<cf/ms/|<cf/us/. Although microseconds
1780 are allowed as units, practical minimum values are usually in order of tens of
1784 protocol bfd [<name>] {
1785 interface <interface pattern> {
1786 interval <time>;
1787 min rx interval <time>;
1788 min tx interval <time>;
1789 idle tx interval <time>;
1790 multiplier <num>;
1791 passive <switch>;
1792 authentication none;
1793 authentication simple;
1794 authentication [meticulous] keyed md5|sha1;
1795 password "<text>";
1796 password "<text>" {
1798 generate from "<date>";
1799 generate to "<date>";
1800 accept from "<date>";
1801 accept to "<date>";
1802 from "<date>";
1807 interval <time>;
1808 min rx interval <time>;
1809 min tx interval <time>;
1810 idle tx interval <time>;
1811 multiplier <num>;
1812 passive <switch>;
1814 neighbor <ip> [dev "<interface>"] [local <ip>] [multihop <switch>];
1819 <tag><label id="bfd-iface">interface <m/pattern/ [, <m/.../] { <m/options/ }</tag>
1820 Interface definitions allow to specify options for sessions associated
1821 with such interfaces and also may contain interface specific options.
1822 See <ref id="proto-iface" name="interface"> common option for a detailed
1823 description of interface patterns. Note that contrary to the behavior of
1824 <cf/interface/ definitions of other protocols, BFD protocol would accept
1825 sessions (in default configuration) even on interfaces not covered by
1828 <tag><label id="bfd-multihop">multihop { <m/options/ }</tag>
1829 Multihop definitions allow to specify options for multihop BFD sessions,
1830 in the same manner as <cf/interface/ definitions are used for directly
1831 connected sessions. Currently only one such definition (for all multihop
1832 sessions) could be used.
1834 <tag><label id="bfd-neighbor">neighbor <m/ip/ [dev "<m/interface/"] [local <m/ip/] [multihop <m/switch/]</tag>
1835 BFD sessions are usually created on demand as requested by other
1836 protocols (like OSPF or BGP). This option allows to explicitly add
1837 a BFD session to the specified neighbor regardless of such requests.
1839 The session is identified by the IP address of the neighbor, with
1840 optional specification of used interface and local IP. By default
1841 the neighbor must be directly connected, unless the session is
1842 configured as multihop. Note that local IP must be specified for
1846 <p>Session specific options (part of <cf/interface/ and <cf/multihop/ definitions):
1849 <tag><label id="bfd-interval">interval <m/time/</tag>
1850 BFD ensures availability of the forwarding path associated with the
1851 session by periodically sending BFD control packets in both
1852 directions. The rate of such packets is controlled by two options,
1853 <cf/min rx interval/ and <cf/min tx interval/ (see below). This option
1854 is just a shorthand to set both of these options together.
1856 <tag><label id="bfd-min-rx-interval">min rx interval <m/time/</tag>
1857 This option specifies the minimum RX interval, which is announced to the
1858 neighbor and used there to limit the neighbor's rate of generated BFD
1859 control packets. Default: 10 ms.
1861 <tag><label id="bfd-min-tx-interval">min tx interval <m/time/</tag>
1862 This option specifies the desired TX interval, which controls the rate
1863 of generated BFD control packets (together with <cf/min rx interval/
1864 announced by the neighbor). Note that this value is used only if the BFD
1865 session is up, otherwise the value of <cf/idle tx interval/ is used
1866 instead. Default: 100 ms.
1868 <tag><label id="bfd-idle-tx-interval">idle tx interval <m/time/</tag>
1869 In order to limit unnecessary traffic in cases where a neighbor is not
1870 available or not running BFD, the rate of generated BFD control packets
1871 is lower when the BFD session is not up. This option specifies the
1872 desired TX interval in such cases instead of <cf/min tx interval/.
1875 <tag><label id="bfd-multiplier">multiplier <m/num/</tag>
1876 Failure detection time for BFD sessions is based on established rate of
1877 BFD control packets (<cf>min rx/tx interval</cf>) multiplied by this
1878 multiplier, which is essentially (ignoring jitter) a number of missed
1879 packets after which the session is declared down. Note that rates and
1880 multipliers could be different in each direction of a BFD session.
1883 <tag><label id="bfd-passive">passive <m/switch/</tag>
1884 Generally, both BFD session endpoints try to establish the session by
1885 sending control packets to the other side. This option allows to enable
1886 passive mode, which means that the router does not send BFD packets
1887 until it has received one from the other side. Default: disabled.
1889 <tag>authentication none</tag>
1890 No passwords are sent in BFD packets. This is the default value.
1892 <tag>authentication simple</tag>
1893 Every packet carries 16 bytes of password. Received packets lacking this
1894 password are ignored. This authentication mechanism is very weak.
1896 <tag>authentication [meticulous] keyed md5|sha1</tag>
1897 An authentication code is appended to each packet. The cryptographic
1898 algorithm is keyed MD5 or keyed SHA-1. Note that the algorithm is common
1899 for all keys (on one interface), in contrast to OSPF or RIP, where it
1900 is a per-key option. Passwords (keys) are not sent open via network.
1902 The <cf/meticulous/ variant means that cryptographic sequence numbers
1903 are increased for each sent packet, while in the basic variant they are
1904 increased about once per second. Generally, the <cf/meticulous/ variant
1905 offers better resistance to replay attacks but may require more
1908 <tag>password "<M>text</M>"</tag>
1909 Specifies a password used for authentication. See <ref id="dsc-pass"
1910 name="password"> common option for detailed description. Note that
1911 password option <cf/algorithm/ is not available in BFD protocol. The
1912 algorithm is selected by <cf/authentication/ option for all passwords.
1917 <label id="bfd-exam">
1922 min rx interval 20 ms;
1923 min tx interval 50 ms;
1924 idle tx interval 300 ms;
1936 neighbor 192.168.1.10;
1937 neighbor 192.168.2.2 dev "eth2";
1938 neighbor 192.168.10.1 local 192.168.1.1 multihop;
1946 <p>The Border Gateway Protocol is the routing protocol used for backbone level
1947 routing in the today's Internet. Contrary to other protocols, its convergence
1948 does not rely on all routers following the same rules for route selection,
1949 making it possible to implement any routing policy at any router in the network,
1950 the only restriction being that if a router advertises a route, it must accept
1951 and forward packets according to it.
1953 <p>BGP works in terms of autonomous systems (often abbreviated as AS). Each AS
1954 is a part of the network with common management and common routing policy. It is
1955 identified by a unique 16-bit number (ASN). Routers within each AS usually
1956 exchange AS-internal routing information with each other using an interior
1957 gateway protocol (IGP, such as OSPF or RIP). Boundary routers at the border of
1958 the AS communicate global (inter-AS) network reachability information with their
1959 neighbors in the neighboring AS'es via exterior BGP (eBGP) and redistribute
1960 received information to other routers in the AS via interior BGP (iBGP).
1962 <p>Each BGP router sends to its neighbors updates of the parts of its routing
1963 table it wishes to export along with complete path information (a list of AS'es
1964 the packet will travel through if it uses the particular route) in order to
1965 avoid routing loops.
1967 <p>BIRD supports all requirements of the BGP4 standard as defined in
1968 <rfc id="4271"> It also supports the community attributes (<rfc id="1997">),
1969 capability negotiation (<rfc id="5492">), MD5 password authentication
1970 (<rfc id="2385">), extended communities (<rfc id="4360">), route reflectors
1971 (<rfc id="4456">), AS confederations (<rfc id="5065">), graceful restart
1972 (<rfc id="4724">), multiprotocol extensions (<rfc id="4760">), 4B AS numbers
1973 (<rfc id="4893">), and 4B AS numbers in extended communities (<rfc id="5668">).
1975 For IPv6, it uses the standard multiprotocol extensions defined in
1976 <rfc id="4760"> and applied to IPv6 according to <rfc id="2545">.
1978 <sect1>Route selection rules
1979 <label id="bgp-route-select-rules">
1981 <p>BGP doesn't have any simple metric, so the rules for selection of an optimal
1982 route among multiple BGP routes with the same preference are a bit more complex
1983 and they are implemented according to the following algorithm. It starts the
1984 first rule, if there are more "best" routes, then it uses the second rule to
1985 choose among them and so on.
1988 <item>Prefer route with the highest Local Preference attribute.
1989 <item>Prefer route with the shortest AS path.
1990 <item>Prefer IGP origin over EGP and EGP origin over incomplete.
1991 <item>Prefer the lowest value of the Multiple Exit Discriminator.
1992 <item>Prefer routes received via eBGP over ones received via iBGP.
1993 <item>Prefer routes with lower internal distance to a boundary router.
1994 <item>Prefer the route with the lowest value of router ID of the
1998 <sect1>IGP routing table
1999 <label id="bgp-igp-routing-table">
2001 <p>BGP is mainly concerned with global network reachability and with routes to
2002 other autonomous systems. When such routes are redistributed to routers in the
2003 AS via BGP, they contain IP addresses of a boundary routers (in route attribute
2004 NEXT_HOP). BGP depends on existing IGP routing table with AS-internal routes to
2005 determine immediate next hops for routes and to know their internal distances to
2006 boundary routers for the purpose of BGP route selection. In BIRD, there is
2007 usually one routing table used for both IGP routes and BGP routes.
2009 <sect1>Configuration
2010 <label id="bgp-config">
2012 <p>Each instance of the BGP corresponds to one neighboring router. This allows
2013 to set routing policy and all the other parameters differently for each neighbor
2014 using the following configuration parameters:
2017 <tag><label id="bgp-local">local [<m/ip/] as <m/number/</tag>
2018 Define which AS we are part of. (Note that contrary to other IP routers,
2019 BIRD is able to act as a router located in multiple AS'es simultaneously,
2020 but in such cases you need to tweak the BGP paths manually in the filters
2021 to get consistent behavior.) Optional <cf/ip/ argument specifies a source
2022 address, equivalent to the <cf/source address/ option (see below). This
2023 parameter is mandatory.
2025 <tag><label id="bgp-neighbor">neighbor [<m/ip/] [port <m/number/] [as <m/number/]</tag>
2026 Define neighboring router this instance will be talking to and what AS
2027 it is located in. In case the neighbor is in the same AS as we are, we
2028 automatically switch to iBGP. Optionally, the remote port may also be
2029 specified. The parameter may be used multiple times with different
2030 sub-options (e.g., both <cf/neighbor 10.0.0.1 as 65000;/ and
2031 <cf/neighbor 10.0.0.1; neighbor as 65000;/ are valid). This parameter is
2034 <tag><label id="bgp-iface">interface <m/string/</tag>
2035 Define interface we should use for link-local BGP IPv6 sessions.
2036 Interface can also be specified as a part of <cf/neighbor address/
2037 (e.g., <cf/neighbor fe80::1234%eth0 as 65000;/). It is an error to use
2038 this parameter for non link-local sessions.
2040 <tag><label id="bgp-direct">direct</tag>
2041 Specify that the neighbor is directly connected. The IP address of the
2042 neighbor must be from a directly reachable IP range (i.e. associated
2043 with one of your router's interfaces), otherwise the BGP session
2044 wouldn't start but it would wait for such interface to appear. The
2045 alternative is the <cf/multihop/ option. Default: enabled for eBGP.
2047 <tag><label id="bgp-multihop">multihop [<m/number/]</tag>
2048 Configure multihop BGP session to a neighbor that isn't directly
2049 connected. Accurately, this option should be used if the configured
2050 neighbor IP address does not match with any local network subnets. Such
2051 IP address have to be reachable through system routing table. The
2052 alternative is the <cf/direct/ option. For multihop BGP it is
2053 recommended to explicitly configure the source address to have it
2054 stable. Optional <cf/number/ argument can be used to specify the number
2055 of hops (used for TTL). Note that the number of networks (edges) in a
2056 path is counted; i.e., if two BGP speakers are separated by one router,
2057 the number of hops is 2. Default: enabled for iBGP.
2059 <tag><label id="bgp-source-address">source address <m/ip/</tag>
2060 Define local address we should use for next hop calculation and as a
2061 source address for the BGP session. Default: the address of the local
2062 end of the interface our neighbor is connected to.
2064 <tag><label id="bgp-strict-bind">strict bind <m/switch/</tag>
2065 Specify whether BGP listening socket should be bound to a specific local
2066 address (the same as the <cf/source address/) and associated interface,
2067 or to all addresses. Binding to a specific address could be useful in
2068 cases like running multiple BIRD instances on a machine, each using its
2069 IP address. Note that listening sockets bound to a specific address and
2070 to all addresses collide, therefore either all BGP protocols (of the
2071 same address family and using the same local port) should have set
2072 <cf/strict bind/, or none of them. Default: disabled.
2074 <tag><label id="bgp-next-hop-self">next hop self</tag>
2075 Avoid calculation of the Next Hop attribute and always advertise our own
2076 source address as a next hop. This needs to be used only occasionally to
2077 circumvent misconfigurations of other routers. Default: disabled.
2079 <tag><label id="bgp-next-hop-keep">next hop keep</tag>
2080 Forward the received Next Hop attribute even in situations where the
2081 local address should be used instead, like when the route is sent to an
2082 interface with a different subnet. Default: disabled.
2084 <tag><label id="bgp-missing-lladdr">missing lladdr self|drop|ignore</tag>
2085 Next Hop attribute in BGP-IPv6 sometimes contains just the global IPv6
2086 address, but sometimes it has to contain both global and link-local IPv6
2087 addresses. This option specifies what to do if BIRD have to send both
2088 addresses but does not know link-local address. This situation might
2089 happen when routes from other protocols are exported to BGP, or when
2090 improper updates are received from BGP peers. <cf/self/ means that BIRD
2091 advertises its own local address instead. <cf/drop/ means that BIRD
2092 skips that prefixes and logs error. <cf/ignore/ means that BIRD ignores
2093 the problem and sends just the global address (and therefore forms
2094 improper BGP update). Default: <cf/self/, unless BIRD is configured as a
2095 route server (option <cf/rs client/), in that case default is <cf/ignore/,
2096 because route servers usually do not forward packets themselves.
2098 <tag><label id="bgp-gateway">gateway direct|recursive</tag>
2099 For received routes, their <cf/gw/ (immediate next hop) attribute is
2100 computed from received <cf/bgp_next_hop/ attribute. This option
2101 specifies how it is computed. Direct mode means that the IP address from
2102 <cf/bgp_next_hop/ is used if it is directly reachable, otherwise the
2103 neighbor IP address is used. Recursive mode means that the gateway is
2104 computed by an IGP routing table lookup for the IP address from
2105 <cf/bgp_next_hop/. Note that there is just one level of indirection in
2106 recursive mode - the route obtained by the lookup must not be recursive
2107 itself, to prevent mutually recursive routes.
2109 Recursive mode is the behavior specified by the BGP
2110 standard. Direct mode is simpler, does not require any routes in a
2111 routing table, and was used in older versions of BIRD, but does not
2112 handle well nontrivial iBGP setups and multihop. Recursive mode is
2113 incompatible with <ref id="dsc-table-sorted" name="sorted tables">. Default:
2114 <cf/direct/ for direct sessions, <cf/recursive/ for multihop sessions.
2116 <tag><label id="bgp-igp-table">igp table <m/name/</tag>
2117 Specifies a table that is used as an IGP routing table. Default: the
2118 same as the table BGP is connected to.
2120 <tag><label id="bgp-check-link">check link <M>switch</M></tag>
2121 BGP could use hardware link state into consideration. If enabled,
2122 BIRD tracks the link state of the associated interface and when link
2123 disappears (e.g. an ethernet cable is unplugged), the BGP session is
2124 immediately shut down. Note that this option cannot be used with
2125 multihop BGP. Default: disabled.
2127 <tag><label id="bgp-bfd">bfd <M>switch</M></tag>
2128 BGP could use BFD protocol as an advisory mechanism for neighbor
2129 liveness and failure detection. If enabled, BIRD setups a BFD session
2130 for the BGP neighbor and tracks its liveness by it. This has an
2131 advantage of an order of magnitude lower detection times in case of
2132 failure. Note that BFD protocol also has to be configured, see
2133 <ref id="bfd" name="BFD"> section for details. Default: disabled.
2135 <tag><label id="bgp-ttl-security">ttl security <m/switch/</tag>
2136 Use GTSM (<rfc id="5082"> - the generalized TTL security mechanism). GTSM
2137 protects against spoofed packets by ignoring received packets with a
2138 smaller than expected TTL. To work properly, GTSM have to be enabled on
2139 both sides of a BGP session. If both <cf/ttl security/ and
2140 <cf/multihop/ options are enabled, <cf/multihop/ option should specify
2141 proper hop value to compute expected TTL. Kernel support required:
2142 Linux: 2.6.34+ (IPv4), 2.6.35+ (IPv6), BSD: since long ago, IPv4 only.
2143 Note that full (ICMP protection, for example) <rfc id="5082"> support is
2144 provided by Linux only. Default: disabled.
2146 <tag><label id="bgp-password">password <m/string/</tag>
2147 Use this password for MD5 authentication of BGP sessions (<rfc id="2385">). When
2148 used on BSD systems, see also <cf/setkey/ option below. Default: no
2151 <tag><label id="bgp-setkey">setkey <m/switch/</tag>
2152 On BSD systems, keys for TCP MD5 authentication are stored in the global
2153 SA/SP database, which can be accessed by external utilities (e.g.
2154 setkey(8)). BIRD configures security associations in the SA/SP database
2155 automatically based on <cf/password/ options (see above), this option
2156 allows to disable automatic updates by BIRD when manual configuration by
2157 external utilities is preferred. Note that automatic SA/SP database
2158 updates are currently implemented only for FreeBSD. Passwords have to be
2159 set manually by an external utility on NetBSD and OpenBSD. Default:
2160 enabled (ignored on non-FreeBSD).
2162 <tag><label id="bgp-passive">passive <m/switch/</tag>
2163 Standard BGP behavior is both initiating outgoing connections and
2164 accepting incoming connections. In passive mode, outgoing connections
2165 are not initiated. Default: off.
2167 <tag><label id="bgp-confederation">confederation <m/number/</tag>
2168 BGP confederations (<rfc id="5065">) are collections of autonomous
2169 systems that act as one entity to external systems, represented by one
2170 confederation identifier (instead of AS numbers). This option allows to
2171 enable BGP confederation behavior and to specify the local confederation
2172 identifier. When BGP confederations are used, all BGP speakers that are
2173 members of the BGP confederation should have the same confederation
2174 identifier configured. Default: 0 (no confederation).
2176 <tag><label id="bgp-confederation-member">confederation member <m/switch/</tag>
2177 When BGP confederations are used, this option allows to specify whether
2178 the BGP neighbor is a member of the same confederation as the local BGP
2179 speaker. The option is unnecessary (and ignored) for IBGP sessions, as
2180 the same AS number implies the same confederation. Default: no.
2182 <tag><label id="bgp-rr-client">rr client</tag>
2183 Be a route reflector and treat the neighbor as a route reflection
2184 client. Default: disabled.
2186 <tag><label id="bgp-rr-cluster-id">rr cluster id <m/IPv4 address/</tag>
2187 Route reflectors use cluster id to avoid route reflection loops. When
2188 there is one route reflector in a cluster it usually uses its router id
2189 as a cluster id, but when there are more route reflectors in a cluster,
2190 these need to be configured (using this option) to use a common cluster
2191 id. Clients in a cluster need not know their cluster id and this option
2192 is not allowed for them. Default: the same as router id.
2194 <tag><label id="bgp-rs-client">rs client</tag>
2195 Be a route server and treat the neighbor as a route server client.
2196 A route server is used as a replacement for full mesh EBGP routing in
2197 Internet exchange points in a similar way to route reflectors used in
2198 IBGP routing. BIRD does not implement obsoleted <rfc id="1863">, but
2199 uses ad-hoc implementation, which behaves like plain EBGP but reduces
2200 modifications to advertised route attributes to be transparent (for
2201 example does not prepend its AS number to AS PATH attribute and
2202 keeps MED attribute). Default: disabled.
2204 <tag><label id="bgp-secondary">secondary <m/switch/</tag>
2205 Usually, if an export filter rejects a selected route, no other route is
2206 propagated for that network. This option allows to try the next route in
2207 order until one that is accepted is found or all routes for that network
2208 are rejected. This can be used for route servers that need to propagate
2209 different tables to each client but do not want to have these tables
2210 explicitly (to conserve memory). This option requires that the connected
2211 routing table is <ref id="dsc-table-sorted" name="sorted">. Default: off.
2213 <tag><label id="bgp-add-paths">add paths <m/switch/|rx|tx</tag>
2214 Standard BGP can propagate only one path (route) per destination network
2215 (usually the selected one). This option controls the add-path protocol
2216 extension, which allows to advertise any number of paths to a
2217 destination. Note that to be active, add-path has to be enabled on both
2218 sides of the BGP session, but it could be enabled separately for RX and
2219 TX direction. When active, all available routes accepted by the export
2220 filter are advertised to the neighbor. Default: off.
2222 <tag><label id="bgp-allow-local-as">allow local as [<m/number/]</tag>
2223 BGP prevents routing loops by rejecting received routes with the local
2224 AS number in the AS path. This option allows to loose or disable the
2225 check. Optional <cf/number/ argument can be used to specify the maximum
2226 number of local ASNs in the AS path that is allowed for received
2227 routes. When the option is used without the argument, the check is
2228 completely disabled and you should ensure loop-free behavior by some
2229 other means. Default: 0 (no local AS number allowed).
2231 <tag><label id="bgp-enable-route-refresh">enable route refresh <m/switch/</tag>
2232 After the initial route exchange, BGP protocol uses incremental updates
2233 to keep BGP speakers synchronized. Sometimes (e.g., if BGP speaker
2234 changes its import filter, or if there is suspicion of inconsistency) it
2235 is necessary to do a new complete route exchange. BGP protocol extension
2236 Route Refresh (<rfc id="2918">) allows BGP speaker to request
2237 re-advertisement of all routes from its neighbor. BGP protocol
2238 extension Enhanced Route Refresh (<rfc id="7313">) specifies explicit
2239 begin and end for such exchanges, therefore the receiver can remove
2240 stale routes that were not advertised during the exchange. This option
2241 specifies whether BIRD advertises these capabilities and supports
2242 related procedures. Note that even when disabled, BIRD can send route
2243 refresh requests. Default: on.
2245 <tag><label id="bgp-graceful-restart">graceful restart <m/switch/|aware</tag>
2246 When a BGP speaker restarts or crashes, neighbors will discard all
2247 received paths from the speaker, which disrupts packet forwarding even
2248 when the forwarding plane of the speaker remains intact. <rfc
2249 id="4724"> specifies an optional graceful restart mechanism to
2250 alleviate this issue. This option controls the mechanism. It has three
2251 states: Disabled, when no support is provided. Aware, when the graceful
2252 restart support is announced and the support for restarting neighbors
2253 is provided, but no local graceful restart is allowed (i.e.
2254 receiving-only role). Enabled, when the full graceful restart
2255 support is provided (i.e. both restarting and receiving role). Note
2256 that proper support for local graceful restart requires also
2257 configuration of other protocols. Default: aware.
2259 <tag><label id="bgp-graceful-restart-time">graceful restart time <m/number/</tag>
2260 The restart time is announced in the BGP graceful restart capability
2261 and specifies how long the neighbor would wait for the BGP session to
2262 re-establish after a restart before deleting stale routes. Default:
2265 <tag><label id="bgp-interpret-communities">interpret communities <m/switch/</tag>
2266 <rfc id="1997"> demands that BGP speaker should process well-known
2267 communities like no-export (65535, 65281) or no-advertise (65535,
2268 65282). For example, received route carrying a no-adverise community
2269 should not be advertised to any of its neighbors. If this option is
2270 enabled (which is by default), BIRD has such behavior automatically (it
2271 is evaluated when a route is exported to the BGP protocol just before
2272 the export filter). Otherwise, this integrated processing of
2273 well-known communities is disabled. In that case, similar behavior can
2274 be implemented in the export filter. Default: on.
2276 <tag><label id="bgp-enable-as4">enable as4 <m/switch/</tag>
2277 BGP protocol was designed to use 2B AS numbers and was extended later to
2278 allow 4B AS number. BIRD supports 4B AS extension, but by disabling this
2279 option it can be persuaded not to advertise it and to maintain old-style
2280 sessions with its neighbors. This might be useful for circumventing bugs
2281 in neighbor's implementation of 4B AS extension. Even when disabled
2282 (off), BIRD behaves internally as AS4-aware BGP router. Default: on.
2284 <tag><label id="bgp-enable-extended-messages">enable extended messages <m/switch/</tag>
2285 The BGP protocol uses maximum message length of 4096 bytes. This option
2286 provides an extension to allow extended messages with length up
2287 to 65535 bytes. Default: off.
2289 <tag><label id="bgp-capabilities">capabilities <m/switch/</tag>
2290 Use capability advertisement to advertise optional capabilities. This is
2291 standard behavior for newer BGP implementations, but there might be some
2292 older BGP implementations that reject such connection attempts. When
2293 disabled (off), features that request it (4B AS support) are also
2294 disabled. Default: on, with automatic fallback to off when received
2295 capability-related error.
2297 <tag><label id="bgp-advertise-ipv4">advertise ipv4 <m/switch/</tag>
2298 Advertise IPv4 multiprotocol capability. This is not a correct behavior
2299 according to the strict interpretation of <rfc id="4760">, but it is
2300 widespread and required by some BGP implementations (Cisco and Quagga).
2301 This option is relevant to IPv4 mode with enabled capability
2302 advertisement only. Default: on.
2304 <tag><label id="bgp-disable-after-error">disable after error <m/switch/</tag>
2305 When an error is encountered (either locally or by the other side),
2306 disable the instance automatically and wait for an administrator to fix
2307 the problem manually. Default: off.
2309 <tag><label id="bgp-hold-time">hold time <m/number/</tag>
2310 Time in seconds to wait for a Keepalive message from the other side
2311 before considering the connection stale. Default: depends on agreement
2312 with the neighboring router, we prefer 240 seconds if the other side is
2313 willing to accept it.
2315 <tag><label id="bgp-startup-hold-time">startup hold time <m/number/</tag>
2316 Value of the hold timer used before the routers have a chance to exchange
2317 open messages and agree on the real value. Default: 240 seconds.
2319 <tag><label id="bgp-keepalive-time">keepalive time <m/number/</tag>
2320 Delay in seconds between sending of two consecutive Keepalive messages.
2321 Default: One third of the hold time.
2323 <tag><label id="bgp-connect-delay-time">connect delay time <m/number/</tag>
2324 Delay in seconds between protocol startup and the first attempt to
2325 connect. Default: 5 seconds.
2327 <tag><label id="bgp-connect-retry-time">connect retry time <m/number/</tag>
2328 Time in seconds to wait before retrying a failed attempt to connect.
2329 Default: 120 seconds.
2331 <tag><label id="bgp-error-wait-time">error wait time <m/number/,<m/number/</tag>
2332 Minimum and maximum delay in seconds between a protocol failure (either
2333 local or reported by the peer) and automatic restart. Doesn't apply
2334 when <cf/disable after error/ is configured. If consecutive errors
2335 happen, the delay is increased exponentially until it reaches the
2336 maximum. Default: 60, 300.
2338 <tag><label id="bgp-error-forget-time">error forget time <m/number/</tag>
2339 Maximum time in seconds between two protocol failures to treat them as a
2340 error sequence which makes <cf/error wait time/ increase exponentially.
2341 Default: 300 seconds.
2343 <tag><label id="bgp-path-metric">path metric <m/switch/</tag>
2344 Enable comparison of path lengths when deciding which BGP route is the
2345 best one. Default: on.
2347 <tag><label id="bgp-med-metric">med metric <m/switch/</tag>
2348 Enable comparison of MED attributes (during best route selection) even
2349 between routes received from different ASes. This may be useful if all
2350 MED attributes contain some consistent metric, perhaps enforced in
2351 import filters of AS boundary routers. If this option is disabled, MED
2352 attributes are compared only if routes are received from the same AS
2353 (which is the standard behavior). Default: off.
2355 <tag><label id="bgp-deterministic-med">deterministic med <m/switch/</tag>
2356 BGP route selection algorithm is often viewed as a comparison between
2357 individual routes (e.g. if a new route appears and is better than the
2358 current best one, it is chosen as the new best one). But the proper
2359 route selection, as specified by <rfc id="4271">, cannot be fully
2360 implemented in that way. The problem is mainly in handling the MED
2361 attribute. BIRD, by default, uses an simplification based on individual
2362 route comparison, which in some cases may lead to temporally dependent
2363 behavior (i.e. the selection is dependent on the order in which routes
2364 appeared). This option enables a different (and slower) algorithm
2365 implementing proper <rfc id="4271"> route selection, which is
2366 deterministic. Alternative way how to get deterministic behavior is to
2367 use <cf/med metric/ option. This option is incompatible with <ref
2368 id="dsc-table-sorted" name="sorted tables">. Default: off.
2370 <tag><label id="bgp-igp-metric">igp metric <m/switch/</tag>
2371 Enable comparison of internal distances to boundary routers during best
2372 route selection. Default: on.
2374 <tag><label id="bgp-prefer-older">prefer older <m/switch/</tag>
2375 Standard route selection algorithm breaks ties by comparing router IDs.
2376 This changes the behavior to prefer older routes (when both are external
2377 and from different peer). For details, see <rfc id="5004">. Default: off.
2379 <tag><label id="bgp-default-med">default bgp_med <m/number/</tag>
2380 Value of the Multiple Exit Discriminator to be used during route
2381 selection when the MED attribute is missing. Default: 0.
2383 <tag><label id="bgp-default-local-pref">default bgp_local_pref <m/number/</tag>
2384 A default value for the Local Preference attribute. It is used when
2385 a new Local Preference attribute is attached to a route by the BGP
2386 protocol itself (for example, if a route is received through eBGP and
2387 therefore does not have such attribute). Default: 100 (0 in pre-1.2.0
2392 <label id="bgp-attr">
2394 <p>BGP defines several route attributes. Some of them (those marked with
2395 `<tt/I/' in the table below) are available on internal BGP connections only,
2396 some of them (marked with `<tt/O/') are optional.
2399 <tag><label id="rta-bgp-path">bgppath bgp_path/</tag>
2400 Sequence of AS numbers describing the AS path the packet will travel
2401 through when forwarded according to the particular route. In case of
2402 internal BGP it doesn't contain the number of the local AS.
2404 <tag><label id="rta-bgp-local-pref">int bgp_local_pref/ [I]</tag>
2405 Local preference value used for selection among multiple BGP routes (see
2406 the selection rules above). It's used as an additional metric which is
2407 propagated through the whole local AS.
2409 <tag><label id="rta-bgp-med">int bgp_med/ [O]</tag>
2410 The Multiple Exit Discriminator of the route is an optional attribute
2411 which is used on external (inter-AS) links to convey to an adjacent AS
2412 the optimal entry point into the local AS. The received attribute is
2413 also propagated over internal BGP links. The attribute value is zeroed
2414 when a route is exported to an external BGP instance to ensure that the
2415 attribute received from a neighboring AS is not propagated to other
2416 neighboring ASes. A new value might be set in the export filter of an
2417 external BGP instance. See <rfc id="4451"> for further discussion of
2420 <tag><label id="rta-bgp-origin">enum bgp_origin/</tag>
2421 Origin of the route: either <cf/ORIGIN_IGP/ if the route has originated
2422 in an interior routing protocol or <cf/ORIGIN_EGP/ if it's been imported
2423 from the <tt>EGP</tt> protocol (nowadays it seems to be obsolete) or
2424 <cf/ORIGIN_INCOMPLETE/ if the origin is unknown.
2426 <tag><label id="rta-bgp-next-hop">ip bgp_next_hop/</tag>
2427 Next hop to be used for forwarding of packets to this destination. On
2428 internal BGP connections, it's an address of the originating router if
2429 it's inside the local AS or a boundary router the packet will leave the
2430 AS through if it's an exterior route, so each BGP speaker within the AS
2431 has a chance to use the shortest interior path possible to this point.
2433 <tag><label id="rta-bgp-atomic-aggr">void bgp_atomic_aggr/ [O]</tag>
2434 This is an optional attribute which carries no value, but the sole
2435 presence of which indicates that the route has been aggregated from
2436 multiple routes by some router on the path from the originator.
2438 <!-- we don't handle aggregators right since they are of a very obscure type
2439 <tag>bgp_aggregator</tag>
2441 <tag><label id="rta-bgp-community">clist bgp_community/ [O]</tag>
2442 List of community values associated with the route. Each such value is a
2443 pair (represented as a <cf/pair/ data type inside the filters) of 16-bit
2444 integers, the first of them containing the number of the AS which
2445 defines the community and the second one being a per-AS identifier.
2446 There are lots of uses of the community mechanism, but generally they
2447 are used to carry policy information like "don't export to USA peers".
2448 As each AS can define its own routing policy, it also has a complete
2449 freedom about which community attributes it defines and what will their
2452 <tag><label id="rta-bgp-ext-community">eclist bgp_ext_community/ [O]</tag>
2453 List of extended community values associated with the route. Extended
2454 communities have similar usage as plain communities, but they have an
2455 extended range (to allow 4B ASNs) and a nontrivial structure with a type
2456 field. Individual community values are represented using an <cf/ec/ data
2457 type inside the filters.
2459 <tag><label id="rta-bgp-large-community">lclist <cf/bgp_large_community/ [O]</tag>
2460 List of large community values associated with the route. Large BGP
2461 communities is another variant of communities, but contrary to extended
2462 communities they behave very much the same way as regular communities,
2463 just larger -- they are uniform untyped triplets of 32bit numbers.
2464 Individual community values are represented using an <cf/lc/ data type
2467 <tag><label id="rta-bgp-originator-id">quad bgp_originator_id/ [I, O]</tag>
2468 This attribute is created by the route reflector when reflecting the
2469 route and contains the router ID of the originator of the route in the
2472 <tag><label id="rta-bgp-cluster-list">clist bgp_cluster_list/ [I, O]</tag>
2473 This attribute contains a list of cluster IDs of route reflectors. Each
2474 route reflector prepends its cluster ID when reflecting the route.
2478 <label id="bgp-exam">
2482 local as 65000; # Use a private AS number
2483 neighbor 198.51.100.130 as 64496; # Our neighbor ...
2484 multihop; # ... which is connected indirectly
2485 export filter { # We use non-trivial export rules
2486 if source = RTS_STATIC then { # Export only static routes
2487 # Assign our community
2488 bgp_community.add((65000,64501));
2489 # Artificially increase path length
2490 # by advertising local AS number twice
2491 if bgp_path ~ [= 65000 =] then
2492 bgp_path.prepend(65000);
2498 source address 198.51.100.14; # Use a non-standard source address
2506 <p>The Device protocol is not a real routing protocol. It doesn't generate any
2507 routes and it only serves as a module for getting information about network
2508 interfaces from the kernel.
2510 <p>Except for very unusual circumstances, you probably should include this
2511 protocol in the configuration since almost all other protocols require network
2512 interfaces to be defined for them to work with.
2514 <sect1>Configuration
2515 <label id="device-config">
2519 <tag><label id="device-scan-time">scan time <m/number/</tag>
2520 Time in seconds between two scans of the network interface list. On
2521 systems where we are notified about interface status changes
2522 asynchronously (such as newer versions of Linux), we need to scan the
2523 list only in order to avoid confusion by lost notification messages,
2524 so the default time is set to a large value.
2526 <tag><label id="device-primary">primary [ "<m/mask/" ] <m/prefix/</tag>
2527 If a network interface has more than one network address, BIRD has to
2528 choose one of them as a primary one. By default, BIRD chooses the
2529 lexicographically smallest address as the primary one.
2531 This option allows to specify which network address should be chosen as
2532 a primary one. Network addresses that match <m/prefix/ are preferred to
2533 non-matching addresses. If more <cf/primary/ options are used, the first
2534 one has the highest preference. If "<m/mask/" is specified, then such
2535 <cf/primary/ option is relevant only to matching network interfaces.
2537 In all cases, an address marked by operating system as secondary cannot
2538 be chosen as the primary one.
2541 <p>As the Device protocol doesn't generate any routes, it cannot have
2542 any attributes. Example configuration looks like this:
2546 scan time 10; # Scan the interfaces often
2547 primary "eth0" 192.168.1.1;
2548 primary 192.168.0.0/16;
2556 <p>The Direct protocol is a simple generator of device routes for all the
2557 directly connected networks according to the list of interfaces provided by the
2558 kernel via the Device protocol.
2560 <p>The question is whether it is a good idea to have such device routes in BIRD
2561 routing table. OS kernel usually handles device routes for directly connected
2562 networks by itself so we don't need (and don't want) to export these routes to
2563 the kernel protocol. OSPF protocol creates device routes for its interfaces
2564 itself and BGP protocol is usually used for exporting aggregate routes. Although
2565 there are some use cases that use the direct protocol (like abusing eBGP as an
2566 IGP routing protocol), in most cases it is not needed to have these device
2567 routes in BIRD routing table and to use the direct protocol.
2569 <p>There is one notable case when you definitely want to use the direct protocol
2570 -- running BIRD on BSD systems. Having high priority device routes for directly
2571 connected networks from the direct protocol protects kernel device routes from
2572 being overwritten or removed by IGP routes during some transient network
2573 conditions, because a lower priority IGP route for the same network is not
2574 exported to the kernel routing table. This is an issue on BSD systems only, as
2575 on Linux systems BIRD cannot change non-BIRD route in the kernel routing table.
2577 <p>There are just few configuration options for the Direct protocol:
2580 <tag><label id="direct-iface">interface <m/pattern/ [, <m/.../]</tag>
2581 By default, the Direct protocol will generate device routes for all the
2582 interfaces available. If you want to restrict it to some subset of
2583 interfaces or addresses (e.g. if you're using multiple routing tables
2584 for policy routing and some of the policy domains don't contain all
2585 interfaces), just use this clause. See <ref id="proto-iface" name="interface">
2586 common option for detailed description. The Direct protocol uses
2587 extended interface clauses.
2589 <tag><label id="direct-check-link">check link <m/switch/</tag>
2590 If enabled, a hardware link state (reported by OS) is taken into
2591 consideration. Routes for directly connected networks are generated only
2592 if link up is reported and they are withdrawn when link disappears
2593 (e.g., an ethernet cable is unplugged). Default value is no.
2596 <p>Direct device routes don't contain any specific attributes.
2598 <p>Example config might look like this:
2602 interface "-arc*", "*"; # Exclude the ARCnets
2610 <p>The Kernel protocol is not a real routing protocol. Instead of communicating
2611 with other routers in the network, it performs synchronization of BIRD's routing
2612 tables with the OS kernel. Basically, it sends all routing table updates to the
2613 kernel and from time to time it scans the kernel tables to see whether some
2614 routes have disappeared (for example due to unnoticed up/down transition of an
2615 interface) or whether an `alien' route has been added by someone else (depending
2616 on the <cf/learn/ switch, such routes are either ignored or accepted to our
2619 <p>Unfortunately, there is one thing that makes the routing table synchronization
2620 a bit more complicated. In the kernel routing table there are also device routes
2621 for directly connected networks. These routes are usually managed by OS itself
2622 (as a part of IP address configuration) and we don't want to touch that. They
2623 are completely ignored during the scan of the kernel tables and also the export
2624 of device routes from BIRD tables to kernel routing tables is restricted to
2625 prevent accidental interference. This restriction can be disabled using
2626 <cf/device routes/ switch.
2628 <p>If your OS supports only a single routing table, you can configure only one
2629 instance of the Kernel protocol. If it supports multiple tables (in order to
2630 allow policy routing; such an OS is for example Linux), you can run as many
2631 instances as you want, but each of them must be connected to a different BIRD
2632 routing table and to a different kernel table.
2634 <p>Because the kernel protocol is partially integrated with the connected
2635 routing table, there are two limitations - it is not possible to connect more
2636 kernel protocols to the same routing table and changing route destination
2637 (gateway) in an export filter of a kernel protocol does not work. Both
2638 limitations can be overcome using another routing table and the pipe protocol.
2640 <sect1>Configuration
2641 <label id="krt-config">
2644 <tag><label id="krt-persist">persist <m/switch/</tag>
2645 Tell BIRD to leave all its routes in the routing tables when it exits
2646 (instead of cleaning them up).
2648 <tag><label id="krt-scan-time">scan time <m/number/</tag>
2649 Time in seconds between two consecutive scans of the kernel routing
2652 <tag><label id="krt-learn">learn <m/switch/</tag>
2653 Enable learning of routes added to the kernel routing tables by other
2654 routing daemons or by the system administrator. This is possible only on
2655 systems which support identification of route authorship.
2657 <tag><label id="krt-device-routes">device routes <m/switch/</tag>
2658 Enable export of device routes to the kernel routing table. By default,
2659 such routes are rejected (with the exception of explicitly configured
2660 device routes from the static protocol) regardless of the export filter
2661 to protect device routes in kernel routing table (managed by OS itself)
2662 from accidental overwriting or erasing.
2664 <tag><label id="krt-kernel-table">kernel table <m/number/</tag>
2665 Select which kernel table should this particular instance of the Kernel
2666 protocol work with. Available only on systems supporting multiple
2669 <tag><label id="krt-metric">metric <m/number/</tag> (Linux)
2670 Use specified value as a kernel metric (priority) for all routes sent to
2671 the kernel. When multiple routes for the same network are in the kernel
2672 routing table, the Linux kernel chooses one with lower metric. Also,
2673 routes with different metrics do not clash with each other, therefore
2674 using dedicated metric value is a reliable way to avoid overwriting
2675 routes from other sources (e.g. kernel device routes). Metric 0 has a
2676 special meaning of undefined metric, in which either OS default is used,
2677 or per-route metric can be set using <cf/krt_metric/ attribute. Default:
2680 <tag><label id="krt-graceful-restart">graceful restart <m/switch/</tag>
2681 Participate in graceful restart recovery. If this option is enabled and
2682 a graceful restart recovery is active, the Kernel protocol will defer
2683 synchronization of routing tables until the end of the recovery. Note
2684 that import of kernel routes to BIRD is not affected.
2686 <tag><label id="krt-merge-paths">merge paths <M>switch</M> [limit <M>number</M>]</tag>
2687 Usually, only best routes are exported to the kernel protocol. With path
2688 merging enabled, both best routes and equivalent non-best routes are
2689 merged during export to generate one ECMP (equal-cost multipath) route
2690 for each network. This is useful e.g. for BGP multipath. Note that best
2691 routes are still pivotal for route export (responsible for most
2692 properties of resulting ECMP routes), while exported non-best routes are
2693 responsible just for additional multipath next hops. This option also
2694 allows to specify a limit on maximal number of nexthops in one route. By
2695 default, multipath merging is disabled. If enabled, default value of the
2700 <label id="krt-attr">
2702 <p>The Kernel protocol defines several attributes. These attributes are
2703 translated to appropriate system (and OS-specific) route attributes. We support
2707 <tag><label id="rta-krt-source">int krt_source/</tag>
2708 The original source of the imported kernel route. The value is
2709 system-dependent. On Linux, it is a value of the protocol field of the
2710 route. See /etc/iproute2/rt_protos for common values. On BSD, it is
2711 based on STATIC and PROTOx flags. The attribute is read-only.
2713 <tag><label id="rta-krt-metric">int krt_metric/</tag> (Linux)
2714 The kernel metric of the route. When multiple same routes are in a
2715 kernel routing table, the Linux kernel chooses one with lower metric.
2716 Note that preferred way to set kernel metric is to use protocol option
2717 <cf/metric/, unless per-route metric values are needed.
2719 <tag><label id="rta-krt-prefsrc">ip krt_prefsrc/</tag> (Linux)
2720 The preferred source address. Used in source address selection for
2721 outgoing packets. Has to be one of the IP addresses of the router.
2723 <tag><label id="rta-krt-realm">int krt_realm/</tag> (Linux)
2724 The realm of the route. Can be used for traffic classification.
2726 <tag><label id="rta-krt-scope">int krt_scope/</tag> (Linux IPv4)
2727 The scope of the route. Valid values are 0-254, although Linux kernel
2728 may reject some values depending on route type and nexthop. It is
2729 supposed to represent `indirectness' of the route, where nexthops of
2730 routes are resolved through routes with a higher scope, but in current
2731 kernels anything below <it/link/ (253) is treated as <it/global/ (0).
2732 When not present, global scope is implied for all routes except device
2733 routes, where link scope is used by default.
2736 <p>In Linux, there is also a plenty of obscure route attributes mostly focused
2737 on tuning TCP performance of local connections. BIRD supports most of these
2738 attributes, see Linux or iproute2 documentation for their meaning. Attributes
2739 <cf/krt_lock_*/ and <cf/krt_feature_*/ have type bool, others have type int.
2740 Supported attributes are:
2742 <cf/krt_mtu/, <cf/krt_lock_mtu/, <cf/krt_window/, <cf/krt_lock_window/,
2743 <cf/krt_rtt/, <cf/krt_lock_rtt/, <cf/krt_rttvar/, <cf/krt_lock_rttvar/,
2744 <cf/krt_sstresh/, <cf/krt_lock_sstresh/, <cf/krt_cwnd/, <cf/krt_lock_cwnd/,
2745 <cf/krt_advmss/, <cf/krt_lock_advmss/, <cf/krt_reordering/, <cf/krt_lock_reordering/,
2746 <cf/krt_hoplimit/, <cf/krt_lock_hoplimit/, <cf/krt_rto_min/, <cf/krt_lock_rto_min/,
2747 <cf/krt_initcwnd/, <cf/krt_initrwnd/, <cf/krt_quickack/,
2748 <cf/krt_feature_ecn/, <cf/krt_feature_allfrag/
2751 <label id="krt-exam">
2753 <p>A simple configuration can look this way:
2761 <p>Or for a system with two routing tables:
2764 protocol kernel { # Primary routing table
2765 learn; # Learn alien routes from the kernel
2766 persist; # Don't remove routes on bird shutdown
2767 scan time 10; # Scan kernel routing table every 10 seconds
2772 protocol kernel { # Secondary routing table
2784 <label id="ospf-intro">
2786 <p>Open Shortest Path First (OSPF) is a quite complex interior gateway
2787 protocol. The current IPv4 version (OSPFv2) is defined in <rfc id="2328"> and
2788 the current IPv6 version (OSPFv3) is defined in <rfc id="5340"> It's a link
2789 state (a.k.a. shortest path first) protocol -- each router maintains a database
2790 describing the autonomous system's topology. Each participating router has an
2791 identical copy of the database and all routers run the same algorithm
2792 calculating a shortest path tree with themselves as a root. OSPF chooses the
2793 least cost path as the best path.
2795 <p>In OSPF, the autonomous system can be split to several areas in order to
2796 reduce the amount of resources consumed for exchanging the routing information
2797 and to protect the other areas from incorrect routing data. Topology of the area
2798 is hidden to the rest of the autonomous system.
2800 <p>Another very important feature of OSPF is that it can keep routing information
2801 from other protocols (like Static or BGP) in its link state database as external
2802 routes. Each external route can be tagged by the advertising router, making it
2803 possible to pass additional information between routers on the boundary of the
2806 <p>OSPF quickly detects topological changes in the autonomous system (such as
2807 router interface failures) and calculates new loop-free routes after a short
2808 period of convergence. Only a minimal amount of routing traffic is involved.
2810 <p>Each router participating in OSPF routing periodically sends Hello messages
2811 to all its interfaces. This allows neighbors to be discovered dynamically. Then
2812 the neighbors exchange theirs parts of the link state database and keep it
2813 identical by flooding updates. The flooding process is reliable and ensures that
2814 each router detects all changes.
2816 <sect1>Configuration
2817 <label id="ospf-config">
2819 <p>In the main part of configuration, there can be multiple definitions of OSPF
2820 areas, each with a different id. These definitions includes many other switches
2821 and multiple definitions of interfaces. Definition of interface may contain many
2822 switches and constant definitions and list of neighbors on nonbroadcast
2826 protocol ospf <name> {
2827 rfc1583compat <switch>;
2828 instance id <num>;
2829 stub router <switch>;
2831 ecmp <switch> [limit <num>];
2832 merge external <switch>;
2836 summary <switch>;
2837 default nssa <switch>;
2838 default cost <num>;
2839 default cost2 <num>;
2840 translator <switch>;
2841 translator stability <num>;
2845 <prefix> hidden;
2849 <prefix> hidden;
2850 <prefix> tag <num>;
2852 stubnet <prefix>;
2853 stubnet <prefix> {
2854 hidden <switch>;
2855 summary <switch>;
2858 interface <interface pattern> [instance <num>] {
2860 stub <switch>;
2863 retransmit <num>;
2864 priority <num>;
2866 dead count <num>;
2868 secondary <switch>;
2869 rx buffer [normal|large|<num>];
2870 tx length <num>;
2871 type [broadcast|bcast|pointopoint|ptp|
2872 nonbroadcast|nbma|pointomultipoint|ptmp];
2873 link lsa suppression <switch>;
2874 strict nonbroadcast <switch>;
2875 real broadcast <switch>;
2876 ptp netmask <switch>;
2877 check link <switch>;
2879 ecmp weight <num>;
2880 ttl security [<switch>; | tx only]
2881 tx class|dscp <num>;
2882 tx priority <num>;
2883 authentication none|simple|cryptographic;
2884 password "<text>";
2885 password "<text>" {
2887 generate from "<date>";
2888 generate to "<date>";
2889 accept from "<date>";
2890 accept to "<date>";
2891 from "<date>";
2893 algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 );
2897 <ip> eligible;
2900 virtual link <id> [instance <num>] {
2902 retransmit <num>;
2904 dead count <num>;
2906 authentication none|simple|cryptographic;
2907 password "<text>";
2908 password "<text>" {
2910 generate from "<date>";
2911 generate to "<date>";
2912 accept from "<date>";
2913 accept to "<date>";
2914 from "<date>";
2916 algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 );
2924 <tag><label id="ospf-rfc1583compat">rfc1583compat <M>switch</M></tag>
2925 This option controls compatibility of routing table calculation with
2926 <rfc id="1583">. Default value is no.
2928 <tag><label id="ospf-instance-id">instance id <m/num/</tag>
2929 When multiple OSPF protocol instances are active on the same links, they
2930 should use different instance IDs to distinguish their packets. Although
2931 it could be done on per-interface basis, it is often preferred to set
2932 one instance ID to whole OSPF domain/topology (e.g., when multiple
2933 instances are used to represent separate logical topologies on the same
2934 physical network). This option specifies the default instance ID for all
2935 interfaces of the OSPF instance. Note that this option, if used, must
2936 precede interface definitions. Default value is 0.
2938 <tag><label id="ospf-stub-router">stub router <M>switch</M></tag>
2939 This option configures the router to be a stub router, i.e., a router
2940 that participates in the OSPF topology but does not allow transit
2941 traffic. In OSPFv2, this is implemented by advertising maximum metric
2942 for outgoing links. In OSPFv3, the stub router behavior is announced by
2943 clearing the R-bit in the router LSA. See <rfc id="6987"> for details.
2944 Default value is no.
2946 <tag><label id="ospf-tick">tick <M>num</M></tag>
2947 The routing table calculation and clean-up of areas' databases is not
2948 performed when a single link state change arrives. To lower the CPU
2949 utilization, it's processed later at periodical intervals of <m/num/
2950 seconds. The default value is 1.
2952 <tag><label id="ospf-ecmp">ecmp <M>switch</M> [limit <M>number</M>]</tag>
2953 This option specifies whether OSPF is allowed to generate ECMP
2954 (equal-cost multipath) routes. Such routes are used when there are
2955 several directions to the destination, each with the same (computed)
2956 cost. This option also allows to specify a limit on maximum number of
2957 nexthops in one route. By default, ECMP is disabled. If enabled,
2958 default value of the limit is 16.
2960 <tag><label id="ospf-merge-external">merge external <M>switch</M></tag>
2961 This option specifies whether OSPF should merge external routes from
2962 different routers/LSAs for the same destination. When enabled together
2963 with <cf/ecmp/, equal-cost external routes will be combined to multipath
2964 routes in the same way as regular routes. When disabled, external routes
2965 from different LSAs are treated as separate even if they represents the
2966 same destination. Default value is no.
2968 <tag><label id="ospf-area">area <M>id</M></tag>
2969 This defines an OSPF area with given area ID (an integer or an IPv4
2970 address, similarly to a router ID). The most important area is the
2971 backbone (ID 0) to which every other area must be connected.
2973 <tag><label id="ospf-stub">stub</tag>
2974 This option configures the area to be a stub area. External routes are
2975 not flooded into stub areas. Also summary LSAs can be limited in stub
2976 areas (see option <cf/summary/). By default, the area is not a stub
2979 <tag><label id="ospf-nssa">nssa</tag>
2980 This option configures the area to be a NSSA (Not-So-Stubby Area). NSSA
2981 is a variant of a stub area which allows a limited way of external route
2982 propagation. Global external routes are not propagated into a NSSA, but
2983 an external route can be imported into NSSA as a (area-wide) NSSA-LSA
2984 (and possibly translated and/or aggregated on area boundary). By
2985 default, the area is not NSSA.
2987 <tag><label id="ospf-summary">summary <M>switch</M></tag>
2988 This option controls propagation of summary LSAs into stub or NSSA
2989 areas. If enabled, summary LSAs are propagated as usual, otherwise just
2990 the default summary route (0.0.0.0/0) is propagated (this is sometimes
2991 called totally stubby area). If a stub area has more area boundary
2992 routers, propagating summary LSAs could lead to more efficient routing
2993 at the cost of larger link state database. Default value is no.
2995 <tag><label id="ospf-default-nssa">default nssa <M>switch</M></tag>
2996 When <cf/summary/ option is enabled, default summary route is no longer
2997 propagated to the NSSA. In that case, this option allows to originate
2998 default route as NSSA-LSA to the NSSA. Default value is no.
3000 <tag><label id="ospf-default-cost">default cost <M>num</M></tag>
3001 This option controls the cost of a default route propagated to stub and
3002 NSSA areas. Default value is 1000.
3004 <tag><label id="ospf-default-cost2">default cost2 <M>num</M></tag>
3005 When a default route is originated as NSSA-LSA, its cost can use either
3006 type 1 or type 2 metric. This option allows to specify the cost of a
3007 default route in type 2 metric. By default, type 1 metric (option
3008 <cf/default cost/) is used.
3010 <tag><label id="ospf-translator">translator <M>switch</M></tag>
3011 This option controls translation of NSSA-LSAs into external LSAs. By
3012 default, one translator per NSSA is automatically elected from area
3013 boundary routers. If enabled, this area boundary router would
3014 unconditionally translate all NSSA-LSAs regardless of translator
3015 election. Default value is no.
3017 <tag><label id="ospf-translator-stability">translator stability <M>num</M></tag>
3018 This option controls the translator stability interval (in seconds).
3019 When the new translator is elected, the old one keeps translating until
3020 the interval is over. Default value is 40.
3022 <tag><label id="ospf-networks">networks { <m/set/ }</tag>
3023 Definition of area IP ranges. This is used in summary LSA origination.
3024 Hidden networks are not propagated into other areas.
3026 <tag><label id="ospf-external">external { <m/set/ }</tag>
3027 Definition of external area IP ranges for NSSAs. This is used for
3028 NSSA-LSA translation. Hidden networks are not translated into external
3029 LSAs. Networks can have configured route tag.
3031 <tag><label id="ospf-stubnet">stubnet <m/prefix/ { <m/options/ }</tag>
3032 Stub networks are networks that are not transit networks between OSPF
3033 routers. They are also propagated through an OSPF area as a part of a
3034 link state database. By default, BIRD generates a stub network record
3035 for each primary network address on each OSPF interface that does not
3036 have any OSPF neighbors, and also for each non-primary network address
3037 on each OSPF interface. This option allows to alter a set of stub
3038 networks propagated by this router.
3040 Each instance of this option adds a stub network with given network
3041 prefix to the set of propagated stub network, unless option <cf/hidden/
3042 is used. It also suppresses default stub networks for given network
3043 prefix. When option <cf/summary/ is used, also default stub networks
3044 that are subnetworks of given stub network are suppressed. This might be
3045 used, for example, to aggregate generated stub networks.
3047 <tag><label id="ospf-iface">interface <M>pattern</M> [instance <m/num/]</tag>
3048 Defines that the specified interfaces belong to the area being defined.
3049 See <ref id="proto-iface" name="interface"> common option for detailed
3050 description. In OSPFv2, extended interface clauses are used, because
3051 each network prefix is handled as a separate virtual interface.
3053 You can specify alternative instance ID for the interface definition,
3054 therefore it is possible to have several instances of that interface
3055 with different options or even in different areas. For OSPFv2, instance
3056 ID support is an extension (<rfc id="6549">) and is supposed to be set
3057 per-protocol. For OSPFv3, it is an integral feature.
3059 <tag><label id="ospf-virtual-link">virtual link <M>id</M> [instance <m/num/]</tag>
3060 Virtual link to router with the router id. Virtual link acts as a
3061 point-to-point interface belonging to backbone. The actual area is used
3062 as a transport area. This item cannot be in the backbone. Like with
3063 <cf/interface/ option, you could also use several virtual links to one
3064 destination with different instance IDs.
3066 <tag><label id="ospf-cost">cost <M>num</M></tag>
3067 Specifies output cost (metric) of an interface. Default value is 10.
3069 <tag><label id="ospf-stub-iface">stub <M>switch</M></tag>
3070 If set to interface it does not listen to any packet and does not send
3071 any hello. Default value is no.
3073 <tag><label id="ospf-hello">hello <M>num</M></tag>
3074 Specifies interval in seconds between sending of Hello messages. Beware,
3075 all routers on the same network need to have the same hello interval.
3076 Default value is 10.
3078 <tag><label id="ospf-poll">poll <M>num</M></tag>
3079 Specifies interval in seconds between sending of Hello messages for some
3080 neighbors on NBMA network. Default value is 20.
3082 <tag><label id="ospf-retransmit">retransmit <M>num</M></tag>
3083 Specifies interval in seconds between retransmissions of unacknowledged
3084 updates. Default value is 5.
3086 <tag><label id="ospf-priority">priority <M>num</M></tag>
3087 On every multiple access network (e.g., the Ethernet) Designated Router
3088 and Backup Designated router are elected. These routers have some special
3089 functions in the flooding process. Higher priority increases preferences
3090 in this election. Routers with priority 0 are not eligible. Default
3093 <tag><label id="ospf-wait">wait <M>num</M></tag>
3094 After start, router waits for the specified number of seconds between
3095 starting election and building adjacency. Default value is 4*<m/hello/.
3097 <tag><label id="ospf-dead-count">dead count <M>num</M></tag>
3098 When the router does not receive any messages from a neighbor in
3099 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
3101 <tag><label id="ospf-dead">dead <M>num</M></tag>
3102 When the router does not receive any messages from a neighbor in
3103 <m/dead/ seconds, it will consider the neighbor down. If both directives
3104 <cf/dead count/ and <cf/dead/ are used, <cf/dead/ has precedence.
3106 <tag><label id="ospf-secondary">secondary <M>switch</M></tag>
3107 On BSD systems, older versions of BIRD supported OSPFv2 only for the
3108 primary IP address of an interface, other IP ranges on the interface
3109 were handled as stub networks. Since v1.4.1, regular operation on
3110 secondary IP addresses is supported, but disabled by default for
3111 compatibility. This option allows to enable it. The option is a
3112 transitional measure, will be removed in the next major release as the
3113 behavior will be changed. On Linux systems, the option is irrelevant, as
3114 operation on non-primary addresses is already the regular behavior.
3116 <tag><label id="ospf-rx-buffer">rx buffer <M>num</M></tag>
3117 This option allows to specify the size of buffers used for packet
3118 processing. The buffer size should be bigger than maximal size of any
3119 packets. By default, buffers are dynamically resized as needed, but a
3120 fixed value could be specified. Value <cf/large/ means maximal allowed
3121 packet size - 65535.
3123 <tag><label id="ospf-tx-length">tx length <M>num</M></tag>
3124 Transmitted OSPF messages that contain large amount of information are
3125 segmented to separate OSPF packets to avoid IP fragmentation. This
3126 option specifies the soft ceiling for the length of generated OSPF
3127 packets. Default value is the MTU of the network interface. Note that
3128 larger OSPF packets may still be generated if underlying OSPF messages
3129 cannot be splitted (e.g. when one large LSA is propagated).
3131 <tag><label id="ospf-type-bcast">type broadcast|bcast</tag>
3132 BIRD detects a type of a connected network automatically, but sometimes
3133 it's convenient to force use of a different type manually. On broadcast
3134 networks (like ethernet), flooding and Hello messages are sent using
3135 multicasts (a single packet for all the neighbors). A designated router
3136 is elected and it is responsible for synchronizing the link-state
3137 databases and originating network LSAs. This network type cannot be used
3138 on physically NBMA networks and on unnumbered networks (networks without
3141 <tag><label id="ospf-type-ptp">type pointopoint|ptp</tag>
3142 Point-to-point networks connect just 2 routers together. No election is
3143 performed and no network LSA is originated, which makes it simpler and
3144 faster to establish. This network type is useful not only for physically
3145 PtP ifaces (like PPP or tunnels), but also for broadcast networks used
3146 as PtP links. This network type cannot be used on physically NBMA
3149 <tag><label id="ospf-type-nbma">type nonbroadcast|nbma</tag>
3150 On NBMA networks, the packets are sent to each neighbor separately
3151 because of lack of multicast capabilities. Like on broadcast networks,
3152 a designated router is elected, which plays a central role in propagation
3153 of LSAs. This network type cannot be used on unnumbered networks.
3155 <tag><label id="ospf-type-ptmp">type pointomultipoint|ptmp</tag>
3156 This is another network type designed to handle NBMA networks. In this
3157 case the NBMA network is treated as a collection of PtP links. This is
3158 useful if not every pair of routers on the NBMA network has direct
3159 communication, or if the NBMA network is used as an (possibly
3160 unnumbered) PtP link.
3162 <tag><label id="ospf-link-lsa-suppression">link lsa suppression <m/switch/</tag>
3163 In OSPFv3, link LSAs are generated for each link, announcing link-local
3164 IPv6 address of the router to its local neighbors. These are useless on
3165 PtP or PtMP networks and this option allows to suppress the link LSA
3166 origination for such interfaces. The option is ignored on other than PtP
3167 or PtMP interfaces. Default value is no.
3169 <tag><label id="ospf-strict-nonbroadcast">strict nonbroadcast <m/switch/</tag>
3170 If set, don't send hello to any undefined neighbor. This switch is
3171 ignored on other than NBMA or PtMP interfaces. Default value is no.
3173 <tag><label id="ospf-real-broadcast">real broadcast <m/switch/</tag>
3174 In <cf/type broadcast/ or <cf/type ptp/ network configuration, OSPF
3175 packets are sent as IP multicast packets. This option changes the
3176 behavior to using old-fashioned IP broadcast packets. This may be useful
3177 as a workaround if IP multicast for some reason does not work or does
3178 not work reliably. This is a non-standard option and probably is not
3179 interoperable with other OSPF implementations. Default value is no.
3181 <tag><label id="ospf-ptp-netmask">ptp netmask <m/switch/</tag>
3182 In <cf/type ptp/ network configurations, OSPFv2 implementations should
3183 ignore received netmask field in hello packets and should send hello
3184 packets with zero netmask field on unnumbered PtP links. But some OSPFv2
3185 implementations perform netmask checking even for PtP links. This option
3186 specifies whether real netmask will be used in hello packets on <cf/type
3187 ptp/ interfaces. You should ignore this option unless you meet some
3188 compatibility problems related to this issue. Default value is no for
3189 unnumbered PtP links, yes otherwise.
3191 <tag><label id="ospf-check-link">check link <M>switch</M></tag>
3192 If set, a hardware link state (reported by OS) is taken into consideration.
3193 When a link disappears (e.g. an ethernet cable is unplugged), neighbors
3194 are immediately considered unreachable and only the address of the iface
3195 (instead of whole network prefix) is propagated. It is possible that
3196 some hardware drivers or platforms do not implement this feature.
3197 Default value is no.
3199 <tag><label id="ospf-bfd">bfd <M>switch</M></tag>
3200 OSPF could use BFD protocol as an advisory mechanism for neighbor
3201 liveness and failure detection. If enabled, BIRD setups a BFD session
3202 for each OSPF neighbor and tracks its liveness by it. This has an
3203 advantage of an order of magnitude lower detection times in case of
3204 failure. Note that BFD protocol also has to be configured, see
3205 <ref id="bfd" name="BFD"> section for details. Default value is no.
3207 <tag><label id="ospf-ttl-security">ttl security [<m/switch/ | tx only]</tag>
3208 TTL security is a feature that protects routing protocols from remote
3209 spoofed packets by using TTL 255 instead of TTL 1 for protocol packets
3210 destined to neighbors. Because TTL is decremented when packets are
3211 forwarded, it is non-trivial to spoof packets with TTL 255 from remote
3212 locations. Note that this option would interfere with OSPF virtual
3215 If this option is enabled, the router will send OSPF packets with TTL
3216 255 and drop received packets with TTL less than 255. If this option si
3217 set to <cf/tx only/, TTL 255 is used for sent packets, but is not
3218 checked for received packets. Default value is no.
3220 <tag><label id="ospf-tx-class">tx class|dscp|priority <m/num/</tag>
3221 These options specify the ToS/DiffServ/Traffic class/Priority of the
3222 outgoing OSPF packets. See <ref id="proto-tx-class" name="tx class"> common
3223 option for detailed description.
3225 <tag><label id="ospf-ecmp-weight">ecmp weight <M>num</M></tag>
3226 When ECMP (multipath) routes are allowed, this value specifies a
3227 relative weight used for nexthops going through the iface. Allowed
3228 values are 1-256. Default value is 1.
3230 <tag><label id="ospf-auth-none">authentication none</tag>
3231 No passwords are sent in OSPF packets. This is the default value.
3233 <tag><label id="ospf-auth-simple">authentication simple</tag>
3234 Every packet carries 8 bytes of password. Received packets lacking this
3235 password are ignored. This authentication mechanism is very weak.
3236 This option is not available in OSPFv3.
3238 <tag><label id="ospf-auth-cryptographic">authentication cryptographic</tag>
3239 An authentication code is appended to every packet. The specific
3240 cryptographic algorithm is selected by option <cf/algorithm/ for each
3241 key. The default cryptographic algorithm for OSPFv2 keys is Keyed-MD5
3242 and for OSPFv3 keys is HMAC-SHA-256. Passwords are not sent open via
3243 network, so this mechanism is quite secure. Packets can still be read by
3246 <tag><label id="ospf-pass">password "<M>text</M>"</tag>
3247 Specifies a password used for authentication. See
3248 <ref id="proto-pass" name="password"> common option for detailed
3251 <tag><label id="ospf-neighbors">neighbors { <m/set/ } </tag>
3252 A set of neighbors to which Hello messages on NBMA or PtMP networks are
3253 to be sent. For NBMA networks, some of them could be marked as eligible.
3254 In OSPFv3, link-local addresses should be used, using global ones is
3255 possible, but it is nonstandard and might be problematic. And definitely,
3256 link-local and global addresses should not be mixed.
3260 <label id="ospf-attr">
3262 <p>OSPF defines four route attributes. Each internal route has a <cf/metric/.
3264 <p>Metric is ranging from 1 to infinity (65535). External routes use
3265 <cf/metric type 1/ or <cf/metric type 2/. A <cf/metric of type 1/ is comparable
3266 with internal <cf/metric/, a <cf/metric of type 2/ is always longer than any
3267 <cf/metric of type 1/ or any <cf/internal metric/. <cf/Internal metric/ or
3268 <cf/metric of type 1/ is stored in attribute <cf/ospf_metric1/, <cf/metric type
3269 2/ is stored in attribute <cf/ospf_metric2/. If you specify both metrics only
3272 <p>Each external route can also carry attribute <cf/ospf_tag/ which is a 32-bit
3273 integer which is used when exporting routes to other protocols; otherwise, it
3274 doesn't affect routing inside the OSPF domain at all. The fourth attribute
3275 <cf/ospf_router_id/ is a router ID of the router advertising that route /
3276 network. This attribute is read-only. Default is <cf/ospf_metric2 = 10000/ and
3280 <label id="ospf-exam">
3283 protocol ospf MyOSPF {
3287 if source = RTS_BGP then {
3299 authentication simple;
3304 authentication cryptographic;
3307 generate to "22-04-2003 11:00:06";
3308 accept from "17-01-2001 12:01:05";
3309 algorithm hmac sha384;
3313 generate to "22-07-2005 17:03:21";
3314 accept from "22-02-2001 11:34:06";
3315 algorithm hmac sha512;
3328 172.16.2.0/24 hidden;
3330 interface "-arc0" , "arc*" {
3332 authentication none;
3333 strict nonbroadcast yes;
3338 192.168.120.1 eligible;
3352 <label id="pipe-intro">
3354 <p>The Pipe protocol serves as a link between two routing tables, allowing
3355 routes to be passed from a table declared as primary (i.e., the one the pipe is
3356 connected to using the <cf/table/ configuration keyword) to the secondary one
3357 (declared using <cf/peer table/) and vice versa, depending on what's allowed by
3358 the filters. Export filters control export of routes from the primary table to
3359 the secondary one, import filters control the opposite direction.
3361 <p>The Pipe protocol may work in the transparent mode mode or in the opaque
3362 mode. In the transparent mode, the Pipe protocol retransmits all routes from
3363 one table to the other table, retaining their original source and attributes.
3364 If import and export filters are set to accept, then both tables would have
3365 the same content. The transparent mode is the default mode.
3367 <p>In the opaque mode, the Pipe protocol retransmits optimal route from one
3368 table to the other table in a similar way like other protocols send and receive
3369 routes. Retransmitted route will have the source set to the Pipe protocol, which
3370 may limit access to protocol specific route attributes. This mode is mainly for
3371 compatibility, it is not suggested for new configs. The mode can be changed by
3374 <p>The primary use of multiple routing tables and the Pipe protocol is for
3375 policy routing, where handling of a single packet doesn't depend only on its
3376 destination address, but also on its source address, source interface, protocol
3377 type and other similar parameters. In many systems (Linux being a good example),
3378 the kernel allows to enforce routing policies by defining routing rules which
3379 choose one of several routing tables to be used for a packet according to its
3380 parameters. Setting of these rules is outside the scope of BIRD's work (on
3381 Linux, you can use the <tt/ip/ command), but you can create several routing
3382 tables in BIRD, connect them to the kernel ones, use filters to control which
3383 routes appear in which tables and also you can employ the Pipe protocol for
3384 exporting a selected subset of one table to another one.
3386 <sect1>Configuration
3387 <label id="pipe-config">
3390 <tag><label id="pipe-peer-table">peer table <m/table/</tag>
3391 Defines secondary routing table to connect to. The primary one is
3392 selected by the <cf/table/ keyword.
3394 <tag><label id="pipe-mode">mode opaque|transparent</tag>
3395 Specifies the mode for the pipe to work in. Default is transparent.
3399 <label id="pipe-attr">
3401 <p>The Pipe protocol doesn't define any route attributes.
3404 <label id="pipe-exam">
3406 <p>Let's consider a router which serves as a boundary router of two different
3407 autonomous systems, each of them connected to a subset of interfaces of the
3408 router, having its own exterior connectivity and wishing to use the other AS as
3409 a backup connectivity in case of outage of its own exterior line.
3411 <p>Probably the simplest solution to this situation is to use two routing tables
3412 (we'll call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that
3413 packets having arrived from interfaces belonging to the first AS will be routed
3414 according to <cf/as1/ and similarly for the second AS. Thus we have split our
3415 router to two logical routers, each one acting on its own routing table, having
3416 its own routing protocols on its own interfaces. In order to use the other AS's
3417 routes for backup purposes, we can pass the routes between the tables through a
3418 Pipe protocol while decreasing their preferences and correcting their BGP paths
3419 to reflect the AS boundary crossing.
3422 table as1; # Define the tables
3425 protocol kernel kern1 { # Synchronize them with the kernel
3430 protocol kernel kern2 {
3435 protocol bgp bgp1 { # The outside connections
3438 neighbor 192.168.0.1 as 1001;
3446 neighbor 10.0.0.1 as 1002;
3451 protocol pipe { # The Pipe
3455 if net ~ [ 1.0.0.0/8+] then { # Only AS1 networks
3456 if preference>10 then preference = preference-10;
3457 if source=RTS_BGP then bgp_path.prepend(1);
3463 if net ~ [ 2.0.0.0/8+] then { # Only AS2 networks
3464 if preference>10 then preference = preference-10;
3465 if source=RTS_BGP then bgp_path.prepend(2);
3478 <label id="radv-intro">
3480 <p>The RAdv protocol is an implementation of Router Advertisements, which are
3481 used in the IPv6 stateless autoconfiguration. IPv6 routers send (in irregular
3482 time intervals or as an answer to a request) advertisement packets to connected
3483 networks. These packets contain basic information about a local network (e.g. a
3484 list of network prefixes), which allows network hosts to autoconfigure network
3485 addresses and choose a default route. BIRD implements router behavior as defined
3486 in <rfc id="4861"> and also the DNS extensions from <rfc id="6106">.
3488 <sect1>Configuration
3489 <label id="radv-config">
3491 <p>There are several classes of definitions in RAdv configuration -- interface
3492 definitions, prefix definitions and DNS definitions:
3495 <tag><label id="radv-iface">interface <m/pattern/ [, <m/.../] { <m/options/ }</tag>
3496 Interface definitions specify a set of interfaces on which the
3497 protocol is activated and contain interface specific options.
3498 See <ref id="proto-iface" name="interface"> common options for
3499 detailed description.
3501 <tag><label id="radv-prefix">prefix <m/prefix/ { <m/options/ }</tag>
3502 Prefix definitions allow to modify a list of advertised prefixes. By
3503 default, the advertised prefixes are the same as the network prefixes
3504 assigned to the interface. For each network prefix, the matching prefix
3505 definition is found and its options are used. If no matching prefix
3506 definition is found, the prefix is used with default options.
3508 Prefix definitions can be either global or interface-specific. The
3509 second ones are part of interface options. The prefix definition
3510 matching is done in the first-match style, when interface-specific
3511 definitions are processed before global definitions. As expected, the
3512 prefix definition is matching if the network prefix is a subnet of the
3513 prefix in prefix definition.
3515 <tag><label id="radv-rdnss">rdnss { <m/options/ }</tag>
3516 RDNSS definitions allow to specify a list of advertised recursive DNS
3517 servers together with their options. As options are seldom necessary,
3518 there is also a short variant <cf>rdnss <m/address/</cf> that just
3519 specifies one DNS server. Multiple definitions are cumulative. RDNSS
3520 definitions may also be interface-specific when used inside interface
3521 options. By default, interface uses both global and interface-specific
3522 options, but that can be changed by <cf/rdnss local/ option.
3524 <tag><label id="radv-dnssl">dnssl { <m/options/ }</tag>
3525 DNSSL definitions allow to specify a list of advertised DNS search
3526 domains together with their options. Like <cf/rdnss/ above, multiple
3527 definitions are cumulative, they can be used also as interface-specific
3528 options and there is a short variant <cf>dnssl <m/domain/</cf> that just
3529 specifies one DNS search domain.
3531 <tag><label id="radv-trigger">trigger <m/prefix/</tag>
3532 RAdv protocol could be configured to change its behavior based on
3533 availability of routes. When this option is used, the protocol waits in
3534 suppressed state until a <it/trigger route/ (for the specified network)
3535 is exported to the protocol, the protocol also returnsd to suppressed
3536 state if the <it/trigger route/ disappears. Note that route export
3537 depends on specified export filter, as usual. This option could be used,
3538 e.g., for handling failover in multihoming scenarios.
3540 During suppressed state, router advertisements are generated, but with
3541 some fields zeroed. Exact behavior depends on which fields are zeroed,
3542 this can be configured by <cf/sensitive/ option for appropriate
3543 fields. By default, just <cf/default lifetime/ (also called <cf/router
3544 lifetime/) is zeroed, which means hosts cannot use the router as a
3545 default router. <cf/preferred lifetime/ and <cf/valid lifetime/ could
3546 also be configured as <cf/sensitive/ for a prefix, which would cause
3547 autoconfigured IPs to be deprecated or even removed.
3550 <p>Interface specific options:
3553 <tag><label id="radv-iface-max-ra-interval">max ra interval <m/expr/</tag>
3554 Unsolicited router advertisements are sent in irregular time intervals.
3555 This option specifies the maximum length of these intervals, in seconds.
3556 Valid values are 4-1800. Default: 600
3558 <tag><label id="radv-iface-min-ra-interval">min ra interval <m/expr/</tag>
3559 This option specifies the minimum length of that intervals, in seconds.
3560 Must be at least 3 and at most 3/4 * <cf/max ra interval/. Default:
3561 about 1/3 * <cf/max ra interval/.
3563 <tag><label id="radv-iface-min-delay">min delay <m/expr/</tag>
3564 The minimum delay between two consecutive router advertisements, in
3567 <tag><label id="radv-iface-managed">managed <m/switch/</tag>
3568 This option specifies whether hosts should use DHCPv6 for IP address
3569 configuration. Default: no
3571 <tag><label id="radv-iface-other-config">other config <m/switch/</tag>
3572 This option specifies whether hosts should use DHCPv6 to receive other
3573 configuration information. Default: no
3575 <tag><label id="radv-iface-link-mtu">link mtu <m/expr/</tag>
3576 This option specifies which value of MTU should be used by hosts. 0
3577 means unspecified. Default: 0
3579 <tag><label id="radv-iface-reachable-time">reachable time <m/expr/</tag>
3580 This option specifies the time (in milliseconds) how long hosts should
3581 assume a neighbor is reachable (from the last confirmation). Maximum is
3582 3600000, 0 means unspecified. Default 0.
3584 <tag><label id="radv-iface-retrans-timer">retrans timer <m/expr/</tag>
3585 This option specifies the time (in milliseconds) how long hosts should
3586 wait before retransmitting Neighbor Solicitation messages. 0 means
3587 unspecified. Default 0.
3589 <tag><label id="radv-iface-current-hop-limit">current hop limit <m/expr/</tag>
3590 This option specifies which value of Hop Limit should be used by
3591 hosts. Valid values are 0-255, 0 means unspecified. Default: 64
3593 <tag><label id="radv-iface-default-lifetime">default lifetime <m/expr/ [sensitive <m/switch/]</tag>
3594 This option specifies the time (in seconds) how long (after the receipt
3595 of RA) hosts may use the router as a default router. 0 means do not use
3596 as a default router. For <cf/sensitive/ option, see <ref id="radv-trigger" name="trigger">.
3597 Default: 3 * <cf/max ra interval/, <cf/sensitive/ yes.
3599 <tag><label id="radv-iface-default-preference-low">default preference low|medium|high</tag>
3600 This option specifies the Default Router Preference value to advertise
3601 to hosts. Default: medium.
3603 <tag><label id="radv-iface-rdnss-local">rdnss local <m/switch/</tag>
3604 Use only local (interface-specific) RDNSS definitions for this
3605 interface. Otherwise, both global and local definitions are used. Could
3606 also be used to disable RDNSS for given interface if no local definitons
3607 are specified. Default: no.
3609 <tag><label id="radv-iface-dnssl-local">dnssl local <m/switch/</tag>
3610 Use only local DNSSL definitions for this interface. See <cf/rdnss local/
3611 option above. Default: no.
3615 <p>Prefix specific options
3618 <tag><label id="radv-prefix-skip">skip <m/switch/</tag>
3619 This option allows to specify that given prefix should not be
3620 advertised. This is useful for making exceptions from a default policy
3621 of advertising all prefixes. Note that for withdrawing an already
3622 advertised prefix it is more useful to advertise it with zero valid
3623 lifetime. Default: no
3625 <tag><label id="radv-prefix-onlink">onlink <m/switch/</tag>
3626 This option specifies whether hosts may use the advertised prefix for
3627 onlink determination. Default: yes
3629 <tag><label id="radv-prefix-autonomous">autonomous <m/switch/</tag>
3630 This option specifies whether hosts may use the advertised prefix for
3631 stateless autoconfiguration. Default: yes
3633 <tag><label id="radv-prefix-valid-lifetime">valid lifetime <m/expr/ [sensitive <m/switch/]</tag>
3634 This option specifies the time (in seconds) how long (after the
3635 receipt of RA) the prefix information is valid, i.e., autoconfigured
3636 IP addresses can be assigned and hosts with that IP addresses are
3637 considered directly reachable. 0 means the prefix is no longer
3638 valid. For <cf/sensitive/ option, see <ref id="radv-trigger" name="trigger">.
3639 Default: 86400 (1 day), <cf/sensitive/ no.
3641 <tag><label id="radv-prefix-preferred-lifetime">preferred lifetime <m/expr/ [sensitive <m/switch/]</tag>
3642 This option specifies the time (in seconds) how long (after the
3643 receipt of RA) IP addresses generated from the prefix using stateless
3644 autoconfiguration remain preferred. For <cf/sensitive/ option,
3645 see <ref id="radv-trigger" name="trigger">. Default: 14400 (4 hours),
3650 <p>RDNSS specific options:
3653 <tag><label id="radv-rdnss-ns">ns <m/address/</tag>
3654 This option specifies one recursive DNS server. Can be used multiple
3655 times for multiple servers. It is mandatory to have at least one
3656 <cf/ns/ option in <cf/rdnss/ definition.
3658 <tag><label id="radv-rdnss-lifetime">lifetime [mult] <m/expr/</tag>
3659 This option specifies the time how long the RDNSS information may be
3660 used by clients after the receipt of RA. It is expressed either in
3661 seconds or (when <cf/mult/ is used) in multiples of <cf/max ra
3662 interval/. Note that RDNSS information is also invalidated when
3663 <cf/default lifetime/ expires. 0 means these addresses are no longer
3664 valid DNS servers. Default: 3 * <cf/max ra interval/.
3668 <p>DNSSL specific options:
3671 <tag><label id="radv-dnssl-domain">domain <m/address/</tag>
3672 This option specifies one DNS search domain. Can be used multiple times
3673 for multiple domains. It is mandatory to have at least one <cf/domain/
3674 option in <cf/dnssl/ definition.
3676 <tag><label id="radv-dnssl-lifetime">lifetime [mult] <m/expr/</tag>
3677 This option specifies the time how long the DNSSL information may be
3678 used by clients after the receipt of RA. Details are the same as for
3679 RDNSS <cf/lifetime/ option above. Default: 3 * <cf/max ra interval/.
3684 <label id="radv-exam">
3689 max ra interval 5; # Fast failover with more routers
3690 managed yes; # Using DHCPv6 on eth2
3692 autonomous off; # So do not autoconfigure any IP
3696 interface "eth*"; # No need for any other options
3698 prefix 2001:0DB8:1234::/48 {
3699 preferred lifetime 0; # Deprecated address range
3702 prefix 2001:0DB8:2000::/48 {
3703 autonomous off; # Do not autoconfigure
3706 rdnss 2001:0DB8:1234::10; # Short form of RDNSS
3710 ns 2001:0DB8:1234::11;
3711 ns 2001:0DB8:1234::12;
3727 <label id="rip-intro">
3729 <p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol,
3730 where each router broadcasts (to all its neighbors) distances to all networks it
3731 can reach. When a router hears distance to another network, it increments it and
3732 broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some
3733 network goes unreachable, routers keep telling each other that its distance is
3734 the original distance plus 1 (actually, plus interface metric, which is usually
3735 one). After some time, the distance reaches infinity (that's 15 in RIP) and all
3736 routers know that network is unreachable. RIP tries to minimize situations where
3737 counting to infinity is necessary, because it is slow. Due to infinity being 16,
3738 you can't use RIP on networks where maximal distance is higher than 15
3741 <p>BIRD supports RIPv1 (<rfc id="1058">), RIPv2 (<rfc id="2453">), RIPng (<rfc
3742 id="2080">), and RIP cryptographic authentication (<rfc id="4822">).
3744 <p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
3745 convergence, big network load and inability to handle larger networks makes it
3746 pretty much obsolete. It is still usable on very small networks.
3748 <sect1>Configuration
3749 <label id="rip-config">
3751 <p>RIP configuration consists mainly of common protocol options and interface
3752 definitions, most RIP options are interface specific.
3755 protocol rip [<name>] {
3756 infinity <number>;
3757 ecmp <switch> [limit <number>];
3758 interface <interface pattern> {
3759 metric <number>;
3760 mode multicast|broadcast;
3761 passive <switch>;
3763 port <number>;
3765 split horizon <switch>;
3766 poison reverse <switch>;
3767 check zero <switch>;
3768 update time <number>;
3769 timeout time <number>;
3770 garbage time <number>;
3771 ecmp weight <number>;
3772 ttl security <switch>; | tx only;
3773 tx class|dscp <number>;
3774 tx priority <number>;
3775 rx buffer <number>;
3776 tx length <number>;
3777 check link <switch>;
3778 authentication none|plaintext|cryptographic;
3779 password "<text>";
3780 password "<text>" {
3782 generate from "<date>";
3783 generate to "<date>";
3784 accept from "<date>";
3785 accept to "<date>";
3786 from "<date>";
3788 algorithm ( keyed md5 | keyed sha1 | hmac sha1 | hmac sha256 | hmac sha384 | hmac sha512 );
3795 <tag><label id="rip-infinity">infinity <M>number</M></tag>
3796 Selects the distance of infinity. Bigger values will make
3797 protocol convergence even slower. The default value is 16.
3799 <tag><label id="rip-ecmp">ecmp <M>switch</M> [limit <M>number</M>]</tag>
3800 This option specifies whether RIP is allowed to generate ECMP
3801 (equal-cost multipath) routes. Such routes are used when there are
3802 several directions to the destination, each with the same (computed)
3803 cost. This option also allows to specify a limit on maximum number of
3804 nexthops in one route. By default, ECMP is disabled. If enabled,
3805 default value of the limit is 16.
3807 <tag><label id="rip-iface">interface <m/pattern/ [, <m/.../] { <m/options/ }</tag>
3808 Interface definitions specify a set of interfaces on which the
3809 protocol is activated and contain interface specific options.
3810 See <ref id="proto-iface" name="interface"> common options for
3811 detailed description.
3814 <p>Interface specific options:
3817 <tag><label id="rip-iface-metric">metric <m/num/</tag>
3818 This option specifies the metric of the interface. When a route is
3819 received from the interface, its metric is increased by this value
3820 before further processing. Valid values are 1-255, but values higher
3821 than infinity has no further meaning. Default: 1.
3823 <tag><label id="rip-iface-mode">mode multicast|broadcast</tag>
3824 This option selects the mode for RIP to use on the interface. The
3825 default is multicast mode for RIPv2 and broadcast mode for RIPv1.
3826 RIPng always uses the multicast mode.
3828 <tag><label id="rip-iface-passive">passive <m/switch/</tag>
3829 Passive interfaces receive routing updates but do not transmit any
3830 messages. Default: no.
3832 <tag><label id="rip-iface-address">address <m/ip/</tag>
3833 This option specifies a destination address used for multicast or
3834 broadcast messages, the default is the official RIP (224.0.0.9) or RIPng
3835 (ff02::9) multicast address, or an appropriate broadcast address in the
3838 <tag><label id="rip-iface-port">port <m/number/</tag>
3839 This option selects an UDP port to operate on, the default is the
3840 official RIP (520) or RIPng (521) port.
3842 <tag><label id="rip-iface-version">version 1|2</tag>
3843 This option selects the version of RIP used on the interface. For RIPv1,
3844 automatic subnet aggregation is not implemented, only classful network
3845 routes and host routes are propagated. Note that BIRD allows RIPv1 to be
3846 configured with features that are defined for RIPv2 only, like
3847 authentication or using multicast sockets. The default is RIPv2 for IPv4
3848 RIP, the option is not supported for RIPng, as no further versions are
3851 <tag><label id="rip-iface-version-only">version only <m/switch/</tag>
3852 Regardless of RIP version configured for the interface, BIRD accepts
3853 incoming packets of any RIP version. This option restrict accepted
3854 packets to the configured version. Default: no.
3856 <tag><label id="rip-iface-split-horizon">split horizon <m/switch/</tag>
3857 Split horizon is a scheme for preventing routing loops. When split
3858 horizon is active, routes are not regularly propagated back to the
3859 interface from which they were received. They are either not propagated
3860 back at all (plain split horizon) or propagated back with an infinity
3861 metric (split horizon with poisoned reverse). Therefore, other routers
3862 on the interface will not consider the router as a part of an
3863 independent path to the destination of the route. Default: yes.
3865 <tag><label id="rip-iface-poison-reverse">poison reverse <m/switch/</tag>
3866 When split horizon is active, this option specifies whether the poisoned
3867 reverse variant (propagating routes back with an infinity metric) is
3868 used. The poisoned reverse has some advantages in faster convergence,
3869 but uses more network traffic. Default: yes.
3871 <tag><label id="rip-iface-check-zero">check zero <m/switch/</tag>
3872 Received RIPv1 packets with non-zero values in reserved fields should
3873 be discarded. This option specifies whether the check is performed or
3874 such packets are just processed as usual. Default: yes.
3876 <tag><label id="rip-iface-update-time">update time <m/number/</tag>
3877 Specifies the number of seconds between periodic updates. A lower number
3878 will mean faster convergence but bigger network load. Default: 30.
3880 <tag><label id="rip-iface-timeout-time">timeout time <m/number/</tag>
3881 Specifies the time interval (in seconds) between the last received route
3882 announcement and the route expiration. After that, the network is
3883 considered unreachable, but still is propagated with infinity distance.
3886 <tag><label id="rip-iface-garbage-time">garbage time <m/number/</tag>
3887 Specifies the time interval (in seconds) between the route expiration
3888 and the removal of the unreachable network entry. The garbage interval,
3889 when a route with infinity metric is propagated, is used for both
3890 internal (after expiration) and external (after withdrawal) routes.
3893 <tag><label id="rip-iface-ecmp-weight">ecmp weight <m/number/</tag>
3894 When ECMP (multipath) routes are allowed, this value specifies a
3895 relative weight used for nexthops going through the iface. Valid
3896 values are 1-256. Default value is 1.
3898 <tag><label id="rip-iface-auth">authentication none|plaintext|cryptographic</tag>
3899 Selects authentication method to be used. <cf/none/ means that packets
3900 are not authenticated at all, <cf/plaintext/ means that a plaintext
3901 password is embedded into each packet, and <cf/cryptographic/ means that
3902 packets are authenticated using some cryptographic hash function
3903 selected by option <cf/algorithm/ for each key. The default
3904 cryptographic algorithm for RIP keys is Keyed-MD5. If you set
3905 authentication to not-none, it is a good idea to add <cf>password</cf>
3906 section. Default: none.
3908 <tag><label id="rip-iface-pass">password "<m/text/"</tag>
3909 Specifies a password used for authentication. See <ref id="proto-pass"
3910 name="password"> common option for detailed description.
3912 <tag><label id="rip-iface-ttl-security">ttl security [<m/switch/ | tx only]</tag>
3913 TTL security is a feature that protects routing protocols from remote
3914 spoofed packets by using TTL 255 instead of TTL 1 for protocol packets
3915 destined to neighbors. Because TTL is decremented when packets are
3916 forwarded, it is non-trivial to spoof packets with TTL 255 from remote
3919 If this option is enabled, the router will send RIP packets with TTL 255
3920 and drop received packets with TTL less than 255. If this option si set
3921 to <cf/tx only/, TTL 255 is used for sent packets, but is not checked
3922 for received packets. Such setting does not offer protection, but offers
3923 compatibility with neighbors regardless of whether they use ttl
3926 For RIPng, TTL security is a standard behavior (required by <rfc
3927 id="2080">) and therefore default value is yes. For IPv4 RIP, default
3930 <tag><label id="rip-iface-tx-class">tx class|dscp|priority <m/number/</tag>
3931 These options specify the ToS/DiffServ/Traffic class/Priority of the
3932 outgoing RIP packets. See <ref id="proto-tx-class" name="tx class"> common
3933 option for detailed description.
3935 <tag><label id="rip-iface-rx-buffer">rx buffer <m/number/</tag>
3936 This option specifies the size of buffers used for packet processing.
3937 The buffer size should be bigger than maximal size of received packets.
3938 The default value is 532 for IPv4 RIP and interface MTU value for RIPng.
3940 <tag><label id="rip-iface-tx-length">tx length <m/number/</tag>
3941 This option specifies the maximum length of generated RIP packets. To
3942 avoid IP fragmentation, it should not exceed the interface MTU value.
3943 The default value is 532 for IPv4 RIP and interface MTU value for RIPng.
3945 <tag><label id="rip-iface-check-link">check link <m/switch/</tag>
3946 If set, the hardware link state (as reported by OS) is taken into
3947 consideration. When the link disappears (e.g. an ethernet cable is
3948 unplugged), neighbors are immediately considered unreachable and all
3949 routes received from them are withdrawn. It is possible that some
3950 hardware drivers or platforms do not implement this feature.
3955 <label id="rip-attr">
3957 <p>RIP defines two route attributes:
3960 <tag>int <cf/rip_metric/</tag>
3961 RIP metric of the route (ranging from 0 to <cf/infinity/). When routes
3962 from different RIP instances are available and all of them have the same
3963 preference, BIRD prefers the route with lowest <cf/rip_metric/. When a
3964 non-RIP route is exported to RIP, the default metric is 1.
3966 <tag><label id="rta-rip-tag">int rip_tag/</tag>
3967 RIP route tag: a 16-bit number which can be used to carry additional
3968 information with the route (for example, an originating AS number in
3969 case of external routes). When a non-RIP route is exported to RIP, the
3974 <label id="rip-exam">
3982 interface "eth0" { metric 3; mode multicast; };
3983 interface "eth*" { metric 2; mode broadcast; };
3984 authentication cryptographic;
3985 password "secret-shared-key" { algorithm hmac sha256; };
3986 import filter { print "importing"; accept; };
3987 export filter { print "exporting"; accept; };
3995 <p>The Resource Public Key Infrastructure (RPKI) is mechanism for origin
3996 validation of BGP routes (RFC 6480). BIRD supports only so-called RPKI-based
3997 origin validation. There is implemented RPKI to Router (RPKI-RTR) protocol (RFC
3998 6810). It uses some of the RPKI data to allow a router to verify that the
3999 autonomous system announcing an IP address prefix is in fact authorized to do
4000 so. This is not crypto checked so can be violated. But it should prevent the
4001 vast majority of accidental hijackings on the Internet today, e.g. the famous
4002 Pakastani accidental announcement of YouTube's address space.
4004 <p>The RPKI-RTR protocol receives and maintains a set of ROAs from a cache
4005 server (also called validator). You can validate routes (RFC 6483) using
4006 function <cf/roa_check()/ in filter and set it as import filter at the BGP
4007 protocol. BIRD should re-validate all of affected routes after RPKI update by
4008 RFC 6811, but we don't support it yet! You can use a BIRD's client command
4009 <cf>reload in <m/bgp_protocol_name/</cf> for manual call of revalidation of all
4012 <sect1>Supported transports
4014 <item>Unprotected transport over TCP uses a port 323. The cache server
4015 and BIRD router should be on the same trusted and controlled network
4016 for security reasons.
4017 <item>SSHv2 encrypted transport connection uses the normal SSH port
4021 <sect1>Configuration
4023 <p>We currently support just one cache server per protocol. However you can
4024 define more RPKI protocols generally.
4027 protocol rpki [<name>] {
4028 roa4 { table <tab>; };
4029 roa6 { table <tab>; };
4030 remote <ip> | "<domain>" [port <num>];
4032 refresh [keep] <num>;
4033 retry [keep] <num>;
4034 expire [keep] <num>;
4037 bird private key "</path/to/id_rsa>";
4038 remote public key "</path/to/known_host>";
4039 user "<name>";
4044 <p>Alse note that you have to specify ROA table into which will be imported
4045 routes from a cache server. If you want to import only IPv4 prefixes you have
4046 to specify only roa4 table. Similarly with IPv6 prefixes only. If you want to
4047 fetch both IPv4 and even IPv6 ROAs you have to specify both types of ROA
4050 <sect2>RPKI protocol options
4053 <tag>remote <m/ip/ | "<m/hostname/" [port <m/num/]</tag> Specifies
4054 a destination address of the cache server. Can be specified by an IP
4055 address or by full domain name string. Only one cache can be specified
4056 per protocol. This option is required.
4058 <tag>port <m/num/</tag> Specifies the port number. The default port
4059 number is 323 for transport without any encryption and 22 for transport
4060 with SSH encryption.
4062 <tag>refresh [keep] <m/num/</tag> Time period in seconds. Tells how
4063 long to wait before next attempting to poll the cache using a Serial
4064 Query or a Reset Query packet. Must be lower than 86400 seconds (one
4065 day). Too low value can caused a false positive detection of
4066 network connection problems. A keyword <cf/keep/ suppresses updating
4067 this value by a cache server.
4068 Default: 3600 seconds
4070 <tag>retry [keep] <m/num/</tag> Time period in seconds between a failed
4071 Serial/Reset Query and a next attempt. Maximum allowed value is 7200
4072 seconds (two hours). Too low value can caused a false positive
4073 detection of network connection problems. A keyword <cf/keep/
4074 suppresses updating this value by a cache server.
4075 Default: 600 seconds
4077 <tag>expire [keep] <m/num/</tag> Time period in seconds. Received
4078 records are deleted if the client was unable to successfully refresh
4079 data for this time period. Must be in range from 600 seconds (ten
4080 minutes) to 172800 seconds (two days). A keyword <cf/keep/
4081 suppresses updating this value by a cache server.
4082 Default: 7200 seconds
4084 <tag>transport tcp</tag> Unprotected transport over TCP. It's a default
4085 transport. Should be used only on secure private networks.
4088 <tag>transport ssh { <m/SSH transport options.../ }</tag> It enables a
4089 SSHv2 transport encryption. Cannot be combined with a TCP transport.
4093 <sect3>SSH transport options
4095 <tag>bird private key "<m>/path/to/id_rsa</m>"</tag>
4096 A path to the BIRD's private SSH key for authentication.
4097 It can be a <cf><m>id_rsa</m></cf> file.
4099 <tag>remote public key "<m>/path/to/known_host</m>"</tag>
4100 A path to the cache's public SSH key for verification identity
4101 of the cache server. It could be a path to <cf><m>known_host</m></cf> file.
4103 <tag>user "<m/name/"</tag>
4104 A SSH user name for authentication. This option is a required.
4108 <sect2>BGP origin validation
4109 <p>Policy: Don't import <cf/ROA_INVALID/ routes.
4120 # Please, do not use rpki-validator.realmv6.org in production
4121 remote "rpki-validator.realmv6.org" port 8282;
4129 if (roa_check(r4, net, bgp_path.last) = ROA_INVALID ||
4130 roa_check(r6, net, bgp_path.last) = ROA_INVALID) then
4132 print "Ignore invalid ROA ", net, " for ASN ", bgp_path.last;
4141 neighbor 192.168.2.1 as 65001;
4142 import filter peer_in;
4146 <sect2>SSHv2 transport encryption
4157 remote 127.0.0.1 port 2345;
4159 bird private key "/home/birdgeek/.ssh/id_rsa";
4160 remote public key "/home/birdgeek/.ssh/known_hosts";
4164 # Default interval values
4173 <p>The Static protocol doesn't communicate with other routers in the network,
4174 but instead it allows you to define routes manually. This is often used for
4175 specifying how to forward packets to parts of the network which don't use
4176 dynamic routing at all and also for defining sink routes (i.e., those telling to
4177 return packets as undeliverable if they are in your IP block, you don't have any
4178 specific destination for them and you don't want to send them out through the
4179 default route to prevent routing loops).
4181 <p>There are four types of static routes: `classical' routes telling to forward
4182 packets to a neighboring router (single path or multipath, possibly weighted),
4183 device routes specifying forwarding to hosts on a directly connected network,
4184 recursive routes computing their nexthops by doing route table lookups for a
4185 given IP, and special routes (sink, blackhole etc.) which specify a special
4186 action to be done instead of forwarding the packet.
4188 <p>When the particular destination is not available (the interface is down or
4189 the next hop of the route is not a neighbor at the moment), Static just
4190 uninstalls the route from the table it is connected to and adds it again as soon
4191 as the destination becomes adjacent again.
4193 <p>There are three classes of definitions in Static protocol configuration --
4194 global options, static route definitions, and per-route options. Usually, the
4195 definition of the protocol contains mainly a list of static routes.
4200 <tag><label id="static-check-link">check link <m/switch/</tag>
4201 If set, hardware link states of network interfaces are taken into
4202 consideration. When link disappears (e.g. ethernet cable is unplugged),
4203 static routes directing to that interface are removed. It is possible
4204 that some hardware drivers or platforms do not implement this feature.
4207 <tag><label id="static-igp-table">igp table <m/name/</tag>
4208 Specifies a table that is used for route table lookups of recursive
4209 routes. Default: the same table as the protocol is connected to.
4212 <p>Route definitions (each may also contain a block of per-route options):
4215 <tag><label id="static-route-via-ip">route <m/prefix/ via <m/ip/ [mpls <m/num/[/<m/num/[/<m/num/[...]]]]</tag>
4216 Static single path route through a neighboring router. For link-local next hops,
4217 interface can be specified as a part of the address (e.g.,
4218 <cf/via fe80::1234%eth0/). MPLS labels should be specified in outer-first order.
4220 <tag><label id="static-route-via-mpath">route <m/prefix/ via <m/ip/ [mpls <m/num/[/<m/num/[/<m/num/[...]]]] [weight <m/num/] [bfd <m/switch/] [via ...]</tag>
4221 Static multipath route. Contains several nexthops (gateways), possibly
4222 with their weights and MPLS labels.
4224 <tag><label id="static-route-via-iface">route <m/prefix/ via <m/"interface"/</tag>
4225 Static device route through an interface to hosts on a directly
4228 <tag><label id="static-route-recursive">route <m/prefix/ recursive <m/ip/</tag>
4229 Static recursive route, its nexthop depends on a route table lookup for
4232 <tag><label id="static-route-drop">route <m/prefix/ blackhole|unreachable|prohibit</tag>
4233 Special routes specifying to silently drop the packet, return it as
4234 unreachable or return it as administratively prohibited. First two
4235 targets are also known as <cf/drop/ and <cf/reject/.
4238 <p>Per-route options:
4241 <tag><label id="static-route-bfd">bfd <m/switch/</tag>
4242 The Static protocol could use BFD protocol for next hop liveness
4243 detection. If enabled, a BFD session to the route next hop is created
4244 and the static route is BFD-controlled -- the static route is announced
4245 only if the next hop liveness is confirmed by BFD. If the BFD session
4246 fails, the static route is removed. Note that this is a bit different
4247 compared to other protocols, which may use BFD as an advisory mechanism
4248 for fast failure detection but ignores it if a BFD session is not even
4251 This option can be used for static routes with a direct next hop, or
4252 also for for individual next hops in a static multipath route (see
4253 above). Note that BFD protocol also has to be configured, see
4254 <ref id="bfd" name="BFD"> section for details. Default value is no.
4256 <tag><label id="static-route-filter"><m/filter expression/</tag>
4257 This is a special option that allows filter expressions to be configured
4258 on per-route basis. Can be used multiple times. These expressions are
4259 evaluated when the route is originated, similarly to the import filter
4260 of the static protocol. This is especially useful for configuring route
4261 attributes, e.g., <cf/ospf_metric1 = 100;/ for a route that will be
4262 exported to the OSPF protocol.
4265 <p>Static routes have no specific attributes.
4267 <p>Example static config might look like this:
4271 table testable; # Connect to a non-default routing table
4272 check link; # Advertise routes only if link is up
4273 route 0.0.0.0/0 via 198.51.100.130; # Default route
4274 route 10.0.0.0/8 multipath # Multipath route
4275 via 198.51.100.10 weight 2
4276 via 198.51.100.20 bfd # BFD-controlled next hop
4278 route 203.0.113.0/24 unreachable; # Sink route
4279 route 10.2.0.0/24 via "arc0"; # Secondary network
4280 route 192.168.10.0/24 via 198.51.100.100 {
4281 ospf_metric1 = 20; # Set extended attribute
4283 route 192.168.10.0/24 via 198.51.100.100 {
4284 ospf_metric2 = 100; # Set extended attribute
4285 ospf_tag = 2; # Set extended attribute
4286 bfd; # BFD-controlled route
4293 <label id="conclusion">
4296 <label id="future-work">
4298 <p>Although BIRD supports all the commonly used routing protocols, there are
4299 still some features which would surely deserve to be implemented in future
4304 <item>Route aggregation and flap dampening
4305 <item>Multipath routes
4306 <item>Multicast routing protocols
4307 <item>Ports to other systems
4311 <sect>Getting more help
4314 <p>If you use BIRD, you're welcome to join the bird-users mailing list
4315 (<HTMLURL URL="mailto:bird-users@network.cz" name="bird-users@network.cz">)
4316 where you can share your experiences with the other users and consult
4317 your problems with the authors. To subscribe to the list, visit
4318 <HTMLURL URL="http://bird.network.cz/?m_list" name="http://bird.network.cz/?m_list">.
4319 The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
4321 <p>BIRD is a relatively young system and it probably contains some bugs. You can
4322 report any problems to the bird-users list and the authors will be glad to solve
4323 them, but before you do so, please make sure you have read the available
4324 documentation and that you are running the latest version (available at
4325 <HTMLURL URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">).
4326 (Of course, a patch which fixes the bug is always welcome as an attachment.)
4328 <p>If you want to understand what is going inside, Internet standards are a good
4329 and interesting reading. You can get them from
4330 <HTMLURL URL="ftp://ftp.rfc-editor.org/" name="ftp.rfc-editor.org"> (or a
4331 nicely sorted version from <HTMLURL URL="ftp://atrey.karlin.mff.cuni.cz/pub/rfc"
4332 name="atrey.karlin.mff.cuni.cz:/pub/rfc">).
4339 LocalWords: GPL IPv GateD BGPv RIPv OSPFv Linux sgml html dvi sgmltools Pavel
4340 LocalWords: linuxdoc dtd descrip config conf syslog stderr auth ospf bgp Mbps
4341 LocalWords: router's eval expr num birdc ctl UNIX if's enums bool int ip GCC
4342 LocalWords: len ipaddress pxlen netmask enum bgppath bgpmask clist gw md eth
4343 LocalWords: RTS printn quitbird iBGP AS'es eBGP RFC multiprotocol IGP Machek
4344 LocalWords: EGP misconfigurations keepalive pref aggr aggregator BIRD's RTC
4345 LocalWords: OS'es AS's multicast nolisten misconfigured UID blackhole MRTD MTU
4346 LocalWords: uninstalls ethernets IP binutils ANYCAST anycast dest RTD ICMP rfc
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4349 LocalWords: proto wildcard Ondrej Filip