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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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	interface "*";
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}
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</code>
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<sect>Global options
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<p><descrip>
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	<tag>log "<m/filename/"|syslog|stderr all|{ <m/list of classes/ }</tag> 
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	Set logging of messages having the given class (either <cf/all/ or <cf/{
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	error, trace }/ etc.) into selected destination. Classes are:
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	<cf/info/, <cf/warning/, <cf/error/ and <cf/fatal/ for messages about local problems,
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	<cf/debug/ for debugging messages, 
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	<cf/trace/ when you want to know what happens in the network, 
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	<cf/remote/ for messages about misbehavior of remote machines, 
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	<cf/auth/ about authentication failures,
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	<cf/bug/ for internal BIRD bugs. You may specify more than one <cf/log/ line to establish logging to multiple
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	destinations. Default: log everything to the system log.
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	<tag>debug protocols all|off|{ states, routes, filters, interfaces, events, packets }</tag>
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	Set global defaults of protocol debugging options. See <cf/debug/ in the following section. Default: off.
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	<tag>debug commands <m/number/</tag>
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	Control logging of client connections (0 for no logging, 1 for
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	logging of connects and disconnects, 2 and higher for logging of
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	all client commands). Default: 0.
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	<tag>filter <m/name local variables/{ <m/commands/ }</tag> Define a filter. You can learn more about filters
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	in the following chapter. 
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	<tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag> Define a function. You can learn more
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	about functions in the following chapter.
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	<tag>protocol rip|ospf|bgp|... <m/[name]/ { <m>protocol options</m> }</tag> Define a protocol
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	instance called <cf><m/name/</cf> (or with a name like "rip5" generated automatically if you don't specify any <cf><m/name/</cf>). You can learn more
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	about configuring protocols in their own chapters. You can run more than one instance of
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	most protocols (like RIP or BGP). By default, no instances are configured.
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	<tag>define <m/constant/ = (<m/expression/)|<m/number/|<m/IP address/</tag> Define a constant. You can use it later in every place
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	you could use a simple integer or an IP address.
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	<tag>router id <m/IPv4 address/</tag> Set BIRD's router ID. It's a world-wide unique identification of your router, usually one of router's IPv4 addresses. Default: in IPv4 version, the lowest IP address of a non-loopback interface. In IPv6 version, this option is mandatory. 
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	<tag>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><label id="dsc-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...] [ { <m/option/ ; [...] } ]</tag>
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	Specifies a set of interfaces on which the protocol is activated with
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	given interface-specific options. A set of interfaces specified by one
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	interface option is described using an interface pattern. The
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	interface pattern consists of a sequence of clauses (separted by
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	commas), each clause may contain a mask, a prefix, or both of them. An
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	interface matches the clause if its name matches the mask (if
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	specified) and its address matches the prefix (if specified). Mask is
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	specified as shell-like pattern.
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	An interface matches the pattern if it matches any of its
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	clauses. If the clause begins with <cf/-/, matching interfaces are
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	excluded. Patterns are parsed left-to-right, thus
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	<cf/interface "eth0", -"eth*", "*";/ means eth0 and all
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	non-ethernets.
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	An interface option can be used more times with different
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	interfaces-specific options, in that case for given interface
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	the first matching interface option is used.
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	This option is allowed in Direct, OSPF and RIP protocols,
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	but in OSPF protocol it is used in <cf/area/ subsection.
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	Default: none.
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	Examples:
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	<cf>interface "*" { type broadcast; };</cf> - start the protocol on all interfaces with
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	<cf>type broadcast</cf> option.
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	<cf>interface "eth1", "eth4", "eth5" { type pointopoint; };</cf> - start the protocol
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	on enumerated interfaces with <cf>type pointopoint</cf> option.
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	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all
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	interfaces that have address from 192.168.0.0/16, but not
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	from 192.168.1.0/24.
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	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all
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	interfaces that have address from 192.168.0.0/16, but not
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	from 192.168.1.0/24.
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	<cf>interface "eth*" 192.168.1.0/24;</cf> - start the protocol on all
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	ethernet interfaces that have address from 192.168.1.0/24.
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	<tag><label id="dsc-pass">password "<m/password/" [ { id <m/num/; generate from <m/time/; generate to <m/time/; accept from <m/time/; accept to <m/time/; } ]</tag>
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	Specifies a password that can be used by the protocol. Password option can
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	be used more times to specify more passwords. If more passwords are
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	specified, it is a protocol-dependent decision which one is really
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	used. Specifying passwords does not mean that authentication is
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	enabled, authentication can be enabled by separate, protocol-dependent
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	<cf/authentication/ option.
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	This option is allowed in OSPF and RIP protocols. BGP has also
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	<cf/password/ option, but it is slightly different and described
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	separately.
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	Default: none.
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</descrip>
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<p>Password option can contain section with some (not necessary all) password sub-options:
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<descrip>
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	<tag>id <M>num</M></tag>
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	 ID of the password, (0-255). If it's not used, BIRD will choose
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	 ID based on an order of the password item in the interface. For
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	 example, second password item in one interface will have default
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	 ID 2. ID is used by some routing protocols to identify which
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	 password was used to authenticate protocol packets.
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	<tag>generate from "<m/time/"</tag>
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	 The start time of the usage of the password for packet signing.
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	 The format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
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	<tag>generate to "<m/time/"</tag>
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	 The last time of the usage of the password for packet signing.
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	<tag>accept from "<m/time/"</tag>
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	 The start time of the usage of the password for packet verification.
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	<tag>accept to "<m/time/"</tag>
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	 The last time of the usage of the password for packet verification.
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</descrip>
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<chapt>Remote control
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<p>You can use the command-line client <file>birdc</file> to talk with
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a running BIRD. Communication is done using a <file/bird.ctl/ UNIX domain
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socket (unless changed with the <tt/-s/ option given to both the server and
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the client). The commands can perform simple actions such as enabling/disabling
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of protocols, telling BIRD to show various information, telling it to
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show routing table filtered by filter, or asking BIRD to
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reconfigure. Press <tt/?/ at any time to get online help. Option
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<tt/-v/ can be passed to the client, to make it dump numeric return
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codes along with the messages. You do not necessarily need to use <file/birdc/ to talk to BIRD, your
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own applications could do that, too -- the format of communication between
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BIRD and <file/birdc/ is stable (see the programmer's documentation).
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Many commands have the <m/name/ of the protocol instance as an argument.
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This argument can be omitted if there exists only a single instance.
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<p>Here is a brief list of supported functions:
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<descrip>
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	<tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
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	Dump contents of internal data structures to the debugging output.
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	<tag>show status</tag>
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	Show router status, that is BIRD version, uptime and time from last reconfiguration.
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	<tag>show protocols [all]</tag>
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	Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified.
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	<tag>show ospf interface [<m/name/] ["<m/interface/"]</tag>
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	Show detailed information about OSPF interfaces.
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	<tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
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	Show a list of OSPF neighbors and a state of adjacency to them.
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	<tag>show ospf state [<m/name/]</tag>
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	Show detailed information about OSPF areas based on a content of link-state database.
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	It shows network topology,  aggregated networks and routers from other areas and external routes.
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	<tag>show ospf topology [<m/name/]</tag>
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	Show a topology of OSPF areas based on a content of link-state database.
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	It is just a stripped-down version of 'show ospf state'.
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	<tag>show static [<m/name/]</tag>
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	Show detailed information about static routes.
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	<tag>show interfaces [summary]</tag>
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	Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. 
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	<tag>show symbols</tag>
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	Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).
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	<tag>show route [[for] <m/prefix/|<m/IP/] [table <m/sym/] [filter <m/f/|where <m/c/] [(export|preexport) <m/p/] [protocol <m/p/] [<m/options/]</tag>
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	Show contents of a routing table (by default of the main one),
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	that is routes, their metrics and (in case the <cf/all/ switch is given)
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	all their attributes.
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	<p>You can specify a <m/prefix/ if you want to print routes for a
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	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
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	the entry which will be used for forwarding of packets to the given
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	destination. By default, all routes for each network are printed with
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	the selected one at the top, unless <cf/primary/ is given in which case
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	only the selected route is shown.
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	<p>You can also ask for printing only routes processed and accepted by
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	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
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	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
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	The <cf/export/ and <cf/preexport/ switches ask for printing of entries
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	that are exported to the specified protocol. With <cf/preexport/, the
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	export filter of the protocol is skipped.
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	<p>You can also select just routes added by a specific protocol.
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	<cf>protocol <m/p/</cf>.
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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
483
being passed between protocols and routing tables. The filter language contains control structures such
484
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>. 
485

    
486
<p>Filter gets the route, looks at its attributes and
487
modifies some of them if it wishes. At the end, it decides whether to
488
pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
489
like this:
490

    
491
<code>
492
filter not_too_far
493
int var;
494
{
495
	if defined( rip_metric ) then
496
		var = rip_metric;
497
	else {
498
		var = 1;
499
		rip_metric = 1;
500
	}
501
	if rip_metric &gt; 10 then
502
		reject "RIP metric is too big";
503
	else
504
		accept "ok";
505
}
506
</code>
507

    
508
<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
509
the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
510
<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
511
<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
512
several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
513
you want to make a bigger block of code conditional.
514

    
515
<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
516
over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
517
look like this:
518

    
519
<code>
520
function name ()
521
int local_variable;
522
{
523
	local_variable = 5;
524
}
525

    
526
function with_parameters (int parameter)
527
{
528
	print parameter;
529
}
530
</code>
531

    
532
<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
533
variables in nested blocks. Functions are called like in C: <cf>name();
534
with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
535
command. Returning a value exits from current function (this is similar to C).
536

    
537
<p>Filters are declared in a way similar to functions except they can't have explicit
538
parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
539
to any functions called. The filter must terminate with either
540
<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
541
is rejected. 
542

    
543
<p>A nice trick to debug filters is to use <cf>show route filter
544
<m/name/</cf> from the command line client. An example session might look
545
like:
546

    
547
<code>
548
pavel@bug:~/bird$ ./birdc -s bird.ctl
549
BIRD 0.0.0 ready.
550
bird> show route
551
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
552
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
553
127.0.0.0/8        dev lo [direct1 23:21] (240)
554
bird> show route ?
555
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
556
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
557
127.0.0.0/8        dev lo [direct1 23:21] (240)
558
bird>
559
</code>
560

    
561
<sect>Data types
562

    
563
<p>Each variable and each value has certain type. Booleans, integers and enums are
564
incompatible with each other (that is to prevent you from shooting in the foot).
565

    
566
<descrip>
567
	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
568
	  <cf/false/. Boolean is the only type you can use in <cf/if/
569
	  statements.
570

    
571
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
572
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
573

    
574
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
575
	  65535. Literals of this type is written as <cf/(1234,5678)/.
576

    
577
	<tag/string/ This is a string of characters. There are no ways to modify strings in
578
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
579
	  such variables, but you can't concatenate two strings. String literals
580
	  are written as <cf/"This is a string constant"/.
581

    
582
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
583
	  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>
584
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
585
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
586

    
587
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
588
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
589
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
590
	  operators on prefixes:
591
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
592
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
593

    
594
	<tag/int|ip|prefix|pair|enum set/
595
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
596
	  but you can't modify them. Literals of type <cf>set int</cf> look like <cf>
597
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
598
	  sets.
599

    
600
	  Sets of prefixes are special: their literals does not allow ranges, but allows
601
	  prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
602
	  Prefix <cf><m>ip1</m>/<m>len1</m></cf> matches prefix pattern <cf><m>ip2</m>/<m>len2</m>{<m>l</m>,<m>h</m>}</cf> iff 
603
	  the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>.
604
	  A valid prefix pattern has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/
605
	  or <cf/high/. Obviously, a prefix matches a prefix set literal iff it matches any prefix pattern in the
606
	  prefix set literal.
607

    
608
	  There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for
609
	  <cf><m>address</m>/<m/len/{<m/len/,<m/maxlen/}</cf> (where <cf><m>maxlen</m></cf> is 32 for IPv4 and 128 for IPv6), 
610
	  that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf>
611
	  is a shorthand for <cf><m>address</m>/<m/len/{0,<m/len/}</cf>, that means network prefix <cf><m>address</m>/<m/len/</cf>
612
	  and all its supernets (network prefixes that contain it).
613

    
614
	  For example, <cf>[ 1.0.0.0/8, 2.0.0.0/8+, 3.0.0.0/8-, 4.0.0.0/8{16,24} ]</cf> matches
615
	  prefix <cf>1.0.0.0/8</cf>, all subprefixes of <cf>2.0.0.0/8</cf>, all superprefixes of <cf>3.0.0.0/8</cf> and prefixes
616
	  <cf/4.X.X.X/ whose prefix length is 16 to 24. <cf>[ 0.0.0.0/0{20,24} ]</cf> matches all prefixes (regardless of
617
	  IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address
618
	  <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf> is true,
619
	  but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
620

    
621
	  Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
622
	  in Bird as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
623
	  <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
624
	  <cf>192.168.0.0/16{24,32}</cf>.
625

    
626
	<tag/enum/
627
	  Enumeration types are fixed sets of possibilities. You can't define your own
628
	  variables of such type, but some route attributes are of enumeration
629
	  type. Enumeration types are incompatible with each other.
630

    
631
	<tag/bgppath/
632
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
633

    
634
	<tag/bgpmask/
635
	  BGP masks are patterns used for BGP path matching
636
	  (using <cf>path &tilde; [= 2 3 5 * =]</cf> syntax). The masks
637
	  resemble wildcard patterns as used by UNIX shells. Autonomous
638
	  system numbers match themselves, <cf/*/ matches any (even empty)
639
	  sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number.
640
	  For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
641
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
642
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
643
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
644
	<tag/clist/ 
645
	  Community list is similar to set of pairs,
646
	  except that unlike other sets, it can be modified.
647
	  There exist no literals of this type.
648

    
649
</descrip>
650

    
651
<sect>Operators
652

    
653
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
654
<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;/). 
655
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
656
used on element and set of elements of the same type (returning true if element is contained in the given set), or
657
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
658
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).
659

    
660

    
661
<sect>Control structures
662

    
663
<p>Filters support two control structures: conditions and case switches. 
664

    
665
<p>Syntax of a condition is: <cf>if
666
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
667
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
668
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.
669

    
670
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
671
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
672
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
673
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
674
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.
675

    
676
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
677

    
678
<code>
679
case arg1 {
680
	2: print "two"; print "I can do more commands without {}";
681
	3 .. 5: print "three to five";
682
	else: print "something else";
683
}
684

    
685
if 1234 = i then printn "."; else { 
686
  print "not 1234"; 
687
  print "You need {} around multiple commands"; 
688
}
689
</code>
690

    
691
<sect>Route attributes
692

    
693
<p>A filter is implicitly passed a route, and it can access its
694
attributes just like it accesses variables. Attempts to access undefined
695
attribute result in a runtime error; you can check if an attribute is
696
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
697

    
698
<descrip>
699
	<tag><m/prefix/ net</tag>
700
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
701

    
702
	<tag><m/enum/ scope</tag>
703
	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).
704

    
705
	<tag><m/int/ preference</tag>
706
	Preference of the route. (See the chapter about routing tables.)
707

    
708
	<tag><m/ip/ from</tag>
709
	The router which the route has originated from. Read-only.
710
	
711
	<tag><m/ip/ gw</tag>
712
	Next hop packets routed using this route should be forwarded to.
713

    
714
	<tag><m/string/ proto</tag>
715
	The name of the protocol which the route has been imported from. Read-only.
716

    
717
	<tag><m/enum/ source</tag>
718
	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/.
719

    
720
	<tag><m/enum/ cast</tag>
721
	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.
722

    
723
	<tag><m/enum/ dest</tag>
724
	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.
725
</descrip>
726

    
727
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
728

    
729
<sect>Other statements
730

    
731
<p>The following statements are available:
732

    
733
<descrip>
734
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
735

    
736
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
737

    
738
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
739

    
740
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
741
	Prints given expressions; useful mainly while debugging
742
	filters. The <cf/printn/ variant does not terminate the line.
743

    
744
	<tag>quitbird</tag>
745
	Terminates BIRD. Useful when debugging the filter interpreter.
746
</descrip>
747

    
748
<chapt>Protocols
749

    
750
<sect>BGP
751

    
752
<p>The Border Gateway Protocol is the routing protocol used for backbone
753
level routing in the today's Internet. Contrary to the other protocols, its convergence
754
doesn't rely on all routers following the same rules for route selection,
755
making it possible to implement any routing policy at any router in the
756
network, the only restriction being that if a router advertises a route,
757
it must accept and forward packets according to it.
758

    
759
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
760
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
761
Routers within each AS usually communicate with each other using either a interior routing
762
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
763
Boundary routers at the border of the AS communicate with their peers
764
in the neighboring AS'es via exterior BGP (eBGP).
765

    
766
<p>Each BGP router sends to its neighbors updates of the parts of its
767
routing table it wishes to export along with complete path information
768
(a list of AS'es the packet will travel through if it uses the particular
769
route) in order to avoid routing loops.
770

    
771
<p>BIRD supports all requirements of the BGP4 standard as defined in
772
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
773
It also supports the community attributes
774
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
775
capability negotiation
776
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
777
MD5 password authentication
778
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
779
route reflectors 
780
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
781
multiprotocol extensions
782
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
783
and 4B AS numbers 
784
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
785

    
786

    
787
For IPv6, it uses the standard multiprotocol extensions defined in
788
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
789
including changes described in the
790
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
791
and applied to IPv6 according to
792
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
793

    
794
<sect1>Route selection rules
795

    
796
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
797
route among multiple BGP routes with the same preference are a bit more complex
798
and they are implemented according to the following algorithm. It starts the first
799
rule, if there are more "best" routes, then it uses the second rule to choose
800
among them and so on.
801

    
802
<itemize>
803
	<item>Prefer route with the highest Local Preference attribute.
804
	<item>Prefer route with the shortest AS path.
805
	<item>Prefer IGP origin over EGP and EGP over incomplete.
806
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
807
	<item>Prefer internal routes over external ones.
808
	<item>Prefer the route with the lowest value of router ID of the
809
	advertising router.
810
</itemize>
811

    
812
<sect1>Configuration
813

    
814
<p>Each instance of the BGP corresponds to one neighboring router.
815
This allows to set routing policy and all the other parameters differently
816
for each neighbor using the following configuration parameters:
817

    
818
<descrip>
819
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
820
	contrary to other IP routers, BIRD is able to act as a router located
821
	in multiple AS'es simultaneously, but in such cases you need to tweak
822
	the BGP paths manually in the filters to get consistent behavior.)
823
	This parameter is mandatory.
824

    
825
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
826
	this instance will be talking to and what AS it's located in. Unless
827
	you use the <cf/multihop/ clause, it must be directly connected to one
828
	of your router's interfaces. In case the neighbor is in the same AS
829
	as we are, we automatically switch to iBGP. This parameter is mandatory.
830

    
831
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
832
	neighbor which is connected at most <m/number/ hops far and to which
833
	we should route via our direct neighbor with address <m/ip/.
834
	Default: switched off.
835

    
836
	<tag>next hop self</tag> Avoid calculation of the Next Hop attribute
837
	and always advertise our own source address (see below) as a next hop.
838
	This needs to be used only
839
	occasionally to circumvent misconfigurations of other routers.
840
	Default: disabled.
841

    
842
	<tag>source address <m/ip/</tag> Define local address we should use
843
	for next hop calculation. Default: the address of the local end
844
	of the interface our neighbor is connected to.
845

    
846
	<tag>password <m/string/</tag> Use this password for MD5 authentication
847
	of BGP sessions. Default: no authentication.
848

    
849
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
850
	a route reflection client. Default: disabled.
851

    
852
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
853
	to avoid route reflection loops. When there is one route reflector in a cluster
854
	it usually uses its router id as a cluster id, but when there are more route
855
	reflectors in a cluster, these need to be configured (using this option) to
856
	use a common cluster id. Clients in a cluster need not know their cluster
857
	id and this option is not allowed for them. Default: the same as router id.
858

    
859
	<tag>rs client</tag> Be a route server and treat the neighbor
860
	as a route server client. A route server is used as a
861
	replacement for full mesh EBGP routing in Internet exchange
862
	points in a similar way to route reflectors used in IBGP routing.
863
	Bird does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
864
	which behaves like plain EBGP but reduces modifications to advertised route
865
	attributes to be transparent (for example does not prepend its AS number to
866
	AS PATH attribute and keep MED attribute). Default: disabled.
867

    
868
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
869
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
870
	but by disabling this option it can be persuaded not to advertise it and
871
	to maintain old-style sessions with its neighbors. This might be useful for
872
	circumventing bugs in neighbor's implementation of 4B AS extension.
873
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
874
	Default: on.
875

    
876
	<tag>capabilities <m/switch/</tag> Use capability advertisement
877
	to advertise optional capabilities. This is standard behavior
878
	for newer BGP implementations, but there might be some older
879
	BGP implementations that reject such connection attempts.
880
	When disabled (off), features that request it (4B AS support)
881
	are also disabled. Default: on, with automatic fallback to
882
	off when received capability-related error.
883

    
884
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
885
	This is not a correct behavior according to the strict interpretation
886
	of RFC 4760, but it is widespread and required by some BGP
887
	implementations (Cisco and Quagga). This option is relevant
888
	to IPv4 mode with enabled capability advertisement only. Default: on.
889

    
890
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
891
	locally or by the other side), disable the instance automatically
892
	and wait for an administrator to fix the problem manually. Default: off.
893

    
894
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
895
	message from the other side before considering the connection stale.
896
	Default: depends on agreement with the neighboring router, we prefer
897
	240 seconds if the other side is willing to accept it.
898

    
899
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
900
	before the routers have a chance to exchange open messages and agree
901
	on the real value. Default: 240 seconds.
902

    
903
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
904
	of two consecutive Keepalive messages. Default: One third of the hold time.
905

    
906
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
907
	retrying a failed attempt to connect. Default: 120 seconds.
908

    
909
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
910
	startup and the first attempt to connect. Default: 5 seconds.
911

    
912
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
913
	failure (either local or reported by the peer) and automatic restart.
914
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
915
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
916

    
917
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
918
	failures to treat them as a error sequence which makes the <cf/error wait time/
919
	increase exponentially. Default: 300 seconds.
920

    
921
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
922
	when deciding which BGP route is the best one. Default: on.
923

    
924
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
925
	Discriminator to be used during route selection when the MED attribute
926
	is missing. Default: 0.
927

    
928
	<tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference
929
	to be used during route selection when the Local Preference attribute
930
	is missing. Default: 0.
931
</descrip>
932

    
933
<sect1>Attributes
934

    
935
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
936
table below) are available on internal BGP connections only, some of them (marked
937
with `<tt/O/') are optional.
938

    
939
<descrip>
940
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
941
	the packet will travel through when forwarded according to the particular route. In case of 
942
	internal BGP it doesn't contain the number of the local AS.
943

    
944
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
945
	selection among multiple BGP routes (see the selection rules above). It's
946
	used as an additional metric which is propagated through the whole local AS.
947

    
948
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
949
	is an optional attribute which is used on on external (inter-AS) links to
950
	convey to an adjacent AS the optimal entry point into the local AS.
951
	The received attribute may be also propagated over internal BGP links
952
	(and this is default behavior). The attribute value is zeroed when a route
953
	is exported from a routing table to a BGP instance to ensure that the attribute
954
	received from a neighboring AS is not propagated to other neighboring ASes.
955
	A new value might be set in the export filter of a BGP instance.
956
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
957
	for further discussion of BGP MED attribute.
958

    
959
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
960
	if the route has originated in an interior routing protocol or
961
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
962
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
963
	is unknown.
964

    
965
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
966
	to this destination. On internal BGP connections, it's an address of the
967
	originating router if it's inside the local AS or a boundary router the
968
	packet will leave the AS through if it's an exterior route, so each BGP
969
	speaker within the AS has a chance to use the shortest interior path
970
	possible to this point.
971

    
972
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
973
	which carries no value, but the sole presence of which indicates that the route
974
	has been aggregated from multiple routes by some router on the path from
975
	the originator.
976

    
977
<!-- we don't handle aggregators right since they are of a very obscure type
978
	<tag>bgp_aggregator</tag>
979
-->
980
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
981
	with the route. Each such value is a pair (represented as a <cf/pair/ data
982
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
983
	the community and the second one being a per-AS identifier. There are lots
984
	of uses of the community mechanism, but generally they are used to carry
985
	policy information like "don't export to USA peers". As each AS can define
986
	its own routing policy, it also has a complete freedom about which community
987
	attributes it defines and what will their semantics be.
988
</descrip>
989

    
990
<sect1>Example
991

    
992
<p><code>
993
protocol bgp {
994
	local as 65000;			     # Use a private AS number
995
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
996
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
997
	export filter {			     # We use non-trivial export rules
998
		if source = RTS_STATIC then { # Export only static routes
999
		        # Assign our community
1000
			bgp_community.add((65000,5678));
1001
			# Artificially increase path length
1002
			# by advertising local AS number twice
1003
			if bgp_path ~ [= 65000 =] then	  
1004
				bgp_path.prepend(65000);  
1005
			accept;
1006
		}
1007
		reject;
1008
	};
1009
	import all;
1010
	source address 62.168.0.1;	# Use a non-standard source address
1011
}
1012
</code>
1013

    
1014
<sect>Device
1015

    
1016
<p>The Device protocol is not a real routing protocol.  It doesn't generate
1017
any routes and it only serves as a module for getting information about network
1018
interfaces from the kernel.
1019

    
1020
<p>Except for very unusual circumstances, you probably should include
1021
this protocol in the configuration since almost all other protocols
1022
require network interfaces to be defined for them to work with.
1023

    
1024
<p>The only configurable thing is interface scan time:
1025

    
1026
<p><descrip>
1027
	<tag>scan time <m/number/</tag> Time in seconds between two scans
1028
	of the network interface list. On systems where we are notified about
1029
	interface status changes asynchronously (such as newer versions of
1030
	Linux), we need to scan the list only in order to avoid confusion by lost
1031
	notification messages, so the default time is set to a large value.
1032
</descrip>
1033

    
1034
<p>As the Device protocol doesn't generate any routes, it cannot have
1035
any attributes. Example configuration looks really simple:
1036

    
1037
<p><code>
1038
protocol device {
1039
	scan time 10;		# Scan the interfaces often
1040
}
1041
</code>
1042

    
1043
<sect>Direct
1044

    
1045
<p>The Direct protocol is a simple generator of device routes for all the
1046
directly connected networks according to the list of interfaces provided
1047
by the kernel via the Device protocol.
1048

    
1049
<p>It's highly recommended to include this protocol in your configuration
1050
unless you want to use BIRD as a route server or a route reflector, that is
1051
on a machine which doesn't forward packets itself and only participates in
1052
distribution of routing information.
1053

    
1054
<p>The only configurable thing about direct is what interfaces it watches:
1055

    
1056
<p><descrip>
1057
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
1058
	protocol will generate device routes for all the interfaces
1059
	available. If you want to restrict it to some subset of interfaces
1060
	(for example if you're using multiple routing tables for policy
1061
	routing and some of the policy domains don't contain all interfaces),
1062
	just use this clause.
1063
</descrip>
1064

    
1065
<p>Direct device routes don't contain any specific attributes.
1066

    
1067
<p>Example config might look like this:
1068

    
1069
<p><code>
1070
protocol direct {
1071
	interface "-arc*", "*";		# Exclude the ARCnets
1072
}
1073
</code>
1074

    
1075
<sect>Kernel
1076

    
1077
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
1078
the with other routers in the network, it performs synchronization of BIRD's routing
1079
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
1080
and from time to time it scans the kernel tables to see whether some routes have
1081
disappeared (for example due to unnoticed up/down transition of an interface)
1082
or whether an `alien' route has been added by someone else (depending on the
1083
<cf/learn/ switch, such routes are either deleted or accepted to our
1084
table).
1085

    
1086
<p>If your OS supports only a single routing table, you can configure only one
1087
instance of the Kernel protocol. If it supports multiple tables (in order to
1088
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
1089
them must be connected to a different BIRD routing table and to a different
1090
kernel table.
1091

    
1092
<sect1>Configuration
1093

    
1094
<p><descrip>
1095
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
1096
	routing tables when it exits (instead of cleaning them up).
1097
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
1098
	kernel routing table.
1099
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
1100
	routing tables by other routing daemons or by the system administrator.
1101
	This is possible only on systems which support identification of route
1102
	authorship.
1103
	<tag>kernel table <m/number/</tag> Select which kernel table should
1104
	this particular instance of the Kernel protocol work with. Available
1105
	only on systems supporting multiple routing tables.
1106
</descrip>
1107

    
1108
<p>The Kernel protocol doesn't define any route attributes.
1109
<p>A simple configuration can look this way:
1110

    
1111
<p><code>
1112
protocol kernel {
1113
	import all;
1114
	export all;
1115
}
1116
</code>
1117

    
1118
<p>Or for a system with two routing tables:
1119

    
1120
<p><code>
1121
protocol kernel {		# Primary routing table
1122
	learn;			# Learn alien routes from the kernel
1123
	persist;		# Don't remove routes on bird shutdown
1124
	scan time 10;		# Scan kernel routing table every 10 seconds
1125
	import all;
1126
	export all;
1127
}
1128

    
1129
protocol kernel {		# Secondary routing table
1130
	table auxtable;
1131
	kernel table 100;
1132
	export all;
1133
}
1134
</code>
1135

    
1136
<sect>OSPF
1137

    
1138
<sect1>Introduction
1139

    
1140
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1141
protocol. The current IPv4 version (OSPFv2) is defined
1142
in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
1143
state (a.k.a. shortest path first) protocol -- each router maintains a database
1144
describing the autonomous system's topology. Each participating router
1145
has an identical copy of the database and all routers run the same algorithm
1146
calculating a shortest path tree with themselves as a root.
1147
OSPF chooses the least cost path as the best path.
1148
(OSPFv3 - OSPF for IPv6 is not supported yet.)
1149

    
1150
<p>In OSPF, the autonomous system can be split to several areas in order
1151
to reduce the amount of resources consumed for exchanging the routing
1152
information and to protect the other areas from incorrect routing data.
1153
Topology of the area is hidden to the rest of the autonomous system.
1154

    
1155
<p>Another very important feature of OSPF is that
1156
it can keep routing information from other protocols (like Static or BGP)
1157
in its link state database as external routes. Each external route can
1158
be tagged by the advertising router, making it possible to pass additional
1159
information between routers on the boundary of the autonomous system.
1160

    
1161
<p>OSPF quickly detects topological changes in the autonomous system (such
1162
as router interface failures) and calculates new loop-free routes after a short
1163
period of convergence. Only a minimal amount of 
1164
routing traffic is involved.
1165

    
1166
<p>Each router participating in OSPF routing periodically sends Hello messages
1167
to all its interfaces. This allows neighbors to be discovered dynamically.
1168
Then the neighbors exchange theirs parts of the link state database and keep it
1169
identical by flooding updates. The flooding process is reliable and ensures
1170
that each router detects all changes.
1171

    
1172
<sect1>Configuration
1173

    
1174
<p>In the main part of configuration, there can be multiple definitions of
1175
OSPF area witch different id included. These definitions includes many other
1176
switches and multiple definitions of interfaces. Definition of interface
1177
may contain many switches and constant definitions and list of neighbors
1178
on nonbroadcast networks.
1179

    
1180
<code>
1181
protocol ospf &lt;name&gt; {
1182
	rfc1583compat &lt;switch&gt;;
1183
	tick &lt;num&gt;;
1184
	area &lt;id&gt; {
1185
		stub cost &lt;num&gt;;
1186
                networks {
1187
			&lt;prefix&gt;;
1188
			&lt;prefix&gt; hidden;
1189
		}
1190
		interface &lt;interface pattern&gt;
1191
		{
1192
			cost &lt;num&gt;;
1193
			stub &lt;switch&gt;;
1194
			hello &lt;num&gt;;
1195
			poll &lt;num&gt;;
1196
			retransmit &lt;num&gt;;
1197
			priority &lt;num&gt;;
1198
			wait &lt;num&gt;;
1199
			dead count &lt;num&gt;;
1200
			dead &lt;num&gt;;
1201
			rx buffer [normal|large|&lt;num&gt;];
1202
			type [broadcast|nonbroadcast|pointopoint];
1203
			strict nonbroadcast &lt;switch&gt;;
1204
			authentication [none|simple|cryptographics];
1205
			password "&lt;text&gt;";
1206
			password "&lt;text&gt;" {
1207
				id &lt;num&gt;;
1208
				generate from "&lt;date&gt;";
1209
				generate to "&lt;date&gt;";
1210
				accept from "&lt;date&gt;";
1211
				accept to "&lt;date&gt;";
1212
			};
1213
			neighbors {
1214
				&lt;ip&gt;;
1215
				&lt;ip&gt; eligible;
1216
			};
1217
		};
1218
		virtual link &lt;id&gt;
1219
		{
1220
			hello &lt;num&gt;;
1221
			retransmit &lt;num&gt;;
1222
			wait &lt;num&gt;;
1223
			dead count &lt;num&gt;;
1224
			dead &lt;num&gt;;
1225
			authentication [none|simple];
1226
			password "&lt;text&gt;";
1227
		};
1228
	};
1229
}
1230
</code>
1231

    
1232
<descrip>
1233
	<tag>rfc1583compat <M>switch</M></tag>
1234
	 This option controls compatibility of routing table
1235
	 calculation with RFC 1583<htmlurl
1236
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1237
	 value is no.
1238
	
1239
	<tag>area <M>id</M></tag>
1240
	 This defines an OSPF area with given area ID (an integer or an IPv4
1241
	 address, similarly to a router ID).
1242
	 The most important area is
1243
	 the backbone (ID 0) to which every other area must be connected.
1244

    
1245
	<tag>stub cost <M>num</M></tag>
1246
	 No external (except default) routes are flooded into stub areas.
1247
         Setting this value marks area stub with defined cost of default route.
1248
	 Default value is no. (Area is not stub.)
1249

    
1250
	<tag>tick <M>num</M></tag>
1251
	 The routing table calculation and clean-up of areas' databases
1252
         is not performed when a single link state
1253
	 change arrives. To lower the CPU utilization, it's processed later
1254
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1255

    
1256
	<tag>networks { <m/set/ }</tag>
1257
         Definition of area IP ranges. This is used in summary lsa origination.
1258
	 Hidden networks are not propagated into other areas.
1259

    
1260
	<tag>interface <M>pattern</M></tag>
1261
	 Defines that the specified interfaces belong to the area being defined.
1262
	 See <ref id="dsc-iface" name="interface"> common option for detailed description.
1263

    
1264
	<tag>virtual link <M>id</M></tag>
1265
	 Virtual link to router with the router id. Virtual link acts as a
1266
         point-to-point interface belonging to backbone. The actual area is
1267
         used as transport area. This item cannot be in the backbone.
1268

    
1269
	<tag>cost <M>num</M></tag>
1270
	 Specifies output cost (metric) of an interface. Default value is 10.
1271

    
1272
	<tag>stub <M>switch</M></tag>
1273
	 If set to interface it does not listen to any packet and does not send
1274
	 any hello. Default value is no.
1275

    
1276
	<tag>hello <M>num</M></tag>
1277
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1278
	 routers on the same network need to have the same hello interval.
1279
	 Default value is 10.
1280

    
1281
	<tag>poll <M>num</M></tag>
1282
	 Specifies interval in seconds between sending of Hello messages for
1283
	 some neighbors on NBMA network. Default value is 20.
1284

    
1285
	<tag>retransmit <M>num</M></tag>
1286
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1287
	 Default value is 5.
1288

    
1289
        <tag>priority <M>num</M></tag>
1290
	 On every multiple access network (e.g., the Ethernet) Designed Router
1291
	 and Backup Designed router are elected. These routers have some
1292
	 special functions in the flooding process. Higher priority increases
1293
	 preferences in this election. Routers with priority 0 are not
1294
	 eligible. Default value is 1.
1295

    
1296
	<tag>wait <M>num</M></tag>
1297
	 After start, router waits for the specified number of seconds between starting
1298
	 election and building adjacency. Default value is 40.
1299
	 
1300
	<tag>dead count <M>num</M></tag>
1301
	 When the router does not receive any messages from a neighbor in
1302
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1303

    
1304
	<tag>dead <M>num</M></tag>
1305
	 When the router does not receive any messages from a neighbor in
1306
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1307
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1308

    
1309
	<tag>rx buffer <M>num</M></tag>
1310
	 This sets the size of buffer used for receiving packets. The buffer should
1311
	 be bigger than maximal size of any packets. Value NORMAL (default)
1312
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1313

    
1314
	<tag>type broadcast</tag>
1315
	 BIRD detects a type of a connected network automatically, but sometimes it's
1316
	 convenient to force use of a different type manually.
1317
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1318
	 (a single packet for all the neighbors).
1319

    
1320
	<tag>type pointopoint</tag>
1321
	 Point-to-point networks connect just 2 routers together. No election
1322
	 is performed there which reduces the number of messages sent.
1323

    
1324
	<tag>type nonbroadcast</tag>
1325
	 On nonbroadcast networks, the packets are sent to each neighbor
1326
	 separately because of lack of multicast capabilities.
1327

    
1328
	<tag>strict nonbroadcast <M>switch</M></tag>
1329
	 If set, don't send hello to any undefined neighbor. This switch
1330
	 is ignored on on any non-NBMA network. Default is No.
1331

    
1332
	<tag>authentication none</tag>
1333
	 No passwords are sent in OSPF packets. This is the default value.
1334

    
1335
	<tag>authentication simple</tag>
1336
	 Every packet carries 8 bytes of password. Received packets
1337
	 lacking this password are ignored. This authentication mechanism is
1338
	 very weak.
1339

    
1340
	<tag>authentication cryptographic</tag>
1341
	 16-byte long MD5 digest is appended to every packet. For the digest
1342
         generation 16-byte long passwords are used. Those passwords are 
1343
         not sent via network, so this mechanismus is quite secure.
1344
         Packets can still be read by an attacker.
1345

    
1346
	<tag>password "<M>text</M>"</tag>
1347
	 An 8-byte or 16-byte password used for authentication.
1348
	 See <ref id="dsc-pass" name="password"> common option for detailed description.
1349

    
1350
	<tag>neighbors { <m/set/ } </tag>
1351
	 A set of neighbors to which Hello messages on nonbroadcast networks
1352
	 are to be sent. Some of them could be marked as eligible.
1353

    
1354
</descrip>
1355

    
1356
<sect1>Attributes
1357

    
1358
<p>OSPF defines three route attributes. Each internal route has a <cf/metric/
1359
Metric is ranging from 1 to infinity (65535).
1360
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1361
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1362
<cf/metric of type 2/ is always longer
1363
than any <cf/metric of type 1/ or any <cf/internal metric/.
1364
If you specify both metrics only metric1 is used.
1365
Each external route can also carry a <cf/tag/ which is a 32-bit
1366
integer which is used when exporting routes to other protocols;
1367
otherwise, it doesn't affect routing inside the OSPF domain at all.
1368
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1369

    
1370
<sect1>Example
1371

    
1372
<p>
1373

    
1374
<code>
1375
protocol ospf MyOSPF {
1376
        rfc1583compatibility yes;
1377
        tick 2;
1378
	export filter {
1379
		if source = RTS_BGP then {
1380
			ospf_metric1 = 100;
1381
			accept;
1382
		}
1383
		reject;
1384
	};
1385
	area 0.0.0.0 {
1386
		interface "eth*" {
1387
			cost 11;
1388
			hello 15;
1389
			priority 100;
1390
			retransmit 7;
1391
			authentication simple;
1392
			password "aaa";
1393
		};
1394
		interface "ppp*" {
1395
			cost 100;
1396
			authentication cryptographic;
1397
			password "abc" {
1398
				id 1;
1399
				generate to "22-04-2003 11:00:06";
1400
				accept from "17-01-2001 12:01:05";
1401
			};
1402
			password "def" {
1403
				id 2;
1404
				generate to "22-07-2005 17:03:21";
1405
				accept from "22-02-2001 11:34:06";
1406
			};
1407
		};
1408
		interface "arc0" {
1409
			cost 10;
1410
			stub yes;
1411
		};
1412
		interface "arc1";
1413
	};
1414
	area 120 {
1415
		stub yes;
1416
		networks {
1417
			172.16.1.0/24;
1418
			172.16.2.0/24 hidden;
1419
		}
1420
		interface "-arc0" , "arc*" {
1421
			type nonbroadcast;
1422
			authentication none;
1423
			strict nonbroadcast yes;
1424
			wait 120;
1425
			poll 40;
1426
			dead count 8;
1427
			neighbors {
1428
				192.168.120.1 eligible;
1429
				192.168.120.2;
1430
				192.168.120.10;
1431
			};
1432
		};
1433
	};
1434
}
1435
</code>
1436

    
1437
<sect>Pipe
1438

    
1439
<sect1>Introduction
1440

    
1441
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1442
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1443
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1444
and vice versa, depending on what's allowed by the filters. Export filters control export
1445
of routes from the primary table to the secondary one, import filters control the opposite
1446
direction.
1447

    
1448
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1449
where handling of a single packet doesn't depend only on its destination address, but also
1450
on its source address, source interface, protocol type and other similar parameters.
1451
In many systems (Linux 2.2 being a good example), the kernel allows to enforce routing policies
1452
by defining routing rules which choose one of several routing tables to be used for a packet
1453
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1454
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1455
connect them to the kernel ones, use filters to control which routes appear in which tables
1456
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1457
another one.
1458

    
1459
<sect1>Configuration
1460

    
1461
<p><descrip>
1462
	<tag>peer table <m/table/</tag> Define secondary routing table to connect to. The
1463
	primary one is selected by the <cf/table/ keyword.
1464
</descrip>
1465

    
1466
<sect1>Attributes
1467

    
1468
<p>The Pipe protocol doesn't define any route attributes.
1469

    
1470
<sect1>Example
1471

    
1472
<p>Let's consider a router which serves as a boundary router of two different autonomous
1473
systems, each of them connected to a subset of interfaces of the router, having its own
1474
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1475
of outage of its own exterior line.
1476

    
1477
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1478
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1479
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1480
and similarly for the second AS. Thus we have split our router to two logical routers,
1481
each one acting on its own routing table, having its own routing protocols on its own
1482
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1483
the routes between the tables through a Pipe protocol while decreasing their preferences
1484
and correcting their BGP paths to reflect the AS boundary crossing.
1485

    
1486
<code>
1487
table as1;				# Define the tables
1488
table as2;
1489

    
1490
protocol kernel kern1 {			# Synchronize them with the kernel
1491
	table as1;
1492
	kernel table 1;
1493
}
1494

    
1495
protocol kernel kern2 {
1496
	table as2;
1497
	kernel table 2;
1498
}
1499

    
1500
protocol bgp bgp1 {			# The outside connections
1501
	table as1;
1502
	local as 1;
1503
	neighbor 192.168.0.1 as 1001;
1504
	export all;
1505
	import all;
1506
}
1507

    
1508
protocol bgp bgp2 {
1509
	table as2;
1510
	local as 2;
1511
	neighbor 10.0.0.1 as 1002;
1512
	export all;
1513
	import all;
1514
}
1515

    
1516
protocol pipe {				# The Pipe
1517
	table as1;
1518
	peer table as2;
1519
	export filter {
1520
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1521
			if preference>10 then preference = preference-10;
1522
			if source=RTS_BGP then bgp_path.prepend(1);
1523
			accept;
1524
		}
1525
		reject;
1526
	};
1527
	import filter {
1528
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1529
			if preference>10 then preference = preference-10;
1530
			if source=RTS_BGP then bgp_path.prepend(2);
1531
			accept;
1532
		}
1533
		reject;
1534
	};
1535
}
1536
</code>
1537

    
1538
<sect>RIP
1539

    
1540
<sect1>Introduction
1541

    
1542
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1543
distances to all networks it can reach. When a router hears distance to another network, it increments
1544
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1545
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1546
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1547
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1548
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1549
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1550
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1551
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1552
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
1553
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1554

    
1555
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1556
convergence, big network load and inability to handle larger networks
1557
makes it pretty much obsolete in IPv4 world. (It is still usable on
1558
very small networks.) It is widely used in IPv6 networks,
1559
because there are no good implementations of OSPFv3.
1560

    
1561
<sect1>Configuration
1562

    
1563
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1564

    
1565
<descrip>
1566
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1567
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1568
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1569
	  hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf>
1570
	  section. Default: none.
1571

    
1572
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1573
	  be honored. (Always, when sent from a  host on a directly connected
1574
	  network or never.) Routing table updates are honored only from
1575
	  neighbors, that is not configurable. Default: never.
1576
</descrip>
1577

    
1578
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1579
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1580
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1581
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1582
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1583
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1584
interface but not listen to it.
1585

    
1586
<p>The following options generally override behavior specified in RFC. If you use any of these
1587
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1588
other than equally configured BIRD. I have warned you.
1589

    
1590
<descrip>
1591
	<tag>port <M>number</M></tag>
1592
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1593
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1594

    
1595
	<tag>infinity <M>number</M></tag>
1596
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1597
	  even slower.
1598

    
1599
	<tag>period <M>number</M>
1600
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1601
	  number will mean faster convergence but bigger network
1602
	  load. Do not use values lower than 10.
1603

    
1604
	<tag>timeout time <M>number</M>
1605
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1606

    
1607
	<tag>garbage time <M>number</M>
1608
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1609
</descrip>
1610

    
1611
<sect1>Attributes
1612

    
1613
<p>RIP defines two route attributes:
1614

    
1615
<descrip>
1616
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1617
	When routes from different RIP instances are available and all of them have the same
1618
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1619
	When importing a non-RIP route, the metric defaults to 5.
1620

    
1621
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1622
	to carry additional information with the route (for example, an originating AS number
1623
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1624
</descrip>
1625

    
1626
<sect1>Example
1627

    
1628
<p><code>
1629
protocol rip MyRIP_test {
1630
        debug all;
1631
        port 1520;
1632
        period 10;
1633
        garbage time 60;
1634
        interface "eth0" { metric 3; mode multicast; };
1635
	interface "eth*" { metric 2; mode broadcast; };
1636
        honor neighbor;
1637
        authentication none;
1638
        import filter { print "importing"; accept; };
1639
        export filter { print "exporting"; accept; };
1640
}
1641
</code>
1642

    
1643
<sect>Static
1644

    
1645
<p>The Static protocol doesn't communicate with other routers in the network,
1646
but instead it allows you to define routes manually. This is often used for
1647
specifying how to forward packets to parts of the network which don't use
1648
dynamic routing at all and also for defining sink routes (i.e., those
1649
telling to return packets as undeliverable if they are in your IP block,
1650
you don't have any specific destination for them and you don't want to send
1651
them out through the default route to prevent routing loops).
1652

    
1653
<p>There are three types of static routes: `classical' routes telling to
1654
forward packets to a neighboring router, device routes specifying forwarding
1655
to hosts on a directly connected network and special routes (sink, blackhole
1656
etc.) which specify a special action to be done instead of forwarding the
1657
packet.
1658

    
1659
<p>When the particular destination is not available (the interface is down or
1660
the next hop of the route is not a neighbor at the moment), Static just
1661
uninstalls the route from the table it is connected to and adds it again as soon
1662
as the destination becomes adjacent again.
1663

    
1664
<p>The Static protocol has no configuration options. Instead, the
1665
definition of the protocol contains a list of static routes:
1666

    
1667
<descrip>
1668
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1669
	a neighboring router.
1670
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1671
	route through an interface to hosts on a directly connected network.
1672
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1673
	specifying to drop the packet, return it as unreachable or return
1674
	it as administratively prohibited.
1675
</descrip>
1676

    
1677
<p>Static routes have no specific attributes.
1678

    
1679
<p>Example static config might look like this:
1680

    
1681
<p><code>
1682
protocol static {
1683
	table testable;			 # Connect to a non-default routing table
1684
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1685
	route 62.168.0.0/25 reject;	 # Sink route
1686
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1687
}
1688
</code>
1689

    
1690
<chapt>Conclusions
1691

    
1692
<sect>Future work
1693

    
1694
<p>Although BIRD supports all the commonly used routing protocols,
1695
there are still some features which would surely deserve to be
1696
implemented in future versions of BIRD:
1697

    
1698
<itemize>
1699
<item>OSPF for IPv6 networks
1700
<item>OSPF NSSA areas and opaque LSA's
1701
<item>Route aggregation and flap dampening
1702
<item>Generation of IPv6 router advertisements
1703
<item>Multipath routes
1704
<item>Multicast routing protocols
1705
<item>Ports to other systems
1706
</itemize>
1707

    
1708
<sect>Getting more help
1709

    
1710
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1711
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1712
where you can share your experiences with the other users and consult
1713
your problems with the authors. To subscribe to the list, just send a
1714
<tt/subscribe bird-users/ command in a body of a mail to
1715
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1716
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1717

    
1718
<p>BIRD is a relatively young system and it probably contains some
1719
bugs. You can report any problems to the bird-users list and the authors
1720
will be glad to solve them, but before you do so,
1721
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1722
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1723
which fixes the bug is always welcome as an attachment.)
1724

    
1725
<p>If you want to understand what is going inside, Internet standards are
1726
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">).
1727

    
1728
<p><it/Good luck!/
1729

    
1730
</book>
1731

    
1732
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1733
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1734
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1735
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1736
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