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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>the Router Advertisements for IPv6 hosts
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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
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been developed and tested under Linux 2.0 to 2.6, and then ported to
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FreeBSD, NetBSD and OpenBSD, porting to other systems (even non-UNIX
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ones) should be relatively easy due to its highly modular
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architecture.
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<p>BIRD supports either IPv4 or IPv6 protocol, but have to be compiled
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separately for each one. Therefore, a dualstack router would run two
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instances of BIRD (one for IPv4 and one for IPv6), with completely
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separate setups (configuration files, tools ...).
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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 [name <m/name/]|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 (a file specified as a filename string,
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	syslog with optional name argument, or the stderr output). 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/] [dual]</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/dual/ can be used to specify that BGP socket should accept
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	both IPv4 and IPv6 connections (but even in that case, BIRD
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	would accept IPv6 routes only). Such behavior was default in
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	older versions of BIRD.
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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 <it/strftime(3)/
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	notation (see <it/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. For IPv6, the prefix part of a clause
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	is generally ignored and interfaces are matched just by their name.
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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, RIP and RAdv 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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409
	<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 ptp; };</cf> - start the protocol
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	on enumerated interfaces with <cf>type ptp</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
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domain socket (unless changed with the <tt/-s/ option given to both
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the server and the client). The commands can perform simple actions
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such as enabling/disabling of protocols, telling BIRD to show various
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information, telling it to show routing table filtered by filter, or
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asking BIRD to reconfigure. Press <tt/?/ at any time to get online
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help. Option <tt/-r/ can be used to enable a restricted mode of BIRD
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client, which allows just read-only commands (<cf/show .../). 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
478
<file/birdc/ to talk to BIRD, your own applications could do that, too
479
-- the format of communication between BIRD and <file/birdc/ is stable
480
(see the programmer's documentation).
481

    
482
Many commands have the <m/name/ of the protocol instance as an argument.
483
This argument can be omitted if there exists only a single instance.
484

    
485
<p>Here is a brief list of supported functions:
486

    
487
<descrip>
488
	<tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
489
	Dump contents of internal data structures to the debugging output.
490

    
491
	<tag>show status</tag>
492
	Show router status, that is BIRD version, uptime and time from last reconfiguration.
493

    
494
	<tag>show protocols [all]</tag>
495
	Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified.
496

    
497
	<tag>show ospf interface [<m/name/] ["<m/interface/"]</tag>
498
	Show detailed information about OSPF interfaces.
499

    
500
	<tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
501
	Show a list of OSPF neighbors and a state of adjacency to them.
502

    
503
	<tag>show ospf state [all] [<m/name/]</tag>
504
	Show detailed information about OSPF areas based on a content
505
	of the link-state database. It shows network topology, stub
506
	networks, aggregated networks and routers from other areas and
507
	external routes. The command shows information about reachable
508
	network nodes, use option <cf/all/ to show information about
509
	all network nodes in the link-state database.
510

    
511
	<tag>show ospf topology [all] [<m/name/]</tag>
512
	Show a topology of OSPF areas based on a content of the
513
	link-state database.  It is just a stripped-down version of
514
	'show ospf state'.
515

    
516
	<tag>show static [<m/name/]</tag>
517
	Show detailed information about static routes.
518

    
519
	<tag>show interfaces [summary]</tag>
520
	Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. 
521

    
522
	<tag>show symbols</tag>
523
	Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).
524

    
525
	<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>
526
	Show contents of a routing table (by default of the main one),
527
	that is routes, their metrics and (in case the <cf/all/ switch is given)
528
	all their attributes.
529

    
530
	<p>You can specify a <m/prefix/ if you want to print routes for a
531
	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
532
	the entry which will be used for forwarding of packets to the given
533
	destination. By default, all routes for each network are printed with
534
	the selected one at the top, unless <cf/primary/ is given in which case
535
	only the selected route is shown.
536

    
537
	<p>You can also ask for printing only routes processed and accepted by
538
	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
539
	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
540
	The <cf/export/ and <cf/preexport/ switches ask for printing of entries
541
	that are exported to the specified protocol. With <cf/preexport/, the
542
	export filter of the protocol is skipped.
543

    
544
	<p>You can also select just routes added by a specific protocol.
545
	<cf>protocol <m/p/</cf>.
546

    
547
	<p>The <cf/stats/ switch requests showing of route statistics (the
548
	number of networks, number of routes before and after filtering). If
549
	you use <cf/count/ instead, only the statistics will be printed.
550

    
551
	<tag>configure [soft] ["<m/config file/"]</tag>
552
	Reload configuration from a given file. BIRD will smoothly
553
	switch itself to the new configuration, protocols are
554
	reconfigured if possible, restarted otherwise. Changes in
555
	filters usually lead to restart of affected protocols. If
556
	<cf/soft/ option is used, changes in filters does not cause
557
	BIRD to restart affected protocols, therefore already accepted
558
	routes (according to old filters) would be still propagated,
559
	but new routes would be processed according to the new
560
	filters.
561

    
562
	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
563
	Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances.
564

    
565
	<tag>reload [in|out] <m/name/|"<m/pattern/"|all</tag>
566
	
567
	Reload a given protocol instance, that means re-import routes
568
	from the protocol instance and re-export preferred routes to
569
	the instance. If <cf/in/ or <cf/out/ options are used, the
570
	command is restricted to one direction (re-import or
571
	re-export).
572

    
573
	This command is useful if appropriate filters have changed but
574
	the protocol instance was not restarted (or reloaded),
575
	therefore it still propagates the old set of routes. For example
576
	when <cf/configure soft/ command was used to change filters.
577

    
578
	Re-export always succeeds, but re-import is protocol-dependent
579
	and might fail (for example, if BGP neighbor does not support
580
	route-refresh extension). In that case, re-export is also
581
	skipped. Note that for the pipe protocol, both directions are
582
	always reloaded together (<cf/in/ or <cf/out/ options are
583
	ignored in that case).
584

    
585
	<tag/down/
586
	Shut BIRD down.
587

    
588
	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
589
	Control protocol debugging.
590
</descrip>
591

    
592
<chapt>Filters
593

    
594
<sect>Introduction
595

    
596
<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
597
two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
598
being passed between protocols and routing tables. The filter language contains control structures such
599
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>. 
600

    
601
<p>Filter gets the route, looks at its attributes and
602
modifies some of them if it wishes. At the end, it decides whether to
603
pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
604
like this:
605

    
606
<code>
607
filter not_too_far
608
int var;
609
{
610
	if defined( rip_metric ) then
611
		var = rip_metric;
612
	else {
613
		var = 1;
614
		rip_metric = 1;
615
	}
616
	if rip_metric &gt; 10 then
617
		reject "RIP metric is too big";
618
	else
619
		accept "ok";
620
}
621
</code>
622

    
623
<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
624
the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
625
<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
626
<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
627
several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
628
you want to make a bigger block of code conditional.
629

    
630
<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
631
over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
632
look like this:
633

    
634
<code>
635
function name ()
636
int local_variable;
637
{
638
	local_variable = 5;
639
}
640

    
641
function with_parameters (int parameter)
642
{
643
	print parameter;
644
}
645
</code>
646

    
647
<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
648
variables in nested blocks. Functions are called like in C: <cf>name();
649
with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
650
command. Returning a value exits from current function (this is similar to C).
651

    
652
<p>Filters are declared in a way similar to functions except they can't have explicit
653
parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
654
to any functions called. The filter must terminate with either
655
<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
656
is rejected. 
657

    
658
<p>A nice trick to debug filters is to use <cf>show route filter
659
<m/name/</cf> from the command line client. An example session might look
660
like:
661

    
662
<code>
663
pavel@bug:~/bird$ ./birdc -s bird.ctl
664
BIRD 0.0.0 ready.
665
bird> show route
666
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
667
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
668
127.0.0.0/8        dev lo [direct1 23:21] (240)
669
bird> show route ?
670
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
671
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
672
127.0.0.0/8        dev lo [direct1 23:21] (240)
673
bird>
674
</code>
675

    
676
<sect>Data types
677

    
678
<p>Each variable and each value has certain type. Booleans, integers and enums are
679
incompatible with each other (that is to prevent you from shooting in the foot).
680

    
681
<descrip>
682
	<tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and
683
	  <cf/false/. Boolean is the only type you can use in <cf/if/
684
	  statements.
685

    
686
	<tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000
687
	  to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
688

    
689
	<tag/pair/ This is a pair of two short integers. Each component can have values from 0 to
690
	  65535. Literals of this type are written as <cf/(1234,5678)/. The same syntax can also be
691
	  used to construct a pair from two arbitrary integer expressions (for example <cf/(1+2,a)/).
692

    
693
	<tag/quad/ This is a dotted quad of numbers used to represent
694
	  router IDs (and others).  Each component can have a value
695
	  from 0 to 255. Literals of this type are written like IPv4
696
	  addresses.
697

    
698
	<tag/string/ This is a string of characters. There are no ways to modify strings in
699
	  filters. You can pass them between functions, assign them to variables of type <cf/string/, print
700
	  such variables, but you can't concatenate two strings. String literals
701
	  are written as <cf/"This is a string constant"/.
702

    
703
	<tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it
704
	  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>
705
	  on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP
706
	  address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
707

    
708
	<tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as
709
	  <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
710
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
711
	  operators on prefixes:
712
	  <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix
713
	  length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
714

    
715
	<tag/int|pair|quad|ip|prefix|enum set/
716
	  Filters recognize four types of sets. Sets are similar to strings: you can pass them around
717
	  but you can't modify them. Literals of type <cf>int set</cf> look like <cf>
718
	  [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in
719
	  sets.
720
	  For pair sets, expressions like <cf/(123,*)/ can be used to denote ranges (in
721
	  that case <cf/(123,0)..(123,65535)/). You can also use <cf/(123,5..100)/ for range
722
	  <cf/(123,5)..(123,100)/. You can also use <cf/(*,123)/ which is translated as
723
	  <cf/(0,123) , (1,123) , (2,123) , ... , (65535, 123)/
724
	  You can also use expressions for both, pair sets and int sets. However it must
725
	  be possible to evaluate these expressions before daemon boots. So you can use
726
	  only constants inside them. E.g.
727
	<code>
728
	 define one=1;
729
	 int set odds;
730
	 pair set ps;
731

    
732
	 odds = [ one, (2+1), (6-one), (2*2*2-1), 9, 11 ]; 
733
	 ps = [ (1,(one+one)), (3,4)..(4,8), (5,*), (6,3..6) ];
734
	</code>
735

    
736
	  Sets of prefixes are special: their literals does not allow ranges, but allows
737
	  prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
738
	  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> if 
739
	  the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>.
740
	  A valid prefix pattern has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/
741
	  or <cf/high/. Obviously, a prefix matches a prefix set literal if it matches any prefix pattern in the
742
	  prefix set literal.
743

    
744
	  There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for
745
	  <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), 
746
	  that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf>
747
	  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>
748
	  and all its supernets (network prefixes that contain it).
749

    
750
	  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
751
	  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
752
	  <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
753
	  IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address
754
	  <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf> is true,
755
	  but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
756

    
757
	  Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
758
	  in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
759
	  <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
760
	  <cf>192.168.0.0/16{24,32}</cf>.
761

    
762
	<tag/enum/
763
	  Enumeration types are fixed sets of possibilities. You can't define your own
764
	  variables of such type, but some route attributes are of enumeration
765
	  type. Enumeration types are incompatible with each other.
766

    
767
	<tag/bgppath/
768
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
769
	  There are several special operators on bgppaths:
770

    
771
	  <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
772

    
773
          <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
774

    
775
	  Both <cf/first/ and <cf/last/ return zero if there is no appropriate ASN,
776
          for example if the path contains an AS set element as the first (or the last) part.
777

    
778
          <cf><m/P/.len</cf> returns the length of path <m/P/.
779

    
780
          <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and returns the result.
781
          Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
782
          <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
783
          (for example <cf/bgp_path/).
784

    
785
	<tag/bgpmask/
786
	  BGP masks are patterns used for BGP path matching
787
	  (using <cf>path &tilde; [= 2 3 5 * =]</cf> syntax). The masks
788
	  resemble wildcard patterns as used by UNIX shells. Autonomous
789
	  system numbers match themselves, <cf/*/ matches any (even empty)
790
	  sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number.
791
	  For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
792
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
793
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
794
	  BGP mask expressions can also contain integer expressions enclosed in parenthesis
795
	  and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>.
796
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
797

    
798
	<tag/clist/
799
	  Clist is similar to a set, except that unlike other sets, it
800
	  can be modified. The type is used for community list (a set
801
	  of pairs) and for cluster list (a set of quads). There exist
802
	  no literals of this type. There are two special operators on
803
	  clists:
804

    
805
          <cf>add(<m/C/,<m/P/)</cf> adds pair (or quad) <m/P/ to clist
806
	  <m/C/ and returns the result.  If item <m/P/ is already in
807
	  clist <m/C/, it does nothing.
808

    
809
          <cf>delete(<m/C/,<m/P/)</cf> deletes pair (or quad)
810
	  <m/P/ from clist <m/C/ and returns the result.  If clist
811
	  <m/C/ does not contain item <m/P/, it does nothing.
812
	  <m/P/ may also be a pair (or quad) set, in that case the
813
	  operator deletes all items from clist <m/C/ that are also
814
	  members of set <m/P/.
815

    
816
          Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
817
          <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute
818
          (for example <cf/bgp_community/). Similarly for <cf/delete/.
819

    
820
</descrip>
821

    
822
<sect>Operators
823

    
824
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
825
<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;/). 
826
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
827
used on element and set of elements of the same type (returning true if element is contained in the given set), or
828
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
829
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/quad and clist (returning true if the pair/quad is element of the clist) or on clist and pair/quad set (returning true if there is an element of the clist that is also a member of the pair/quad set).
830

    
831

    
832
<sect>Control structures
833

    
834
<p>Filters support two control structures: conditions and case switches. 
835

    
836
<p>Syntax of a condition is: <cf>if
837
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
838
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
839
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.
840

    
841
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else: |
842
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
843
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
844
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
845
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.
846

    
847
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
848

    
849
<code>
850
case arg1 {
851
	2: print "two"; print "I can do more commands without {}";
852
	3 .. 5: print "three to five";
853
	else: print "something else";
854
}
855

    
856
if 1234 = i then printn "."; else { 
857
  print "not 1234"; 
858
  print "You need {} around multiple commands"; 
859
}
860
</code>
861

    
862
<sect>Route attributes
863

    
864
<p>A filter is implicitly passed a route, and it can access its
865
attributes just like it accesses variables. Attempts to access undefined
866
attribute result in a runtime error; you can check if an attribute is
867
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
868
One notable exception to this rule are attributes of clist type, where
869
undefined value is regarded as empty clist for most purposes.
870

    
871
<descrip>
872
	<tag><m/prefix/ net</tag>
873
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
874

    
875
	<tag><m/enum/ scope</tag>
876
	The scope of the route. Possible values: <cf/SCOPE_HOST/ for
877
	routes local to this host, <cf/SCOPE_LINK/ for those specific
878
	for a physical link, <cf/SCOPE_SITE/ and
879
	<cf/SCOPE_ORGANIZATION/ for private routes and
880
	<cf/SCOPE_UNIVERSE/ for globally visible routes. This
881
	attribute is not interpreted by BIRD and can be used to mark
882
	routes in filters. The default value for new routes is
883
	<cf/SCOPE_UNIVERSE/.
884

    
885
	<tag><m/int/ preference</tag>
886
	Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.)
887

    
888
	<tag><m/ip/ from</tag>
889
	The router which the route has originated from. Read-only.
890
	
891
	<tag><m/ip/ gw</tag>
892
	Next hop packets routed using this route should be forwarded to.
893

    
894
	<tag><m/string/ proto</tag>
895
	The name of the protocol which the route has been imported from. Read-only.
896

    
897
	<tag><m/enum/ source</tag>
898
	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_EXT1/, <cf/RTS_OSPF_EXT2/, <cf/RTS_BGP/, <cf/RTS_PIPE/.
899

    
900
	<tag><m/enum/ cast</tag>
901

    
902
	Route type (Currently <cf/RTC_UNICAST/ for normal routes,
903
	<cf/RTC_BROADCAST/, <cf/RTC_MULTICAST/, <cf/RTC_ANYCAST/ will
904
	be used in the future for broadcast, multicast and anycast
905
	routes). Read-only.
906

    
907
	<tag><m/enum/ dest</tag>
908
	Type of destination the packets should be sent to (<cf/RTD_ROUTER/ for forwarding to a neighboring router, <cf/RTD_DEVICE/ 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.
909

    
910
	<tag><m/int/ igp_metric</tag>
911
	The optional attribute that can be used to specify a distance
912
	to the network for routes that do not have a native protocol
913
	metric attribute (like <cf/ospf_metric1/ for OSPF routes). It
914
	is used mainly by BGP to compare internal distances to boundary
915
	routers (see below). It is also used when the route is exported
916
	to OSPF as a default value for OSPF type 1 metric.
917
</descrip>
918

    
919
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
920

    
921
<sect>Other statements
922

    
923
<p>The following statements are available:
924

    
925
<descrip>
926
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
927

    
928
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
929

    
930
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
931

    
932
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
933
	Prints given expressions; useful mainly while debugging
934
	filters. The <cf/printn/ variant does not terminate the line.
935

    
936
	<tag>quitbird</tag>
937
	Terminates BIRD. Useful when debugging the filter interpreter.
938
</descrip>
939

    
940
<chapt>Protocols
941

    
942
<sect>BGP
943

    
944
<p>The Border Gateway Protocol is the routing protocol used for backbone
945
level routing in the today's Internet. Contrary to the other protocols, its convergence
946
doesn't rely on all routers following the same rules for route selection,
947
making it possible to implement any routing policy at any router in the
948
network, the only restriction being that if a router advertises a route,
949
it must accept and forward packets according to it.
950

    
951
<p>BGP works in terms of autonomous systems (often abbreviated as
952
AS). Each AS is a part of the network with common management and
953
common routing policy. It is identified by a unique 16-bit number
954
(ASN).  Routers within each AS usually exchange AS-internal routing
955
information with each other using an interior gateway protocol (IGP,
956
such as OSPF or RIP). Boundary routers at the border of
957
the AS communicate global (inter-AS) network reachability information with
958
their neighbors in the neighboring AS'es via exterior BGP (eBGP) and
959
redistribute received information to other routers in the AS via
960
interior BGP (iBGP).
961

    
962
<p>Each BGP router sends to its neighbors updates of the parts of its
963
routing table it wishes to export along with complete path information
964
(a list of AS'es the packet will travel through if it uses the particular
965
route) in order to avoid routing loops.
966

    
967
<p>BIRD supports all requirements of the BGP4 standard as defined in
968
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
969
It also supports the community attributes
970
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
971
capability negotiation
972
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
973
MD5 password authentication
974
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
975
route reflectors 
976
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
977
multiprotocol extensions
978
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
979
and 4B AS numbers 
980
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">).
981

    
982

    
983
For IPv6, it uses the standard multiprotocol extensions defined in
984
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
985
including changes described in the
986
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
987
and applied to IPv6 according to
988
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
989

    
990
<sect1>Route selection rules
991

    
992
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
993
route among multiple BGP routes with the same preference are a bit more complex
994
and they are implemented according to the following algorithm. It starts the first
995
rule, if there are more "best" routes, then it uses the second rule to choose
996
among them and so on.
997

    
998
<itemize>
999
	<item>Prefer route with the highest Local Preference attribute.
1000
	<item>Prefer route with the shortest AS path.
1001
	<item>Prefer IGP origin over EGP and EGP origin over incomplete.
1002
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
1003
	<item>Prefer routes received via eBGP over ones received via iBGP.
1004
	<item>Prefer routes with lower internal distance to a boundary router.
1005
	<item>Prefer the route with the lowest value of router ID of the
1006
	advertising router.
1007
</itemize>
1008

    
1009
<sect1>IGP routing table
1010

    
1011
<p>BGP is mainly concerned with global network reachability and with
1012
routes to other autonomous systems. When such routes are redistributed
1013
to routers in the AS via BGP, they contain IP addresses of a boundary
1014
routers (in route attribute NEXT_HOP). BGP depends on existing IGP
1015
routing table with AS-internal routes to determine immediate next hops
1016
for routes and to know their internal distances to boundary routers
1017
for the purpose of BGP route selection. In BIRD, there is usually
1018
one routing table used for both IGP routes and BGP routes.
1019

    
1020
<sect1>Configuration
1021

    
1022
<p>Each instance of the BGP corresponds to one neighboring router.
1023
This allows to set routing policy and all the other parameters differently
1024
for each neighbor using the following configuration parameters:
1025

    
1026
<descrip>
1027
	<tag>local [<m/ip/] as <m/number/</tag> Define which AS we
1028
	are part of. (Note that contrary to other IP routers, BIRD is
1029
	able to act as a router located in multiple AS'es
1030
	simultaneously, but in such cases you need to tweak the BGP
1031
	paths manually in the filters to get consistent behavior.)
1032
	Optional <cf/ip/ argument specifies a source address,
1033
	equivalent to the <cf/source address/ option (see below).
1034
	This parameter is mandatory.
1035

    
1036
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
1037
	this instance will be talking to and what AS it's located in. Unless
1038
	you use the <cf/multihop/ clause, it must be directly connected to one
1039
	of your router's interfaces. In case the neighbor is in the same AS
1040
	as we are, we automatically switch to iBGP. This parameter is mandatory.
1041

    
1042
	<tag>multihop [<m/number/]</tag> Configure multihop BGP
1043
	session to a neighbor that isn't directly connected.
1044
	Accurately, this option should be used if the configured
1045
	neighbor IP address does not match with any local network
1046
	subnets. Such IP address have to be reachable through system
1047
	routing table. For multihop BGP it is recommended to
1048
	explicitly configure <cf/source address/ to have it
1049
	stable. Optional <cf/number/ argument can be used to limit TTL
1050
	(the number of hops).
1051
	Default: switched off.
1052

    
1053
	<tag>source address <m/ip/</tag> Define local address we
1054
	should use for next hop calculation and as a source address
1055
	for the BGP session. Default: the address of the local
1056
	end of the interface our neighbor is connected to.
1057

    
1058
	<tag>next hop self</tag> Avoid calculation of the Next Hop
1059
	attribute and always advertise our own source address as a
1060
	next hop.  This needs to be used only occasionally to
1061
	circumvent misconfigurations of other routers.  Default:
1062
	disabled.
1063

    
1064
	<tag>missing lladdr self|drop|ignore</tag>Next Hop attribute
1065
	in BGP-IPv6 sometimes contains just the global IPv6 address,
1066
	but sometimes it has to contain both global and link-local
1067
	IPv6 addresses. This option specifies what to do if BIRD have
1068
	to send both addresses but does not know link-local address.
1069
	This situation might happen when routes from other protocols
1070
	are exported to BGP, or when improper updates are received
1071
	from BGP peers.  <cf/self/ means that BIRD advertises its own
1072
	local address instead. <cf/drop/ means that BIRD skips that
1073
	prefixes and logs error. <cf/ignore/ means that BIRD ignores
1074
	the problem and sends just the global address (and therefore
1075
	forms improper BGP update). Default: <cf/self/, unless BIRD
1076
	is configured as a route server (option <cf/rs client/), in
1077
	that case default is <cf/ignore/, because route servers usually
1078
	do not forward packets themselves.
1079

    
1080
	<tag>gateway direct|recursive</tag>For received routes, their
1081
	<cf/gw/ (immediate next hop) attribute is computed from
1082
	received <cf/bgp_next_hop/ attribute. This option specifies
1083
	how it is computed. Direct mode means that the IP address from
1084
	<cf/bgp_next_hop/ is used if it is directly reachable,
1085
	otherwise the neighbor IP address is used. Recursive mode
1086
	means that the gateway is computed by an IGP routing table
1087
	lookup for the IP address from <cf/bgp_next_hop/. Recursive
1088
	mode is the behavior specified by the BGP standard. Direct
1089
	mode is simpler, does not require any routes in a routing
1090
	table, and was used in older versions of BIRD, but does not
1091
	handle well nontrivial iBGP setups and multihop. Default:
1092
	<cf/direct/ for singlehop eBGP, <cf/recursive/ otherwise.
1093

    
1094
	<tag>igp table <m/name/</tag> Specifies a table that is used
1095
	as an IGP routing table. Default: the same as the table BGP is
1096
	connected to.
1097
	
1098
	<tag>password <m/string/</tag> Use this password for MD5 authentication
1099
	of BGP sessions. Default: no authentication. Password has to be set by
1100
	external utility (e.g. setkey(8)) on BSD systems.
1101

    
1102
	<tag>passive <m/switch/</tag> Standard BGP behavior is both
1103
        initiating outgoing connections and accepting incoming
1104
        connections. In passive mode, outgoing connections are not
1105
        initiated. Default: off.
1106

    
1107
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
1108
	a route reflection client. Default: disabled.
1109

    
1110
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
1111
	to avoid route reflection loops. When there is one route reflector in a cluster
1112
	it usually uses its router id as a cluster id, but when there are more route
1113
	reflectors in a cluster, these need to be configured (using this option) to
1114
	use a common cluster id. Clients in a cluster need not know their cluster
1115
	id and this option is not allowed for them. Default: the same as router id.
1116

    
1117
	<tag>rs client</tag> Be a route server and treat the neighbor
1118
	as a route server client. A route server is used as a
1119
	replacement for full mesh EBGP routing in Internet exchange
1120
	points in a similar way to route reflectors used in IBGP routing.
1121
	BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
1122
	which behaves like plain EBGP but reduces modifications to advertised route
1123
	attributes to be transparent (for example does not prepend its AS number to
1124
	AS PATH attribute and keep MED attribute). Default: disabled.
1125

    
1126
	<tag>enable route refresh <m/switch/</tag> When BGP speaker
1127
	changes its import filter, it has to re-examine all routes
1128
	received from its neighbor against the new filter. As these
1129
	routes might not be available, there is a BGP protocol
1130
	extension Route Refresh (specified in RFC 2918) that allows
1131
	BGP speaker to request re-advertisement of all routes from its
1132
	neighbor. This option specifies whether BIRD advertises this
1133
	capability and accepts such requests. Even when disabled, BIRD
1134
	can send route refresh requests. Default: on.
1135

    
1136
	<tag>interpret communities <m/switch/</tag> RFC 1997 demands
1137
	that BGP speaker should process well-known communities like
1138
	no-export (65535, 65281) or no-advertise (65535, 65282). For
1139
	example, received route carrying a no-adverise community
1140
	should not be advertised to any of its neighbors. If this
1141
	option is enabled (which is by default), BIRD has such
1142
	behavior automatically (it is evaluated when a route is
1143
	exported to the BGP protocol just before the export filter).
1144
	Otherwise, this integrated processing of well-known
1145
	communities is disabled. In that case, similar behavior can be
1146
	implemented in the export filter.  Default: on.
1147

    
1148
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
1149
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
1150
	but by disabling this option it can be persuaded not to advertise it and
1151
	to maintain old-style sessions with its neighbors. This might be useful for
1152
	circumventing bugs in neighbor's implementation of 4B AS extension.
1153
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
1154
	Default: on.
1155

    
1156
	<tag>capabilities <m/switch/</tag> Use capability advertisement
1157
	to advertise optional capabilities. This is standard behavior
1158
	for newer BGP implementations, but there might be some older
1159
	BGP implementations that reject such connection attempts.
1160
	When disabled (off), features that request it (4B AS support)
1161
	are also disabled. Default: on, with automatic fallback to
1162
	off when received capability-related error.
1163

    
1164
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
1165
	This is not a correct behavior according to the strict interpretation
1166
	of RFC 4760, but it is widespread and required by some BGP
1167
	implementations (Cisco and Quagga). This option is relevant
1168
	to IPv4 mode with enabled capability advertisement only. Default: on.
1169

    
1170
	<tag>route limit <m/number/</tag> The maximal number of routes
1171
	that may be imported from the protocol. If the route limit is
1172
	exceeded, the connection is closed with error. Default: no limit.
1173

    
1174
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
1175
	locally or by the other side), disable the instance automatically
1176
	and wait for an administrator to fix the problem manually. Default: off.
1177

    
1178
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
1179
	message from the other side before considering the connection stale.
1180
	Default: depends on agreement with the neighboring router, we prefer
1181
	240 seconds if the other side is willing to accept it.
1182

    
1183
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
1184
	before the routers have a chance to exchange open messages and agree
1185
	on the real value. Default: 240 seconds.
1186

    
1187
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
1188
	of two consecutive Keepalive messages. Default: One third of the hold time.
1189

    
1190
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
1191
	retrying a failed attempt to connect. Default: 120 seconds.
1192

    
1193
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
1194
	startup and the first attempt to connect. Default: 5 seconds.
1195

    
1196
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
1197
	failure (either local or reported by the peer) and automatic restart.
1198
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
1199
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
1200

    
1201
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
1202
	failures to treat them as a error sequence which makes the <cf/error wait time/
1203
	increase exponentially. Default: 300 seconds.
1204

    
1205
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
1206
	when deciding which BGP route is the best one. Default: on.
1207

    
1208
	<tag>igp metric <m/switch/</tag> Enable comparison of internal
1209
 	distances to boundary routers during best route selection. Default: on.
1210

    
1211
	<tag>prefer older <m/switch/</tag> Standard route selection algorithm
1212
	breaks ties by comparing router IDs. This changes the behavior
1213
	to prefer older routes (when both are external and from different
1214
	peer). For details, see RFC 5004. Default: off.
1215

    
1216
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
1217
	Discriminator to be used during route selection when the MED attribute
1218
	is missing. Default: 0.
1219

    
1220
	<tag>default bgp_local_pref <m/number/</tag> A default value
1221
	for the Local Preference attribute. It is used when a new
1222
	Local Preference attribute is attached to a route by the BGP
1223
	protocol itself (for example, if a route is received through
1224
	eBGP and therefore does not have such attribute). Default: 100
1225
	(0 in pre-1.2.0 versions of BIRD).
1226
</descrip>
1227

    
1228
<sect1>Attributes
1229

    
1230
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
1231
table below) are available on internal BGP connections only, some of them (marked
1232
with `<tt/O/') are optional.
1233

    
1234
<descrip>
1235
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
1236
	the packet will travel through when forwarded according to the particular route. In case of 
1237
	internal BGP it doesn't contain the number of the local AS.
1238

    
1239
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
1240
	selection among multiple BGP routes (see the selection rules above). It's
1241
	used as an additional metric which is propagated through the whole local AS.
1242

    
1243
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
1244
	is an optional attribute which is used on on external (inter-AS) links to
1245
	convey to an adjacent AS the optimal entry point into the local AS.
1246
	The received attribute may be also propagated over internal BGP links
1247
	(and this is default behavior). The attribute value is zeroed when a route
1248
	is exported from a routing table to a BGP instance to ensure that the attribute
1249
	received from a neighboring AS is not propagated to other neighboring ASes.
1250
	A new value might be set in the export filter of a BGP instance.
1251
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1252
	for further discussion of BGP MED attribute.
1253

    
1254
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
1255
	if the route has originated in an interior routing protocol or
1256
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
1257
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
1258
	is unknown.
1259

    
1260
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
1261
	to this destination. On internal BGP connections, it's an address of the
1262
	originating router if it's inside the local AS or a boundary router the
1263
	packet will leave the AS through if it's an exterior route, so each BGP
1264
	speaker within the AS has a chance to use the shortest interior path
1265
	possible to this point.
1266

    
1267
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
1268
	which carries no value, but the sole presence of which indicates that the route
1269
	has been aggregated from multiple routes by some router on the path from
1270
	the originator.
1271

    
1272
<!-- we don't handle aggregators right since they are of a very obscure type
1273
	<tag>bgp_aggregator</tag>
1274
-->
1275
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
1276
	with the route. Each such value is a pair (represented as a <cf/pair/ data
1277
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
1278
	the community and the second one being a per-AS identifier. There are lots
1279
	of uses of the community mechanism, but generally they are used to carry
1280
	policy information like "don't export to USA peers". As each AS can define
1281
	its own routing policy, it also has a complete freedom about which community
1282
	attributes it defines and what will their semantics be.
1283

    
1284
	<tag>quad <cf/bgp_originator_id/ [O]</tag> This attribute is created by the
1285
	route reflector when reflecting the route and contains the router ID of the
1286
	originator of the route in the local AS.
1287

    
1288
	<tag>clist <cf/bgp_cluster_list/ [O]</tag> This attribute contains a list
1289
	of cluster IDs of route reflectors. Each route reflector prepends its
1290
	cluster ID when reflecting the route.
1291
</descrip>
1292

    
1293
<sect1>Example
1294

    
1295
<p><code>
1296
protocol bgp {
1297
	local as 65000;			     # Use a private AS number
1298
	neighbor 62.168.0.130 as 5588;	     # Our neighbor ...
1299
	multihop;			     # ... which is connected indirectly
1300
	export filter {			     # We use non-trivial export rules
1301
		if source = RTS_STATIC then { # Export only static routes
1302
		        # Assign our community
1303
			bgp_community.add((65000,5678));
1304
			# Artificially increase path length
1305
			# by advertising local AS number twice
1306
			if bgp_path ~ [= 65000 =] then	  
1307
				bgp_path.prepend(65000);  
1308
			accept;
1309
		}
1310
		reject;
1311
	};
1312
	import all;
1313
	source address 62.168.0.1;	# Use a non-standard source address
1314
}
1315
</code>
1316

    
1317
<sect>Device
1318

    
1319
<p>The Device protocol is not a real routing protocol.  It doesn't generate
1320
any routes and it only serves as a module for getting information about network
1321
interfaces from the kernel.
1322

    
1323
<p>Except for very unusual circumstances, you probably should include
1324
this protocol in the configuration since almost all other protocols
1325
require network interfaces to be defined for them to work with.
1326

    
1327
<sect1>Configuration
1328

    
1329
<p><descrip>
1330
	<tag>scan time <m/number/</tag> Time in seconds between two scans
1331
	of the network interface list. On systems where we are notified about
1332
	interface status changes asynchronously (such as newer versions of
1333
	Linux), we need to scan the list only in order to avoid confusion by lost
1334
	notification messages, so the default time is set to a large value.
1335

    
1336
	<tag>primary  [ "<m/mask/" ] <m/prefix/</tag>
1337
	If a network interface has more than one network address, BIRD
1338
	has to choose one of them as a primary one. By default, BIRD
1339
	chooses the lexicographically smallest address as the primary
1340
	one.
1341

    
1342
	This option allows to specify which network address should be
1343
	chosen as a primary one. Network addresses that match
1344
	<m/prefix/ are preferred to non-matching addresses. If more
1345
	<cf/primary/ options are used, the first one has the highest
1346
	preference. If "<m/mask/" is specified, then such
1347
	<cf/primary/ option is relevant only to matching network
1348
	interfaces.
1349

    
1350
	In all cases, an address marked by operating system as
1351
	secondary cannot be chosen as the primary one. 
1352
</descrip>
1353

    
1354
<p>As the Device protocol doesn't generate any routes, it cannot have
1355
any attributes. Example configuration looks like this:
1356

    
1357
<p><code>
1358
protocol device {
1359
	scan time 10;		# Scan the interfaces often
1360
	primary "eth0" 192.168.1.1;
1361
	primary 192.168.0.0/16;
1362
}
1363
</code>
1364

    
1365
<sect>Direct
1366

    
1367
<p>The Direct protocol is a simple generator of device routes for all the
1368
directly connected networks according to the list of interfaces provided
1369
by the kernel via the Device protocol.
1370

    
1371
<p>The question is whether it is a good idea to have such device
1372
routes in BIRD routing table. OS kernel usually handles device routes
1373
for directly connected networks by itself so we don't need (and don't
1374
want) to export these routes to the kernel protocol. OSPF protocol
1375
creates device routes for its interfaces itself and BGP protocol is
1376
usually used for exporting aggregate routes. Although there are some
1377
use cases that use the direct protocol (like abusing eBGP as an IGP
1378
routing protocol), in most cases it is not needed to have these device
1379
routes in BIRD routing table and to use the direct protocol.
1380

    
1381
<p>The only configurable thing about direct is what interfaces it watches:
1382

    
1383
<p><descrip>
1384
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
1385
	protocol will generate device routes for all the interfaces
1386
	available. If you want to restrict it to some subset of interfaces
1387
	(for example if you're using multiple routing tables for policy
1388
	routing and some of the policy domains don't contain all interfaces),
1389
	just use this clause.
1390
</descrip>
1391

    
1392
<p>Direct device routes don't contain any specific attributes.
1393

    
1394
<p>Example config might look like this:
1395

    
1396
<p><code>
1397
protocol direct {
1398
	interface "-arc*", "*";		# Exclude the ARCnets
1399
}
1400
</code>
1401

    
1402
<sect>Kernel
1403

    
1404
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
1405
with other routers in the network, it performs synchronization of BIRD's routing
1406
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
1407
and from time to time it scans the kernel tables to see whether some routes have
1408
disappeared (for example due to unnoticed up/down transition of an interface)
1409
or whether an `alien' route has been added by someone else (depending on the
1410
<cf/learn/ switch, such routes are either ignored or accepted to our
1411
table).
1412

    
1413
<p>Unfortunately, there is one thing that makes the routing table
1414
synchronization a bit more complicated. In the kernel routing table
1415
there are also device routes for directly connected networks. These
1416
routes are usually managed by OS itself (as a part of IP address
1417
configuration) and we don't want to touch that.  They are completely
1418
ignored during the scan of the kernel tables and also the export of
1419
device routes from BIRD tables to kernel routing tables is restricted
1420
to prevent accidental interference. This restriction can be disabled using
1421
<cf/device routes/ switch.
1422

    
1423
<p>If your OS supports only a single routing table, you can configure
1424
only one instance of the Kernel protocol. If it supports multiple
1425
tables (in order to allow policy routing; such an OS is for example
1426
Linux), you can run as many instances as you want, but each of them
1427
must be connected to a different BIRD routing table and to a different
1428
kernel table.
1429

    
1430
<p>Because the kernel protocol is partially integrated with the
1431
connected routing table, there are two limitations - it is not
1432
possible to connect more kernel protocols to the same routing table
1433
and changing route attributes (even the kernel ones) in an export
1434
filter of a kernel protocol does not work. Both limitations can be
1435
overcome using another routing table and the pipe protocol.
1436

    
1437
<sect1>Configuration
1438

    
1439
<p><descrip>
1440
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
1441
	routing tables when it exits (instead of cleaning them up).
1442
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
1443
	kernel routing table.
1444
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
1445
	routing tables by other routing daemons or by the system administrator.
1446
	This is possible only on systems which support identification of route
1447
	authorship.
1448

    
1449
	<tag>device routes <m/switch/</tag> Enable export of device
1450
	routes to the kernel routing table. By default, such routes
1451
	are rejected (with the exception of explicitly configured
1452
	device routes from the static protocol) regardless of the
1453
	export filter to protect device routes in kernel routing table
1454
	(managed by OS itself) from accidental overwriting or erasing.
1455

    
1456
	<tag>kernel table <m/number/</tag> Select which kernel table should
1457
	this particular instance of the Kernel protocol work with. Available
1458
	only on systems supporting multiple routing tables.
1459
</descrip>
1460

    
1461
<sect1>Attributes
1462

    
1463
<p>The Kernel protocol defines several attributes. These attributes
1464
are translated to appropriate system (and OS-specific) route attributes.
1465
We support these attributes:
1466

    
1467
<descrip>
1468
	<tag>ip <cf/krt_prefsrc/</tag> (Linux) The preferred source address.
1469
 	Used in source address selection for outgoing packets. Have to
1470
 	be one of IP addresses of the router.
1471

    
1472
	<tag>int <cf/krt_realm/</tag> (Linux) The realm of the route. Can be
1473
	used for traffic classification.
1474
</descrip>
1475

    
1476
<sect1>Example
1477

    
1478
<p>A simple configuration can look this way:
1479

    
1480
<p><code>
1481
protocol kernel {
1482
	export all;
1483
}
1484
</code>
1485

    
1486
<p>Or for a system with two routing tables:
1487

    
1488
<p><code>
1489
protocol kernel {		# Primary routing table
1490
	learn;			# Learn alien routes from the kernel
1491
	persist;		# Don't remove routes on bird shutdown
1492
	scan time 10;		# Scan kernel routing table every 10 seconds
1493
	import all;
1494
	export all;
1495
}
1496

    
1497
protocol kernel {		# Secondary routing table
1498
	table auxtable;
1499
	kernel table 100;
1500
	export all;
1501
}
1502
</code>
1503

    
1504
<sect>OSPF
1505

    
1506
<sect1>Introduction
1507

    
1508
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
1509
protocol. The current IPv4 version (OSPFv2) is defined in RFC
1510
2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt"> and
1511
the current IPv6 version (OSPFv3) is defined in RFC 5340<htmlurl
1512
url="ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt">  It's a link state
1513
(a.k.a. shortest path first) protocol -- each router maintains a
1514
database describing the autonomous system's topology. Each participating
1515
router has an identical copy of the database and all routers run the
1516
same algorithm calculating a shortest path tree with themselves as a
1517
root. OSPF chooses the least cost path as the best path.
1518

    
1519
<p>In OSPF, the autonomous system can be split to several areas in order
1520
to reduce the amount of resources consumed for exchanging the routing
1521
information and to protect the other areas from incorrect routing data.
1522
Topology of the area is hidden to the rest of the autonomous system.
1523

    
1524
<p>Another very important feature of OSPF is that
1525
it can keep routing information from other protocols (like Static or BGP)
1526
in its link state database as external routes. Each external route can
1527
be tagged by the advertising router, making it possible to pass additional
1528
information between routers on the boundary of the autonomous system.
1529

    
1530
<p>OSPF quickly detects topological changes in the autonomous system (such
1531
as router interface failures) and calculates new loop-free routes after a short
1532
period of convergence. Only a minimal amount of 
1533
routing traffic is involved.
1534

    
1535
<p>Each router participating in OSPF routing periodically sends Hello messages
1536
to all its interfaces. This allows neighbors to be discovered dynamically.
1537
Then the neighbors exchange theirs parts of the link state database and keep it
1538
identical by flooding updates. The flooding process is reliable and ensures
1539
that each router detects all changes.
1540

    
1541
<sect1>Configuration
1542

    
1543
<p>In the main part of configuration, there can be multiple definitions of
1544
OSPF areas, each with a different id. These definitions includes many other
1545
switches and multiple definitions of interfaces. Definition of interface
1546
may contain many switches and constant definitions and list of neighbors
1547
on nonbroadcast networks.
1548

    
1549
<code>
1550
protocol ospf &lt;name&gt; {
1551
	rfc1583compat &lt;switch&gt;;
1552
	tick &lt;num&gt;;
1553
	ecmp &lt;switch&gt; [limit &lt;num&gt;];
1554
	area &lt;id&gt; {
1555
		stub cost &lt;num&gt;;
1556
                networks {
1557
			&lt;prefix&gt;;
1558
			&lt;prefix&gt; hidden;
1559
		}
1560
		stubnet &lt;prefix&gt;;
1561
		stubnet &lt;prefix&gt; {
1562
			hidden &lt;switch&gt;;
1563
			summary &lt;switch&gt;;
1564
			cost &lt;num&gt;;
1565
		}
1566
		interface &lt;interface pattern&gt; {
1567
			cost &lt;num&gt;;
1568
			stub &lt;switch&gt;;
1569
			hello &lt;num&gt;;
1570
			poll &lt;num&gt;;
1571
			retransmit &lt;num&gt;;
1572
			priority &lt;num&gt;;
1573
			wait &lt;num&gt;;
1574
			dead count &lt;num&gt;;
1575
			dead &lt;num&gt;;
1576
			rx buffer [normal|large|&lt;num&gt;];
1577
			type [broadcast|bcast|pointopoint|ptp|
1578
				nonbroadcast|nbma|pointomultipoint|ptmp];
1579
			strict nonbroadcast &lt;switch&gt;;
1580
			check link &lt;switch&gt;;
1581
			ecmp weight &lt;num&gt;;
1582
			authentication [none|simple|cryptographic];
1583
			password "&lt;text&gt;";
1584
			password "&lt;text&gt;" {
1585
				id &lt;num&gt;;
1586
				generate from "&lt;date&gt;";
1587
				generate to "&lt;date&gt;";
1588
				accept from "&lt;date&gt;";
1589
				accept to "&lt;date&gt;";
1590
			};
1591
			neighbors {
1592
				&lt;ip&gt;;
1593
				&lt;ip&gt; eligible;
1594
			};
1595
		};
1596
		virtual link &lt;id&gt;	{
1597
			hello &lt;num&gt;;
1598
			retransmit &lt;num&gt;;
1599
			wait &lt;num&gt;;
1600
			dead count &lt;num&gt;;
1601
			dead &lt;num&gt;;
1602
			authentication [none|simple|cryptographic];
1603
			password "&lt;text&gt;";
1604
		};
1605
	};
1606
}
1607
</code>
1608

    
1609
<descrip>
1610
	<tag>rfc1583compat <M>switch</M></tag>
1611
	 This option controls compatibility of routing table
1612
	 calculation with RFC 1583<htmlurl
1613
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
1614
	 value is no.
1615

    
1616
	<tag>tick <M>num</M></tag>
1617
	 The routing table calculation and clean-up of areas' databases
1618
         is not performed when a single link state
1619
	 change arrives. To lower the CPU utilization, it's processed later
1620
	 at periodical intervals of <m/num/ seconds. The default value is 1.
1621

    
1622
	<tag>ecmp <M>switch</M> [limit <M>number</M>]</tag>
1623
	 This option specifies whether OSPF is allowed to generate
1624
	 ECMP (equal-cost multipath) routes. Such routes are used when
1625
	 there are several directions to the destination, each with
1626
	 the same (computed) cost. This option also allows to specify
1627
	 a limit on maximal number of nexthops in one route. By
1628
	 default, ECMP is disabled.  If enabled, default value of the
1629
	 limit is 16.
1630

    
1631
	<tag>area <M>id</M></tag>
1632
	 This defines an OSPF area with given area ID (an integer or an IPv4
1633
	 address, similarly to a router ID). The most important area is
1634
	 the backbone (ID 0) to which every other area must be connected.
1635

    
1636
	<tag>stub cost <M>num</M></tag>
1637
	 No external (except default) routes are flooded into stub areas.
1638
         Setting this value marks area stub with defined cost of default route.
1639
	 Default value is no. (Area is not stub.)
1640

    
1641
	<tag>networks { <m/set/ }</tag>
1642
         Definition of area IP ranges. This is used in summary LSA origination.
1643
	 Hidden networks are not propagated into other areas.
1644

    
1645
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
1646
	 Stub networks are networks that are not transit networks
1647
	 between OSPF routers. They are also propagated through an
1648
	 OSPF area as a part of a link state database. By default,
1649
	 BIRD generates a stub network record for each primary network
1650
	 address on each OSPF interface that does not have any OSPF
1651
	 neighbors, and also for each non-primary network address on
1652
	 each OSPF interface. This option allows to alter a set of
1653
	 stub networks propagated by this router. 
1654

    
1655
	 Each instance of this option adds a stub network with given
1656
	 network prefix to the set of propagated stub network, unless
1657
	 option <cf/hidden/ is used. It also suppresses default stub
1658
	 networks for given network prefix. When option
1659
	 <cf/summary/ is used, also default stub networks that are
1660
	 subnetworks of given stub network are suppressed. This might
1661
	 be used, for example, to aggregate generated stub networks.
1662
	 
1663
	<tag>interface <M>pattern</M></tag>
1664
	 Defines that the specified interfaces belong to the area being defined.
1665
	 See <ref id="dsc-iface" name="interface"> common option for detailed description.
1666

    
1667
	<tag>virtual link <M>id</M></tag>
1668
	 Virtual link to router with the router id. Virtual link acts as a
1669
         point-to-point interface belonging to backbone. The actual area is
1670
         used as transport area. This item cannot be in the backbone.
1671

    
1672
	<tag>cost <M>num</M></tag>
1673
	 Specifies output cost (metric) of an interface. Default value is 10.
1674

    
1675
	<tag>stub <M>switch</M></tag>
1676
	 If set to interface it does not listen to any packet and does not send
1677
	 any hello. Default value is no.
1678

    
1679
	<tag>hello <M>num</M></tag>
1680
	 Specifies interval in seconds between sending of Hello messages. Beware, all
1681
	 routers on the same network need to have the same hello interval.
1682
	 Default value is 10.
1683

    
1684
	<tag>poll <M>num</M></tag>
1685
	 Specifies interval in seconds between sending of Hello messages for
1686
	 some neighbors on NBMA network. Default value is 20.
1687

    
1688
	<tag>retransmit <M>num</M></tag>
1689
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
1690
	 Default value is 5.
1691

    
1692
        <tag>priority <M>num</M></tag>
1693
	 On every multiple access network (e.g., the Ethernet) Designed Router
1694
	 and Backup Designed router are elected. These routers have some
1695
	 special functions in the flooding process. Higher priority increases
1696
	 preferences in this election. Routers with priority 0 are not
1697
	 eligible. Default value is 1.
1698

    
1699
	<tag>wait <M>num</M></tag>
1700
	 After start, router waits for the specified number of seconds between starting
1701
	 election and building adjacency. Default value is 40.
1702
	 
1703
	<tag>dead count <M>num</M></tag>
1704
	 When the router does not receive any messages from a neighbor in
1705
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
1706

    
1707
	<tag>dead <M>num</M></tag>
1708
	 When the router does not receive any messages from a neighbor in
1709
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
1710
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
1711

    
1712
	<tag>rx buffer <M>num</M></tag>
1713
	 This sets the size of buffer used for receiving packets. The buffer should
1714
	 be bigger than maximal size of any packets. Value NORMAL (default)
1715
	 means 2*MTU, value LARGE means maximal allowed packet - 65535.
1716

    
1717
	<tag>type broadcast|bcast</tag>
1718
	 BIRD detects a type of a connected network automatically, but
1719
	 sometimes it's convenient to force use of a different type
1720
	 manually. On broadcast networks (like ethernet), flooding
1721
	 and Hello messages are sent using multicasts (a single packet
1722
	 for all the neighbors). A designated router is elected and it
1723
	 is responsible for synchronizing the link-state databases and
1724
	 originating network LSAs. This network type cannot be used on
1725
	 physically NBMA networks and on unnumbered networks (networks
1726
	 without proper IP prefix).
1727

    
1728
	<tag>type pointopoint|ptp</tag>
1729
	 Point-to-point networks connect just 2 routers together. No
1730
	 election is performed and no network LSA is originated, which
1731
	 makes it simpler and faster to establish. This network type
1732
	 is useful not only for physically PtP ifaces (like PPP or
1733
	 tunnels), but also for broadcast networks used as PtP links.
1734
	 This network type cannot be used on physically NBMA networks.
1735

    
1736
	<tag>type nonbroadcast|nbma</tag>
1737
	 On NBMA networks, the packets are sent to each neighbor
1738
	 separately because of lack of multicast capabilities.
1739
	 Like on broadcast networks, a designated router is elected,
1740
	 which plays a central role in propagation of LSAs.
1741
	 This network type cannot be used on unnumbered networks.
1742

    
1743
	<tag>type pointomultipoint|ptmp</tag>
1744
	 This is another network type designed to handle NBMA
1745
	 networks. In this case the NBMA network is treated as a
1746
	 collection of PtP links. This is useful if not every pair of
1747
	 routers on the NBMA network has direct communication, or if
1748
	 the NBMA network is used as an (possibly unnumbered) PtP
1749
	 link.
1750

    
1751
	<tag>strict nonbroadcast <M>switch</M></tag>
1752
	 If set, don't send hello to any undefined neighbor. This switch
1753
	 is ignored on other than NBMA or PtMP networks. Default value is no.
1754

    
1755
	<tag>check link <M>switch</M></tag>
1756
	 If set, a hardware link state (reported by OS) is taken into
1757
	 consideration. When a link disappears (e.g. an ethernet cable is
1758
	 unplugged), neighbors are immediately considered unreachable
1759
	 and only the address of the iface (instead of whole network
1760
	 prefix) is propagated. It is possible that some hardware
1761
	 drivers or platforms do not implement this feature. Default value is no.
1762

    
1763
	<tag>ecmp weight <M>num</M></tag>
1764
	 When ECMP (multipath) routes are allowed, this value specifies
1765
	 a relative weight used for nexthops going through the iface.
1766
	 Allowed values are 1-256. Default value is 1.
1767

    
1768
	<tag>authentication none</tag>
1769
	 No passwords are sent in OSPF packets. This is the default value.
1770

    
1771
	<tag>authentication simple</tag>
1772
	 Every packet carries 8 bytes of password. Received packets
1773
	 lacking this password are ignored. This authentication mechanism is
1774
	 very weak.
1775

    
1776
	<tag>authentication cryptographic</tag>
1777
	 16-byte long MD5 digest is appended to every packet. For the digest
1778
         generation 16-byte long passwords are used. Those passwords are 
1779
         not sent via network, so this mechanism is quite secure.
1780
         Packets can still be read by an attacker.
1781

    
1782
	<tag>password "<M>text</M>"</tag>
1783
	 An 8-byte or 16-byte password used for authentication.
1784
	 See <ref id="dsc-pass" name="password"> common option for detailed description.
1785

    
1786
	<tag>neighbors { <m/set/ } </tag>
1787
	 A set of neighbors to which Hello messages on NBMA or PtMP
1788
	 networks are to be sent. For NBMA networks, some of them
1789
	 could be marked as eligible.
1790

    
1791
</descrip>
1792

    
1793
<sect1>Attributes
1794

    
1795
<p>OSPF defines four route attributes. Each internal route has a <cf/metric/.
1796
Metric is ranging from 1 to infinity (65535).
1797
External routes use <cf/metric type 1/ or <cf/metric type 2/.
1798
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
1799
<cf/metric of type 2/ is always longer
1800
than any <cf/metric of type 1/ or any <cf/internal metric/.
1801
<cf/Internal metric/ or <cf/metric of type 1/ is stored in attribute
1802
<cf/ospf_metric1/, <cf/metric type 2/ is stored in attribute <cf/ospf_metric2/.
1803
If you specify both metrics only metric1 is used.
1804

    
1805
Each external route can also carry attribute <cf/ospf_tag/ which is a
1806
32-bit integer which is used when exporting routes to other protocols;
1807
otherwise, it doesn't affect routing inside the OSPF domain at all.
1808
The fourth attribute <cf/ospf_router_id/ is a router ID of the router
1809
advertising that route/network. This attribute is read-only. Default
1810
is <cf/ospf_metric2 = 10000/ and <cf/ospf_tag = 0/.
1811

    
1812
<sect1>Example
1813

    
1814
<p>
1815

    
1816
<code>
1817
protocol ospf MyOSPF {
1818
        rfc1583compat yes;
1819
        tick 2;
1820
	export filter {
1821
		if source = RTS_BGP then {
1822
			ospf_metric1 = 100;
1823
			accept;
1824
		}
1825
		reject;
1826
	};
1827
	area 0.0.0.0 {
1828
		interface "eth*" {
1829
			cost 11;
1830
			hello 15;
1831
			priority 100;
1832
			retransmit 7;
1833
			authentication simple;
1834
			password "aaa";
1835
		};
1836
		interface "ppp*" {
1837
			cost 100;
1838
			authentication cryptographic;
1839
			password "abc" {
1840
				id 1;
1841
				generate to "22-04-2003 11:00:06";
1842
				accept from "17-01-2001 12:01:05";
1843
			};
1844
			password "def" {
1845
				id 2;
1846
				generate to "22-07-2005 17:03:21";
1847
				accept from "22-02-2001 11:34:06";
1848
			};
1849
		};
1850
		interface "arc0" {
1851
			cost 10;
1852
			stub yes;
1853
		};
1854
		interface "arc1";
1855
	};
1856
	area 120 {
1857
		stub yes;
1858
		networks {
1859
			172.16.1.0/24;
1860
			172.16.2.0/24 hidden;
1861
		}
1862
		interface "-arc0" , "arc*" {
1863
			type nonbroadcast;
1864
			authentication none;
1865
			strict nonbroadcast yes;
1866
			wait 120;
1867
			poll 40;
1868
			dead count 8;
1869
			neighbors {
1870
				192.168.120.1 eligible;
1871
				192.168.120.2;
1872
				192.168.120.10;
1873
			};
1874
		};
1875
	};
1876
}
1877
</code>
1878

    
1879
<sect>Pipe
1880

    
1881
<sect1>Introduction
1882

    
1883
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
1884
passed from a table declared as primary (i.e., the one the pipe is connected to using the
1885
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
1886
and vice versa, depending on what's allowed by the filters. Export filters control export
1887
of routes from the primary table to the secondary one, import filters control the opposite
1888
direction.
1889

    
1890
<p>The Pipe protocol may work in the opaque mode or in the transparent
1891
mode. In the opaque mode, the Pipe protocol retransmits optimal route
1892
from one table to the other table in a similar way like other
1893
protocols send and receive routes. Retransmitted route will have the
1894
source set to the Pipe protocol, which may limit access to protocol
1895
specific route attributes. The opaque mode is a default mode.
1896

    
1897
<p>In transparent mode, the Pipe protocol retransmits all routes from
1898
one table to the other table, retaining their original source and
1899
attributes.  If import and export filters are set to accept, then both
1900
tables would have the same content. The mode can be set by
1901
<tt/mode/ option.
1902

    
1903
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
1904
where handling of a single packet doesn't depend only on its destination address, but also
1905
on its source address, source interface, protocol type and other similar parameters.
1906
In many systems (Linux being a good example), the kernel allows to enforce routing policies
1907
by defining routing rules which choose one of several routing tables to be used for a packet
1908
according to its parameters. Setting of these rules is outside the scope of BIRD's work
1909
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
1910
connect them to the kernel ones, use filters to control which routes appear in which tables
1911
and also you can employ the Pipe protocol for exporting a selected subset of one table to
1912
another one.
1913

    
1914
<sect1>Configuration
1915

    
1916
<p><descrip>
1917
	<tag>peer table <m/table/</tag> Defines secondary routing table to connect to. The
1918
	primary one is selected by the <cf/table/ keyword.
1919

    
1920
	<tag>mode opaque|transparent</tag> Specifies the mode for the pipe to work in. Default is opaque.
1921
</descrip>
1922

    
1923
<sect1>Attributes
1924

    
1925
<p>The Pipe protocol doesn't define any route attributes.
1926

    
1927
<sect1>Example
1928

    
1929
<p>Let's consider a router which serves as a boundary router of two different autonomous
1930
systems, each of them connected to a subset of interfaces of the router, having its own
1931
exterior connectivity and wishing to use the other AS as a backup connectivity in case
1932
of outage of its own exterior line.
1933

    
1934
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
1935
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
1936
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
1937
and similarly for the second AS. Thus we have split our router to two logical routers,
1938
each one acting on its own routing table, having its own routing protocols on its own
1939
interfaces. In order to use the other AS's routes for backup purposes, we can pass
1940
the routes between the tables through a Pipe protocol while decreasing their preferences
1941
and correcting their BGP paths to reflect the AS boundary crossing.
1942

    
1943
<code>
1944
table as1;				# Define the tables
1945
table as2;
1946

    
1947
protocol kernel kern1 {			# Synchronize them with the kernel
1948
	table as1;
1949
	kernel table 1;
1950
}
1951

    
1952
protocol kernel kern2 {
1953
	table as2;
1954
	kernel table 2;
1955
}
1956

    
1957
protocol bgp bgp1 {			# The outside connections
1958
	table as1;
1959
	local as 1;
1960
	neighbor 192.168.0.1 as 1001;
1961
	export all;
1962
	import all;
1963
}
1964

    
1965
protocol bgp bgp2 {
1966
	table as2;
1967
	local as 2;
1968
	neighbor 10.0.0.1 as 1002;
1969
	export all;
1970
	import all;
1971
}
1972

    
1973
protocol pipe {				# The Pipe
1974
	table as1;
1975
	peer table as2;
1976
	export filter {
1977
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
1978
			if preference>10 then preference = preference-10;
1979
			if source=RTS_BGP then bgp_path.prepend(1);
1980
			accept;
1981
		}
1982
		reject;
1983
	};
1984
	import filter {
1985
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
1986
			if preference>10 then preference = preference-10;
1987
			if source=RTS_BGP then bgp_path.prepend(2);
1988
			accept;
1989
		}
1990
		reject;
1991
	};
1992
}
1993
</code>
1994

    
1995
<sect>RAdv
1996

    
1997
<sect1>Introduction
1998

    
1999
<p>The RAdv protocol is an implementation of Router Advertisements,
2000
which are used in the IPv6 stateless autoconfiguration. IPv6 routers
2001
send (in irregular time intervals or as an answer to a request)
2002
advertisement packets to connected networks. These packets contain
2003
basic information about a local network (e.g. a list of network
2004
prefixes), which allows network hosts to autoconfigure network
2005
addresses and choose a default route. BIRD implements router behavior
2006
as defined in RFC 4861<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4861.txt">.
2007

    
2008
<sect1>Configuration
2009

    
2010
<p>There are two classes of definitions in RAdv configuration --
2011
interface definitions and prefix definitions:
2012

    
2013
<descrip>
2014
	<tag>interface <m/pattern [, ...]/  { <m/options/ }</tag> 
2015
	Interface definitions specify a set of interfaces on which the
2016
	protocol is activated and contain interface specific options.
2017
	See <ref id="dsc-iface" name="interface"> common options for
2018
	detailed description.
2019

    
2020
	<tag>prefix <m/prefix/ { <m/options/ }</tag> 
2021
	Prefix definitions allows to modify a list of advertised
2022
	prefixes. By default, the advertised prefixes are the same as
2023
	the network prefixes assigned to the interface. For each
2024
	network prefix, the matching prefix definition is found and
2025
	its options are used. If no matching prefix definition is
2026
	found, the prefix is used with default options.
2027

    
2028
	Prefix definitions can be either global or interface-specific.
2029
	The second ones are part of interface options. The prefix
2030
	definition matching is done in the first-match style, when
2031
	interface-specific definitions are processed before global
2032
	definitions. As expected, the prefix definition is matching if
2033
	the network prefix is a subnet of the prefix in prefix
2034
	definition.
2035
</descrip>
2036

    
2037
<p>Interface specific options:
2038

    
2039
<descrip>
2040
	<tag>max ra interval <m/expr/</tag>
2041
	Unsolicited router advertisements are sent in irregular time
2042
	intervals. This option specifies the maximum length of these
2043
	intervals, in seconds. Valid values are 4-1800. Default: 600
2044

    
2045
	<tag>min ra interval <m/expr/</tag>
2046
	This option specifies the minimum length of that intervals, in
2047
	seconds. Must be at least 3 and at most 3/4 * max ra interval.
2048
	Default: about 1/3 * max ra interval.
2049

    
2050
	<tag>min delay <m/expr/</tag>
2051
	The minimum delay between two consecutive router advertisements,
2052
	in seconds. Default: 3
2053

    
2054
	<tag>managed <m/switch/</tag>
2055
	This option specifies whether hosts should use DHCPv6 for
2056
	IP address configuration. Default: no
2057

    
2058
	<tag>other config <m/switch/</tag>
2059
	This option specifies whether hosts should use DHCPv6 to
2060
	receive other configuration information. Default: no
2061

    
2062
	<tag>link mtu <m/expr/</tag>
2063
	This option specifies which value of MTU should be used by
2064
	hosts. 0 means unspecified. Default: 0
2065

    
2066
	<tag>reachable time <m/expr/</tag>
2067
	This option specifies the time (in milliseconds) how long
2068
	hosts should assume a neighbor is reachable (from the last
2069
	confirmation). Maximum is 3600000, 0 means unspecified.
2070
	Default 0.
2071

    
2072
	<tag>retrans timer <m/expr/</tag>
2073
	This option specifies the time (in milliseconds) how long
2074
	hosts should wait before retransmitting Neighbor Solicitation
2075
	messages. 0 means unspecified. Default 0.
2076

    
2077
	<tag>current hop limit <m/expr/</tag>
2078
	This option specifies which value of Hop Limit should be used
2079
	by hosts. Valid values are 0-255, 0 means unspecified. Default: 64
2080

    
2081
	<tag>default lifetime <m/expr/</tag>
2082
	This option specifies the time (in seconds) how long (after
2083
	the receipt of RA) hosts may use the router as a default
2084
	router. 0 means do not use as a default router. Default: 3 *
2085
	max ra interval.
2086
</descrip>
2087

    
2088

    
2089
<p>Prefix specific options:
2090

    
2091
<descrip>
2092
	<tag>onlink <m/switch/</tag>
2093
	This option specifies whether hosts may use the advertised
2094
	prefix for onlink determination. Default: yes
2095

    
2096
	<tag>autonomous <m/switch/</tag>
2097
	This option specifies whether hosts may use the advertised
2098
	prefix for stateless autoconfiguration. Default: yes
2099

    
2100
	<tag>valid lifetime <m/expr/</tag>
2101
	This option specifies the time (in seconds) how long (after
2102
	the receipt of RA) the prefix information is valid, i.e.,
2103
	autoconfigured IP addresses can be assigned and hosts with
2104
	that IP addresses are considered directly reachable. 0 means
2105
	the prefix is no longer valid. Default: 86400 (1 day)
2106

    
2107
	<tag>preferred lifetime <m/expr/</tag>
2108
	This option specifies the time (in seconds) how long (after
2109
	the receipt of RA) IP addresses generated from the prefix
2110
	using stateless autoconfiguration remain preferred. Default:
2111
	14400 (4 hours)
2112
</descrip>
2113

    
2114
<sect1>Example
2115

    
2116
<p><code>
2117
protocol radv {
2118
	interface "eth2" {
2119
		max ra interval 5;	# Fast failover with more routers
2120
		managed yes;		# Using DHCPv6 on eth2
2121
		prefix ::/0 {
2122
			autonomous off;	# So do not autoconfigure any IP
2123
		};
2124
	};
2125

    
2126
	interface "eth*";		# No need for any other options
2127

    
2128
	prefix 2001:0DB8:1234::/48 {
2129
		preferred lifetime 0;	# Deprecated address range
2130
	};
2131

    
2132
	prefix 2001:0DB8:2000::/48 {
2133
		autonomous off;		# Do not autoconfigure
2134
	};
2135
}
2136
</code>
2137

    
2138
<sect>RIP
2139

    
2140
<sect1>Introduction
2141

    
2142
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
2143
distances to all networks it can reach. When a router hears distance to another network, it increments
2144
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
2145
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
2146
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
2147
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
2148
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
2149
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
2150
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
2151
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
2152
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
2153
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
2154

    
2155
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
2156
convergence, big network load and inability to handle larger networks
2157
makes it pretty much obsolete. (It is still usable on very small networks.)
2158

    
2159
<sect1>Configuration
2160

    
2161
<p>In addition to options common for all to other protocols, RIP supports the following ones:
2162

    
2163
<descrip>
2164
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
2165
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
2166
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
2167
	  hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf>
2168
	  section. Default: none.
2169

    
2170
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
2171
	  be honored. (Always, when sent from a  host on a directly connected
2172
	  network or never.) Routing table updates are honored only from
2173
	  neighbors, that is not configurable. Default: never.
2174
</descrip>
2175

    
2176
<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with
2177
default one.  Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for
2178
rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is
2179
currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even
2180
through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit
2181
any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this
2182
interface but not listen to it.
2183

    
2184
<p>The following options generally override behavior specified in RFC. If you use any of these
2185
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
2186
other than equally configured BIRD. I have warned you.
2187

    
2188
<descrip>
2189
	<tag>port <M>number</M></tag>
2190
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
2191
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
2192

    
2193
	<tag>infinity <M>number</M></tag>
2194
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
2195
	  even slower.
2196

    
2197
	<tag>period <M>number</M>
2198
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
2199
	  number will mean faster convergence but bigger network
2200
	  load. Do not use values lower than 10.
2201

    
2202
	<tag>timeout time <M>number</M>
2203
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
2204

    
2205
	<tag>garbage time <M>number</M>
2206
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
2207
</descrip>
2208

    
2209
<sect1>Attributes
2210

    
2211
<p>RIP defines two route attributes:
2212

    
2213
<descrip>
2214
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
2215
	When routes from different RIP instances are available and all of them have the same
2216
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
2217
	When importing a non-RIP route, the metric defaults to 5.
2218

    
2219
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
2220
	to carry additional information with the route (for example, an originating AS number
2221
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
2222
</descrip>
2223

    
2224
<sect1>Example
2225

    
2226
<p><code>
2227
protocol rip MyRIP_test {
2228
        debug all;
2229
        port 1520;
2230
        period 10;
2231
        garbage time 60;
2232
        interface "eth0" { metric 3; mode multicast; };
2233
	interface "eth*" { metric 2; mode broadcast; };
2234
        honor neighbor;
2235
        authentication none;
2236
        import filter { print "importing"; accept; };
2237
        export filter { print "exporting"; accept; };
2238
}
2239
</code>
2240

    
2241
<sect>Static
2242

    
2243
<p>The Static protocol doesn't communicate with other routers in the network,
2244
but instead it allows you to define routes manually. This is often used for
2245
specifying how to forward packets to parts of the network which don't use
2246
dynamic routing at all and also for defining sink routes (i.e., those
2247
telling to return packets as undeliverable if they are in your IP block,
2248
you don't have any specific destination for them and you don't want to send
2249
them out through the default route to prevent routing loops).
2250

    
2251
<p>There are three types of static routes: `classical' routes telling to
2252
forward packets to a neighboring router, device routes specifying forwarding
2253
to hosts on a directly connected network and special routes (sink, blackhole
2254
etc.) which specify a special action to be done instead of forwarding the
2255
packet.
2256

    
2257
<p>When the particular destination is not available (the interface is down or
2258
the next hop of the route is not a neighbor at the moment), Static just
2259
uninstalls the route from the table it is connected to and adds it again as soon
2260
as the destination becomes adjacent again.
2261

    
2262
<p>The Static protocol does not have many configuration options. The
2263
definition of the protocol contains mainly a list of static routes:
2264

    
2265
<descrip>
2266
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
2267
	a neighboring router.
2268
	<tag>route <m/prefix/ multipath via <m/ip/ [weight <m/num/] [via ...]</tag>
2269
	Static multipath route. Contains several nexthops (gateways), possibly
2270
 	with their weights.
2271
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
2272
	route through an interface to hosts on a directly connected network.
2273
	<tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes
2274
	specifying to drop the packet, return it as unreachable or return
2275
	it as administratively prohibited.
2276

    
2277
	<tag>check link <M>switch</M></tag>
2278
	The only option of the static protocol. If set, hardware link
2279
	states of network interfaces are taken into consideration.
2280
	When link disappears (e.g. ethernet cable is unplugged),
2281
	static routes directing to that interface are removed. It is
2282
	possible that some hardware drivers or platforms do not
2283
	implement this feature. Default: off.
2284
</descrip>
2285

    
2286
<p>Static routes have no specific attributes.
2287

    
2288
<p>Example static config might look like this:
2289

    
2290
<p><code>
2291
protocol static {
2292
	table testable;			 # Connect to a non-default routing table
2293
	route 0.0.0.0/0 via 62.168.0.13; # Default route
2294
	route 10.0.0.0/8 multipath	 # Multipath route
2295
		via 62.168.0.14 weight 2
2296
		via 62.168.1.10
2297
		via 62.168.1.11;
2298
	route 62.168.0.0/25 reject;	 # Sink route
2299
	route 10.2.0.0/24 via "arc0";	 # Secondary network
2300
}
2301
</code>
2302

    
2303
<chapt>Conclusions
2304

    
2305
<sect>Future work
2306

    
2307
<p>Although BIRD supports all the commonly used routing protocols,
2308
there are still some features which would surely deserve to be
2309
implemented in future versions of BIRD:
2310

    
2311
<itemize>
2312
<item>OSPF NSSA areas and opaque LSA's
2313
<item>Route aggregation and flap dampening
2314
<item>Generation of IPv6 router advertisements
2315
<item>Multipath routes
2316
<item>Multicast routing protocols
2317
<item>Ports to other systems
2318
</itemize>
2319

    
2320
<sect>Getting more help
2321

    
2322
<p>If you use BIRD, you're welcome to join the bird-users mailing list
2323
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
2324
where you can share your experiences with the other users and consult
2325
your problems with the authors. To subscribe to the list, just send a
2326
<tt/subscribe bird-users/ command in a body of a mail to
2327
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
2328
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
2329

    
2330
<p>BIRD is a relatively young system and it probably contains some
2331
bugs. You can report any problems to the bird-users list and the authors
2332
will be glad to solve them, but before you do so,
2333
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
2334
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
2335
which fixes the bug is always welcome as an attachment.)
2336

    
2337
<p>If you want to understand what is going inside, Internet standards are
2338
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">).
2339

    
2340
<p><it/Good luck!/
2341

    
2342
</book>
2343

    
2344
<!--
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LocalWords:  GPL IPv GateD BGPv RIPv OSPFv Linux sgml html dvi sgmltools Pavel
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2347
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2348
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2349
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2351
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2352
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2353
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2354
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LocalWords:  proto wildcard Ondrej Filip
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