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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
548
on two strings (returning true if first string matches a shell-like pattern stored in second string) or on IP and prefix (returning true if IP is within the range defined by that prefix), or on
549
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).
550

    
551

    
552
<sect>Control structures
553

    
554
<p>Filters support two control structures: conditions and case switches. 
555

    
556
<p>Syntax of a condition is: <cf>if
557
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
558
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
559
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.
560

    
561
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
562
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
563
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
564
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
565
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.
566

    
567
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
568

    
569
<code>
570
case arg1 {
571
	2: print "two"; print "I can do more commands without {}";
572
	3 .. 5: print "three to five";
573
	else: print "something else";
574
}
575

    
576
if 1234 = i then printn "."; else { 
577
  print "not 1234"; 
578
  print "You need {} around multiple commands"; 
579
}
580
</code>
581

    
582
<sect>Route attributes
583

    
584
<p>A filter is implicitly passed a route, and it can access its
585
attributes just like it accesses variables. Attempts to access undefined
586
attribute result in a runtime error; you can check if an attribute is
587
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
588

    
589
<descrip>
590
	<tag><m/prefix/ net</tag>
591
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
592

    
593
	<tag><m/enum/ scope</tag>
594
	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).
595

    
596
	<tag><m/int/ preference</tag>
597
	Preference of the route. (See the chapter about routing tables.)
598

    
599
	<tag><m/ip/ from</tag>
600
	The router which the route has originated from. Read-only.
601
	
602
	<tag><m/ip/ gw</tag>
603
	Next hop packets routed using this route should be forwarded to.
604

    
605
	<tag><m/string/ proto</tag>
606
	The name of the protocol which the route has been imported from. Read-only.
607

    
608
	<tag><m/enum/ source</tag>
609
	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/.
610

    
611
	<tag><m/enum/ cast</tag>
612
	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.
613

    
614
	<tag><m/enum/ dest</tag>
615
	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.
616
</descrip>
617

    
618
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
619

    
620
<sect>Other statements
621

    
622
<p>The following statements are available:
623

    
624
<descrip>
625
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
626

    
627
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
628

    
629
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
630

    
631
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
632
	Prints given expressions; useful mainly while debugging
633
	filters. The <cf/printn/ variant does not terminate the line.
634

    
635
	<tag>quitbird</tag>
636
	Terminates BIRD. Useful when debugging the filter interpreter.
637
</descrip>
638

    
639
<chapt>Protocols
640

    
641
<sect>BGP
642

    
643
<p>The Border Gateway Protocol is the routing protocol used for backbone
644
level routing in the today's Internet. Contrary to the other protocols, its convergence
645
doesn't rely on all routers following the same rules for route selection,
646
making it possible to implement any routing policy at any router in the
647
network, the only restriction being that if a router advertises a route,
648
it must accept and forward packets according to it.
649

    
650
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
651
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
652
Routers within each AS usually communicate with each other using either a interior routing
653
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
654
Boundary routers at the border of the AS communicate with their peers
655
in the neighboring AS'es via exterior BGP (eBGP).
656

    
657
<p>Each BGP router sends to its neighbors updates of the parts of its
658
routing table it wishes to export along with complete path information
659
(a list of AS'es the packet will travel through if it uses the particular
660
route) in order to avoid routing loops.
661

    
662
<p>BIRD supports all requirements of the BGP4 standard as defined in
663
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
664
It also supports the community attributes
665
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
666
capability negotiation
667
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
668
MD5 password authentication
669
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
670
route reflectors 
671
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
672
and 4B AS numbers 
673
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
674

    
675

    
676
For IPv6, it uses the standard multiprotocol extensions defined in
677
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
678
including changes described in the
679
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
680
and applied to IPv6 according to
681
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
682

    
683
<sect1>Route selection rules
684

    
685
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
686
route among multiple BGP routes with the same preference are a bit more complex
687
and they are implemented according to the following algorithm. It starts the first
688
rule, if there are more "best" routes, then it uses the second rule to choose
689
among them and so on.
690

    
691
<itemize>
692
	<item>Prefer route with the highest Local Preference attribute.
693
	<item>Prefer route with the shortest AS path.
694
	<item>Prefer IGP origin over EGP and EGP over incomplete.
695
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
696
	<item>Prefer internal routes over external ones.
697
	<item>Prefer the route with the lowest value of router ID of the
698
	advertising router.
699
</itemize>
700

    
701
<sect1>Configuration
702

    
703
<p>Each instance of the BGP corresponds to one neighboring router.
704
This allows to set routing policy and all the other parameters differently
705
for each neighbor using the following configuration parameters:
706

    
707
<descrip>
708
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
709
	contrary to other IP routers, BIRD is able to act as a router located
710
	in multiple AS'es simultaneously, but in such cases you need to tweak
711
	the BGP paths manually in the filters to get consistent behavior.)
712
	This parameter is mandatory.
713

    
714
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
715
	this instance will be talking to and what AS it's located in. Unless
716
	you use the <cf/multihop/ clause, it must be directly connected to one
717
	of your router's interfaces. In case the neighbor is in the same AS
718
	as we are, we automatically switch to iBGP. This parameter is mandatory.
719

    
720
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
721
	neighbor which is connected at most <m/number/ hops far and to which
722
	we should route via our direct neighbor with address <m/ip/.
723
	Default: switched off.
724

    
725
	<tag>next hop self</tag> Avoid calculation of the Next Hop attribute
726
	and always advertise our own source address (see below) as a next hop.
727
	This needs to be used only
728
	occasionally to circumvent misconfigurations of other routers.
729
	Default: disabled.
730

    
731
	<tag>source address <m/ip/</tag> Define local address we should use
732
	for next hop calculation. Default: the address of the local end
733
	of the interface our neighbor is connected to.
734

    
735
	<tag>password <m/string/</tag> Use this password for MD5 authentication
736
	of BGP sessions. Default: no authentication.
737

    
738
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
739
	a route reflection client. Default: disabled.
740

    
741
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
742
	to avoid route reflection loops. When there is one route reflector in a cluster
743
	it usually uses its router id as a cluster id, but when there are more route
744
	reflectors in a cluster, these need to be configured (using this option) to
745
	use a common cluster id. Clients in a cluster need not known their cluster
746
	id and this option is not allowed to them  Default: a same as router id.
747

    
748
	<tag>rs client</tag> Be a route server and treat the neighbor
749
	as a route server client. A route server is used as a
750
	replacement for full mesh EBGP routing in Internet exchange
751
	points in a similar way to route reflectors used in IBGP routing.
752
	Bird does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
753
	which behaves like plain EBGP but reduces modifications to advertised route
754
	attributes to be transparent (for example does not prepend its AS number to
755
	AS PATH attribute and keep MED attribute). Default: disabled.
756

    
757
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
758
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
759
	but by disabling this option it can be persuaded not to advertise it and
760
	to maintain old-style sessions with its neighbors. This might be useful for
761
	circumventing bugs in neighbor's implementation of 4B AS extension.
762
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
763
	Default: on.
764

    
765
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
766
	locally or by the other side), disable the instance automatically
767
	and wait for an administrator to fix the problem manually. Default: off.
768

    
769
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
770
	message from the other side before considering the connection stale.
771
	Default: depends on agreement with the neighboring router, we prefer
772
	240 seconds if the other side is willing to accept it.
773

    
774
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
775
	before the routers have a chance to exchange open messages and agree
776
	on the real value. Default: 240 seconds.
777

    
778
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
779
	of two consecutive Keepalive messages. Default: One third of the hold time.
780

    
781
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
782
	retrying a failed attempt to connect. Default: 120 seconds.
783

    
784
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
785
	startup and the first attempt to connect. Default: 5 seconds.
786

    
787
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
788
	failure (either local or reported by the peer) and automatic restart.
789
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
790
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
791

    
792
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
793
	failures to treat them as a error sequence which makes the <cf/error wait time/
794
	increase exponentially. Default: 300 seconds.
795

    
796
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
797
	when deciding which BGP route is the best one. Default: on.
798

    
799
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
800
	Discriminator to be used during route selection when the MED attribute
801
	is missing. Default: 0.
802

    
803
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
804
	to be used during route selection when the Local Preference attribute
805
	is missing. Default: 0.
806
</descrip>
807

    
808
<sect1>Attributes
809

    
810
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
811
table below) are available on internal BGP connections only, some of them (marked
812
with `<tt/O/') are optional.
813

    
814
<descrip>
815
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
816
	the packet will travel through when forwarded according to the particular route. In case of 
817
	internal BGP it doesn't contain the number of the local AS.
818

    
819
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
820
	selection among multiple BGP routes (see the selection rules above). It's
821
	used as an additional metric which is propagated through the whole local AS.
822

    
823
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
824
	is an optional attribute which is used on on external (inter-AS) links to
825
	convey to an adjacent AS the optimal entry point into the local AS.
826
	The received attribute may be also propagated over internal BGP links
827
	(and this is default behavior). The attribute value is zeroed when a route
828
	is exported from a routing table to a BGP instance to ensure that the attribute
829
	received from a neighboring AS is not propagated to other neighboring ASes.
830
	A new value might be set in the export filter of a BGP instance.
831
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
832
	for further discussion of BGP MED attribute.
833

    
834
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
835
	if the route has originated in an interior routing protocol or
836
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
837
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
838
	is unknown.
839

    
840
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
841
	to this destination. On internal BGP connections, it's an address of the
842
	originating router if it's inside the local AS or a boundary router the
843
	packet will leave the AS through if it's an exterior route, so each BGP
844
	speaker within the AS has a chance to use the shortest interior path
845
	possible to this point.
846

    
847
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
848
	which carries no value, but the sole presence of which indicates that the route
849
	has been aggregated from multiple routes by some router on the path from
850
	the originator.
851

    
852
<!-- we don't handle aggregators right since they are of a very obscure type
853
	<tag>bgp_aggregator</tag>
854
-->
855
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
856
	with the route. Each such value is a pair (represented as a <cf/pair/ data
857
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
858
	the community and the second one being a per-AS identifier. There are lots
859
	of uses of the community mechanism, but generally they are used to carry
860
	policy information like "don't export to USA peers". As each AS can define
861
	its own routing policy, it also has a complete freedom about which community
862
	attributes it defines and what will their semantics be.
863
</descrip>
864

    
865
<sect1>Example
866

    
867
<p><code>
868
protocol bgp {
869
	local as 65000;			     # Use a private AS number
870
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
871
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
872
	export filter {			     # We use non-trivial export rules
873
		if source = RTS_STATIC then { # Export only static routes
874
		        # Assign our community
875
			bgp_community.add((65000,5678));
876
			# Artificially increase path length
877
			# by advertising local AS number twice
878
			if bgp_path ~ / 65000 / then	  
879
				bgp_path.prepend(65000);  
880
			accept;
881
		}
882
		reject;
883
	};
884
	import all;
885
	source address 62.168.0.1;	# Use a non-standard source address
886
}
887
</code>
888

    
889
<sect>Device
890

    
891
<p>The Device protocol is not a real routing protocol.  It doesn't generate
892
any routes and it only serves as a module for getting information about network
893
interfaces from the kernel.
894

    
895
<p>Except for very unusual circumstances, you probably should include
896
this protocol in the configuration since almost all other protocols
897
require network interfaces to be defined for them to work with.
898

    
899
<p>The only configurable thing is interface scan time:
900

    
901
<p><descrip>
902
	<tag>scan time <m/number/</tag> Time in seconds between two scans
903
	of the network interface list. On systems where we are notified about
904
	interface status changes asynchronously (such as newer versions of
905
	Linux), we need to scan the list only in order to avoid confusion by lost
906
	notification messages, so the default time is set to a large value.
907
</descrip>
908

    
909
<p>As the Device protocol doesn't generate any routes, it cannot have
910
any attributes. Example configuration looks really simple:
911

    
912
<p><code>
913
protocol device {
914
	scan time 10;		# Scan the interfaces often
915
}
916
</code>
917

    
918
<sect>Direct
919

    
920
<p>The Direct protocol is a simple generator of device routes for all the
921
directly connected networks according to the list of interfaces provided
922
by the kernel via the Device protocol.
923

    
924
<p>It's highly recommended to include this protocol in your configuration
925
unless you want to use BIRD as a route server or a route reflector, that is
926
on a machine which doesn't forward packets itself and only participates in
927
distribution of routing information.
928

    
929
<p>The only configurable thing about direct is what interfaces it watches:
930

    
931
<p><descrip>
932
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
933
	protocol will generate device routes for all the interfaces
934
	available. If you want to restrict it to some subset of interfaces
935
	(for example if you're using multiple routing tables for policy
936
	routing and some of the policy domains don't contain all interfaces),
937
	just use this clause.
938
</descrip>
939

    
940
<p>Direct device routes don't contain any specific attributes.
941

    
942
<p>Example config might look like this:
943

    
944
<p><code>
945
protocol direct {
946
	interface "-arc*", "*";		# Exclude the ARCnets
947
}
948
</code>
949

    
950
<sect>Kernel
951

    
952
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
953
the with other routers in the network, it performs synchronization of BIRD's routing
954
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
955
and from time to time it scans the kernel tables to see whether some routes have
956
disappeared (for example due to unnoticed up/down transition of an interface)
957
or whether an `alien' route has been added by someone else (depending on the
958
<cf/learn/ switch, such routes are either deleted or accepted to our
959
table).
960

    
961
<p>If your OS supports only a single routing table, you can configure only one
962
instance of the Kernel protocol. If it supports multiple tables (in order to
963
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
964
them must be connected to a different BIRD routing table and to a different
965
kernel table.
966

    
967
<sect1>Configuration
968

    
969
<p><descrip>
970
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
971
	routing tables when it exits (instead of cleaning them up).
972
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
973
	kernel routing table.
974
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
975
	routing tables by other routing daemons or by the system administrator.
976
	This is possible only on systems which support identification of route
977
	authorship.
978
	<tag>kernel table <m/number/</tag> Select which kernel table should
979
	this particular instance of the Kernel protocol work with. Available
980
	only on systems supporting multiple routing tables.
981
</descrip>
982

    
983
<p>The Kernel protocol doesn't define any route attributes.
984
<p>A simple configuration can look this way:
985

    
986
<p><code>
987
protocol kernel {
988
	import all;
989
	export all;
990
}
991
</code>
992

    
993
<p>Or for a system with two routing tables:
994

    
995
<p><code>
996
protocol kernel {		# Primary routing table
997
	learn;			# Learn alien routes from the kernel
998
	persist;		# Don't remove routes on bird shutdown
999
	scan time 10;		# Scan kernel routing table every 10 seconds
1000
	import all;
1001
	export all;
1002
}
1003

    
1004
protocol kernel {		# Secondary routing table
1005
	table auxtable;
1006
	kernel table 100;
1007
	export all;
1008
}
1009
</code>
1010

    
1011
<sect>OSPF
1012

    
1013
<sect1>Introduction
1014

    
1015
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1016
protocol. The current IPv4 version (OSPFv2) is defined
1017
in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
1018
state (a.k.a. shortest path first) protocol -- each router maintains a database
1019
describing the autonomous system's topology. Each participating router
1020
has an identical copy of the database and all routers run the same algorithm
1021
calculating a shortest path tree with themselves as a root.
1022
OSPF chooses the least cost path as the best path.
1023
(OSPFv3 - OSPF for IPv6 is not supported yet.)
1024

    
1025
<p>In OSPF, the autonomous system can be split to several areas in order
1026
to reduce the amount of resources consumed for exchanging the routing
1027
information and to protect the other areas from incorrect routing data.
1028
Topology of the area is hidden to the rest of the autonomous system.
1029

    
1030
<p>Another very important feature of OSPF is that
1031
it can keep routing information from other protocols (like Static or BGP)
1032
in its link state database as external routes. Each external route can
1033
be tagged by the advertising router, making it possible to pass additional
1034
information between routers on the boundary of the autonomous system.
1035

    
1036
<p>OSPF quickly detects topological changes in the autonomous system (such
1037
as router interface failures) and calculates new loop-free routes after a short
1038
period of convergence. Only a minimal amount of 
1039
routing traffic is involved.
1040

    
1041
<p>Each router participating in OSPF routing periodically sends Hello messages
1042
to all its interfaces. This allows neighbors to be discovered dynamically.
1043
Then the neighbors exchange theirs parts of the link state database and keep it
1044
identical by flooding updates. The flooding process is reliable and ensures
1045
that each router detects all changes.
1046

    
1047
<sect1>Configuration
1048

    
1049
<p>In the main part of configuration, there can be multiple definitions of
1050
OSPF area witch different id included. These definitions includes many other
1051
switches and multiple definitions of interfaces. Definition of interface
1052
may contain many switches and constant definitions and list of neighbors
1053
on nonbroadcast networks.
1054

    
1055
<code>
1056
protocol ospf &lt;name&gt; {
1057
	rfc1583compat &lt;switch&gt;;
1058
	tick &lt;num&gt;;
1059
	area &lt;id&gt; {
1060
		stub cost &lt;num&gt;;
1061
                networks {
1062
			&lt;prefix&gt;;
1063
			&lt;prefix&gt; hidden;
1064
		}
1065
		interface &lt;interface pattern&gt;
1066
		{
1067
			cost &lt;num&gt;;
1068
			stub &lt;switch&gt;;
1069
			hello &lt;num&gt;;
1070
			poll &lt;num&gt;;
1071
			retransmit &lt;num&gt;;
1072
			priority &lt;num&gt;;
1073
			wait &lt;num&gt;;
1074
			dead count &lt;num&gt;;
1075
			dead &lt;num&gt;;
1076
			rx buffer [normal|large|&lt;num&gt;];
1077
			type [broadcast|nonbroadcast|pointopoint];
1078
			strict nonbroadcast &lt;switch&gt;;
1079
			authentication [none|simple|cryptographics];
1080
			password "&lt;text&gt;";
1081
			password "&lt;text&gt;" {
1082
				id &lt;num&gt;;
1083
				generate from "&lt;date&gt;";
1084
				generate to "&lt;date&gt;";
1085
				accept from "&lt;date&gt;";
1086
				accept to "&lt;date&gt;";
1087
			};
1088
			neighbors {
1089
				&lt;ip&gt;;
1090
				&lt;ip&gt; eligible;
1091
			};
1092
		};
1093
		virtual link &lt;id&gt;
1094
		{
1095
			hello &lt;num&gt;;
1096
			retransmit &lt;num&gt;;
1097
			wait &lt;num&gt;;
1098
			dead count &lt;num&gt;;
1099
			dead &lt;num&gt;;
1100
			authentication [none|simple];
1101
			password "&lt;text&gt;";
1102
		};
1103
	};
1104
}
1105
</code>
1106

    
1107
<descrip>
1108
	<tag>rfc1583compat <M>switch</M></tag>
1109
	 This option controls compatibility of routing table
1110
	 calculation with RFC 1583<htmlurl
1111
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1112
	 value is no.
1113
	
1114
	<tag>area <M>id</M></tag>
1115
	 This defines an OSPF area with given area ID (an integer or an IPv4
1116
	 address, similarly to a router ID).
1117
	 The most important area is
1118
	 the backbone (ID 0) to which every other area must be connected.
1119

    
1120
	<tag>stub cost <M>num</M></tag>
1121
	 No external (except default) routes are flooded into stub areas.
1122
         Setting this value marks area stub with defined cost of default route.
1123
	 Default value is no. (Area is not stub.)
1124

    
1125
	<tag>tick <M>num</M></tag>
1126
	 The routing table calculation and clean-up of areas' databases
1127
         is not performed when a single link state
1128
	 change arrives. To lower the CPU utilization, it's processed later
1129
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1130

    
1131
	<tag>networks { <m/set/ }</tag>
1132
         Definition of area IP ranges. This is used in summary lsa origination.
1133
	 Hidden networks are not propagated into other areas.
1134

    
1135
	<tag>interface <M>pattern</M></tag>
1136
	 Defines that the specified interfaces belong to the area being defined.
1137

    
1138
	<tag>virtual link <M>id</M></tag>
1139
	 Virtual link to router with the router id. Virtual link acts as a
1140
         point-to-point interface belonging to backbone. The actual area is
1141
         used as transport area. This item cannot be in the backbone.
1142

    
1143
	<tag>cost <M>num</M></tag>
1144
	 Specifies output cost (metric) of an interface. Default value is 10.
1145

    
1146
	<tag>stub <M>switch</M></tag>
1147
	 If set to interface it does not listen to any packet and does not send
1148
	 any hello. Default value is no.
1149

    
1150
	<tag>hello <M>num</M></tag>
1151
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1152
	 routers on the same network need to have the same hello interval.
1153
	 Default value is 10.
1154

    
1155
	<tag>poll <M>num</M></tag>
1156
	 Specifies interval in seconds between sending of Hello messages for
1157
	 some neighbors on NBMA network. Default value is 20.
1158

    
1159
	<tag>retransmit <M>num</M></tag>
1160
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1161
	 Default value is 5.
1162

    
1163
        <tag>priority <M>num</M></tag>
1164
	 On every multiple access network (e.g., the Ethernet) Designed Router
1165
	 and Backup Designed router are elected. These routers have some
1166
	 special functions in the flooding process. Higher priority increases
1167
	 preferences in this election. Routers with priority 0 are not
1168
	 eligible. Default value is 1.
1169

    
1170
	<tag>wait <M>num</M></tag>
1171
	 After start, router waits for the specified number of seconds between starting
1172
	 election and building adjacency. Default value is 40.
1173
	 
1174
	<tag>dead count <M>num</M></tag>
1175
	 When the router does not receive any messages from a neighbor in
1176
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1177

    
1178
	<tag>dead <M>num</M></tag>
1179
	 When the router does not receive any messages from a neighbor in
1180
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1181
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1182

    
1183
	<tag>rx buffer <M>num</M></tag>
1184
	 This sets the size of buffer used for receiving packets. The buffer should
1185
	 be bigger than maximal size of any packets. Value NORMAL (default)
1186
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1187

    
1188
	<tag>type broadcast</tag>
1189
	 BIRD detects a type of a connected network automatically, but sometimes it's
1190
	 convenient to force use of a different type manually.
1191
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1192
	 (a single packet for all the neighbors).
1193

    
1194
	<tag>type pointopoint</tag>
1195
	 Point-to-point networks connect just 2 routers together. No election
1196
	 is performed there which reduces the number of messages sent.
1197

    
1198
	<tag>type nonbroadcast</tag>
1199
	 On nonbroadcast networks, the packets are sent to each neighbor
1200
	 separately because of lack of multicast capabilities.
1201

    
1202
	<tag>strict nonbroadcast <M>switch</M></tag>
1203
	 If set, don't send hello to any undefined neighbor. This switch
1204
	 is ignored on on any non-NBMA network. Default is No.
1205

    
1206
	<tag>authentication none</tag>
1207
	 No passwords are sent in OSPF packets. This is the default value.
1208

    
1209
	<tag>authentication simple</tag>
1210
	 Every packet carries 8 bytes of password. Received packets
1211
	 lacking this password are ignored. This authentication mechanism is
1212
	 very weak.
1213

    
1214
	<tag>authentication cryptographic</tag>
1215
	 16-byte long MD5 digest is appended to every packet. For the digest
1216
         generation 16-byte long passwords are used. Those passwords are 
1217
         not sent via network, so this mechanismus is quite secure.
1218
         Packets can still be read by an attacker.
1219

    
1220
	<tag>password "<M>text</M>"</tag>
1221
	 An 8-byte or 16-byte password used for authentication.
1222

    
1223
	<tag>id <M>num</M></tag>
1224
	 ID of the password, (0-255). If it's not used, BIRD will choose
1225
	 ID based on an order of the password item in the interface. For
1226
	 example, second password item in one interface will have default
1227
	 ID 2.  
1228

    
1229
	<tag>generate from <M>date</M></tag>
1230
	 The start time of the usage of the password for packet signing.
1231

    
1232
	<tag>generate to <M>date</M></tag>
1233
	 The last time of the usage of the password for packet signing.
1234

    
1235
	<tag>accept from <M>date</M></tag>
1236
	 The start time of the usage of the password for packet verification.
1237

    
1238
	<tag>accept to <M>date</M></tag>
1239
	 The last time of the usage of the password for packet verification.
1240

    
1241
	<tag>neighbors { <m/set/ } </tag>
1242
	 A set of neighbors to which Hello messages on nonbroadcast networks
1243
	 are to be sent. Some of them could be marked as eligible.
1244

    
1245
</descrip>
1246

    
1247
<sect1>Attributes
1248

    
1249
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1250
Metric is ranging from 1 to infinity (65535).
1251
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1252
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1253
<cf/metric of type 2/ is always longer
1254
than any <cf/metric of type 1/ or any <cf/internal metric/.
1255
If you specify both metrics only metric1 is used.
1256
Each external route can also carry a <cf/tag/ which is a 32-bit
1257
integer which is used when exporting routes to other protocols;
1258
otherwise, it doesn't affect routing inside the OSPF domain at all.
1259
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1260

    
1261
<sect1>Example
1262

    
1263
<p>
1264

    
1265
<code>
1266
protocol ospf MyOSPF {
1267
        rfc1583compatibility yes;
1268
        tick 2;
1269
	export filter {
1270
		if source = RTS_BGP then {
1271
			ospf_metric1 = 100;
1272
			accept;
1273
		}
1274
		reject;
1275
	};                                                                      
1276
	area 0.0.0.0 {
1277
		interface "eth*" {
1278
			cost 11;
1279
			hello 15;
1280
			priority 100;
1281
			retransmit 7;
1282
			authentication simple;
1283
			password "aaa";
1284
		};
1285
		interface "ppp*" {
1286
			cost 100;
1287
			authentication cryptographic;
1288
			passwords {
1289
				password "abc" {
1290
					id 1;
1291
					generate to "22-04-2003 11:00:06";
1292
					accept from "17-01-2001 12:01:05";
1293
				};
1294
				password "def" {
1295
					id 2;
1296
					generate to "22-07-2005 17:03:21";
1297
					accept from "22-02-2001 11:34:06";
1298
				};
1299
			};
1300
		};
1301
		interface "arc0" {
1302
			cost 10;
1303
			stub yes;
1304
		};
1305
		interface "arc1";
1306
	};
1307
	area 120 {
1308
		stub yes;
1309
		networks {
1310
			172.16.1.0/24;
1311
			172.16.2.0/24 hidden;
1312
		}
1313
		interface "-arc0" , "arc*" {
1314
			type nonbroadcast;
1315
			authentication none;
1316
			strict nonbroadcast yes;
1317
			wait 120;
1318
			poll 40;
1319
			dead count 8;
1320
			neighbors {
1321
				192.168.120.1 eligible;
1322
				192.168.120.2;
1323
				192.168.120.10;
1324
			};
1325
		};
1326
	};
1327
}
1328
</code>
1329

    
1330
<sect>Pipe
1331

    
1332
<sect1>Introduction
1333

    
1334
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1335
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1336
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1337
and vice versa, depending on what's allowed by the filters. Export filters control export
1338
of routes from the primary table to the secondary one, import filters control the opposite
1339
direction.
1340

    
1341
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1342
where handling of a single packet doesn't depend only on its destination address, but also
1343
on its source address, source interface, protocol type and other similar parameters.
1344
In many systems (Linux 2.2 being a good example), the kernel allows to enforce routing policies
1345
by defining routing rules which choose one of several routing tables to be used for a packet
1346
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1347
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1348
connect them to the kernel ones, use filters to control which routes appear in which tables
1349
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1350
another one.
1351

    
1352
<sect1>Configuration
1353

    
1354
<p><descrip>
1355
	<tag>peer table <m/table/</tag> Define secondary routing table to connect to. The
1356
	primary one is selected by the <cf/table/ keyword.
1357
</descrip>
1358

    
1359
<sect1>Attributes
1360

    
1361
<p>The Pipe protocol doesn't define any route attributes.
1362

    
1363
<sect1>Example
1364

    
1365
<p>Let's consider a router which serves as a boundary router of two different autonomous
1366
systems, each of them connected to a subset of interfaces of the router, having its own
1367
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1368
of outage of its own exterior line.
1369

    
1370
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1371
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1372
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1373
and similarly for the second AS. Thus we have split our router to two logical routers,
1374
each one acting on its own routing table, having its own routing protocols on its own
1375
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1376
the routes between the tables through a Pipe protocol while decreasing their preferences
1377
and correcting their BGP paths to reflect the AS boundary crossing.
1378

    
1379
<code>
1380
table as1;				# Define the tables
1381
table as2;
1382

    
1383
protocol kernel kern1 {			# Synchronize them with the kernel
1384
	table as1;
1385
	kernel table 1;
1386
}
1387

    
1388
protocol kernel kern2 {
1389
	table as2;
1390
	kernel table 2;
1391
}
1392

    
1393
protocol bgp bgp1 {			# The outside connections
1394
	table as1;
1395
	local as 1;
1396
	neighbor 192.168.0.1 as 1001;
1397
	export all;
1398
	import all;
1399
}
1400

    
1401
protocol bgp bgp2 {
1402
	table as2;
1403
	local as 2;
1404
	neighbor 10.0.0.1 as 1002;
1405
	export all;
1406
	import all;
1407
}
1408

    
1409
protocol pipe {				# The Pipe
1410
	table as1;
1411
	peer table as2;
1412
	export filter {
1413
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1414
			if preference>10 then preference = preference-10;
1415
			if source=RTS_BGP then bgp_path.prepend(1);
1416
			accept;
1417
		}
1418
		reject;
1419
	};
1420
	import filter {
1421
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1422
			if preference>10 then preference = preference-10;
1423
			if source=RTS_BGP then bgp_path.prepend(2);
1424
			accept;
1425
		}
1426
		reject;
1427
	};
1428
}
1429
</code>
1430

    
1431
<sect>RIP
1432

    
1433
<sect1>Introduction
1434

    
1435
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1436
distances to all networks it can reach. When a router hears distance to another network, it increments
1437
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1438
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1439
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1440
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1441
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1442
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1443
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1444
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1445
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
1446
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1447

    
1448
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1449
convergence, big network load and inability to handle larger networks
1450
makes it pretty much obsolete in IPv4 world. (It is still usable on
1451
very small networks.) It is widely used in IPv6 networks,
1452
because there are no good implementations of OSPFv3.
1453

    
1454
<sect1>Configuration
1455

    
1456
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1457

    
1458
<descrip>
1459
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1460
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1461
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1462
	  hash. If you set authentication to not-none, it is a good idea to add <cf>passwords { }</cf>
1463
	  section. Default: none.
1464

    
1465
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1466
	  be honored. (Always, when sent from a  host on a directly connected
1467
	  network or never.) Routing table updates are honored only from
1468
	  neighbors, that is not configurable. Default: never.
1469
</descrip>
1470

    
1471
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1472
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1473
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1474
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1475
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1476
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1477
interface but not listen to it.
1478

    
1479
<p>The following options generally override behavior specified in RFC. If you use any of these
1480
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1481
other than equally configured BIRD. I have warned you.
1482

    
1483
<descrip>
1484
	<tag>port <M>number</M></tag>
1485
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1486
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1487

    
1488
	<tag>infinity <M>number</M></tag>
1489
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1490
	  even slower.
1491

    
1492
	<tag>period <M>number</M>
1493
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1494
	  number will mean faster convergence but bigger network
1495
	  load. Do not use values lower than 10.
1496

    
1497
	<tag>timeout time <M>number</M>
1498
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1499

    
1500
	<tag>garbage time <M>number</M>
1501
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1502
</descrip>
1503

    
1504
<sect1>Attributes
1505

    
1506
<p>RIP defines two route attributes:
1507

    
1508
<descrip>
1509
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1510
	When routes from different RIP instances are available and all of them have the same
1511
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1512
	When importing a non-RIP route, the metric defaults to 5.
1513

    
1514
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1515
	to carry additional information with the route (for example, an originating AS number
1516
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1517
</descrip>
1518

    
1519
<sect1>Example
1520

    
1521
<p><code>
1522
protocol rip MyRIP_test {
1523
        debug all;
1524
        port 1520;
1525
        period 10;
1526
        garbage time 60;
1527
        interface "eth0" { metric 3; mode multicast; }
1528
	          "eth1" { metric 2; mode broadcast; };
1529
        honor neighbor;
1530
        authentication none;
1531
        import filter { print "importing"; accept; };
1532
        export filter { print "exporting"; accept; };
1533
}
1534
</code>
1535

    
1536
<sect>Static
1537

    
1538
<p>The Static protocol doesn't communicate with other routers in the network,
1539
but instead it allows you to define routes manually. This is often used for
1540
specifying how to forward packets to parts of the network which don't use
1541
dynamic routing at all and also for defining sink routes (i.e., those
1542
telling to return packets as undeliverable if they are in your IP block,
1543
you don't have any specific destination for them and you don't want to send
1544
them out through the default route to prevent routing loops).
1545

    
1546
<p>There are three types of static routes: `classical' routes telling to
1547
forward packets to a neighboring router, device routes specifying forwarding
1548
to hosts on a directly connected network and special routes (sink, blackhole
1549
etc.) which specify a special action to be done instead of forwarding the
1550
packet.
1551

    
1552
<p>When the particular destination is not available (the interface is down or
1553
the next hop of the route is not a neighbor at the moment), Static just
1554
uninstalls the route from the table it is connected to and adds it again as soon
1555
as the destination becomes adjacent again.
1556

    
1557
<p>The Static protocol has no configuration options. Instead, the
1558
definition of the protocol contains a list of static routes:
1559

    
1560
<descrip>
1561
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1562
	a neighboring router.
1563
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1564
	route through an interface to hosts on a directly connected network.
1565
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1566
	specifying to drop the packet, return it as unreachable or return
1567
	it as administratively prohibited.
1568
</descrip>
1569

    
1570
<p>Static routes have no specific attributes.
1571

    
1572
<p>Example static config might look like this:
1573

    
1574
<p><code>
1575
protocol static {
1576
	table testable;			 # Connect to a non-default routing table
1577
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1578
	route 62.168.0.0/25 reject;	 # Sink route
1579
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1580
}
1581
</code>
1582

    
1583
<chapt>Conclusions
1584

    
1585
<sect>Future work
1586

    
1587
<p>Although BIRD supports all the commonly used routing protocols,
1588
there are still some features which would surely deserve to be
1589
implemented in future versions of BIRD:
1590

    
1591
<itemize>
1592
<item>OSPF for IPv6 networks
1593
<item>OSPF NSSA areas and opaque LSA's
1594
<item>Route aggregation and flap dampening
1595
<item>Generation of IPv6 router advertisements
1596
<item>Multipath routes
1597
<item>Multicast routing protocols
1598
<item>Ports to other systems
1599
</itemize>
1600

    
1601
<sect>Getting more help
1602

    
1603
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1604
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1605
where you can share your experiences with the other users and consult
1606
your problems with the authors. To subscribe to the list, just send a
1607
<tt/subscribe bird-users/ command in a body of a mail to
1608
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1609
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1610

    
1611
<p>BIRD is a relatively young system and it probably contains some
1612
bugs. You can report any problems to the bird-users list and the authors
1613
will be glad to solve them, but before you do so,
1614
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1615
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1616
which fixes the bug is always welcome as an attachment.)
1617

    
1618
<p>If you want to understand what is going inside, Internet standards are
1619
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">).
1620

    
1621
<p><it/Good luck!/
1622

    
1623
</book>
1624

    
1625
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1626
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1627
LocalWords:  linuxdoc dtd descrip config conf syslog stderr auth ospf bgp Mbps
1628
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1637
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