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<!doctype birddoc system>
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<!--
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	BIRD documentation
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This documentation can have 4 forms: sgml (this is master copy), html,
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ASCII text and dvi/postscript (generated from sgml using
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sgmltools). You should always edit master copy.
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This is a slightly modified linuxdoc dtd.  Anything in <descrip> tags is considered definition of
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configuration primitives, <cf> is fragment of configuration within normal text, <m> is
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"meta" information within fragment of configuration - something in config which is not keyword.
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    (set-fill-column 100)
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    Copyright 1999,2000 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later.
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 -->
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<book>
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<title>BIRD User's Guide
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<author>
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Ondrej Filip <it/&lt;feela@network.cz&gt;/,
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Pavel Machek <it/&lt;pavel@ucw.cz&gt;/,
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Martin Mares <it/&lt;mj@ucw.cz&gt;/
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</author>
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<abstract>
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This document contains user documentation for the BIRD Internet Routing Daemon project.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<chapt>Introduction
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<sect>What is BIRD
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<p><label id="intro">
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The name `BIRD' is actually an acronym standing for `BIRD Internet Routing Daemon'.
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Let's take a closer look at the meaning of the name:
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<p><em/BIRD/: Well, we think we have already explained that. It's an acronym standing
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for `BIRD Internet Routing Daemon', you remember, don't you? :-)
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<p><em/Internet Routing/: It's a program (well, a daemon, as you are going to discover in a moment)
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which works as a dynamic router in an Internet type network (that is, in a network running either
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the IPv4 or the IPv6 protocol). Routers are devices which forward packets between interconnected
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networks in order to allow hosts not connected directly to the same local area network to
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communicate with each other. They also communicate with the other routers in the Internet to discover
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the topology of the network which allows them to find optimal (in terms of some metric) rules for
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forwarding of packets (which are called routing tables) and to adapt themselves to the
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changing conditions such as outages of network links, building of new connections and so on. Most of
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these routers are costly dedicated devices running obscure firmware which is hard to configure and
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not open to any changes (on the other hand, their special hardware design allows them to keep up with lots of high-speed network interfaces, better than general-purpose computer does). Fortunately, most operating systems of the UNIX family allow an ordinary 
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computer to act as a router and forward packets belonging to the other hosts, but only according to
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a statically configured table.
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<p>A <em/Routing Daemon/ is in UNIX terminology a non-interactive program running on
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background which does the dynamic part of Internet routing, that is it communicates
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with the other routers, calculates routing tables and sends them to the OS kernel
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which does the actual packet forwarding. There already exist other such routing daemons: routed (RIP only), GateD<HTMLURL URL="http://www.gated.org/">
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 (non-free), Zebra<HTMLURL URL="http://www.zebra.org"> and MRTD<HTMLURL URL="http://www.zcu.cz/ftp/mirrors/mmrz/mrtd">, but their capabilities are limited and
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they are relatively hard to configure and maintain.
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<p>BIRD is an Internet Routing Daemon designed to avoid all of these shortcomings,
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to support all the routing technology used in the today's Internet or planned to be
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used in near future and to have a clean extensible architecture allowing new routing
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protocols to be incorporated easily. Among other features, BIRD supports:
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<itemize>
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	<item>both IPv4 and IPv6 protocols
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	<item>multiple routing tables
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	<item>the Border Gateway Protocol (BGPv4)
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	<item>the Routing Information Protocol (RIPv2)
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	<item>the Open Shortest Path First protocol (OSPFv2)
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	<item>a virtual protocol for exchange of routes between different routing tables on a single host
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	<item>a command-line interface allowing on-line control and inspection
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		of status of the daemon
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	<item>soft reconfiguration (no need to use complex online commands
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		to change the configuration, just edit the configuration file
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		and notify BIRD to re-read it and it will smoothly switch itself
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		to the new configuration, not disturbing routing protocols
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		unless they are affected by the configuration changes)
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	<item>a powerful language for route filtering
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</itemize>
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<p>BIRD has been developed at the Faculty of Math and Physics, Charles University, Prague,
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Czech Republic as a student project. It can be freely distributed under the terms of the GNU General
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Public License.
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<p>BIRD has been designed to work on all UNIX-like systems. It has been developed and
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tested under Linux 2.0 to 2.4, but porting to other systems (even non-UNIX ones) should
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be relatively easy due to its highly modular architecture.
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<sect>Installing BIRD
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<p>On a recent UNIX system with GNU development tools (GCC, binutils, m4, make) and Perl, installing BIRD should be as easy as:
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<code>
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        ./configure
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        make
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        make install
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        vi /usr/local/etc/bird.conf
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	bird
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</code>
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<p>You can use <tt>./configure --help</tt> to get a list of configure
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options. The most important ones are:
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<tt/--enable-ipv6/ which enables building of an IPv6 version of BIRD,
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<tt/--with-protocols=/ to produce a slightly smaller BIRD executable by configuring out routing protocols you don't use, and
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<tt/--prefix=/ to install BIRD to a place different from.
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<file>/usr/local</file>.
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<sect>Running BIRD
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<p>You can pass several command-line options to bird:
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<descrip>
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	<tag>-c <m/config name/</tag>
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	use given configuration file instead of <it/prefix/<file>/etc/bird.conf</file>.
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	<tag>-d</tag>
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	enable debug messages and run bird in foreground.
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	<tag>-D <m/filename of debug log/</tag>
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	log debugging information to given file instead of stderr
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	<tag>-s <m/name of communication socket/</tag>
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	use given filename for a  socket for communications with the client, default is <it/prefix/<file>/var/run/bird.ctl</file>.
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</descrip>
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<p>BIRD writes messages about its work to log files or syslog (according to config).
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<chapt>About routing tables
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<p>BIRD has one or more routing tables which may or may not be
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synchronized with OS kernel and which may or may not be synchronized with
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each other (see the Pipe protocol). Each routing table contains a list of
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known routes. Each route consists of:
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<itemize>
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	<item>network prefix this route is for (network address and prefix length -- the number of bits forming the network part of the address; also known as a netmask)
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	<item>preference of this route
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	<item>IP address of router which told us about this route
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	<item>IP address of router we should forward the packets to
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	using this route
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	<item>other attributes common to all routes
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	<item>dynamic attributes defined by protocols which may or
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	may not be present (typically protocol metrics)
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</itemize>
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Routing table maintains multiple entries
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for a network, but at most one entry for one network and one
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protocol. The entry with the highest preference is used for routing (we
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will call such an entry the <it/selected route/). If
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there are more entries with the same preference and they are from the same
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protocol, the protocol decides (typically according to metrics). If they aren't,
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an internal ordering is used to break the tie. You can
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get the list of route attributes in the Route attributes section.
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<p>Each protocol is connected to a routing table through two filters
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which can accept, reject and modify the routes. An <it/export/
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filter checks routes passed from the routing table to the protocol,
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an <it/import/ filter checks routes in the opposite direction.
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When the routing table gets a route from a protocol, it recalculates
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the selected route and broadcasts it to all protocols connected to
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the table. The protocols typically send the update to other routers
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in the network.
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<chapt>Configuration
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<sect>Introduction
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<p>BIRD is configured using a text configuration file. Upon startup, BIRD reads <it/prefix/<file>/etc/bird.conf</file> (unless the
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<tt/-c/ command line option is given). Configuration may be changed at user's request: if you modify
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the config file and then signal BIRD with <tt/SIGHUP/, it will adjust to the new
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config. Then there's the client
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which allows you to talk with BIRD in an extensive way.
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<p>In the config, everything on a line after <cf/#/ or inside <cf>/*
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*/</cf> is a comment, whitespace characters are treated as a single space. If there's a variable number of options, they are grouped using
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the <cf/{ }/ brackets. Each option is terminated by a <cf/;/. Configuration
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is case sensitive.
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<p>Here is an example of a simple config file. It enables
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synchronization of routing tables with OS kernel, scans for 
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new network interfaces every 10 seconds and runs RIP on all network interfaces found.
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<code>
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protocol kernel {
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	persist;		# Don't remove routes on BIRD shutdown
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	scan time 20;		# Scan kernel routing table every 20 seconds
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	export all;		# Default is export none
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}
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protocol device {
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	scan time 10;		# Scan interfaces every 10 seconds
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}
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protocol rip {
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	export all;
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	import all;
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}
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</code>
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<sect>Global options
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<p><descrip>
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	<tag>log "<m/filename/"|syslog|stderr all|{ <m/list of classes/ }</tag> 
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	Set logging of messages having the given class (either <cf/all/ or <cf/{
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	error, trace }/ etc.) into selected destination. Classes are:
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	<cf/info/, <cf/warning/, <cf/error/ and <cf/fatal/ for messages about local problems,
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	<cf/debug/ for debugging messages, 
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	<cf/trace/ when you want to know what happens in the network, 
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	<cf/remote/ for messages about misbehavior of remote machines, 
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	<cf/auth/ about authentication failures,
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	<cf/bug/ for internal BIRD bugs. You may specify more than one <cf/log/ line to establish logging to multiple
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	destinations. Default: log everything to the system log.
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	<tag>debug protocols all|off|{ states, routes, filters, interfaces, events, packets }</tag>
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	Set global defaults of protocol debugging options. See <cf/debug/ in the following section. Default: off.
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	<tag>debug commands <m/number/</tag>
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	Control logging of client connections (0 for no logging, 1 for
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	logging of connects and disconnects, 2 and higher for logging of
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	all client commands). Default: 0.
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	<tag>filter <m/name local variables/{ <m/commands/ }</tag> Define a filter. You can learn more about filters
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	in the following chapter. 
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	<tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag> Define a function. You can learn more
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	about functions in the following chapter.
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	<tag>protocol rip|ospf|bgp|... <m/[name]/ { <m>protocol options</m> }</tag> Define a protocol
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	instance called <cf><m/name/</cf> (or with a name like "rip5" generated automatically if you don't specify any <cf><m/name/</cf>). You can learn more
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	about configuring protocols in their own chapters. You can run more than one instance of
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	most protocols (like RIP or BGP). By default, no instances are configured.
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	<tag>define <m/constant/ = (<m/expression/)|<m/number/|<m/IP address/</tag> Define a constant. You can use it later in every place
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	you could use a simple integer or an IP address.
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	<tag>router id <m/IPv4 address/</tag> Set BIRD's router ID. It's a world-wide unique identification of your router, usually one of router's IPv4 addresses. Default: in IPv4 version, the lowest IP address of a non-loopback interface. In IPv6 version, this option is mandatory. 
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	<tag>table <m/name/</tag> Create a new routing table. The default
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	routing table is created implicitly, other routing tables have
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	to be added by this command.
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	<tag>eval <m/expr/</tag> Evaluates given filter expression. It
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	is used by us for testing of filters.
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</descrip>
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<sect>Protocol options
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<p>For each protocol instance, you can configure a bunch of options.
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Some of them (those described in this section) are generic, some are
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specific to the protocol (see sections talking about the protocols).
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<p>Several options use a <cf><m/switch/</cf> argument. It can be either
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<cf/on/, <cf/yes/ or a numeric expression with a non-zero value for the
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option to be enabled or <cf/off/, <cf/no/ or a numeric expression evaluating
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to zero to disable it. An empty <cf><m/switch/</cf> is equivalent to <cf/on/
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("silence means agreement").
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<descrip>
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	<tag>preference <m/expr/</tag> Sets the preference of routes generated by this protocol. Default: protocol dependent.
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	<tag>disabled <m/switch/</tag> Disables the protocol. You can change the disable/enable status from the command
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	line interface without needing to touch the configuration. Disabled protocols are not activated. Default: protocol is enabled.
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	<tag>debug all|off|{ states, routes, filters, interfaces, events, packets }</tag>
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	Set protocol debugging options. If asked, each protocol is capable of
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	writing trace messages about its work to the log (with category
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	<cf/trace/). You can either request printing of <cf/all/ trace messages
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	or only of the types selected: <cf/states/ for protocol state changes
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	(protocol going up, down, starting, stopping etc.),
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	<cf/routes/ for routes exchanged with the routing table,
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	<cf/filters/ for details on route filtering,
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	<cf/interfaces/ for interface change events sent to the protocol,
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	<cf/events/ for events internal to the protocol and
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	<cf/packets/ for packets sent and received by the protocol. Default: off.
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	<tag>import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag> 
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	Specify a filter to be used for filtering routes coming from the protocol to the routing table. <cf/all/ is shorthand for <cf/where true/ and <cf/none/ is shorthand for <cf/where false/. Default: <cf/all/.
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	<tag>export <m/filter/</tag> This is similar to the <cf>import</cf> keyword, except that it
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	works in the direction from the routing table to the protocol. Default: <cf/none/.
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	<tag>table <m/name/</tag> Connect this protocol to a non-default routing table.
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</descrip>
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<p>There are several options that give sense only with certain protocols:
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<descrip>
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	<tag>passwords { password "<m/password/" from <m/time/ to <m/time/ passive <m/time/ id
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	<m/num/ [...] }</tag> Specifies passwords to be used with this protocol. <cf>Passive <m/time/</cf> is
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	time from which the password is not used for sending, but it is recognized on reception. <cf/id/ is password ID as needed by
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	certain protocols. Format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
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	<tag>interface "<m/mask/"|<m/prefix/ [ { <m/option/ ; [...] } ]</tag> Specifies which
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	interfaces is this protocol active on and allows you to set options on a
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	per-interface basis. Mask is specified as in shell-like patterns, thus <cf>interface
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	"*" { mode broadcast; };</cf> will start the protocol on all interfaces with <cf>mode
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	broadcast;</cf> option. If the first character of mask is <cf/-/, such interfaces are
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	excluded. Masks are parsed left-to-right, thus <cf/interface "-eth*", "*";/ means all but
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	the ethernets. Default: none.
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</descrip>
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<chapt>Remote control
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<p>You can use the command-line client <file>birdc</file> to talk with
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a running BIRD. Communication is done using a <file/bird.ctl/ UNIX domain
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socket (unless changed with the <tt/-s/ option given to both the server and
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the client). The commands can perform simple actions such as enabling/disabling
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of protocols, telling BIRD to show various information, telling it to
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show routing table filtered by filter, or asking BIRD to
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reconfigure. Press <tt/?/ at any time to get online help. Option
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<tt/-v/ can be passed to the client, to make it dump numeric return
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codes along with the messages. You do not necessarily need to use <file/birdc/ to talk to BIRD, your
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own applications could do that, too -- the format of communication between
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BIRD and <file/birdc/ is stable (see the programmer's documentation).
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<p>Here is a brief list of supported functions:
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<descrip>
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	<tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
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	Dump contents of internal data structures to the debugging output.
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	<tag>show status</tag>
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	Show router status, that is BIRD version, uptime and time from last reconfiguration.
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	<tag>show protocols [all]</tag>
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	Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified.
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	<tag>show ospf [interface|neighbors] [<m/name/] ["<m/interface/"]</tag>
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	Show detailed information about OSPF protocol, possibly giving a verbose list of interfaces and neighbors. The <m/name/ of the protocol instance can be omitted if there exists only a single instance.
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	<tag>show static [<m/name/]</tag>
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	Show detailed information about static routes. The <m/name/ of the protocol instance can be omitted if there exists only a single instance.
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	<tag>show interfaces [summary]</tag>
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	Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. 
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	<tag>show symbols</tag>
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	Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).
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	<tag>show route [[for] <m/prefix/|<m/IP/] [table <m/sym/] [filter <m/f/|where <m/c/] [(import|proto) <m/p/] [<m/options/]</tag>
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	Show contents of a routing table (by default of the main one),
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	that is routes, their metrics and (in case the <cf/all/ switch is given)
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	all their attributes.
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	<p>You can specify a <m/prefix/ if you want to print routes for a
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	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
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	the entry which will be used for forwarding of packets to the given
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	destination. By default, all routes for each network are printed with
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	the selected one at the top, unless <cf/primary/ is given in which case
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	only the selected route is shown.
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	<p>You can also ask for printing only routes processed and accepted by
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	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
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	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
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	The <cf/import/ and <cf/proto/ switches ask for printing of entries as
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	they would be seen by the specified protocol. With <cf/import/, the
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	export filter of the protocol is skipped.
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	<p>The <cf/stats/ switch requests showing of route statistics (the
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	number of networks, number of routes before and after filtering). If
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	you use <cf/count/ instead, only the statistics will be printed.
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	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
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	Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances.
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	<tag>configure ["<m/config file/"]</tag>
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	Reload configuration from a given file.
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	<tag/down/
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	Shut BIRD down.
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	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
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	Control protocol debugging.
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</descrip>
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<chapt>Filters
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<sect>Introduction
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<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
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two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
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being passed between protocols and routing tables. The filter language contains control structures such
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as if's and switches, but it allows no loops. An example of a filter using many features can be found in <file>filter/test.conf</file>. 
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<p>Filter gets the route, looks at its attributes and
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modifies some of them if it wishes. At the end, it decides whether to
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pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
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like this:
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<code>
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filter not_too_far
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int var;
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{
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	if defined( rip_metric ) then
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		var = rip_metric;
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	else {
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		var = 1;
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		rip_metric = 1;
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	}
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	if rip_metric &gt; 10 then
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		reject "RIP metric is too big";
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	else
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		accept "ok";
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}
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</code>
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<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
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the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
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<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
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<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
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several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
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you want to make a bigger block of code conditional.
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<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
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over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
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look like this:
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<code>
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function name ()
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int local_variable;
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{
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	local_variable = 5;
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}
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function with_parameters (int parameter)
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{
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	print parameter;
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}
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</code>
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<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
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variables in nested blocks. Functions are called like in C: <cf>name();
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with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
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command. Returning a value exits from current function (this is similar to C).
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<p>Filters are declared in a way similar to functions except they can't have explicit
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parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
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to any functions called. The filter must terminate with either
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<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
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is rejected. 
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<p>A nice trick to debug filters is to use <cf>show route filter
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<m/name/</cf> from the command line client. An example session might look
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like:
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<code>
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pavel@bug:~/bird$ ./birdc -s bird.ctl
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BIRD 0.0.0 ready.
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bird> show route
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10.0.0.0/8         dev eth0 [direct1 23:21] (240)
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195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
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127.0.0.0/8        dev lo [direct1 23:21] (240)
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bird> show route ?
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show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
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bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
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127.0.0.0/8        dev lo [direct1 23:21] (240)
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bird>
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</code>
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<sect>Data types
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<p>Each variable and each value has certain type. Booleans, integers and enums are
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incompatible with each other (that is to prevent you from shooting in the foot).
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<descrip>
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	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
480
	  <cf/false/. Boolean is the only type you can use in <cf/if/
481
	  statements.
482

    
483
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
484
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
485

    
486
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
487
	  65535. Literals of this type is written as <cf/(1234,5678)/.
488

    
489
	<tag/string/ This is a string of characters. There are no ways to modify strings in
490
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
491
	  such variables, but you can't concatenate two strings. String literals
492
	  are written as <cf/"This is a string constant"/.
493

    
494
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
495
	  is either an IPv4 or IPv6 address. IP addresses are written in the standard notation (<cf/10.20.30.40/ or <cf/fec0:3:4::1/). You can apply special operator <cf>.mask(<M>num</M>)</cf>
496
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
497
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
498

    
499
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
500
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
501
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
502
	  operators on prefixes:
503
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
504
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
505

    
506
	<tag/int|ip|prefix|pair|enum set/
507
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
508
	  but you can't modify them. Literals of type <cf>set int</cf> look like <cf>
509
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
510
	  sets. Sets of prefixes are special: you can specify which prefix lengths should match them by
511
	  using <cf>[ 1.0.0.0/8+, 2.0.0.0/8-, 3.0.0.0/8{5,6} ]</cf>. <cf>3.0.0.0/8{5,6}</cf> matches
512
	  prefixes <cf/3.X.X.X/ whose prefix length is 5 to 6. <cf><m>address</m>/<m>num</m>+</cf> is a shorthand for <cf><m>address</m>/{0,<m/num/}</cf>,
513
	  <cf><m>address</m>/<m/num/-</cf> is a shorthand for <cf><m>address</m>/{0,<m/num-1/}</cf>. For example,
514
	  <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{ 15 , 17 } ]</cf> is true, but
515
	  <cf>1.0.0.0/8 &tilde; [ 1.0.0.0/8- ]</cf> is false.
516

    
517
	<tag/enum/
518
	  Enumeration types are fixed sets of possibilities. You can't define your own
519
	  variables of such type, but some route attributes are of enumeration
520
	  type. Enumeration types are incompatible with each other.
521

    
522
	<tag/bgppath/
523
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
524

    
525
	<tag/bgpmask/
526
	  BGP masks are patterns used for BGP path matching
527
	  (using <cf>path &tilde; /2 3 5 ?/</cf> syntax). The masks
528
	  resemble wildcard patterns as used by UNIX shells. Autonomous
529
	  system numbers match themselves, <cf/?/ matches any (even empty)
530
	  sequence of arbitrary AS numbers (<cf/*/ hasn't been chosen, because
531
	  <cf>/*</cf> starts a comment). For example:
532
	  <tt>/4 3 2 1/ &tilde; /? 4 3 ?/</tt> is true, but 
533
	  <tt>/4 3 2 1/ &tilde; /? 4 5 ?/</tt> is false.
534
	<tag/clist/ 
535
	  Community list is similar to set of pairs,
536
	  except that unlike other sets, it can be modified.
537
	  There exist no literals of this type.
538

    
539
</descrip>
540

    
541
<sect>Operators
542

    
543
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
544
<cf/(a=b, a!=b, a&lt;b, a&gt;=b)/. Logical operations include unary not (<cf/!/), and (<cf/&amp;&amp;/) and or (<cf/&verbar;&verbar;/). 
545
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
546
used on element and set of elements of the same type (returning true if element is contained in the given set), or on IP and prefix (returning true if IP is within the range defined by that prefix), or on
547
prefix and prefix (returning true if first prefix is more specific than second one) or on bgppath and bgpmask (returning true if the path matches the mask) or on pair and clist (returning true if the community is element of the community list).
548

    
549

    
550
<sect>Control structures
551

    
552
<p>Filters support two control structures: conditions and case switches. 
553

    
554
<p>Syntax of a condition is: <cf>if
555
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
556
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
557
clause may be omitted. If the <cf><m>boolean expression</m></cf> is true, <cf><m>command1</m></cf> is executed, otherwise <cf><m>command2</m></cf> is executed.
558

    
559
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
560
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
561
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
562
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
563
If <cf><m/expr/</cf> matches one of the <cf/:/ clauses, statements between it and next <cf/:/ statement are executed. If <cf><m/expr/</cf> matches neither of the <cf/:/ clauses, the statements after <cf/else:/ are executed.
564

    
565
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
566

    
567
<code>
568
case arg1 {
569
	2: print "two"; print "I can do more commands without {}";
570
	3 .. 5: print "three to five";
571
	else: print "something else";
572
}
573

    
574
if 1234 = i then printn "."; else { 
575
  print "not 1234"; 
576
  print "You need {} around multiple commands"; 
577
}
578
</code>
579

    
580
<sect>Route attributes
581

    
582
<p>A filter is implicitly passed a route, and it can access its
583
attributes just like it accesses variables. Attempts to access undefined
584
attribute result in a runtime error; you can check if an attribute is
585
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
586

    
587
<descrip>
588
	<tag><m/prefix/ net</tag>
589
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
590

    
591
	<tag><m/enum/ scope</tag>
592
	Address scope of the network (<cf/SCOPE_HOST/ for addresses local to this host, <cf/SCOPE_LINK/ for those specific for a physical link, <cf/SCOPE_SITE/ and <cf/SCOPE_ORGANIZATION/ for private addresses, <cf/SCOPE_UNIVERSE/ for globally visible addresses).
593

    
594
	<tag><m/int/ preference</tag>
595
	Preference of the route. (See the chapter about routing tables.)
596

    
597
	<tag><m/ip/ from</tag>
598
	The router which the route has originated from. Read-only.
599
	
600
	<tag><m/ip/ gw</tag>
601
	Next hop packets routed using this route should be forwarded to.
602

    
603
	<tag><m/enum/ source</tag>
604
	what protocol has told me about this route. Possible values: <cf/RTS_DUMMY/, <cf/RTS_STATIC/, <cf/RTS_INHERIT/, <cf/RTS_DEVICE/, <cf/RTS_STATIC_DEVICE/, <cf/RTS_REDIRECT/, <cf/RTS_RIP/, <cf/RTS_OSPF/, <cf/RTS_OSPF_EXT/, <cf/RTS_OSPF_IA/, <cf/RTS_OSPF_BOUNDARY/, <cf/RTS_BGP/, <cf/RTS_PIPE/.
605

    
606
	<tag><m/enum/ cast</tag>
607
	Route type (<cf/RTC_UNICAST/ for normal routes, <cf/RTC_BROADCAST/, <cf/RTC_MULTICAST/, <cf/RTC_ANYCAST/ for broadcast, multicast and anycast routes). Read-only.
608

    
609
	<tag><m/enum/ dest</tag>
610
	Type of destination the packets should be sent to (<cf/RTD_ROUTER/ for forwarding to a neighboring router, <cf/RTD_NETWORK/ for routing to a directly-connected network, <cf/RTD_BLACKHOLE/ for packets to be silently discarded, <cf/RTD_UNREACHABLE/, <cf/RTD_PROHIBIT/ for packets that should be returned with ICMP host unreachable / ICMP administratively prohibited messages). Read-only.
611
</descrip>
612

    
613
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
614

    
615
<sect>Other statements
616

    
617
<p>The following statements are available:
618

    
619
<descrip>
620
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
621

    
622
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
623

    
624
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
625

    
626
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
627
	Prints given expressions; useful mainly while debugging
628
	filters. The <cf/printn/ variant does not terminate the line.
629

    
630
	<tag>quitbird</tag>
631
	Terminates BIRD. Useful when debugging the filter interpreter.
632
</descrip>
633

    
634
<chapt>Protocols
635

    
636
<sect>BGP
637

    
638
<p>The Border Gateway Protocol is the routing protocol used for backbone
639
level routing in the today's Internet. Contrary to the other protocols, its convergence
640
doesn't rely on all routers following the same rules for route selection,
641
making it possible to implement any routing policy at any router in the
642
network, the only restriction being that if a router advertises a route,
643
it must accept and forward packets according to it.
644

    
645
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
646
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
647
Routers within each AS usually communicate with each other using either a interior routing
648
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
649
Boundary routers at the border of the AS communicate with their peers
650
in the neighboring AS'es via exterior BGP (eBGP).
651

    
652
<p>Each BGP router sends to its neighbors updates of the parts of its
653
routing table it wishes to export along with complete path information
654
(a list of AS'es the packet will travel through if it uses the particular
655
route) in order to avoid routing loops.
656

    
657
<p>BIRD supports all requirements of the BGP4 standard as defined in
658
RFC 1771<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1771.txt">
659
including several enhancements from the
660
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-09.txt">.
661
It also supports the community attributes as per
662
RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">,
663
capability negotiation defined in
664
RFC 2842<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2842.txt">.
665
For IPv6, it uses the standard multiprotocol extensions defined in
666
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
667
including changes described in the
668
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
669
and applied to IPv6 according to
670
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
671

    
672
<sect1>Route selection rules
673

    
674
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
675
route among multiple BGP routes with the same preference are a bit more complex
676
and they are implemented according to the following algorithm. It starts the first
677
rule, if there are more "best" routes, then it uses the second rule to choose
678
among them and so on.
679

    
680
<itemize>
681
	<item>Prefer route with the highest Local Preference attribute.
682
	<item>Prefer route with the shortest AS path.
683
	<item>Prefer IGP origin over EGP and EGP over incomplete.
684
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
685
	<item>Prefer internal routes over external ones.
686
	<item>Prefer the route with the lowest value of router ID of the
687
	advertising router.
688
</itemize>
689

    
690
<sect1>Configuration
691

    
692
<p>Each instance of the BGP corresponds to one neighboring router.
693
This allows to set routing policy and all the other parameters differently
694
for each neighbor using the following configuration parameters:
695

    
696
<descrip>
697
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
698
	contrary to other IP routers, BIRD is able to act as a router located
699
	in multiple AS'es simultaneously, but in such cases you need to tweak
700
	the BGP paths manually in the filters to get consistent behavior.)
701
	This parameter is mandatory.
702

    
703
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
704
	this instance will be talking to and what AS it's located in. Unless
705
	you use the <cf/multihop/ clause, it must be directly connected to one
706
	of your router's interfaces. In case the neighbor is in the same AS
707
	as we are, we automatically switch to iBGP. This parameter is mandatory.
708

    
709
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
710
	neighbor which is connected at most <m/number/ hops far and to which
711
	we should route via our direct neighbor with address <m/ip/.
712
	Default: switched off.
713

    
714
	<tag>next hop self</tag> Avoid calculation of the Next Hop attribute
715
	and always advertise our own source address (see below) as a next hop.
716
	This needs to be used only
717
	occasionally to circumvent misconfigurations of other routers.
718
	Default: disabled.
719

    
720
	<tag>source address <m/ip/</tag> Define local address we should use
721
	for next hop calculation. Default: the address of the local end
722
	of the interface our neighbor is connected to.
723

    
724
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
725
	locally or by the other side), disable the instance automatically
726
	and wait for an administrator to fix the problem manually. Default: off.
727

    
728
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
729
	message from the other side before considering the connection stale.
730
	Default: depends on agreement with the neighboring router, we prefer
731
	240 seconds if the other side is willing to accept it.
732

    
733
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
734
	before the routers have a chance to exchange open messages and agree
735
	on the real value. Default: 240 seconds.
736

    
737
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
738
	of two consecutive Keepalive messages. Default: One third of the hold time.
739

    
740
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
741
	retrying a failed attempt to connect. Default: 120 seconds.
742

    
743
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
744
	startup and the first attempt to connect. Default: 5 seconds.
745

    
746
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
747
	failure (either local or reported by the peer) and automatic restart.
748
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
749
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
750

    
751
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
752
	failures to treat them as a error sequence which makes the <cf/error wait time/
753
	increase exponentially. Default: 300 seconds.
754

    
755
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
756
	when deciding which BGP route is the best one. Default: on.
757

    
758
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
759
	Discriminator to be used during route selection when the MED attribute
760
	is missing. Default: infinite.
761

    
762
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
763
	to be used during route selection when the Local Preference attribute
764
	is missing. Default: 0.
765
</descrip>
766

    
767
<sect1>Attributes
768

    
769
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
770
table below) are available on internal BGP connections only, some of them (marked
771
with `<tt/O/') are optional.
772

    
773
<descrip>
774
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
775
	the packet will travel through when forwarded according to the particular route. In case of 
776
	internal BGP it doesn't contain the number of the local AS.
777

    
778
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
779
	selection among multiple BGP routes (see the selection rules above). It's
780
	used as an additional metric which is propagated through the whole local AS.
781

    
782
	<tag>int <cf/bgp_med/ [IO]</tag> The Multiple Exit Discriminator of the route
783
	is an optional attribute which is often used within the local AS to
784
	reflect interior distances to various boundary routers. See the route selection
785
	rules above for exact semantics.
786

    
787
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
788
	if the route has originated in an interior routing protocol or
789
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
790
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
791
	is unknown.
792

    
793
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
794
	to this destination. On internal BGP connections, it's an address of the
795
	originating router if it's inside the local AS or a boundary router the
796
	packet will leave the AS through if it's an exterior route, so each BGP
797
	speaker within the AS has a chance to use the shortest interior path
798
	possible to this point.
799

    
800
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
801
	which carries no value, but the sole presence of which indicates that the route
802
	has been aggregated from multiple routes by some router on the path from
803
	the originator.
804

    
805
<!-- we don't handle aggregators right since they are of a very obscure type
806
	<tag>bgp_aggregator</tag>
807
-->
808
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
809
	with the route. Each such value is a pair (represented as a <cf/pair/ data
810
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
811
	the community and the second one being a per-AS identifier. There are lots
812
	of uses of the community mechanism, but generally they are used to carry
813
	policy information like "don't export to USA peers". As each AS can define
814
	its own routing policy, it also has a complete freedom about which community
815
	attributes it defines and what will their semantics be.
816
</descrip>
817

    
818
<sect1>Example
819

    
820
<p><code>
821
protocol bgp {
822
	local as 65000;			     # Use a private AS number
823
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
824
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
825
	export filter {			     # We use non-trivial export rules
826
		if source = RTS_STATIC then { # Export only static routes
827
		        # Assign our community
828
			bgp_community.add((65000,5678));
829
			# Artificially increase path length
830
			# by advertising local AS number twice
831
			if bgp_path ~ / 65000 / then	  
832
				bgp_path.prepend(65000);  
833
			accept;
834
		}
835
		reject;
836
	};
837
	import all;
838
	source address 62.168.0.1;	# Use a non-standard source address
839
}
840
</code>
841

    
842
<sect>Device
843

    
844
<p>The Device protocol is not a real routing protocol.  It doesn't generate
845
any routes and it only serves as a module for getting information about network
846
interfaces from the kernel.
847

    
848
<p>Except for very unusual circumstances, you probably should include
849
this protocol in the configuration since almost all other protocols
850
require network interfaces to be defined for them to work with.
851

    
852
<p>The only configurable thing is interface scan time:
853

    
854
<p><descrip>
855
	<tag>scan time <m/number/</tag> Time in seconds between two scans
856
	of the network interface list. On systems where we are notified about
857
	interface status changes asynchronously (such as newer versions of
858
	Linux), we need to scan the list only in order to avoid confusion by lost
859
	notification messages, so the default time is set to a large value.
860
</descrip>
861

    
862
<p>As the Device protocol doesn't generate any routes, it cannot have
863
any attributes. Example configuration looks really simple:
864

    
865
<p><code>
866
protocol device {
867
	scan time 10;		# Scan the interfaces often
868
}
869
</code>
870

    
871
<sect>Direct
872

    
873
<p>The Direct protocol is a simple generator of device routes for all the
874
directly connected networks according to the list of interfaces provided
875
by the kernel via the Device protocol.
876

    
877
<p>It's highly recommended to include this protocol in your configuration
878
unless you want to use BIRD as a route server or a route reflector, that is
879
on a machine which doesn't forward packets itself and only participates in
880
distribution of routing information.
881

    
882
<p>The only configurable thing about direct is what interfaces it watches:
883

    
884
<p><descrip>
885
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
886
	protocol will generate device routes for all the interfaces
887
	available. If you want to restrict it to some subset of interfaces
888
	(for example if you're using multiple routing tables for policy
889
	routing and some of the policy domains don't contain all interfaces),
890
	just use this clause.
891
</descrip>
892

    
893
<p>Direct device routes don't contain any specific attributes.
894

    
895
<p>Example config might look like this:
896

    
897
<p><code>
898
protocol direct {
899
	interface "-arc*", "*";		# Exclude the ARCnets
900
}
901
</code>
902

    
903
<sect>Kernel
904

    
905
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
906
the with other routers in the network, it performs synchronization of BIRD's routing
907
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
908
and from time to time it scans the kernel tables to see whether some routes have
909
disappeared (for example due to unnoticed up/down transition of an interface)
910
or whether an `alien' route has been added by someone else (depending on the
911
<cf/learn/ switch, such routes are either deleted or accepted to our
912
table).
913

    
914
<p>If your OS supports only a single routing table, you can configure only one
915
instance of the Kernel protocol. If it supports multiple tables (in order to
916
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
917
them must be connected to a different BIRD routing table and to a different
918
kernel table.
919

    
920
<sect1>Configuration
921

    
922
<p><descrip>
923
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
924
	routing tables when it exits (instead of cleaning them up).
925
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
926
	kernel routing table.
927
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
928
	routing tables by other routing daemons or by the system administrator.
929
	This is possible only on systems which support identification of route
930
	authorship.
931
	<tag>kernel table <m/number/</tag> Select which kernel table should
932
	this particular instance of the Kernel protocol work with. Available
933
	only on systems supporting multiple routing tables.
934
</descrip>
935

    
936
<p>The Kernel protocol doesn't define any route attributes.
937
<p>A simple configuration can look this way:
938

    
939
<p><code>
940
protocol kernel {
941
	import all;
942
	export all;
943
}
944
</code>
945

    
946
<p>Or for a system with two routing tables:
947

    
948
<p><code>
949
protocol kernel {		# Primary routing table
950
	learn;			# Learn alien routes from the kernel
951
	persist;		# Don't remove routes on bird shutdown
952
	scan time 10;		# Scan kernel routing table every 10 seconds
953
	import all;
954
	export all;
955
}
956

    
957
protocol kernel {		# Secondary routing table
958
	table auxtable;
959
	kernel table 100;
960
	export all;
961
}
962
</code>
963

    
964
<sect>OSPF
965

    
966
<sect1>Introduction
967

    
968
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
969
protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
970
state (a.k.a. shortest path first) protocol -- each router maintains a database
971
describing the autonomous system's topology. Each participating router
972
has an identical copy of the database and all routers run the same algorithm
973
calculating a shortest path tree with themselves as a root.
974
OSPF chooses the least cost path as the best path.
975

    
976
<p>In OSPF, the autonomous system can be split to several areas in order
977
to reduce the amount of resources consumed for exchanging the routing
978
information and to protect the other areas from incorrect routing data.
979
Topology of the area is hidden to the rest of the autonomous system.
980
Unfortunately, multiple OSPF areas are not yet fully supported
981
by this version of BIRD and neither is the IPv6 version (OSPFv3).
982

    
983
<p>Another very important feature of OSPF is that
984
it can keep routing information from other protocols (like Static or BGP)
985
in its link state database as external routes. Each external route can
986
be tagged by the advertising router, making it possible to pass additional
987
information between routers on the boundary of the autonomous system.
988

    
989
<p>OSPF quickly detects topological changes in the autonomous system (such
990
as router interface failures) and calculates new loop-free routes after a short
991
period of convergence. Only a minimal ammount of 
992
routing traffic is involved.
993

    
994
<p>Each router participating in OSPF routing periodically sends Hello messages
995
to all its interfaces. This allows neighbors to be discovered dynamically.
996
Then the neighbors exchange theirs parts of the link state database and keep it
997
identical by flooding updates. The flooding process is reliable and ensures
998
that each router detects all changes.
999

    
1000
<sect1>Configuration
1001

    
1002
<p>In the main part of configuration, there can be multiple definitions of
1003
OSPF area witch different id included. These definitions includes many other
1004
switches and mutliple definitions of interfaces. Definition of interface
1005
may contain many switches and constant definitinons and list of neighbors
1006
on nonbroadcast networks.
1007

    
1008
<code>
1009
protocol ospf &lt;name&gt; {
1010
	rfc1583compat &lt;switch&gt;;
1011
	area &lt;id&gt; {
1012
		stub &lt;switch&gt;;
1013
		tick &lt;num&gt;;
1014
		interface &lt;interface pattern&gt;
1015
		{
1016
			cost &lt;num&gt;;
1017
			hello &lt;num&gt;;
1018
			retransmit &lt;num&gt;;
1019
			priority &lt;num&gt;;
1020
			wait &lt;num&gt;;
1021
			dead count &lt;num&gt;;
1022
			type [broadcast|nonbroadcast|pointopoint];
1023
			authetication [none|simple];
1024
			password "&lt;text&gt;";
1025
			neighbors {
1026
				&lt;ip&gt;;
1027
			};
1028
		};
1029
	};
1030
}
1031
</code>
1032

    
1033
<descrip>
1034
	<tag>rfc1583compat <M>switch</M></tag>
1035
	 This option controls compatibility of routing table
1036
	 calculation with RFC 1583<htmlurl
1037
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1038
	 value is no.
1039
	
1040
	<tag>area <M>id</M></tag>
1041
	 This defines an OSPF area with given area ID (an integer or an IPv4
1042
	 address, similarly to a router ID).
1043
	 The most important area is
1044
	 the backbone (ID 0) to which every other area must be connected.
1045

    
1046
	<tag>stub <M>switch</M></tag>
1047
	 No external routes are flooded into stub areas. Default value is no.
1048

    
1049
	<tag>tick <M>num</M></tag>
1050
	 The routing table calculation is not performed when a single link state
1051
	 change arrives. To lower the CPU utilization, it's processed later
1052
	 at periodical intervals of <m/num/ seconds. The default value is 7.
1053

    
1054
	<tag>interface <M>pattern</M></tag>
1055
	 Defines that the specified interfaces belong to the area being defined.
1056

    
1057
	<tag>cost <M>num</M></tag>
1058
	 Specifies output cost (metric) of an interface. Default value is 10.
1059

    
1060
	<tag>hello <M>num</M></tag>
1061
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1062
	 routers on the same network need to have the same hello interval.
1063
	 Default value is 10.
1064

    
1065
	<tag>retransmit <M>num</M></tag>
1066
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1067
	 Default value is 5.
1068

    
1069
        <tag>priority <M>num</M></tag>
1070
	 On every multiple access network (e.g., the Ethernet) Designed Router
1071
	 and Backup Designed router are elected. These routers have some
1072
	 special functions in the flooding process. Higher priority increases
1073
	 preferences in this election. Routers with priority 0 are not
1074
	 eligible. Default value is 1.
1075

    
1076
	<tag>wait <M>num</M></tag>
1077
	 After start, router waits for the specified number of seconds between starting
1078
	 election and building adjacency. Default value is 40.
1079
	 
1080
	<tag>dead count <M>num</M></tag>
1081
	 When the router does not receive any messages from a neighbor in
1082
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1083

    
1084
	<tag>type broadcast</tag>
1085
	 BIRD detects a type of a connected network automatically, but sometimes it's
1086
	 convenient to force use of a different type manually.
1087
	 On broadcast networks, flooding and Hello messages are sent using multicasts (a single packet for all the neighbors).
1088

    
1089
	<tag>type nonbroadcast</tag>
1090
	 On nonbroadcast networks, the packets are sent to each neighbor
1091
	 separately because of lack of multicast capabilities.
1092

    
1093
	<tag>type pointopoint</tag>
1094
	 Point-to-point networks connect just 2 routers together. No election
1095
	 is performed there which reduces the number of messages sent.
1096

    
1097
	<tag>authentication none</tag>
1098
	 No passwords are sent in OSPF packets. This is the default value.
1099

    
1100
	<tag>authentication simple</tag>
1101
	 Every packet carries 8 bytes of password. Received packets
1102
	 lacking this password are ignored. This authentication mechanism is
1103
	 very weak.
1104

    
1105
	<tag>password "<M>text</M>"</tag>
1106
	 An 8-byte password used for authentication.
1107

    
1108
	<tag>neighbors { <m/set/ } </tag>
1109
	 A set of neighbors to which Hello messages on nonbroadcast networks
1110
	 are to be sent.
1111
</descrip>
1112

    
1113
<sect1>Attributes
1114

    
1115
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1116
Metric is ranging from 1 to infinity (65535).
1117
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1118
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1119
<cf/metric of type 2/ is always longer
1120
than any <cf/metric of type 1/ or any <cf/internal metric/.
1121
Each external route can also carry a <cf/tag/ which is a 32-bit
1122
integer which is used when exporting routes to other protocols;
1123
otherwise, it doesn't affect routing inside the OSPF domain at all.
1124

    
1125
<sect1>Example
1126

    
1127
<p>
1128

    
1129
<code>
1130
protocol ospf MyOSPF {
1131
	export filter {
1132
		if source = RTS_BGP then {
1133
			ospf_metric1 = 100;
1134
			accept;
1135
		}
1136
	reject;
1137
	};                                                                      
1138
	area 0.0.0.0 {
1139
		tick 8;
1140
		interface "eth*" {
1141
			cost 11;
1142
			hello 15;
1143
			priority 100;
1144
			retransmit 7;
1145
			authentication simple;
1146
			password "aaa";
1147
		};
1148
		interface "ppp*" {
1149
			cost 100;
1150
		};
1151
	};
1152
	area 120 {
1153
		stub yes;
1154
		interface "-arc0" , "arc*" {
1155
			type nonbroadcast;
1156
			authentication none;
1157
			wait 50;
1158
			dead count 6;
1159
			neighbors {
1160
				192.168.120.1;
1161
				192.168.120.2;
1162
				192.168.120.10;
1163
			};
1164
		};
1165
	};
1166
}
1167
</code>
1168

    
1169
<sect>Pipe
1170

    
1171
<sect1>Introduction
1172

    
1173
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1174
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1175
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1176
and vice versa, depending on what's allowed by the filters. Export filters control export
1177
of routes from the primary table to the secondary one, import filters control the opposite
1178
direction.
1179

    
1180
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1181
where handling of a single packet doesn't depend only on its destination address, but also
1182
on its source address, source interface, protocol type and other similar parameters.
1183
In many systems (Linux 2.2 being a good example), the kernel allows to enforce routing policies
1184
by defining routing rules which choose one of several routing tables to be used for a packet
1185
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1186
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1187
connect them to the kernel ones, use filters to control which routes appear in which tables
1188
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1189
another one.
1190

    
1191
<sect1>Configuration
1192

    
1193
<p><descrip>
1194
	<tag>peer table <m/table/</tag> Define secondary routing table to connect to. The
1195
	primary one is selected by the <cf/table/ keyword.
1196
</descrip>
1197

    
1198
<sect1>Attributes
1199

    
1200
<p>The Pipe protocol doesn't define any route attributes.
1201

    
1202
<sect1>Example
1203

    
1204
<p>Let's consider a router which serves as a boundary router of two different autonomous
1205
systems, each of them connected to a subset of interfaces of the router, having its own
1206
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1207
of outage of its own exterior line.
1208

    
1209
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1210
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1211
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1212
and similarly for the second AS. Thus we have split our router to two logical routers,
1213
each one acting on its own routing table, having its own routing protocols on its own
1214
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1215
the routes between the tables through a Pipe protocol while decreasing their preferences
1216
and correcting their BGP paths to reflect the AS boundary crossing.
1217

    
1218
<code>
1219
table as1;				# Define the tables
1220
table as2;
1221

    
1222
protocol kernel kern1 {			# Synchronize them with the kernel
1223
	table as1;
1224
	kernel table 1;
1225
}
1226

    
1227
protocol kernel kern2 {
1228
	table as2;
1229
	kernel table 2;
1230
}
1231

    
1232
protocol bgp bgp1 {			# The outside connections
1233
	table as1;
1234
	local as 1;
1235
	neighbor 192.168.0.1 as 1001;
1236
	export all;
1237
	import all;
1238
}
1239

    
1240
protocol bgp bgp2 {
1241
	table as2;
1242
	local as 2;
1243
	neighbor 10.0.0.1 as 1002;
1244
	export all;
1245
	import all;
1246
}
1247

    
1248
protocol pipe {				# The Pipe
1249
	table as1;
1250
	peer table as2;
1251
	export filter {
1252
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1253
			if preference>10 then preference = preference-10;
1254
			if source=RTS_BGP then bgp_path.prepend(1);
1255
			accept;
1256
		}
1257
		reject;
1258
	};
1259
	import filter {
1260
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1261
			if preference>10 then preference = preference-10;
1262
			if source=RTS_BGP then bgp_path.prepend(2);
1263
			accept;
1264
		}
1265
		reject;
1266
	};
1267
}
1268
</code>
1269

    
1270
<sect>RIP
1271

    
1272
<sect1>Introduction
1273

    
1274
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1275
distances to all networks it can reach. When a router hears distance to another network, it increments
1276
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1277
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1278
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1279
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1280
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1281
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1282
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1283
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1284
and IPv6 (RFC 2080<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2080.txt">) versions of RIP are supported by BIRD, historical RIPv1 (RFC 1058<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1058.txt">)is
1285
not currently supported. RIPv4 md5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1286

    
1287
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1288
convergence, big network load and inability to handle larger networks
1289
makes it pretty much obsolete in IPv4 world. (It is still usable on
1290
very small networks.) It is widely used in IPv6 networks,
1291
because there are no good implementations of OSPFv3.
1292

    
1293
<sect1>Configuration
1294

    
1295
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1296

    
1297
<descrip>
1298
	<tag/authentication none|password|md5/ selects authentication method to be used. <cf/none/ means that
1299
	  packets are not authenticated at all, <cf/password/ means that a plaintext password is embedded
1300
	  into each packet, and <cf/md5/ means that packets are authenticated using a md5 cryptographic
1301
	  hash. If you set authentication to not-none, it is a good idea to add <cf>passwords { }</cf>
1302
	  section. Default: none.
1303

    
1304
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1305
	  be honored. (Always, when sent from a  host on a directly connected
1306
	  network or never.) Routing table updates are honored only from
1307
	  neighbors, that is not configurable. Default: never.
1308
</descrip>
1309

    
1310
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1311
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1312
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1313
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1314
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1315
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1316
interface but not listen to it.
1317

    
1318
<p>The following options generally override behavior specified in RFC. If you use any of these
1319
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1320
other than equally configured BIRD. I have warned you.
1321

    
1322
<descrip>
1323
	<tag>port <M>number</M></tag>
1324
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1325
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1326

    
1327
	<tag>infinity <M>number</M></tag>
1328
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1329
	  even slower.
1330

    
1331
	<tag>period <M>number</M>
1332
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1333
	  number will mean faster convergence but bigger network
1334
	  load. Do not use values lower than 10.
1335

    
1336
	<tag>timeout time <M>number</M>
1337
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1338

    
1339
	<tag>garbage time <M>number</M>
1340
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1341
</descrip>
1342

    
1343
<sect1>Attributes
1344

    
1345
<p>RIP defines two route attributes:
1346

    
1347
<descrip>
1348
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1349
	When routes from different RIP instances are available and all of them have the same
1350
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1351
	When importing a non-RIP route, the metric defaults to 5.
1352

    
1353
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1354
	to carry additional information with the route (for example, an originating AS number
1355
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1356
</descrip>
1357

    
1358
<sect1>Example
1359

    
1360
<p><code>
1361
protocol rip MyRIP_test {
1362
        debug all;
1363
        port 1520;
1364
        period 10;
1365
        garbage time 60;
1366
        interface "eth0" { metric 3; mode multicast; }
1367
	          "eth1" { metric 2; mode broadcast; };
1368
        honor neighbor;
1369
        authentication none;
1370
        import filter { print "importing"; accept; };
1371
        export filter { print "exporting"; accept; };
1372
}
1373
</code>
1374

    
1375
<sect>Static
1376

    
1377
<p>The Static protocol doesn't communicate with other routers in the network,
1378
but instead it allows you to define routes manually. This is often used for
1379
specifying how to forward packets to parts of the network which don't use
1380
dynamic routing at all and also for defining sink routes (i.e., those
1381
telling to return packets as undeliverable if they are in your IP block,
1382
you don't have any specific destination for them and you don't want to send
1383
them out through the default route to prevent routing loops).
1384

    
1385
<p>There are three types of static routes: `classical' routes telling to
1386
forward packets to a neighboring router, device routes specifying forwarding
1387
to hosts on a directly connected network and special routes (sink, blackhole
1388
etc.) which specify a special action to be done instead of forwarding the
1389
packet.
1390

    
1391
<p>When the particular destination is not available (the interface is down or
1392
the next hop of the route is not a neighbor at the moment), Static just
1393
uninstalls the route from the table it is connected to and adds it again as soon
1394
as the destination becomes adjacent again.
1395

    
1396
<p>The Static protocol has no configuration options. Instead, the
1397
definition of the protocol contains a list of static routes:
1398

    
1399
<descrip>
1400
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1401
	a neighboring router.
1402
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1403
	route through an interface to hosts on a directly connected network.
1404
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1405
	specifying to drop the packet, return it as unreachable or return
1406
	it as administratively prohibited.
1407
</descrip>
1408

    
1409
<p>Static routes have no specific attributes.
1410

    
1411
<p>Example static config might look like this:
1412

    
1413
<p><code>
1414
protocol static {
1415
	table testable;			 # Connect to a non-default routing table
1416
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1417
	route 62.168.0.0/25 reject;	 # Sink route
1418
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1419
}
1420
</code>
1421

    
1422
<chapt>Conclusions
1423

    
1424
<sect>Future work
1425

    
1426
<p>Although BIRD supports all the commonly used routing protocols,
1427
there are still some features which would surely deserve to be
1428
implemented in future versions of BIRD:
1429

    
1430
<itemize>
1431
<item>OSPF for IPv6 networks
1432
<item>OSPF NSSA areas and opaque LSA's
1433
<item>Route aggregation and flap dampening
1434
<item>Generation of IPv6 router advertisements
1435
<item>Multipath routes
1436
<item>Multicast routing protocols
1437
<item>Ports to other systems
1438
</itemize>
1439

    
1440
<sect>Getting more help
1441

    
1442
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1443
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1444
where you can share your experiences with the other users and consult
1445
your problems with the authors. To subscribe to the list, just send a
1446
<tt/subscribe bird-users/ command in a body of a mail to
1447
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1448
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1449

    
1450
<p>BIRD is a relatively young system and it probably contains some
1451
bugs. You can report any problems to the bird-users list and the authors
1452
will be glad to solve them, but before you do so,
1453
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1454
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1455
which fixes the bug is always welcome as an attachment.)
1456

    
1457
<p>If you want to understand what is going inside, Internet standards are
1458
a good and interesting reading. You can get them from <HTMLURL URL="ftp://ftp.rfc-editor.org/" name="ftp.rfc-editor.org"> (or a nicely sorted version from <HTMLURL URL="ftp://atrey.karlin.mff.cuni.cz/pub/rfc" name="atrey.karlin.mff.cuni.cz:/pub/rfc">).
1459

    
1460
<p><it/Good luck!/
1461

    
1462
</book>
1463

    
1464
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1465
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1476
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