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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.
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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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426
<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.
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	<p>You can also select just routes added by a specific protocol.
479
	<cf>protocol <m/p/</cf>.
480

    
481
	<p>The <cf/stats/ switch requests showing of route statistics (the
482
	number of networks, number of routes before and after filtering). If
483
	you use <cf/count/ instead, only the statistics will be printed.
484

    
485
	<tag>configure [soft] ["<m/config file/"]</tag>
486
	Reload configuration from a given file. BIRD will smoothly
487
	switch itself to the new configuration, protocols are
488
	reconfigured if possible, restarted otherwise. Changes in
489
	filters usualy lead to restart of affected protocols. If
490
	<cf/soft/ option is used, changes in filters does not cause
491
	BIRD to restart affected protocols, therefore already accepted
492
	routes (according to old filters) would be still propagated,
493
	but new routes would be processed according to the new
494
	filters.
495

    
496
	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
497
	Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances.
498

    
499
	<tag/down/
500
	Shut BIRD down.
501

    
502
	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
503
	Control protocol debugging.
504
</descrip>
505

    
506
<chapt>Filters
507

    
508
<sect>Introduction
509

    
510
<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
511
two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
512
being passed between protocols and routing tables. The filter language contains control structures such
513
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>. 
514

    
515
<p>Filter gets the route, looks at its attributes and
516
modifies some of them if it wishes. At the end, it decides whether to
517
pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
518
like this:
519

    
520
<code>
521
filter not_too_far
522
int var;
523
{
524
	if defined( rip_metric ) then
525
		var = rip_metric;
526
	else {
527
		var = 1;
528
		rip_metric = 1;
529
	}
530
	if rip_metric &gt; 10 then
531
		reject "RIP metric is too big";
532
	else
533
		accept "ok";
534
}
535
</code>
536

    
537
<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
538
the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
539
<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
540
<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
541
several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
542
you want to make a bigger block of code conditional.
543

    
544
<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
545
over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
546
look like this:
547

    
548
<code>
549
function name ()
550
int local_variable;
551
{
552
	local_variable = 5;
553
}
554

    
555
function with_parameters (int parameter)
556
{
557
	print parameter;
558
}
559
</code>
560

    
561
<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
562
variables in nested blocks. Functions are called like in C: <cf>name();
563
with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
564
command. Returning a value exits from current function (this is similar to C).
565

    
566
<p>Filters are declared in a way similar to functions except they can't have explicit
567
parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
568
to any functions called. The filter must terminate with either
569
<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
570
is rejected. 
571

    
572
<p>A nice trick to debug filters is to use <cf>show route filter
573
<m/name/</cf> from the command line client. An example session might look
574
like:
575

    
576
<code>
577
pavel@bug:~/bird$ ./birdc -s bird.ctl
578
BIRD 0.0.0 ready.
579
bird> show route
580
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
581
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
582
127.0.0.0/8        dev lo [direct1 23:21] (240)
583
bird> show route ?
584
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
585
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
586
127.0.0.0/8        dev lo [direct1 23:21] (240)
587
bird>
588
</code>
589

    
590
<sect>Data types
591

    
592
<p>Each variable and each value has certain type. Booleans, integers and enums are
593
incompatible with each other (that is to prevent you from shooting in the foot).
594

    
595
<descrip>
596
	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
597
	  <cf/false/. Boolean is the only type you can use in <cf/if/
598
	  statements.
599

    
600
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
601
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
602

    
603
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
604
	  65535. Literals of this type are written as <cf/(1234,5678)/. The same syntax can also be
605
	  used to construct a pair from two arbitrary integer expressions (for example <cf/(1+2,a)/).
606

    
607
	<tag/string/ This is a string of characters. There are no ways to modify strings in
608
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
609
	  such variables, but you can't concatenate two strings. String literals
610
	  are written as <cf/"This is a string constant"/.
611

    
612
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
613
	  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>
614
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
615
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
616

    
617
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
618
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
619
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
620
	  operators on prefixes:
621
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
622
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
623

    
624
	<tag/int|ip|prefix|pair|enum set/
625
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
626
	  but you can't modify them. Literals of type <cf>set int</cf> look like <cf>
627
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
628
	  sets.
629

    
630
	  Sets of prefixes are special: their literals does not allow ranges, but allows
631
	  prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
632
	  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 
633
	  the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>.
634
	  A valid prefix pattern has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/
635
	  or <cf/high/. Obviously, a prefix matches a prefix set literal iff it matches any prefix pattern in the
636
	  prefix set literal.
637

    
638
	  There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for
639
	  <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), 
640
	  that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf>
641
	  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>
642
	  and all its supernets (network prefixes that contain it).
643

    
644
	  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
645
	  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
646
	  <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
647
	  IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address
648
	  <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf> is true,
649
	  but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
650

    
651
	  Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
652
	  in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
653
	  <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
654
	  <cf>192.168.0.0/16{24,32}</cf>.
655

    
656
	<tag/enum/
657
	  Enumeration types are fixed sets of possibilities. You can't define your own
658
	  variables of such type, but some route attributes are of enumeration
659
	  type. Enumeration types are incompatible with each other.
660

    
661
	<tag/bgppath/
662
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
663
	  There are several special operators on bgppaths:
664

    
665
	  <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
666

    
667
          <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
668

    
669
	  Both <cf/first/ and <cf/last/ return zero if there is no appropriate ASN,
670
          for example if the path contains an AS set element as the first (or the last) part.
671

    
672
          <cf><m/P/.len</cf> returns the length of path <m/P/.
673

    
674
          <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and returns the result.
675
          Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
676
          <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
677
          (for example <cf/bgp_path/).
678

    
679
	<tag/bgpmask/
680
	  BGP masks are patterns used for BGP path matching
681
	  (using <cf>path &tilde; [= 2 3 5 * =]</cf> syntax). The masks
682
	  resemble wildcard patterns as used by UNIX shells. Autonomous
683
	  system numbers match themselves, <cf/*/ matches any (even empty)
684
	  sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number.
685
	  For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
686
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
687
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
688
	  BGP mask expressions can also contain integer expressions enclosed in parenthesis
689
	  and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>.
690
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
691

    
692
	<tag/clist/ 
693
	  Community list is similar to set of pairs,
694
	  except that unlike other sets, it can be modified.
695
	  There exist no literals of this type.
696
	  There are two special operators on clists:
697

    
698
          <cf>add(<m/C/,<m/P/)</cf> adds pair <m/P/ to clist <m/C/ and returns the result.
699

    
700
          <cf>delete(<m/C/,<m/P/)</cf> deletes pair <m/P/ from clist <m/C/ and returns the result.
701

    
702
          Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
703
          <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute
704
          (for example <cf/bgp_community/). Similarly for <cf/delete/.
705

    
706
</descrip>
707

    
708
<sect>Operators
709

    
710
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
711
<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;/). 
712
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
713
used on element and set of elements of the same type (returning true if element is contained in the given set), or
714
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
715
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).
716

    
717

    
718
<sect>Control structures
719

    
720
<p>Filters support two control structures: conditions and case switches. 
721

    
722
<p>Syntax of a condition is: <cf>if
723
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
724
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
725
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.
726

    
727
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
728
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
729
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
730
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
731
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.
732

    
733
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
734

    
735
<code>
736
case arg1 {
737
	2: print "two"; print "I can do more commands without {}";
738
	3 .. 5: print "three to five";
739
	else: print "something else";
740
}
741

    
742
if 1234 = i then printn "."; else { 
743
  print "not 1234"; 
744
  print "You need {} around multiple commands"; 
745
}
746
</code>
747

    
748
<sect>Route attributes
749

    
750
<p>A filter is implicitly passed a route, and it can access its
751
attributes just like it accesses variables. Attempts to access undefined
752
attribute result in a runtime error; you can check if an attribute is
753
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
754

    
755
<descrip>
756
	<tag><m/prefix/ net</tag>
757
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
758

    
759
	<tag><m/enum/ scope</tag>
760
	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).
761

    
762
	<tag><m/int/ preference</tag>
763
	Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.)
764

    
765
	<tag><m/ip/ from</tag>
766
	The router which the route has originated from. Read-only.
767
	
768
	<tag><m/ip/ gw</tag>
769
	Next hop packets routed using this route should be forwarded to.
770

    
771
	<tag><m/string/ proto</tag>
772
	The name of the protocol which the route has been imported from. Read-only.
773

    
774
	<tag><m/enum/ source</tag>
775
	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/.
776

    
777
	<tag><m/enum/ cast</tag>
778
	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.
779

    
780
	<tag><m/enum/ dest</tag>
781
	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.
782
</descrip>
783

    
784
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
785

    
786
<sect>Other statements
787

    
788
<p>The following statements are available:
789

    
790
<descrip>
791
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
792

    
793
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
794

    
795
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
796

    
797
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
798
	Prints given expressions; useful mainly while debugging
799
	filters. The <cf/printn/ variant does not terminate the line.
800

    
801
	<tag>quitbird</tag>
802
	Terminates BIRD. Useful when debugging the filter interpreter.
803
</descrip>
804

    
805
<chapt>Protocols
806

    
807
<sect>BGP
808

    
809
<p>The Border Gateway Protocol is the routing protocol used for backbone
810
level routing in the today's Internet. Contrary to the other protocols, its convergence
811
doesn't rely on all routers following the same rules for route selection,
812
making it possible to implement any routing policy at any router in the
813
network, the only restriction being that if a router advertises a route,
814
it must accept and forward packets according to it.
815

    
816
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
817
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
818
Routers within each AS usually communicate with each other using either a interior routing
819
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
820
Boundary routers at the border of the AS communicate with their peers
821
in the neighboring AS'es via exterior BGP (eBGP).
822

    
823
<p>Each BGP router sends to its neighbors updates of the parts of its
824
routing table it wishes to export along with complete path information
825
(a list of AS'es the packet will travel through if it uses the particular
826
route) in order to avoid routing loops.
827

    
828
<p>BIRD supports all requirements of the BGP4 standard as defined in
829
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
830
It also supports the community attributes
831
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
832
capability negotiation
833
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
834
MD5 password authentication
835
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
836
route reflectors 
837
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
838
multiprotocol extensions
839
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
840
and 4B AS numbers 
841
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
842

    
843

    
844
For IPv6, it uses the standard multiprotocol extensions defined in
845
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
846
including changes described in the
847
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
848
and applied to IPv6 according to
849
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
850

    
851
<sect1>Route selection rules
852

    
853
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
854
route among multiple BGP routes with the same preference are a bit more complex
855
and they are implemented according to the following algorithm. It starts the first
856
rule, if there are more "best" routes, then it uses the second rule to choose
857
among them and so on.
858

    
859
<itemize>
860
	<item>Prefer route with the highest Local Preference attribute.
861
	<item>Prefer route with the shortest AS path.
862
	<item>Prefer IGP origin over EGP and EGP over incomplete.
863
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
864
	<item>Prefer internal routes over external ones.
865
	<item>Prefer the route with the lowest value of router ID of the
866
	advertising router.
867
</itemize>
868

    
869
<sect1>Configuration
870

    
871
<p>Each instance of the BGP corresponds to one neighboring router.
872
This allows to set routing policy and all the other parameters differently
873
for each neighbor using the following configuration parameters:
874

    
875
<descrip>
876
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
877
	contrary to other IP routers, BIRD is able to act as a router located
878
	in multiple AS'es simultaneously, but in such cases you need to tweak
879
	the BGP paths manually in the filters to get consistent behavior.)
880
	This parameter is mandatory.
881

    
882
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
883
	this instance will be talking to and what AS it's located in. Unless
884
	you use the <cf/multihop/ clause, it must be directly connected to one
885
	of your router's interfaces. In case the neighbor is in the same AS
886
	as we are, we automatically switch to iBGP. This parameter is mandatory.
887

    
888
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
889
	neighbor which is connected at most <m/number/ hops far and to which
890
	we should route via our direct neighbor with address <m/ip/.
891
	Default: switched off.
892

    
893
	<tag>next hop self</tag> Avoid calculation of the Next Hop
894
	attribute and always advertise our own source address (see
895
	below) as a next hop.  This needs to be used only occasionally
896
	to circumvent misconfigurations of other routers.
897
	Default: disabled.
898

    
899
	<tag>missing lladdr self|drop|ignore</tag>Next Hop attribute
900
	in BGP-IPv6 sometimes contains just the global IPv6 address,
901
	but sometimes it has to contain both global and link-local
902
	IPv6 addresses. This option specifies what to do if BIRD have
903
	to send both addresses but does not know link-local address.
904
	This situation might happen when routes from other protocols
905
	are exported to BGP, or when improper updates are received
906
	from BGP peers.  <cf/self/ means that BIRD advertises its own
907
	local address instead. <cf/drop/ means that BIRD skips that
908
	prefixes and logs error. <cf/ignore/ means that BIRD ignores
909
	the problem and sends just the global address (and therefore
910
	forms improper BGP update). Default: <cf/self/, unless BIRD
911
	is configured as a route server (option <cf/rs client/), in
912
	that case default is <cf/drop/, because route servers usually
913
	does not forward packets ifselves.
914
	
915
	<tag>source address <m/ip/</tag> Define local address we should use
916
	for next hop calculation. Default: the address of the local end
917
	of the interface our neighbor is connected to.
918

    
919
	<tag>password <m/string/</tag> Use this password for MD5 authentication
920
	of BGP sessions. Default: no authentication. Password has to be set by
921
	external utility (e.g. setkey(8)) on BSD systems.
922

    
923
	<tag>passive <m/switch/</tag> Standard BGP behavior is both
924
        initiating outgoing connections and accepting incoming
925
        connections. In passive mode, outgoing connections are not
926
        initiated. Default: off.
927

    
928
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
929
	a route reflection client. Default: disabled.
930

    
931
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
932
	to avoid route reflection loops. When there is one route reflector in a cluster
933
	it usually uses its router id as a cluster id, but when there are more route
934
	reflectors in a cluster, these need to be configured (using this option) to
935
	use a common cluster id. Clients in a cluster need not know their cluster
936
	id and this option is not allowed for them. Default: the same as router id.
937

    
938
	<tag>rs client</tag> Be a route server and treat the neighbor
939
	as a route server client. A route server is used as a
940
	replacement for full mesh EBGP routing in Internet exchange
941
	points in a similar way to route reflectors used in IBGP routing.
942
	BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
943
	which behaves like plain EBGP but reduces modifications to advertised route
944
	attributes to be transparent (for example does not prepend its AS number to
945
	AS PATH attribute and keep MED attribute). Default: disabled.
946

    
947
	<tag>enable route refresh <m/switch/</tag> When BGP speaker
948
	changes its import filter, it has to re-examine all routes
949
	received from its neighbor against the new filter. As these
950
	routes might not be available, there is a BGP protocol
951
	extension Route Refresh (specified in RFC 2918) that allows
952
	BGP speaker to request re-advertisment of all routes from its
953
	neighbor. This option specifies whether BIRD advertises this
954
	capability and accepts such requests. Even when disabled, BIRD
955
	can send route refresh requests. Default: on.
956

    
957
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
958
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
959
	but by disabling this option it can be persuaded not to advertise it and
960
	to maintain old-style sessions with its neighbors. This might be useful for
961
	circumventing bugs in neighbor's implementation of 4B AS extension.
962
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
963
	Default: on.
964

    
965
	<tag>capabilities <m/switch/</tag> Use capability advertisement
966
	to advertise optional capabilities. This is standard behavior
967
	for newer BGP implementations, but there might be some older
968
	BGP implementations that reject such connection attempts.
969
	When disabled (off), features that request it (4B AS support)
970
	are also disabled. Default: on, with automatic fallback to
971
	off when received capability-related error.
972

    
973
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
974
	This is not a correct behavior according to the strict interpretation
975
	of RFC 4760, but it is widespread and required by some BGP
976
	implementations (Cisco and Quagga). This option is relevant
977
	to IPv4 mode with enabled capability advertisement only. Default: on.
978

    
979
	<tag>route limit <m/number/</tag> The maximal number of routes
980
	that may be imported from the protocol. If the route limit is
981
	exceeded, the connection is closed with error. Default: no limit.
982

    
983
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
984
	locally or by the other side), disable the instance automatically
985
	and wait for an administrator to fix the problem manually. Default: off.
986

    
987
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
988
	message from the other side before considering the connection stale.
989
	Default: depends on agreement with the neighboring router, we prefer
990
	240 seconds if the other side is willing to accept it.
991

    
992
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
993
	before the routers have a chance to exchange open messages and agree
994
	on the real value. Default: 240 seconds.
995

    
996
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
997
	of two consecutive Keepalive messages. Default: One third of the hold time.
998

    
999
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
1000
	retrying a failed attempt to connect. Default: 120 seconds.
1001

    
1002
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
1003
	startup and the first attempt to connect. Default: 5 seconds.
1004

    
1005
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
1006
	failure (either local or reported by the peer) and automatic restart.
1007
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
1008
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
1009

    
1010
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
1011
	failures to treat them as a error sequence which makes the <cf/error wait time/
1012
	increase exponentially. Default: 300 seconds.
1013

    
1014
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
1015
	when deciding which BGP route is the best one. Default: on.
1016

    
1017
	<tag>prefer older <m/switch/</tag> Standard route selection algorithm
1018
	breaks ties by comparing router IDs. This changes the behavior
1019
	to prefer older routes (when both are external and from different
1020
	peer). For details, see RFC 5004. Default: off.
1021

    
1022
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
1023
	Discriminator to be used during route selection when the MED attribute
1024
	is missing. Default: 0.
1025

    
1026
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
1027
	to be used during route selection when the Local Preference attribute
1028
	is missing. Default: 0.
1029
</descrip>
1030

    
1031
<sect1>Attributes
1032

    
1033
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
1034
table below) are available on internal BGP connections only, some of them (marked
1035
with `<tt/O/') are optional.
1036

    
1037
<descrip>
1038
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
1039
	the packet will travel through when forwarded according to the particular route. In case of 
1040
	internal BGP it doesn't contain the number of the local AS.
1041

    
1042
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
1043
	selection among multiple BGP routes (see the selection rules above). It's
1044
	used as an additional metric which is propagated through the whole local AS.
1045

    
1046
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
1047
	is an optional attribute which is used on on external (inter-AS) links to
1048
	convey to an adjacent AS the optimal entry point into the local AS.
1049
	The received attribute may be also propagated over internal BGP links
1050
	(and this is default behavior). The attribute value is zeroed when a route
1051
	is exported from a routing table to a BGP instance to ensure that the attribute
1052
	received from a neighboring AS is not propagated to other neighboring ASes.
1053
	A new value might be set in the export filter of a BGP instance.
1054
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1055
	for further discussion of BGP MED attribute.
1056

    
1057
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
1058
	if the route has originated in an interior routing protocol or
1059
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
1060
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
1061
	is unknown.
1062

    
1063
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
1064
	to this destination. On internal BGP connections, it's an address of the
1065
	originating router if it's inside the local AS or a boundary router the
1066
	packet will leave the AS through if it's an exterior route, so each BGP
1067
	speaker within the AS has a chance to use the shortest interior path
1068
	possible to this point.
1069

    
1070
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
1071
	which carries no value, but the sole presence of which indicates that the route
1072
	has been aggregated from multiple routes by some router on the path from
1073
	the originator.
1074

    
1075
<!-- we don't handle aggregators right since they are of a very obscure type
1076
	<tag>bgp_aggregator</tag>
1077
-->
1078
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
1079
	with the route. Each such value is a pair (represented as a <cf/pair/ data
1080
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
1081
	the community and the second one being a per-AS identifier. There are lots
1082
	of uses of the community mechanism, but generally they are used to carry
1083
	policy information like "don't export to USA peers". As each AS can define
1084
	its own routing policy, it also has a complete freedom about which community
1085
	attributes it defines and what will their semantics be.
1086
</descrip>
1087

    
1088
<sect1>Example
1089

    
1090
<p><code>
1091
protocol bgp {
1092
	local as 65000;			     # Use a private AS number
1093
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
1094
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
1095
	export filter {			     # We use non-trivial export rules
1096
		if source = RTS_STATIC then { # Export only static routes
1097
		        # Assign our community
1098
			bgp_community.add((65000,5678));
1099
			# Artificially increase path length
1100
			# by advertising local AS number twice
1101
			if bgp_path ~ [= 65000 =] then	  
1102
				bgp_path.prepend(65000);  
1103
			accept;
1104
		}
1105
		reject;
1106
	};
1107
	import all;
1108
	source address 62.168.0.1;	# Use a non-standard source address
1109
}
1110
</code>
1111

    
1112
<sect>Device
1113

    
1114
<p>The Device protocol is not a real routing protocol.  It doesn't generate
1115
any routes and it only serves as a module for getting information about network
1116
interfaces from the kernel.
1117

    
1118
<p>Except for very unusual circumstances, you probably should include
1119
this protocol in the configuration since almost all other protocols
1120
require network interfaces to be defined for them to work with.
1121

    
1122
<sect1>Configuration
1123

    
1124
<p><descrip>
1125
	<tag>scan time <m/number/</tag> Time in seconds between two scans
1126
	of the network interface list. On systems where we are notified about
1127
	interface status changes asynchronously (such as newer versions of
1128
	Linux), we need to scan the list only in order to avoid confusion by lost
1129
	notification messages, so the default time is set to a large value.
1130

    
1131
	<tag>primary  [ "<m/mask/" ] <m/prefix/</tag>
1132
	If a network interface has more than one network address,
1133
	BIRD has to choose one of them as a primary one, because some
1134
	routing protocols (for example OSPFv2) suppose there is only
1135
	one network address per interface. By default, BIRD chooses
1136
	the lexicographically smallest address as the primary one.
1137

    
1138
	This option allows to specify which network address should be
1139
	chosen as a primary one. Network addresses that match
1140
	<m/prefix/ are preferred to non-matching addresses. If more
1141
	<cf/primary/ options are used, the first one has the highest
1142
	preference. If "<m/mask/" is specified, then such
1143
	<cf/primary/ option is relevant only to matching network
1144
	interfaces.
1145

    
1146
	In all cases, an address marked by operating system as
1147
	secondary cannot be chosen as the primary one. 
1148
</descrip>
1149

    
1150
<p>As the Device protocol doesn't generate any routes, it cannot have
1151
any attributes. Example configuration looks like this:
1152

    
1153
<p><code>
1154
protocol device {
1155
	scan time 10;		# Scan the interfaces often
1156
	primary "eth0" 192.168.1.1;
1157
	primary 192.168.0.0/16;
1158
}
1159
</code>
1160

    
1161
<sect>Direct
1162

    
1163
<p>The Direct protocol is a simple generator of device routes for all the
1164
directly connected networks according to the list of interfaces provided
1165
by the kernel via the Device protocol.
1166

    
1167
<p>It's highly recommended to include this protocol in your configuration
1168
unless you want to use BIRD as a route server or a route reflector, that is
1169
on a machine which doesn't forward packets itself and only participates in
1170
distribution of routing information.
1171

    
1172
<p>The only configurable thing about direct is what interfaces it watches:
1173

    
1174
<p><descrip>
1175
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
1176
	protocol will generate device routes for all the interfaces
1177
	available. If you want to restrict it to some subset of interfaces
1178
	(for example if you're using multiple routing tables for policy
1179
	routing and some of the policy domains don't contain all interfaces),
1180
	just use this clause.
1181
</descrip>
1182

    
1183
<p>Direct device routes don't contain any specific attributes.
1184

    
1185
<p>Example config might look like this:
1186

    
1187
<p><code>
1188
protocol direct {
1189
	interface "-arc*", "*";		# Exclude the ARCnets
1190
}
1191
</code>
1192

    
1193
<sect>Kernel
1194

    
1195
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
1196
the with other routers in the network, it performs synchronization of BIRD's routing
1197
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
1198
and from time to time it scans the kernel tables to see whether some routes have
1199
disappeared (for example due to unnoticed up/down transition of an interface)
1200
or whether an `alien' route has been added by someone else (depending on the
1201
<cf/learn/ switch, such routes are either deleted or accepted to our
1202
table).
1203

    
1204
<p>If your OS supports only a single routing table, you can configure only one
1205
instance of the Kernel protocol. If it supports multiple tables (in order to
1206
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
1207
them must be connected to a different BIRD routing table and to a different
1208
kernel table.
1209

    
1210
<sect1>Configuration
1211

    
1212
<p><descrip>
1213
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
1214
	routing tables when it exits (instead of cleaning them up).
1215
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
1216
	kernel routing table.
1217
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
1218
	routing tables by other routing daemons or by the system administrator.
1219
	This is possible only on systems which support identification of route
1220
	authorship.
1221
	<tag>kernel table <m/number/</tag> Select which kernel table should
1222
	this particular instance of the Kernel protocol work with. Available
1223
	only on systems supporting multiple routing tables.
1224
</descrip>
1225

    
1226
<p>The Kernel protocol doesn't define any route attributes.
1227
<p>A simple configuration can look this way:
1228

    
1229
<p><code>
1230
protocol kernel {
1231
	import all;
1232
	export all;
1233
}
1234
</code>
1235

    
1236
<p>Or for a system with two routing tables:
1237

    
1238
<p><code>
1239
protocol kernel {		# Primary routing table
1240
	learn;			# Learn alien routes from the kernel
1241
	persist;		# Don't remove routes on bird shutdown
1242
	scan time 10;		# Scan kernel routing table every 10 seconds
1243
	import all;
1244
	export all;
1245
}
1246

    
1247
protocol kernel {		# Secondary routing table
1248
	table auxtable;
1249
	kernel table 100;
1250
	export all;
1251
}
1252
</code>
1253

    
1254
<sect>OSPF
1255

    
1256
<sect1>Introduction
1257

    
1258
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1259
protocol. The current IPv4 version (OSPFv2) is defined
1260
in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
1261
state (a.k.a. shortest path first) protocol -- each router maintains a database
1262
describing the autonomous system's topology. Each participating router
1263
has an identical copy of the database and all routers run the same algorithm
1264
calculating a shortest path tree with themselves as a root.
1265
OSPF chooses the least cost path as the best path.
1266
(OSPFv3 - OSPF for IPv6 is not supported yet.)
1267

    
1268
<p>In OSPF, the autonomous system can be split to several areas in order
1269
to reduce the amount of resources consumed for exchanging the routing
1270
information and to protect the other areas from incorrect routing data.
1271
Topology of the area is hidden to the rest of the autonomous system.
1272

    
1273
<p>Another very important feature of OSPF is that
1274
it can keep routing information from other protocols (like Static or BGP)
1275
in its link state database as external routes. Each external route can
1276
be tagged by the advertising router, making it possible to pass additional
1277
information between routers on the boundary of the autonomous system.
1278

    
1279
<p>OSPF quickly detects topological changes in the autonomous system (such
1280
as router interface failures) and calculates new loop-free routes after a short
1281
period of convergence. Only a minimal amount of 
1282
routing traffic is involved.
1283

    
1284
<p>Each router participating in OSPF routing periodically sends Hello messages
1285
to all its interfaces. This allows neighbors to be discovered dynamically.
1286
Then the neighbors exchange theirs parts of the link state database and keep it
1287
identical by flooding updates. The flooding process is reliable and ensures
1288
that each router detects all changes.
1289

    
1290
<sect1>Configuration
1291

    
1292
<p>In the main part of configuration, there can be multiple definitions of
1293
OSPF area witch different id included. These definitions includes many other
1294
switches and multiple definitions of interfaces. Definition of interface
1295
may contain many switches and constant definitions and list of neighbors
1296
on nonbroadcast networks.
1297

    
1298
<code>
1299
protocol ospf &lt;name&gt; {
1300
	rfc1583compat &lt;switch&gt;;
1301
	tick &lt;num&gt;;
1302
	area &lt;id&gt; {
1303
		stub cost &lt;num&gt;;
1304
                networks {
1305
			&lt;prefix&gt;;
1306
			&lt;prefix&gt; hidden;
1307
		}
1308
		stubnet &lt;prefix&gt;;
1309
		stubnet &lt;prefix&gt; {
1310
			hidden &lt;switch&gt;;
1311
			summary &lt;switch&gt;;
1312
			cost &lt;num&gt;;
1313
		}
1314
		interface &lt;interface pattern&gt; {
1315
			cost &lt;num&gt;;
1316
			stub &lt;switch&gt;;
1317
			hello &lt;num&gt;;
1318
			poll &lt;num&gt;;
1319
			retransmit &lt;num&gt;;
1320
			priority &lt;num&gt;;
1321
			wait &lt;num&gt;;
1322
			dead count &lt;num&gt;;
1323
			dead &lt;num&gt;;
1324
			rx buffer [normal|large|&lt;num&gt;];
1325
			type [broadcast|nonbroadcast|pointopoint];
1326
			strict nonbroadcast &lt;switch&gt;;
1327
			authentication [none|simple|cryptographics];
1328
			password "&lt;text&gt;";
1329
			password "&lt;text&gt;" {
1330
				id &lt;num&gt;;
1331
				generate from "&lt;date&gt;";
1332
				generate to "&lt;date&gt;";
1333
				accept from "&lt;date&gt;";
1334
				accept to "&lt;date&gt;";
1335
			};
1336
			neighbors {
1337
				&lt;ip&gt;;
1338
				&lt;ip&gt; eligible;
1339
			};
1340
		};
1341
		virtual link &lt;id&gt;	{
1342
			hello &lt;num&gt;;
1343
			retransmit &lt;num&gt;;
1344
			wait &lt;num&gt;;
1345
			dead count &lt;num&gt;;
1346
			dead &lt;num&gt;;
1347
			authentication [none|simple];
1348
			password "&lt;text&gt;";
1349
		};
1350
	};
1351
}
1352
</code>
1353

    
1354
<descrip>
1355
	<tag>rfc1583compat <M>switch</M></tag>
1356
	 This option controls compatibility of routing table
1357
	 calculation with RFC 1583<htmlurl
1358
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1359
	 value is no.
1360
	
1361
	<tag>area <M>id</M></tag>
1362
	 This defines an OSPF area with given area ID (an integer or an IPv4
1363
	 address, similarly to a router ID).
1364
	 The most important area is
1365
	 the backbone (ID 0) to which every other area must be connected.
1366

    
1367
	<tag>stub cost <M>num</M></tag>
1368
	 No external (except default) routes are flooded into stub areas.
1369
         Setting this value marks area stub with defined cost of default route.
1370
	 Default value is no. (Area is not stub.)
1371

    
1372
	<tag>tick <M>num</M></tag>
1373
	 The routing table calculation and clean-up of areas' databases
1374
         is not performed when a single link state
1375
	 change arrives. To lower the CPU utilization, it's processed later
1376
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1377

    
1378
	<tag>networks { <m/set/ }</tag>
1379
         Definition of area IP ranges. This is used in summary lsa origination.
1380
	 Hidden networks are not propagated into other areas.
1381

    
1382
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
1383
	 Stub networks are networks that are not transit networks
1384
	 between OSPF routers. They are also propagated through an
1385
	 OSPF area as a part of a link state database. By default,
1386
	 BIRD generates a stub network record for each primary network
1387
	 address on each OSPF interface that does not have any OSPF
1388
	 neighbors, and also for each non-primary network address on
1389
	 each OSPF interface. This option allows to alter a set of
1390
	 stub networks propagated by this router. 
1391

    
1392
	 Each instance of this option adds a stub network with given
1393
	 network prefix to the set of propagated stub network, unless
1394
	 option <cf/hidden/ is used. It also suppresses default stub
1395
	 networks for given network prefix. When option
1396
	 <cf/summary/ is used, also default stub networks that are
1397
	 subnetworks of given stub network are suppressed. This might
1398
	 be used, for example, to aggregate generated stub networks.
1399
	 
1400
	<tag>interface <M>pattern</M></tag>
1401
	 Defines that the specified interfaces belong to the area being defined.
1402
	 See <ref id="dsc-iface" name="interface"> common option for detailed description.
1403

    
1404
	<tag>virtual link <M>id</M></tag>
1405
	 Virtual link to router with the router id. Virtual link acts as a
1406
         point-to-point interface belonging to backbone. The actual area is
1407
         used as transport area. This item cannot be in the backbone.
1408

    
1409
	<tag>cost <M>num</M></tag>
1410
	 Specifies output cost (metric) of an interface. Default value is 10.
1411

    
1412
	<tag>stub <M>switch</M></tag>
1413
	 If set to interface it does not listen to any packet and does not send
1414
	 any hello. Default value is no.
1415

    
1416
	<tag>hello <M>num</M></tag>
1417
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1418
	 routers on the same network need to have the same hello interval.
1419
	 Default value is 10.
1420

    
1421
	<tag>poll <M>num</M></tag>
1422
	 Specifies interval in seconds between sending of Hello messages for
1423
	 some neighbors on NBMA network. Default value is 20.
1424

    
1425
	<tag>retransmit <M>num</M></tag>
1426
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1427
	 Default value is 5.
1428

    
1429
        <tag>priority <M>num</M></tag>
1430
	 On every multiple access network (e.g., the Ethernet) Designed Router
1431
	 and Backup Designed router are elected. These routers have some
1432
	 special functions in the flooding process. Higher priority increases
1433
	 preferences in this election. Routers with priority 0 are not
1434
	 eligible. Default value is 1.
1435

    
1436
	<tag>wait <M>num</M></tag>
1437
	 After start, router waits for the specified number of seconds between starting
1438
	 election and building adjacency. Default value is 40.
1439
	 
1440
	<tag>dead count <M>num</M></tag>
1441
	 When the router does not receive any messages from a neighbor in
1442
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1443

    
1444
	<tag>dead <M>num</M></tag>
1445
	 When the router does not receive any messages from a neighbor in
1446
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1447
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1448

    
1449
	<tag>rx buffer <M>num</M></tag>
1450
	 This sets the size of buffer used for receiving packets. The buffer should
1451
	 be bigger than maximal size of any packets. Value NORMAL (default)
1452
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1453

    
1454
	<tag>type broadcast</tag>
1455
	 BIRD detects a type of a connected network automatically, but sometimes it's
1456
	 convenient to force use of a different type manually.
1457
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1458
	 (a single packet for all the neighbors).
1459

    
1460
	<tag>type pointopoint</tag>
1461
	 Point-to-point networks connect just 2 routers together. No election
1462
	 is performed there which reduces the number of messages sent.
1463

    
1464
	<tag>type nonbroadcast</tag>
1465
	 On nonbroadcast networks, the packets are sent to each neighbor
1466
	 separately because of lack of multicast capabilities.
1467

    
1468
	<tag>strict nonbroadcast <M>switch</M></tag>
1469
	 If set, don't send hello to any undefined neighbor. This switch
1470
	 is ignored on on any non-NBMA network. Default is No.
1471

    
1472
	<tag>authentication none</tag>
1473
	 No passwords are sent in OSPF packets. This is the default value.
1474

    
1475
	<tag>authentication simple</tag>
1476
	 Every packet carries 8 bytes of password. Received packets
1477
	 lacking this password are ignored. This authentication mechanism is
1478
	 very weak.
1479

    
1480
	<tag>authentication cryptographic</tag>
1481
	 16-byte long MD5 digest is appended to every packet. For the digest
1482
         generation 16-byte long passwords are used. Those passwords are 
1483
         not sent via network, so this mechanismus is quite secure.
1484
         Packets can still be read by an attacker.
1485

    
1486
	<tag>password "<M>text</M>"</tag>
1487
	 An 8-byte or 16-byte password used for authentication.
1488
	 See <ref id="dsc-pass" name="password"> common option for detailed description.
1489

    
1490
	<tag>neighbors { <m/set/ } </tag>
1491
	 A set of neighbors to which Hello messages on nonbroadcast networks
1492
	 are to be sent. Some of them could be marked as eligible.
1493

    
1494
</descrip>
1495

    
1496
<sect1>Attributes
1497

    
1498
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1499
Metric is ranging from 1 to infinity (65535).
1500
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1501
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1502
<cf/metric of type 2/ is always longer
1503
than any <cf/metric of type 1/ or any <cf/internal metric/.
1504
If you specify both metrics only metric1 is used.
1505
Each external route can also carry a <cf/tag/ which is a 32-bit
1506
integer which is used when exporting routes to other protocols;
1507
otherwise, it doesn't affect routing inside the OSPF domain at all.
1508
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1509

    
1510
<sect1>Example
1511

    
1512
<p>
1513

    
1514
<code>
1515
protocol ospf MyOSPF {
1516
        rfc1583compatibility yes;
1517
        tick 2;
1518
	export filter {
1519
		if source = RTS_BGP then {
1520
			ospf_metric1 = 100;
1521
			accept;
1522
		}
1523
		reject;
1524
	};
1525
	area 0.0.0.0 {
1526
		interface "eth*" {
1527
			cost 11;
1528
			hello 15;
1529
			priority 100;
1530
			retransmit 7;
1531
			authentication simple;
1532
			password "aaa";
1533
		};
1534
		interface "ppp*" {
1535
			cost 100;
1536
			authentication cryptographic;
1537
			password "abc" {
1538
				id 1;
1539
				generate to "22-04-2003 11:00:06";
1540
				accept from "17-01-2001 12:01:05";
1541
			};
1542
			password "def" {
1543
				id 2;
1544
				generate to "22-07-2005 17:03:21";
1545
				accept from "22-02-2001 11:34:06";
1546
			};
1547
		};
1548
		interface "arc0" {
1549
			cost 10;
1550
			stub yes;
1551
		};
1552
		interface "arc1";
1553
	};
1554
	area 120 {
1555
		stub yes;
1556
		networks {
1557
			172.16.1.0/24;
1558
			172.16.2.0/24 hidden;
1559
		}
1560
		interface "-arc0" , "arc*" {
1561
			type nonbroadcast;
1562
			authentication none;
1563
			strict nonbroadcast yes;
1564
			wait 120;
1565
			poll 40;
1566
			dead count 8;
1567
			neighbors {
1568
				192.168.120.1 eligible;
1569
				192.168.120.2;
1570
				192.168.120.10;
1571
			};
1572
		};
1573
	};
1574
}
1575
</code>
1576

    
1577
<sect>Pipe
1578

    
1579
<sect1>Introduction
1580

    
1581
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1582
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1583
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1584
and vice versa, depending on what's allowed by the filters. Export filters control export
1585
of routes from the primary table to the secondary one, import filters control the opposite
1586
direction.
1587

    
1588
<p>The Pipe protocol may work in the opaque mode or in the transparent
1589
mode. In the opaque mode, the Pipe protocol retransmits optimal route
1590
from one table to the other table in a similar way like other
1591
protocols send and receive routes. Retransmitted route will have the
1592
source set to the Pipe protocol, which may limit access to protocol
1593
specific route attributes. The opaque mode is a default mode.
1594

    
1595
<p>In transparent mode, the Pipe protocol retransmits all routes from
1596
one table to the other table, retaining their original source and
1597
attributes.  If import and export filters are set to accept, then both
1598
tables would have the same content. The mode can be set by
1599
<tt/mode/ option.
1600

    
1601
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1602
where handling of a single packet doesn't depend only on its destination address, but also
1603
on its source address, source interface, protocol type and other similar parameters.
1604
In many systems (Linux being a good example), the kernel allows to enforce routing policies
1605
by defining routing rules which choose one of several routing tables to be used for a packet
1606
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1607
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1608
connect them to the kernel ones, use filters to control which routes appear in which tables
1609
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1610
another one.
1611

    
1612
<sect1>Configuration
1613

    
1614
<p><descrip>
1615
	<tag>peer table <m/table/</tag> Defines secondary routing table to connect to. The
1616
	primary one is selected by the <cf/table/ keyword.
1617

    
1618
	<tag>mode opaque|transparent</tag> Specifies the mode for the pipe to work in. Default is opaque.
1619
</descrip>
1620

    
1621
<sect1>Attributes
1622

    
1623
<p>The Pipe protocol doesn't define any route attributes.
1624

    
1625
<sect1>Example
1626

    
1627
<p>Let's consider a router which serves as a boundary router of two different autonomous
1628
systems, each of them connected to a subset of interfaces of the router, having its own
1629
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1630
of outage of its own exterior line.
1631

    
1632
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1633
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1634
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1635
and similarly for the second AS. Thus we have split our router to two logical routers,
1636
each one acting on its own routing table, having its own routing protocols on its own
1637
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1638
the routes between the tables through a Pipe protocol while decreasing their preferences
1639
and correcting their BGP paths to reflect the AS boundary crossing.
1640

    
1641
<code>
1642
table as1;				# Define the tables
1643
table as2;
1644

    
1645
protocol kernel kern1 {			# Synchronize them with the kernel
1646
	table as1;
1647
	kernel table 1;
1648
}
1649

    
1650
protocol kernel kern2 {
1651
	table as2;
1652
	kernel table 2;
1653
}
1654

    
1655
protocol bgp bgp1 {			# The outside connections
1656
	table as1;
1657
	local as 1;
1658
	neighbor 192.168.0.1 as 1001;
1659
	export all;
1660
	import all;
1661
}
1662

    
1663
protocol bgp bgp2 {
1664
	table as2;
1665
	local as 2;
1666
	neighbor 10.0.0.1 as 1002;
1667
	export all;
1668
	import all;
1669
}
1670

    
1671
protocol pipe {				# The Pipe
1672
	table as1;
1673
	peer table as2;
1674
	export filter {
1675
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1676
			if preference>10 then preference = preference-10;
1677
			if source=RTS_BGP then bgp_path.prepend(1);
1678
			accept;
1679
		}
1680
		reject;
1681
	};
1682
	import filter {
1683
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1684
			if preference>10 then preference = preference-10;
1685
			if source=RTS_BGP then bgp_path.prepend(2);
1686
			accept;
1687
		}
1688
		reject;
1689
	};
1690
}
1691
</code>
1692

    
1693
<sect>RIP
1694

    
1695
<sect1>Introduction
1696

    
1697
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1698
distances to all networks it can reach. When a router hears distance to another network, it increments
1699
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1700
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1701
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1702
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1703
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1704
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1705
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1706
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1707
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
1708
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1709

    
1710
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1711
convergence, big network load and inability to handle larger networks
1712
makes it pretty much obsolete in IPv4 world. (It is still usable on
1713
very small networks.) It is widely used in IPv6 networks,
1714
because there are no good implementations of OSPFv3.
1715

    
1716
<sect1>Configuration
1717

    
1718
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1719

    
1720
<descrip>
1721
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1722
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1723
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1724
	  hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf>
1725
	  section. Default: none.
1726

    
1727
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1728
	  be honored. (Always, when sent from a  host on a directly connected
1729
	  network or never.) Routing table updates are honored only from
1730
	  neighbors, that is not configurable. Default: never.
1731
</descrip>
1732

    
1733
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1734
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1735
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1736
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1737
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1738
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1739
interface but not listen to it.
1740

    
1741
<p>The following options generally override behavior specified in RFC. If you use any of these
1742
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1743
other than equally configured BIRD. I have warned you.
1744

    
1745
<descrip>
1746
	<tag>port <M>number</M></tag>
1747
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1748
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1749

    
1750
	<tag>infinity <M>number</M></tag>
1751
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1752
	  even slower.
1753

    
1754
	<tag>period <M>number</M>
1755
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1756
	  number will mean faster convergence but bigger network
1757
	  load. Do not use values lower than 10.
1758

    
1759
	<tag>timeout time <M>number</M>
1760
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1761

    
1762
	<tag>garbage time <M>number</M>
1763
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1764
</descrip>
1765

    
1766
<sect1>Attributes
1767

    
1768
<p>RIP defines two route attributes:
1769

    
1770
<descrip>
1771
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1772
	When routes from different RIP instances are available and all of them have the same
1773
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1774
	When importing a non-RIP route, the metric defaults to 5.
1775

    
1776
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1777
	to carry additional information with the route (for example, an originating AS number
1778
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1779
</descrip>
1780

    
1781
<sect1>Example
1782

    
1783
<p><code>
1784
protocol rip MyRIP_test {
1785
        debug all;
1786
        port 1520;
1787
        period 10;
1788
        garbage time 60;
1789
        interface "eth0" { metric 3; mode multicast; };
1790
	interface "eth*" { metric 2; mode broadcast; };
1791
        honor neighbor;
1792
        authentication none;
1793
        import filter { print "importing"; accept; };
1794
        export filter { print "exporting"; accept; };
1795
}
1796
</code>
1797

    
1798
<sect>Static
1799

    
1800
<p>The Static protocol doesn't communicate with other routers in the network,
1801
but instead it allows you to define routes manually. This is often used for
1802
specifying how to forward packets to parts of the network which don't use
1803
dynamic routing at all and also for defining sink routes (i.e., those
1804
telling to return packets as undeliverable if they are in your IP block,
1805
you don't have any specific destination for them and you don't want to send
1806
them out through the default route to prevent routing loops).
1807

    
1808
<p>There are three types of static routes: `classical' routes telling to
1809
forward packets to a neighboring router, device routes specifying forwarding
1810
to hosts on a directly connected network and special routes (sink, blackhole
1811
etc.) which specify a special action to be done instead of forwarding the
1812
packet.
1813

    
1814
<p>When the particular destination is not available (the interface is down or
1815
the next hop of the route is not a neighbor at the moment), Static just
1816
uninstalls the route from the table it is connected to and adds it again as soon
1817
as the destination becomes adjacent again.
1818

    
1819
<p>The Static protocol has no configuration options. Instead, the
1820
definition of the protocol contains a list of static routes:
1821

    
1822
<descrip>
1823
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1824
	a neighboring router.
1825
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1826
	route through an interface to hosts on a directly connected network.
1827
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1828
	specifying to drop the packet, return it as unreachable or return
1829
	it as administratively prohibited.
1830
</descrip>
1831

    
1832
<p>Static routes have no specific attributes.
1833

    
1834
<p>Example static config might look like this:
1835

    
1836
<p><code>
1837
protocol static {
1838
	table testable;			 # Connect to a non-default routing table
1839
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1840
	route 62.168.0.0/25 reject;	 # Sink route
1841
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1842
}
1843
</code>
1844

    
1845
<chapt>Conclusions
1846

    
1847
<sect>Future work
1848

    
1849
<p>Although BIRD supports all the commonly used routing protocols,
1850
there are still some features which would surely deserve to be
1851
implemented in future versions of BIRD:
1852

    
1853
<itemize>
1854
<item>OSPF for IPv6 networks
1855
<item>OSPF NSSA areas and opaque LSA's
1856
<item>Route aggregation and flap dampening
1857
<item>Generation of IPv6 router advertisements
1858
<item>Multipath routes
1859
<item>Multicast routing protocols
1860
<item>Ports to other systems
1861
</itemize>
1862

    
1863
<sect>Getting more help
1864

    
1865
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1866
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1867
where you can share your experiences with the other users and consult
1868
your problems with the authors. To subscribe to the list, just send a
1869
<tt/subscribe bird-users/ command in a body of a mail to
1870
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1871
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1872

    
1873
<p>BIRD is a relatively young system and it probably contains some
1874
bugs. You can report any problems to the bird-users list and the authors
1875
will be glad to solve them, but before you do so,
1876
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1877
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1878
which fixes the bug is always welcome as an attachment.)
1879

    
1880
<p>If you want to understand what is going inside, Internet standards are
1881
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">).
1882

    
1883
<p><it/Good luck!/
1884

    
1885
</book>
1886

    
1887
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