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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, ASCII
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text and dvi/postscript (generated from sgml using sgmltools). You should always
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edit master copy.
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This is a slightly modified linuxdoc dtd. Anything in <descrip> tags is
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considered definition of configuration primitives, <cf> is fragment of
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configuration within normal text, <m> is "meta" information within fragment of
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configuration - something in config which is not keyword.
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    (set-fill-column 80)
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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
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Daemon'. 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
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standing 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
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discover in a moment) which works as a dynamic router in an Internet type
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network (that is, in a network running either the IPv4 or the IPv6 protocol).
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Routers are devices which forward packets between interconnected networks in
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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
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Internet to discover the topology of the network which allows them to find
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optimal (in terms of some metric) rules for forwarding of packets (which are
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called routing tables) and to adapt themselves to the changing conditions such
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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
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hard to configure and not open to any changes (on the other hand, their special
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hardware design allows them to keep up with lots of high-speed network
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interfaces, better than general-purpose computer does). Fortunately, most
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operating systems of the UNIX family allow an ordinary computer to act as a
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router and forward packets belonging to the other hosts, but only according to a
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statically configured table.
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<p>A <em/Routing Daemon/ is in UNIX terminology a non-interactive program
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running on background which does the dynamic part of Internet routing, that is
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it communicates with the other routers, calculates routing tables and sends them
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to the OS kernel which does the actual packet forwarding. There already exist
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other such routing daemons: routed (RIP only), GateD (non-free),
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Zebra <HTMLURL URL="http://www.zebra.org"> and
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MRTD <HTMLURL URL="http://sourceforge.net/projects/mrt">,
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but their capabilities are limited and they are relatively hard to configure
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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
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be used in near future and to have a clean extensible architecture allowing new
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routing protocols to be incorporated easily. Among other features, BIRD
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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
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		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 to
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		change the configuration, just edit the configuration file and
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		notify BIRD to re-read it and it will smoothly switch itself to
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		the new configuration, not disturbing routing protocols unless
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		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
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University, Prague, Czech Republic as a student project. It can be freely
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distributed under the terms of the GNU General Public License.
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<p>BIRD has been designed to work on all UNIX-like systems. It has been
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developed and tested under Linux 2.0 to 2.6, and then ported to FreeBSD, NetBSD
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and OpenBSD, porting to other systems (even non-UNIX ones) should be relatively
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easy due to its highly modular architecture.
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<p>BIRD supports either IPv4 or IPv6 protocol, but have to be compiled separately
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for each one. Therefore, a dualstack router would run two instances of BIRD (one
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for IPv4 and one for IPv6), with completely separate setups (configuration
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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)
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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: <tt/--enable-ipv6/ which enables building
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of an IPv6 version of BIRD, <tt/--with-protocols=/ to produce a slightly smaller
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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 <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
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	file is valid, 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,
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	default is <it/prefix/<file>/var/run/bird.ctl</file>.
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	<tag>-P <m/name of PID file/</tag>
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	create a PID file with given filename.
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	<tag>-u <m/user/</tag>
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	drop privileges and use that user ID, see the next section for details.
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	<tag>-g <m/group/</tag>
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	use that group ID, see the next section for details.
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	<tag>-f</tag>
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	run bird in foreground.
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	<tag>-R</tag>
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	apply graceful restart recovery after start.
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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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<sect>Privileges
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<p>BIRD, as a routing daemon, uses several privileged operations (like setting
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routing table and using raw sockets). Traditionally, BIRD is executed and runs
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with root privileges, which may be prone to security problems. The recommended
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way is to use a privilege restriction (options <cf/-u/, <cf/-g/). In that case
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BIRD is executed with root privileges, but it changes its user and group ID to
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an unprivileged ones, while using Linux capabilities to retain just required
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privileges (capabilities CAP_NET_*). Note that the control socket is created
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before the privileges are dropped, but the config file is read after that. The
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privilege restriction is not implemented in BSD port of BIRD.
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<p>A nonprivileged user (as an argument to <cf/-u/ options) may be the user
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<cf/nobody/, but it is suggested to use a new dedicated user account (like
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<cf/bird/). The similar considerations apply for the group option, but there is
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one more condition -- the users in the same group can use <file/birdc/ to
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control BIRD.
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<p>Finally, there is a possibility to use external tools to run BIRD in an
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environment with restricted privileges. This may need some configuration, but it
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is generally easy -- BIRD needs just the standard library, privileges to read
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the config file and create the control socket and the CAP_NET_* capabilities.
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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 synchronized with
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OS kernel and which may or may not be synchronized with each other (see the Pipe
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protocol). Each routing table contains a list of known routes. Each route
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consists of:
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<itemize>
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	<item>network prefix this route is for (network address and prefix
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		length -- the number of bits forming the network part of the
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		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 using this
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		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 may not be
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		present (typically protocol metrics)
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</itemize>
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Routing table maintains multiple entries for a network, but at most one entry
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for one network and one protocol. The entry with the highest preference is used
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for routing (we will call such an entry the <it/selected route/). If there are
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more entries with the same preference and they are from the same protocol, the
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protocol decides (typically according to metrics). If they aren't, an internal
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ordering is used to break the tie. You can get the list of route attributes in
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the Route attributes section.
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<p>Each protocol is connected to a routing table through two filters which can
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accept, reject and modify the routes. An <it/export/ filter checks routes passed
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from the routing table to the protocol, an <it/import/ filter checks routes in
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the opposite direction. When the routing table gets a route from a protocol, it
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recalculates 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 in the
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network. Note that although most protocols are interested in receiving just
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selected routes, some protocols (e.g. the <cf/Pipe/ protocol) receive and
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process all entries in routing tables (accepted by filters).
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<p><label id="dsc-sorted">Usually, a routing table just chooses a selected route
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from a list of entries for one network. But if the <cf/sorted/ option is
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activated, these lists of entries are kept completely sorted (according to
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preference or some protocol-dependent metric). This is needed for some features
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of some protocols (e.g. <cf/secondary/ option of BGP protocol, which allows to
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accept not just a selected route, but the first route (in the sorted list) that
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is accepted by filters), but it is incompatible with some other features (e.g.
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<cf/deterministic med/ option of BGP protocol, which activates a way of choosing
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selected route that cannot be described using comparison and ordering). Minor
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advantage is that routes are shown sorted in <cf/show route/, minor disadvantage
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is that it is slightly more computationally expensive.
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<sect>Graceful restart
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<p>When BIRD is started after restart or crash, it repopulates routing tables in
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an uncoordinated manner, like after clean start. This may be impractical in some
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cases, because if the forwarding plane (i.e. kernel routing tables) remains
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intact, then its synchronization with BIRD would temporarily disrupt packet
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forwarding until protocols converge. Graceful restart is a mechanism that could
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help with this issue. Generally, it works by starting protocols and letting them
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repopulate routing tables while deferring route propagation until protocols
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acknowledge their convergence. Note that graceful restart behavior have to be
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configured for all relevant protocols and requires protocol-specific support
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(currently implemented for Kernel and BGP protocols), it is activated for
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particular boot by option <cf/-R/.
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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
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<it/prefix/<file>/etc/bird.conf</file> (unless the <tt/-c/ command line option
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is given). Configuration may be changed at user's request: if you modify the
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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 which allows you to talk with BIRD in an
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extensive way.
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<p>In the config, everything on a line after <cf/#/ or inside <cf>/* */</cf> is
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a comment, whitespace characters are treated as a single space. If there's a
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variable number of options, they are grouped using the <cf/{ }/ brackets. Each
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option is terminated by a <cf/;/. Configuration is case sensitive. There are two
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ways how to name symbols (like protocol names, filter names, constats etc.). You
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can either use a simple string starting with a letter followed by any
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combination of letters and numbers (e.g. "R123", "myfilter", "bgp5") or you can
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enclose the name into apostrophes (<cf/'/) and than you can use any combination
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of numbers, letters. hyphens, dots and colons (e.g. "'1:strange-name'",
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"'-NAME-'", "'cool::name'").
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<p>Here is an example of a simple config file. It enables synchronization of
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routing tables with OS kernel, scans for new network interfaces every 10 seconds
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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>include "<m/filename/"</tag> 
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	This statement causes inclusion of a new file. <m/Filename/ could also
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	be a wildcard. The maximal depth is 5. Note that this statement could be
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	used anywhere in the config file, not just as a top-level option.
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	<tag><label id="dsc-log">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
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	<cf/{ error, trace }/ etc.) into selected destination (a file specified
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	as a filename string, syslog with optional name argument, or the stderr
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	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.
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	You may specify more than one <cf/log/ line to establish logging to
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	multiple 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
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	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 logging
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	of connects and disconnects, 2 and higher for logging of all client
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	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
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	feature. 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
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	following section. Default: off.
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	<tag>filter <m/name local variables/{ <m/commands/ }</tag>
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	Define a filter. You can learn more about filters in the following
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	chapter.
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	<tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag>
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	Define a function. You can learn more about functions in the following chapter.
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	<tag>protocol rip|ospf|bgp|... [<m/name/ [from <m/name2/]] { <m>protocol options</m> }</tag>
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	Define a protocol instance called <cf><m/name/</cf> (or with a name like
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	"rip5" generated automatically if you don't specify any
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	<cf><m/name/</cf>). You can learn more about configuring protocols in
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	their own chapters. When <cf>from <m/name2/</cf> expression is used,
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	initial protocol options are taken from protocol or template
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	<cf><m/name2/</cf> You can run more than one instance of most protocols
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	(like RIP or BGP). By default, no instances are configured.
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	<tag>template rip|bgp|... [<m/name/ [from <m/name2/]] { <m>protocol options</m> }</tag>
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	Define a protocol template instance called <m/name/ (or with a name like
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	"bgp1" generated automatically if you don't specify any	<m/name/).
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	Protocol templates can be used to group common options when many
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	similarly configured protocol instances are to be defined. Protocol
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	instances (and other templates) can use templates by using <cf/from/
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	expression and the name of the template. At the moment templates (and
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	<cf/from/ expression) are not implemented for OSPF protocol.
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	<tag>define <m/constant/ = <m/expression/</tag>
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	Define a constant. You can use it later in every place you could use a
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	value of the same type. Besides, there are some predefined numeric
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	constants based on /etc/iproute2/rt_* files. A list of defined constants
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	can be seen (together with other symbols) using 'show symbols' command.
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	<tag>router id <m/IPv4 address/</tag>
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 	Set BIRD's router ID. It's a world-wide unique identification of your
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	router, usually one of router's IPv4 addresses. Default: in IPv4
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	version, the lowest IP address of a non-loopback interface. In IPv6
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	version, this option is mandatory.
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	<tag>router id from [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...]</tag>
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	Set BIRD's router ID based on an IP address of an interface specified by
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	an interface pattern. The option is applicable for IPv4 version only.
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	See <ref id="dsc-iface" name="interface"> section for detailed
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	description of interface patterns with extended clauses.
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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 protocol should
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	listen. It is global option as listening socket is common to all BGP
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	instances. Default is to listen on all addresses (0.0.0.0) and port 179.
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	In IPv6 mode, option <cf/dual/ can be used to specify that BGP socket
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	should accept both IPv4 and IPv6 connections (but even in that case,
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	BIRD would accept IPv6 routes only). Such behavior was default in older
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	versions of BIRD.
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	<tag>graceful restart wait <m/number/</tag>
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	During graceful restart recovery, BIRD waits for convergence of routing
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	protocols. This option allows to specify a timeout for the recovery to
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	prevent waiting indefinitely if some protocols cannot converge. Default:
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	240 seconds.
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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 BIRD. The
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	first argument specifies for which purpose such format is used.
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	<cf/route/ is a format used in 'show route' command output,
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	<cf/protocol/ is used in 'show protocols' command output, <cf/base/ is
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	used for other commands and <cf/log/ is used in a log file.
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	"<m/format1/" is a format string using <it/strftime(3)/ notation (see
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	<it/man strftime/ for details). <m/limit> and "<m/format2/" allow to
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	specify the second format string for times in past deeper than <m/limit/
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 	seconds. There are few shorthands: <cf/iso long/ is a ISO 8601 date/time
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	format (YYYY-MM-DD hh:mm:ss) that can be also specified using <cf/"%F %T"/.
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	<cf/iso short/ is a variant of ISO 8601 that uses just the time format
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	(hh:mm:ss) for near times (up to 20 hours in the past) and the date
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	format (YYYY-MM-DD) for far times. This is a shorthand for
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	<cf/"%T" 72000 "%F"/.
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	By default, BIRD uses the <cf/iso short/ format for <cf/route/ and
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	<cf/protocol/ times, and the <cf/iso long/ format for <cf/base/ and
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	<cf/log/ times.
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	In pre-1.4.0 versions, BIRD used an short, ad-hoc format for <cf/route/
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	and <cf/protocol/ times, and a <cf/iso long/ similar format (DD-MM-YYYY
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	hh:mm:ss) for <cf/base/ and <cf/log/. These timeformats could be set by
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	<cf/old short/ and <cf/old long/ compatibility shorthands.
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	<tag>table <m/name/ [sorted]</tag>
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	Create a new routing table. The default routing table is created
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	implicitly, other routing tables have to be added by this command.
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	Option <cf/sorted/ can be used to enable sorting of routes, see
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	<ref id="dsc-sorted" name="sorted table"> description for details.
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	<tag>roa table <m/name/ [ { roa table options ... } ]</tag>
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	Create a new ROA (Route Origin Authorization) table. ROA tables can be
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	used to validate route origination of BGP routes. A ROA table contains
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	ROA entries, each consist of a network prefix, a max prefix length and
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	an AS number. A ROA entry specifies prefixes which could be originated
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	by that AS number. ROA tables could be filled with data from RPKI (RFC
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	6480) or from public databases like Whois. ROA tables are examined by
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	<cf/roa_check()/ operator in filters.
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	Currently, there is just one option, <cf>roa <m/prefix/ max <m/num/ as
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	<m/num/</cf>, which can be used to populate the ROA table with static
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	ROA entries. The option may be used multiple times. Other entries can be
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	added dynamically by <cf/add roa/ command.
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	<tag>eval <m/expr/</tag>
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	Evaluates given filter expression. It 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. Some of
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them (those described in this section) are generic, some are specific to the
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protocol (see sections talking about the protocols).
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<p>Several options use a <m/switch/ argument. It can be either <cf/on/,
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<cf/yes/ or a numeric expression with a non-zero value for the option to be
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enabled or <cf/off/, <cf/no/ or a numeric expression evaluating to zero to
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disable it. An empty <m/switch/ is equivalent to <cf/on/ ("silence means
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agreement").
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<descrip>
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	<tag>preference <m/expr/</tag>
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	Sets the preference of routes generated by this protocol. Default:
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	protocol dependent.
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	<tag>disabled <m/switch/</tag>
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	Disables the protocol. You can change the disable/enable status from the
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	command line interface without needing to touch the configuration.
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	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
488
	writing trace messages about its work to the log (with category
489
	<cf/trace/). You can either request printing of <cf/all/ trace messages
490
	or only of the types selected: <cf/states/ for protocol state changes
491
	(protocol going up, down, starting, stopping etc.), <cf/routes/ for
492
	routes exchanged with the routing table, <cf/filters/ for details on
493
	route filtering, <cf/interfaces/ for interface change events sent to the
494
	protocol, <cf/events/ for events internal to the protocol and <cf/packets/
495
	for packets sent and received by the protocol. Default: off.
496

    
497
	<tag>mrtdump all|off|{ states, messages }</tag>
498
	Set protocol MRTdump flags. MRTdump is a standard binary format for
499
	logging information from routing protocols and daemons. These flags
500
	control what kind of information is logged from the protocol to the
501
	MRTdump file (which must be specified by global <cf/mrtdump/ option, see
502
	the previous section). Although these flags are similar to flags of
503
	<cf/debug/ option, their meaning is different and protocol-specific. For
504
	BGP protocol, <cf/states/ logs BGP state changes and <cf/messages/ logs
505
	received BGP messages. Other protocols does not support MRTdump yet.
506

    
507
	<tag>router id <m/IPv4 address/</tag>
508
	This option can be used to override global router id for a given
509
	protocol. Default: uses global router id.
510

    
511
	<tag>import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag> 
512
	Specify a filter to be used for filtering routes coming from the
513
	protocol to the routing table. <cf/all/ is shorthand for <cf/where true/
514
	and <cf/none/ is shorthand for <cf/where false/. Default: <cf/all/.
515

    
516
	<tag>export <m/filter/</tag>
517
	This is similar to the <cf>import</cf> keyword, except that it works in
518
	the direction from the routing table to the protocol. Default: <cf/none/.
519

    
520
	<tag>import keep filtered <m/switch/</tag>
521
	Usually, if an import filter rejects a route, the route is forgotten.
522
	When this option is active, these routes are kept in the routing table,
523
	but they are hidden and not propagated to other protocols. But it is
524
	possible to show them using <cf/show route filtered/. Note that this
525
	option does not work for the pipe protocol. Default: off.
526

    
527
	<tag><label id="import-limit">import limit [<m/number/ | off ] [action warn | block | restart | disable]</tag>
528
	Specify an import route limit (a maximum number of routes imported from
529
	the protocol) and optionally the action to be taken when the limit is
530
	hit. Warn action just prints warning log message. Block action discards
531
	new routes coming from the protocol. Restart and disable actions shut
532
	the protocol down like appropriate commands. Disable is the default
533
	action if an action is not explicitly specified. Note that limits are
534
	reset during protocol reconfigure, reload or restart. Default: <cf/off/.
535

    
536
	<tag>receive limit [<m/number/ | off ] [action warn | block | restart | disable]</tag>
537
	Specify an receive route limit (a maximum number of routes received from
538
	the protocol and remembered). It works almost identically to <cf>import
539
	limit</cf> option, the only difference is that if <cf/import keep
540
	filtered/ option is active, filtered routes are counted towards the
541
	limit and blocked routes are forgotten, as the main purpose of the
542
	receive limit is to protect routing tables from overflow. Import limit,
543
	on the contrary, counts accepted routes only and routes blocked by the
544
	limit are handled like filtered routes. Default: <cf/off/.
545

    
546
	<tag>export limit [ <m/number/ | off ] [action warn | block | restart | disable]</tag>
547
	Specify an export route limit, works similarly to the <cf>import
548
	limit</cf> option, but for the routes exported to the protocol. This
549
	option is experimental, there are some problems in details of its
550
	behavior -- the number of exported routes can temporarily exceed the
551
	limit without triggering it during protocol reload, exported routes
552
	counter ignores route blocking and block action also blocks route
553
	updates of already accepted routes -- and these details will probably
554
	change in the future. Default: <cf/off/.
555

    
556
	<tag>description "<m/text/"</tag>
557
	This is an optional description of the protocol. It is displayed as a
558
	part of the output of 'show route all' command.
559

    
560
	<tag>table <m/name/</tag>
561
	Connect this protocol to a non-default routing table.
562
</descrip>
563

    
564
<p>There are several options that give sense only with certain protocols:
565

    
566
<descrip>
567
	<tag><label id="dsc-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...] [ { <m/option/ ; [...] } ]</tag>
568
	Specifies a set of interfaces on which the protocol is activated with
569
	given interface-specific options. A set of interfaces specified by one
570
	interface option is described using an interface pattern. The interface
571
	pattern consists of a sequence of clauses (separated by commas), each
572
	clause is a mask specified as a shell-like pattern. Interfaces are
573
	matched by their name.
574

    
575
	An interface matches the pattern if it matches any of its clauses. If
576
	the clause begins with <cf/-/, matching interfaces are excluded. Patterns
577
	are processed left-to-right, thus <cf/interface "eth0", -"eth*", "*";/
578
	means eth0 and all non-ethernets.
579

    
580
	Some protocols (namely OSPFv2 and Direct) support extended clauses that
581
	may contain a mask, a prefix, or both of them. An interface matches such
582
	clause if its name matches the mask (if specified) and its address
583
	matches the prefix (if specified). Extended clauses are used when the
584
	protocol handles multiple addresses on an interface independently.
585

    
586
	An interface option can be used more times with different interface-specific
587
	options, in that case for given interface the first matching interface
588
	option is used.
589
	
590
	This option is allowed in BFD, Direct, OSPF, RAdv and RIP protocols, but
591
	in OSPF protocol it is used in the <cf/area/ subsection.
592

    
593
	Default: none.
594

    
595
	Examples:
596

    
597
	<cf>interface "*" { type broadcast; };</cf> - start the protocol on all
598
	interfaces with <cf>type broadcast</cf> option.
599

    
600
	<cf>interface "eth1", "eth4", "eth5" { type ptp; };</cf> - start the
601
	protocol on enumerated interfaces with <cf>type ptp</cf> option.
602
	
603
	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol
604
	on all interfaces that have address from 192.168.0.0/16, but not from
605
	192.168.1.0/24.
606

    
607
	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol
608
	on all interfaces that have address from 192.168.0.0/16, but not from
609
	192.168.1.0/24.
610

    
611
	<cf>interface "eth*" 192.168.1.0/24;</cf> - start the protocol on all
612
	ethernet interfaces that have address from 192.168.1.0/24.
613

    
614
	<tag><label id="dsc-prio">tx class|dscp <m/num/</tag>
615
	This option specifies the value of ToS/DS/Class field in IP headers of
616
	the outgoing protocol packets. This may affect how the protocol packets
617
	are processed by the network relative to the other network traffic. With
618
	<cf/class/ keyword, the value (0-255) is used for the whole ToS/Class
619
	octet (but two bits reserved for ECN are ignored). With	<cf/dscp/
620
	keyword, the value (0-63) is used just for the DS field in the octet.
621
	Default value is 0xc0 (DSCP 0x30 - CS6).
622

    
623
	<tag>tx priority <m/num/</tag>
624
	This option specifies the local packet priority. This may affect how the
625
	protocol packets are processed in the local TX queues. This option is
626
	Linux specific. Default value is 7 (highest priority, privileged traffic).
627

    
628
	<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>
629
	Specifies a password that can be used by the protocol. Password option
630
	can be used more times to specify more passwords. If more passwords are
631
	specified, it is a protocol-dependent decision which one is really
632
	used. Specifying passwords does not mean that authentication is enabled,
633
	authentication can be enabled by separate, protocol-dependent
634
	<cf/authentication/ option.
635
	
636
	This option is allowed in OSPF and RIP protocols. BGP has also
637
	<cf/password/ option, but it is slightly different and described
638
	separately.
639

    
640
	Default: none.
641
</descrip>
642

    
643
<p>Password option can contain section with some (not necessary all) password sub-options:
644

    
645
<descrip>
646
	<tag>id <M>num</M></tag>
647
	ID of the password, (0-255). If it's not used, BIRD will choose ID based
648
	on an order of the password item in the interface. For example, second
649
	password item in one interface will have default ID 2. ID is used by
650
	some routing protocols to identify which password was used to
651
	authenticate protocol packets.
652

    
653
	<tag>generate from "<m/time/"</tag>
654
	The start time of the usage of the password for packet signing.
655
	The format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
656

    
657
	<tag>generate to "<m/time/"</tag>
658
	The last time of the usage of the password for packet signing.
659

    
660
	<tag>accept from "<m/time/"</tag>
661
	The start time of the usage of the password for packet verification.
662

    
663
	<tag>accept to "<m/time/"</tag>
664
	The last time of the usage of the password for packet verification.
665
</descrip>
666

    
667
<chapt>Remote control
668

    
669
<p>You can use the command-line client <file>birdc</file> to talk with a running
670
BIRD. Communication is done using a <file/bird.ctl/ UNIX domain socket (unless
671
changed with the <tt/-s/ option given to both the server and the client). The
672
commands can perform simple actions such as enabling/disabling of protocols,
673
telling BIRD to show various information, telling it to show routing table
674
filtered by filter, or asking BIRD to reconfigure. Press <tt/?/ at any time to
675
get online help. Option <tt/-r/ can be used to enable a restricted mode of BIRD
676
client, which allows just read-only commands (<cf/show .../). Option <tt/-v/ can
677
be passed to the client, to make it dump numeric return codes along with the
678
messages. You do not necessarily need to use <file/birdc/ to talk to BIRD, your
679
own applications could do that, too -- the format of communication between BIRD
680
and <file/birdc/ is stable (see the programmer's documentation).
681

    
682
<p>There is also lightweight variant of BIRD client called <file/birdcl/, which
683
does not support command line editing and history and has minimal dependencies.
684
This is useful for running BIRD in resource constrained environments, where
685
Readline library (required for regular BIRD client) is not available.
686

    
687
<p>Many commands have the <m/name/ of the protocol instance as an argument.
688
This argument can be omitted if there exists only a single instance.
689

    
690
<p>Here is a brief list of supported functions:
691

    
692
<descrip>
693
	<tag>show status</tag>
694
	Show router status, that is BIRD version, uptime and time from last
695
	reconfiguration.
696

    
697
	<tag>show protocols [all]</tag>
698
	Show list of protocol instances along with tables they are connected to
699
	and protocol status, possibly giving verbose information, if <cf/all/ is
700
	specified.
701

    
702
	<tag>show ospf interface [<m/name/] ["<m/interface/"]</tag>
703
	Show detailed information about OSPF interfaces.
704

    
705
	<tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
706
	Show a list of OSPF neighbors and a state of adjacency to them.
707

    
708
	<tag>show ospf state [all] [<m/name/]</tag>
709
	Show detailed information about OSPF areas based on a content of the
710
	link-state database. It shows network topology, stub networks,
711
	aggregated networks and routers from other areas and external routes.
712
	The command shows information about reachable network nodes, use option
713
	<cf/all/ to show information about all network nodes in the link-state
714
	database.
715

    
716
	<tag>show ospf topology [all] [<m/name/]</tag>
717
	Show a topology of OSPF areas based on a content of the link-state
718
	database. It is just a stripped-down version of 'show ospf state'.
719

    
720
	<tag>show ospf lsadb [global | area <m/id/ | link] [type <m/num/] [lsid <m/id/] [self | router <m/id/] [<m/name/] </tag>
721
	Show contents of an OSPF LSA database. Options could be used to filter
722
	entries.
723

    
724
	<tag>show static [<m/name/]</tag>
725
	Show detailed information about static routes.
726

    
727
	<tag>show bfd sessions [<m/name/]</tag>
728
	Show information about BFD sessions.
729

    
730
	<tag>show interfaces [summary]</tag>
731
	Show the list of interfaces. For each interface, print its type, state,
732
	MTU and addresses assigned.
733

    
734
	<tag>show symbols [table|filter|function|protocol|template|roa|<m/symbol/]</tag>
735
	Show the list of symbols defined in the configuration (names of
736
	protocols, routing tables etc.).
737

    
738
	<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>
739
	Show contents of a routing table (by default of the main one or the
740
	table attached to a respective protocol), that is routes, their metrics
741
	and (in case the <cf/all/ switch is given) all their attributes.
742

    
743
	<p>You can specify a <m/prefix/ if you want to print routes for a
744
	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
745
	the entry which will be used for forwarding of packets to the given
746
	destination. By default, all routes for each network are printed with
747
	the selected one at the top, unless <cf/primary/ is given in which case
748
	only the selected route is shown.
749

    
750
	<p>You can also ask for printing only routes processed and accepted by
751
	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
752
	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
753
	The <cf/export/ and <cf/preexport/ switches ask for printing of entries
754
	that are exported to the specified protocol. With <cf/preexport/, the
755
	export filter of the protocol is skipped.
756

    
757
	<p>You can also select just routes added by a specific protocol.
758
	<cf>protocol <m/p/</cf>.
759

    
760
	<p>If BIRD is configured to keep filtered routes (see <cf/import keep
761
	filtered/ option), you can show them instead of routes by using
762
	<cf/filtered/ switch.
763

    
764
	<p>The <cf/stats/ switch requests showing of route statistics (the
765
	number of networks, number of routes before and after filtering). If
766
	you use <cf/count/ instead, only the statistics will be printed.
767

    
768
	<tag>show roa [<m/prefix/ | in <m/prefix/ | for <m/prefix/] [as <m/num/] [table <m/t/>]</tag>
769
	Show contents of a ROA table (by default of the first one). You can
770
	specify a <m/prefix/ to print ROA entries for a specific network. If you
771
	use <cf>for <m/prefix/</cf>, you'll get all entries relevant for route
772
	validation of the network prefix; i.e., ROA entries whose prefixes cover
773
	the network prefix. Or you can use <cf>in <m/prefix/</cf> to get ROA
774
	entries covered by the network prefix. You could also use <cf/as/ option
775
	to show just entries for given AS.
776

    
777
	<tag>add roa <m/prefix/ max <m/num/] as <m/num/ [table <m/t/>]</tag>
778
	Add a new ROA entry to a ROA table. Such entry is called <it/dynamic/
779
	compared to <it/static/ entries specified in the config file. These
780
	dynamic entries survive reconfiguration.
781

    
782
	<tag>delete roa <m/prefix/ max <m/num/] as <m/num/ [table <m/t/>]</tag>
783
	Delete the specified ROA entry from a ROA table. Only dynamic ROA
784
	entries (i.e., the ones added by <cf/add roa/ command) can be deleted.
785

    
786
	<tag>flush roa [table <m/t/>]</tag>
787
	Remove all dynamic ROA entries from a ROA table.
788

    
789
	<tag>configure [soft] ["<m/config file/"] [timeout [<m/num/]]</tag>
790
	Reload configuration from a given file. BIRD will smoothly switch itself
791
	to the new configuration, protocols are reconfigured if possible,
792
	restarted otherwise. Changes in filters usually lead to restart of
793
	affected protocols.
794

    
795
	If <cf/soft/ option is used, changes in filters does not cause BIRD to
796
	restart affected protocols, therefore already accepted routes (according
797
	to old filters) would be still propagated, but new routes would be
798
	processed according to the new filters.
799

    
800
	If <cf/timeout/ option is used, config timer is activated. The new
801
	configuration could be either confirmed using <cf/configure confirm/
802
	command, or it will be reverted to the old one when the config timer
803
	expires. This is useful for cases when reconfiguration breaks current
804
	routing and a router becames inaccessible for an administrator. The
805
	config timeout expiration is equivalent to <cf/configure undo/
806
	command. The timeout duration could be specified, default is 300 s.
807

    
808
	<tag>configure confirm</tag>
809
	Deactivate the config undo timer and therefore confirm the current
810
	configuration.
811

    
812
	<tag>configure undo</tag>
813
	Undo the last configuration change and smoothly switch back to the
814
	previous (stored) configuration. If the last configuration change was
815
	soft, the undo change is also soft. There is only one level of undo, but
816
	in some specific cases when several reconfiguration requests are given
817
	immediately in a row and the intermediate ones are skipped then the undo
818
	also skips them back.
819

    
820
	<tag>configure check ["<m/config file/"]</tag>
821
	Read and parse given config file, but do not use it. useful for checking
822
	syntactic and some semantic validity of an config file.
823

    
824
	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
825
	Enable, disable or restart a given protocol instance, instances matching
826
	the <cf><m/pattern/</cf> or <cf/all/ instances.
827

    
828
	<tag>reload [in|out] <m/name/|"<m/pattern/"|all</tag>
829
	Reload a given protocol instance, that means re-import routes from the
830
	protocol instance and re-export preferred routes to the instance. If
831
	<cf/in/ or <cf/out/ options are used, the command is restricted to one
832
	direction (re-import or re-export).
833

    
834
	This command is useful if appropriate filters have changed but the
835
	protocol instance was not restarted (or reloaded), therefore it still
836
	propagates the old set of routes. For example when <cf/configure soft/
837
	command was used to change filters.
838

    
839
	Re-export always succeeds, but re-import is protocol-dependent and might
840
	fail (for example, if BGP neighbor does not support route-refresh
841
	extension). In that case, re-export is also skipped. Note that for the
842
	pipe protocol, both directions are always reloaded together (<cf/in/ or
843
	<cf/out/ options are ignored in that case).
844

    
845
	<tag/down/
846
	Shut BIRD down.
847

    
848
	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
849
	Control protocol debugging.
850

    
851
	<tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
852
	Dump contents of internal data structures to the debugging output.
853

    
854
	<tag>echo all|off|{ <m/list of log classes/ } [ <m/buffer-size/ ]</tag>
855
	Control echoing of log messages to the command-line output.
856
	See <ref id="dsc-log" name="log option"> for a list of log classes.
857

    
858
	<tag>eval <m/expr/</tag>
859
	Evaluate given expression.
860
</descrip>
861

    
862

    
863
<chapt>Filters
864

    
865
<sect>Introduction
866

    
867
<p>BIRD contains a simple programming language. (No, it can't yet read mail :-).
868
There are two objects in this language: filters and functions. Filters are
869
interpreted by BIRD core when a route is being passed between protocols and
870
routing tables. The filter language contains control structures such as if's and
871
switches, but it allows no loops. An example of a filter using many features can
872
be found in <file>filter/test.conf</file>.
873

    
874
<p>Filter gets the route, looks at its attributes and modifies some of them if
875
it wishes. At the end, it decides whether to pass the changed route through
876
(using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks like
877
this:
878

    
879
<code>
880
filter not_too_far
881
int var;
882
{
883
	if defined( rip_metric ) then
884
		var = rip_metric;
885
	else {
886
		var = 1;
887
		rip_metric = 1;
888
	}
889
	if rip_metric &gt; 10 then
890
		reject "RIP metric is too big";
891
	else
892
		accept "ok";
893
}
894
</code>
895

    
896
<p>As you can see, a filter has a header, a list of local variables, and a body.
897
The header consists of the <cf/filter/ keyword followed by a (unique) name of
898
filter. The list of local variables consists of <cf><M>type name</M>;</cf>
899
pairs where each pair defines one local variable. The body consists of <cf>
900
{ <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You
901
can group several statements to a single compound statement by using braces
902
(<cf>{ <M>statements</M> }</cf>) which is useful if you want to make a bigger
903
block of code conditional.
904

    
905
<p>BIRD supports functions, so that you don't have to repeat the same blocks of
906
code over and over. Functions can have zero or more parameters and they can have
907
local variables. Recursion is not allowed. Function definitions look like this:
908

    
909
<code>
910
function name ()
911
int local_variable;
912
{
913
	local_variable = 5;
914
}
915

    
916
function with_parameters (int parameter)
917
{
918
	print parameter;
919
}
920
</code>
921

    
922
<p>Unlike in C, variables are declared after the <cf/function/ line, but before
923
the first <cf/{/. You can't declare variables in nested blocks. Functions are
924
called like in C: <cf>name(); with_parameters(5);</cf>. Function may return
925
values using the <cf>return <m/[expr]/</cf> command. Returning a value exits
926
from current function (this is similar to C).
927

    
928
<p>Filters are declared in a way similar to functions except they can't have
929
explicit parameters. They get a route table entry as an implicit parameter, it
930
is also passed automatically to any functions called. The filter must terminate
931
with either <cf/accept/ or <cf/reject/ statement. If there's a runtime error in
932
filter, the route is rejected.
933

    
934
<p>A nice trick to debug filters is to use <cf>show route filter <m/name/</cf>
935
from the command line client. An example session might look like:
936

    
937
<code>
938
pavel@bug:~/bird$ ./birdc -s bird.ctl
939
BIRD 0.0.0 ready.
940
bird> show route
941
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
942
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
943
127.0.0.0/8        dev lo [direct1 23:21] (240)
944
bird> show route ?
945
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
946
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
947
127.0.0.0/8        dev lo [direct1 23:21] (240)
948
bird>
949
</code>
950

    
951

    
952
<sect>Data types
953

    
954
<p>Each variable and each value has certain type. Booleans, integers and enums
955
are incompatible with each other (that is to prevent you from shooting in the
956
foot).
957

    
958
<descrip>
959
	<tag/bool/
960
	This is a boolean type, it can have only two values, <cf/true/ and
961
	<cf/false/. Boolean is the only type you can use in <cf/if/ statements.
962

    
963
	<tag/int/
964
	This is a general integer type. It is an unsigned 32bit type; i.e., you
965
	can expect it to store values from 0 to 4294967295. Overflows are not
966
	checked. You can use <cf/0x1234/ syntax to write hexadecimal values.
967

    
968
	<tag/pair/
969
	This is a pair of two short integers. Each component can have values
970
	from 0 to 65535. Literals of this type are written as <cf/(1234,5678)/.
971
	The same syntax can also be used to construct a pair from two arbitrary
972
	integer expressions (for example <cf/(1+2,a)/).
973

    
974
	<tag/quad/
975
	This is a dotted quad of numbers used to represent router IDs (and
976
	others). Each component can have a value from 0 to 255. Literals of
977
	this type are written like IPv4 addresses.
978

    
979
	<tag/string/
980
	This is a string of characters. There are no ways to modify strings in
981
	filters. You can pass them between functions, assign them to variables
982
	of type <cf/string/, print such variables, use standard string
983
	comparison operations (e.g. <cf/=, !=, &lt;, &gt;, &lt;=, &gt;=/), but
984
	you can't concatenate two strings. String literals are written as
985
	<cf/"This is a string constant"/. Additionaly matching <cf/&tilde;/
986
	operator could be used to match a string value against a shell pattern
987
	(represented also as a string).
988

    
989
	<tag/ip/
990
	This type can hold a single IP address. Depending on the compile-time
991
	configuration of BIRD you are using, it is either an IPv4 or IPv6
992
	address. IP addresses are written in the standard notation
993
	(<cf/10.20.30.40/ or <cf/fec0:3:4::1/). You can apply special operator
994
	<cf>.mask(<M>num</M>)</cf> on values of type ip. It masks out all but
995
	first <cf><M>num</M></cf> bits from the IP address. So
996
	<cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
997

    
998
	<tag/prefix/
999
	This type can hold a network prefix consisting of IP address and prefix
1000
	length. Prefix literals are written as <cf><m/ipaddress//<m/pxlen/</cf>,
1001
	or <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
1002
	operators on prefixes: <cf/.ip/ which extracts the IP address from the
1003
	pair, and <cf/.len/, which separates prefix length from the pair.
1004
	So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
1005

    
1006
	<tag/ec/
1007

    
1008
	This is a specialized type used to represent BGP extended community
1009
	values. It is essentially a 64bit value, literals of this type are
1010
	usually written as <cf>(<m/kind/, <m/key/, <m/value/)</cf>, where
1011
	<cf/kind/ is a kind of extended community (e.g. <cf/rt/ / <cf/ro/ for a
1012
	route target / route origin communities), the format and possible values
1013
	of <cf/key/ and <cf/value/ are usually integers, but it depends on the
1014
	used kind. Similarly to pairs, ECs can be constructed using expressions
1015
	for <cf/key/ and <cf/value/ parts, (e.g. <cf/(ro, myas, 3*10)/, where
1016
	<cf/myas/ is an integer variable).
1017
 
1018
	<tag/int|pair|quad|ip|prefix|ec|enum set/
1019
	Filters recognize four types of sets. Sets are similar to strings: you
1020
	can pass them around but you can't modify them. Literals of type <cf>int
1021
	set</cf> look like <cf> [ 1, 2, 5..7 ]</cf>. As you can see, both simple
1022
	values and ranges are permitted in sets.
1023

    
1024
	For pair sets, expressions like <cf/(123,*)/ can be used to denote
1025
	ranges (in that case <cf/(123,0)..(123,65535)/). You can also use
1026
	<cf/(123,5..100)/ for range <cf/(123,5)..(123,100)/. You can also use
1027
	<cf/*/ and <cf/a..b/ expressions in the first part of a pair, note that
1028
	such expressions are translated to a set of intervals, which may be
1029
	memory intensive. E.g. <cf/(*,4..20)/ is translated to <cf/(0,4..20),
1030
	(1,4..20), (2,4..20), ... (65535, 4..20)/.
1031

    
1032
	EC sets use similar expressions like pair sets, e.g. <cf/(rt, 123,
1033
	10..20)/ or <cf/(ro, 123, *)/. Expressions requiring the translation
1034
	(like <cf/(rt, *, 3)/) are not allowed (as they usually have 4B range
1035
	for ASNs).
1036

    
1037
	You can also use expressions for int, pair and EC set values. However it
1038
	must be possible to evaluate these expressions before daemon boots. So
1039
	you can use only constants inside them. E.g.
1040

    
1041
	<code>
1042
	 define one=1;
1043
	 define myas=64500;
1044
	 int set odds;
1045
	 pair set ps;
1046
	 ec set es;
1047

    
1048
	 odds = [ one, 2+1, 6-one, 2*2*2-1, 9, 11 ];
1049
	 ps = [ (1,one+one), (3,4)..(4,8), (5,*), (6,3..6), (7..9,*) ];
1050
	 es = [ (rt, myas, 3*10), (rt, myas+one, 0..16*16*16-1), (ro, myas+2, *) ];
1051
	</code>
1052

    
1053
	Sets of prefixes are special: their literals does not allow ranges, but
1054
	allows prefix patterns that are written
1055
	as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
1056
	Prefix <cf><m>ip1</m>/<m>len1</m></cf> matches prefix
1057
	pattern <cf><m>ip2</m>/<m>len2</m>{<m>l</m>,<m>h</m>}</cf> if the
1058
	first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are
1059
	identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>. A valid prefix pattern
1060
	has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not
1061
	constrained by <cf/low/ or <cf/high/. Obviously, a prefix matches a
1062
	prefix set literal if it matches any prefix pattern in the prefix set
1063
	literal.
1064

    
1065
	There are also two shorthands for prefix patterns: <cf><m/address//<m/len/+</cf>
1066
	is a shorthand for <cf><m/address//<m/len/{<m/len/,<m/maxlen/}</cf>
1067
	(where <cf><m/maxlen/</cf> is 32 for IPv4 and 128 for IPv6), that means
1068
	network prefix <cf><m/address//<m/len/</cf> and all its	subnets.
1069
	<cf><m/address//<m/len/-</cf> is a shorthand for
1070
	<cf><m/address//<m/len/{0,<m/len/}</cf>, that means network prefix
1071
	<cf><m/address//<m/len/</cf> and all its supernets (network prefixes
1072
	that contain it).
1073

    
1074
	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}
1075
	]</cf> matches prefix <cf>1.0.0.0/8</cf>, all subprefixes of
1076
	<cf>2.0.0.0/8</cf>, all superprefixes of <cf>3.0.0.0/8</cf> and prefixes
1077
	<cf/4.X.X.X/ whose prefix length is 16 to 24. <cf>[ 0.0.0.0/0{20,24} ]</cf>
1078
	matches all prefixes (regardless of IP address) whose prefix length is
1079
	20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP
1080
	address <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf>
1081
	is true, but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
1082

    
1083
	Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
1084
	in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
1085
	<cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
1086
	<cf>192.168.0.0/16{24,32}</cf>.
1087

    
1088
	<tag/enum/
1089
	Enumeration types are fixed sets of possibilities. You can't define your
1090
	own variables of such type, but some route attributes are of enumeration
1091
	type. Enumeration types are incompatible with each other.
1092

    
1093
	<tag/bgppath/
1094
	BGP path is a list of autonomous system numbers. You can't write
1095
	literals of this type. There are several special operators on bgppaths:
1096

    
1097
	<cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
1098

    
1099
	<cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
1100

    
1101
	Both <cf/first/ and <cf/last/ return zero if there is no appropriate
1102
	ASN, for example if the path contains an AS set element as the first (or
1103
	the last) part.
1104

    
1105
	<cf><m/P/.len</cf> returns the length of path <m/P/.
1106

    
1107
	<cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and
1108
	returns the result.
1109

    
1110
	<cf>delete(<m/P/,<m/A/)</cf> deletes all instances of ASN <m/A/ from
1111
	from path <m/P/ and returns the result. <m/A/ may also be an integer
1112
	set, in that case the operator deletes all ASNs from path <m/P/ that are
1113
	also members of set <m/A/.
1114

    
1115
	<cf>filter(<m/P/,<m/A/)</cf> deletes all ASNs from path <m/P/ that are
1116
	not members of integer set <m/A/. I.e., <cf/filter/ do the same as
1117
	<cf/delete/ with inverted set <m/A/.
1118

    
1119
	Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
1120
	<cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
1121
	(for example <cf/bgp_path/). Similarly for <cf/delete/ and <cf/filter/.
1122

    
1123
	<tag/bgpmask/
1124
	BGP masks are patterns used for BGP path matching (using <cf>path
1125
	&tilde; [= 2 3 5 * =]</cf> syntax). The masks resemble wildcard patterns
1126
	as used by UNIX shells. Autonomous system numbers match themselves,
1127
	<cf/*/ matches any (even empty) sequence of arbitrary AS numbers and
1128
	<cf/?/ matches one arbitrary AS number. For example, if <cf>bgp_path</cf> 
1129
 	is 4 3 2 1, then: <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true,
1130
	but <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false. BGP mask
1131
	expressions can also contain integer expressions enclosed in parenthesis
1132
	and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>. There is
1133
	also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
1134

    
1135
	<tag/clist/
1136
	Clist is similar to a set, except that unlike other sets, it can be
1137
	modified. The type is used for community list (a set of pairs) and for
1138
	cluster list (a set of quads). There exist no literals of this type.
1139
	There are three special operators on clists:
1140

    
1141
	<cf><m/C/.len</cf> returns the length of clist <m/C/.
1142

    
1143
	<cf>add(<m/C/,<m/P/)</cf> adds pair (or quad) <m/P/ to clist <m/C/ and
1144
	returns the result. If item <m/P/ is already in clist <m/C/, it does
1145
	nothing. <m/P/ may also be a clist, in that case all its members are
1146
	added; i.e., it works as clist union.
1147

    
1148
	<cf>delete(<m/C/,<m/P/)</cf> deletes pair (or quad) <m/P/ from clist
1149
	<m/C/ and returns the result. If clist <m/C/ does not contain item
1150
	<m/P/, it does nothing. <m/P/ may also be a pair (or quad) set, in that
1151
	case the operator deletes all items from clist <m/C/ that are also
1152
	members of set <m/P/. Moreover, <m/P/ may also be a clist, which works
1153
	analogously; i.e., it works as clist difference.
1154

    
1155
	<cf>filter(<m/C/,<m/P/)</cf> deletes all items from clist <m/C/ that are
1156
	not members of pair (or quad) set <m/P/. I.e., <cf/filter/ do the same
1157
	as <cf/delete/ with inverted set <m/P/. <m/P/ may also be a clist, which
1158
	works analogously; i.e., it works as clist intersection.
1159

    
1160
	Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
1161
	<cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute (for
1162
	example <cf/bgp_community/). Similarly for <cf/delete/ and <cf/filter/.
1163

    
1164
	<tag/eclist/
1165
	Eclist is a data type used for BGP extended community lists. Eclists
1166
	are very similar to clists, but they are sets of ECs instead of pairs.
1167
	The same operations (like <cf/add/, <cf/delete/, or <cf/&tilde;/
1168
	membership operator) can be used to modify or test eclists, with ECs
1169
	instead of pairs as arguments.
1170
</descrip>
1171

    
1172

    
1173
<sect>Operators
1174

    
1175
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>,
1176
parentheses <cf/(a*(b+c))/, comparison <cf/(a=b, a!=b, a&lt;b, a&gt;=b)/.
1177
Logical operations include unary not (<cf/!/), and (<cf/&amp;&amp;/) and or
1178
(<cf/&verbar;&verbar;/). Special operators include <cf/&tilde;/ for "is element
1179
of a set" operation - it can be used on element and set of elements of the same
1180
type (returning true if element is contained in the given set), or on two
1181
strings (returning true if first string matches a shell-like pattern stored in
1182
second string) or on IP and prefix (returning true if IP is within the range
1183
defined by that prefix), or on prefix and prefix (returning true if first prefix
1184
is more specific than second one) or on bgppath and bgpmask (returning true if
1185
the path matches the mask) or on number and bgppath (returning true if the
1186
number is in the path) or on bgppath and int (number) set (returning true if any
1187
ASN from the path is in the set) or on pair/quad and clist (returning true if
1188
the pair/quad is element of the clist) or on clist and pair/quad set (returning
1189
true if there is an element of the clist that is also a member of the pair/quad
1190
set).
1191

    
1192
<p>There is one operator related to ROA infrastructure - <cf/roa_check()/. It
1193
examines a ROA table and does RFC 6483 route origin validation for a given
1194
network prefix. The basic usage is <cf>roa_check(<m/table/)</cf>, which checks
1195
current route (which should be from BGP to have AS_PATH argument) in the
1196
specified ROA table and returns ROA_UNKNOWN if there is no relevant ROA,
1197
ROA_VALID if there is a matching ROA, or ROA_INVALID if there are some relevant
1198
ROAs but none of them match. There is also an extended variant
1199
<cf>roa_check(<m/table/, <m/prefix/, <m/asn/)</cf>, which allows to specify a
1200
prefix and an ASN as arguments.
1201

    
1202

    
1203
<sect>Control structures
1204

    
1205
<p>Filters support two control structures: conditions and case switches. 
1206

    
1207
<p>Syntax of a condition is: <cf>if <M>boolean expression</M> then <m/command1/;
1208
else <m/command2/;</cf> and you can use <cf>{ <m/command_1/; <m/command_2/;
1209
<M>...</M> }</cf> instead of either command. The <cf>else</cf> clause may be
1210
omitted. If the <cf><m>boolean expression</m></cf> is true, <m/command1/ is
1211
executed, otherwise <m/command2/ is executed.
1212

    
1213
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case
1214
<m/expr/ { else: | <m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [
1215
... ] }</cf>. The expression after <cf>case</cf> can be of any type which can be
1216
on the left side of the &tilde; operator and anything that could be a member of
1217
a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/
1218
grouping. If <cf><m/expr/</cf> matches one of the <cf/:/ clauses, statements
1219
between it and next <cf/:/ statement are executed. If <cf><m/expr/</cf> matches
1220
neither of the <cf/:/ clauses, the statements after <cf/else:/ are executed.
1221

    
1222
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
1223

    
1224
<code>
1225
case arg1 {
1226
	2: print "two"; print "I can do more commands without {}";
1227
	3 .. 5: print "three to five";
1228
	else: print "something else";
1229
}
1230

    
1231
if 1234 = i then printn "."; else { 
1232
  print "not 1234"; 
1233
  print "You need {} around multiple commands"; 
1234
}
1235
</code>
1236

    
1237

    
1238
<sect>Route attributes
1239

    
1240
<p>A filter is implicitly passed a route, and it can access its attributes just
1241
like it accesses variables. Attempts to access undefined attribute result in a
1242
runtime error; you can check if an attribute is defined by using the
1243
<cf>defined( <m>attribute</m> )</cf> operator. One notable exception to this
1244
rule are attributes of clist type, where undefined value is regarded as empty
1245
clist for most purposes.
1246

    
1247
<descrip>
1248
	<tag><m/prefix/ net</tag>
1249
	Network the route is talking about. Read-only. (See the chapter about
1250
	routing tables.)
1251

    
1252
	<tag><m/enum/ scope</tag>
1253
	The scope of the route. Possible values: <cf/SCOPE_HOST/ for routes
1254
	local to this host, <cf/SCOPE_LINK/ for those specific for a physical
1255
	link, <cf/SCOPE_SITE/ and <cf/SCOPE_ORGANIZATION/ for private routes and
1256
	<cf/SCOPE_UNIVERSE/ for globally visible routes. This attribute is not
1257
	interpreted by BIRD and can be used to mark routes in filters. The
1258
	default value for new routes is <cf/SCOPE_UNIVERSE/.
1259

    
1260
	<tag><m/int/ preference</tag>
1261
	Preference of the route. Valid values are 0-65535. (See the chapter
1262
	about routing tables.)
1263

    
1264
	<tag><m/ip/ from</tag>
1265
	The router which the route has originated from.
1266
	
1267
	<tag><m/ip/ gw</tag>
1268
	Next hop packets routed using this route should be forwarded to.
1269

    
1270
	<tag><m/string/ proto</tag>
1271
	The name of the protocol which the route has been imported from.
1272
	Read-only.
1273

    
1274
	<tag><m/enum/ source</tag>
1275
	what protocol has told me about this route. Possible values:
1276
	<cf/RTS_DUMMY/, <cf/RTS_STATIC/, <cf/RTS_INHERIT/, <cf/RTS_DEVICE/,
1277
	<cf/RTS_STATIC_DEVICE/, <cf/RTS_REDIRECT/, <cf/RTS_RIP/, <cf/RTS_OSPF/,
1278
	<cf/RTS_OSPF_IA/, <cf/RTS_OSPF_EXT1/, <cf/RTS_OSPF_EXT2/, <cf/RTS_BGP/,
1279
	<cf/RTS_PIPE/.
1280

    
1281
	<tag><m/enum/ cast</tag>
1282
	Route type (Currently <cf/RTC_UNICAST/ for normal routes,
1283
	<cf/RTC_BROADCAST/, <cf/RTC_MULTICAST/, <cf/RTC_ANYCAST/ will be used in
1284
	the future for broadcast, multicast and anycast routes). Read-only.
1285

    
1286
	<tag><m/enum/ dest</tag>
1287
	Type of destination the packets should be sent to
1288
	(<cf/RTD_ROUTER/ for forwarding to a neighboring router,
1289
	<cf/RTD_DEVICE/ for routing to a directly-connected network,
1290
	<cf/RTD_MULTIPATH/ for multipath destinations,
1291
	<cf/RTD_BLACKHOLE/ for packets to be silently discarded,
1292
	<cf/RTD_UNREACHABLE/, <cf/RTD_PROHIBIT/ for packets that should be
1293
	returned with ICMP host unreachable / ICMP administratively prohibited
1294
	messages). Can be changed, but only to <cf/RTD_BLACKHOLE/,
1295
	<cf/RTD_UNREACHABLE/ or <cf/RTD_PROHIBIT/.
1296

    
1297
	<tag><m/string/ ifname</tag>
1298
	Name of the outgoing interface. Sink routes (like blackhole, unreachable
1299
	or prohibit) and multipath routes have no interface associated with
1300
	them, so <cf/ifname/ returns an empty string for such routes. Read-only.
1301

    
1302
	<tag><m/int/ ifindex</tag>
1303
	Index of the outgoing interface. System wide index of the interface. May
1304
	be used for interface matching, however indexes might change on interface
1305
	creation/removal. Zero is returned for routes with undefined outgoing
1306
	interfaces. Read-only.
1307

    
1308
	<tag><m/int/ igp_metric</tag>
1309
	The optional attribute that can be used to specify a distance to the
1310
	network for routes that do not have a native protocol metric attribute
1311
	(like <cf/ospf_metric1/ for OSPF routes). It is used mainly by BGP to
1312
	compare internal distances to boundary routers (see below). It is also
1313
	used when the route is exported to OSPF as a default value for OSPF type
1314
	1 metric.
1315
</descrip>
1316

    
1317
<p>There also exist some protocol-specific attributes which are described in the
1318
corresponding protocol sections.
1319

    
1320

    
1321
<sect>Other statements
1322

    
1323
<p>The following statements are available:
1324

    
1325
<descrip>
1326
	<tag><m/variable/ = <m/expr/</tag>
1327
	Set variable to a given value.
1328

    
1329
	<tag>accept|reject [ <m/expr/ ]</tag>
1330
	Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
1331

    
1332
	<tag>return <m/expr/</tag>
1333
	Return <cf><m>expr</m></cf> from the current function, the function ends
1334
	at this point.
1335

    
1336
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
1337
	Prints given expressions; useful mainly while debugging filters. The
1338
	<cf/printn/ variant does not terminate the line.
1339

    
1340
	<tag>quitbird</tag>
1341
	Terminates BIRD. Useful when debugging the filter interpreter.
1342
</descrip>
1343

    
1344

    
1345
<chapt>Protocols
1346

    
1347
<sect><label id="sect-bfd">BFD
1348

    
1349
<sect1>Introduction
1350

    
1351
<p>Bidirectional Forwarding Detection (BFD) is not a routing protocol itself, it
1352
is an independent tool providing liveness and failure detection. Routing
1353
protocols like OSPF and BGP use integrated periodic "hello" messages to monitor
1354
liveness of neighbors, but detection times of these mechanisms are high (e.g. 40
1355
seconds by default in OSPF, could be set down to several seconds). BFD offers
1356
universal, fast and low-overhead mechanism for failure detection, which could be
1357
attached to any routing protocol in an advisory role.
1358

    
1359
<p>BFD consists of mostly independent BFD sessions. Each session monitors an
1360
unicast bidirectional path between two BFD-enabled routers. This is done by
1361
periodically sending control packets in both directions. BFD does not handle
1362
neighbor discovery, BFD sessions are created on demand by request of other
1363
protocols (like OSPF or BGP), which supply appropriate information like IP
1364
addresses and associated interfaces. When a session changes its state, these
1365
protocols are notified and act accordingly (e.g. break an OSPF adjacency when
1366
the BFD session went down).
1367

    
1368
<p>BIRD implements basic BFD behavior as defined in
1369
RFC 5880<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5880.txt">
1370
(some advanced features like the echo mode or authentication are not implemented),
1371
IP transport for BFD as defined in
1372
RFC 5881<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5881.txt"> and
1373
RFC 5883<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5883.txt">
1374
and interaction with client protocols as defined in
1375
RFC 5882<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5882.txt">.
1376

    
1377
<p>Note that BFD implementation in BIRD is currently a new feature in
1378
development, expect some rough edges and possible UI and configuration changes
1379
in the future. Also note that we currently support at most one protocol instance.
1380

    
1381
<sect1>Configuration
1382

    
1383
<p>BFD configuration consists mainly of multiple definitions of interfaces.
1384
Most BFD config options are session specific. When a new session is requested
1385
and dynamically created, it is configured from one of these definitions. For
1386
sessions to directly connected neighbors, <cf/interface/ definitions are chosen
1387
based on the interface associated with the session, while <cf/multihop/
1388
definition is used for multihop sessions. If no definition is relevant, the
1389
session is just created with the default configuration. Therefore, an empty BFD
1390
configuration is often sufficient.
1391

    
1392
<p>Note that to use BFD for other protocols like OSPF or BGP, these protocols
1393
also have to be configured to request BFD sessions, usually by <cf/bfd/ option.
1394

    
1395
<p>Some of BFD session options require <m/time/ value, which has to be specified
1396
with the appropriate unit: <m/num/ <cf/s/|<cf/ms/|<cf/us/. Although microseconds
1397
are allowed as units, practical minimum values are usually in order of tens of
1398
milliseconds.
1399

    
1400
<code>
1401
protocol bfd [&lt;name&gt;] {
1402
	interface &lt;interface pattern&gt; {
1403
		interval &lt;time&gt;;
1404
		min rx interval &lt;time&gt;;
1405
		min tx interval &lt;time&gt;;
1406
		idle tx interval &lt;time&gt;;
1407
		multiplier &lt;num&gt;;
1408
		passive &lt;switch&gt;;
1409
	};
1410
	multihop {
1411
		interval &lt;time&gt;;
1412
		min rx interval &lt;time&gt;;
1413
		min tx interval &lt;time&gt;;
1414
		idle tx interval &lt;time&gt;;
1415
		multiplier &lt;num&gt;;
1416
		passive &lt;switch&gt;;
1417
	};
1418
	neighbor &lt;ip&gt; [dev "&lt;interface&gt;"] [local &lt;ip&gt;] [multihop &lt;switch&gt;];
1419
}
1420
</code>
1421

    
1422
<descrip>
1423
	<tag>interface <m/pattern [, ...]/ { <m/options/ }</tag>
1424
	Interface definitions allow to specify options for sessions associated
1425
	with such interfaces and also may contain interface specific options.
1426
	See <ref id="dsc-iface" name="interface"> common option for a detailed
1427
	description of interface patterns. Note that contrary to the behavior of
1428
	<cf/interface/ definitions of other protocols, BFD protocol would accept
1429
	sessions (in default configuration) even on interfaces not covered by
1430
	such definitions.
1431

    
1432
	<tag>multihop { <m/options/ }</tag>
1433
	Multihop definitions allow to specify options for multihop BFD sessions,
1434
	in the same manner as <cf/interface/ definitions are used for directly
1435
	connected sessions. Currently only one such definition (for all multihop
1436
	sessions) could be used.
1437

    
1438
	<tag>neighbor <m/ip/ [dev "<m/interface/"] [local <m/ip/] [multihop <m/switch/]</tag>
1439
	BFD sessions are usually created on demand as requested by other
1440
	protocols (like OSPF or BGP). This option allows to explicitly add
1441
	a BFD session to the specified neighbor regardless of such requests.
1442
	
1443
	The session is identified by the IP address of the neighbor, with
1444
	optional specification of used interface and local IP. By default
1445
	the neighbor must be directly connected, unless the the session is
1446
	configured as multihop. Note that local IP must be specified for
1447
	multihop sessions.
1448
</descrip>
1449

    
1450
<p>Session specific options (part of <cf/interface/ and <cf/multihop/ definitions):
1451

    
1452
<descrip>
1453
	<tag>interval <m/time/</tag>
1454
	BFD ensures availability of the forwarding path associated with the
1455
	session by periodically sending BFD control packets in both
1456
	directions. The rate of such packets is controlled by two options,
1457
	<cf/min rx interval/ and <cf/min tx interval/ (see below). This option
1458
	is just a shorthand to set both of these options together.
1459

    
1460
	<tag>min rx interval <m/time/</tag>
1461
	This option specifies the minimum RX interval, which is announced to the
1462
	neighbor and used there to limit the neighbor's rate of generated BFD
1463
	control packets. Default: 10 ms.
1464

    
1465
	<tag>min tx interval <m/time/</tag>
1466
	This option specifies the desired TX interval, which controls the rate
1467
	of generated BFD control packets (together with <cf/min rx interval/
1468
	announced by the neighbor). Note that this value is used only if the BFD
1469
	session is up, otherwise the value of <cf/idle tx interval/ is used
1470
	instead. Default: 100 ms.
1471

    
1472
	<tag>idle tx interval <m/time/</tag>
1473
	In order to limit unnecessary traffic in cases where a neighbor is not
1474
	available or not running BFD, the rate of generated BFD control packets
1475
	is lower when the BFD session is not up. This option specifies the
1476
	desired TX interval in such cases instead of <cf/min tx interval/.
1477
	Default: 1 s.
1478

    
1479
	<tag>multiplier <m/num/</tag>
1480
	Failure detection time for BFD sessions is based on established rate of
1481
	BFD control packets (<cf>min rx/tx interval</cf>) multiplied by this
1482
	multiplier, which is essentially (ignoring jitter) a number of missed
1483
	packets after which the session is declared down. Note that rates and
1484
	multipliers could be different in each direction of a BFD session.
1485
	Default: 5.
1486

    
1487
	<tag>passive <m/switch/</tag>
1488
	Generally, both BFD session endpoinds try to establish the session by
1489
	sending control packets to the other side. This option allows to enable
1490
	passive mode, which means that the router does not send BFD packets
1491
	until it has received one from the other side. Default: disabled.
1492
</descrip>
1493

    
1494
<sect1>Example
1495

    
1496
<p><code>
1497
protocol bfd {
1498
	interface "eth*" {
1499
		min rx interval 20 ms;
1500
		min tx interval 50 ms;
1501
		idle tx interval 300 ms;
1502
	};
1503
	interface "gre*" {
1504
		interval 200 ms;
1505
		multiplier 10;
1506
		passive;
1507
	};
1508
	multihop {
1509
		interval 200 ms;
1510
		multiplier 10;
1511
	};
1512

    
1513
	neighbor 192.168.1.10;
1514
	neighbor 192.168.2.2 dev "eth2";
1515
	neighbor 192.168.10.1 local 192.168.1.1 multihop;
1516
}
1517
</code>
1518

    
1519

    
1520
<sect>BGP
1521

    
1522
<p>The Border Gateway Protocol is the routing protocol used for backbone level
1523
routing in the today's Internet. Contrary to other protocols, its convergence
1524
does not rely on all routers following the same rules for route selection,
1525
making it possible to implement any routing policy at any router in the network,
1526
the only restriction being that if a router advertises a route, it must accept
1527
and forward packets according to it.
1528

    
1529
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each AS
1530
is a part of the network with common management and common routing policy. It is
1531
identified by a unique 16-bit number (ASN). Routers within each AS usually
1532
exchange AS-internal routing information with each other using an interior
1533
gateway protocol (IGP, such as OSPF or RIP). Boundary routers at the border of
1534
the AS communicate global (inter-AS) network reachability information with their
1535
neighbors in the neighboring AS'es via exterior BGP (eBGP) and redistribute
1536
received information to other routers in the AS via interior BGP (iBGP).
1537

    
1538
<p>Each BGP router sends to its neighbors updates of the parts of its routing
1539
table it wishes to export along with complete path information (a list of AS'es
1540
the packet will travel through if it uses the particular route) in order to
1541
avoid routing loops.
1542

    
1543
<p>BIRD supports all requirements of the BGP4 standard as defined in
1544
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
1545
It also supports the community attributes
1546
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
1547
capability negotiation
1548
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
1549
MD5 password authentication
1550
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
1551
extended communities
1552
(RFC 4360<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4360.txt">),
1553
route reflectors 
1554
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
1555
graceful restart
1556
(RFC 4724<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4724.txt">),
1557
multiprotocol extensions
1558
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
1559
4B AS numbers 
1560
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">),
1561
and 4B AS numbers in extended communities
1562
(RFC 5668<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5668.txt">).
1563

    
1564

    
1565
For IPv6, it uses the standard multiprotocol extensions defined in
1566
RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">
1567
and applied to IPv6 according to
1568
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
1569

    
1570
<sect1>Route selection rules
1571

    
1572
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
1573
route among multiple BGP routes with the same preference are a bit more complex
1574
and they are implemented according to the following algorithm. It starts the
1575
first rule, if there are more "best" routes, then it uses the second rule to
1576
choose among them and so on.
1577

    
1578
<itemize>
1579
	<item>Prefer route with the highest Local Preference attribute.
1580
	<item>Prefer route with the shortest AS path.
1581
	<item>Prefer IGP origin over EGP and EGP origin over incomplete.
1582
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
1583
	<item>Prefer routes received via eBGP over ones received via iBGP.
1584
	<item>Prefer routes with lower internal distance to a boundary router.
1585
	<item>Prefer the route with the lowest value of router ID of the
1586
	advertising router.
1587
</itemize>
1588

    
1589
<sect1>IGP routing table
1590

    
1591
<p>BGP is mainly concerned with global network reachability and with routes to
1592
other autonomous systems. When such routes are redistributed to routers in the
1593
AS via BGP, they contain IP addresses of a boundary routers (in route attribute
1594
NEXT_HOP). BGP depends on existing IGP routing table with AS-internal routes to
1595
determine immediate next hops for routes and to know their internal distances to
1596
boundary routers for the purpose of BGP route selection. In BIRD, there is
1597
usually one routing table used for both IGP routes and BGP routes.
1598

    
1599
<sect1>Configuration
1600

    
1601
<p>Each instance of the BGP corresponds to one neighboring router. This allows
1602
to set routing policy and all the other parameters differently for each neighbor
1603
using the following configuration parameters:
1604

    
1605
<descrip>
1606
	<tag>local [<m/ip/] as <m/number/</tag>
1607
	Define which AS we are part of. (Note that contrary to other IP routers,
1608
	BIRD is able to act as a router located in multiple AS'es simultaneously,
1609
	but in such cases you need to tweak the BGP paths manually in the filters
1610
	to get consistent behavior.) Optional <cf/ip/ argument specifies a source
1611
	address, equivalent to the <cf/source address/ option (see below). This
1612
	parameter is mandatory.
1613

    
1614
	<tag>neighbor <m/ip/ as <m/number/</tag>
1615
	Define neighboring router this instance will be talking to and what AS
1616
	it's located in. In case the neighbor is in the same AS as we are, we
1617
	automatically switch to iBGP. This parameter is mandatory.
1618

    
1619
	<tag>direct</tag>
1620
	Specify that the neighbor is directly connected. The IP address of the
1621
	neighbor must be from a directly reachable IP range (i.e. associated
1622
	with one of your router's interfaces), otherwise the BGP session
1623
	wouldn't start but it would wait for such interface to appear. The
1624
	alternative is the <cf/multihop/ option. Default: enabled for eBGP.
1625

    
1626
	<tag>multihop [<m/number/]</tag>
1627
	Configure multihop BGP session to a neighbor that isn't directly
1628
	connected. Accurately, this option should be used if the configured
1629
	neighbor IP address does not match with any local network subnets. Such
1630
	IP address have to be reachable through system routing table. The
1631
	alternative is the <cf/direct/ option. For multihop BGP it is
1632
	recommended to explicitly configure the source address to have it
1633
	stable. Optional <cf/number/ argument can be used to specify the number
1634
	of hops (used for TTL). Note that the number of networks (edges) in a
1635
	path is counted; i.e., if two BGP speakers are separated by one router,
1636
	the number of hops is 2. Default: enabled for iBGP.
1637

    
1638
	<tag>source address <m/ip/</tag>
1639
	Define local address we should use for next hop calculation and as a
1640
	source address for the BGP session. Default: the address of the local
1641
	end of the interface our neighbor is connected to.
1642

    
1643
	<tag>next hop self</tag>
1644
	Avoid calculation of the Next Hop attribute and always advertise our own
1645
	source address as a next hop. This needs to be used only occasionally to
1646
	circumvent misconfigurations of other routers. Default: disabled.
1647

    
1648
	<tag>next hop keep</tag>
1649
	Forward the received Next Hop attribute even in situations where the
1650
	local address should be used instead, like when the route is sent to an
1651
	interface with a different subnet. Default: disabled.
1652

    
1653
	<tag>missing lladdr self|drop|ignore</tag>
1654
	Next Hop attribute in BGP-IPv6 sometimes contains just the global IPv6
1655
	address, but sometimes it has to contain both global and link-local IPv6
1656
	addresses. This option specifies what to do if BIRD have to send both
1657
	addresses but does not know link-local address. This situation might
1658
	happen when routes from other protocols are exported to BGP, or when
1659
	improper updates are received from BGP peers. <cf/self/ means that BIRD
1660
	advertises its own local address instead. <cf/drop/ means that BIRD
1661
	skips that prefixes and logs error. <cf/ignore/ means that BIRD ignores
1662
	the problem and sends just the global address (and therefore forms
1663
	improper BGP update). Default: <cf/self/, unless BIRD is configured as a
1664
	route server (option <cf/rs client/), in that case default is <cf/ignore/,
1665
	because route servers usually do not forward packets themselves.
1666

    
1667
	<tag>gateway direct|recursive</tag>
1668
	For received routes, their <cf/gw/ (immediate next hop) attribute is
1669
	computed from received <cf/bgp_next_hop/ attribute. This option
1670
	specifies how it is computed. Direct mode means that the IP address from
1671
	<cf/bgp_next_hop/ is used if it is directly reachable, otherwise the
1672
	neighbor IP address is used. Recursive mode means that the gateway is
1673
	computed by an IGP routing table lookup for the IP address from
1674
	<cf/bgp_next_hop/. Recursive mode is the behavior specified by the BGP
1675
	standard. Direct mode is simpler, does not require any routes in a
1676
	routing table, and was used in older versions of BIRD, but does not
1677
	handle well nontrivial iBGP setups and multihop. Recursive mode is
1678
	incompatible with <ref id="dsc-sorted" name="sorted tables">. Default:
1679
	<cf/direct/ for direct sessions, <cf/recursive/ for multihop sessions.
1680

    
1681
	<tag>igp table <m/name/</tag>
1682
	Specifies a table that is used as an IGP routing table. Default: the
1683
	same as the table BGP is connected to.
1684

    
1685
	<tag>bfd <M>switch</M></tag>
1686
	BGP could use BFD protocol as an advisory mechanism for neighbor
1687
	liveness and failure detection. If enabled, BIRD setups a BFD session
1688
	for the BGP neighbor and tracks its liveness by it. This has an
1689
	advantage of an order of magnitude lower detection times in case of
1690
	failure. Note that BFD protocol also has to be configured, see
1691
	<ref id="sect-bfd" name="BFD"> section for details. Default: disabled.
1692

    
1693
	<tag>ttl security <m/switch/</tag>
1694
	Use GTSM (RFC 5082 - the generalized TTL security mechanism). GTSM
1695
	protects against spoofed packets by ignoring received packets with a
1696
	smaller than expected TTL. To work properly, GTSM have to be enabled on
1697
	both sides of a BGP session. If both <cf/ttl security/ and <cf/multihop/
1698
	options are enabled, <cf/multihop/ option should specify proper hop
1699
	value to compute expected TTL. Kernel support required: Linux: 2.6.34+
1700
	(IPv4), 2.6.35+ (IPv6), BSD: since long ago, IPv4 only. Note that full
1701
	(ICMP protection, for example) RFC 5082 support is provided by Linux
1702
	only. Default: disabled.
1703
	
1704
	<tag>password <m/string/</tag>
1705
	Use this password for MD5 authentication of BGP sessions. Default: no
1706
	authentication. Password has to be set by external utility
1707
	(e.g. setkey(8)) on BSD systems.
1708

    
1709
	<tag>passive <m/switch/</tag>
1710
	Standard BGP behavior is both initiating outgoing connections and
1711
	accepting incoming connections. In passive mode, outgoing connections
1712
	are not initiated. Default: off.
1713

    
1714
	<tag>rr client</tag>
1715
	Be a route reflector and treat the neighbor as a route reflection
1716
	client. Default: disabled.
1717

    
1718
	<tag>rr cluster id <m/IPv4 address/</tag>
1719
	Route reflectors use cluster id to avoid route reflection loops. When
1720
	there is one route reflector in a cluster it usually uses its router id
1721
	as a cluster id, but when there are more route reflectors in a cluster,
1722
	these need to be configured (using this option) to use a common cluster
1723
	id. Clients in a cluster need not know their cluster id and this option
1724
	is not allowed for them. Default: the same as router id.
1725

    
1726
	<tag>rs client</tag> 
1727
	Be a route server and treat the neighbor as a route server client.
1728
	A route server is used as a replacement for full mesh EBGP routing in
1729
	Internet exchange points in a similar way to route reflectors used in
1730
	IBGP routing. BIRD does not implement obsoleted RFC 1863, but uses
1731
	ad-hoc implementation, which behaves like plain EBGP but reduces
1732
	modifications to advertised route attributes to be transparent (for
1733
	example does not prepend its AS number to AS PATH attribute and keeps
1734
	MED attribute). Default: disabled.
1735

    
1736
	<tag>secondary <m/switch/</tag>
1737
	Usually, if an export filter rejects a selected route, no other route is
1738
	propagated for that network. This option allows to try the next route in
1739
	order until one that is accepted is found or all routes for that network
1740
	are rejected. This can be used for route servers that need to propagate
1741
	different tables to each client but do not want to have these tables
1742
	explicitly (to conserve memory). This option requires that the connected
1743
	routing table is <ref id="dsc-sorted" name="sorted">. Default: off.
1744

    
1745
	<tag>add paths <m/switch/|rx|tx</tag>
1746
	Standard BGP can propagate only one path (route) per destination network
1747
	(usually the selected one). This option controls the add-path protocol
1748
	extension, which allows to advertise any number of paths to a
1749
	destination. Note that to be active, add-path has to be enabled on both
1750
	sides of the BGP session, but it could be enabled separately for RX and
1751
	TX direction. When active, all available routes accepted by the export
1752
	filter are advertised to the neighbor. Default: off.
1753

    
1754
	<tag>allow local as [<m/number/]</tag> 
1755
	BGP prevents routing loops by rejecting received routes with the local
1756
	AS number in the AS path. This option allows to loose or disable the
1757
	check. Optional <cf/number/ argument can be used to specify the maximum
1758
	number of local ASNs in the AS path that is allowed for received
1759
	routes. When the option is used without the argument, the check is
1760
	completely disabled and you should ensure loop-free behavior by some
1761
	other means. Default: 0 (no local AS number allowed).
1762

    
1763
	<tag>enable route refresh <m/switch/</tag>
1764
	When BGP speaker changes its import filter, it has to re-examine all
1765
	routes received from its neighbor against the new filter. As these
1766
	routes might not be available, there is a BGP protocol extension Route
1767
	Refresh (specified in RFC 2918) that allows BGP speaker to request
1768
	re-advertisement of all routes from its neighbor. This option specifies
1769
	whether BIRD advertises this capability and accepts such requests. Even
1770
	when disabled, BIRD can send route refresh requests. Default: on.
1771

    
1772
	<tag>graceful restart <m/switch/|aware</tag>
1773
	When a BGP speaker restarts or crashes, neighbors will discard all
1774
	received paths from the speaker, which disrupts packet forwarding even
1775
	when the forwarding plane of the speaker remains intact. RFC 4724
1776
	specifies an optional graceful restart mechanism to alleviate this
1777
	issue. This option controls the mechanism. It has three states:
1778
	Disabled, when no support is provided. Aware, when the graceful restart
1779
	support is announced and the support for restarting neighbors is
1780
	provided, but no local graceful restart is allowed (i.e. receiving-only
1781
	role). Enabled, when the full graceful restart support is provided
1782
	(i.e. both restarting and receiving role). Note that proper support for
1783
	local graceful restart requires also configuration of other protocols.
1784
	Default: aware.
1785

    
1786
	<tag>graceful restart time <m/number/</tag>
1787
	The restart time is announced in the BGP graceful restart capability
1788
	and specifies how long the neighbor would wait for the BGP session to
1789
	re-establish after a restart before deleting stale routes. Default:
1790
	120 seconds.
1791

    
1792
	<tag>interpret communities <m/switch/</tag>
1793
	RFC 1997 demands that BGP speaker should process well-known communities
1794
	like no-export (65535, 65281) or no-advertise (65535, 65282). For
1795
	example, received route carrying a no-adverise community should not be
1796
	advertised to any of its neighbors. If this option is enabled (which is
1797
	by default), BIRD has such behavior automatically (it is evaluated when
1798
	a route is exported to the BGP protocol just before the export filter).
1799
	Otherwise, this integrated processing of well-known communities is
1800
	disabled. In that case, similar behavior can be implemented in the
1801
	export filter. Default: on.
1802

    
1803
	<tag>enable as4 <m/switch/</tag>
1804
	BGP protocol was designed to use 2B AS numbers and was extended later to
1805
	allow 4B AS number. BIRD supports 4B AS extension, but by disabling this
1806
	option it can be persuaded not to advertise it and to maintain old-style
1807
	sessions with its neighbors. This might be useful for circumventing bugs
1808
	in neighbor's implementation of 4B AS extension. Even when disabled
1809
	(off), BIRD behaves internally as AS4-aware BGP router. Default: on.
1810

    
1811
	<tag>capabilities <m/switch/</tag>
1812
	Use capability advertisement to advertise optional capabilities. This is
1813
	standard behavior for newer BGP implementations, but there might be some
1814
	older BGP implementations that reject such connection attempts. When
1815
	disabled (off), features that request it (4B AS support) are also
1816
	disabled. Default: on, with automatic fallback to off when received
1817
	capability-related error.
1818

    
1819
	<tag>advertise ipv4 <m/switch/</tag>
1820
	Advertise IPv4 multiprotocol capability. This is not a correct behavior
1821
	according to the strict interpretation of RFC 4760, but it is widespread
1822
	and required by some BGP implementations (Cisco and Quagga). This option
1823
	is relevant to IPv4 mode with enabled capability advertisement
1824
	only. Default: on.
1825

    
1826
	<tag>route limit <m/number/</tag>
1827
	The maximal number of routes that may be imported from the protocol. If
1828
	the route limit is exceeded, the connection is closed with an error.
1829
	Limit is currently implemented as <cf>import limit <m/number/ action
1830
	restart</cf>. This option is obsolete and it is replaced by
1831
	<ref id="import-limit" name="import limit option">. Default: no	limit.
1832

    
1833
	<tag>disable after error <m/switch/</tag>
1834
	When an error is encountered (either locally or by the other side),
1835
	disable the instance automatically and wait for an administrator to fix
1836
	the problem manually. Default: off.
1837

    
1838
	<tag>hold time <m/number/</tag>
1839
	Time in seconds to wait for a Keepalive message from the other side
1840
	before considering the connection stale. Default: depends on agreement
1841
	with the neighboring router, we prefer 240 seconds if the other side is
1842
	willing to accept it.
1843

    
1844
	<tag>startup hold time <m/number/</tag>
1845
	Value of the hold timer used before the routers have a chance to exchange
1846
	open messages and agree on the real value. Default: 240	seconds.
1847

    
1848
	<tag>keepalive time <m/number/</tag>
1849
	Delay in seconds between sending of two consecutive Keepalive messages.
1850
	Default: One third of the hold time.
1851

    
1852
	<tag>connect retry time <m/number/</tag>
1853
	Time in seconds to wait before retrying a failed attempt to connect.
1854
	Default: 120 seconds.
1855

    
1856
	<tag>start delay time <m/number/</tag>
1857
	Delay in seconds between protocol startup and the first attempt to
1858
	connect. Default: 5 seconds.
1859

    
1860
	<tag>error wait time <m/number/,<m/number/</tag>
1861
	Minimum and maximum delay in seconds between a protocol failure (either
1862
	local or reported by the peer) and automatic restart. Doesn't apply
1863
	when <cf/disable after error/ is configured. If consecutive errors
1864
	happen, the delay is increased exponentially until it reaches the
1865
	maximum. Default: 60, 300.
1866

    
1867
	<tag>error forget time <m/number/</tag>
1868
	Maximum time in seconds between two protocol failures to treat them as a
1869
	error sequence which makes <cf/error wait time/ increase exponentially.
1870
	Default: 300 seconds.
1871

    
1872
	<tag>path metric <m/switch/</tag>
1873
	Enable comparison of path lengths when deciding which BGP route is the
1874
	best one. Default: on.
1875

    
1876
	<tag>med metric <m/switch/</tag>
1877
	Enable comparison of MED attributes (during best route selection) even
1878
	between routes received from different ASes. This may be useful if all
1879
	MED attributes contain some consistent metric, perhaps enforced in
1880
	import filters of AS boundary routers. If this option is disabled, MED
1881
	attributes are compared only if routes are received from the same AS
1882
	(which is the standard behavior). Default: off.
1883

    
1884
	<tag>deterministic med <m/switch/</tag>
1885
	BGP route selection algorithm is often viewed as a comparison between
1886
	individual routes (e.g. if a new route appears and is better than the
1887
	current best one, it is chosen as the new best one). But the proper
1888
	route selection, as specified by RFC 4271, cannot be fully implemented
1889
	in that way. The problem is mainly in handling the MED attribute. BIRD,
1890
	by default, uses an simplification based on individual route comparison,
1891
	which in some cases may lead to temporally dependent behavior (i.e. the
1892
	selection is dependent on the order in which routes appeared). This
1893
	option enables a different (and slower) algorithm implementing proper
1894
	RFC 4271 route selection, which is deterministic. Alternative way how to
1895
	get deterministic behavior is to use <cf/med metric/ option. This option
1896
	is incompatible with <ref id="dsc-sorted" name="sorted tables">.
1897
	Default: off.
1898

    
1899
	<tag>igp metric <m/switch/</tag>
1900
	Enable comparison of internal distances to boundary routers during best
1901
 	route selection. Default: on.
1902

    
1903
	<tag>prefer older <m/switch/</tag>
1904
	Standard route selection algorithm breaks ties by comparing router IDs.
1905
	This changes the behavior to prefer older routes (when both are external
1906
	and from different peer). For details, see RFC 5004. Default: off.
1907

    
1908
	<tag>default bgp_med <m/number/</tag>
1909
	Value of the Multiple Exit Discriminator to be used during route
1910
	selection when the MED attribute is missing. Default: 0.
1911

    
1912
	<tag>default bgp_local_pref <m/number/</tag>
1913
	A default value for the Local Preference attribute. It is used when
1914
	a new Local Preference attribute is attached to a route by the BGP
1915
	protocol itself (for example, if a route is received through eBGP and
1916
	therefore does not have such attribute). Default: 100 (0 in pre-1.2.0
1917
	versions of BIRD).
1918
</descrip>
1919

    
1920
<sect1>Attributes
1921

    
1922
<p>BGP defines several route attributes. Some of them (those marked with
1923
`<tt/I/' in the table below) are available on internal BGP connections only,
1924
some of them (marked with `<tt/O/') are optional.
1925

    
1926
<descrip>
1927
	<tag>bgppath <cf/bgp_path/</tag>
1928
	Sequence of AS numbers describing the AS path the packet will travel
1929
	through when forwarded according to the particular route. In case of
1930
	internal BGP it doesn't contain the number of the local AS.
1931

    
1932
	<tag>int <cf/bgp_local_pref/ [I]</tag>
1933
	Local preference value used for selection among multiple BGP routes (see
1934
	the selection rules above). It's used as an additional metric which is
1935
	propagated through the whole local AS.
1936

    
1937
	<tag>int <cf/bgp_med/ [O]</tag>
1938
	The Multiple Exit Discriminator of the route is an optional attribute
1939
	which is used on external (inter-AS) links to convey to an adjacent AS
1940
	the optimal entry point into the local AS. The received attribute is
1941
	also propagated over internal BGP links. The attribute value is zeroed
1942
	when a route is exported to an external BGP instance to ensure that the
1943
	attribute received from a neighboring AS is not propagated to other
1944
	neighboring ASes. A new value might be set in the export filter of an
1945
	external BGP instance. See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1946
	for further discussion of BGP MED attribute.
1947

    
1948
	<tag>enum <cf/bgp_origin/</tag>
1949
	Origin of the route: either <cf/ORIGIN_IGP/ if the route has originated
1950
	in an interior routing protocol or <cf/ORIGIN_EGP/ if it's been imported
1951
	from the <tt>EGP</tt> protocol (nowadays it seems to be obsolete) or
1952
	<cf/ORIGIN_INCOMPLETE/ if the origin is unknown.
1953

    
1954
	<tag>ip <cf/bgp_next_hop/</tag>
1955
	Next hop to be used for forwarding of packets to this destination. On
1956
	internal BGP connections, it's an address of the originating router if
1957
	it's inside the local AS or a boundary router the packet will leave the
1958
	AS through if it's an exterior route, so each BGP speaker within the AS
1959
	has a chance to use the shortest interior path possible to this point.
1960

    
1961
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag>
1962
	This is an optional attribute which carries no value, but the sole
1963
	presence of which indicates that the route has been aggregated from
1964
	multiple routes by some router on the path from the originator.
1965

    
1966
<!-- we don't handle aggregators right since they are of a very obscure type
1967
	<tag>bgp_aggregator</tag>
1968
-->
1969
	<tag>clist <cf/bgp_community/ [O]</tag>
1970
	List of community values associated with the route. Each such value is a
1971
	pair (represented as a <cf/pair/ data type inside the filters) of 16-bit
1972
	integers, the first of them containing the number of the AS which
1973
	defines the community and the second one being a per-AS identifier.
1974
	There are lots of uses of the community mechanism, but generally they
1975
	are used to carry policy information like "don't export to USA peers".
1976
	As each AS can define its own routing policy, it also has a complete
1977
	freedom about which community attributes it defines and what will their
1978
	semantics be.
1979

    
1980
	<tag>eclist <cf/bgp_ext_community/ [O]</tag>
1981
	List of extended community values associated with the route. Extended
1982
	communities have similar usage as plain communities, but they have an
1983
	extended range (to allow 4B ASNs) and a nontrivial structure with a type
1984
	field. Individual community values are represented using an <cf/ec/ data
1985
	type inside the filters.
1986

    
1987
	<tag>quad <cf/bgp_originator_id/ [I, O]</tag>
1988
	This attribute is created by the route reflector when reflecting the
1989
	route and contains the router ID of the originator of the route in the
1990
	local AS.
1991

    
1992
	<tag>clist <cf/bgp_cluster_list/ [I, O]</tag>
1993
	This attribute contains a list of cluster IDs of route reflectors. Each
1994
	route reflector prepends its cluster ID when reflecting the route.
1995
</descrip>
1996

    
1997
<sect1>Example
1998

    
1999
<p><code>
2000
protocol bgp {
2001
	local as 65000;			     # Use a private AS number
2002
	neighbor 198.51.100.130 as 64496;    # Our neighbor ...
2003
	multihop;			     # ... which is connected indirectly
2004
	export filter {			     # We use non-trivial export rules
2005
		if source = RTS_STATIC then { # Export only static routes
2006
		        # Assign our community
2007
			bgp_community.add((65000,64501));
2008
			# Artificially increase path length
2009
			# by advertising local AS number twice
2010
			if bgp_path ~ [= 65000 =] then
2011
				bgp_path.prepend(65000);
2012
			accept;
2013
		}
2014
		reject;
2015
	};
2016
	import all;
2017
	source address 198.51.100.14;	# Use a non-standard source address
2018
}
2019
</code>
2020

    
2021

    
2022
<sect>Device
2023

    
2024
<p>The Device protocol is not a real routing protocol. It doesn't generate any
2025
routes and it only serves as a module for getting information about network
2026
interfaces from the kernel.
2027

    
2028
<p>Except for very unusual circumstances, you probably should include this
2029
protocol in the configuration since almost all other protocols require network
2030
interfaces to be defined for them to work with.
2031

    
2032
<sect1>Configuration
2033

    
2034
<p><descrip>
2035

    
2036
	<tag>scan time <m/number/</tag>
2037

    
2038
	Time in seconds between two scans of the network interface list. On
2039
	systems where we are notified about interface status changes
2040
	asynchronously (such as newer versions of Linux), we need to scan the
2041
	list only in order to avoid confusion by lost notification messages,
2042
	so the default time is set to a large value.
2043

    
2044
	<tag>primary [ "<m/mask/" ] <m/prefix/</tag>
2045
	If a network interface has more than one network address, BIRD has to
2046
	choose one of them as a primary one. By default, BIRD chooses the
2047
	lexicographically smallest address as the primary one.
2048

    
2049
	This option allows to specify which network address should be chosen as
2050
	a primary one. Network addresses that match <m/prefix/ are preferred to
2051
	non-matching addresses. If more <cf/primary/ options are used, the first
2052
	one has the highest preference. If "<m/mask/" is specified, then such
2053
	<cf/primary/ option is relevant only to matching network interfaces.
2054

    
2055
	In all cases, an address marked by operating system as secondary cannot
2056
	be chosen as the primary one.
2057
</descrip>
2058

    
2059
<p>As the Device protocol doesn't generate any routes, it cannot have
2060
any attributes. Example configuration looks like this:
2061

    
2062
<p><code>
2063
protocol device {
2064
	scan time 10;		# Scan the interfaces often
2065
	primary "eth0" 192.168.1.1;
2066
	primary 192.168.0.0/16;
2067
}
2068
</code>
2069

    
2070

    
2071
<sect>Direct
2072

    
2073
<p>The Direct protocol is a simple generator of device routes for all the
2074
directly connected networks according to the list of interfaces provided by the
2075
kernel via the Device protocol.
2076

    
2077
<p>The question is whether it is a good idea to have such device routes in BIRD
2078
routing table. OS kernel usually handles device routes for directly connected
2079
networks by itself so we don't need (and don't want) to export these routes to
2080
the kernel protocol. OSPF protocol creates device routes for its interfaces
2081
itself and BGP protocol is usually used for exporting aggregate routes. Although
2082
there are some use cases that use the direct protocol (like abusing eBGP as an
2083
IGP routing protocol), in most cases it is not needed to have these device
2084
routes in BIRD routing table and to use the direct protocol.
2085

    
2086
<p>There is one notable case when you definitely want to use the direct protocol
2087
-- running BIRD on BSD systems. Having high priority device routes for directly
2088
connected networks from the direct protocol protects kernel device routes from
2089
being overwritten or removed by IGP routes during some transient network
2090
conditions, because a lower priority IGP route for the same network is not
2091
exported to the kernel routing table. This is an issue on BSD systems only, as
2092
on Linux systems BIRD cannot change non-BIRD route in the kernel routing table.
2093

    
2094
<p>The only configurable thing about direct is what interfaces it watches:
2095

    
2096
<p><descrip>
2097
	<tag>interface <m/pattern [, ...]/</tag>
2098
	By default, the Direct protocol will generate device routes for all the
2099
	interfaces available. If you want to restrict it to some subset of
2100
	interfaces or addresses (e.g. if you're using multiple routing tables
2101
	for policy routing and some of the policy domains don't contain all
2102
	interfaces), just use this clause. See <ref id="dsc-iface" name="interface">
2103
	common option for detailed description. The Direct protocol uses
2104
	extended interface clauses.
2105
</descrip>
2106

    
2107
<p>Direct device routes don't contain any specific attributes.
2108

    
2109
<p>Example config might look like this:
2110

    
2111
<p><code>
2112
protocol direct {
2113
	interface "-arc*", "*";		# Exclude the ARCnets
2114
}
2115
</code>
2116

    
2117

    
2118
<sect>Kernel
2119

    
2120
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
2121
with other routers in the network, it performs synchronization of BIRD's routing
2122
tables with the OS kernel. Basically, it sends all routing table updates to the
2123
kernel and from time to time it scans the kernel tables to see whether some
2124
routes have disappeared (for example due to unnoticed up/down transition of an
2125
interface) or whether an `alien' route has been added by someone else (depending
2126
on the <cf/learn/ switch, such routes are either ignored or accepted to our
2127
table).
2128

    
2129
<p>Unfortunately, there is one thing that makes the routing table synchronization
2130
a bit more complicated. In the kernel routing table there are also device routes
2131
for directly connected networks. These routes are usually managed by OS itself
2132
(as a part of IP address configuration) and we don't want to touch that. They
2133
are completely ignored during the scan of the kernel tables and also the export
2134
of device routes from BIRD tables to kernel routing tables is restricted to
2135
prevent accidental interference. This restriction can be disabled using
2136
<cf/device routes/ switch.
2137

    
2138
<p>If your OS supports only a single routing table, you can configure only one
2139
instance of the Kernel protocol. If it supports multiple tables (in order to
2140
allow policy routing; such an OS is for example Linux), you can run as many
2141
instances as you want, but each of them must be connected to a different BIRD
2142
routing table and to a different kernel table.
2143

    
2144
<p>Because the kernel protocol is partially integrated with the connected
2145
routing table, there are two limitations - it is not possible to connect more
2146
kernel protocols to the same routing table and changing route destination
2147
(gateway) in an export filter of a kernel protocol does not work. Both
2148
limitations can be overcome using another routing table and the pipe protocol.
2149

    
2150
<sect1>Configuration
2151

    
2152
<p><descrip>
2153
	<tag>persist <m/switch/</tag>
2154
	Tell BIRD to leave all its routes in the routing tables when it exits
2155
	(instead of cleaning them up).
2156

    
2157
	<tag>scan time <m/number/</tag>
2158
	Time in seconds between two consecutive scans of the kernel routing
2159
	table.
2160

    
2161
	<tag>learn <m/switch/</tag>
2162
	Enable learning of routes added to the kernel routing tables by other
2163
	routing daemons or by the system administrator. This is possible only on
2164
	systems which support identification of route authorship.
2165

    
2166
	<tag>device routes <m/switch/</tag>
2167
	Enable export of device routes to the kernel routing table. By default,
2168
	such routes are rejected (with the exception of explicitly configured
2169
	device routes from the static protocol) regardless of the export filter
2170
	to protect device routes in kernel routing table (managed by OS itself)
2171
	from accidental overwriting or erasing.
2172

    
2173
	<tag>kernel table <m/number/</tag>
2174
	Select which kernel table should this particular instance of the Kernel
2175
	protocol work with. Available only on systems supporting multiple
2176
	routing tables.
2177

    
2178
	<tag>graceful restart <m/switch/</tag>
2179
	Participate in graceful restart recovery. If this option is enabled and
2180
	a graceful restart recovery is active, the Kernel protocol will defer
2181
	synchronization of routing tables until the end of the recovery. Note
2182
	that import of kernel routes to BIRD is not affected.
2183
</descrip>
2184

    
2185
<sect1>Attributes
2186

    
2187
<p>The Kernel protocol defines several attributes. These attributes are
2188
translated to appropriate system (and OS-specific) route attributes. We support
2189
these attributes:
2190

    
2191
<descrip>
2192
	<tag>int <cf/krt_source/</tag>
2193
	The original source of the imported kernel route. The value is
2194
	system-dependent. On Linux, it is a value of the protocol field of the
2195
	route. See /etc/iproute2/rt_protos for common values. On BSD, it is
2196
	based on STATIC and PROTOx flags. The attribute is read-only.
2197

    
2198
	<tag>int <cf/krt_metric/</tag>
2199
	The kernel metric of the route. When multiple same routes are in a
2200
	kernel routing table, the Linux kernel chooses one with lower metric.
2201

    
2202
	<tag>ip <cf/krt_prefsrc/</tag> (Linux)
2203
	The preferred source address. Used in source address selection for
2204
 	outgoing packets. Have to be one of IP addresses of the router.
2205

    
2206
	<tag>int <cf/krt_realm/</tag> (Linux)
2207
	The realm of the route. Can be used for traffic classification.
2208
</descrip>
2209

    
2210
<sect1>Example
2211

    
2212
<p>A simple configuration can look this way:
2213

    
2214
<p><code>
2215
protocol kernel {
2216
	export all;
2217
}
2218
</code>
2219

    
2220
<p>Or for a system with two routing tables:
2221

    
2222
<p><code>
2223
protocol kernel {		# Primary routing table
2224
	learn;			# Learn alien routes from the kernel
2225
	persist;		# Don't remove routes on bird shutdown
2226
	scan time 10;		# Scan kernel routing table every 10 seconds
2227
	import all;
2228
	export all;
2229
}
2230

    
2231
protocol kernel {		# Secondary routing table
2232
	table auxtable;
2233
	kernel table 100;
2234
	export all;
2235
}
2236
</code>
2237

    
2238

    
2239
<sect>OSPF
2240

    
2241
<sect1>Introduction
2242

    
2243
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
2244
protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328
2245
<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">
2246
and the current IPv6 version (OSPFv3) is defined in RFC 5340
2247
<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt">
2248
It's a link state (a.k.a. shortest path first) protocol -- each router maintains
2249
a database describing the autonomous system's topology. Each participating
2250
router has an identical copy of the database and all routers run the same
2251
algorithm calculating a shortest path tree with themselves as a root. OSPF
2252
chooses the least cost path as the best path.
2253

    
2254
<p>In OSPF, the autonomous system can be split to several areas in order to
2255
reduce the amount of resources consumed for exchanging the routing information
2256
and to protect the other areas from incorrect routing data. Topology of the area
2257
is hidden to the rest of the autonomous system.
2258

    
2259
<p>Another very important feature of OSPF is that it can keep routing information
2260
from other protocols (like Static or BGP) in its link state database as external
2261
routes. Each external route can be tagged by the advertising router, making it
2262
possible to pass additional information between routers on the boundary of the
2263
autonomous system.
2264

    
2265
<p>OSPF quickly detects topological changes in the autonomous system (such as
2266
router interface failures) and calculates new loop-free routes after a short
2267
period of convergence. Only a minimal amount of routing traffic is involved.
2268

    
2269
<p>Each router participating in OSPF routing periodically sends Hello messages
2270
to all its interfaces. This allows neighbors to be discovered dynamically. Then
2271
the neighbors exchange theirs parts of the link state database and keep it
2272
identical by flooding updates. The flooding process is reliable and ensures that
2273
each router detects all changes.
2274

    
2275
<sect1>Configuration
2276

    
2277
<p>In the main part of configuration, there can be multiple definitions of OSPF
2278
areas, each with a different id. These definitions includes many other switches
2279
and multiple definitions of interfaces. Definition of interface may contain many
2280
switches and constant definitions and list of neighbors on nonbroadcast
2281
networks.
2282

    
2283
<code>
2284
protocol ospf &lt;name&gt; {
2285
	rfc1583compat &lt;switch&gt;;
2286
	stub router &lt;switch&gt;;
2287
	tick &lt;num&gt;;
2288
	ecmp &lt;switch&gt; [limit &lt;num&gt;];
2289
	area &lt;id&gt; {
2290
		stub;
2291
		nssa;
2292
		summary &lt;switch&gt;;
2293
		default nssa &lt;switch&gt;;
2294
		default cost &lt;num&gt;;
2295
		default cost2 &lt;num&gt;;
2296
		translator &lt;switch&gt;;
2297
		translator stability &lt;num&gt;;
2298

    
2299
                networks {
2300
			&lt;prefix&gt;;
2301
			&lt;prefix&gt; hidden;
2302
		}
2303
                external {
2304
			&lt;prefix&gt;;
2305
			&lt;prefix&gt; hidden;
2306
			&lt;prefix&gt; tag &lt;num&gt;;
2307
		}
2308
		stubnet &lt;prefix&gt;;
2309
		stubnet &lt;prefix&gt; {
2310
			hidden &lt;switch&gt;;
2311
			summary &lt;switch&gt;;
2312
			cost &lt;num&gt;;
2313
		}
2314
		interface &lt;interface pattern&gt; [instance &lt;num&gt;] {
2315
			cost &lt;num&gt;;
2316
			stub &lt;switch&gt;;
2317
			hello &lt;num&gt;;
2318
			poll &lt;num&gt;;
2319
			retransmit &lt;num&gt;;
2320
			priority &lt;num&gt;;
2321
			wait &lt;num&gt;;
2322
			dead count &lt;num&gt;;
2323
			dead &lt;num&gt;;
2324
			secondary &lt;switch&gt;;
2325
			rx buffer [normal|large|&lt;num&gt;];
2326
			tx length &lt;num&gt;;
2327
			type [broadcast|bcast|pointopoint|ptp|
2328
				nonbroadcast|nbma|pointomultipoint|ptmp];
2329
			strict nonbroadcast &lt;switch&gt;;
2330
			real broadcast &lt;switch&gt;;
2331
			ptp netmask &lt;switch&gt;;
2332
			check link &lt;switch&gt;;
2333
			bfd &lt;switch&gt;;
2334
			ecmp weight &lt;num&gt;;
2335
			ttl security [&lt;switch&gt;; | tx only]
2336
			tx class|dscp &lt;num&gt;;
2337
			tx priority &lt;num&gt;;
2338
			authentication [none|simple|cryptographic];
2339
			password "&lt;text&gt;";
2340
			password "&lt;text&gt;" {
2341
				id &lt;num&gt;;
2342
				generate from "&lt;date&gt;";
2343
				generate to "&lt;date&gt;";
2344
				accept from "&lt;date&gt;";
2345
				accept to "&lt;date&gt;";
2346
			};
2347
			neighbors {
2348
				&lt;ip&gt;;
2349
				&lt;ip&gt; eligible;
2350
			};
2351
		};
2352
		virtual link &lt;id&gt; [instance &lt;num&gt;] {
2353
			hello &lt;num&gt;;
2354
			retransmit &lt;num&gt;;
2355
			wait &lt;num&gt;;
2356
			dead count &lt;num&gt;;
2357
			dead &lt;num&gt;;
2358
			authentication [none|simple|cryptographic];
2359
			password "&lt;text&gt;";
2360
		};
2361
	};
2362
}
2363
</code>
2364

    
2365
<descrip>
2366
	<tag>rfc1583compat <M>switch</M></tag>
2367
	This option controls compatibility of routing table calculation with
2368
	RFC 1583 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">.
2369
	Default	value is no.
2370

    
2371
	<tag>stub router <M>switch</M></tag>
2372
	This option configures the router to be a stub router, i.e., a router
2373
	that participates in the OSPF topology but does not allow transit
2374
	traffic. In OSPFv2, this is implemented by advertising maximum metric
2375
	for outgoing links, as suggested by
2376
	RFC 3137 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3137.txt">.
2377
	In OSPFv3, the stub router behavior is announced by clearing the R-bit
2378
	in the router LSA. Default value is no.
2379

    
2380
	<tag>tick <M>num</M></tag>
2381
	The routing table calculation and clean-up of areas' databases is not
2382
	performed when a single link state change arrives. To lower the CPU
2383
	utilization, it's processed later at periodical intervals of <m/num/
2384
	seconds. The default value is 1.
2385

    
2386
	<tag>ecmp <M>switch</M> [limit <M>number</M>]</tag>
2387
	This option specifies whether OSPF is allowed to generate ECMP
2388
	(equal-cost multipath) routes. Such routes are used when there are
2389
	several directions to the destination, each with the same (computed)
2390
	cost. This option also allows to specify a limit on maximal number of
2391
	nexthops in one route. By default, ECMP is disabled. If enabled,
2392
	default	value of the limit is 16.
2393

    
2394
	<tag>area <M>id</M></tag>
2395
	This defines an OSPF area with given area ID (an integer or an IPv4
2396
	address, similarly to a router ID). The most important area is the
2397
	backbone (ID 0) to which every other area must be connected.
2398

    
2399
	<tag>stub</tag>
2400
	This option configures the area to be a stub area. External routes are
2401
	not flooded into stub areas. Also summary LSAs can be limited in stub
2402
	areas (see option <cf/summary/). By default, the area is not a stub
2403
	area.
2404

    
2405
	<tag>nssa</tag>
2406
	This option configures the area to be a NSSA (Not-So-Stubby Area). NSSA
2407
	is a variant of a stub area which allows a limited way of external route
2408
	propagation. Global external routes are not propagated into a NSSA, but
2409
	an external route can be imported into NSSA as a (area-wide) NSSA-LSA
2410
	(and possibly translated and/or aggregated on area boundary). By
2411
	default, the area is not NSSA.
2412

    
2413
	<tag>summary <M>switch</M></tag>
2414
	This option controls propagation of summary LSAs into stub or NSSA
2415
	areas. If enabled, summary LSAs are propagated as usual, otherwise just
2416
	the default summary route (0.0.0.0/0) is propagated (this is sometimes
2417
	called totally stubby area). If a stub area has more area boundary
2418
	routers, propagating summary LSAs could lead to more efficient routing
2419
	at the cost of larger link state database. Default value is no.
2420

    
2421
	<tag>default nssa <M>switch</M></tag>
2422
	When <cf/summary/ option is enabled, default summary route is no longer
2423
	propagated to the NSSA. In that case, this option allows to originate
2424
	default route as NSSA-LSA to the NSSA. Default value is no.
2425

    
2426
	<tag>default cost <M>num</M></tag>
2427
	This option controls the cost of a default route propagated to stub and
2428
	NSSA areas. Default value is 1000.
2429

    
2430
	<tag>default cost2 <M>num</M></tag>
2431
	When a default route is originated as NSSA-LSA, its cost can use either
2432
	type 1 or type 2 metric. This option allows to specify the cost of a
2433
	default route in type 2 metric. By default, type 1 metric (option
2434
	<cf/default cost/) is used.
2435

    
2436
	<tag>translator <M>switch</M></tag>
2437
	This option controls translation of NSSA-LSAs into external LSAs. By
2438
	default, one translator per NSSA is automatically elected from area
2439
	boundary routers. If enabled, this area boundary router would
2440
	unconditionally translate all NSSA-LSAs regardless of translator
2441
	election. Default value is no.
2442

    
2443
	<tag>translator stability <M>num</M></tag>
2444
	This option controls the translator stability interval (in seconds).
2445
	When the new translator is elected, the old one keeps translating until
2446
	the interval is over. Default value is 40.
2447

    
2448
	<tag>networks { <m/set/ }</tag>
2449
	Definition of area IP ranges. This is used in summary LSA origination.
2450
	Hidden networks are not propagated into other areas.
2451

    
2452
	<tag>external { <m/set/ }</tag>
2453
	Definition of external area IP ranges for NSSAs. This is used for
2454
	NSSA-LSA translation. Hidden networks are not translated into external
2455
	LSAs. Networks can have configured route tag.
2456

    
2457
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
2458
	Stub networks are networks that are not transit networks between OSPF
2459
	routers. They are also propagated through an OSPF area as a part of a
2460
	link state database. By default, BIRD generates a stub network record
2461
	for each primary network address on each OSPF interface that does not
2462
	have any OSPF neighbors, and also for each non-primary network address
2463
	on each OSPF interface. This option allows to alter a set of stub
2464
	networks propagated by this router.
2465

    
2466
	Each instance of this option adds a stub network with given network
2467
	prefix to the set of propagated stub network, unless option <cf/hidden/
2468
	is used. It also suppresses default stub networks for given network
2469
	prefix. When option <cf/summary/ is used, also default stub networks
2470
	that are subnetworks of given stub network are suppressed. This might be
2471
	used, for example, to aggregate generated stub networks.
2472
	 
2473
	<tag>interface <M>pattern</M> [instance <m/num/]</tag>
2474
	Defines that the specified interfaces belong to the area being defined.
2475
	See <ref id="dsc-iface" name="interface"> common option for detailed
2476
	description. In OSPFv2, extended interface clauses are used, because
2477
	OSPFv2 handles each network prefix as a separate virtual interface. In
2478
	OSPFv3, you can specify instance ID for that interface description, so
2479
	it is possible to have several instances of that interface with
2480
	different options or even in different areas.
2481

    
2482
	<tag>virtual link <M>id</M> [instance <m/num/]</tag>
2483
	Virtual link to router with the router id. Virtual link acts as a
2484
	point-to-point interface belonging to backbone. The actual area is used
2485
	as transport area. This item cannot be in the backbone. In OSPFv3, you
2486
	could also use several virtual links to one destination with different
2487
	instance IDs.
2488

    
2489
	<tag>cost <M>num</M></tag>
2490
	Specifies output cost (metric) of an interface. Default value is 10.
2491

    
2492
	<tag>stub <M>switch</M></tag>
2493
	If set to interface it does not listen to any packet and does not send
2494
	any hello. Default value is no.
2495

    
2496
	<tag>hello <M>num</M></tag>
2497
	Specifies interval in seconds between sending of Hello messages. Beware,
2498
	all routers on the same network need to have the same hello interval.
2499
	Default value is 10.
2500

    
2501
	<tag>poll <M>num</M></tag>
2502
	Specifies interval in seconds between sending of Hello messages for some
2503
	neighbors on NBMA network. Default value is 20.
2504

    
2505
	<tag>retransmit <M>num</M></tag>
2506
	Specifies interval in seconds between retransmissions of unacknowledged
2507
	updates. Default value is 5.
2508

    
2509
	<tag>priority <M>num</M></tag>
2510
	On every multiple access network (e.g., the Ethernet) Designed Router
2511
	and Backup Designed router are elected. These routers have some special
2512
	functions in the flooding process. Higher priority increases preferences
2513
	in this election. Routers with priority 0 are not eligible. Default
2514
	value is 1.
2515

    
2516
	<tag>wait <M>num</M></tag>
2517
	After start, router waits for the specified number of seconds between
2518
	starting election and building adjacency. Default value is 40.
2519
	 
2520
	<tag>dead count <M>num</M></tag>
2521
	When the router does not receive any messages from a neighbor in
2522
	<m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
2523

    
2524
	<tag>dead <M>num</M></tag>
2525
	When the router does not receive any messages from a neighbor in
2526
	<m/dead/ seconds, it will consider the neighbor down. If both directives
2527
	<cf/dead count/ and <cf/dead/ are used, <cf/dead/ has precendence.
2528

    
2529
	<tag>secondary <M>switch</M></tag>
2530
	On BSD systems, older versions of BIRD supported OSPFv2 only for the
2531
	primary IP address of an interface, other IP ranges on the interface
2532
	were handled as stub networks. Since v1.4.1, regular operation on
2533
	secondary IP addresses is supported, but disabled by default for
2534
	compatibility. This option allows to enable it. The option is a
2535
	transitional measure, will be removed in the next major release as the
2536
	behavior will be changed. On Linux systems, the option is irrelevant, as
2537
	operation on non-primary addresses is already the regular behavior.
2538

    
2539
	<tag>rx buffer <M>num</M></tag>
2540
	This option allows to specify the size of buffers used for packet
2541
	processing. The buffer size should be bigger than maximal size of any
2542
	packets. By default, buffers are dynamically resized as needed, but a
2543
	fixed value could be specified. Value <cf/large/ means maximal allowed
2544
	packet size - 65535.
2545

    
2546
	<tag>tx length <M>num</M></tag>
2547
	Transmitted OSPF messages that contain large amount of information are
2548
	segmented to separate OSPF packets to avoid IP fragmentation. This
2549
	option specifies the soft ceiling for the length of generated OSPF
2550
	packets. Default value is the MTU of the network interface. Note that
2551
	larger OSPF packets may still be generated if underlying OSPF messages
2552
	cannot be splitted (e.g. when one large LSA is propagated).
2553

    
2554
	<tag>type broadcast|bcast</tag>
2555
	BIRD detects a type of a connected network automatically, but sometimes
2556
	it's convenient to force use of a different type manually. On broadcast
2557
	networks (like ethernet), flooding and Hello messages are sent using
2558
	multicasts (a single packet for all the neighbors). A designated router
2559
	is elected and it is responsible for synchronizing the link-state
2560
	databases and originating network LSAs. This network type cannot be used
2561
	on physically NBMA networks and on unnumbered networks (networks without
2562
	proper IP prefix).
2563

    
2564
	<tag>type pointopoint|ptp</tag>
2565
	Point-to-point networks connect just 2 routers together. No election is
2566
	performed and no network LSA is originated, which makes it simpler and
2567
	faster to establish. This network type is useful not only for physically
2568
	PtP ifaces (like PPP or tunnels), but also for broadcast networks used
2569
	as PtP links. This network type cannot be used on physically NBMA
2570
	networks.
2571

    
2572
	<tag>type nonbroadcast|nbma</tag>
2573
	On NBMA networks, the packets are sent to each neighbor separately
2574
	because of lack of multicast capabilities. Like on broadcast networks,
2575
	a designated router is elected, which plays a central role in propagation
2576
	of LSAs. This network type cannot be used on unnumbered networks.
2577

    
2578
	<tag>type pointomultipoint|ptmp</tag>
2579
	This is another network type designed to handle NBMA networks. In this
2580
	case the NBMA network is treated as a collection of PtP links. This is
2581
	useful if not every pair of routers on the NBMA network has direct
2582
	communication, or if the NBMA network is used as an (possibly
2583
	unnumbered) PtP link.
2584

    
2585
	<tag>strict nonbroadcast <M>switch</M></tag>
2586
	If set, don't send hello to any undefined neighbor. This switch is
2587
	ignored on other than NBMA or PtMP networks. Default value is no.
2588

    
2589
	<tag>real broadcast <m/switch/</tag>
2590
	In <cf/type broadcast/ or <cf/type ptp/ network configuration, OSPF
2591
	packets are sent as IP multicast packets. This option changes the
2592
	behavior to using old-fashioned IP broadcast packets. This may be useful
2593
	as a workaround if IP multicast for some reason does not work or does
2594
	not work reliably. This is a non-standard option and probably is not
2595
	interoperable with other OSPF implementations. Default value is no.
2596

    
2597
	<tag>ptp netmask <m/switch/</tag>
2598
	In <cf/type ptp/ network configurations, OSPFv2 implementations should
2599
	ignore received netmask field in hello packets and should send hello
2600
	packets with zero netmask field on unnumbered PtP links. But some OSPFv2
2601
	implementations perform netmask checking even for PtP links. This option
2602
	specifies whether real netmask will be used in hello packets on <cf/type
2603
 	ptp/ interfaces. You should ignore this option unless you meet some
2604
	compatibility problems related to this issue. Default value is no for
2605
	unnumbered PtP links, yes otherwise.
2606

    
2607
	<tag>check link <M>switch</M></tag>
2608
	If set, a hardware link state (reported by OS) is taken into consideration.
2609
	When a link disappears (e.g. an ethernet cable is unplugged), neighbors
2610
	are immediately considered unreachable and only the address of the iface
2611
	(instead of whole network prefix) is propagated. It is possible that
2612
	some hardware drivers or platforms do not implement this feature.
2613
	Default value is no.
2614

    
2615
	<tag>bfd <M>switch</M></tag>
2616
	OSPF could use BFD protocol as an advisory mechanism for neighbor
2617
	liveness and failure detection. If enabled, BIRD setups a BFD session
2618
	for each OSPF neighbor and tracks its liveness by it. This has an
2619
	advantage of an order of magnitude lower detection times in case of
2620
	failure. Note that BFD protocol also has to be configured, see
2621
	<ref id="sect-bfd" name="BFD"> section for details. Default value is no.
2622

    
2623
	<tag>ttl security [<m/switch/ | tx only]</tag>
2624
	TTL security is a feature that protects routing protocols from remote
2625
	spoofed packets by using TTL 255 instead of TTL 1 for protocol packets
2626
	destined to neighbors. Because TTL is decremented when packets are
2627
	forwarded, it is non-trivial to spoof packets with TTL 255 from remote
2628
	locations. Note that this option would interfere with OSPF virtual
2629
	links.
2630

    
2631
	If this option is enabled, the router will send OSPF packets with TTL
2632
	255 and drop received packets with TTL less than 255. If this option si
2633
	set to <cf/tx only/, TTL 255 is used for sent packets, but is not
2634
	checked for received packets. Default value is no.
2635

    
2636
	<tag>tx class|dscp|priority <m/num/</tag>
2637
	These options specify the ToS/DiffServ/Traffic class/Priority of the
2638
	outgoing OSPF packets. See <ref id="dsc-prio" name="tx class"> common
2639
	option for detailed description.
2640

    
2641
	<tag>ecmp weight <M>num</M></tag>
2642
	When ECMP (multipath) routes are allowed, this value specifies a
2643
	relative weight used for nexthops going through the iface. Allowed
2644
	values are 1-256. Default value is 1.
2645

    
2646
	<tag>authentication none</tag>
2647
	No passwords are sent in OSPF packets. This is the default value.
2648

    
2649
	<tag>authentication simple</tag>
2650
	Every packet carries 8 bytes of password. Received packets lacking this
2651
	password are ignored. This authentication mechanism is very weak.
2652

    
2653
	<tag>authentication cryptographic</tag>
2654
	16-byte long MD5 digest is appended to every packet. For the digest
2655
	generation 16-byte long passwords are used. Those passwords are not sent
2656
	via network, so this mechanism is quite secure. Packets can still be
2657
	read by an attacker.
2658

    
2659
	<tag>password "<M>text</M>"</tag>
2660
	An 8-byte or 16-byte password used for authentication. See
2661
	<ref id="dsc-pass" name="password"> common option for detailed
2662
	description.
2663

    
2664
	<tag>neighbors { <m/set/ } </tag>
2665
	A set of neighbors to which Hello messages on NBMA or PtMP networks are
2666
	to be sent. For NBMA networks, some of them could be marked as eligible.
2667
	In OSPFv3, link-local addresses should be used, using global ones is
2668
	possible, but it is nonstandard and might be problematic. And definitely,
2669
	link-local and global addresses should not be mixed.
2670
</descrip>
2671

    
2672
<sect1>Attributes
2673

    
2674
<p>OSPF defines four route attributes. Each internal route has a <cf/metric/.
2675

    
2676
<p>Metric is ranging from 1 to infinity (65535). External routes use
2677
<cf/metric type 1/ or <cf/metric type 2/. A <cf/metric of type 1/ is comparable
2678
with internal <cf/metric/, a <cf/metric of type 2/ is always longer than any
2679
<cf/metric of type 1/ or any <cf/internal metric/. <cf/Internal metric/ or
2680
<cf/metric of type 1/ is stored in attribute <cf/ospf_metric1/, <cf/metric type
2681
2/ is stored in attribute <cf/ospf_metric2/. If you specify both metrics only
2682
metric1 is used.
2683

    
2684
<p>Each external route can also carry attribute <cf/ospf_tag/ which is a 32-bit
2685
integer which is used when exporting routes to other protocols; otherwise, it
2686
doesn't affect routing inside the OSPF domain at all. The fourth attribute
2687
<cf/ospf_router_id/ is a router ID of the router advertising that route /
2688
network. This attribute is read-only. Default is <cf/ospf_metric2 = 10000/ and
2689
<cf/ospf_tag = 0/.
2690

    
2691
<sect1>Example
2692

    
2693
<p><code>
2694
protocol ospf MyOSPF {
2695
	rfc1583compat yes;
2696
	tick 2;
2697
	export filter {
2698
		if source = RTS_BGP then {
2699
			ospf_metric1 = 100;
2700
			accept;
2701
		}
2702
		reject;
2703
	};
2704
	area 0.0.0.0 {
2705
		interface "eth*" {
2706
			cost 11;
2707
			hello 15;
2708
			priority 100;
2709
			retransmit 7;
2710
			authentication simple;
2711
			password "aaa";
2712
		};
2713
		interface "ppp*" {
2714
			cost 100;
2715
			authentication cryptographic;
2716
			password "abc" {
2717
				id 1;
2718
				generate to "22-04-2003 11:00:06";
2719
				accept from "17-01-2001 12:01:05";
2720
			};
2721
			password "def" {
2722
				id 2;
2723
				generate to "22-07-2005 17:03:21";
2724
				accept from "22-02-2001 11:34:06";
2725
			};
2726
		};
2727
		interface "arc0" {
2728
			cost 10;
2729
			stub yes;
2730
		};
2731
		interface "arc1";
2732
	};
2733
	area 120 {
2734
		stub yes;
2735
		networks {
2736
			172.16.1.0/24;
2737
			172.16.2.0/24 hidden;
2738
		}
2739
		interface "-arc0" , "arc*" {
2740
			type nonbroadcast;
2741
			authentication none;
2742
			strict nonbroadcast yes;
2743
			wait 120;
2744
			poll 40;
2745
			dead count 8;
2746
			neighbors {
2747
				192.168.120.1 eligible;
2748
				192.168.120.2;
2749
				192.168.120.10;
2750
			};
2751
		};
2752
	};
2753
}
2754
</code>
2755

    
2756

    
2757
<sect>Pipe
2758

    
2759
<sect1>Introduction
2760

    
2761
<p>The Pipe protocol serves as a link between two routing tables, allowing
2762
routes to be passed from a table declared as primary (i.e., the one the pipe is
2763
connected to using the <cf/table/ configuration keyword) to the secondary one
2764
(declared using <cf/peer table/) and vice versa, depending on what's allowed by
2765
the filters. Export filters control export of routes from the primary table to
2766
the secondary one, import filters control the opposite direction.
2767

    
2768
<p>The Pipe protocol may work in the transparent mode mode or in the opaque
2769
mode. In the transparent mode, the Pipe protocol retransmits all routes from
2770
one table to the other table, retaining their original source and attributes.
2771
If import and export filters are set to accept, then both tables would have
2772
the same content. The transparent mode is the default mode.
2773

    
2774
<p>In the opaque mode, the Pipe protocol retransmits optimal route from one
2775
table to the other table in a similar way like other protocols send and receive
2776
routes. Retransmitted route will have the source set to the Pipe protocol, which
2777
may limit access to protocol specific route attributes. This mode is mainly for
2778
compatibility, it is not suggested for new configs. The mode can be changed by
2779
<tt/mode/ option.
2780

    
2781
<p>The primary use of multiple routing tables and the Pipe protocol is for
2782
policy routing, where handling of a single packet doesn't depend only on its
2783
destination address, but also on its source address, source interface, protocol
2784
type and other similar parameters. In many systems (Linux being a good example),
2785
the kernel allows to enforce routing policies by defining routing rules which
2786
choose one of several routing tables to be used for a packet according to its
2787
parameters. Setting of these rules is outside the scope of BIRD's work (on
2788
Linux, you can use the <tt/ip/ command), but you can create several routing
2789
tables in BIRD, connect them to the kernel ones, use filters to control which
2790
routes appear in which tables and also you can employ the Pipe protocol for
2791
exporting a selected subset of one table to another one.
2792

    
2793
<sect1>Configuration
2794

    
2795
<p><descrip>
2796
	<tag>peer table <m/table/</tag>
2797
	Defines secondary routing table to connect to. The primary one is
2798
	selected by the <cf/table/ keyword.
2799

    
2800
	<tag>mode opaque|transparent</tag>
2801
	Specifies the mode for the pipe to work in. Default is transparent.
2802
</descrip>
2803

    
2804
<sect1>Attributes
2805

    
2806
<p>The Pipe protocol doesn't define any route attributes.
2807

    
2808
<sect1>Example
2809

    
2810
<p>Let's consider a router which serves as a boundary router of two different
2811
autonomous systems, each of them connected to a subset of interfaces of the
2812
router, having its own exterior connectivity and wishing to use the other AS as
2813
a backup connectivity in case of outage of its own exterior line.
2814

    
2815
<p>Probably the simplest solution to this situation is to use two routing tables
2816
(we'll call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that
2817
packets having arrived from interfaces belonging to the first AS will be routed
2818
according to <cf/as1/ and similarly for the second AS. Thus we have split our
2819
router to two logical routers, each one acting on its own routing table, having
2820
its own routing protocols on its own interfaces. In order to use the other AS's
2821
routes for backup purposes, we can pass the routes between the tables through a
2822
Pipe protocol while decreasing their preferences and correcting their BGP paths
2823
to reflect the AS boundary crossing.
2824

    
2825
<code>
2826
table as1;				# Define the tables
2827
table as2;
2828

    
2829
protocol kernel kern1 {			# Synchronize them with the kernel
2830
	table as1;
2831
	kernel table 1;
2832
}
2833

    
2834
protocol kernel kern2 {
2835
	table as2;
2836
	kernel table 2;
2837
}
2838

    
2839
protocol bgp bgp1 {			# The outside connections
2840
	table as1;
2841
	local as 1;
2842
	neighbor 192.168.0.1 as 1001;
2843
	export all;
2844
	import all;
2845
}
2846

    
2847
protocol bgp bgp2 {
2848
	table as2;
2849
	local as 2;
2850
	neighbor 10.0.0.1 as 1002;
2851
	export all;
2852
	import all;
2853
}
2854

    
2855
protocol pipe {				# The Pipe
2856
	table as1;
2857
	peer table as2;
2858
	export filter {
2859
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
2860
			if preference>10 then preference = preference-10;
2861
			if source=RTS_BGP then bgp_path.prepend(1);
2862
			accept;
2863
		}
2864
		reject;
2865
	};
2866
	import filter {
2867
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
2868
			if preference>10 then preference = preference-10;
2869
			if source=RTS_BGP then bgp_path.prepend(2);
2870
			accept;
2871
		}
2872
		reject;
2873
	};
2874
}
2875
</code>
2876

    
2877

    
2878
<sect>RAdv
2879

    
2880
<sect1>Introduction
2881

    
2882
<p>The RAdv protocol is an implementation of Router Advertisements, which are
2883
used in the IPv6 stateless autoconfiguration. IPv6 routers send (in irregular
2884
time intervals or as an answer to a request) advertisement packets to connected
2885
networks. These packets contain basic information about a local network (e.g. a
2886
list of network prefixes), which allows network hosts to autoconfigure network
2887
addresses and choose a default route. BIRD implements router behavior as defined
2888
in RFC 4861<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4861.txt">
2889
and also the DNS extensions from
2890
RFC 6106<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc6106.txt">.
2891

    
2892
<sect1>Configuration
2893

    
2894
<p>There are several classes of definitions in RAdv configuration -- interface
2895
definitions, prefix definitions and DNS definitions:
2896

    
2897
<descrip>
2898
	<tag>interface <m/pattern [, ...]/ { <m/options/ }</tag>
2899
	Interface definitions specify a set of interfaces on which the
2900
	protocol is activated and contain interface specific options.
2901
	See <ref id="dsc-iface" name="interface"> common options for
2902
	detailed description.
2903

    
2904
	<tag>prefix <m/prefix/ { <m/options/ }</tag>
2905
	Prefix definitions allow to modify a list of advertised prefixes. By
2906
	default, the advertised prefixes are the same as the network prefixes
2907
	assigned to the interface. For each network prefix, the matching prefix
2908
	definition is found and its options are used. If no matching prefix
2909
	definition is found, the prefix is used with default options.
2910

    
2911
	Prefix definitions can be either global or interface-specific. The
2912
	second ones are part of interface options. The prefix definition
2913
	matching is done in the first-match style, when interface-specific
2914
	definitions are processed before global definitions. As expected, the
2915
	prefix definition is matching if the network prefix is a subnet of the
2916
	prefix in prefix definition.
2917

    
2918
	<tag>rdnss { <m/options/ }</tag>
2919
	RDNSS definitions allow to specify a list of advertised recursive DNS
2920
	servers together with their options. As options are seldom necessary,
2921
	there is also a short variant <cf>rdnss <m/address/</cf> that just
2922
	specifies one DNS server. Multiple definitions are cumulative. RDNSS
2923
	definitions may also be interface-specific when used inside interface
2924
	options. By default, interface uses both global and interface-specific
2925
	options, but that can be changed by <cf/rdnss local/ option.
2926

    
2927
	<tag>dnssl { <m/options/ }</tag>
2928
	DNSSL definitions allow to specify a list of advertised DNS search
2929
	domains together with their options. Like <cf/rdnss/ above, multiple
2930
	definitions are cumulative, they can be used also as interface-specific
2931
	options and there is a short variant <cf>dnssl <m/domain/</cf> that just
2932
	specifies one DNS search domain.
2933

    
2934
	<label id="dsc-trigger"> <tag>trigger <m/prefix/</tag>
2935
	RAdv protocol could be configured to change its behavior based on
2936
	availability of routes. When this option is used, the protocol waits in
2937
	suppressed state until a <it/trigger route/ (for the specified network)
2938
	is exported to the protocol, the protocol also returnsd to suppressed
2939
	state if the <it/trigger route/ disappears. Note that route export
2940
	depends on specified export filter, as usual. This option could be used,
2941
	e.g., for handling failover in multihoming scenarios.
2942

    
2943
	During suppressed state, router advertisements are generated, but with
2944
	some fields zeroed. Exact behavior depends on which fields are zeroed,
2945
	this can be configured by <cf/sensitive/ option for appropriate
2946
	fields. By default, just <cf/default lifetime/ (also called <cf/router
2947
	lifetime/) is zeroed, which means hosts cannot use the router as a
2948
	default router. <cf/preferred lifetime/ and <cf/valid lifetime/ could
2949
	also be configured as <cf/sensitive/ for a prefix, which would cause
2950
	autoconfigured IPs to be deprecated or even removed.
2951
</descrip>
2952

    
2953
<p>Interface specific options:
2954

    
2955
<descrip>
2956
	<tag>max ra interval <m/expr/</tag>
2957
	Unsolicited router advertisements are sent in irregular time intervals.
2958
	This option specifies the maximum length of these intervals, in seconds.
2959
	Valid values are 4-1800. Default: 600
2960

    
2961
	<tag>min ra interval <m/expr/</tag>
2962
	This option specifies the minimum length of that intervals, in seconds.
2963
	Must be at least 3 and at most 3/4 * <cf/max ra interval/. Default:
2964
	about 1/3 * <cf/max ra interval/.
2965

    
2966
	<tag>min delay <m/expr/</tag>
2967
	The minimum delay between two consecutive router advertisements, in
2968
	seconds. Default: 3
2969

    
2970
	<tag>managed <m/switch/</tag>
2971
	This option specifies whether hosts should use DHCPv6 for IP address
2972
	configuration. Default: no
2973

    
2974
	<tag>other config <m/switch/</tag>
2975
	This option specifies whether hosts should use DHCPv6 to receive other
2976
	configuration information. Default: no
2977

    
2978
	<tag>link mtu <m/expr/</tag>
2979
	This option specifies which value of MTU should be used by hosts. 0
2980
	means unspecified. Default: 0
2981

    
2982
	<tag>reachable time <m/expr/</tag>
2983
	This option specifies the time (in milliseconds) how long hosts should
2984
	assume a neighbor is reachable (from the last confirmation). Maximum is
2985
	3600000, 0 means unspecified. Default 0.
2986

    
2987
	<tag>retrans timer <m/expr/</tag>
2988
	This option specifies the time (in milliseconds) how long hosts should
2989
	wait before retransmitting Neighbor Solicitation messages. 0 means
2990
	unspecified. Default 0.
2991

    
2992
	<tag>current hop limit <m/expr/</tag>
2993
	This option specifies which value of Hop Limit should be used by
2994
	hosts. Valid values are 0-255, 0 means unspecified. Default: 64
2995

    
2996
	<tag>default lifetime <m/expr/ [sensitive <m/switch/]</tag>
2997
	This option specifies the time (in seconds) how long (after the receipt
2998
	of RA) hosts may use the router as a default router. 0 means do not use
2999
	as a default router. For <cf/sensitive/ option, see <ref id="dsc-trigger" name="trigger">.
3000
	Default: 3 * <cf/max ra	interval/, <cf/sensitive/ yes.
3001

    
3002
	<tag>rdnss local <m/switch/</tag>
3003
	Use only local (interface-specific) RDNSS definitions for this
3004
	interface. Otherwise, both global and local definitions are used. Could
3005
	also be used to disable RDNSS for given interface if no local definitons
3006
	are specified. Default: no.
3007

    
3008
	<tag>dnssl local <m/switch/</tag>
3009
	Use only local DNSSL definitions for this interface. See <cf/rdnss local/
3010
	option above. Default: no.
3011
</descrip>
3012

    
3013

    
3014
<p>Prefix specific options:
3015

    
3016
<descrip>
3017
	<tag>skip <m/switch/</tag>
3018
	This option allows to specify that given prefix should not be
3019
	advertised. This is useful for making exceptions from a default policy
3020
	of advertising all prefixes. Note that for withdrawing an already
3021
	advertised prefix it is more useful to advertise it with zero valid
3022
	lifetime. Default: no
3023

    
3024
	<tag>onlink <m/switch/</tag>
3025
	This option specifies whether hosts may use the advertised prefix for
3026
	onlink determination. Default: yes
3027

    
3028
	<tag>autonomous <m/switch/</tag>
3029
	This option specifies whether hosts may use the advertised prefix for
3030
	stateless autoconfiguration. Default: yes
3031

    
3032
	<tag>valid lifetime <m/expr/ [sensitive <m/switch/]</tag>
3033
	This option specifies the time (in seconds) how long (after the
3034
	receipt of RA) the prefix information is valid, i.e., autoconfigured
3035
	IP addresses can be assigned and hosts with that IP addresses are
3036
	considered directly reachable. 0 means the prefix is no longer
3037
	valid. For <cf/sensitive/ option, see <ref id="dsc-trigger" name="trigger">.
3038
	Default: 86400 (1 day), <cf/sensitive/ no.
3039

    
3040
	<tag>preferred lifetime <m/expr/ [sensitive <m/switch/]</tag>
3041
	This option specifies the time (in seconds) how long (after the
3042
	receipt of RA) IP addresses generated from the prefix using stateless
3043
	autoconfiguration remain preferred. For <cf/sensitive/ option,
3044
	see <ref id="dsc-trigger" name="trigger">. Default: 14400 (4 hours),
3045
	<cf/sensitive/ no.
3046
</descrip>
3047

    
3048

    
3049
<p>RDNSS specific options:
3050

    
3051
<descrip>
3052
	<tag>ns <m/address/</tag>
3053
	This option specifies one recursive DNS server. Can be used multiple
3054
	times for multiple servers. It is mandatory to have at least one
3055
	<cf/ns/ option in <cf/rdnss/ definition.
3056

    
3057
	<tag>lifetime [mult] <m/expr/</tag>
3058
	This option specifies the time how long the RDNSS information may be
3059
	used by clients after the receipt of RA. It is expressed either in
3060
	seconds or (when <cf/mult/ is used) in multiples of <cf/max ra
3061
	interval/. Note that RDNSS information is also invalidated when
3062
	<cf/default lifetime/ expires. 0 means these addresses are no longer
3063
	valid DNS servers. Default: 3 * <cf/max ra interval/.
3064
</descrip>
3065

    
3066

    
3067
<p>DNSSL specific options:
3068

    
3069
<descrip>
3070
	<tag>domain <m/address/</tag>
3071
	This option specifies one DNS search domain. Can be used multiple times
3072
	for multiple domains. It is mandatory to have at least one <cf/domain/
3073
	option in <cf/dnssl/ definition.
3074

    
3075
	<tag>lifetime [mult] <m/expr/</tag>
3076
	This option specifies the time how long the DNSSL information may be
3077
	used by clients after the receipt of RA. Details are the same as for
3078
	RDNSS <cf/lifetime/ option above. Default: 3 * <cf/max ra interval/.
3079
</descrip>
3080

    
3081

    
3082
<sect1>Example
3083

    
3084
<p><code>
3085
protocol radv {
3086
	interface "eth2" {
3087
		max ra interval 5;	# Fast failover with more routers
3088
		managed yes;		# Using DHCPv6 on eth2
3089
		prefix ::/0 {
3090
			autonomous off;	# So do not autoconfigure any IP
3091
		};
3092
	};
3093

    
3094
	interface "eth*";		# No need for any other options
3095

    
3096
	prefix 2001:0DB8:1234::/48 {
3097
		preferred lifetime 0;	# Deprecated address range
3098
	};
3099

    
3100
	prefix 2001:0DB8:2000::/48 {
3101
		autonomous off;		# Do not autoconfigure
3102
	};
3103

    
3104
	rdnss 2001:0DB8:1234::10;	# Short form of RDNSS
3105

    
3106
	rdnss {
3107
		lifetime mult 10;
3108
		ns 2001:0DB8:1234::11;
3109
		ns 2001:0DB8:1234::12;
3110
	};
3111

    
3112
	dnssl {
3113
		lifetime 3600;
3114
		domain "abc.com";
3115
		domain "xyz.com";
3116
	};
3117
}
3118
</code>
3119

    
3120

    
3121
<sect>RIP
3122

    
3123
<sect1>Introduction
3124

    
3125
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol,
3126
where each router broadcasts (to all its neighbors) distances to all networks it
3127
can reach. When a router hears distance to another network, it increments it and
3128
broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some
3129
network goes unreachable, routers keep telling each other that its distance is
3130
the original distance plus 1 (actually, plus interface metric, which is usually
3131
one). After some time, the distance reaches infinity (that's 15 in RIP) and all
3132
routers know that network is unreachable. RIP tries to minimize situations where
3133
counting to infinity is necessary, because it is slow. Due to infinity being 16,
3134
you can't use RIP on networks where maximal distance is higher than 15
3135
hosts. You can read more about RIP at
3136
<HTMLURL URL="http://www.ietf.org/html.charters/rip-charter.html"
3137
name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4
3138
(RFC 1723 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">) and IPv6
3139
(RFC 2080 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2080.txt">) versions
3140
of RIP are supported by BIRD, historical RIPv1
3141
(RFC 1058 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1058.txt">) is not
3142
currently supported. RIPv4 MD5 authentication
3143
(RFC 2082 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is
3144
supported.
3145

    
3146
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
3147
convergence, big network load and inability to handle larger networks makes it
3148
pretty much obsolete. It is still usable on very small networks.
3149

    
3150
<sect1>Configuration
3151

    
3152
<p>In addition to options common for all to other protocols, RIP supports the
3153
following ones:
3154

    
3155
<descrip>
3156
	<tag>authentication none|plaintext|md5</tag>
3157
	Selects authentication method to be used. <cf/none/ means that packets
3158
	are not authenticated at all, <cf/plaintext/ means that a plaintext
3159
	password is embedded into each packet, and <cf/md5/ means that packets
3160
	are authenticated using a MD5 cryptographic hash. If you set
3161
	authentication to not-none, it is a good idea to add <cf>password</cf>
3162
	section. Default: none.
3163

    
3164
	<tag>honor always|neighbor|never</tag>
3165
	Specifies when should requests for dumping routing table be honored.
3166
	(Always, when sent from a host on a directly connected network or
3167
	never.) Routing table updates are honored only from neighbors, that is
3168
	not configurable. Default: never.
3169
</descrip>
3170

    
3171
<p>There are some options that can be specified per-interface:
3172

    
3173
<descrip>
3174
	<tag>metric <m/num/</tag>
3175
	This option specifies the metric of the interface. Valid
3176

    
3177
	<tag>mode multicast|broadcast|quiet|nolisten|version1</tag>
3178
	This option selects the mode for RIP to use on the interface. If nothing
3179
	is specified, RIP runs in multicast mode. <cf/version1/ is currently
3180
	equivalent to <cf/broadcast/, and it makes RIP talk to a broadcast
3181
	address even through multicast mode is possible. <cf/quiet/ option means
3182
	that RIP will not transmit any periodic messages to this interface and
3183
	<cf/nolisten/ means that RIP will send to this interface butnot listen
3184
	to it.
3185

    
3186
	<tag>ttl security [<m/switch/ | tx only]</tag>
3187
	TTL security is a feature that protects routing protocols from remote
3188
	spoofed packets by using TTL 255 instead of TTL 1 for protocol packets
3189
	destined to neighbors. Because TTL is decremented when packets are
3190
	forwarded, it is non-trivial to spoof packets with TTL 255 from remote
3191
	locations.
3192

    
3193
	If this option is enabled, the router will send RIP packets with TTL 255
3194
	and drop received packets with TTL less than 255. If this option si set
3195
	to <cf/tx only/, TTL 255 is used for sent packets, but is not checked
3196
	for received packets. Such setting does not offer protection, but offers
3197
	compatibility with neighbors regardless of whether they use ttl
3198
	security.
3199

    
3200
	Note that for RIPng, TTL security is a standard behavior (required by
3201
	RFC 2080), but BIRD uses <cf/tx only/ by default, for compatibility with
3202
	older versions. For IPv4 RIP, default value is no.
3203

    
3204
	<tag>tx class|dscp|priority <m/num/</tag>
3205
	These options specify the ToS/DiffServ/Traffic class/Priority of the
3206
	outgoing RIP packets. See <ref id="dsc-prio" name="tx class"> common
3207
	option for detailed description.
3208
</descrip>
3209

    
3210
<p>The following options generally override behavior specified in RFC. If you
3211
use any of these options, BIRD will no longer be RFC-compliant, which means it
3212
will not be able to talk to anything other than equally configured BIRD. I have
3213
warned you.
3214

    
3215
<descrip>
3216
	<tag>port <M>number</M></tag>
3217
	Selects IP port to operate on, default 520. (This is useful when testing
3218
	BIRD, if you set this to an address &gt;1024, you will not need to run
3219
	bird with UID==0).
3220

    
3221
	<tag>infinity <M>number</M></tag>
3222
	Selects the value of infinity, default is 16. Bigger values will make
3223
	protocol convergence even slower.
3224

    
3225
	<tag>period <M>number</M></tag>
3226
	Specifies the number of seconds between periodic updates. Default is 30
3227
	seconds. A lower number will mean faster convergence but bigger network
3228
	load. Do not use values lower than 12.
3229

    
3230
	<tag>timeout time <M>number</M></tag>
3231
	Specifies how old route has to be to be considered unreachable.
3232
	Default is 4*<cf/period/.
3233

    
3234
	<tag>garbage time <M>number</M></tag>
3235
	Specifies how old route has to be to be discarded. Default is
3236
	10*<cf/period/.
3237
</descrip>
3238

    
3239
<sect1>Attributes
3240

    
3241
<p>RIP defines two route attributes:
3242

    
3243
<descrip>
3244
	<tag>int <cf/rip_metric/</tag>
3245
	RIP metric of the route (ranging from 0 to <cf/infinity/).  When routes
3246
	from different RIP instances are available and all of them have the same
3247
	preference, BIRD prefers the route with lowest <cf/rip_metric/. When
3248
	importing a non-RIP route, the metric defaults to 5.
3249

    
3250
	<tag>int <cf/rip_tag/</tag>
3251
	RIP route tag: a 16-bit number which can be used to carry additional
3252
	information with the route (for example, an originating AS number in
3253
	case of external routes). When importing a non-RIP route, the tag
3254
	defaults to 0.
3255
</descrip>
3256

    
3257
<sect1>Example
3258

    
3259
<p><code>
3260
protocol rip MyRIP_test {
3261
        debug all;
3262
        port 1520;
3263
        period 12;
3264
        garbage time 60;
3265
        interface "eth0" { metric 3; mode multicast; };
3266
	interface "eth*" { metric 2; mode broadcast; };
3267
        honor neighbor;
3268
        authentication none;
3269
        import filter { print "importing"; accept; };
3270
        export filter { print "exporting"; accept; };
3271
}
3272
</code>
3273

    
3274

    
3275
<sect>Static
3276

    
3277
<p>The Static protocol doesn't communicate with other routers in the network,
3278
but instead it allows you to define routes manually. This is often used for
3279
specifying how to forward packets to parts of the network which don't use
3280
dynamic routing at all and also for defining sink routes (i.e., those telling to
3281
return packets as undeliverable if they are in your IP block, you don't have any
3282
specific destination for them and you don't want to send them out through the
3283
default route to prevent routing loops).
3284

    
3285
<p>There are five types of static routes: `classical' routes telling to forward
3286
packets to a neighboring router, multipath routes specifying several (possibly
3287
weighted) neighboring routers, device routes specifying forwarding to hosts on a
3288
directly connected network, recursive routes computing their nexthops by doing
3289
route table lookups for a given IP and special routes (sink, blackhole etc.)
3290
which specify a special action to be done instead of forwarding the packet.
3291

    
3292
<p>When the particular destination is not available (the interface is down or
3293
the next hop of the route is not a neighbor at the moment), Static just
3294
uninstalls the route from the table it is connected to and adds it again as soon
3295
as the destination becomes adjacent again.
3296

    
3297
<p>The Static protocol does not have many configuration options. The definition
3298
of the protocol contains mainly a list of static routes:
3299

    
3300
<descrip>
3301
	<tag>route <m/prefix/ via <m/ip/</tag>
3302
	Static route through a neighboring router.
3303

    
3304
	<tag>route <m/prefix/ multipath via <m/ip/ [weight <m/num/] [via ...]</tag>
3305
	Static multipath route. Contains several nexthops (gateways), possibly
3306
 	with their weights.
3307

    
3308
	<tag>route <m/prefix/ via <m/"interface"/</tag>
3309
	Static device route through an interface to hosts on a directly
3310
	connected network.
3311

    
3312
	<tag>route <m/prefix/ recursive <m/ip/</tag>
3313
	Static recursive route, its nexthop depends on a route table lookup for
3314
	given IP address.
3315

    
3316
	<tag>route <m/prefix/ blackhole|unreachable|prohibit</tag>
3317
	Special routes specifying to silently drop the packet, return it as
3318
	unreachable or return it as administratively prohibited. First two
3319
	targets are also known as <cf/drop/ and <cf/reject/.
3320

    
3321
	<tag>check link <m/switch/</tag>
3322
	If set, hardware link states of network interfaces are taken into
3323
	consideration.  When link disappears (e.g. ethernet cable is unplugged),
3324
	static routes directing to that interface are removed. It is possible
3325
	that some hardware drivers or platforms do not implement this feature.
3326
	Default: off.
3327

    
3328
	<tag>igp table <m/name/</tag>
3329
	Specifies a table that is used for route table lookups of recursive
3330
	routes. Default: the same table as the protocol is connected to.
3331
</descrip>
3332

    
3333
<p>Static routes have no specific attributes.
3334

    
3335
<p>Example static config might look like this:
3336

    
3337
<p><code>
3338
protocol static {
3339
	table testable;			 # Connect to a non-default routing table
3340
	route 0.0.0.0/0 via 198.51.100.130; # Default route
3341
	route 10.0.0.0/8 multipath	 # Multipath route
3342
		via 198.51.100.10 weight 2
3343
		via 198.51.100.20
3344
		via 192.0.2.1;
3345
	route 203.0.113.0/24 unreachable; # Sink route
3346
	route 10.2.0.0/24 via "arc0";	 # Secondary network
3347
}
3348
</code>
3349

    
3350

    
3351
<chapt>Conclusions
3352

    
3353
<sect>Future work
3354

    
3355
<p>Although BIRD supports all the commonly used routing protocols, there are
3356
still some features which would surely deserve to be implemented in future
3357
versions of BIRD:
3358

    
3359
<itemize>
3360
<item>Opaque LSA's
3361
<item>Route aggregation and flap dampening
3362
<item>Multipath routes
3363
<item>Multicast routing protocols
3364
<item>Ports to other systems
3365
</itemize>
3366

    
3367

    
3368
<sect>Getting more help
3369

    
3370
<p>If you use BIRD, you're welcome to join the bird-users mailing list
3371
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
3372
where you can share your experiences with the other users and consult
3373
your problems with the authors. To subscribe to the list, just send a
3374
<tt/subscribe bird-users/ command in a body of a mail to
3375
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
3376
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
3377

    
3378
<p>BIRD is a relatively young system and it probably contains some bugs. You can
3379
report any problems to the bird-users list and the authors will be glad to solve
3380
them, but before you do so, please make sure you have read the available
3381
documentation and that you are running the latest version (available at
3382
<HTMLURL URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">).
3383
(Of course, a patch which fixes the bug is always welcome as an attachment.)
3384

    
3385
<p>If you want to understand what is going inside, Internet standards are a good
3386
and interesting reading. You can get them from
3387
<HTMLURL URL="ftp://ftp.rfc-editor.org/" name="ftp.rfc-editor.org"> (or a
3388
nicely sorted version from <HTMLURL URL="ftp://atrey.karlin.mff.cuni.cz/pub/rfc"
3389
name="atrey.karlin.mff.cuni.cz:/pub/rfc">).
3390

    
3391
<p><it/Good luck!/
3392

    
3393
</book>
3394

    
3395
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3396
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3397
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3398
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3407
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