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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
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	  <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. For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
532
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
533
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
534
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
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
multiprotocol extensions
673
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
674
and 4B AS numbers 
675
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
676

    
677

    
678
For IPv6, it uses the standard multiprotocol extensions defined in
679
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
680
including changes described in the
681
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
682
and applied to IPv6 according to
683
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
684

    
685
<sect1>Route selection rules
686

    
687
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
688
route among multiple BGP routes with the same preference are a bit more complex
689
and they are implemented according to the following algorithm. It starts the first
690
rule, if there are more "best" routes, then it uses the second rule to choose
691
among them and so on.
692

    
693
<itemize>
694
	<item>Prefer route with the highest Local Preference attribute.
695
	<item>Prefer route with the shortest AS path.
696
	<item>Prefer IGP origin over EGP and EGP over incomplete.
697
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
698
	<item>Prefer internal routes over external ones.
699
	<item>Prefer the route with the lowest value of router ID of the
700
	advertising router.
701
</itemize>
702

    
703
<sect1>Configuration
704

    
705
<p>Each instance of the BGP corresponds to one neighboring router.
706
This allows to set routing policy and all the other parameters differently
707
for each neighbor using the following configuration parameters:
708

    
709
<descrip>
710
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
711
	contrary to other IP routers, BIRD is able to act as a router located
712
	in multiple AS'es simultaneously, but in such cases you need to tweak
713
	the BGP paths manually in the filters to get consistent behavior.)
714
	This parameter is mandatory.
715

    
716
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
717
	this instance will be talking to and what AS it's located in. Unless
718
	you use the <cf/multihop/ clause, it must be directly connected to one
719
	of your router's interfaces. In case the neighbor is in the same AS
720
	as we are, we automatically switch to iBGP. This parameter is mandatory.
721

    
722
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
723
	neighbor which is connected at most <m/number/ hops far and to which
724
	we should route via our direct neighbor with address <m/ip/.
725
	Default: switched off.
726

    
727
	<tag>next hop self</tag> Avoid calculation of the Next Hop attribute
728
	and always advertise our own source address (see below) as a next hop.
729
	This needs to be used only
730
	occasionally to circumvent misconfigurations of other routers.
731
	Default: disabled.
732

    
733
	<tag>source address <m/ip/</tag> Define local address we should use
734
	for next hop calculation. Default: the address of the local end
735
	of the interface our neighbor is connected to.
736

    
737
	<tag>password <m/string/</tag> Use this password for MD5 authentication
738
	of BGP sessions. Default: no authentication.
739

    
740
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
741
	a route reflection client. Default: disabled.
742

    
743
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
744
	to avoid route reflection loops. When there is one route reflector in a cluster
745
	it usually uses its router id as a cluster id, but when there are more route
746
	reflectors in a cluster, these need to be configured (using this option) to
747
	use a common cluster id. Clients in a cluster need not know their cluster
748
	id and this option is not allowed for them. Default: the same as router id.
749

    
750
	<tag>rs client</tag> Be a route server and treat the neighbor
751
	as a route server client. A route server is used as a
752
	replacement for full mesh EBGP routing in Internet exchange
753
	points in a similar way to route reflectors used in IBGP routing.
754
	Bird does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
755
	which behaves like plain EBGP but reduces modifications to advertised route
756
	attributes to be transparent (for example does not prepend its AS number to
757
	AS PATH attribute and keep MED attribute). Default: disabled.
758

    
759
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
760
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
761
	but by disabling this option it can be persuaded not to advertise it and
762
	to maintain old-style sessions with its neighbors. This might be useful for
763
	circumventing bugs in neighbor's implementation of 4B AS extension.
764
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
765
	Default: on.
766

    
767
	<tag>capabilities <m/switch/</tag> Use capability advertisement
768
	to advertise optional capabilities. This is standard behavior
769
	for newer BGP implementations, but there might be some older
770
	BGP implementations that reject such connection attempts.
771
	When disabled (off), features that request it (4B AS support)
772
	are also disabled. Default: on, with automatic fallback to
773
	off when received capability-related error.
774

    
775
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
776
	This is not a correct behavior according to the strict interpretation
777
	of RFC 4760, but it is widespread and required by some BGP
778
	implementations (Cisco and Quagga). This option is relevant
779
	to IPv4 mode with enabled capability advertisement only. Default: on.
780

    
781
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
782
	locally or by the other side), disable the instance automatically
783
	and wait for an administrator to fix the problem manually. Default: off.
784

    
785
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
786
	message from the other side before considering the connection stale.
787
	Default: depends on agreement with the neighboring router, we prefer
788
	240 seconds if the other side is willing to accept it.
789

    
790
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
791
	before the routers have a chance to exchange open messages and agree
792
	on the real value. Default: 240 seconds.
793

    
794
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
795
	of two consecutive Keepalive messages. Default: One third of the hold time.
796

    
797
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
798
	retrying a failed attempt to connect. Default: 120 seconds.
799

    
800
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
801
	startup and the first attempt to connect. Default: 5 seconds.
802

    
803
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
804
	failure (either local or reported by the peer) and automatic restart.
805
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
806
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
807

    
808
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
809
	failures to treat them as a error sequence which makes the <cf/error wait time/
810
	increase exponentially. Default: 300 seconds.
811

    
812
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
813
	when deciding which BGP route is the best one. Default: on.
814

    
815
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
816
	Discriminator to be used during route selection when the MED attribute
817
	is missing. Default: 0.
818

    
819
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
820
	to be used during route selection when the Local Preference attribute
821
	is missing. Default: 0.
822
</descrip>
823

    
824
<sect1>Attributes
825

    
826
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
827
table below) are available on internal BGP connections only, some of them (marked
828
with `<tt/O/') are optional.
829

    
830
<descrip>
831
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
832
	the packet will travel through when forwarded according to the particular route. In case of 
833
	internal BGP it doesn't contain the number of the local AS.
834

    
835
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
836
	selection among multiple BGP routes (see the selection rules above). It's
837
	used as an additional metric which is propagated through the whole local AS.
838

    
839
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
840
	is an optional attribute which is used on on external (inter-AS) links to
841
	convey to an adjacent AS the optimal entry point into the local AS.
842
	The received attribute may be also propagated over internal BGP links
843
	(and this is default behavior). The attribute value is zeroed when a route
844
	is exported from a routing table to a BGP instance to ensure that the attribute
845
	received from a neighboring AS is not propagated to other neighboring ASes.
846
	A new value might be set in the export filter of a BGP instance.
847
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
848
	for further discussion of BGP MED attribute.
849

    
850
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
851
	if the route has originated in an interior routing protocol or
852
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
853
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
854
	is unknown.
855

    
856
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
857
	to this destination. On internal BGP connections, it's an address of the
858
	originating router if it's inside the local AS or a boundary router the
859
	packet will leave the AS through if it's an exterior route, so each BGP
860
	speaker within the AS has a chance to use the shortest interior path
861
	possible to this point.
862

    
863
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
864
	which carries no value, but the sole presence of which indicates that the route
865
	has been aggregated from multiple routes by some router on the path from
866
	the originator.
867

    
868
<!-- we don't handle aggregators right since they are of a very obscure type
869
	<tag>bgp_aggregator</tag>
870
-->
871
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
872
	with the route. Each such value is a pair (represented as a <cf/pair/ data
873
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
874
	the community and the second one being a per-AS identifier. There are lots
875
	of uses of the community mechanism, but generally they are used to carry
876
	policy information like "don't export to USA peers". As each AS can define
877
	its own routing policy, it also has a complete freedom about which community
878
	attributes it defines and what will their semantics be.
879
</descrip>
880

    
881
<sect1>Example
882

    
883
<p><code>
884
protocol bgp {
885
	local as 65000;			     # Use a private AS number
886
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
887
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
888
	export filter {			     # We use non-trivial export rules
889
		if source = RTS_STATIC then { # Export only static routes
890
		        # Assign our community
891
			bgp_community.add((65000,5678));
892
			# Artificially increase path length
893
			# by advertising local AS number twice
894
			if bgp_path ~ [= 65000 =] then	  
895
				bgp_path.prepend(65000);  
896
			accept;
897
		}
898
		reject;
899
	};
900
	import all;
901
	source address 62.168.0.1;	# Use a non-standard source address
902
}
903
</code>
904

    
905
<sect>Device
906

    
907
<p>The Device protocol is not a real routing protocol.  It doesn't generate
908
any routes and it only serves as a module for getting information about network
909
interfaces from the kernel.
910

    
911
<p>Except for very unusual circumstances, you probably should include
912
this protocol in the configuration since almost all other protocols
913
require network interfaces to be defined for them to work with.
914

    
915
<p>The only configurable thing is interface scan time:
916

    
917
<p><descrip>
918
	<tag>scan time <m/number/</tag> Time in seconds between two scans
919
	of the network interface list. On systems where we are notified about
920
	interface status changes asynchronously (such as newer versions of
921
	Linux), we need to scan the list only in order to avoid confusion by lost
922
	notification messages, so the default time is set to a large value.
923
</descrip>
924

    
925
<p>As the Device protocol doesn't generate any routes, it cannot have
926
any attributes. Example configuration looks really simple:
927

    
928
<p><code>
929
protocol device {
930
	scan time 10;		# Scan the interfaces often
931
}
932
</code>
933

    
934
<sect>Direct
935

    
936
<p>The Direct protocol is a simple generator of device routes for all the
937
directly connected networks according to the list of interfaces provided
938
by the kernel via the Device protocol.
939

    
940
<p>It's highly recommended to include this protocol in your configuration
941
unless you want to use BIRD as a route server or a route reflector, that is
942
on a machine which doesn't forward packets itself and only participates in
943
distribution of routing information.
944

    
945
<p>The only configurable thing about direct is what interfaces it watches:
946

    
947
<p><descrip>
948
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
949
	protocol will generate device routes for all the interfaces
950
	available. If you want to restrict it to some subset of interfaces
951
	(for example if you're using multiple routing tables for policy
952
	routing and some of the policy domains don't contain all interfaces),
953
	just use this clause.
954
</descrip>
955

    
956
<p>Direct device routes don't contain any specific attributes.
957

    
958
<p>Example config might look like this:
959

    
960
<p><code>
961
protocol direct {
962
	interface "-arc*", "*";		# Exclude the ARCnets
963
}
964
</code>
965

    
966
<sect>Kernel
967

    
968
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
969
the with other routers in the network, it performs synchronization of BIRD's routing
970
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
971
and from time to time it scans the kernel tables to see whether some routes have
972
disappeared (for example due to unnoticed up/down transition of an interface)
973
or whether an `alien' route has been added by someone else (depending on the
974
<cf/learn/ switch, such routes are either deleted or accepted to our
975
table).
976

    
977
<p>If your OS supports only a single routing table, you can configure only one
978
instance of the Kernel protocol. If it supports multiple tables (in order to
979
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
980
them must be connected to a different BIRD routing table and to a different
981
kernel table.
982

    
983
<sect1>Configuration
984

    
985
<p><descrip>
986
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
987
	routing tables when it exits (instead of cleaning them up).
988
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
989
	kernel routing table.
990
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
991
	routing tables by other routing daemons or by the system administrator.
992
	This is possible only on systems which support identification of route
993
	authorship.
994
	<tag>kernel table <m/number/</tag> Select which kernel table should
995
	this particular instance of the Kernel protocol work with. Available
996
	only on systems supporting multiple routing tables.
997
</descrip>
998

    
999
<p>The Kernel protocol doesn't define any route attributes.
1000
<p>A simple configuration can look this way:
1001

    
1002
<p><code>
1003
protocol kernel {
1004
	import all;
1005
	export all;
1006
}
1007
</code>
1008

    
1009
<p>Or for a system with two routing tables:
1010

    
1011
<p><code>
1012
protocol kernel {		# Primary routing table
1013
	learn;			# Learn alien routes from the kernel
1014
	persist;		# Don't remove routes on bird shutdown
1015
	scan time 10;		# Scan kernel routing table every 10 seconds
1016
	import all;
1017
	export all;
1018
}
1019

    
1020
protocol kernel {		# Secondary routing table
1021
	table auxtable;
1022
	kernel table 100;
1023
	export all;
1024
}
1025
</code>
1026

    
1027
<sect>OSPF
1028

    
1029
<sect1>Introduction
1030

    
1031
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1032
protocol. The current IPv4 version (OSPFv2) is defined
1033
in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
1034
state (a.k.a. shortest path first) protocol -- each router maintains a database
1035
describing the autonomous system's topology. Each participating router
1036
has an identical copy of the database and all routers run the same algorithm
1037
calculating a shortest path tree with themselves as a root.
1038
OSPF chooses the least cost path as the best path.
1039
(OSPFv3 - OSPF for IPv6 is not supported yet.)
1040

    
1041
<p>In OSPF, the autonomous system can be split to several areas in order
1042
to reduce the amount of resources consumed for exchanging the routing
1043
information and to protect the other areas from incorrect routing data.
1044
Topology of the area is hidden to the rest of the autonomous system.
1045

    
1046
<p>Another very important feature of OSPF is that
1047
it can keep routing information from other protocols (like Static or BGP)
1048
in its link state database as external routes. Each external route can
1049
be tagged by the advertising router, making it possible to pass additional
1050
information between routers on the boundary of the autonomous system.
1051

    
1052
<p>OSPF quickly detects topological changes in the autonomous system (such
1053
as router interface failures) and calculates new loop-free routes after a short
1054
period of convergence. Only a minimal amount of 
1055
routing traffic is involved.
1056

    
1057
<p>Each router participating in OSPF routing periodically sends Hello messages
1058
to all its interfaces. This allows neighbors to be discovered dynamically.
1059
Then the neighbors exchange theirs parts of the link state database and keep it
1060
identical by flooding updates. The flooding process is reliable and ensures
1061
that each router detects all changes.
1062

    
1063
<sect1>Configuration
1064

    
1065
<p>In the main part of configuration, there can be multiple definitions of
1066
OSPF area witch different id included. These definitions includes many other
1067
switches and multiple definitions of interfaces. Definition of interface
1068
may contain many switches and constant definitions and list of neighbors
1069
on nonbroadcast networks.
1070

    
1071
<code>
1072
protocol ospf &lt;name&gt; {
1073
	rfc1583compat &lt;switch&gt;;
1074
	tick &lt;num&gt;;
1075
	area &lt;id&gt; {
1076
		stub cost &lt;num&gt;;
1077
                networks {
1078
			&lt;prefix&gt;;
1079
			&lt;prefix&gt; hidden;
1080
		}
1081
		interface &lt;interface pattern&gt;
1082
		{
1083
			cost &lt;num&gt;;
1084
			stub &lt;switch&gt;;
1085
			hello &lt;num&gt;;
1086
			poll &lt;num&gt;;
1087
			retransmit &lt;num&gt;;
1088
			priority &lt;num&gt;;
1089
			wait &lt;num&gt;;
1090
			dead count &lt;num&gt;;
1091
			dead &lt;num&gt;;
1092
			rx buffer [normal|large|&lt;num&gt;];
1093
			type [broadcast|nonbroadcast|pointopoint];
1094
			strict nonbroadcast &lt;switch&gt;;
1095
			authentication [none|simple|cryptographics];
1096
			password "&lt;text&gt;";
1097
			password "&lt;text&gt;" {
1098
				id &lt;num&gt;;
1099
				generate from "&lt;date&gt;";
1100
				generate to "&lt;date&gt;";
1101
				accept from "&lt;date&gt;";
1102
				accept to "&lt;date&gt;";
1103
			};
1104
			neighbors {
1105
				&lt;ip&gt;;
1106
				&lt;ip&gt; eligible;
1107
			};
1108
		};
1109
		virtual link &lt;id&gt;
1110
		{
1111
			hello &lt;num&gt;;
1112
			retransmit &lt;num&gt;;
1113
			wait &lt;num&gt;;
1114
			dead count &lt;num&gt;;
1115
			dead &lt;num&gt;;
1116
			authentication [none|simple];
1117
			password "&lt;text&gt;";
1118
		};
1119
	};
1120
}
1121
</code>
1122

    
1123
<descrip>
1124
	<tag>rfc1583compat <M>switch</M></tag>
1125
	 This option controls compatibility of routing table
1126
	 calculation with RFC 1583<htmlurl
1127
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1128
	 value is no.
1129
	
1130
	<tag>area <M>id</M></tag>
1131
	 This defines an OSPF area with given area ID (an integer or an IPv4
1132
	 address, similarly to a router ID).
1133
	 The most important area is
1134
	 the backbone (ID 0) to which every other area must be connected.
1135

    
1136
	<tag>stub cost <M>num</M></tag>
1137
	 No external (except default) routes are flooded into stub areas.
1138
         Setting this value marks area stub with defined cost of default route.
1139
	 Default value is no. (Area is not stub.)
1140

    
1141
	<tag>tick <M>num</M></tag>
1142
	 The routing table calculation and clean-up of areas' databases
1143
         is not performed when a single link state
1144
	 change arrives. To lower the CPU utilization, it's processed later
1145
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1146

    
1147
	<tag>networks { <m/set/ }</tag>
1148
         Definition of area IP ranges. This is used in summary lsa origination.
1149
	 Hidden networks are not propagated into other areas.
1150

    
1151
	<tag>interface <M>pattern</M></tag>
1152
	 Defines that the specified interfaces belong to the area being defined.
1153

    
1154
	<tag>virtual link <M>id</M></tag>
1155
	 Virtual link to router with the router id. Virtual link acts as a
1156
         point-to-point interface belonging to backbone. The actual area is
1157
         used as transport area. This item cannot be in the backbone.
1158

    
1159
	<tag>cost <M>num</M></tag>
1160
	 Specifies output cost (metric) of an interface. Default value is 10.
1161

    
1162
	<tag>stub <M>switch</M></tag>
1163
	 If set to interface it does not listen to any packet and does not send
1164
	 any hello. Default value is no.
1165

    
1166
	<tag>hello <M>num</M></tag>
1167
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1168
	 routers on the same network need to have the same hello interval.
1169
	 Default value is 10.
1170

    
1171
	<tag>poll <M>num</M></tag>
1172
	 Specifies interval in seconds between sending of Hello messages for
1173
	 some neighbors on NBMA network. Default value is 20.
1174

    
1175
	<tag>retransmit <M>num</M></tag>
1176
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1177
	 Default value is 5.
1178

    
1179
        <tag>priority <M>num</M></tag>
1180
	 On every multiple access network (e.g., the Ethernet) Designed Router
1181
	 and Backup Designed router are elected. These routers have some
1182
	 special functions in the flooding process. Higher priority increases
1183
	 preferences in this election. Routers with priority 0 are not
1184
	 eligible. Default value is 1.
1185

    
1186
	<tag>wait <M>num</M></tag>
1187
	 After start, router waits for the specified number of seconds between starting
1188
	 election and building adjacency. Default value is 40.
1189
	 
1190
	<tag>dead count <M>num</M></tag>
1191
	 When the router does not receive any messages from a neighbor in
1192
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1193

    
1194
	<tag>dead <M>num</M></tag>
1195
	 When the router does not receive any messages from a neighbor in
1196
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1197
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1198

    
1199
	<tag>rx buffer <M>num</M></tag>
1200
	 This sets the size of buffer used for receiving packets. The buffer should
1201
	 be bigger than maximal size of any packets. Value NORMAL (default)
1202
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1203

    
1204
	<tag>type broadcast</tag>
1205
	 BIRD detects a type of a connected network automatically, but sometimes it's
1206
	 convenient to force use of a different type manually.
1207
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1208
	 (a single packet for all the neighbors).
1209

    
1210
	<tag>type pointopoint</tag>
1211
	 Point-to-point networks connect just 2 routers together. No election
1212
	 is performed there which reduces the number of messages sent.
1213

    
1214
	<tag>type nonbroadcast</tag>
1215
	 On nonbroadcast networks, the packets are sent to each neighbor
1216
	 separately because of lack of multicast capabilities.
1217

    
1218
	<tag>strict nonbroadcast <M>switch</M></tag>
1219
	 If set, don't send hello to any undefined neighbor. This switch
1220
	 is ignored on on any non-NBMA network. Default is No.
1221

    
1222
	<tag>authentication none</tag>
1223
	 No passwords are sent in OSPF packets. This is the default value.
1224

    
1225
	<tag>authentication simple</tag>
1226
	 Every packet carries 8 bytes of password. Received packets
1227
	 lacking this password are ignored. This authentication mechanism is
1228
	 very weak.
1229

    
1230
	<tag>authentication cryptographic</tag>
1231
	 16-byte long MD5 digest is appended to every packet. For the digest
1232
         generation 16-byte long passwords are used. Those passwords are 
1233
         not sent via network, so this mechanismus is quite secure.
1234
         Packets can still be read by an attacker.
1235

    
1236
	<tag>password "<M>text</M>"</tag>
1237
	 An 8-byte or 16-byte password used for authentication.
1238

    
1239
	<tag>id <M>num</M></tag>
1240
	 ID of the password, (0-255). If it's not used, BIRD will choose
1241
	 ID based on an order of the password item in the interface. For
1242
	 example, second password item in one interface will have default
1243
	 ID 2.  
1244

    
1245
	<tag>generate from <M>date</M></tag>
1246
	 The start time of the usage of the password for packet signing.
1247

    
1248
	<tag>generate to <M>date</M></tag>
1249
	 The last time of the usage of the password for packet signing.
1250

    
1251
	<tag>accept from <M>date</M></tag>
1252
	 The start time of the usage of the password for packet verification.
1253

    
1254
	<tag>accept to <M>date</M></tag>
1255
	 The last time of the usage of the password for packet verification.
1256

    
1257
	<tag>neighbors { <m/set/ } </tag>
1258
	 A set of neighbors to which Hello messages on nonbroadcast networks
1259
	 are to be sent. Some of them could be marked as eligible.
1260

    
1261
</descrip>
1262

    
1263
<sect1>Attributes
1264

    
1265
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1266
Metric is ranging from 1 to infinity (65535).
1267
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1268
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1269
<cf/metric of type 2/ is always longer
1270
than any <cf/metric of type 1/ or any <cf/internal metric/.
1271
If you specify both metrics only metric1 is used.
1272
Each external route can also carry a <cf/tag/ which is a 32-bit
1273
integer which is used when exporting routes to other protocols;
1274
otherwise, it doesn't affect routing inside the OSPF domain at all.
1275
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1276

    
1277
<sect1>Example
1278

    
1279
<p>
1280

    
1281
<code>
1282
protocol ospf MyOSPF {
1283
        rfc1583compatibility yes;
1284
        tick 2;
1285
	export filter {
1286
		if source = RTS_BGP then {
1287
			ospf_metric1 = 100;
1288
			accept;
1289
		}
1290
		reject;
1291
	};                                                                      
1292
	area 0.0.0.0 {
1293
		interface "eth*" {
1294
			cost 11;
1295
			hello 15;
1296
			priority 100;
1297
			retransmit 7;
1298
			authentication simple;
1299
			password "aaa";
1300
		};
1301
		interface "ppp*" {
1302
			cost 100;
1303
			authentication cryptographic;
1304
			passwords {
1305
				password "abc" {
1306
					id 1;
1307
					generate to "22-04-2003 11:00:06";
1308
					accept from "17-01-2001 12:01:05";
1309
				};
1310
				password "def" {
1311
					id 2;
1312
					generate to "22-07-2005 17:03:21";
1313
					accept from "22-02-2001 11:34:06";
1314
				};
1315
			};
1316
		};
1317
		interface "arc0" {
1318
			cost 10;
1319
			stub yes;
1320
		};
1321
		interface "arc1";
1322
	};
1323
	area 120 {
1324
		stub yes;
1325
		networks {
1326
			172.16.1.0/24;
1327
			172.16.2.0/24 hidden;
1328
		}
1329
		interface "-arc0" , "arc*" {
1330
			type nonbroadcast;
1331
			authentication none;
1332
			strict nonbroadcast yes;
1333
			wait 120;
1334
			poll 40;
1335
			dead count 8;
1336
			neighbors {
1337
				192.168.120.1 eligible;
1338
				192.168.120.2;
1339
				192.168.120.10;
1340
			};
1341
		};
1342
	};
1343
}
1344
</code>
1345

    
1346
<sect>Pipe
1347

    
1348
<sect1>Introduction
1349

    
1350
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1351
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1352
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1353
and vice versa, depending on what's allowed by the filters. Export filters control export
1354
of routes from the primary table to the secondary one, import filters control the opposite
1355
direction.
1356

    
1357
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1358
where handling of a single packet doesn't depend only on its destination address, but also
1359
on its source address, source interface, protocol type and other similar parameters.
1360
In many systems (Linux 2.2 being a good example), the kernel allows to enforce routing policies
1361
by defining routing rules which choose one of several routing tables to be used for a packet
1362
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1363
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1364
connect them to the kernel ones, use filters to control which routes appear in which tables
1365
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1366
another one.
1367

    
1368
<sect1>Configuration
1369

    
1370
<p><descrip>
1371
	<tag>peer table <m/table/</tag> Define secondary routing table to connect to. The
1372
	primary one is selected by the <cf/table/ keyword.
1373
</descrip>
1374

    
1375
<sect1>Attributes
1376

    
1377
<p>The Pipe protocol doesn't define any route attributes.
1378

    
1379
<sect1>Example
1380

    
1381
<p>Let's consider a router which serves as a boundary router of two different autonomous
1382
systems, each of them connected to a subset of interfaces of the router, having its own
1383
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1384
of outage of its own exterior line.
1385

    
1386
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1387
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1388
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1389
and similarly for the second AS. Thus we have split our router to two logical routers,
1390
each one acting on its own routing table, having its own routing protocols on its own
1391
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1392
the routes between the tables through a Pipe protocol while decreasing their preferences
1393
and correcting their BGP paths to reflect the AS boundary crossing.
1394

    
1395
<code>
1396
table as1;				# Define the tables
1397
table as2;
1398

    
1399
protocol kernel kern1 {			# Synchronize them with the kernel
1400
	table as1;
1401
	kernel table 1;
1402
}
1403

    
1404
protocol kernel kern2 {
1405
	table as2;
1406
	kernel table 2;
1407
}
1408

    
1409
protocol bgp bgp1 {			# The outside connections
1410
	table as1;
1411
	local as 1;
1412
	neighbor 192.168.0.1 as 1001;
1413
	export all;
1414
	import all;
1415
}
1416

    
1417
protocol bgp bgp2 {
1418
	table as2;
1419
	local as 2;
1420
	neighbor 10.0.0.1 as 1002;
1421
	export all;
1422
	import all;
1423
}
1424

    
1425
protocol pipe {				# The Pipe
1426
	table as1;
1427
	peer table as2;
1428
	export filter {
1429
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1430
			if preference>10 then preference = preference-10;
1431
			if source=RTS_BGP then bgp_path.prepend(1);
1432
			accept;
1433
		}
1434
		reject;
1435
	};
1436
	import filter {
1437
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1438
			if preference>10 then preference = preference-10;
1439
			if source=RTS_BGP then bgp_path.prepend(2);
1440
			accept;
1441
		}
1442
		reject;
1443
	};
1444
}
1445
</code>
1446

    
1447
<sect>RIP
1448

    
1449
<sect1>Introduction
1450

    
1451
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1452
distances to all networks it can reach. When a router hears distance to another network, it increments
1453
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1454
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1455
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1456
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1457
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1458
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1459
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1460
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1461
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
1462
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1463

    
1464
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1465
convergence, big network load and inability to handle larger networks
1466
makes it pretty much obsolete in IPv4 world. (It is still usable on
1467
very small networks.) It is widely used in IPv6 networks,
1468
because there are no good implementations of OSPFv3.
1469

    
1470
<sect1>Configuration
1471

    
1472
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1473

    
1474
<descrip>
1475
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1476
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1477
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1478
	  hash. If you set authentication to not-none, it is a good idea to add <cf>passwords { }</cf>
1479
	  section. Default: none.
1480

    
1481
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1482
	  be honored. (Always, when sent from a  host on a directly connected
1483
	  network or never.) Routing table updates are honored only from
1484
	  neighbors, that is not configurable. Default: never.
1485
</descrip>
1486

    
1487
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1488
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1489
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1490
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1491
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1492
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1493
interface but not listen to it.
1494

    
1495
<p>The following options generally override behavior specified in RFC. If you use any of these
1496
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1497
other than equally configured BIRD. I have warned you.
1498

    
1499
<descrip>
1500
	<tag>port <M>number</M></tag>
1501
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1502
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1503

    
1504
	<tag>infinity <M>number</M></tag>
1505
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1506
	  even slower.
1507

    
1508
	<tag>period <M>number</M>
1509
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1510
	  number will mean faster convergence but bigger network
1511
	  load. Do not use values lower than 10.
1512

    
1513
	<tag>timeout time <M>number</M>
1514
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1515

    
1516
	<tag>garbage time <M>number</M>
1517
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1518
</descrip>
1519

    
1520
<sect1>Attributes
1521

    
1522
<p>RIP defines two route attributes:
1523

    
1524
<descrip>
1525
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1526
	When routes from different RIP instances are available and all of them have the same
1527
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1528
	When importing a non-RIP route, the metric defaults to 5.
1529

    
1530
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1531
	to carry additional information with the route (for example, an originating AS number
1532
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1533
</descrip>
1534

    
1535
<sect1>Example
1536

    
1537
<p><code>
1538
protocol rip MyRIP_test {
1539
        debug all;
1540
        port 1520;
1541
        period 10;
1542
        garbage time 60;
1543
        interface "eth0" { metric 3; mode multicast; }
1544
	          "eth1" { metric 2; mode broadcast; };
1545
        honor neighbor;
1546
        authentication none;
1547
        import filter { print "importing"; accept; };
1548
        export filter { print "exporting"; accept; };
1549
}
1550
</code>
1551

    
1552
<sect>Static
1553

    
1554
<p>The Static protocol doesn't communicate with other routers in the network,
1555
but instead it allows you to define routes manually. This is often used for
1556
specifying how to forward packets to parts of the network which don't use
1557
dynamic routing at all and also for defining sink routes (i.e., those
1558
telling to return packets as undeliverable if they are in your IP block,
1559
you don't have any specific destination for them and you don't want to send
1560
them out through the default route to prevent routing loops).
1561

    
1562
<p>There are three types of static routes: `classical' routes telling to
1563
forward packets to a neighboring router, device routes specifying forwarding
1564
to hosts on a directly connected network and special routes (sink, blackhole
1565
etc.) which specify a special action to be done instead of forwarding the
1566
packet.
1567

    
1568
<p>When the particular destination is not available (the interface is down or
1569
the next hop of the route is not a neighbor at the moment), Static just
1570
uninstalls the route from the table it is connected to and adds it again as soon
1571
as the destination becomes adjacent again.
1572

    
1573
<p>The Static protocol has no configuration options. Instead, the
1574
definition of the protocol contains a list of static routes:
1575

    
1576
<descrip>
1577
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1578
	a neighboring router.
1579
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1580
	route through an interface to hosts on a directly connected network.
1581
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1582
	specifying to drop the packet, return it as unreachable or return
1583
	it as administratively prohibited.
1584
</descrip>
1585

    
1586
<p>Static routes have no specific attributes.
1587

    
1588
<p>Example static config might look like this:
1589

    
1590
<p><code>
1591
protocol static {
1592
	table testable;			 # Connect to a non-default routing table
1593
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1594
	route 62.168.0.0/25 reject;	 # Sink route
1595
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1596
}
1597
</code>
1598

    
1599
<chapt>Conclusions
1600

    
1601
<sect>Future work
1602

    
1603
<p>Although BIRD supports all the commonly used routing protocols,
1604
there are still some features which would surely deserve to be
1605
implemented in future versions of BIRD:
1606

    
1607
<itemize>
1608
<item>OSPF for IPv6 networks
1609
<item>OSPF NSSA areas and opaque LSA's
1610
<item>Route aggregation and flap dampening
1611
<item>Generation of IPv6 router advertisements
1612
<item>Multipath routes
1613
<item>Multicast routing protocols
1614
<item>Ports to other systems
1615
</itemize>
1616

    
1617
<sect>Getting more help
1618

    
1619
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1620
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1621
where you can share your experiences with the other users and consult
1622
your problems with the authors. To subscribe to the list, just send a
1623
<tt/subscribe bird-users/ command in a body of a mail to
1624
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1625
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1626

    
1627
<p>BIRD is a relatively young system and it probably contains some
1628
bugs. You can report any problems to the bird-users list and the authors
1629
will be glad to solve them, but before you do so,
1630
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1631
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1632
which fixes the bug is always welcome as an attachment.)
1633

    
1634
<p>If you want to understand what is going inside, Internet standards are
1635
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">).
1636

    
1637
<p><it/Good luck!/
1638

    
1639
</book>
1640

    
1641
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1642
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1643
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1644
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1653
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