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<!doctype birddoc system>
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<!--
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	BIRD documentation
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This documentation can have 4 forms: sgml (this is master copy), html,
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ASCII text and dvi/postscript (generated from sgml using
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sgmltools). You should always edit master copy.
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This is a slightly modified linuxdoc dtd.  Anything in <descrip> tags is considered definition of
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configuration primitives, <cf> is fragment of configuration within normal text, <m> is
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"meta" information within fragment of configuration - something in config which is not keyword.
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    (set-fill-column 100)
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    Copyright 1999,2000 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later.
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 -->
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<book>
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<title>BIRD User's Guide
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<author>
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Ondrej Filip <it/&lt;feela@network.cz&gt;/,
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Pavel Machek <it/&lt;pavel@ucw.cz&gt;/,
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Martin Mares <it/&lt;mj@ucw.cz&gt;/
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</author>
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<abstract>
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This document contains user documentation for the BIRD Internet Routing Daemon project.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<chapt>Introduction
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<sect>What is BIRD
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<p><label id="intro">
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The name `BIRD' is actually an acronym standing for `BIRD Internet Routing Daemon'.
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Let's take a closer look at the meaning of the name:
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<p><em/BIRD/: Well, we think we have already explained that. It's an acronym standing
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for `BIRD Internet Routing Daemon', you remember, don't you? :-)
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<p><em/Internet Routing/: It's a program (well, a daemon, as you are going to discover in a moment)
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which works as a dynamic router in an Internet type network (that is, in a network running either
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the IPv4 or the IPv6 protocol). Routers are devices which forward packets between interconnected
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networks in order to allow hosts not connected directly to the same local area network to
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communicate with each other. They also communicate with the other routers in the Internet to discover
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the topology of the network which allows them to find optimal (in terms of some metric) rules for
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forwarding of packets (which are called routing tables) and to adapt themselves to the
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changing conditions such as outages of network links, building of new connections and so on. Most of
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these routers are costly dedicated devices running obscure firmware which is hard to configure and
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not open to any changes (on the other hand, their special hardware design allows them to keep up with lots of high-speed network interfaces, better than general-purpose computer does). Fortunately, most operating systems of the UNIX family allow an ordinary 
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computer to act as a router and forward packets belonging to the other hosts, but only according to
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a statically configured table.
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<p>A <em/Routing Daemon/ is in UNIX terminology a non-interactive program running on
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background which does the dynamic part of Internet routing, that is it communicates
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with the other routers, calculates routing tables and sends them to the OS kernel
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which does the actual packet forwarding. There already exist other such routing
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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>-s <m/name of communication socket/</tag>
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	use given filename for a  socket for communications with the client, default is <it/prefix/<file>/var/run/bird.ctl</file>.
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</descrip>
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<p>BIRD writes messages about its work to log files or syslog (according to config).
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<chapt>About routing tables
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<p>BIRD has one or more routing tables which may or may not be
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synchronized with OS kernel and which may or may not be synchronized with
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each other (see the Pipe protocol). Each routing table contains a list of
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known routes. Each route consists of:
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<itemize>
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	<item>network prefix this route is for (network address and prefix length -- the number of bits forming the network part of the address; also known as a netmask)
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	<item>preference of this route
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	<item>IP address of router which told us about this route
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	<item>IP address of router we should forward the packets to
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	using this route
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	<item>other attributes common to all routes
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	<item>dynamic attributes defined by protocols which may or
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	may not be present (typically protocol metrics)
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</itemize>
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Routing table maintains multiple entries
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for a network, but at most one entry for one network and one
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protocol. The entry with the highest preference is used for routing (we
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will call such an entry the <it/selected route/). If
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there are more entries with the same preference and they are from the same
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protocol, the protocol decides (typically according to metrics). If they aren't,
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an internal ordering is used to break the tie. You can
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get the list of route attributes in the Route attributes section.
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<p>Each protocol is connected to a routing table through two filters
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which can accept, reject and modify the routes. An <it/export/
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filter checks routes passed from the routing table to the protocol,
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an <it/import/ filter checks routes in the opposite direction.
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When the routing table gets a route from a protocol, it recalculates
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the selected route and broadcasts it to all protocols connected to
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the table. The protocols typically send the update to other routers
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in the network.
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<chapt>Configuration
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<sect>Introduction
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<p>BIRD is configured using a text configuration file. Upon startup, BIRD reads <it/prefix/<file>/etc/bird.conf</file> (unless the
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<tt/-c/ command line option is given). Configuration may be changed at user's request: if you modify
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the config file and then signal BIRD with <tt/SIGHUP/, it will adjust to the new
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config. Then there's the client
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which allows you to talk with BIRD in an extensive way.
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<p>In the config, everything on a line after <cf/#/ or inside <cf>/*
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*/</cf> is a comment, whitespace characters are treated as a single space. If there's a variable number of options, they are grouped using
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the <cf/{ }/ brackets. Each option is terminated by a <cf/;/. Configuration
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is case sensitive.
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<p>Here is an example of a simple config file. It enables
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synchronization of routing tables with OS kernel, scans for 
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new network interfaces every 10 seconds and runs RIP on all network interfaces found.
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<code>
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protocol kernel {
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	persist;		# Don't remove routes on BIRD shutdown
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	scan time 20;		# Scan kernel routing table every 20 seconds
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	export all;		# Default is export none
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}
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protocol device {
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	scan time 10;		# Scan interfaces every 10 seconds
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}
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protocol rip {
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	export all;
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	import all;
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}
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</code>
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<sect>Global options
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<p><descrip>
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	<tag>log "<m/filename/"|syslog|stderr all|{ <m/list of classes/ }</tag> 
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	Set logging of messages having the given class (either <cf/all/ or <cf/{
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	error, trace }/ etc.) into selected destination. Classes are:
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	<cf/info/, <cf/warning/, <cf/error/ and <cf/fatal/ for messages about local problems,
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	<cf/debug/ for debugging messages, 
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	<cf/trace/ when you want to know what happens in the network, 
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	<cf/remote/ for messages about misbehavior of remote machines, 
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	<cf/auth/ about authentication failures,
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	<cf/bug/ for internal BIRD bugs. You may specify more than one <cf/log/ line to establish logging to multiple
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	destinations. Default: log everything to the system log.
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	<tag>debug protocols all|off|{ states, routes, filters, interfaces, events, packets }</tag>
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	Set global defaults of protocol debugging options. See <cf/debug/ in the following section. Default: off.
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	<tag>debug commands <m/number/</tag>
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	Control logging of client connections (0 for no logging, 1 for
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	logging of connects and disconnects, 2 and higher for logging of
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	all client commands). Default: 0.
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	<tag>filter <m/name local variables/{ <m/commands/ }</tag> Define a filter. You can learn more about filters
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	in the following chapter. 
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	<tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag> Define a function. You can learn more
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	about functions in the following chapter.
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	<tag>protocol rip|ospf|bgp|... <m/[name]/ { <m>protocol options</m> }</tag> Define a protocol
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	instance called <cf><m/name/</cf> (or with a name like "rip5" generated automatically if you don't specify any <cf><m/name/</cf>). You can learn more
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	about configuring protocols in their own chapters. You can run more than one instance of
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	most protocols (like RIP or BGP). By default, no instances are configured.
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	<tag>define <m/constant/ = (<m/expression/)|<m/number/|<m/IP address/</tag> Define a constant. You can use it later in every place
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	you could use a simple integer or an IP address.
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	<tag>router id <m/IPv4 address/</tag> Set BIRD's router ID. It's a world-wide unique identification of your router, usually one of router's IPv4 addresses. Default: in IPv4 version, the lowest IP address of a non-loopback interface. In IPv6 version, this option is mandatory. 
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	<tag>table <m/name/</tag> Create a new routing table. The default
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	routing table is created implicitly, other routing tables have
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	to be added by this command.
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	<tag>eval <m/expr/</tag> Evaluates given filter expression. It
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	is used by us for testing of filters.
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</descrip>
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<sect>Protocol options
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<p>For each protocol instance, you can configure a bunch of options.
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Some of them (those described in this section) are generic, some are
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specific to the protocol (see sections talking about the protocols).
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<p>Several options use a <cf><m/switch/</cf> argument. It can be either
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<cf/on/, <cf/yes/ or a numeric expression with a non-zero value for the
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option to be enabled or <cf/off/, <cf/no/ or a numeric expression evaluating
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to zero to disable it. An empty <cf><m/switch/</cf> is equivalent to <cf/on/
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("silence means agreement").
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<descrip>
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	<tag>preference <m/expr/</tag> Sets the preference of routes generated by this protocol. Default: protocol dependent.
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	<tag>disabled <m/switch/</tag> Disables the protocol. You can change the disable/enable status from the command
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	line interface without needing to touch the configuration. Disabled protocols are not activated. Default: protocol is enabled.
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	<tag>debug all|off|{ states, routes, filters, interfaces, events, packets }</tag>
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	Set protocol debugging options. If asked, each protocol is capable of
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	writing trace messages about its work to the log (with category
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	<cf/trace/). You can either request printing of <cf/all/ trace messages
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	or only of the types selected: <cf/states/ for protocol state changes
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	(protocol going up, down, starting, stopping etc.),
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	<cf/routes/ for routes exchanged with the routing table,
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	<cf/filters/ for details on route filtering,
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	<cf/interfaces/ for interface change events sent to the protocol,
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	<cf/events/ for events internal to the protocol and
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	<cf/packets/ for packets sent and received by the protocol. Default: off.
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	<tag>import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag> 
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	Specify a filter to be used for filtering routes coming from the protocol to the routing table. <cf/all/ is shorthand for <cf/where true/ and <cf/none/ is shorthand for <cf/where false/. Default: <cf/all/.
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	<tag>export <m/filter/</tag> This is similar to the <cf>import</cf> keyword, except that it
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	works in the direction from the routing table to the protocol. Default: <cf/none/.
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	<tag>table <m/name/</tag> Connect this protocol to a non-default routing table.
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</descrip>
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<p>There are several options that give sense only with certain protocols:
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<descrip>
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	<tag>passwords { password "<m/password/" from <m/time/ to <m/time/ passive <m/time/ id
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	<m/num/ [...] }</tag> Specifies passwords to be used with this protocol. <cf>Passive <m/time/</cf> is
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	time from which the password is not used for sending, but it is recognized on reception. <cf/id/ is password ID as needed by
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	certain protocols. Format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
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	<tag>interface "<m/mask/"|<m/prefix/ [ { <m/option/ ; [...] } ]</tag> Specifies which
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	interfaces is this protocol active on and allows you to set options on a
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	per-interface basis. Mask is specified as in shell-like patterns, thus <cf>interface
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	"*" { mode broadcast; };</cf> will start the protocol on all interfaces with <cf>mode
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	broadcast;</cf> option. If the first character of mask is <cf/-/, such interfaces are
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	excluded. Masks are parsed left-to-right, thus <cf/interface "-eth*", "*";/ means all but
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	the ethernets. Default: none.
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</descrip>
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<chapt>Remote control
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<p>You can use the command-line client <file>birdc</file> to talk with
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a running BIRD. Communication is done using a <file/bird.ctl/ UNIX domain
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socket (unless changed with the <tt/-s/ option given to both the server and
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the client). The commands can perform simple actions such as enabling/disabling
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of protocols, telling BIRD to show various information, telling it to
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show routing table filtered by filter, or asking BIRD to
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reconfigure. Press <tt/?/ at any time to get online help. Option
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<tt/-v/ can be passed to the client, to make it dump numeric return
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codes along with the messages. You do not necessarily need to use <file/birdc/ to talk to BIRD, your
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own applications could do that, too -- the format of communication between
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BIRD and <file/birdc/ is stable (see the programmer's documentation).
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<p>Here is a brief list of supported functions:
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<descrip>
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	<tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
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	Dump contents of internal data structures to the debugging output.
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	<tag>show status</tag>
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	Show router status, that is BIRD version, uptime and time from last reconfiguration.
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	<tag>show protocols [all]</tag>
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	Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified.
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	<tag>show ospf [interface|neighbors] [<m/name/] ["<m/interface/"]</tag>
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	Show detailed information about OSPF protocol, possibly giving a verbose list of interfaces and neighbors. The <m/name/ of the protocol instance can be omitted if there exists only a single instance.
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	<tag>show static [<m/name/]</tag>
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	Show detailed information about static routes. The <m/name/ of the protocol instance can be omitted if there exists only a single instance.
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	<tag>show interfaces [summary]</tag>
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	Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. 
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	<tag>show symbols</tag>
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	Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).
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	<tag>show route [[for] <m/prefix/|<m/IP/] [table <m/sym/] [filter <m/f/|where <m/c/] [(import|preimport) <m/p/] [<m/options/]</tag>
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	Show contents of a routing table (by default of the main one),
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	that is routes, their metrics and (in case the <cf/all/ switch is given)
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	all their attributes.
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	<p>You can specify a <m/prefix/ if you want to print routes for a
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	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
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	the entry which will be used for forwarding of packets to the given
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	destination. By default, all routes for each network are printed with
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	the selected one at the top, unless <cf/primary/ is given in which case
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	only the selected route is shown.
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	<p>You can also ask for printing only routes processed and accepted by
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	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
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	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
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	The <cf/import/ and <cf/preimport/ switches ask for printing of entries
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        that are imported to the specified protocol. With <cf/preimport/, the
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	import filter of the protocol is skipped.
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	<p>The <cf/stats/ switch requests showing of route statistics (the
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	number of networks, number of routes before and after filtering). If
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	you use <cf/count/ instead, only the statistics will be printed.
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	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
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	Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances.
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	<tag>configure ["<m/config file/"]</tag>
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	Reload configuration from a given file.
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	<tag/down/
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	Shut BIRD down.
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	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
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	Control protocol debugging.
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</descrip>
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<chapt>Filters
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<sect>Introduction
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<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
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two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
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being passed between protocols and routing tables. The filter language contains control structures such
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as if's and switches, but it allows no loops. An example of a filter using many features can be found in <file>filter/test.conf</file>. 
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<p>Filter gets the route, looks at its attributes and
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modifies some of them if it wishes. At the end, it decides whether to
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pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
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like this:
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<code>
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filter not_too_far
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int var;
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{
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	if defined( rip_metric ) then
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		var = rip_metric;
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	else {
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		var = 1;
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		rip_metric = 1;
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	}
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	if rip_metric &gt; 10 then
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		reject "RIP metric is too big";
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	else
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		accept "ok";
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}
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</code>
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<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
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the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
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<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
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<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
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several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
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you want to make a bigger block of code conditional.
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<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
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over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
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look like this:
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<code>
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function name ()
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int local_variable;
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{
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	local_variable = 5;
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}
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function with_parameters (int parameter)
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{
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	print parameter;
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}
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</code>
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<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
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variables in nested blocks. Functions are called like in C: <cf>name();
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with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
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command. Returning a value exits from current function (this is similar to C).
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<p>Filters are declared in a way similar to functions except they can't have explicit
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parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
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to any functions called. The filter must terminate with either
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<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
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is rejected. 
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<p>A nice trick to debug filters is to use <cf>show route filter
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<m/name/</cf> from the command line client. An example session might look
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like:
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<code>
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pavel@bug:~/bird$ ./birdc -s bird.ctl
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BIRD 0.0.0 ready.
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bird> show route
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10.0.0.0/8         dev eth0 [direct1 23:21] (240)
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195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
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127.0.0.0/8        dev lo [direct1 23:21] (240)
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bird> show route ?
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show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
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bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
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127.0.0.0/8        dev lo [direct1 23:21] (240)
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bird>
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</code>
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<sect>Data types
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<p>Each variable and each value has certain type. Booleans, integers and enums are
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incompatible with each other (that is to prevent you from shooting in the foot).
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<descrip>
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	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
481
	  <cf/false/. Boolean is the only type you can use in <cf/if/
482
	  statements.
483

    
484
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
485
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
486

    
487
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
488
	  65535. Literals of this type is written as <cf/(1234,5678)/.
489

    
490
	<tag/string/ This is a string of characters. There are no ways to modify strings in
491
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
492
	  such variables, but you can't concatenate two strings. String literals
493
	  are written as <cf/"This is a string constant"/.
494

    
495
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
496
	  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>
497
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
498
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
499

    
500
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
501
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
502
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
503
	  operators on prefixes:
504
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
505
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
506

    
507
	<tag/int|ip|prefix|pair|enum set/
508
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
509
	  but you can't modify them. Literals of type <cf>set int</cf> look like <cf>
510
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
511
	  sets. Sets of prefixes are special: you can specify which prefix lengths should match them by
512
	  using <cf>[ 1.0.0.0/8+, 2.0.0.0/8-, 3.0.0.0/8{5,6} ]</cf>. <cf>3.0.0.0/8{5,6}</cf> matches
513
	  prefixes <cf/3.X.X.X/ whose prefix length is 5 to 6. <cf><m>address</m>/<m>num</m>+</cf> is a shorthand for <cf><m>address</m>/{0,<m/num/}</cf>,
514
	  <cf><m>address</m>/<m/num/-</cf> is a shorthand for <cf><m>address</m>/{0,<m/num-1/}</cf>. For example,
515
	  <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{ 15 , 17 } ]</cf> is true, but
516
	  <cf>1.0.0.0/8 &tilde; [ 1.0.0.0/8- ]</cf> is false.
517

    
518
	<tag/enum/
519
	  Enumeration types are fixed sets of possibilities. You can't define your own
520
	  variables of such type, but some route attributes are of enumeration
521
	  type. Enumeration types are incompatible with each other.
522

    
523
	<tag/bgppath/
524
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
525

    
526
	<tag/bgpmask/
527
	  BGP masks are patterns used for BGP path matching
528
	  (using <cf>path &tilde; /2 3 5 ?/</cf> syntax). The masks
529
	  resemble wildcard patterns as used by UNIX shells. Autonomous
530
	  system numbers match themselves, <cf/?/ matches any (even empty)
531
	  sequence of arbitrary AS numbers (<cf/*/ hasn't been chosen, because
532
	  <cf>/*</cf> starts a comment). For example:
533
	  <tt>/4 3 2 1/ &tilde; /? 4 3 ?/</tt> is true, but 
534
	  <tt>/4 3 2 1/ &tilde; /? 4 5 ?/</tt> is false.
535
	<tag/clist/ 
536
	  Community list is similar to set of pairs,
537
	  except that unlike other sets, it can be modified.
538
	  There exist no literals of this type.
539

    
540
</descrip>
541

    
542
<sect>Operators
543

    
544
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
545
<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;/). 
546
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
547
used on element and set of elements of the same type (returning true if element is contained in the given set), or on IP and prefix (returning true if IP is within the range defined by that prefix), or on
548
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).
549

    
550

    
551
<sect>Control structures
552

    
553
<p>Filters support two control structures: conditions and case switches. 
554

    
555
<p>Syntax of a condition is: <cf>if
556
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
557
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
558
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.
559

    
560
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
561
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
562
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
563
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
564
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.
565

    
566
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
567

    
568
<code>
569
case arg1 {
570
	2: print "two"; print "I can do more commands without {}";
571
	3 .. 5: print "three to five";
572
	else: print "something else";
573
}
574

    
575
if 1234 = i then printn "."; else { 
576
  print "not 1234"; 
577
  print "You need {} around multiple commands"; 
578
}
579
</code>
580

    
581
<sect>Route attributes
582

    
583
<p>A filter is implicitly passed a route, and it can access its
584
attributes just like it accesses variables. Attempts to access undefined
585
attribute result in a runtime error; you can check if an attribute is
586
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
587

    
588
<descrip>
589
	<tag><m/prefix/ net</tag>
590
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
591

    
592
	<tag><m/enum/ scope</tag>
593
	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).
594

    
595
	<tag><m/int/ preference</tag>
596
	Preference of the route. (See the chapter about routing tables.)
597

    
598
	<tag><m/ip/ from</tag>
599
	The router which the route has originated from. Read-only.
600
	
601
	<tag><m/ip/ gw</tag>
602
	Next hop packets routed using this route should be forwarded to.
603

    
604
	<tag><m/enum/ source</tag>
605
	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/.
606

    
607
	<tag><m/enum/ cast</tag>
608
	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.
609

    
610
	<tag><m/enum/ dest</tag>
611
	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.
612
</descrip>
613

    
614
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
615

    
616
<sect>Other statements
617

    
618
<p>The following statements are available:
619

    
620
<descrip>
621
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
622

    
623
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
624

    
625
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
626

    
627
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
628
	Prints given expressions; useful mainly while debugging
629
	filters. The <cf/printn/ variant does not terminate the line.
630

    
631
	<tag>quitbird</tag>
632
	Terminates BIRD. Useful when debugging the filter interpreter.
633
</descrip>
634

    
635
<chapt>Protocols
636

    
637
<sect>BGP
638

    
639
<p>The Border Gateway Protocol is the routing protocol used for backbone
640
level routing in the today's Internet. Contrary to the other protocols, its convergence
641
doesn't rely on all routers following the same rules for route selection,
642
making it possible to implement any routing policy at any router in the
643
network, the only restriction being that if a router advertises a route,
644
it must accept and forward packets according to it.
645

    
646
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
647
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
648
Routers within each AS usually communicate with each other using either a interior routing
649
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
650
Boundary routers at the border of the AS communicate with their peers
651
in the neighboring AS'es via exterior BGP (eBGP).
652

    
653
<p>Each BGP router sends to its neighbors updates of the parts of its
654
routing table it wishes to export along with complete path information
655
(a list of AS'es the packet will travel through if it uses the particular
656
route) in order to avoid routing loops.
657

    
658
<p>BIRD supports all requirements of the BGP4 standard as defined in
659
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
660
It also supports the community attributes
661
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
662
capability negotiation
663
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
664
MD5 password authentication
665
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
666
route reflectors 
667
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
668
and 4B AS numbers 
669
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
670

    
671

    
672
For IPv6, it uses the standard multiprotocol extensions defined in
673
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
674
including changes described in the
675
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
676
and applied to IPv6 according to
677
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
678

    
679
<sect1>Route selection rules
680

    
681
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
682
route among multiple BGP routes with the same preference are a bit more complex
683
and they are implemented according to the following algorithm. It starts the first
684
rule, if there are more "best" routes, then it uses the second rule to choose
685
among them and so on.
686

    
687
<itemize>
688
	<item>Prefer route with the highest Local Preference attribute.
689
	<item>Prefer route with the shortest AS path.
690
	<item>Prefer IGP origin over EGP and EGP over incomplete.
691
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
692
	<item>Prefer internal routes over external ones.
693
	<item>Prefer the route with the lowest value of router ID of the
694
	advertising router.
695
</itemize>
696

    
697
<sect1>Configuration
698

    
699
<p>Each instance of the BGP corresponds to one neighboring router.
700
This allows to set routing policy and all the other parameters differently
701
for each neighbor using the following configuration parameters:
702

    
703
<descrip>
704
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
705
	contrary to other IP routers, BIRD is able to act as a router located
706
	in multiple AS'es simultaneously, but in such cases you need to tweak
707
	the BGP paths manually in the filters to get consistent behavior.)
708
	This parameter is mandatory.
709

    
710
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
711
	this instance will be talking to and what AS it's located in. Unless
712
	you use the <cf/multihop/ clause, it must be directly connected to one
713
	of your router's interfaces. In case the neighbor is in the same AS
714
	as we are, we automatically switch to iBGP. This parameter is mandatory.
715

    
716
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
717
	neighbor which is connected at most <m/number/ hops far and to which
718
	we should route via our direct neighbor with address <m/ip/.
719
	Default: switched off.
720

    
721
	<tag>next hop self</tag> Avoid calculation of the Next Hop attribute
722
	and always advertise our own source address (see below) as a next hop.
723
	This needs to be used only
724
	occasionally to circumvent misconfigurations of other routers.
725
	Default: disabled.
726

    
727
	<tag>source address <m/ip/</tag> Define local address we should use
728
	for next hop calculation. Default: the address of the local end
729
	of the interface our neighbor is connected to.
730

    
731
	<tag>password <m/string/</tag> Use this password for MD5 authentication
732
	of BGP sessions. Default: no authentication.
733

    
734
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
735
	a route reflection client. Default: disabled.
736

    
737
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
738
	to avoid route reflection loops. When there is one route reflector in a cluster
739
	it usually uses its router id as a cluster id, but when there are more route
740
	reflectors in a cluster, these need to be configured (using this option) to
741
	use a common cluster id. Clients in a cluster need not known their cluster
742
	id and this option is not allowed to them  Default: a same as router id.
743

    
744
	<tag>rs client</tag> Be a route server and treat the neighbor
745
	as a route server client. A route server is used as a
746
	replacement for full mesh EBGP routing in Internet exchange
747
	points in a similar way to route reflectors used in IBGP routing.
748
	Bird does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
749
	which behaves like plain EBGP but reduces modifications to advertised route
750
	attributes to be transparent (for example does not prepend its AS number to
751
	AS PATH attribute and keep MED attribute). Default: disabled.
752

    
753
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
754
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
755
	but by disabling this option it can be persuaded not to advertise it and
756
	to maintain old-style sessions with its neighbors. This might be useful for
757
	circumventing bugs in neighbor's implementation of 4B AS extension.
758
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
759
	Default: on.
760

    
761
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
762
	locally or by the other side), disable the instance automatically
763
	and wait for an administrator to fix the problem manually. Default: off.
764

    
765
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
766
	message from the other side before considering the connection stale.
767
	Default: depends on agreement with the neighboring router, we prefer
768
	240 seconds if the other side is willing to accept it.
769

    
770
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
771
	before the routers have a chance to exchange open messages and agree
772
	on the real value. Default: 240 seconds.
773

    
774
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
775
	of two consecutive Keepalive messages. Default: One third of the hold time.
776

    
777
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
778
	retrying a failed attempt to connect. Default: 120 seconds.
779

    
780
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
781
	startup and the first attempt to connect. Default: 5 seconds.
782

    
783
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
784
	failure (either local or reported by the peer) and automatic restart.
785
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
786
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
787

    
788
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
789
	failures to treat them as a error sequence which makes the <cf/error wait time/
790
	increase exponentially. Default: 300 seconds.
791

    
792
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
793
	when deciding which BGP route is the best one. Default: on.
794

    
795
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
796
	Discriminator to be used during route selection when the MED attribute
797
	is missing. Default: 0.
798

    
799
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
800
	to be used during route selection when the Local Preference attribute
801
	is missing. Default: 0.
802
</descrip>
803

    
804
<sect1>Attributes
805

    
806
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
807
table below) are available on internal BGP connections only, some of them (marked
808
with `<tt/O/') are optional.
809

    
810
<descrip>
811
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
812
	the packet will travel through when forwarded according to the particular route. In case of 
813
	internal BGP it doesn't contain the number of the local AS.
814

    
815
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
816
	selection among multiple BGP routes (see the selection rules above). It's
817
	used as an additional metric which is propagated through the whole local AS.
818

    
819
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
820
	is an optional attribute which is used on on external (inter-AS) links to
821
	convey to an adjacent AS the optimal entry point into the local AS.
822
	The received attribute may be also propagated over internal BGP links
823
	(and this is default behavior). The attribute value is zeroed when a route
824
	is exported from a routing table to a BGP instance to ensure that the attribute
825
	received from a neighboring AS is not propagated to other neighboring ASes.
826
	A new value might be set in the export filter of a BGP instance.
827
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
828
	for further discussion of BGP MED attribute.
829

    
830
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
831
	if the route has originated in an interior routing protocol or
832
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
833
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
834
	is unknown.
835

    
836
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
837
	to this destination. On internal BGP connections, it's an address of the
838
	originating router if it's inside the local AS or a boundary router the
839
	packet will leave the AS through if it's an exterior route, so each BGP
840
	speaker within the AS has a chance to use the shortest interior path
841
	possible to this point.
842

    
843
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
844
	which carries no value, but the sole presence of which indicates that the route
845
	has been aggregated from multiple routes by some router on the path from
846
	the originator.
847

    
848
<!-- we don't handle aggregators right since they are of a very obscure type
849
	<tag>bgp_aggregator</tag>
850
-->
851
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
852
	with the route. Each such value is a pair (represented as a <cf/pair/ data
853
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
854
	the community and the second one being a per-AS identifier. There are lots
855
	of uses of the community mechanism, but generally they are used to carry
856
	policy information like "don't export to USA peers". As each AS can define
857
	its own routing policy, it also has a complete freedom about which community
858
	attributes it defines and what will their semantics be.
859
</descrip>
860

    
861
<sect1>Example
862

    
863
<p><code>
864
protocol bgp {
865
	local as 65000;			     # Use a private AS number
866
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
867
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
868
	export filter {			     # We use non-trivial export rules
869
		if source = RTS_STATIC then { # Export only static routes
870
		        # Assign our community
871
			bgp_community.add((65000,5678));
872
			# Artificially increase path length
873
			# by advertising local AS number twice
874
			if bgp_path ~ / 65000 / then	  
875
				bgp_path.prepend(65000);  
876
			accept;
877
		}
878
		reject;
879
	};
880
	import all;
881
	source address 62.168.0.1;	# Use a non-standard source address
882
}
883
</code>
884

    
885
<sect>Device
886

    
887
<p>The Device protocol is not a real routing protocol.  It doesn't generate
888
any routes and it only serves as a module for getting information about network
889
interfaces from the kernel.
890

    
891
<p>Except for very unusual circumstances, you probably should include
892
this protocol in the configuration since almost all other protocols
893
require network interfaces to be defined for them to work with.
894

    
895
<p>The only configurable thing is interface scan time:
896

    
897
<p><descrip>
898
	<tag>scan time <m/number/</tag> Time in seconds between two scans
899
	of the network interface list. On systems where we are notified about
900
	interface status changes asynchronously (such as newer versions of
901
	Linux), we need to scan the list only in order to avoid confusion by lost
902
	notification messages, so the default time is set to a large value.
903
</descrip>
904

    
905
<p>As the Device protocol doesn't generate any routes, it cannot have
906
any attributes. Example configuration looks really simple:
907

    
908
<p><code>
909
protocol device {
910
	scan time 10;		# Scan the interfaces often
911
}
912
</code>
913

    
914
<sect>Direct
915

    
916
<p>The Direct protocol is a simple generator of device routes for all the
917
directly connected networks according to the list of interfaces provided
918
by the kernel via the Device protocol.
919

    
920
<p>It's highly recommended to include this protocol in your configuration
921
unless you want to use BIRD as a route server or a route reflector, that is
922
on a machine which doesn't forward packets itself and only participates in
923
distribution of routing information.
924

    
925
<p>The only configurable thing about direct is what interfaces it watches:
926

    
927
<p><descrip>
928
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
929
	protocol will generate device routes for all the interfaces
930
	available. If you want to restrict it to some subset of interfaces
931
	(for example if you're using multiple routing tables for policy
932
	routing and some of the policy domains don't contain all interfaces),
933
	just use this clause.
934
</descrip>
935

    
936
<p>Direct device routes don't contain any specific attributes.
937

    
938
<p>Example config might look like this:
939

    
940
<p><code>
941
protocol direct {
942
	interface "-arc*", "*";		# Exclude the ARCnets
943
}
944
</code>
945

    
946
<sect>Kernel
947

    
948
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
949
the with other routers in the network, it performs synchronization of BIRD's routing
950
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
951
and from time to time it scans the kernel tables to see whether some routes have
952
disappeared (for example due to unnoticed up/down transition of an interface)
953
or whether an `alien' route has been added by someone else (depending on the
954
<cf/learn/ switch, such routes are either deleted or accepted to our
955
table).
956

    
957
<p>If your OS supports only a single routing table, you can configure only one
958
instance of the Kernel protocol. If it supports multiple tables (in order to
959
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
960
them must be connected to a different BIRD routing table and to a different
961
kernel table.
962

    
963
<sect1>Configuration
964

    
965
<p><descrip>
966
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
967
	routing tables when it exits (instead of cleaning them up).
968
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
969
	kernel routing table.
970
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
971
	routing tables by other routing daemons or by the system administrator.
972
	This is possible only on systems which support identification of route
973
	authorship.
974
	<tag>kernel table <m/number/</tag> Select which kernel table should
975
	this particular instance of the Kernel protocol work with. Available
976
	only on systems supporting multiple routing tables.
977
</descrip>
978

    
979
<p>The Kernel protocol doesn't define any route attributes.
980
<p>A simple configuration can look this way:
981

    
982
<p><code>
983
protocol kernel {
984
	import all;
985
	export all;
986
}
987
</code>
988

    
989
<p>Or for a system with two routing tables:
990

    
991
<p><code>
992
protocol kernel {		# Primary routing table
993
	learn;			# Learn alien routes from the kernel
994
	persist;		# Don't remove routes on bird shutdown
995
	scan time 10;		# Scan kernel routing table every 10 seconds
996
	import all;
997
	export all;
998
}
999

    
1000
protocol kernel {		# Secondary routing table
1001
	table auxtable;
1002
	kernel table 100;
1003
	export all;
1004
}
1005
</code>
1006

    
1007
<sect>OSPF
1008

    
1009
<sect1>Introduction
1010

    
1011
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1012
protocol. The current IPv4 version (OSPFv2) is defined
1013
in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
1014
state (a.k.a. shortest path first) protocol -- each router maintains a database
1015
describing the autonomous system's topology. Each participating router
1016
has an identical copy of the database and all routers run the same algorithm
1017
calculating a shortest path tree with themselves as a root.
1018
OSPF chooses the least cost path as the best path.
1019
(OSPFv3 - OSPF for IPv6 is not supported yet.)
1020

    
1021
<p>In OSPF, the autonomous system can be split to several areas in order
1022
to reduce the amount of resources consumed for exchanging the routing
1023
information and to protect the other areas from incorrect routing data.
1024
Topology of the area is hidden to the rest of the autonomous system.
1025

    
1026
<p>Another very important feature of OSPF is that
1027
it can keep routing information from other protocols (like Static or BGP)
1028
in its link state database as external routes. Each external route can
1029
be tagged by the advertising router, making it possible to pass additional
1030
information between routers on the boundary of the autonomous system.
1031

    
1032
<p>OSPF quickly detects topological changes in the autonomous system (such
1033
as router interface failures) and calculates new loop-free routes after a short
1034
period of convergence. Only a minimal amount of 
1035
routing traffic is involved.
1036

    
1037
<p>Each router participating in OSPF routing periodically sends Hello messages
1038
to all its interfaces. This allows neighbors to be discovered dynamically.
1039
Then the neighbors exchange theirs parts of the link state database and keep it
1040
identical by flooding updates. The flooding process is reliable and ensures
1041
that each router detects all changes.
1042

    
1043
<sect1>Configuration
1044

    
1045
<p>In the main part of configuration, there can be multiple definitions of
1046
OSPF area witch different id included. These definitions includes many other
1047
switches and multiple definitions of interfaces. Definition of interface
1048
may contain many switches and constant definitions and list of neighbors
1049
on nonbroadcast networks.
1050

    
1051
<code>
1052
protocol ospf &lt;name&gt; {
1053
	rfc1583compat &lt;switch&gt;;
1054
	tick &lt;num&gt;;
1055
	area &lt;id&gt; {
1056
		stub cost &lt;num&gt;;
1057
                networks {
1058
			&lt;prefix&gt;;
1059
			&lt;prefix&gt; hidden;
1060
		}
1061
		interface &lt;interface pattern&gt;
1062
		{
1063
			cost &lt;num&gt;;
1064
			stub &lt;switch&gt;;
1065
			hello &lt;num&gt;;
1066
			poll &lt;num&gt;;
1067
			retransmit &lt;num&gt;;
1068
			priority &lt;num&gt;;
1069
			wait &lt;num&gt;;
1070
			dead count &lt;num&gt;;
1071
			dead &lt;num&gt;;
1072
			rx buffer [normal|large|&lt;num&gt;];
1073
			type [broadcast|nonbroadcast|pointopoint];
1074
			strict nonbroadcast &lt;switch&gt;;
1075
			authentication [none|simple|cryptographics];
1076
			password "&lt;text&gt;";
1077
			password "&lt;text&gt;" {
1078
				id &lt;num&gt;;
1079
				generate from "&lt;date&gt;";
1080
				generate to "&lt;date&gt;";
1081
				accept from "&lt;date&gt;";
1082
				accept to "&lt;date&gt;";
1083
			};
1084
			neighbors {
1085
				&lt;ip&gt;;
1086
				&lt;ip&gt; eligible;
1087
			};
1088
		};
1089
		virtual link &lt;id&gt;
1090
		{
1091
			hello &lt;num&gt;;
1092
			retransmit &lt;num&gt;;
1093
			wait &lt;num&gt;;
1094
			dead count &lt;num&gt;;
1095
			dead &lt;num&gt;;
1096
			authentication [none|simple];
1097
			password "&lt;text&gt;";
1098
		};
1099
	};
1100
}
1101
</code>
1102

    
1103
<descrip>
1104
	<tag>rfc1583compat <M>switch</M></tag>
1105
	 This option controls compatibility of routing table
1106
	 calculation with RFC 1583<htmlurl
1107
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1108
	 value is no.
1109
	
1110
	<tag>area <M>id</M></tag>
1111
	 This defines an OSPF area with given area ID (an integer or an IPv4
1112
	 address, similarly to a router ID).
1113
	 The most important area is
1114
	 the backbone (ID 0) to which every other area must be connected.
1115

    
1116
	<tag>stub cost <M>num</M></tag>
1117
	 No external (except default) routes are flooded into stub areas.
1118
         Setting this value marks area stub with defined cost of default route.
1119
	 Default value is no. (Area is not stub.)
1120

    
1121
	<tag>tick <M>num</M></tag>
1122
	 The routing table calculation and clean-up of areas' databases
1123
         is not performed when a single link state
1124
	 change arrives. To lower the CPU utilization, it's processed later
1125
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1126

    
1127
	<tag>networks { <m/set/ }</tag>
1128
         Definition of area IP ranges. This is used in summary lsa origination.
1129
	 Hidden networks are not propagated into other areas.
1130

    
1131
	<tag>interface <M>pattern</M></tag>
1132
	 Defines that the specified interfaces belong to the area being defined.
1133

    
1134
	<tag>virtual link <M>id</M></tag>
1135
	 Virtual link to router with the router id. Virtual link acts as a
1136
         point-to-point interface belonging to backbone. The actual area is
1137
         used as transport area. This item cannot be in the backbone.
1138

    
1139
	<tag>cost <M>num</M></tag>
1140
	 Specifies output cost (metric) of an interface. Default value is 10.
1141

    
1142
	<tag>stub <M>switch</M></tag>
1143
	 If set to interface it does not listen to any packet and does not send
1144
	 any hello. Default value is no.
1145

    
1146
	<tag>hello <M>num</M></tag>
1147
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1148
	 routers on the same network need to have the same hello interval.
1149
	 Default value is 10.
1150

    
1151
	<tag>poll <M>num</M></tag>
1152
	 Specifies interval in seconds between sending of Hello messages for
1153
	 some neighbors on NBMA network. Default value is 20.
1154

    
1155
	<tag>retransmit <M>num</M></tag>
1156
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1157
	 Default value is 5.
1158

    
1159
        <tag>priority <M>num</M></tag>
1160
	 On every multiple access network (e.g., the Ethernet) Designed Router
1161
	 and Backup Designed router are elected. These routers have some
1162
	 special functions in the flooding process. Higher priority increases
1163
	 preferences in this election. Routers with priority 0 are not
1164
	 eligible. Default value is 1.
1165

    
1166
	<tag>wait <M>num</M></tag>
1167
	 After start, router waits for the specified number of seconds between starting
1168
	 election and building adjacency. Default value is 40.
1169
	 
1170
	<tag>dead count <M>num</M></tag>
1171
	 When the router does not receive any messages from a neighbor in
1172
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1173

    
1174
	<tag>dead <M>num</M></tag>
1175
	 When the router does not receive any messages from a neighbor in
1176
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1177
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1178

    
1179
	<tag>rx buffer <M>num</M></tag>
1180
	 This sets the size of buffer used for receiving packets. The buffer should
1181
	 be bigger than maximal size of any packets. Value NORMAL (default)
1182
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1183

    
1184
	<tag>type broadcast</tag>
1185
	 BIRD detects a type of a connected network automatically, but sometimes it's
1186
	 convenient to force use of a different type manually.
1187
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1188
	 (a single packet for all the neighbors).
1189

    
1190
	<tag>type pointopoint</tag>
1191
	 Point-to-point networks connect just 2 routers together. No election
1192
	 is performed there which reduces the number of messages sent.
1193

    
1194
	<tag>type nonbroadcast</tag>
1195
	 On nonbroadcast networks, the packets are sent to each neighbor
1196
	 separately because of lack of multicast capabilities.
1197

    
1198
	<tag>strict nonbroadcast <M>switch</M></tag>
1199
	 If set, don't send hello to any undefined neighbor. This switch
1200
	 is ignored on on any non-NBMA network. Default is No.
1201

    
1202
	<tag>authentication none</tag>
1203
	 No passwords are sent in OSPF packets. This is the default value.
1204

    
1205
	<tag>authentication simple</tag>
1206
	 Every packet carries 8 bytes of password. Received packets
1207
	 lacking this password are ignored. This authentication mechanism is
1208
	 very weak.
1209

    
1210
	<tag>authentication cryptographic</tag>
1211
	 16-byte long MD5 digest is appended to every packet. For the digest
1212
         generation 16-byte long passwords are used. Those passwords are 
1213
         not sent via network, so this mechanismus is quite secure.
1214
         Packets can still be read by an attacker.
1215

    
1216
	<tag>password "<M>text</M>"</tag>
1217
	 An 8-byte or 16-byte password used for authentication.
1218

    
1219
	<tag>id <M>num</M></tag>
1220
	 ID of the password, (0-255). If it's not used, BIRD will choose
1221
	 ID based on an order of the password item in the interface. For
1222
	 example, second password item in one interface will have default
1223
	 ID 2.  
1224

    
1225
	<tag>generate from <M>date</M></tag>
1226
	 The start time of the usage of the password for packet signing.
1227

    
1228
	<tag>generate to <M>date</M></tag>
1229
	 The last time of the usage of the password for packet signing.
1230

    
1231
	<tag>accept from <M>date</M></tag>
1232
	 The start time of the usage of the password for packet verification.
1233

    
1234
	<tag>accept to <M>date</M></tag>
1235
	 The last time of the usage of the password for packet verification.
1236

    
1237
	<tag>neighbors { <m/set/ } </tag>
1238
	 A set of neighbors to which Hello messages on nonbroadcast networks
1239
	 are to be sent. Some of them could be marked as eligible.
1240

    
1241
</descrip>
1242

    
1243
<sect1>Attributes
1244

    
1245
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1246
Metric is ranging from 1 to infinity (65535).
1247
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1248
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1249
<cf/metric of type 2/ is always longer
1250
than any <cf/metric of type 1/ or any <cf/internal metric/.
1251
If you specify both metrics only metric1 is used.
1252
Each external route can also carry a <cf/tag/ which is a 32-bit
1253
integer which is used when exporting routes to other protocols;
1254
otherwise, it doesn't affect routing inside the OSPF domain at all.
1255
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1256

    
1257
<sect1>Example
1258

    
1259
<p>
1260

    
1261
<code>
1262
protocol ospf MyOSPF {
1263
        rfc1583compatibility yes;
1264
        tick 2;
1265
	export filter {
1266
		if source = RTS_BGP then {
1267
			ospf_metric1 = 100;
1268
			accept;
1269
		}
1270
		reject;
1271
	};                                                                      
1272
	area 0.0.0.0 {
1273
		interface "eth*" {
1274
			cost 11;
1275
			hello 15;
1276
			priority 100;
1277
			retransmit 7;
1278
			authentication simple;
1279
			password "aaa";
1280
		};
1281
		interface "ppp*" {
1282
			cost 100;
1283
			authentication cryptographic;
1284
			passwords {
1285
				password "abc" {
1286
					id 1;
1287
					generate to "22-04-2003 11:00:06";
1288
					accept from "17-01-2001 12:01:05";
1289
				};
1290
				password "def" {
1291
					id 2;
1292
					generate to "22-07-2005 17:03:21";
1293
					accept from "22-02-2001 11:34:06";
1294
				};
1295
			};
1296
		};
1297
		interface "arc0" {
1298
			cost 10;
1299
			stub yes;
1300
		};
1301
		interface "arc1";
1302
	};
1303
	area 120 {
1304
		stub yes;
1305
		networks {
1306
			172.16.1.0/24;
1307
			172.16.2.0/24 hidden;
1308
		}
1309
		interface "-arc0" , "arc*" {
1310
			type nonbroadcast;
1311
			authentication none;
1312
			strict nonbroadcast yes;
1313
			wait 120;
1314
			poll 40;
1315
			dead count 8;
1316
			neighbors {
1317
				192.168.120.1 eligible;
1318
				192.168.120.2;
1319
				192.168.120.10;
1320
			};
1321
		};
1322
	};
1323
}
1324
</code>
1325

    
1326
<sect>Pipe
1327

    
1328
<sect1>Introduction
1329

    
1330
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1331
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1332
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1333
and vice versa, depending on what's allowed by the filters. Export filters control export
1334
of routes from the primary table to the secondary one, import filters control the opposite
1335
direction.
1336

    
1337
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1338
where handling of a single packet doesn't depend only on its destination address, but also
1339
on its source address, source interface, protocol type and other similar parameters.
1340
In many systems (Linux 2.2 being a good example), the kernel allows to enforce routing policies
1341
by defining routing rules which choose one of several routing tables to be used for a packet
1342
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1343
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1344
connect them to the kernel ones, use filters to control which routes appear in which tables
1345
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1346
another one.
1347

    
1348
<sect1>Configuration
1349

    
1350
<p><descrip>
1351
	<tag>peer table <m/table/</tag> Define secondary routing table to connect to. The
1352
	primary one is selected by the <cf/table/ keyword.
1353
</descrip>
1354

    
1355
<sect1>Attributes
1356

    
1357
<p>The Pipe protocol doesn't define any route attributes.
1358

    
1359
<sect1>Example
1360

    
1361
<p>Let's consider a router which serves as a boundary router of two different autonomous
1362
systems, each of them connected to a subset of interfaces of the router, having its own
1363
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1364
of outage of its own exterior line.
1365

    
1366
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1367
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1368
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1369
and similarly for the second AS. Thus we have split our router to two logical routers,
1370
each one acting on its own routing table, having its own routing protocols on its own
1371
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1372
the routes between the tables through a Pipe protocol while decreasing their preferences
1373
and correcting their BGP paths to reflect the AS boundary crossing.
1374

    
1375
<code>
1376
table as1;				# Define the tables
1377
table as2;
1378

    
1379
protocol kernel kern1 {			# Synchronize them with the kernel
1380
	table as1;
1381
	kernel table 1;
1382
}
1383

    
1384
protocol kernel kern2 {
1385
	table as2;
1386
	kernel table 2;
1387
}
1388

    
1389
protocol bgp bgp1 {			# The outside connections
1390
	table as1;
1391
	local as 1;
1392
	neighbor 192.168.0.1 as 1001;
1393
	export all;
1394
	import all;
1395
}
1396

    
1397
protocol bgp bgp2 {
1398
	table as2;
1399
	local as 2;
1400
	neighbor 10.0.0.1 as 1002;
1401
	export all;
1402
	import all;
1403
}
1404

    
1405
protocol pipe {				# The Pipe
1406
	table as1;
1407
	peer table as2;
1408
	export filter {
1409
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1410
			if preference>10 then preference = preference-10;
1411
			if source=RTS_BGP then bgp_path.prepend(1);
1412
			accept;
1413
		}
1414
		reject;
1415
	};
1416
	import filter {
1417
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1418
			if preference>10 then preference = preference-10;
1419
			if source=RTS_BGP then bgp_path.prepend(2);
1420
			accept;
1421
		}
1422
		reject;
1423
	};
1424
}
1425
</code>
1426

    
1427
<sect>RIP
1428

    
1429
<sect1>Introduction
1430

    
1431
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1432
distances to all networks it can reach. When a router hears distance to another network, it increments
1433
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1434
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1435
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1436
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1437
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1438
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1439
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1440
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1441
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
1442
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1443

    
1444
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1445
convergence, big network load and inability to handle larger networks
1446
makes it pretty much obsolete in IPv4 world. (It is still usable on
1447
very small networks.) It is widely used in IPv6 networks,
1448
because there are no good implementations of OSPFv3.
1449

    
1450
<sect1>Configuration
1451

    
1452
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1453

    
1454
<descrip>
1455
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1456
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1457
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1458
	  hash. If you set authentication to not-none, it is a good idea to add <cf>passwords { }</cf>
1459
	  section. Default: none.
1460

    
1461
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1462
	  be honored. (Always, when sent from a  host on a directly connected
1463
	  network or never.) Routing table updates are honored only from
1464
	  neighbors, that is not configurable. Default: never.
1465
</descrip>
1466

    
1467
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1468
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1469
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1470
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1471
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1472
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1473
interface but not listen to it.
1474

    
1475
<p>The following options generally override behavior specified in RFC. If you use any of these
1476
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1477
other than equally configured BIRD. I have warned you.
1478

    
1479
<descrip>
1480
	<tag>port <M>number</M></tag>
1481
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1482
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1483

    
1484
	<tag>infinity <M>number</M></tag>
1485
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1486
	  even slower.
1487

    
1488
	<tag>period <M>number</M>
1489
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1490
	  number will mean faster convergence but bigger network
1491
	  load. Do not use values lower than 10.
1492

    
1493
	<tag>timeout time <M>number</M>
1494
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1495

    
1496
	<tag>garbage time <M>number</M>
1497
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1498
</descrip>
1499

    
1500
<sect1>Attributes
1501

    
1502
<p>RIP defines two route attributes:
1503

    
1504
<descrip>
1505
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1506
	When routes from different RIP instances are available and all of them have the same
1507
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1508
	When importing a non-RIP route, the metric defaults to 5.
1509

    
1510
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1511
	to carry additional information with the route (for example, an originating AS number
1512
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1513
</descrip>
1514

    
1515
<sect1>Example
1516

    
1517
<p><code>
1518
protocol rip MyRIP_test {
1519
        debug all;
1520
        port 1520;
1521
        period 10;
1522
        garbage time 60;
1523
        interface "eth0" { metric 3; mode multicast; }
1524
	          "eth1" { metric 2; mode broadcast; };
1525
        honor neighbor;
1526
        authentication none;
1527
        import filter { print "importing"; accept; };
1528
        export filter { print "exporting"; accept; };
1529
}
1530
</code>
1531

    
1532
<sect>Static
1533

    
1534
<p>The Static protocol doesn't communicate with other routers in the network,
1535
but instead it allows you to define routes manually. This is often used for
1536
specifying how to forward packets to parts of the network which don't use
1537
dynamic routing at all and also for defining sink routes (i.e., those
1538
telling to return packets as undeliverable if they are in your IP block,
1539
you don't have any specific destination for them and you don't want to send
1540
them out through the default route to prevent routing loops).
1541

    
1542
<p>There are three types of static routes: `classical' routes telling to
1543
forward packets to a neighboring router, device routes specifying forwarding
1544
to hosts on a directly connected network and special routes (sink, blackhole
1545
etc.) which specify a special action to be done instead of forwarding the
1546
packet.
1547

    
1548
<p>When the particular destination is not available (the interface is down or
1549
the next hop of the route is not a neighbor at the moment), Static just
1550
uninstalls the route from the table it is connected to and adds it again as soon
1551
as the destination becomes adjacent again.
1552

    
1553
<p>The Static protocol has no configuration options. Instead, the
1554
definition of the protocol contains a list of static routes:
1555

    
1556
<descrip>
1557
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1558
	a neighboring router.
1559
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1560
	route through an interface to hosts on a directly connected network.
1561
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1562
	specifying to drop the packet, return it as unreachable or return
1563
	it as administratively prohibited.
1564
</descrip>
1565

    
1566
<p>Static routes have no specific attributes.
1567

    
1568
<p>Example static config might look like this:
1569

    
1570
<p><code>
1571
protocol static {
1572
	table testable;			 # Connect to a non-default routing table
1573
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1574
	route 62.168.0.0/25 reject;	 # Sink route
1575
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1576
}
1577
</code>
1578

    
1579
<chapt>Conclusions
1580

    
1581
<sect>Future work
1582

    
1583
<p>Although BIRD supports all the commonly used routing protocols,
1584
there are still some features which would surely deserve to be
1585
implemented in future versions of BIRD:
1586

    
1587
<itemize>
1588
<item>OSPF for IPv6 networks
1589
<item>OSPF NSSA areas and opaque LSA's
1590
<item>Route aggregation and flap dampening
1591
<item>Generation of IPv6 router advertisements
1592
<item>Multipath routes
1593
<item>Multicast routing protocols
1594
<item>Ports to other systems
1595
</itemize>
1596

    
1597
<sect>Getting more help
1598

    
1599
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1600
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1601
where you can share your experiences with the other users and consult
1602
your problems with the authors. To subscribe to the list, just send a
1603
<tt/subscribe bird-users/ command in a body of a mail to
1604
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1605
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1606

    
1607
<p>BIRD is a relatively young system and it probably contains some
1608
bugs. You can report any problems to the bird-users list and the authors
1609
will be glad to solve them, but before you do so,
1610
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1611
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1612
which fixes the bug is always welcome as an attachment.)
1613

    
1614
<p>If you want to understand what is going inside, Internet standards are
1615
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">).
1616

    
1617
<p><it/Good luck!/
1618

    
1619
</book>
1620

    
1621
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1622
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1624
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1633
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