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<!doctype birddoc system>
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<!--
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	BIRD documentation
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This documentation can have 4 forms: sgml (this is master copy), html,
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ASCII text and dvi/postscript (generated from sgml using
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sgmltools). You should always edit master copy.
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This is a slightly modified linuxdoc dtd.  Anything in <descrip> tags is considered definition of
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configuration primitives, <cf> is fragment of configuration within normal text, <m> is
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"meta" information within fragment of configuration - something in config which is not keyword.
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    (set-fill-column 100)
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    Copyright 1999,2000 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later.
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 -->
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<book>
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<title>BIRD User's Guide
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<author>
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Ondrej Filip <it/&lt;feela@network.cz&gt;/,
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Pavel Machek <it/&lt;pavel@ucw.cz&gt;/,
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Martin Mares <it/&lt;mj@ucw.cz&gt;/,
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Ondrej Zajicek <it/&lt;santiago@crfreenet.org&gt;/
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</author>
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<abstract>
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This document contains user documentation for the BIRD Internet Routing Daemon project.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<chapt>Introduction
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<sect>What is BIRD
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<p><label id="intro">
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The name `BIRD' is actually an acronym standing for `BIRD Internet Routing Daemon'.
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Let's take a closer look at the meaning of the name:
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<p><em/BIRD/: Well, we think we have already explained that. It's an acronym standing
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for `BIRD Internet Routing Daemon', you remember, don't you? :-)
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<p><em/Internet Routing/: It's a program (well, a daemon, as you are going to discover in a moment)
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which works as a dynamic router in an Internet type network (that is, in a network running either
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the IPv4 or the IPv6 protocol). Routers are devices which forward packets between interconnected
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networks in order to allow hosts not connected directly to the same local area network to
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communicate with each other. They also communicate with the other routers in the Internet to discover
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the topology of the network which allows them to find optimal (in terms of some metric) rules for
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forwarding of packets (which are called routing tables) and to adapt themselves to the
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changing conditions such as outages of network links, building of new connections and so on. Most of
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these routers are costly dedicated devices running obscure firmware which is hard to configure and
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not open to any changes (on the other hand, their special hardware design allows them to keep up with lots of high-speed network interfaces, better than general-purpose computer does). Fortunately, most operating systems of the UNIX family allow an ordinary 
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computer to act as a router and forward packets belonging to the other hosts, but only according to
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a statically configured table.
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<p>A <em/Routing Daemon/ is in UNIX terminology a non-interactive program running on
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background which does the dynamic part of Internet routing, that is it communicates
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with the other routers, calculates routing tables and sends them to the OS kernel
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which does the actual packet forwarding. There already exist other such routing
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daemons: routed (RIP only), GateD (non-free), Zebra<HTMLURL URL="http://www.zebra.org">
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and MRTD<HTMLURL URL="http://sourceforge.net/projects/mrt">, but their capabilities are
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limited and they are relatively hard to configure and maintain.
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<p>BIRD is an Internet Routing Daemon designed to avoid all of these shortcomings,
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to support all the routing technology used in the today's Internet or planned to be
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used in near future and to have a clean extensible architecture allowing new routing
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protocols to be incorporated easily. Among other features, BIRD supports:
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<itemize>
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	<item>both IPv4 and IPv6 protocols
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	<item>multiple routing tables
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	<item>the Border Gateway Protocol (BGPv4)
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	<item>the Routing Information Protocol (RIPv2)
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	<item>the Open Shortest Path First protocol (OSPFv2, OSPFv3)
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	<item>a virtual protocol for exchange of routes between different routing tables on a single host
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	<item>a command-line interface allowing on-line control and inspection
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		of status of the daemon
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	<item>soft reconfiguration (no need to use complex online commands
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		to change the configuration, just edit the configuration file
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		and notify BIRD to re-read it and it will smoothly switch itself
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		to the new configuration, not disturbing routing protocols
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		unless they are affected by the configuration changes)
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	<item>a powerful language for route filtering
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</itemize>
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<p>BIRD has been developed at the Faculty of Math and Physics, Charles University, Prague,
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Czech Republic as a student project. It can be freely distributed under the terms of the GNU General
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Public License.
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<p>BIRD has been designed to work on all UNIX-like systems. It has been developed and
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tested under Linux 2.0 to 2.4, and then ported to FreeBSD and NetBSD, porting to other
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systems (even non-UNIX ones) should be relatively easy due to its highly modular architecture.
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<sect>Installing BIRD
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<p>On a recent UNIX system with GNU development tools (GCC, binutils, m4, make) and Perl, installing BIRD should be as easy as:
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<code>
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        ./configure
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        make
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        make install
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        vi /usr/local/etc/bird.conf
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	bird
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</code>
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<p>You can use <tt>./configure --help</tt> to get a list of configure
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options. The most important ones are:
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<tt/--enable-ipv6/ which enables building of an IPv6 version of BIRD,
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<tt/--with-protocols=/ to produce a slightly smaller BIRD executable by configuring out routing protocols you don't use, and
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<tt/--prefix=/ to install BIRD to a place different from.
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<file>/usr/local</file>.
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<sect>Running BIRD
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<p>You can pass several command-line options to bird:
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<descrip>
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	<tag>-c <m/config name/</tag>
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	use given configuration file instead of <it/prefix/<file>/etc/bird.conf</file>.
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	<tag>-d</tag>
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	enable debug messages and run bird in foreground.
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	<tag>-D <m/filename of debug log/</tag>
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	log debugging information to given file instead of stderr.
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	<tag>-p</tag>
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	just parse the config file and exit. Return value is zero if the config file is valid,
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	nonzero if there are some errors.
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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>mrtdump "<m/filename/"</tag>
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	Set MRTdump file name. This option must be specified to allow MRTdump feature.
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	Default: no dump file.
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	<tag>mrtdump protocols all|off|{ states, messages }</tag>
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	Set global defaults of MRTdump options. See <cf/mrtdump/ in the following section.
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	Default: off.
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	<tag>filter <m/name local variables/{ <m/commands/ }</tag> Define a filter. You can learn more about filters
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	in the following chapter. 
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	<tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag> Define a function. You can learn more
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	about functions in the following chapter.
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	<tag>protocol rip|ospf|bgp|... <m/[name]/ { <m>protocol options</m> }</tag> Define a protocol
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	instance called <cf><m/name/</cf> (or with a name like "rip5" generated automatically if you don't specify any <cf><m/name/</cf>). You can learn more
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	about configuring protocols in their own chapters. You can run more than one instance of
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	most protocols (like RIP or BGP). By default, no instances are configured.
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	<tag>define <m/constant/ = (<m/expression/)|<m/number/|<m/IP address/</tag> Define a constant. You can use it later in every place
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	you could use a simple integer or an IP address.
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	<tag>router id <m/IPv4 address/</tag> Set BIRD's router ID. It's a world-wide unique identification of your router, usually one of router's IPv4 addresses. Default: in IPv4 version, the lowest IP address of a non-loopback interface. In IPv6 version, this option is mandatory. 
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	<tag>listen bgp [address <m/address/] [port <m/port/] [v6only]</tag>
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	This option allows to specify address and port where BGP
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	protocol should listen. It is global option as listening
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	socket is common to all BGP instances. Default is to listen on
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	all addresses (0.0.0.0) and port 179. In IPv6 mode, option
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	<cf/v6only/ can be used to specify that BGP socket should
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	listen to IPv6 connections only. This is needed if you want to
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	run both bird and bird6 on the same port.
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	<tag>timeformat route|protocol|base|log "<m/format1/" [<m/limit> "<m/format2/"]</tag>
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	This option allows to specify a format of date/time used by
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	BIRD.  The first argument specifies for which purpose such
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	format is used. <cf/route/ is a format used in 'show route'
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	command output, <cf/protocol/ is used in 'show protocols'
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	command output, <cf/base/ is used for other commands and
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	<cf/log/ is used in a log file.
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	"<m/format1/" is a format string using <i/strftime(3)/
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	notation (see <i/man strftime/ for details). <m/limit> and
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	"<m/format2/" allow to specify the second format string for
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	times in past deeper than <m/limit/ seconds. There are two
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	shorthands: <cf/iso long/ is a ISO 8601 date/time format
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	(YYYY-MM-DD hh:mm:ss) that can be also specified using <cf/"%F
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	%T"/. <cf/iso short/ is a variant of ISO 8601 that uses just
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	the time format (hh:mm:ss) for near times (up to 20 hours in
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	the past) and the date format (YYYY-MM-DD) for far times. This
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	is a shorthand for <cf/"%T" 72000 "%F"/.
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	By default, BIRD uses an short, ad-hoc format for <cf/route/
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	and <cf/protocol/ times, and a <cf/iso long/ similar format
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	(DD-MM-YYYY hh:mm:ss) for <cf/base/ and <cf/log/. These
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	defaults are here for a compatibility with older versions
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	and might change in the future.
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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>mrtdump all|off|{ states, messages }</tag>
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	Set protocol MRTdump flags. MRTdump is a standard binary
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	format for logging information from routing protocols and
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	daemons.  These flags control what kind of information is
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	logged from the protocol to the MRTdump file (which must be
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	specified by global <cf/mrtdump/ option, see the previous
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	section). Although these flags are similar to flags of
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	<cf/debug/ option, their meaning is different and
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	protocol-specific. For BGP protocol, <cf/states/ logs BGP
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	state changes and <cf/messages/ logs received BGP messages.
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	Other protocols does not support MRTdump yet.
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	<tag>router id <m/IPv4 address/</tag> This option can be used
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	to override global router id for a given protocol. Default:
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	uses global router id.
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	<tag>import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag> 
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	Specify a filter to be used for filtering routes coming from the protocol to the routing table. <cf/all/ is shorthand for <cf/where true/ and <cf/none/ is shorthand for <cf/where false/. Default: <cf/all/.
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	<tag>export <m/filter/</tag> This is similar to the <cf>import</cf> keyword, except that it
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	works in the direction from the routing table to the protocol. Default: <cf/none/.
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	<tag>description "<m/text/"</tag> This is an optional
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	description of the protocol. It is displayed as a part of the
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	output of 'show route all' command.
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	<tag>table <m/name/</tag> Connect this protocol to a non-default routing table.
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</descrip>
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<p>There are several options that give sense only with certain protocols:
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<descrip>
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	<tag><label id="dsc-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...] [ { <m/option/ ; [...] } ]</tag>
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	Specifies a set of interfaces on which the protocol is activated with
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	given interface-specific options. A set of interfaces specified by one
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	interface option is described using an interface pattern. The
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	interface pattern consists of a sequence of clauses (separated 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>
474
	<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.
479

    
480
	<tag>show protocols [all]</tag>
481
	Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified.
482

    
483
	<tag>show ospf interface [<m/name/] ["<m/interface/"]</tag>
484
	Show detailed information about OSPF interfaces.
485

    
486
	<tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
487
	Show a list of OSPF neighbors and a state of adjacency to them.
488

    
489
	<tag>show ospf state [<m/name/]</tag>
490
	Show detailed information about OSPF areas based on a content of link-state database.
491
	It shows network topology,  aggregated networks and routers from other areas and external routes.
492

    
493
	<tag>show ospf topology [<m/name/]</tag>
494
	Show a topology of OSPF areas based on a content of link-state database.
495
	It is just a stripped-down version of 'show ospf state'.
496

    
497
	<tag>show static [<m/name/]</tag>
498
	Show detailed information about static routes.
499

    
500
	<tag>show interfaces [summary]</tag>
501
	Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. 
502

    
503
	<tag>show symbols</tag>
504
	Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).
505

    
506
	<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>
507
	Show contents of a routing table (by default of the main one),
508
	that is routes, their metrics and (in case the <cf/all/ switch is given)
509
	all their attributes.
510

    
511
	<p>You can specify a <m/prefix/ if you want to print routes for a
512
	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
513
	the entry which will be used for forwarding of packets to the given
514
	destination. By default, all routes for each network are printed with
515
	the selected one at the top, unless <cf/primary/ is given in which case
516
	only the selected route is shown.
517

    
518
	<p>You can also ask for printing only routes processed and accepted by
519
	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
520
	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
521
	The <cf/export/ and <cf/preexport/ switches ask for printing of entries
522
	that are exported to the specified protocol. With <cf/preexport/, the
523
	export filter of the protocol is skipped.
524

    
525
	<p>You can also select just routes added by a specific protocol.
526
	<cf>protocol <m/p/</cf>.
527

    
528
	<p>The <cf/stats/ switch requests showing of route statistics (the
529
	number of networks, number of routes before and after filtering). If
530
	you use <cf/count/ instead, only the statistics will be printed.
531

    
532
	<tag>configure [soft] ["<m/config file/"]</tag>
533
	Reload configuration from a given file. BIRD will smoothly
534
	switch itself to the new configuration, protocols are
535
	reconfigured if possible, restarted otherwise. Changes in
536
	filters usually lead to restart of affected protocols. If
537
	<cf/soft/ option is used, changes in filters does not cause
538
	BIRD to restart affected protocols, therefore already accepted
539
	routes (according to old filters) would be still propagated,
540
	but new routes would be processed according to the new
541
	filters.
542

    
543
	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
544
	Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances.
545

    
546
	<tag>reload [in|out] <m/name/|"<m/pattern/"|all</tag>
547
	
548
	Reload a given protocol instance, that means re-import routes
549
	from the protocol instance and re-export preferred routes to
550
	the instance. If <cf/in/ or <cf/out/ options are used, the
551
	command is restricted to one direction (re-import or
552
	re-export).
553

    
554
	This command is useful if appropriate filters have changed but
555
	the protocol instance was not restarted (or reloaded),
556
	therefore it still propagates the old set of routes. For example
557
	when <cf/configure soft/ command was used to change filters.
558

    
559
	Re-export always succeeds, but re-import is protocol-dependent
560
	and might fail (for example, if BGP neighbor does not support
561
	route-refresh extension). In that case, re-export is also
562
	skipped. Note that for the pipe protocol, both directions are
563
	always reloaded together (<cf/in/ or <cf/out/ options are
564
	ignored in that case).
565

    
566
	<tag/down/
567
	Shut BIRD down.
568

    
569
	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
570
	Control protocol debugging.
571
</descrip>
572

    
573
<chapt>Filters
574

    
575
<sect>Introduction
576

    
577
<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
578
two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
579
being passed between protocols and routing tables. The filter language contains control structures such
580
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>. 
581

    
582
<p>Filter gets the route, looks at its attributes and
583
modifies some of them if it wishes. At the end, it decides whether to
584
pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
585
like this:
586

    
587
<code>
588
filter not_too_far
589
int var;
590
{
591
	if defined( rip_metric ) then
592
		var = rip_metric;
593
	else {
594
		var = 1;
595
		rip_metric = 1;
596
	}
597
	if rip_metric &gt; 10 then
598
		reject "RIP metric is too big";
599
	else
600
		accept "ok";
601
}
602
</code>
603

    
604
<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
605
the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
606
<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
607
<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
608
several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
609
you want to make a bigger block of code conditional.
610

    
611
<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
612
over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
613
look like this:
614

    
615
<code>
616
function name ()
617
int local_variable;
618
{
619
	local_variable = 5;
620
}
621

    
622
function with_parameters (int parameter)
623
{
624
	print parameter;
625
}
626
</code>
627

    
628
<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
629
variables in nested blocks. Functions are called like in C: <cf>name();
630
with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
631
command. Returning a value exits from current function (this is similar to C).
632

    
633
<p>Filters are declared in a way similar to functions except they can't have explicit
634
parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
635
to any functions called. The filter must terminate with either
636
<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
637
is rejected. 
638

    
639
<p>A nice trick to debug filters is to use <cf>show route filter
640
<m/name/</cf> from the command line client. An example session might look
641
like:
642

    
643
<code>
644
pavel@bug:~/bird$ ./birdc -s bird.ctl
645
BIRD 0.0.0 ready.
646
bird> show route
647
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
648
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
649
127.0.0.0/8        dev lo [direct1 23:21] (240)
650
bird> show route ?
651
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
652
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
653
127.0.0.0/8        dev lo [direct1 23:21] (240)
654
bird>
655
</code>
656

    
657
<sect>Data types
658

    
659
<p>Each variable and each value has certain type. Booleans, integers and enums are
660
incompatible with each other (that is to prevent you from shooting in the foot).
661

    
662
<descrip>
663
	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
664
	  <cf/false/. Boolean is the only type you can use in <cf/if/
665
	  statements.
666

    
667
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
668
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
669

    
670
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
671
	  65535. Literals of this type are written as <cf/(1234,5678)/. The same syntax can also be
672
	  used to construct a pair from two arbitrary integer expressions (for example <cf/(1+2,a)/).
673

    
674
	<tag/string/ This is a string of characters. There are no ways to modify strings in
675
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
676
	  such variables, but you can't concatenate two strings. String literals
677
	  are written as <cf/"This is a string constant"/.
678

    
679
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
680
	  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>
681
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
682
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
683

    
684
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
685
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
686
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
687
	  operators on prefixes:
688
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
689
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
690

    
691
	<tag/int|ip|prefix|pair|enum set/
692
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
693
	  but you can't modify them. Literals of type <cf>set int</cf> look like <cf>
694
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
695
	  sets.
696

    
697
	  Sets of prefixes are special: their literals does not allow ranges, but allows
698
	  prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
699
	  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 
700
	  the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>.
701
	  A valid prefix pattern has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/
702
	  or <cf/high/. Obviously, a prefix matches a prefix set literal iff it matches any prefix pattern in the
703
	  prefix set literal.
704

    
705
	  There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for
706
	  <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), 
707
	  that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf>
708
	  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>
709
	  and all its supernets (network prefixes that contain it).
710

    
711
	  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
712
	  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
713
	  <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
714
	  IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address
715
	  <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf> is true,
716
	  but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
717

    
718
	  Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
719
	  in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
720
	  <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
721
	  <cf>192.168.0.0/16{24,32}</cf>.
722

    
723
	<tag/enum/
724
	  Enumeration types are fixed sets of possibilities. You can't define your own
725
	  variables of such type, but some route attributes are of enumeration
726
	  type. Enumeration types are incompatible with each other.
727

    
728
	<tag/bgppath/
729
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
730
	  There are several special operators on bgppaths:
731

    
732
	  <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
733

    
734
          <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
735

    
736
	  Both <cf/first/ and <cf/last/ return zero if there is no appropriate ASN,
737
          for example if the path contains an AS set element as the first (or the last) part.
738

    
739
          <cf><m/P/.len</cf> returns the length of path <m/P/.
740

    
741
          <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and returns the result.
742
          Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
743
          <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
744
          (for example <cf/bgp_path/).
745

    
746
	<tag/bgpmask/
747
	  BGP masks are patterns used for BGP path matching
748
	  (using <cf>path &tilde; [= 2 3 5 * =]</cf> syntax). The masks
749
	  resemble wildcard patterns as used by UNIX shells. Autonomous
750
	  system numbers match themselves, <cf/*/ matches any (even empty)
751
	  sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number.
752
	  For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
753
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
754
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
755
	  BGP mask expressions can also contain integer expressions enclosed in parenthesis
756
	  and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>.
757
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
758

    
759
	<tag/clist/ 
760
	  Community list is similar to set of pairs,
761
	  except that unlike other sets, it can be modified.
762
	  There exist no literals of this type.
763
	  There are two special operators on clists:
764

    
765
          <cf>add(<m/C/,<m/P/)</cf> adds pair <m/P/ to clist <m/C/ and returns the result.
766

    
767
          <cf>delete(<m/C/,<m/P/)</cf> deletes pair <m/P/ from clist <m/C/ and returns the result.
768

    
769
          Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
770
          <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute
771
          (for example <cf/bgp_community/). Similarly for <cf/delete/.
772

    
773
</descrip>
774

    
775
<sect>Operators
776

    
777
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
778
<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;/). 
779
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
780
used on element and set of elements of the same type (returning true if element is contained in the given set), or
781
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
782
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).
783

    
784

    
785
<sect>Control structures
786

    
787
<p>Filters support two control structures: conditions and case switches. 
788

    
789
<p>Syntax of a condition is: <cf>if
790
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
791
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
792
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.
793

    
794
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else |
795
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
796
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
797
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
798
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.
799

    
800
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
801

    
802
<code>
803
case arg1 {
804
	2: print "two"; print "I can do more commands without {}";
805
	3 .. 5: print "three to five";
806
	else: print "something else";
807
}
808

    
809
if 1234 = i then printn "."; else { 
810
  print "not 1234"; 
811
  print "You need {} around multiple commands"; 
812
}
813
</code>
814

    
815
<sect>Route attributes
816

    
817
<p>A filter is implicitly passed a route, and it can access its
818
attributes just like it accesses variables. Attempts to access undefined
819
attribute result in a runtime error; you can check if an attribute is
820
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
821

    
822
<descrip>
823
	<tag><m/prefix/ net</tag>
824
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
825

    
826
	<tag><m/enum/ scope</tag>
827
	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).
828

    
829
	<tag><m/int/ preference</tag>
830
	Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.)
831

    
832
	<tag><m/ip/ from</tag>
833
	The router which the route has originated from. Read-only.
834
	
835
	<tag><m/ip/ gw</tag>
836
	Next hop packets routed using this route should be forwarded to.
837

    
838
	<tag><m/string/ proto</tag>
839
	The name of the protocol which the route has been imported from. Read-only.
840

    
841
	<tag><m/enum/ source</tag>
842
	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/.
843

    
844
	<tag><m/enum/ cast</tag>
845
	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.
846

    
847
	<tag><m/enum/ dest</tag>
848
	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.
849
</descrip>
850

    
851
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
852

    
853
<sect>Other statements
854

    
855
<p>The following statements are available:
856

    
857
<descrip>
858
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
859

    
860
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
861

    
862
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
863

    
864
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
865
	Prints given expressions; useful mainly while debugging
866
	filters. The <cf/printn/ variant does not terminate the line.
867

    
868
	<tag>quitbird</tag>
869
	Terminates BIRD. Useful when debugging the filter interpreter.
870
</descrip>
871

    
872
<chapt>Protocols
873

    
874
<sect>BGP
875

    
876
<p>The Border Gateway Protocol is the routing protocol used for backbone
877
level routing in the today's Internet. Contrary to the other protocols, its convergence
878
doesn't rely on all routers following the same rules for route selection,
879
making it possible to implement any routing policy at any router in the
880
network, the only restriction being that if a router advertises a route,
881
it must accept and forward packets according to it.
882

    
883
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each
884
AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number.
885
Routers within each AS usually communicate with each other using either a interior routing
886
protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP).
887
Boundary routers at the border of the AS communicate with their peers
888
in the neighboring AS'es via exterior BGP (eBGP).
889

    
890
<p>Each BGP router sends to its neighbors updates of the parts of its
891
routing table it wishes to export along with complete path information
892
(a list of AS'es the packet will travel through if it uses the particular
893
route) in order to avoid routing loops.
894

    
895
<p>BIRD supports all requirements of the BGP4 standard as defined in
896
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
897
It also supports the community attributes
898
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
899
capability negotiation
900
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
901
MD5 password authentication
902
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
903
route reflectors 
904
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
905
multiprotocol extensions
906
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
907
and 4B AS numbers 
908
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
909

    
910

    
911
For IPv6, it uses the standard multiprotocol extensions defined in
912
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
913
including changes described in the
914
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
915
and applied to IPv6 according to
916
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
917

    
918
<sect1>Route selection rules
919

    
920
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
921
route among multiple BGP routes with the same preference are a bit more complex
922
and they are implemented according to the following algorithm. It starts the first
923
rule, if there are more "best" routes, then it uses the second rule to choose
924
among them and so on.
925

    
926
<itemize>
927
	<item>Prefer route with the highest Local Preference attribute.
928
	<item>Prefer route with the shortest AS path.
929
	<item>Prefer IGP origin over EGP and EGP over incomplete.
930
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
931
	<item>Prefer internal routes over external ones.
932
	<item>Prefer the route with the lowest value of router ID of the
933
	advertising router.
934
</itemize>
935

    
936
<sect1>Configuration
937

    
938
<p>Each instance of the BGP corresponds to one neighboring router.
939
This allows to set routing policy and all the other parameters differently
940
for each neighbor using the following configuration parameters:
941

    
942
<descrip>
943
	<tag>local as <m/number/</tag> Define which AS we are part of. (Note that
944
	contrary to other IP routers, BIRD is able to act as a router located
945
	in multiple AS'es simultaneously, but in such cases you need to tweak
946
	the BGP paths manually in the filters to get consistent behavior.)
947
	This parameter is mandatory.
948

    
949
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
950
	this instance will be talking to and what AS it's located in. Unless
951
	you use the <cf/multihop/ clause, it must be directly connected to one
952
	of your router's interfaces. In case the neighbor is in the same AS
953
	as we are, we automatically switch to iBGP. This parameter is mandatory.
954

    
955
	<tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a
956
	neighbor which is connected at most <m/number/ hops far and to which
957
	we should route via our direct neighbor with address <m/ip/.
958
	Default: switched off.
959

    
960
	<tag>next hop self</tag> Avoid calculation of the Next Hop
961
	attribute and always advertise our own source address (see
962
	below) as a next hop.  This needs to be used only occasionally
963
	to circumvent misconfigurations of other routers.
964
	Default: disabled.
965

    
966
	<tag>missing lladdr self|drop|ignore</tag>Next Hop attribute
967
	in BGP-IPv6 sometimes contains just the global IPv6 address,
968
	but sometimes it has to contain both global and link-local
969
	IPv6 addresses. This option specifies what to do if BIRD have
970
	to send both addresses but does not know link-local address.
971
	This situation might happen when routes from other protocols
972
	are exported to BGP, or when improper updates are received
973
	from BGP peers.  <cf/self/ means that BIRD advertises its own
974
	local address instead. <cf/drop/ means that BIRD skips that
975
	prefixes and logs error. <cf/ignore/ means that BIRD ignores
976
	the problem and sends just the global address (and therefore
977
	forms improper BGP update). Default: <cf/self/, unless BIRD
978
	is configured as a route server (option <cf/rs client/), in
979
	that case default is <cf/drop/, because route servers usually
980
	does not forward packets ifselves.
981
	
982
	<tag>source address <m/ip/</tag> Define local address we should use
983
	for next hop calculation. Default: the address of the local end
984
	of the interface our neighbor is connected to.
985

    
986
	<tag>password <m/string/</tag> Use this password for MD5 authentication
987
	of BGP sessions. Default: no authentication. Password has to be set by
988
	external utility (e.g. setkey(8)) on BSD systems.
989

    
990
	<tag>passive <m/switch/</tag> Standard BGP behavior is both
991
        initiating outgoing connections and accepting incoming
992
        connections. In passive mode, outgoing connections are not
993
        initiated. Default: off.
994

    
995
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
996
	a route reflection client. Default: disabled.
997

    
998
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
999
	to avoid route reflection loops. When there is one route reflector in a cluster
1000
	it usually uses its router id as a cluster id, but when there are more route
1001
	reflectors in a cluster, these need to be configured (using this option) to
1002
	use a common cluster id. Clients in a cluster need not know their cluster
1003
	id and this option is not allowed for them. Default: the same as router id.
1004

    
1005
	<tag>rs client</tag> Be a route server and treat the neighbor
1006
	as a route server client. A route server is used as a
1007
	replacement for full mesh EBGP routing in Internet exchange
1008
	points in a similar way to route reflectors used in IBGP routing.
1009
	BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
1010
	which behaves like plain EBGP but reduces modifications to advertised route
1011
	attributes to be transparent (for example does not prepend its AS number to
1012
	AS PATH attribute and keep MED attribute). Default: disabled.
1013

    
1014
	<tag>enable route refresh <m/switch/</tag> When BGP speaker
1015
	changes its import filter, it has to re-examine all routes
1016
	received from its neighbor against the new filter. As these
1017
	routes might not be available, there is a BGP protocol
1018
	extension Route Refresh (specified in RFC 2918) that allows
1019
	BGP speaker to request re-advertisement of all routes from its
1020
	neighbor. This option specifies whether BIRD advertises this
1021
	capability and accepts such requests. Even when disabled, BIRD
1022
	can send route refresh requests. Default: on.
1023

    
1024
	<tag>interpret communities <m/switch/</tag> RFC 1997 demands
1025
	that BGP speaker should process well-known communities like
1026
	no-export (65535, 65281) or no-advertise (65535, 65282). For
1027
	example, received route carrying a no-adverise community
1028
	should not be advertised to any of its neighbors. If this
1029
	option is enabled (which is by default), BIRD has such
1030
	behavior automatically (it is evaluated when a route is
1031
	exported to the protocol just before the export filter).
1032
	Otherwise, this integrated processing of well-known
1033
	communities is disabled. In that case, similar behavior can be
1034
	implemented in the export filter.  Default: on.
1035

    
1036
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
1037
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
1038
	but by disabling this option it can be persuaded not to advertise it and
1039
	to maintain old-style sessions with its neighbors. This might be useful for
1040
	circumventing bugs in neighbor's implementation of 4B AS extension.
1041
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
1042
	Default: on.
1043

    
1044
	<tag>capabilities <m/switch/</tag> Use capability advertisement
1045
	to advertise optional capabilities. This is standard behavior
1046
	for newer BGP implementations, but there might be some older
1047
	BGP implementations that reject such connection attempts.
1048
	When disabled (off), features that request it (4B AS support)
1049
	are also disabled. Default: on, with automatic fallback to
1050
	off when received capability-related error.
1051

    
1052
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
1053
	This is not a correct behavior according to the strict interpretation
1054
	of RFC 4760, but it is widespread and required by some BGP
1055
	implementations (Cisco and Quagga). This option is relevant
1056
	to IPv4 mode with enabled capability advertisement only. Default: on.
1057

    
1058
	<tag>route limit <m/number/</tag> The maximal number of routes
1059
	that may be imported from the protocol. If the route limit is
1060
	exceeded, the connection is closed with error. Default: no limit.
1061

    
1062
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
1063
	locally or by the other side), disable the instance automatically
1064
	and wait for an administrator to fix the problem manually. Default: off.
1065

    
1066
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
1067
	message from the other side before considering the connection stale.
1068
	Default: depends on agreement with the neighboring router, we prefer
1069
	240 seconds if the other side is willing to accept it.
1070

    
1071
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
1072
	before the routers have a chance to exchange open messages and agree
1073
	on the real value. Default: 240 seconds.
1074

    
1075
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
1076
	of two consecutive Keepalive messages. Default: One third of the hold time.
1077

    
1078
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
1079
	retrying a failed attempt to connect. Default: 120 seconds.
1080

    
1081
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
1082
	startup and the first attempt to connect. Default: 5 seconds.
1083

    
1084
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
1085
	failure (either local or reported by the peer) and automatic restart.
1086
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
1087
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
1088

    
1089
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
1090
	failures to treat them as a error sequence which makes the <cf/error wait time/
1091
	increase exponentially. Default: 300 seconds.
1092

    
1093
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
1094
	when deciding which BGP route is the best one. Default: on.
1095

    
1096
	<tag>prefer older <m/switch/</tag> Standard route selection algorithm
1097
	breaks ties by comparing router IDs. This changes the behavior
1098
	to prefer older routes (when both are external and from different
1099
	peer). For details, see RFC 5004. Default: off.
1100

    
1101
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
1102
	Discriminator to be used during route selection when the MED attribute
1103
	is missing. Default: 0.
1104

    
1105
	<tag>default bgp_local_pref <m/number/</tag> A default value
1106
	for the Local Preference attribute. It is used when a new
1107
	Local Preference attribute is attached to a route by the BGP
1108
	protocol itself (for example, if a route is received through
1109
	eBGP and therefore does not have such attribute). Default: 100
1110
	(0 in pre-1.2.0 versions of BIRD).
1111
</descrip>
1112

    
1113
<sect1>Attributes
1114

    
1115
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
1116
table below) are available on internal BGP connections only, some of them (marked
1117
with `<tt/O/') are optional.
1118

    
1119
<descrip>
1120
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
1121
	the packet will travel through when forwarded according to the particular route. In case of 
1122
	internal BGP it doesn't contain the number of the local AS.
1123

    
1124
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
1125
	selection among multiple BGP routes (see the selection rules above). It's
1126
	used as an additional metric which is propagated through the whole local AS.
1127

    
1128
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
1129
	is an optional attribute which is used on on external (inter-AS) links to
1130
	convey to an adjacent AS the optimal entry point into the local AS.
1131
	The received attribute may be also propagated over internal BGP links
1132
	(and this is default behavior). The attribute value is zeroed when a route
1133
	is exported from a routing table to a BGP instance to ensure that the attribute
1134
	received from a neighboring AS is not propagated to other neighboring ASes.
1135
	A new value might be set in the export filter of a BGP instance.
1136
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1137
	for further discussion of BGP MED attribute.
1138

    
1139
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
1140
	if the route has originated in an interior routing protocol or
1141
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
1142
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
1143
	is unknown.
1144

    
1145
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
1146
	to this destination. On internal BGP connections, it's an address of the
1147
	originating router if it's inside the local AS or a boundary router the
1148
	packet will leave the AS through if it's an exterior route, so each BGP
1149
	speaker within the AS has a chance to use the shortest interior path
1150
	possible to this point.
1151

    
1152
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
1153
	which carries no value, but the sole presence of which indicates that the route
1154
	has been aggregated from multiple routes by some router on the path from
1155
	the originator.
1156

    
1157
<!-- we don't handle aggregators right since they are of a very obscure type
1158
	<tag>bgp_aggregator</tag>
1159
-->
1160
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
1161
	with the route. Each such value is a pair (represented as a <cf/pair/ data
1162
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
1163
	the community and the second one being a per-AS identifier. There are lots
1164
	of uses of the community mechanism, but generally they are used to carry
1165
	policy information like "don't export to USA peers". As each AS can define
1166
	its own routing policy, it also has a complete freedom about which community
1167
	attributes it defines and what will their semantics be.
1168
</descrip>
1169

    
1170
<sect1>Example
1171

    
1172
<p><code>
1173
protocol bgp {
1174
	local as 65000;			     # Use a private AS number
1175
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
1176
	multihop 20 via 62.168.0.13;	     # ... which is connected indirectly
1177
	export filter {			     # We use non-trivial export rules
1178
		if source = RTS_STATIC then { # Export only static routes
1179
		        # Assign our community
1180
			bgp_community.add((65000,5678));
1181
			# Artificially increase path length
1182
			# by advertising local AS number twice
1183
			if bgp_path ~ [= 65000 =] then	  
1184
				bgp_path.prepend(65000);  
1185
			accept;
1186
		}
1187
		reject;
1188
	};
1189
	import all;
1190
	source address 62.168.0.1;	# Use a non-standard source address
1191
}
1192
</code>
1193

    
1194
<sect>Device
1195

    
1196
<p>The Device protocol is not a real routing protocol.  It doesn't generate
1197
any routes and it only serves as a module for getting information about network
1198
interfaces from the kernel.
1199

    
1200
<p>Except for very unusual circumstances, you probably should include
1201
this protocol in the configuration since almost all other protocols
1202
require network interfaces to be defined for them to work with.
1203

    
1204
<sect1>Configuration
1205

    
1206
<p><descrip>
1207
	<tag>scan time <m/number/</tag> Time in seconds between two scans
1208
	of the network interface list. On systems where we are notified about
1209
	interface status changes asynchronously (such as newer versions of
1210
	Linux), we need to scan the list only in order to avoid confusion by lost
1211
	notification messages, so the default time is set to a large value.
1212

    
1213
	<tag>primary  [ "<m/mask/" ] <m/prefix/</tag>
1214
	If a network interface has more than one network address,
1215
	BIRD has to choose one of them as a primary one, because some
1216
	routing protocols (for example OSPFv2) suppose there is only
1217
	one network address per interface. By default, BIRD chooses
1218
	the lexicographically smallest address as the primary one.
1219

    
1220
	This option allows to specify which network address should be
1221
	chosen as a primary one. Network addresses that match
1222
	<m/prefix/ are preferred to non-matching addresses. If more
1223
	<cf/primary/ options are used, the first one has the highest
1224
	preference. If "<m/mask/" is specified, then such
1225
	<cf/primary/ option is relevant only to matching network
1226
	interfaces.
1227

    
1228
	In all cases, an address marked by operating system as
1229
	secondary cannot be chosen as the primary one. 
1230
</descrip>
1231

    
1232
<p>As the Device protocol doesn't generate any routes, it cannot have
1233
any attributes. Example configuration looks like this:
1234

    
1235
<p><code>
1236
protocol device {
1237
	scan time 10;		# Scan the interfaces often
1238
	primary "eth0" 192.168.1.1;
1239
	primary 192.168.0.0/16;
1240
}
1241
</code>
1242

    
1243
<sect>Direct
1244

    
1245
<p>The Direct protocol is a simple generator of device routes for all the
1246
directly connected networks according to the list of interfaces provided
1247
by the kernel via the Device protocol.
1248

    
1249
<p>It's highly recommended to include this protocol in your configuration
1250
unless you want to use BIRD as a route server or a route reflector, that is
1251
on a machine which doesn't forward packets itself and only participates in
1252
distribution of routing information.
1253

    
1254
<p>The only configurable thing about direct is what interfaces it watches:
1255

    
1256
<p><descrip>
1257
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
1258
	protocol will generate device routes for all the interfaces
1259
	available. If you want to restrict it to some subset of interfaces
1260
	(for example if you're using multiple routing tables for policy
1261
	routing and some of the policy domains don't contain all interfaces),
1262
	just use this clause.
1263
</descrip>
1264

    
1265
<p>Direct device routes don't contain any specific attributes.
1266

    
1267
<p>Example config might look like this:
1268

    
1269
<p><code>
1270
protocol direct {
1271
	interface "-arc*", "*";		# Exclude the ARCnets
1272
}
1273
</code>
1274

    
1275
<sect>Kernel
1276

    
1277
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
1278
the with other routers in the network, it performs synchronization of BIRD's routing
1279
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
1280
and from time to time it scans the kernel tables to see whether some routes have
1281
disappeared (for example due to unnoticed up/down transition of an interface)
1282
or whether an `alien' route has been added by someone else (depending on the
1283
<cf/learn/ switch, such routes are either deleted or accepted to our
1284
table).
1285

    
1286
<p>If your OS supports only a single routing table, you can configure only one
1287
instance of the Kernel protocol. If it supports multiple tables (in order to
1288
allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of
1289
them must be connected to a different BIRD routing table and to a different
1290
kernel table.
1291

    
1292
<sect1>Configuration
1293

    
1294
<p><descrip>
1295
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
1296
	routing tables when it exits (instead of cleaning them up).
1297
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
1298
	kernel routing table.
1299
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
1300
	routing tables by other routing daemons or by the system administrator.
1301
	This is possible only on systems which support identification of route
1302
	authorship.
1303
	<tag>kernel table <m/number/</tag> Select which kernel table should
1304
	this particular instance of the Kernel protocol work with. Available
1305
	only on systems supporting multiple routing tables.
1306
</descrip>
1307

    
1308
<p>The Kernel protocol doesn't define any route attributes.
1309
<p>A simple configuration can look this way:
1310

    
1311
<p><code>
1312
protocol kernel {
1313
	import all;
1314
	export all;
1315
}
1316
</code>
1317

    
1318
<p>Or for a system with two routing tables:
1319

    
1320
<p><code>
1321
protocol kernel {		# Primary routing table
1322
	learn;			# Learn alien routes from the kernel
1323
	persist;		# Don't remove routes on bird shutdown
1324
	scan time 10;		# Scan kernel routing table every 10 seconds
1325
	import all;
1326
	export all;
1327
}
1328

    
1329
protocol kernel {		# Secondary routing table
1330
	table auxtable;
1331
	kernel table 100;
1332
	export all;
1333
}
1334
</code>
1335

    
1336
<sect>OSPF
1337

    
1338
<sect1>Introduction
1339

    
1340
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1341
protocol. The current IPv4 version (OSPFv2) is defined in RFC
1342
2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt"> and
1343
the current IPv6 version (OSPFv3) is defined in RFC 5340<htmlurl
1344
url="ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt">  It's a link state
1345
(a.k.a. shortest path first) protocol -- each router maintains a
1346
database describing the autonomous system's topology. Each participating
1347
router has an identical copy of the database and all routers run the
1348
same algorithm calculating a shortest path tree with themselves as a
1349
root. OSPF chooses the least cost path as the best path.
1350

    
1351
<p>In OSPF, the autonomous system can be split to several areas in order
1352
to reduce the amount of resources consumed for exchanging the routing
1353
information and to protect the other areas from incorrect routing data.
1354
Topology of the area is hidden to the rest of the autonomous system.
1355

    
1356
<p>Another very important feature of OSPF is that
1357
it can keep routing information from other protocols (like Static or BGP)
1358
in its link state database as external routes. Each external route can
1359
be tagged by the advertising router, making it possible to pass additional
1360
information between routers on the boundary of the autonomous system.
1361

    
1362
<p>OSPF quickly detects topological changes in the autonomous system (such
1363
as router interface failures) and calculates new loop-free routes after a short
1364
period of convergence. Only a minimal amount of 
1365
routing traffic is involved.
1366

    
1367
<p>Each router participating in OSPF routing periodically sends Hello messages
1368
to all its interfaces. This allows neighbors to be discovered dynamically.
1369
Then the neighbors exchange theirs parts of the link state database and keep it
1370
identical by flooding updates. The flooding process is reliable and ensures
1371
that each router detects all changes.
1372

    
1373
<sect1>Configuration
1374

    
1375
<p>In the main part of configuration, there can be multiple definitions of
1376
OSPF area witch different id included. These definitions includes many other
1377
switches and multiple definitions of interfaces. Definition of interface
1378
may contain many switches and constant definitions and list of neighbors
1379
on nonbroadcast networks.
1380

    
1381
<code>
1382
protocol ospf &lt;name&gt; {
1383
	rfc1583compat &lt;switch&gt;;
1384
	tick &lt;num&gt;;
1385
	area &lt;id&gt; {
1386
		stub cost &lt;num&gt;;
1387
                networks {
1388
			&lt;prefix&gt;;
1389
			&lt;prefix&gt; hidden;
1390
		}
1391
		stubnet &lt;prefix&gt;;
1392
		stubnet &lt;prefix&gt; {
1393
			hidden &lt;switch&gt;;
1394
			summary &lt;switch&gt;;
1395
			cost &lt;num&gt;;
1396
		}
1397
		interface &lt;interface pattern&gt; {
1398
			cost &lt;num&gt;;
1399
			stub &lt;switch&gt;;
1400
			hello &lt;num&gt;;
1401
			poll &lt;num&gt;;
1402
			retransmit &lt;num&gt;;
1403
			priority &lt;num&gt;;
1404
			wait &lt;num&gt;;
1405
			dead count &lt;num&gt;;
1406
			dead &lt;num&gt;;
1407
			rx buffer [normal|large|&lt;num&gt;];
1408
			type [broadcast|nonbroadcast|pointopoint];
1409
			strict nonbroadcast &lt;switch&gt;;
1410
			authentication [none|simple|cryptographic];
1411
			password "&lt;text&gt;";
1412
			password "&lt;text&gt;" {
1413
				id &lt;num&gt;;
1414
				generate from "&lt;date&gt;";
1415
				generate to "&lt;date&gt;";
1416
				accept from "&lt;date&gt;";
1417
				accept to "&lt;date&gt;";
1418
			};
1419
			neighbors {
1420
				&lt;ip&gt;;
1421
				&lt;ip&gt; eligible;
1422
			};
1423
		};
1424
		virtual link &lt;id&gt;	{
1425
			hello &lt;num&gt;;
1426
			retransmit &lt;num&gt;;
1427
			wait &lt;num&gt;;
1428
			dead count &lt;num&gt;;
1429
			dead &lt;num&gt;;
1430
			authentication [none|simple|cryptographic];
1431
			password "&lt;text&gt;";
1432
		};
1433
	};
1434
}
1435
</code>
1436

    
1437
<descrip>
1438
	<tag>rfc1583compat <M>switch</M></tag>
1439
	 This option controls compatibility of routing table
1440
	 calculation with RFC 1583<htmlurl
1441
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1442
	 value is no.
1443
	
1444
	<tag>area <M>id</M></tag>
1445
	 This defines an OSPF area with given area ID (an integer or an IPv4
1446
	 address, similarly to a router ID).
1447
	 The most important area is
1448
	 the backbone (ID 0) to which every other area must be connected.
1449

    
1450
	<tag>stub cost <M>num</M></tag>
1451
	 No external (except default) routes are flooded into stub areas.
1452
         Setting this value marks area stub with defined cost of default route.
1453
	 Default value is no. (Area is not stub.)
1454

    
1455
	<tag>tick <M>num</M></tag>
1456
	 The routing table calculation and clean-up of areas' databases
1457
         is not performed when a single link state
1458
	 change arrives. To lower the CPU utilization, it's processed later
1459
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1460

    
1461
	<tag>networks { <m/set/ }</tag>
1462
         Definition of area IP ranges. This is used in summary LSA origination.
1463
	 Hidden networks are not propagated into other areas.
1464

    
1465
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
1466
	 Stub networks are networks that are not transit networks
1467
	 between OSPF routers. They are also propagated through an
1468
	 OSPF area as a part of a link state database. By default,
1469
	 BIRD generates a stub network record for each primary network
1470
	 address on each OSPF interface that does not have any OSPF
1471
	 neighbors, and also for each non-primary network address on
1472
	 each OSPF interface. This option allows to alter a set of
1473
	 stub networks propagated by this router. 
1474

    
1475
	 Each instance of this option adds a stub network with given
1476
	 network prefix to the set of propagated stub network, unless
1477
	 option <cf/hidden/ is used. It also suppresses default stub
1478
	 networks for given network prefix. When option
1479
	 <cf/summary/ is used, also default stub networks that are
1480
	 subnetworks of given stub network are suppressed. This might
1481
	 be used, for example, to aggregate generated stub networks.
1482
	 
1483
	<tag>interface <M>pattern</M></tag>
1484
	 Defines that the specified interfaces belong to the area being defined.
1485
	 See <ref id="dsc-iface" name="interface"> common option for detailed description.
1486

    
1487
	<tag>virtual link <M>id</M></tag>
1488
	 Virtual link to router with the router id. Virtual link acts as a
1489
         point-to-point interface belonging to backbone. The actual area is
1490
         used as transport area. This item cannot be in the backbone.
1491

    
1492
	<tag>cost <M>num</M></tag>
1493
	 Specifies output cost (metric) of an interface. Default value is 10.
1494

    
1495
	<tag>stub <M>switch</M></tag>
1496
	 If set to interface it does not listen to any packet and does not send
1497
	 any hello. Default value is no.
1498

    
1499
	<tag>hello <M>num</M></tag>
1500
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1501
	 routers on the same network need to have the same hello interval.
1502
	 Default value is 10.
1503

    
1504
	<tag>poll <M>num</M></tag>
1505
	 Specifies interval in seconds between sending of Hello messages for
1506
	 some neighbors on NBMA network. Default value is 20.
1507

    
1508
	<tag>retransmit <M>num</M></tag>
1509
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1510
	 Default value is 5.
1511

    
1512
        <tag>priority <M>num</M></tag>
1513
	 On every multiple access network (e.g., the Ethernet) Designed Router
1514
	 and Backup Designed router are elected. These routers have some
1515
	 special functions in the flooding process. Higher priority increases
1516
	 preferences in this election. Routers with priority 0 are not
1517
	 eligible. Default value is 1.
1518

    
1519
	<tag>wait <M>num</M></tag>
1520
	 After start, router waits for the specified number of seconds between starting
1521
	 election and building adjacency. Default value is 40.
1522
	 
1523
	<tag>dead count <M>num</M></tag>
1524
	 When the router does not receive any messages from a neighbor in
1525
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1526

    
1527
	<tag>dead <M>num</M></tag>
1528
	 When the router does not receive any messages from a neighbor in
1529
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1530
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1531

    
1532
	<tag>rx buffer <M>num</M></tag>
1533
	 This sets the size of buffer used for receiving packets. The buffer should
1534
	 be bigger than maximal size of any packets. Value NORMAL (default)
1535
	 means 2*MTU, value LARGE means maximal allowed packet - 65536.
1536

    
1537
	<tag>type broadcast</tag>
1538
	 BIRD detects a type of a connected network automatically, but sometimes it's
1539
	 convenient to force use of a different type manually.
1540
	 On broadcast networks, flooding and Hello messages are sent using multicasts
1541
	 (a single packet for all the neighbors).
1542

    
1543
	<tag>type pointopoint</tag>
1544
	 Point-to-point networks connect just 2 routers together. No election
1545
	 is performed there which reduces the number of messages sent.
1546

    
1547
	<tag>type nonbroadcast</tag>
1548
	 On nonbroadcast networks, the packets are sent to each neighbor
1549
	 separately because of lack of multicast capabilities.
1550

    
1551
	<tag>strict nonbroadcast <M>switch</M></tag>
1552
	 If set, don't send hello to any undefined neighbor. This switch
1553
	 is ignored on any non-NBMA network. Default is No.
1554

    
1555
	<tag>authentication none</tag>
1556
	 No passwords are sent in OSPF packets. This is the default value.
1557

    
1558
	<tag>authentication simple</tag>
1559
	 Every packet carries 8 bytes of password. Received packets
1560
	 lacking this password are ignored. This authentication mechanism is
1561
	 very weak.
1562

    
1563
	<tag>authentication cryptographic</tag>
1564
	 16-byte long MD5 digest is appended to every packet. For the digest
1565
         generation 16-byte long passwords are used. Those passwords are 
1566
         not sent via network, so this mechanism is quite secure.
1567
         Packets can still be read by an attacker.
1568

    
1569
	<tag>password "<M>text</M>"</tag>
1570
	 An 8-byte or 16-byte password used for authentication.
1571
	 See <ref id="dsc-pass" name="password"> common option for detailed description.
1572

    
1573
	<tag>neighbors { <m/set/ } </tag>
1574
	 A set of neighbors to which Hello messages on nonbroadcast networks
1575
	 are to be sent. Some of them could be marked as eligible.
1576

    
1577
</descrip>
1578

    
1579
<sect1>Attributes
1580

    
1581
<p>OSPF defines four route attributes. Each internal route has a <cf/metric/.
1582
Metric is ranging from 1 to infinity (65535).
1583
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1584
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1585
<cf/metric of type 2/ is always longer
1586
than any <cf/metric of type 1/ or any <cf/internal metric/.
1587
If you specify both metrics only metric1 is used.
1588
Each external route can also carry a <cf/tag/ which is a 32-bit
1589
integer which is used when exporting routes to other protocols;
1590
otherwise, it doesn't affect routing inside the OSPF domain at all.
1591
The fourth attribute is a <cf/router_id/ of the router advertising
1592
that route/network. This attribute is read-only.
1593
Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/.
1594

    
1595
<sect1>Example
1596

    
1597
<p>
1598

    
1599
<code>
1600
protocol ospf MyOSPF {
1601
        rfc1583compat yes;
1602
        tick 2;
1603
	export filter {
1604
		if source = RTS_BGP then {
1605
			ospf_metric1 = 100;
1606
			accept;
1607
		}
1608
		reject;
1609
	};
1610
	area 0.0.0.0 {
1611
		interface "eth*" {
1612
			cost 11;
1613
			hello 15;
1614
			priority 100;
1615
			retransmit 7;
1616
			authentication simple;
1617
			password "aaa";
1618
		};
1619
		interface "ppp*" {
1620
			cost 100;
1621
			authentication cryptographic;
1622
			password "abc" {
1623
				id 1;
1624
				generate to "22-04-2003 11:00:06";
1625
				accept from "17-01-2001 12:01:05";
1626
			};
1627
			password "def" {
1628
				id 2;
1629
				generate to "22-07-2005 17:03:21";
1630
				accept from "22-02-2001 11:34:06";
1631
			};
1632
		};
1633
		interface "arc0" {
1634
			cost 10;
1635
			stub yes;
1636
		};
1637
		interface "arc1";
1638
	};
1639
	area 120 {
1640
		stub yes;
1641
		networks {
1642
			172.16.1.0/24;
1643
			172.16.2.0/24 hidden;
1644
		}
1645
		interface "-arc0" , "arc*" {
1646
			type nonbroadcast;
1647
			authentication none;
1648
			strict nonbroadcast yes;
1649
			wait 120;
1650
			poll 40;
1651
			dead count 8;
1652
			neighbors {
1653
				192.168.120.1 eligible;
1654
				192.168.120.2;
1655
				192.168.120.10;
1656
			};
1657
		};
1658
	};
1659
}
1660
</code>
1661

    
1662
<sect>Pipe
1663

    
1664
<sect1>Introduction
1665

    
1666
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1667
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1668
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1669
and vice versa, depending on what's allowed by the filters. Export filters control export
1670
of routes from the primary table to the secondary one, import filters control the opposite
1671
direction.
1672

    
1673
<p>The Pipe protocol may work in the opaque mode or in the transparent
1674
mode. In the opaque mode, the Pipe protocol retransmits optimal route
1675
from one table to the other table in a similar way like other
1676
protocols send and receive routes. Retransmitted route will have the
1677
source set to the Pipe protocol, which may limit access to protocol
1678
specific route attributes. The opaque mode is a default mode.
1679

    
1680
<p>In transparent mode, the Pipe protocol retransmits all routes from
1681
one table to the other table, retaining their original source and
1682
attributes.  If import and export filters are set to accept, then both
1683
tables would have the same content. The mode can be set by
1684
<tt/mode/ option.
1685

    
1686
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1687
where handling of a single packet doesn't depend only on its destination address, but also
1688
on its source address, source interface, protocol type and other similar parameters.
1689
In many systems (Linux being a good example), the kernel allows to enforce routing policies
1690
by defining routing rules which choose one of several routing tables to be used for a packet
1691
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1692
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1693
connect them to the kernel ones, use filters to control which routes appear in which tables
1694
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1695
another one.
1696

    
1697
<sect1>Configuration
1698

    
1699
<p><descrip>
1700
	<tag>peer table <m/table/</tag> Defines secondary routing table to connect to. The
1701
	primary one is selected by the <cf/table/ keyword.
1702

    
1703
	<tag>mode opaque|transparent</tag> Specifies the mode for the pipe to work in. Default is opaque.
1704
</descrip>
1705

    
1706
<sect1>Attributes
1707

    
1708
<p>The Pipe protocol doesn't define any route attributes.
1709

    
1710
<sect1>Example
1711

    
1712
<p>Let's consider a router which serves as a boundary router of two different autonomous
1713
systems, each of them connected to a subset of interfaces of the router, having its own
1714
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1715
of outage of its own exterior line.
1716

    
1717
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1718
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1719
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1720
and similarly for the second AS. Thus we have split our router to two logical routers,
1721
each one acting on its own routing table, having its own routing protocols on its own
1722
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1723
the routes between the tables through a Pipe protocol while decreasing their preferences
1724
and correcting their BGP paths to reflect the AS boundary crossing.
1725

    
1726
<code>
1727
table as1;				# Define the tables
1728
table as2;
1729

    
1730
protocol kernel kern1 {			# Synchronize them with the kernel
1731
	table as1;
1732
	kernel table 1;
1733
}
1734

    
1735
protocol kernel kern2 {
1736
	table as2;
1737
	kernel table 2;
1738
}
1739

    
1740
protocol bgp bgp1 {			# The outside connections
1741
	table as1;
1742
	local as 1;
1743
	neighbor 192.168.0.1 as 1001;
1744
	export all;
1745
	import all;
1746
}
1747

    
1748
protocol bgp bgp2 {
1749
	table as2;
1750
	local as 2;
1751
	neighbor 10.0.0.1 as 1002;
1752
	export all;
1753
	import all;
1754
}
1755

    
1756
protocol pipe {				# The Pipe
1757
	table as1;
1758
	peer table as2;
1759
	export filter {
1760
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1761
			if preference>10 then preference = preference-10;
1762
			if source=RTS_BGP then bgp_path.prepend(1);
1763
			accept;
1764
		}
1765
		reject;
1766
	};
1767
	import filter {
1768
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1769
			if preference>10 then preference = preference-10;
1770
			if source=RTS_BGP then bgp_path.prepend(2);
1771
			accept;
1772
		}
1773
		reject;
1774
	};
1775
}
1776
</code>
1777

    
1778
<sect>RIP
1779

    
1780
<sect1>Introduction
1781

    
1782
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
1783
distances to all networks it can reach. When a router hears distance to another network, it increments
1784
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
1785
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
1786
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
1787
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
1788
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
1789
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
1790
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
1791
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
1792
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
1793
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
1794

    
1795
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
1796
convergence, big network load and inability to handle larger networks
1797
makes it pretty much obsolete. (It is still usable on very small networks.)
1798

    
1799
<sect1>Configuration
1800

    
1801
<p>In addition to options common for all to other protocols, RIP supports the following ones:
1802

    
1803
<descrip>
1804
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
1805
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
1806
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
1807
	  hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf>
1808
	  section. Default: none.
1809

    
1810
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
1811
	  be honored. (Always, when sent from a  host on a directly connected
1812
	  network or never.) Routing table updates are honored only from
1813
	  neighbors, that is not configurable. Default: never.
1814
</descrip>
1815

    
1816
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
1817
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
1818
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
1819
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
1820
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
1821
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
1822
interface but not listen to it.
1823

    
1824
<p>The following options generally override behavior specified in RFC. If you use any of these
1825
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
1826
other than equally configured BIRD. I have warned you.
1827

    
1828
<descrip>
1829
	<tag>port <M>number</M></tag>
1830
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
1831
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
1832

    
1833
	<tag>infinity <M>number</M></tag>
1834
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
1835
	  even slower.
1836

    
1837
	<tag>period <M>number</M>
1838
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
1839
	  number will mean faster convergence but bigger network
1840
	  load. Do not use values lower than 10.
1841

    
1842
	<tag>timeout time <M>number</M>
1843
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
1844

    
1845
	<tag>garbage time <M>number</M>
1846
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
1847
</descrip>
1848

    
1849
<sect1>Attributes
1850

    
1851
<p>RIP defines two route attributes:
1852

    
1853
<descrip>
1854
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
1855
	When routes from different RIP instances are available and all of them have the same
1856
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
1857
	When importing a non-RIP route, the metric defaults to 5.
1858

    
1859
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
1860
	to carry additional information with the route (for example, an originating AS number
1861
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
1862
</descrip>
1863

    
1864
<sect1>Example
1865

    
1866
<p><code>
1867
protocol rip MyRIP_test {
1868
        debug all;
1869
        port 1520;
1870
        period 10;
1871
        garbage time 60;
1872
        interface "eth0" { metric 3; mode multicast; };
1873
	interface "eth*" { metric 2; mode broadcast; };
1874
        honor neighbor;
1875
        authentication none;
1876
        import filter { print "importing"; accept; };
1877
        export filter { print "exporting"; accept; };
1878
}
1879
</code>
1880

    
1881
<sect>Static
1882

    
1883
<p>The Static protocol doesn't communicate with other routers in the network,
1884
but instead it allows you to define routes manually. This is often used for
1885
specifying how to forward packets to parts of the network which don't use
1886
dynamic routing at all and also for defining sink routes (i.e., those
1887
telling to return packets as undeliverable if they are in your IP block,
1888
you don't have any specific destination for them and you don't want to send
1889
them out through the default route to prevent routing loops).
1890

    
1891
<p>There are three types of static routes: `classical' routes telling to
1892
forward packets to a neighboring router, device routes specifying forwarding
1893
to hosts on a directly connected network and special routes (sink, blackhole
1894
etc.) which specify a special action to be done instead of forwarding the
1895
packet.
1896

    
1897
<p>When the particular destination is not available (the interface is down or
1898
the next hop of the route is not a neighbor at the moment), Static just
1899
uninstalls the route from the table it is connected to and adds it again as soon
1900
as the destination becomes adjacent again.
1901

    
1902
<p>The Static protocol has no configuration options. Instead, the
1903
definition of the protocol contains a list of static routes:
1904

    
1905
<descrip>
1906
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
1907
	a neighboring router.
1908
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
1909
	route through an interface to hosts on a directly connected network.
1910
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
1911
	specifying to drop the packet, return it as unreachable or return
1912
	it as administratively prohibited.
1913
</descrip>
1914

    
1915
<p>Static routes have no specific attributes.
1916

    
1917
<p>Example static config might look like this:
1918

    
1919
<p><code>
1920
protocol static {
1921
	table testable;			 # Connect to a non-default routing table
1922
	route 0.0.0.0/0 via 62.168.0.13; # Default route
1923
	route 62.168.0.0/25 reject;	 # Sink route
1924
	route 10.2.0.0/24 via "arc0";	 # Secondary network
1925
}
1926
</code>
1927

    
1928
<chapt>Conclusions
1929

    
1930
<sect>Future work
1931

    
1932
<p>Although BIRD supports all the commonly used routing protocols,
1933
there are still some features which would surely deserve to be
1934
implemented in future versions of BIRD:
1935

    
1936
<itemize>
1937
<item>OSPF NSSA areas and opaque LSA's
1938
<item>Route aggregation and flap dampening
1939
<item>Generation of IPv6 router advertisements
1940
<item>Multipath routes
1941
<item>Multicast routing protocols
1942
<item>Ports to other systems
1943
</itemize>
1944

    
1945
<sect>Getting more help
1946

    
1947
<p>If you use BIRD, you're welcome to join the bird-users mailing list
1948
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
1949
where you can share your experiences with the other users and consult
1950
your problems with the authors. To subscribe to the list, just send a
1951
<tt/subscribe bird-users/ command in a body of a mail to
1952
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
1953
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
1954

    
1955
<p>BIRD is a relatively young system and it probably contains some
1956
bugs. You can report any problems to the bird-users list and the authors
1957
will be glad to solve them, but before you do so,
1958
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
1959
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
1960
which fixes the bug is always welcome as an attachment.)
1961

    
1962
<p>If you want to understand what is going inside, Internet standards are
1963
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">).
1964

    
1965
<p><it/Good luck!/
1966

    
1967
</book>
1968

    
1969
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