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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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Ondrej Zajicek <it/&lt;santiago@crfreenet.org&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
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daemons: routed (RIP only), GateD (non-free), Zebra<HTMLURL URL="http://www.zebra.org">
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and MRTD<HTMLURL URL="http://sourceforge.net/projects/mrt">, but their capabilities are
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limited and 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, and then ported to FreeBSD and NetBSD, porting to other
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systems (even non-UNIX ones) should 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>-p</tag>
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	just parse the config file and exit. Return value is zero if the config file is valid,
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	nonzero if there are some errors.
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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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	interface "*";
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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>listen bgp [address <m/address/] [port <m/port/] [v6only]</tag>
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	This option allows to specify address and port where BGP
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	protocol should listen. It is global option as listening
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	socket is common to all BGP instances. Default is to listen on
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	all addresses (0.0.0.0) and port 179. In IPv6 mode, option
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	<cf/v6only/ can be used to specify that BGP socket should
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	listen to IPv6 connections only. This is needed if you want to
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	run both bird and bird6 on the same port.
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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>router id <m/IPv4 address/</tag> This option can be used to override global
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	router id for a given protocol. This option is not yet implemented for OSPF
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	protocol. Default: uses global router id.
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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>description "<m/text/"</tag> This is an optional
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	description of the protocol. It is displayed as a part of the
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	output of 'show route all' command.
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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><label id="dsc-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...] [ { <m/option/ ; [...] } ]</tag>
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	Specifies a set of interfaces on which the protocol is activated with
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	given interface-specific options. A set of interfaces specified by one
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	interface option is described using an interface pattern. The
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	interface pattern consists of a sequence of clauses (separted by
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	commas), each clause may contain a mask, a prefix, or both of them. An
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	interface matches the clause if its name matches the mask (if
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	specified) and its address matches the prefix (if specified). Mask is
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	specified as shell-like pattern.
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	An interface matches the pattern if it matches any of its
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	clauses. If the clause begins with <cf/-/, matching interfaces are
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	excluded. Patterns are parsed left-to-right, thus
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	<cf/interface "eth0", -"eth*", "*";/ means eth0 and all
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	non-ethernets.
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	An interface option can be used more times with different
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	interfaces-specific options, in that case for given interface
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	the first matching interface option is used.
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	This option is allowed in Direct, OSPF and RIP protocols,
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	but in OSPF protocol it is used in <cf/area/ subsection.
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	Default: none.
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	Examples:
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	<cf>interface "*" { type broadcast; };</cf> - start the protocol on all interfaces with
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	<cf>type broadcast</cf> option.
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	<cf>interface "eth1", "eth4", "eth5" { type pointopoint; };</cf> - start the protocol
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	on enumerated interfaces with <cf>type pointopoint</cf> option.
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	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all
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	interfaces that have address from 192.168.0.0/16, but not
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	from 192.168.1.0/24.
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	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all
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	interfaces that have address from 192.168.0.0/16, but not
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	from 192.168.1.0/24.
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	<cf>interface "eth*" 192.168.1.0/24;</cf> - start the protocol on all
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	ethernet interfaces that have address from 192.168.1.0/24.
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	<tag><label id="dsc-pass">password "<m/password/" [ { id <m/num/; generate from <m/time/; generate to <m/time/; accept from <m/time/; accept to <m/time/; } ]</tag>
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	Specifies a password that can be used by the protocol. Password option can
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	be used more times to specify more passwords. If more passwords are
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	specified, it is a protocol-dependent decision which one is really
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	used. Specifying passwords does not mean that authentication is
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	enabled, authentication can be enabled by separate, protocol-dependent
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	<cf/authentication/ option.
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	This option is allowed in OSPF and RIP protocols. BGP has also
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	<cf/password/ option, but it is slightly different and described
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	separately.
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	Default: none.
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</descrip>
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<p>Password option can contain section with some (not necessary all) password sub-options:
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<descrip>
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	<tag>id <M>num</M></tag>
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	 ID of the password, (0-255). If it's not used, BIRD will choose
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	 ID based on an order of the password item in the interface. For
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	 example, second password item in one interface will have default
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	 ID 2. ID is used by some routing protocols to identify which
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	 password was used to authenticate protocol packets.
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	<tag>generate from "<m/time/"</tag>
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	 The start time of the usage of the password for packet signing.
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	 The format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
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	<tag>generate to "<m/time/"</tag>
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	 The last time of the usage of the password for packet signing.
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	<tag>accept from "<m/time/"</tag>
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	 The start time of the usage of the password for packet verification.
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	<tag>accept to "<m/time/"</tag>
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	 The last time of the usage of the password for packet verification.
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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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Many commands have the <m/name/ of the protocol instance as an argument.
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This argument can be omitted if there exists only a single instance.
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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 [<m/name/] ["<m/interface/"]</tag>
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	Show detailed information about OSPF interfaces.
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	<tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
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	Show a list of OSPF neighbors and a state of adjacency to them.
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	<tag>show ospf state [<m/name/]</tag>
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	Show detailed information about OSPF areas based on a content of link-state database.
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	It shows network topology,  aggregated networks and routers from other areas and external routes.
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	<tag>show ospf topology [<m/name/]</tag>
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	Show a topology of OSPF areas based on a content of link-state database.
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	It is just a stripped-down version of 'show ospf state'.
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	<tag>show static [<m/name/]</tag>
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	Show detailed information about static routes.
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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/] [(export|preexport) <m/p/] [protocol <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/export/ and <cf/preexport/ switches ask for printing of entries
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	that are exported to the specified protocol. With <cf/preexport/, the
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	export filter of the protocol is skipped.
478

    
479
	<p>You can also select just routes added by a specific protocol.
480
	<cf>protocol <m/p/</cf>.
481

    
482
	<p>The <cf/stats/ switch requests showing of route statistics (the
483
	number of networks, number of routes before and after filtering). If
484
	you use <cf/count/ instead, only the statistics will be printed.
485

    
486
	<tag>configure [soft] ["<m/config file/"]</tag>
487
	Reload configuration from a given file. BIRD will smoothly
488
	switch itself to the new configuration, protocols are
489
	reconfigured if possible, restarted otherwise. Changes in
490
	filters usualy lead to restart of affected protocols. If
491
	<cf/soft/ option is used, changes in filters does not cause
492
	BIRD to restart affected protocols, therefore already accepted
493
	routes (according to old filters) would be still propagated,
494
	but new routes would be processed according to the new
495
	filters.
496

    
497
	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
498
	Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances.
499

    
500
	<tag>reload [in|out] <m/name/|"<m/pattern/"|all</tag>
501
	
502
	Reload a given protocol instance, that means re-import routes
503
	from the protocol instance and re-export preferred routes to
504
	the instance. If <cf/in/ or <cf/out/ options are used, the
505
	command is restricted to one direction (re-import or
506
	re-export).
507

    
508
	This command is useful if appropriate filters have changed but
509
	the protocol instance was not restarted (or reloaded),
510
	therefore it still propagates the old set of routes. For example
511
	when <cf/configure soft/ command was used to change filters.
512

    
513
	Re-export always succeeds, but re-import is protocol-dependent
514
	and might fail (for example, if BGP neighbor does not support
515
	route-refresh extension). In that case, re-export is also
516
	skipped.
517

    
518
	<tag/down/
519
	Shut BIRD down.
520

    
521
	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
522
	Control protocol debugging.
523
</descrip>
524

    
525
<chapt>Filters
526

    
527
<sect>Introduction
528

    
529
<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
530
two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
531
being passed between protocols and routing tables. The filter language contains control structures such
532
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>. 
533

    
534
<p>Filter gets the route, looks at its attributes and
535
modifies some of them if it wishes. At the end, it decides whether to
536
pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
537
like this:
538

    
539
<code>
540
filter not_too_far
541
int var;
542
{
543
	if defined( rip_metric ) then
544
		var = rip_metric;
545
	else {
546
		var = 1;
547
		rip_metric = 1;
548
	}
549
	if rip_metric &gt; 10 then
550
		reject "RIP metric is too big";
551
	else
552
		accept "ok";
553
}
554
</code>
555

    
556
<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
557
the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
558
<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
559
<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
560
several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
561
you want to make a bigger block of code conditional.
562

    
563
<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
564
over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
565
look like this:
566

    
567
<code>
568
function name ()
569
int local_variable;
570
{
571
	local_variable = 5;
572
}
573

    
574
function with_parameters (int parameter)
575
{
576
	print parameter;
577
}
578
</code>
579

    
580
<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
581
variables in nested blocks. Functions are called like in C: <cf>name();
582
with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
583
command. Returning a value exits from current function (this is similar to C).
584

    
585
<p>Filters are declared in a way similar to functions except they can't have explicit
586
parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
587
to any functions called. The filter must terminate with either
588
<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
589
is rejected. 
590

    
591
<p>A nice trick to debug filters is to use <cf>show route filter
592
<m/name/</cf> from the command line client. An example session might look
593
like:
594

    
595
<code>
596
pavel@bug:~/bird$ ./birdc -s bird.ctl
597
BIRD 0.0.0 ready.
598
bird> show route
599
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
600
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
601
127.0.0.0/8        dev lo [direct1 23:21] (240)
602
bird> show route ?
603
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
604
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
605
127.0.0.0/8        dev lo [direct1 23:21] (240)
606
bird>
607
</code>
608

    
609
<sect>Data types
610

    
611
<p>Each variable and each value has certain type. Booleans, integers and enums are
612
incompatible with each other (that is to prevent you from shooting in the foot).
613

    
614
<descrip>
615
	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
616
	  <cf/false/. Boolean is the only type you can use in <cf/if/
617
	  statements.
618

    
619
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
620
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
621

    
622
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
623
	  65535. Literals of this type are written as <cf/(1234,5678)/. The same syntax can also be
624
	  used to construct a pair from two arbitrary integer expressions (for example <cf/(1+2,a)/).
625

    
626
	<tag/string/ This is a string of characters. There are no ways to modify strings in
627
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
628
	  such variables, but you can't concatenate two strings. String literals
629
	  are written as <cf/"This is a string constant"/.
630

    
631
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
632
	  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>
633
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
634
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
635

    
636
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
637
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
638
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
639
	  operators on prefixes:
640
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
641
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
642

    
643
	<tag/int|ip|prefix|pair|enum set/
644
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
645
	  but you can't modify them. Literals of type <cf>set int</cf> look like <cf>
646
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
647
	  sets.
648

    
649
	  Sets of prefixes are special: their literals does not allow ranges, but allows
650
	  prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
651
	  Prefix <cf><m>ip1</m>/<m>len1</m></cf> matches prefix pattern <cf><m>ip2</m>/<m>len2</m>{<m>l</m>,<m>h</m>}</cf> iff 
652
	  the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>.
653
	  A valid prefix pattern has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/
654
	  or <cf/high/. Obviously, a prefix matches a prefix set literal iff it matches any prefix pattern in the
655
	  prefix set literal.
656

    
657
	  There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for
658
	  <cf><m>address</m>/<m/len/{<m/len/,<m/maxlen/}</cf> (where <cf><m>maxlen</m></cf> is 32 for IPv4 and 128 for IPv6), 
659
	  that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf>
660
	  is a shorthand for <cf><m>address</m>/<m/len/{0,<m/len/}</cf>, that means network prefix <cf><m>address</m>/<m/len/</cf>
661
	  and all its supernets (network prefixes that contain it).
662

    
663
	  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} ]</cf> matches
664
	  prefix <cf>1.0.0.0/8</cf>, all subprefixes of <cf>2.0.0.0/8</cf>, all superprefixes of <cf>3.0.0.0/8</cf> and prefixes
665
	  <cf/4.X.X.X/ whose prefix length is 16 to 24. <cf>[ 0.0.0.0/0{20,24} ]</cf> matches all prefixes (regardless of
666
	  IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address
667
	  <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf> is true,
668
	  but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
669

    
670
	  Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
671
	  in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
672
	  <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
673
	  <cf>192.168.0.0/16{24,32}</cf>.
674

    
675
	<tag/enum/
676
	  Enumeration types are fixed sets of possibilities. You can't define your own
677
	  variables of such type, but some route attributes are of enumeration
678
	  type. Enumeration types are incompatible with each other.
679

    
680
	<tag/bgppath/
681
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
682
	  There are several special operators on bgppaths:
683

    
684
	  <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
685

    
686
          <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
687

    
688
	  Both <cf/first/ and <cf/last/ return zero if there is no appropriate ASN,
689
          for example if the path contains an AS set element as the first (or the last) part.
690

    
691
          <cf><m/P/.len</cf> returns the length of path <m/P/.
692

    
693
          <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and returns the result.
694
          Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
695
          <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
696
          (for example <cf/bgp_path/).
697

    
698
	<tag/bgpmask/
699
	  BGP masks are patterns used for BGP path matching
700
	  (using <cf>path &tilde; [= 2 3 5 * =]</cf> syntax). The masks
701
	  resemble wildcard patterns as used by UNIX shells. Autonomous
702
	  system numbers match themselves, <cf/*/ matches any (even empty)
703
	  sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number.
704
	  For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
705
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
706
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
707
	  BGP mask expressions can also contain integer expressions enclosed in parenthesis
708
	  and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>.
709
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
710

    
711
	<tag/clist/ 
712
	  Community list is similar to set of pairs,
713
	  except that unlike other sets, it can be modified.
714
	  There exist no literals of this type.
715
	  There are two special operators on clists:
716

    
717
          <cf>add(<m/C/,<m/P/)</cf> adds pair <m/P/ to clist <m/C/ and returns the result.
718

    
719
          <cf>delete(<m/C/,<m/P/)</cf> deletes pair <m/P/ from clist <m/C/ and returns the result.
720

    
721
          Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
722
          <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute
723
          (for example <cf/bgp_community/). Similarly for <cf/delete/.
724

    
725
</descrip>
726

    
727
<sect>Operators
728

    
729
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
730
<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;/). 
731
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
732
used on element and set of elements of the same type (returning true if element is contained in the given set), or
733
on two strings (returning true if first string matches a shell-like pattern stored in second string) or on IP and prefix (returning true if IP is within the range defined by that prefix), or on
734
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).
735

    
736

    
737
<sect>Control structures
738

    
739
<p>Filters support two control structures: conditions and case switches. 
740

    
741
<p>Syntax of a condition is: <cf>if
742
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
743
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
744
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.
745

    
746
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
747
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
748
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
749
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
750
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.
751

    
752
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
753

    
754
<code>
755
case arg1 {
756
	2: print "two"; print "I can do more commands without {}";
757
	3 .. 5: print "three to five";
758
	else: print "something else";
759
}
760

    
761
if 1234 = i then printn "."; else { 
762
  print "not 1234"; 
763
  print "You need {} around multiple commands"; 
764
}
765
</code>
766

    
767
<sect>Route attributes
768

    
769
<p>A filter is implicitly passed a route, and it can access its
770
attributes just like it accesses variables. Attempts to access undefined
771
attribute result in a runtime error; you can check if an attribute is
772
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
773

    
774
<descrip>
775
	<tag><m/prefix/ net</tag>
776
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
777

    
778
	<tag><m/enum/ scope</tag>
779
	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).
780

    
781
	<tag><m/int/ preference</tag>
782
	Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.)
783

    
784
	<tag><m/ip/ from</tag>
785
	The router which the route has originated from. Read-only.
786
	
787
	<tag><m/ip/ gw</tag>
788
	Next hop packets routed using this route should be forwarded to.
789

    
790
	<tag><m/string/ proto</tag>
791
	The name of the protocol which the route has been imported from. Read-only.
792

    
793
	<tag><m/enum/ source</tag>
794
	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_IA/, <cf/RTS_OSPF_EXT/, <cf/RTS_BGP/, <cf/RTS_PIPE/.
795

    
796
	<tag><m/enum/ cast</tag>
797
	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.
798

    
799
	<tag><m/enum/ dest</tag>
800
	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.
801
</descrip>
802

    
803
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
804

    
805
<sect>Other statements
806

    
807
<p>The following statements are available:
808

    
809
<descrip>
810
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
811

    
812
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
813

    
814
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
815

    
816
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
817
	Prints given expressions; useful mainly while debugging
818
	filters. The <cf/printn/ variant does not terminate the line.
819

    
820
	<tag>quitbird</tag>
821
	Terminates BIRD. Useful when debugging the filter interpreter.
822
</descrip>
823

    
824
<chapt>Protocols
825

    
826
<sect>BGP
827

    
828
<p>The Border Gateway Protocol is the routing protocol used for backbone
829
level routing in the today's Internet. Contrary to the other protocols, its convergence
830
doesn't rely on all routers following the same rules for route selection,
831
making it possible to implement any routing policy at any router in the
832
network, the only restriction being that if a router advertises a route,
833
it must accept and forward packets according to it.
834

    
835
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
836
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
837
Routers within each AS usually communicate with each other using either a interior routing
838
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
839
Boundary routers at the border of the AS communicate with their peers
840
in the neighboring AS'es via exterior BGP (eBGP).
841

    
842
<p>Each BGP router sends to its neighbors updates of the parts of its
843
routing table it wishes to export along with complete path information
844
(a list of AS'es the packet will travel through if it uses the particular
845
route) in order to avoid routing loops.
846

    
847
<p>BIRD supports all requirements of the BGP4 standard as defined in
848
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
849
It also supports the community attributes
850
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
851
capability negotiation
852
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
853
MD5 password authentication
854
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
855
route reflectors 
856
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
857
multiprotocol extensions
858
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
859
and 4B AS numbers 
860
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
861

    
862

    
863
For IPv6, it uses the standard multiprotocol extensions defined in
864
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
865
including changes described in the
866
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
867
and applied to IPv6 according to
868
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
869

    
870
<sect1>Route selection rules
871

    
872
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
873
route among multiple BGP routes with the same preference are a bit more complex
874
and they are implemented according to the following algorithm. It starts the first
875
rule, if there are more "best" routes, then it uses the second rule to choose
876
among them and so on.
877

    
878
<itemize>
879
	<item>Prefer route with the highest Local Preference attribute.
880
	<item>Prefer route with the shortest AS path.
881
	<item>Prefer IGP origin over EGP and EGP over incomplete.
882
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
883
	<item>Prefer internal routes over external ones.
884
	<item>Prefer the route with the lowest value of router ID of the
885
	advertising router.
886
</itemize>
887

    
888
<sect1>Configuration
889

    
890
<p>Each instance of the BGP corresponds to one neighboring router.
891
This allows to set routing policy and all the other parameters differently
892
for each neighbor using the following configuration parameters:
893

    
894
<descrip>
895
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
896
	contrary to other IP routers, BIRD is able to act as a router located
897
	in multiple AS'es simultaneously, but in such cases you need to tweak
898
	the BGP paths manually in the filters to get consistent behavior.)
899
	This parameter is mandatory.
900

    
901
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
902
	this instance will be talking to and what AS it's located in. Unless
903
	you use the <cf/multihop/ clause, it must be directly connected to one
904
	of your router's interfaces. In case the neighbor is in the same AS
905
	as we are, we automatically switch to iBGP. This parameter is mandatory.
906

    
907
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
908
	neighbor which is connected at most <m/number/ hops far and to which
909
	we should route via our direct neighbor with address <m/ip/.
910
	Default: switched off.
911

    
912
	<tag>next hop self</tag> Avoid calculation of the Next Hop
913
	attribute and always advertise our own source address (see
914
	below) as a next hop.  This needs to be used only occasionally
915
	to circumvent misconfigurations of other routers.
916
	Default: disabled.
917

    
918
	<tag>missing lladdr self|drop|ignore</tag>Next Hop attribute
919
	in BGP-IPv6 sometimes contains just the global IPv6 address,
920
	but sometimes it has to contain both global and link-local
921
	IPv6 addresses. This option specifies what to do if BIRD have
922
	to send both addresses but does not know link-local address.
923
	This situation might happen when routes from other protocols
924
	are exported to BGP, or when improper updates are received
925
	from BGP peers.  <cf/self/ means that BIRD advertises its own
926
	local address instead. <cf/drop/ means that BIRD skips that
927
	prefixes and logs error. <cf/ignore/ means that BIRD ignores
928
	the problem and sends just the global address (and therefore
929
	forms improper BGP update). Default: <cf/self/, unless BIRD
930
	is configured as a route server (option <cf/rs client/), in
931
	that case default is <cf/drop/, because route servers usually
932
	does not forward packets ifselves.
933
	
934
	<tag>source address <m/ip/</tag> Define local address we should use
935
	for next hop calculation. Default: the address of the local end
936
	of the interface our neighbor is connected to.
937

    
938
	<tag>password <m/string/</tag> Use this password for MD5 authentication
939
	of BGP sessions. Default: no authentication. Password has to be set by
940
	external utility (e.g. setkey(8)) on BSD systems.
941

    
942
	<tag>passive <m/switch/</tag> Standard BGP behavior is both
943
        initiating outgoing connections and accepting incoming
944
        connections. In passive mode, outgoing connections are not
945
        initiated. Default: off.
946

    
947
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
948
	a route reflection client. Default: disabled.
949

    
950
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
951
	to avoid route reflection loops. When there is one route reflector in a cluster
952
	it usually uses its router id as a cluster id, but when there are more route
953
	reflectors in a cluster, these need to be configured (using this option) to
954
	use a common cluster id. Clients in a cluster need not know their cluster
955
	id and this option is not allowed for them. Default: the same as router id.
956

    
957
	<tag>rs client</tag> Be a route server and treat the neighbor
958
	as a route server client. A route server is used as a
959
	replacement for full mesh EBGP routing in Internet exchange
960
	points in a similar way to route reflectors used in IBGP routing.
961
	BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
962
	which behaves like plain EBGP but reduces modifications to advertised route
963
	attributes to be transparent (for example does not prepend its AS number to
964
	AS PATH attribute and keep MED attribute). Default: disabled.
965

    
966
	<tag>enable route refresh <m/switch/</tag> When BGP speaker
967
	changes its import filter, it has to re-examine all routes
968
	received from its neighbor against the new filter. As these
969
	routes might not be available, there is a BGP protocol
970
	extension Route Refresh (specified in RFC 2918) that allows
971
	BGP speaker to request re-advertisment of all routes from its
972
	neighbor. This option specifies whether BIRD advertises this
973
	capability and accepts such requests. Even when disabled, BIRD
974
	can send route refresh requests. Default: on.
975

    
976
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
977
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
978
	but by disabling this option it can be persuaded not to advertise it and
979
	to maintain old-style sessions with its neighbors. This might be useful for
980
	circumventing bugs in neighbor's implementation of 4B AS extension.
981
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
982
	Default: on.
983

    
984
	<tag>capabilities <m/switch/</tag> Use capability advertisement
985
	to advertise optional capabilities. This is standard behavior
986
	for newer BGP implementations, but there might be some older
987
	BGP implementations that reject such connection attempts.
988
	When disabled (off), features that request it (4B AS support)
989
	are also disabled. Default: on, with automatic fallback to
990
	off when received capability-related error.
991

    
992
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
993
	This is not a correct behavior according to the strict interpretation
994
	of RFC 4760, but it is widespread and required by some BGP
995
	implementations (Cisco and Quagga). This option is relevant
996
	to IPv4 mode with enabled capability advertisement only. Default: on.
997

    
998
	<tag>route limit <m/number/</tag> The maximal number of routes
999
	that may be imported from the protocol. If the route limit is
1000
	exceeded, the connection is closed with error. Default: no limit.
1001

    
1002
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
1003
	locally or by the other side), disable the instance automatically
1004
	and wait for an administrator to fix the problem manually. Default: off.
1005

    
1006
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
1007
	message from the other side before considering the connection stale.
1008
	Default: depends on agreement with the neighboring router, we prefer
1009
	240 seconds if the other side is willing to accept it.
1010

    
1011
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
1012
	before the routers have a chance to exchange open messages and agree
1013
	on the real value. Default: 240 seconds.
1014

    
1015
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
1016
	of two consecutive Keepalive messages. Default: One third of the hold time.
1017

    
1018
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
1019
	retrying a failed attempt to connect. Default: 120 seconds.
1020

    
1021
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
1022
	startup and the first attempt to connect. Default: 5 seconds.
1023

    
1024
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
1025
	failure (either local or reported by the peer) and automatic restart.
1026
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
1027
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
1028

    
1029
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
1030
	failures to treat them as a error sequence which makes the <cf/error wait time/
1031
	increase exponentially. Default: 300 seconds.
1032

    
1033
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
1034
	when deciding which BGP route is the best one. Default: on.
1035

    
1036
	<tag>prefer older <m/switch/</tag> Standard route selection algorithm
1037
	breaks ties by comparing router IDs. This changes the behavior
1038
	to prefer older routes (when both are external and from different
1039
	peer). For details, see RFC 5004. Default: off.
1040

    
1041
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
1042
	Discriminator to be used during route selection when the MED attribute
1043
	is missing. Default: 0.
1044

    
1045
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
1046
	to be used during route selection when the Local Preference attribute
1047
	is missing. Default: 0.
1048
</descrip>
1049

    
1050
<sect1>Attributes
1051

    
1052
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
1053
table below) are available on internal BGP connections only, some of them (marked
1054
with `<tt/O/') are optional.
1055

    
1056
<descrip>
1057
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
1058
	the packet will travel through when forwarded according to the particular route. In case of 
1059
	internal BGP it doesn't contain the number of the local AS.
1060

    
1061
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
1062
	selection among multiple BGP routes (see the selection rules above). It's
1063
	used as an additional metric which is propagated through the whole local AS.
1064

    
1065
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
1066
	is an optional attribute which is used on on external (inter-AS) links to
1067
	convey to an adjacent AS the optimal entry point into the local AS.
1068
	The received attribute may be also propagated over internal BGP links
1069
	(and this is default behavior). The attribute value is zeroed when a route
1070
	is exported from a routing table to a BGP instance to ensure that the attribute
1071
	received from a neighboring AS is not propagated to other neighboring ASes.
1072
	A new value might be set in the export filter of a BGP instance.
1073
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1074
	for further discussion of BGP MED attribute.
1075

    
1076
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
1077
	if the route has originated in an interior routing protocol or
1078
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
1079
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
1080
	is unknown.
1081

    
1082
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
1083
	to this destination. On internal BGP connections, it's an address of the
1084
	originating router if it's inside the local AS or a boundary router the
1085
	packet will leave the AS through if it's an exterior route, so each BGP
1086
	speaker within the AS has a chance to use the shortest interior path
1087
	possible to this point.
1088

    
1089
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
1090
	which carries no value, but the sole presence of which indicates that the route
1091
	has been aggregated from multiple routes by some router on the path from
1092
	the originator.
1093

    
1094
<!-- we don't handle aggregators right since they are of a very obscure type
1095
	<tag>bgp_aggregator</tag>
1096
-->
1097
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
1098
	with the route. Each such value is a pair (represented as a <cf/pair/ data
1099
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
1100
	the community and the second one being a per-AS identifier. There are lots
1101
	of uses of the community mechanism, but generally they are used to carry
1102
	policy information like "don't export to USA peers". As each AS can define
1103
	its own routing policy, it also has a complete freedom about which community
1104
	attributes it defines and what will their semantics be.
1105
</descrip>
1106

    
1107
<sect1>Example
1108

    
1109
<p><code>
1110
protocol bgp {
1111
	local as 65000;			     # Use a private AS number
1112
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
1113
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
1114
	export filter {			     # We use non-trivial export rules
1115
		if source = RTS_STATIC then { # Export only static routes
1116
		        # Assign our community
1117
			bgp_community.add((65000,5678));
1118
			# Artificially increase path length
1119
			# by advertising local AS number twice
1120
			if bgp_path ~ [= 65000 =] then	  
1121
				bgp_path.prepend(65000);  
1122
			accept;
1123
		}
1124
		reject;
1125
	};
1126
	import all;
1127
	source address 62.168.0.1;	# Use a non-standard source address
1128
}
1129
</code>
1130

    
1131
<sect>Device
1132

    
1133
<p>The Device protocol is not a real routing protocol.  It doesn't generate
1134
any routes and it only serves as a module for getting information about network
1135
interfaces from the kernel.
1136

    
1137
<p>Except for very unusual circumstances, you probably should include
1138
this protocol in the configuration since almost all other protocols
1139
require network interfaces to be defined for them to work with.
1140

    
1141
<sect1>Configuration
1142

    
1143
<p><descrip>
1144
	<tag>scan time <m/number/</tag> Time in seconds between two scans
1145
	of the network interface list. On systems where we are notified about
1146
	interface status changes asynchronously (such as newer versions of
1147
	Linux), we need to scan the list only in order to avoid confusion by lost
1148
	notification messages, so the default time is set to a large value.
1149

    
1150
	<tag>primary  [ "<m/mask/" ] <m/prefix/</tag>
1151
	If a network interface has more than one network address,
1152
	BIRD has to choose one of them as a primary one, because some
1153
	routing protocols (for example OSPFv2) suppose there is only
1154
	one network address per interface. By default, BIRD chooses
1155
	the lexicographically smallest address as the primary one.
1156

    
1157
	This option allows to specify which network address should be
1158
	chosen as a primary one. Network addresses that match
1159
	<m/prefix/ are preferred to non-matching addresses. If more
1160
	<cf/primary/ options are used, the first one has the highest
1161
	preference. If "<m/mask/" is specified, then such
1162
	<cf/primary/ option is relevant only to matching network
1163
	interfaces.
1164

    
1165
	In all cases, an address marked by operating system as
1166
	secondary cannot be chosen as the primary one. 
1167
</descrip>
1168

    
1169
<p>As the Device protocol doesn't generate any routes, it cannot have
1170
any attributes. Example configuration looks like this:
1171

    
1172
<p><code>
1173
protocol device {
1174
	scan time 10;		# Scan the interfaces often
1175
	primary "eth0" 192.168.1.1;
1176
	primary 192.168.0.0/16;
1177
}
1178
</code>
1179

    
1180
<sect>Direct
1181

    
1182
<p>The Direct protocol is a simple generator of device routes for all the
1183
directly connected networks according to the list of interfaces provided
1184
by the kernel via the Device protocol.
1185

    
1186
<p>It's highly recommended to include this protocol in your configuration
1187
unless you want to use BIRD as a route server or a route reflector, that is
1188
on a machine which doesn't forward packets itself and only participates in
1189
distribution of routing information.
1190

    
1191
<p>The only configurable thing about direct is what interfaces it watches:
1192

    
1193
<p><descrip>
1194
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
1195
	protocol will generate device routes for all the interfaces
1196
	available. If you want to restrict it to some subset of interfaces
1197
	(for example if you're using multiple routing tables for policy
1198
	routing and some of the policy domains don't contain all interfaces),
1199
	just use this clause.
1200
</descrip>
1201

    
1202
<p>Direct device routes don't contain any specific attributes.
1203

    
1204
<p>Example config might look like this:
1205

    
1206
<p><code>
1207
protocol direct {
1208
	interface "-arc*", "*";		# Exclude the ARCnets
1209
}
1210
</code>
1211

    
1212
<sect>Kernel
1213

    
1214
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
1215
the with other routers in the network, it performs synchronization of BIRD's routing
1216
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
1217
and from time to time it scans the kernel tables to see whether some routes have
1218
disappeared (for example due to unnoticed up/down transition of an interface)
1219
or whether an `alien' route has been added by someone else (depending on the
1220
<cf/learn/ switch, such routes are either deleted or accepted to our
1221
table).
1222

    
1223
<p>If your OS supports only a single routing table, you can configure only one
1224
instance of the Kernel protocol. If it supports multiple tables (in order to
1225
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
1226
them must be connected to a different BIRD routing table and to a different
1227
kernel table.
1228

    
1229
<sect1>Configuration
1230

    
1231
<p><descrip>
1232
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
1233
	routing tables when it exits (instead of cleaning them up).
1234
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
1235
	kernel routing table.
1236
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
1237
	routing tables by other routing daemons or by the system administrator.
1238
	This is possible only on systems which support identification of route
1239
	authorship.
1240
	<tag>kernel table <m/number/</tag> Select which kernel table should
1241
	this particular instance of the Kernel protocol work with. Available
1242
	only on systems supporting multiple routing tables.
1243
</descrip>
1244

    
1245
<p>The Kernel protocol doesn't define any route attributes.
1246
<p>A simple configuration can look this way:
1247

    
1248
<p><code>
1249
protocol kernel {
1250
	import all;
1251
	export all;
1252
}
1253
</code>
1254

    
1255
<p>Or for a system with two routing tables:
1256

    
1257
<p><code>
1258
protocol kernel {		# Primary routing table
1259
	learn;			# Learn alien routes from the kernel
1260
	persist;		# Don't remove routes on bird shutdown
1261
	scan time 10;		# Scan kernel routing table every 10 seconds
1262
	import all;
1263
	export all;
1264
}
1265

    
1266
protocol kernel {		# Secondary routing table
1267
	table auxtable;
1268
	kernel table 100;
1269
	export all;
1270
}
1271
</code>
1272

    
1273
<sect>OSPF
1274

    
1275
<sect1>Introduction
1276

    
1277
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1278
protocol. The current IPv4 version (OSPFv2) is defined
1279
in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
1280
state (a.k.a. shortest path first) protocol -- each router maintains a database
1281
describing the autonomous system's topology. Each participating router
1282
has an identical copy of the database and all routers run the same algorithm
1283
calculating a shortest path tree with themselves as a root.
1284
OSPF chooses the least cost path as the best path.
1285
(OSPFv3 - OSPF for IPv6 is not supported yet.)
1286

    
1287
<p>In OSPF, the autonomous system can be split to several areas in order
1288
to reduce the amount of resources consumed for exchanging the routing
1289
information and to protect the other areas from incorrect routing data.
1290
Topology of the area is hidden to the rest of the autonomous system.
1291

    
1292
<p>Another very important feature of OSPF is that
1293
it can keep routing information from other protocols (like Static or BGP)
1294
in its link state database as external routes. Each external route can
1295
be tagged by the advertising router, making it possible to pass additional
1296
information between routers on the boundary of the autonomous system.
1297

    
1298
<p>OSPF quickly detects topological changes in the autonomous system (such
1299
as router interface failures) and calculates new loop-free routes after a short
1300
period of convergence. Only a minimal amount of 
1301
routing traffic is involved.
1302

    
1303
<p>Each router participating in OSPF routing periodically sends Hello messages
1304
to all its interfaces. This allows neighbors to be discovered dynamically.
1305
Then the neighbors exchange theirs parts of the link state database and keep it
1306
identical by flooding updates. The flooding process is reliable and ensures
1307
that each router detects all changes.
1308

    
1309
<sect1>Configuration
1310

    
1311
<p>In the main part of configuration, there can be multiple definitions of
1312
OSPF area witch different id included. These definitions includes many other
1313
switches and multiple definitions of interfaces. Definition of interface
1314
may contain many switches and constant definitions and list of neighbors
1315
on nonbroadcast networks.
1316

    
1317
<code>
1318
protocol ospf &lt;name&gt; {
1319
	rfc1583compat &lt;switch&gt;;
1320
	tick &lt;num&gt;;
1321
	area &lt;id&gt; {
1322
		stub cost &lt;num&gt;;
1323
                networks {
1324
			&lt;prefix&gt;;
1325
			&lt;prefix&gt; hidden;
1326
		}
1327
		stubnet &lt;prefix&gt;;
1328
		stubnet &lt;prefix&gt; {
1329
			hidden &lt;switch&gt;;
1330
			summary &lt;switch&gt;;
1331
			cost &lt;num&gt;;
1332
		}
1333
		interface &lt;interface pattern&gt; {
1334
			cost &lt;num&gt;;
1335
			stub &lt;switch&gt;;
1336
			hello &lt;num&gt;;
1337
			poll &lt;num&gt;;
1338
			retransmit &lt;num&gt;;
1339
			priority &lt;num&gt;;
1340
			wait &lt;num&gt;;
1341
			dead count &lt;num&gt;;
1342
			dead &lt;num&gt;;
1343
			rx buffer [normal|large|&lt;num&gt;];
1344
			type [broadcast|nonbroadcast|pointopoint];
1345
			strict nonbroadcast &lt;switch&gt;;
1346
			authentication [none|simple|cryptographics];
1347
			password "&lt;text&gt;";
1348
			password "&lt;text&gt;" {
1349
				id &lt;num&gt;;
1350
				generate from "&lt;date&gt;";
1351
				generate to "&lt;date&gt;";
1352
				accept from "&lt;date&gt;";
1353
				accept to "&lt;date&gt;";
1354
			};
1355
			neighbors {
1356
				&lt;ip&gt;;
1357
				&lt;ip&gt; eligible;
1358
			};
1359
		};
1360
		virtual link &lt;id&gt;	{
1361
			hello &lt;num&gt;;
1362
			retransmit &lt;num&gt;;
1363
			wait &lt;num&gt;;
1364
			dead count &lt;num&gt;;
1365
			dead &lt;num&gt;;
1366
			authentication [none|simple];
1367
			password "&lt;text&gt;";
1368
		};
1369
	};
1370
}
1371
</code>
1372

    
1373
<descrip>
1374
	<tag>rfc1583compat <M>switch</M></tag>
1375
	 This option controls compatibility of routing table
1376
	 calculation with RFC 1583<htmlurl
1377
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1378
	 value is no.
1379
	
1380
	<tag>area <M>id</M></tag>
1381
	 This defines an OSPF area with given area ID (an integer or an IPv4
1382
	 address, similarly to a router ID).
1383
	 The most important area is
1384
	 the backbone (ID 0) to which every other area must be connected.
1385

    
1386
	<tag>stub cost <M>num</M></tag>
1387
	 No external (except default) routes are flooded into stub areas.
1388
         Setting this value marks area stub with defined cost of default route.
1389
	 Default value is no. (Area is not stub.)
1390

    
1391
	<tag>tick <M>num</M></tag>
1392
	 The routing table calculation and clean-up of areas' databases
1393
         is not performed when a single link state
1394
	 change arrives. To lower the CPU utilization, it's processed later
1395
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1396

    
1397
	<tag>networks { <m/set/ }</tag>
1398
         Definition of area IP ranges. This is used in summary lsa origination.
1399
	 Hidden networks are not propagated into other areas.
1400

    
1401
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
1402
	 Stub networks are networks that are not transit networks
1403
	 between OSPF routers. They are also propagated through an
1404
	 OSPF area as a part of a link state database. By default,
1405
	 BIRD generates a stub network record for each primary network
1406
	 address on each OSPF interface that does not have any OSPF
1407
	 neighbors, and also for each non-primary network address on
1408
	 each OSPF interface. This option allows to alter a set of
1409
	 stub networks propagated by this router. 
1410

    
1411
	 Each instance of this option adds a stub network with given
1412
	 network prefix to the set of propagated stub network, unless
1413
	 option <cf/hidden/ is used. It also suppresses default stub
1414
	 networks for given network prefix. When option
1415
	 <cf/summary/ is used, also default stub networks that are
1416
	 subnetworks of given stub network are suppressed. This might
1417
	 be used, for example, to aggregate generated stub networks.
1418
	 
1419
	<tag>interface <M>pattern</M></tag>
1420
	 Defines that the specified interfaces belong to the area being defined.
1421
	 See <ref id="dsc-iface" name="interface"> common option for detailed description.
1422

    
1423
	<tag>virtual link <M>id</M></tag>
1424
	 Virtual link to router with the router id. Virtual link acts as a
1425
         point-to-point interface belonging to backbone. The actual area is
1426
         used as transport area. This item cannot be in the backbone.
1427

    
1428
	<tag>cost <M>num</M></tag>
1429
	 Specifies output cost (metric) of an interface. Default value is 10.
1430

    
1431
	<tag>stub <M>switch</M></tag>
1432
	 If set to interface it does not listen to any packet and does not send
1433
	 any hello. Default value is no.
1434

    
1435
	<tag>hello <M>num</M></tag>
1436
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1437
	 routers on the same network need to have the same hello interval.
1438
	 Default value is 10.
1439

    
1440
	<tag>poll <M>num</M></tag>
1441
	 Specifies interval in seconds between sending of Hello messages for
1442
	 some neighbors on NBMA network. Default value is 20.
1443

    
1444
	<tag>retransmit <M>num</M></tag>
1445
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1446
	 Default value is 5.
1447

    
1448
        <tag>priority <M>num</M></tag>
1449
	 On every multiple access network (e.g., the Ethernet) Designed Router
1450
	 and Backup Designed router are elected. These routers have some
1451
	 special functions in the flooding process. Higher priority increases
1452
	 preferences in this election. Routers with priority 0 are not
1453
	 eligible. Default value is 1.
1454

    
1455
	<tag>wait <M>num</M></tag>
1456
	 After start, router waits for the specified number of seconds between starting
1457
	 election and building adjacency. Default value is 40.
1458
	 
1459
	<tag>dead count <M>num</M></tag>
1460
	 When the router does not receive any messages from a neighbor in
1461
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1462

    
1463
	<tag>dead <M>num</M></tag>
1464
	 When the router does not receive any messages from a neighbor in
1465
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1466
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1467

    
1468
	<tag>rx buffer <M>num</M></tag>
1469
	 This sets the size of buffer used for receiving packets. The buffer should
1470
	 be bigger than maximal size of any packets. Value NORMAL (default)
1471
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1472

    
1473
	<tag>type broadcast</tag>
1474
	 BIRD detects a type of a connected network automatically, but sometimes it's
1475
	 convenient to force use of a different type manually.
1476
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1477
	 (a single packet for all the neighbors).
1478

    
1479
	<tag>type pointopoint</tag>
1480
	 Point-to-point networks connect just 2 routers together. No election
1481
	 is performed there which reduces the number of messages sent.
1482

    
1483
	<tag>type nonbroadcast</tag>
1484
	 On nonbroadcast networks, the packets are sent to each neighbor
1485
	 separately because of lack of multicast capabilities.
1486

    
1487
	<tag>strict nonbroadcast <M>switch</M></tag>
1488
	 If set, don't send hello to any undefined neighbor. This switch
1489
	 is ignored on on any non-NBMA network. Default is No.
1490

    
1491
	<tag>authentication none</tag>
1492
	 No passwords are sent in OSPF packets. This is the default value.
1493

    
1494
	<tag>authentication simple</tag>
1495
	 Every packet carries 8 bytes of password. Received packets
1496
	 lacking this password are ignored. This authentication mechanism is
1497
	 very weak.
1498

    
1499
	<tag>authentication cryptographic</tag>
1500
	 16-byte long MD5 digest is appended to every packet. For the digest
1501
         generation 16-byte long passwords are used. Those passwords are 
1502
         not sent via network, so this mechanismus is quite secure.
1503
         Packets can still be read by an attacker.
1504

    
1505
	<tag>password "<M>text</M>"</tag>
1506
	 An 8-byte or 16-byte password used for authentication.
1507
	 See <ref id="dsc-pass" name="password"> common option for detailed description.
1508

    
1509
	<tag>neighbors { <m/set/ } </tag>
1510
	 A set of neighbors to which Hello messages on nonbroadcast networks
1511
	 are to be sent. Some of them could be marked as eligible.
1512

    
1513
</descrip>
1514

    
1515
<sect1>Attributes
1516

    
1517
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1518
Metric is ranging from 1 to infinity (65535).
1519
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1520
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1521
<cf/metric of type 2/ is always longer
1522
than any <cf/metric of type 1/ or any <cf/internal metric/.
1523
If you specify both metrics only metric1 is used.
1524
Each external route can also carry a <cf/tag/ which is a 32-bit
1525
integer which is used when exporting routes to other protocols;
1526
otherwise, it doesn't affect routing inside the OSPF domain at all.
1527
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1528

    
1529
<sect1>Example
1530

    
1531
<p>
1532

    
1533
<code>
1534
protocol ospf MyOSPF {
1535
        rfc1583compatibility yes;
1536
        tick 2;
1537
	export filter {
1538
		if source = RTS_BGP then {
1539
			ospf_metric1 = 100;
1540
			accept;
1541
		}
1542
		reject;
1543
	};
1544
	area 0.0.0.0 {
1545
		interface "eth*" {
1546
			cost 11;
1547
			hello 15;
1548
			priority 100;
1549
			retransmit 7;
1550
			authentication simple;
1551
			password "aaa";
1552
		};
1553
		interface "ppp*" {
1554
			cost 100;
1555
			authentication cryptographic;
1556
			password "abc" {
1557
				id 1;
1558
				generate to "22-04-2003 11:00:06";
1559
				accept from "17-01-2001 12:01:05";
1560
			};
1561
			password "def" {
1562
				id 2;
1563
				generate to "22-07-2005 17:03:21";
1564
				accept from "22-02-2001 11:34:06";
1565
			};
1566
		};
1567
		interface "arc0" {
1568
			cost 10;
1569
			stub yes;
1570
		};
1571
		interface "arc1";
1572
	};
1573
	area 120 {
1574
		stub yes;
1575
		networks {
1576
			172.16.1.0/24;
1577
			172.16.2.0/24 hidden;
1578
		}
1579
		interface "-arc0" , "arc*" {
1580
			type nonbroadcast;
1581
			authentication none;
1582
			strict nonbroadcast yes;
1583
			wait 120;
1584
			poll 40;
1585
			dead count 8;
1586
			neighbors {
1587
				192.168.120.1 eligible;
1588
				192.168.120.2;
1589
				192.168.120.10;
1590
			};
1591
		};
1592
	};
1593
}
1594
</code>
1595

    
1596
<sect>Pipe
1597

    
1598
<sect1>Introduction
1599

    
1600
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1601
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1602
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1603
and vice versa, depending on what's allowed by the filters. Export filters control export
1604
of routes from the primary table to the secondary one, import filters control the opposite
1605
direction.
1606

    
1607
<p>The Pipe protocol may work in the opaque mode or in the transparent
1608
mode. In the opaque mode, the Pipe protocol retransmits optimal route
1609
from one table to the other table in a similar way like other
1610
protocols send and receive routes. Retransmitted route will have the
1611
source set to the Pipe protocol, which may limit access to protocol
1612
specific route attributes. The opaque mode is a default mode.
1613

    
1614
<p>In transparent mode, the Pipe protocol retransmits all routes from
1615
one table to the other table, retaining their original source and
1616
attributes.  If import and export filters are set to accept, then both
1617
tables would have the same content. The mode can be set by
1618
<tt/mode/ option.
1619

    
1620
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1621
where handling of a single packet doesn't depend only on its destination address, but also
1622
on its source address, source interface, protocol type and other similar parameters.
1623
In many systems (Linux being a good example), the kernel allows to enforce routing policies
1624
by defining routing rules which choose one of several routing tables to be used for a packet
1625
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1626
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1627
connect them to the kernel ones, use filters to control which routes appear in which tables
1628
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1629
another one.
1630

    
1631
<sect1>Configuration
1632

    
1633
<p><descrip>
1634
	<tag>peer table <m/table/</tag> Defines secondary routing table to connect to. The
1635
	primary one is selected by the <cf/table/ keyword.
1636

    
1637
	<tag>mode opaque|transparent</tag> Specifies the mode for the pipe to work in. Default is opaque.
1638
</descrip>
1639

    
1640
<sect1>Attributes
1641

    
1642
<p>The Pipe protocol doesn't define any route attributes.
1643

    
1644
<sect1>Example
1645

    
1646
<p>Let's consider a router which serves as a boundary router of two different autonomous
1647
systems, each of them connected to a subset of interfaces of the router, having its own
1648
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1649
of outage of its own exterior line.
1650

    
1651
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1652
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1653
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1654
and similarly for the second AS. Thus we have split our router to two logical routers,
1655
each one acting on its own routing table, having its own routing protocols on its own
1656
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1657
the routes between the tables through a Pipe protocol while decreasing their preferences
1658
and correcting their BGP paths to reflect the AS boundary crossing.
1659

    
1660
<code>
1661
table as1;				# Define the tables
1662
table as2;
1663

    
1664
protocol kernel kern1 {			# Synchronize them with the kernel
1665
	table as1;
1666
	kernel table 1;
1667
}
1668

    
1669
protocol kernel kern2 {
1670
	table as2;
1671
	kernel table 2;
1672
}
1673

    
1674
protocol bgp bgp1 {			# The outside connections
1675
	table as1;
1676
	local as 1;
1677
	neighbor 192.168.0.1 as 1001;
1678
	export all;
1679
	import all;
1680
}
1681

    
1682
protocol bgp bgp2 {
1683
	table as2;
1684
	local as 2;
1685
	neighbor 10.0.0.1 as 1002;
1686
	export all;
1687
	import all;
1688
}
1689

    
1690
protocol pipe {				# The Pipe
1691
	table as1;
1692
	peer table as2;
1693
	export filter {
1694
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1695
			if preference>10 then preference = preference-10;
1696
			if source=RTS_BGP then bgp_path.prepend(1);
1697
			accept;
1698
		}
1699
		reject;
1700
	};
1701
	import filter {
1702
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1703
			if preference>10 then preference = preference-10;
1704
			if source=RTS_BGP then bgp_path.prepend(2);
1705
			accept;
1706
		}
1707
		reject;
1708
	};
1709
}
1710
</code>
1711

    
1712
<sect>RIP
1713

    
1714
<sect1>Introduction
1715

    
1716
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1717
distances to all networks it can reach. When a router hears distance to another network, it increments
1718
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1719
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1720
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1721
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1722
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1723
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1724
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1725
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1726
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
1727
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1728

    
1729
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1730
convergence, big network load and inability to handle larger networks
1731
makes it pretty much obsolete in IPv4 world. (It is still usable on
1732
very small networks.) It is widely used in IPv6 networks,
1733
because there are no good implementations of OSPFv3.
1734

    
1735
<sect1>Configuration
1736

    
1737
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1738

    
1739
<descrip>
1740
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1741
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1742
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1743
	  hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf>
1744
	  section. Default: none.
1745

    
1746
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1747
	  be honored. (Always, when sent from a  host on a directly connected
1748
	  network or never.) Routing table updates are honored only from
1749
	  neighbors, that is not configurable. Default: never.
1750
</descrip>
1751

    
1752
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1753
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1754
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1755
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1756
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1757
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1758
interface but not listen to it.
1759

    
1760
<p>The following options generally override behavior specified in RFC. If you use any of these
1761
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1762
other than equally configured BIRD. I have warned you.
1763

    
1764
<descrip>
1765
	<tag>port <M>number</M></tag>
1766
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1767
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1768

    
1769
	<tag>infinity <M>number</M></tag>
1770
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1771
	  even slower.
1772

    
1773
	<tag>period <M>number</M>
1774
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1775
	  number will mean faster convergence but bigger network
1776
	  load. Do not use values lower than 10.
1777

    
1778
	<tag>timeout time <M>number</M>
1779
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1780

    
1781
	<tag>garbage time <M>number</M>
1782
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1783
</descrip>
1784

    
1785
<sect1>Attributes
1786

    
1787
<p>RIP defines two route attributes:
1788

    
1789
<descrip>
1790
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1791
	When routes from different RIP instances are available and all of them have the same
1792
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1793
	When importing a non-RIP route, the metric defaults to 5.
1794

    
1795
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1796
	to carry additional information with the route (for example, an originating AS number
1797
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1798
</descrip>
1799

    
1800
<sect1>Example
1801

    
1802
<p><code>
1803
protocol rip MyRIP_test {
1804
        debug all;
1805
        port 1520;
1806
        period 10;
1807
        garbage time 60;
1808
        interface "eth0" { metric 3; mode multicast; };
1809
	interface "eth*" { metric 2; mode broadcast; };
1810
        honor neighbor;
1811
        authentication none;
1812
        import filter { print "importing"; accept; };
1813
        export filter { print "exporting"; accept; };
1814
}
1815
</code>
1816

    
1817
<sect>Static
1818

    
1819
<p>The Static protocol doesn't communicate with other routers in the network,
1820
but instead it allows you to define routes manually. This is often used for
1821
specifying how to forward packets to parts of the network which don't use
1822
dynamic routing at all and also for defining sink routes (i.e., those
1823
telling to return packets as undeliverable if they are in your IP block,
1824
you don't have any specific destination for them and you don't want to send
1825
them out through the default route to prevent routing loops).
1826

    
1827
<p>There are three types of static routes: `classical' routes telling to
1828
forward packets to a neighboring router, device routes specifying forwarding
1829
to hosts on a directly connected network and special routes (sink, blackhole
1830
etc.) which specify a special action to be done instead of forwarding the
1831
packet.
1832

    
1833
<p>When the particular destination is not available (the interface is down or
1834
the next hop of the route is not a neighbor at the moment), Static just
1835
uninstalls the route from the table it is connected to and adds it again as soon
1836
as the destination becomes adjacent again.
1837

    
1838
<p>The Static protocol has no configuration options. Instead, the
1839
definition of the protocol contains a list of static routes:
1840

    
1841
<descrip>
1842
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1843
	a neighboring router.
1844
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1845
	route through an interface to hosts on a directly connected network.
1846
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1847
	specifying to drop the packet, return it as unreachable or return
1848
	it as administratively prohibited.
1849
</descrip>
1850

    
1851
<p>Static routes have no specific attributes.
1852

    
1853
<p>Example static config might look like this:
1854

    
1855
<p><code>
1856
protocol static {
1857
	table testable;			 # Connect to a non-default routing table
1858
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1859
	route 62.168.0.0/25 reject;	 # Sink route
1860
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1861
}
1862
</code>
1863

    
1864
<chapt>Conclusions
1865

    
1866
<sect>Future work
1867

    
1868
<p>Although BIRD supports all the commonly used routing protocols,
1869
there are still some features which would surely deserve to be
1870
implemented in future versions of BIRD:
1871

    
1872
<itemize>
1873
<item>OSPF for IPv6 networks
1874
<item>OSPF NSSA areas and opaque LSA's
1875
<item>Route aggregation and flap dampening
1876
<item>Generation of IPv6 router advertisements
1877
<item>Multipath routes
1878
<item>Multicast routing protocols
1879
<item>Ports to other systems
1880
</itemize>
1881

    
1882
<sect>Getting more help
1883

    
1884
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1885
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1886
where you can share your experiences with the other users and consult
1887
your problems with the authors. To subscribe to the list, just send a
1888
<tt/subscribe bird-users/ command in a body of a mail to
1889
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1890
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1891

    
1892
<p>BIRD is a relatively young system and it probably contains some
1893
bugs. You can report any problems to the bird-users list and the authors
1894
will be glad to solve them, but before you do so,
1895
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1896
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1897
which fixes the bug is always welcome as an attachment.)
1898

    
1899
<p>If you want to understand what is going inside, Internet standards are
1900
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">).
1901

    
1902
<p><it/Good luck!/
1903

    
1904
</book>
1905

    
1906
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1907
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