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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
<p>BFD packets are sent with a dynamic source port number. Linux systems use by
1382
default a bit different dynamic port range than the IANA approved one
1383
(49152-65535). If you experience problems with compatibility, please adjust
1384
<cf>/proc/sys/net/ipv4/ip_local_port_range</cf>
1385

    
1386
<sect1>Configuration
1387

    
1388
<p>BFD configuration consists mainly of multiple definitions of interfaces.
1389
Most BFD config options are session specific. When a new session is requested
1390
and dynamically created, it is configured from one of these definitions. For
1391
sessions to directly connected neighbors, <cf/interface/ definitions are chosen
1392
based on the interface associated with the session, while <cf/multihop/
1393
definition is used for multihop sessions. If no definition is relevant, the
1394
session is just created with the default configuration. Therefore, an empty BFD
1395
configuration is often sufficient.
1396

    
1397
<p>Note that to use BFD for other protocols like OSPF or BGP, these protocols
1398
also have to be configured to request BFD sessions, usually by <cf/bfd/ option.
1399

    
1400
<p>Some of BFD session options require <m/time/ value, which has to be specified
1401
with the appropriate unit: <m/num/ <cf/s/|<cf/ms/|<cf/us/. Although microseconds
1402
are allowed as units, practical minimum values are usually in order of tens of
1403
milliseconds.
1404

    
1405
<code>
1406
protocol bfd [&lt;name&gt;] {
1407
	interface &lt;interface pattern&gt; {
1408
		interval &lt;time&gt;;
1409
		min rx interval &lt;time&gt;;
1410
		min tx interval &lt;time&gt;;
1411
		idle tx interval &lt;time&gt;;
1412
		multiplier &lt;num&gt;;
1413
		passive &lt;switch&gt;;
1414
	};
1415
	multihop {
1416
		interval &lt;time&gt;;
1417
		min rx interval &lt;time&gt;;
1418
		min tx interval &lt;time&gt;;
1419
		idle tx interval &lt;time&gt;;
1420
		multiplier &lt;num&gt;;
1421
		passive &lt;switch&gt;;
1422
	};
1423
	neighbor &lt;ip&gt; [dev "&lt;interface&gt;"] [local &lt;ip&gt;] [multihop &lt;switch&gt;];
1424
}
1425
</code>
1426

    
1427
<descrip>
1428
	<tag>interface <m/pattern [, ...]/ { <m/options/ }</tag>
1429
	Interface definitions allow to specify options for sessions associated
1430
	with such interfaces and also may contain interface specific options.
1431
	See <ref id="dsc-iface" name="interface"> common option for a detailed
1432
	description of interface patterns. Note that contrary to the behavior of
1433
	<cf/interface/ definitions of other protocols, BFD protocol would accept
1434
	sessions (in default configuration) even on interfaces not covered by
1435
	such definitions.
1436

    
1437
	<tag>multihop { <m/options/ }</tag>
1438
	Multihop definitions allow to specify options for multihop BFD sessions,
1439
	in the same manner as <cf/interface/ definitions are used for directly
1440
	connected sessions. Currently only one such definition (for all multihop
1441
	sessions) could be used.
1442

    
1443
	<tag>neighbor <m/ip/ [dev "<m/interface/"] [local <m/ip/] [multihop <m/switch/]</tag>
1444
	BFD sessions are usually created on demand as requested by other
1445
	protocols (like OSPF or BGP). This option allows to explicitly add
1446
	a BFD session to the specified neighbor regardless of such requests.
1447
	
1448
	The session is identified by the IP address of the neighbor, with
1449
	optional specification of used interface and local IP. By default
1450
	the neighbor must be directly connected, unless the the session is
1451
	configured as multihop. Note that local IP must be specified for
1452
	multihop sessions.
1453
</descrip>
1454

    
1455
<p>Session specific options (part of <cf/interface/ and <cf/multihop/ definitions):
1456

    
1457
<descrip>
1458
	<tag>interval <m/time/</tag>
1459
	BFD ensures availability of the forwarding path associated with the
1460
	session by periodically sending BFD control packets in both
1461
	directions. The rate of such packets is controlled by two options,
1462
	<cf/min rx interval/ and <cf/min tx interval/ (see below). This option
1463
	is just a shorthand to set both of these options together.
1464

    
1465
	<tag>min rx interval <m/time/</tag>
1466
	This option specifies the minimum RX interval, which is announced to the
1467
	neighbor and used there to limit the neighbor's rate of generated BFD
1468
	control packets. Default: 10 ms.
1469

    
1470
	<tag>min tx interval <m/time/</tag>
1471
	This option specifies the desired TX interval, which controls the rate
1472
	of generated BFD control packets (together with <cf/min rx interval/
1473
	announced by the neighbor). Note that this value is used only if the BFD
1474
	session is up, otherwise the value of <cf/idle tx interval/ is used
1475
	instead. Default: 100 ms.
1476

    
1477
	<tag>idle tx interval <m/time/</tag>
1478
	In order to limit unnecessary traffic in cases where a neighbor is not
1479
	available or not running BFD, the rate of generated BFD control packets
1480
	is lower when the BFD session is not up. This option specifies the
1481
	desired TX interval in such cases instead of <cf/min tx interval/.
1482
	Default: 1 s.
1483

    
1484
	<tag>multiplier <m/num/</tag>
1485
	Failure detection time for BFD sessions is based on established rate of
1486
	BFD control packets (<cf>min rx/tx interval</cf>) multiplied by this
1487
	multiplier, which is essentially (ignoring jitter) a number of missed
1488
	packets after which the session is declared down. Note that rates and
1489
	multipliers could be different in each direction of a BFD session.
1490
	Default: 5.
1491

    
1492
	<tag>passive <m/switch/</tag>
1493
	Generally, both BFD session endpoinds try to establish the session by
1494
	sending control packets to the other side. This option allows to enable
1495
	passive mode, which means that the router does not send BFD packets
1496
	until it has received one from the other side. Default: disabled.
1497
</descrip>
1498

    
1499
<sect1>Example
1500

    
1501
<p><code>
1502
protocol bfd {
1503
	interface "eth*" {
1504
		min rx interval 20 ms;
1505
		min tx interval 50 ms;
1506
		idle tx interval 300 ms;
1507
	};
1508
	interface "gre*" {
1509
		interval 200 ms;
1510
		multiplier 10;
1511
		passive;
1512
	};
1513
	multihop {
1514
		interval 200 ms;
1515
		multiplier 10;
1516
	};
1517

    
1518
	neighbor 192.168.1.10;
1519
	neighbor 192.168.2.2 dev "eth2";
1520
	neighbor 192.168.10.1 local 192.168.1.1 multihop;
1521
}
1522
</code>
1523

    
1524

    
1525
<sect>BGP
1526

    
1527
<p>The Border Gateway Protocol is the routing protocol used for backbone level
1528
routing in the today's Internet. Contrary to other protocols, its convergence
1529
does not rely on all routers following the same rules for route selection,
1530
making it possible to implement any routing policy at any router in the network,
1531
the only restriction being that if a router advertises a route, it must accept
1532
and forward packets according to it.
1533

    
1534
<p>BGP works in terms of autonomous systems (often abbreviated as AS). Each AS
1535
is a part of the network with common management and common routing policy. It is
1536
identified by a unique 16-bit number (ASN). Routers within each AS usually
1537
exchange AS-internal routing information with each other using an interior
1538
gateway protocol (IGP, such as OSPF or RIP). Boundary routers at the border of
1539
the AS communicate global (inter-AS) network reachability information with their
1540
neighbors in the neighboring AS'es via exterior BGP (eBGP) and redistribute
1541
received information to other routers in the AS via interior BGP (iBGP).
1542

    
1543
<p>Each BGP router sends to its neighbors updates of the parts of its routing
1544
table it wishes to export along with complete path information (a list of AS'es
1545
the packet will travel through if it uses the particular route) in order to
1546
avoid routing loops.
1547

    
1548
<p>BIRD supports all requirements of the BGP4 standard as defined in
1549
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
1550
It also supports the community attributes
1551
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
1552
capability negotiation
1553
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
1554
MD5 password authentication
1555
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
1556
extended communities
1557
(RFC 4360<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4360.txt">),
1558
route reflectors 
1559
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
1560
graceful restart
1561
(RFC 4724<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4724.txt">),
1562
multiprotocol extensions
1563
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
1564
4B AS numbers 
1565
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">),
1566
and 4B AS numbers in extended communities
1567
(RFC 5668<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5668.txt">).
1568

    
1569

    
1570
For IPv6, it uses the standard multiprotocol extensions defined in
1571
RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">
1572
and applied to IPv6 according to
1573
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
1574

    
1575
<sect1>Route selection rules
1576

    
1577
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
1578
route among multiple BGP routes with the same preference are a bit more complex
1579
and they are implemented according to the following algorithm. It starts the
1580
first rule, if there are more "best" routes, then it uses the second rule to
1581
choose among them and so on.
1582

    
1583
<itemize>
1584
	<item>Prefer route with the highest Local Preference attribute.
1585
	<item>Prefer route with the shortest AS path.
1586
	<item>Prefer IGP origin over EGP and EGP origin over incomplete.
1587
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
1588
	<item>Prefer routes received via eBGP over ones received via iBGP.
1589
	<item>Prefer routes with lower internal distance to a boundary router.
1590
	<item>Prefer the route with the lowest value of router ID of the
1591
	advertising router.
1592
</itemize>
1593

    
1594
<sect1>IGP routing table
1595

    
1596
<p>BGP is mainly concerned with global network reachability and with routes to
1597
other autonomous systems. When such routes are redistributed to routers in the
1598
AS via BGP, they contain IP addresses of a boundary routers (in route attribute
1599
NEXT_HOP). BGP depends on existing IGP routing table with AS-internal routes to
1600
determine immediate next hops for routes and to know their internal distances to
1601
boundary routers for the purpose of BGP route selection. In BIRD, there is
1602
usually one routing table used for both IGP routes and BGP routes.
1603

    
1604
<sect1>Configuration
1605

    
1606
<p>Each instance of the BGP corresponds to one neighboring router. This allows
1607
to set routing policy and all the other parameters differently for each neighbor
1608
using the following configuration parameters:
1609

    
1610
<descrip>
1611
	<tag>local [<m/ip/] as <m/number/</tag>
1612
	Define which AS we are part of. (Note that contrary to other IP routers,
1613
	BIRD is able to act as a router located in multiple AS'es simultaneously,
1614
	but in such cases you need to tweak the BGP paths manually in the filters
1615
	to get consistent behavior.) Optional <cf/ip/ argument specifies a source
1616
	address, equivalent to the <cf/source address/ option (see below). This
1617
	parameter is mandatory.
1618

    
1619
	<tag>neighbor <m/ip/ as <m/number/</tag>
1620
	Define neighboring router this instance will be talking to and what AS
1621
	it's located in. In case the neighbor is in the same AS as we are, we
1622
	automatically switch to iBGP. This parameter is mandatory.
1623

    
1624
	<tag>direct</tag>
1625
	Specify that the neighbor is directly connected. The IP address of the
1626
	neighbor must be from a directly reachable IP range (i.e. associated
1627
	with one of your router's interfaces), otherwise the BGP session
1628
	wouldn't start but it would wait for such interface to appear. The
1629
	alternative is the <cf/multihop/ option. Default: enabled for eBGP.
1630

    
1631
	<tag>multihop [<m/number/]</tag>
1632
	Configure multihop BGP session to a neighbor that isn't directly
1633
	connected. Accurately, this option should be used if the configured
1634
	neighbor IP address does not match with any local network subnets. Such
1635
	IP address have to be reachable through system routing table. The
1636
	alternative is the <cf/direct/ option. For multihop BGP it is
1637
	recommended to explicitly configure the source address to have it
1638
	stable. Optional <cf/number/ argument can be used to specify the number
1639
	of hops (used for TTL). Note that the number of networks (edges) in a
1640
	path is counted; i.e., if two BGP speakers are separated by one router,
1641
	the number of hops is 2. Default: enabled for iBGP.
1642

    
1643
	<tag>source address <m/ip/</tag>
1644
	Define local address we should use for next hop calculation and as a
1645
	source address for the BGP session. Default: the address of the local
1646
	end of the interface our neighbor is connected to.
1647

    
1648
	<tag>next hop self</tag>
1649
	Avoid calculation of the Next Hop attribute and always advertise our own
1650
	source address as a next hop. This needs to be used only occasionally to
1651
	circumvent misconfigurations of other routers. Default: disabled.
1652

    
1653
	<tag>next hop keep</tag>
1654
	Forward the received Next Hop attribute even in situations where the
1655
	local address should be used instead, like when the route is sent to an
1656
	interface with a different subnet. Default: disabled.
1657

    
1658
	<tag>missing lladdr self|drop|ignore</tag>
1659
	Next Hop attribute in BGP-IPv6 sometimes contains just the global IPv6
1660
	address, but sometimes it has to contain both global and link-local IPv6
1661
	addresses. This option specifies what to do if BIRD have to send both
1662
	addresses but does not know link-local address. This situation might
1663
	happen when routes from other protocols are exported to BGP, or when
1664
	improper updates are received from BGP peers. <cf/self/ means that BIRD
1665
	advertises its own local address instead. <cf/drop/ means that BIRD
1666
	skips that prefixes and logs error. <cf/ignore/ means that BIRD ignores
1667
	the problem and sends just the global address (and therefore forms
1668
	improper BGP update). Default: <cf/self/, unless BIRD is configured as a
1669
	route server (option <cf/rs client/), in that case default is <cf/ignore/,
1670
	because route servers usually do not forward packets themselves.
1671

    
1672
	<tag>gateway direct|recursive</tag>
1673
	For received routes, their <cf/gw/ (immediate next hop) attribute is
1674
	computed from received <cf/bgp_next_hop/ attribute. This option
1675
	specifies how it is computed. Direct mode means that the IP address from
1676
	<cf/bgp_next_hop/ is used if it is directly reachable, otherwise the
1677
	neighbor IP address is used. Recursive mode means that the gateway is
1678
	computed by an IGP routing table lookup for the IP address from
1679
	<cf/bgp_next_hop/. Recursive mode is the behavior specified by the BGP
1680
	standard. Direct mode is simpler, does not require any routes in a
1681
	routing table, and was used in older versions of BIRD, but does not
1682
	handle well nontrivial iBGP setups and multihop. Recursive mode is
1683
	incompatible with <ref id="dsc-sorted" name="sorted tables">. Default:
1684
	<cf/direct/ for direct sessions, <cf/recursive/ for multihop sessions.
1685

    
1686
	<tag>igp table <m/name/</tag>
1687
	Specifies a table that is used as an IGP routing table. Default: the
1688
	same as the table BGP is connected to.
1689

    
1690
	<tag>bfd <M>switch</M></tag>
1691
	BGP could use BFD protocol as an advisory mechanism for neighbor
1692
	liveness and failure detection. If enabled, BIRD setups a BFD session
1693
	for the BGP neighbor and tracks its liveness by it. This has an
1694
	advantage of an order of magnitude lower detection times in case of
1695
	failure. Note that BFD protocol also has to be configured, see
1696
	<ref id="sect-bfd" name="BFD"> section for details. Default: disabled.
1697

    
1698
	<tag>ttl security <m/switch/</tag>
1699
	Use GTSM (RFC 5082 - the generalized TTL security mechanism). GTSM
1700
	protects against spoofed packets by ignoring received packets with a
1701
	smaller than expected TTL. To work properly, GTSM have to be enabled on
1702
	both sides of a BGP session. If both <cf/ttl security/ and <cf/multihop/
1703
	options are enabled, <cf/multihop/ option should specify proper hop
1704
	value to compute expected TTL. Kernel support required: Linux: 2.6.34+
1705
	(IPv4), 2.6.35+ (IPv6), BSD: since long ago, IPv4 only. Note that full
1706
	(ICMP protection, for example) RFC 5082 support is provided by Linux
1707
	only. Default: disabled.
1708
	
1709
	<tag>password <m/string/</tag>
1710
	Use this password for MD5 authentication of BGP sessions. Default: no
1711
	authentication. Password has to be set by external utility
1712
	(e.g. setkey(8)) on BSD systems.
1713

    
1714
	<tag>passive <m/switch/</tag>
1715
	Standard BGP behavior is both initiating outgoing connections and
1716
	accepting incoming connections. In passive mode, outgoing connections
1717
	are not initiated. Default: off.
1718

    
1719
	<tag>rr client</tag>
1720
	Be a route reflector and treat the neighbor as a route reflection
1721
	client. Default: disabled.
1722

    
1723
	<tag>rr cluster id <m/IPv4 address/</tag>
1724
	Route reflectors use cluster id to avoid route reflection loops. When
1725
	there is one route reflector in a cluster it usually uses its router id
1726
	as a cluster id, but when there are more route reflectors in a cluster,
1727
	these need to be configured (using this option) to use a common cluster
1728
	id. Clients in a cluster need not know their cluster id and this option
1729
	is not allowed for them. Default: the same as router id.
1730

    
1731
	<tag>rs client</tag> 
1732
	Be a route server and treat the neighbor as a route server client.
1733
	A route server is used as a replacement for full mesh EBGP routing in
1734
	Internet exchange points in a similar way to route reflectors used in
1735
	IBGP routing. BIRD does not implement obsoleted RFC 1863, but uses
1736
	ad-hoc implementation, which behaves like plain EBGP but reduces
1737
	modifications to advertised route attributes to be transparent (for
1738
	example does not prepend its AS number to AS PATH attribute and keeps
1739
	MED attribute). Default: disabled.
1740

    
1741
	<tag>secondary <m/switch/</tag>
1742
	Usually, if an export filter rejects a selected route, no other route is
1743
	propagated for that network. This option allows to try the next route in
1744
	order until one that is accepted is found or all routes for that network
1745
	are rejected. This can be used for route servers that need to propagate
1746
	different tables to each client but do not want to have these tables
1747
	explicitly (to conserve memory). This option requires that the connected
1748
	routing table is <ref id="dsc-sorted" name="sorted">. Default: off.
1749

    
1750
	<tag>add paths <m/switch/|rx|tx</tag>
1751
	Standard BGP can propagate only one path (route) per destination network
1752
	(usually the selected one). This option controls the add-path protocol
1753
	extension, which allows to advertise any number of paths to a
1754
	destination. Note that to be active, add-path has to be enabled on both
1755
	sides of the BGP session, but it could be enabled separately for RX and
1756
	TX direction. When active, all available routes accepted by the export
1757
	filter are advertised to the neighbor. Default: off.
1758

    
1759
	<tag>allow local as [<m/number/]</tag> 
1760
	BGP prevents routing loops by rejecting received routes with the local
1761
	AS number in the AS path. This option allows to loose or disable the
1762
	check. Optional <cf/number/ argument can be used to specify the maximum
1763
	number of local ASNs in the AS path that is allowed for received
1764
	routes. When the option is used without the argument, the check is
1765
	completely disabled and you should ensure loop-free behavior by some
1766
	other means. Default: 0 (no local AS number allowed).
1767

    
1768
	<tag>enable route refresh <m/switch/</tag>
1769
	When BGP speaker changes its import filter, it has to re-examine all
1770
	routes received from its neighbor against the new filter. As these
1771
	routes might not be available, there is a BGP protocol extension Route
1772
	Refresh (specified in RFC 2918) that allows BGP speaker to request
1773
	re-advertisement of all routes from its neighbor. This option specifies
1774
	whether BIRD advertises this capability and accepts such requests. Even
1775
	when disabled, BIRD can send route refresh requests. Default: on.
1776

    
1777
	<tag>graceful restart <m/switch/|aware</tag>
1778
	When a BGP speaker restarts or crashes, neighbors will discard all
1779
	received paths from the speaker, which disrupts packet forwarding even
1780
	when the forwarding plane of the speaker remains intact. RFC 4724
1781
	specifies an optional graceful restart mechanism to alleviate this
1782
	issue. This option controls the mechanism. It has three states:
1783
	Disabled, when no support is provided. Aware, when the graceful restart
1784
	support is announced and the support for restarting neighbors is
1785
	provided, but no local graceful restart is allowed (i.e. receiving-only
1786
	role). Enabled, when the full graceful restart support is provided
1787
	(i.e. both restarting and receiving role). Note that proper support for
1788
	local graceful restart requires also configuration of other protocols.
1789
	Default: aware.
1790

    
1791
	<tag>graceful restart time <m/number/</tag>
1792
	The restart time is announced in the BGP graceful restart capability
1793
	and specifies how long the neighbor would wait for the BGP session to
1794
	re-establish after a restart before deleting stale routes. Default:
1795
	120 seconds.
1796

    
1797
	<tag>interpret communities <m/switch/</tag>
1798
	RFC 1997 demands that BGP speaker should process well-known communities
1799
	like no-export (65535, 65281) or no-advertise (65535, 65282). For
1800
	example, received route carrying a no-adverise community should not be
1801
	advertised to any of its neighbors. If this option is enabled (which is
1802
	by default), BIRD has such behavior automatically (it is evaluated when
1803
	a route is exported to the BGP protocol just before the export filter).
1804
	Otherwise, this integrated processing of well-known communities is
1805
	disabled. In that case, similar behavior can be implemented in the
1806
	export filter. Default: on.
1807

    
1808
	<tag>enable as4 <m/switch/</tag>
1809
	BGP protocol was designed to use 2B AS numbers and was extended later to
1810
	allow 4B AS number. BIRD supports 4B AS extension, but by disabling this
1811
	option it can be persuaded not to advertise it and to maintain old-style
1812
	sessions with its neighbors. This might be useful for circumventing bugs
1813
	in neighbor's implementation of 4B AS extension. Even when disabled
1814
	(off), BIRD behaves internally as AS4-aware BGP router. Default: on.
1815

    
1816
	<tag>capabilities <m/switch/</tag>
1817
	Use capability advertisement to advertise optional capabilities. This is
1818
	standard behavior for newer BGP implementations, but there might be some
1819
	older BGP implementations that reject such connection attempts. When
1820
	disabled (off), features that request it (4B AS support) are also
1821
	disabled. Default: on, with automatic fallback to off when received
1822
	capability-related error.
1823

    
1824
	<tag>advertise ipv4 <m/switch/</tag>
1825
	Advertise IPv4 multiprotocol capability. This is not a correct behavior
1826
	according to the strict interpretation of RFC 4760, but it is widespread
1827
	and required by some BGP implementations (Cisco and Quagga). This option
1828
	is relevant to IPv4 mode with enabled capability advertisement
1829
	only. Default: on.
1830

    
1831
	<tag>route limit <m/number/</tag>
1832
	The maximal number of routes that may be imported from the protocol. If
1833
	the route limit is exceeded, the connection is closed with an error.
1834
	Limit is currently implemented as <cf>import limit <m/number/ action
1835
	restart</cf>. This option is obsolete and it is replaced by
1836
	<ref id="import-limit" name="import limit option">. Default: no	limit.
1837

    
1838
	<tag>disable after error <m/switch/</tag>
1839
	When an error is encountered (either locally or by the other side),
1840
	disable the instance automatically and wait for an administrator to fix
1841
	the problem manually. Default: off.
1842

    
1843
	<tag>hold time <m/number/</tag>
1844
	Time in seconds to wait for a Keepalive message from the other side
1845
	before considering the connection stale. Default: depends on agreement
1846
	with the neighboring router, we prefer 240 seconds if the other side is
1847
	willing to accept it.
1848

    
1849
	<tag>startup hold time <m/number/</tag>
1850
	Value of the hold timer used before the routers have a chance to exchange
1851
	open messages and agree on the real value. Default: 240	seconds.
1852

    
1853
	<tag>keepalive time <m/number/</tag>
1854
	Delay in seconds between sending of two consecutive Keepalive messages.
1855
	Default: One third of the hold time.
1856

    
1857
	<tag>connect retry time <m/number/</tag>
1858
	Time in seconds to wait before retrying a failed attempt to connect.
1859
	Default: 120 seconds.
1860

    
1861
	<tag>start delay time <m/number/</tag>
1862
	Delay in seconds between protocol startup and the first attempt to
1863
	connect. Default: 5 seconds.
1864

    
1865
	<tag>error wait time <m/number/,<m/number/</tag>
1866
	Minimum and maximum delay in seconds between a protocol failure (either
1867
	local or reported by the peer) and automatic restart. Doesn't apply
1868
	when <cf/disable after error/ is configured. If consecutive errors
1869
	happen, the delay is increased exponentially until it reaches the
1870
	maximum. Default: 60, 300.
1871

    
1872
	<tag>error forget time <m/number/</tag>
1873
	Maximum time in seconds between two protocol failures to treat them as a
1874
	error sequence which makes <cf/error wait time/ increase exponentially.
1875
	Default: 300 seconds.
1876

    
1877
	<tag>path metric <m/switch/</tag>
1878
	Enable comparison of path lengths when deciding which BGP route is the
1879
	best one. Default: on.
1880

    
1881
	<tag>med metric <m/switch/</tag>
1882
	Enable comparison of MED attributes (during best route selection) even
1883
	between routes received from different ASes. This may be useful if all
1884
	MED attributes contain some consistent metric, perhaps enforced in
1885
	import filters of AS boundary routers. If this option is disabled, MED
1886
	attributes are compared only if routes are received from the same AS
1887
	(which is the standard behavior). Default: off.
1888

    
1889
	<tag>deterministic med <m/switch/</tag>
1890
	BGP route selection algorithm is often viewed as a comparison between
1891
	individual routes (e.g. if a new route appears and is better than the
1892
	current best one, it is chosen as the new best one). But the proper
1893
	route selection, as specified by RFC 4271, cannot be fully implemented
1894
	in that way. The problem is mainly in handling the MED attribute. BIRD,
1895
	by default, uses an simplification based on individual route comparison,
1896
	which in some cases may lead to temporally dependent behavior (i.e. the
1897
	selection is dependent on the order in which routes appeared). This
1898
	option enables a different (and slower) algorithm implementing proper
1899
	RFC 4271 route selection, which is deterministic. Alternative way how to
1900
	get deterministic behavior is to use <cf/med metric/ option. This option
1901
	is incompatible with <ref id="dsc-sorted" name="sorted tables">.
1902
	Default: off.
1903

    
1904
	<tag>igp metric <m/switch/</tag>
1905
	Enable comparison of internal distances to boundary routers during best
1906
 	route selection. Default: on.
1907

    
1908
	<tag>prefer older <m/switch/</tag>
1909
	Standard route selection algorithm breaks ties by comparing router IDs.
1910
	This changes the behavior to prefer older routes (when both are external
1911
	and from different peer). For details, see RFC 5004. Default: off.
1912

    
1913
	<tag>default bgp_med <m/number/</tag>
1914
	Value of the Multiple Exit Discriminator to be used during route
1915
	selection when the MED attribute is missing. Default: 0.
1916

    
1917
	<tag>default bgp_local_pref <m/number/</tag>
1918
	A default value for the Local Preference attribute. It is used when
1919
	a new Local Preference attribute is attached to a route by the BGP
1920
	protocol itself (for example, if a route is received through eBGP and
1921
	therefore does not have such attribute). Default: 100 (0 in pre-1.2.0
1922
	versions of BIRD).
1923
</descrip>
1924

    
1925
<sect1>Attributes
1926

    
1927
<p>BGP defines several route attributes. Some of them (those marked with
1928
`<tt/I/' in the table below) are available on internal BGP connections only,
1929
some of them (marked with `<tt/O/') are optional.
1930

    
1931
<descrip>
1932
	<tag>bgppath <cf/bgp_path/</tag>
1933
	Sequence of AS numbers describing the AS path the packet will travel
1934
	through when forwarded according to the particular route. In case of
1935
	internal BGP it doesn't contain the number of the local AS.
1936

    
1937
	<tag>int <cf/bgp_local_pref/ [I]</tag>
1938
	Local preference value used for selection among multiple BGP routes (see
1939
	the selection rules above). It's used as an additional metric which is
1940
	propagated through the whole local AS.
1941

    
1942
	<tag>int <cf/bgp_med/ [O]</tag>
1943
	The Multiple Exit Discriminator of the route is an optional attribute
1944
	which is used on external (inter-AS) links to convey to an adjacent AS
1945
	the optimal entry point into the local AS. The received attribute is
1946
	also propagated over internal BGP links. The attribute value is zeroed
1947
	when a route is exported to an external BGP instance to ensure that the
1948
	attribute received from a neighboring AS is not propagated to other
1949
	neighboring ASes. A new value might be set in the export filter of an
1950
	external BGP instance. See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1951
	for further discussion of BGP MED attribute.
1952

    
1953
	<tag>enum <cf/bgp_origin/</tag>
1954
	Origin of the route: either <cf/ORIGIN_IGP/ if the route has originated
1955
	in an interior routing protocol or <cf/ORIGIN_EGP/ if it's been imported
1956
	from the <tt>EGP</tt> protocol (nowadays it seems to be obsolete) or
1957
	<cf/ORIGIN_INCOMPLETE/ if the origin is unknown.
1958

    
1959
	<tag>ip <cf/bgp_next_hop/</tag>
1960
	Next hop to be used for forwarding of packets to this destination. On
1961
	internal BGP connections, it's an address of the originating router if
1962
	it's inside the local AS or a boundary router the packet will leave the
1963
	AS through if it's an exterior route, so each BGP speaker within the AS
1964
	has a chance to use the shortest interior path possible to this point.
1965

    
1966
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag>
1967
	This is an optional attribute which carries no value, but the sole
1968
	presence of which indicates that the route has been aggregated from
1969
	multiple routes by some router on the path from the originator.
1970

    
1971
<!-- we don't handle aggregators right since they are of a very obscure type
1972
	<tag>bgp_aggregator</tag>
1973
-->
1974
	<tag>clist <cf/bgp_community/ [O]</tag>
1975
	List of community values associated with the route. Each such value is a
1976
	pair (represented as a <cf/pair/ data type inside the filters) of 16-bit
1977
	integers, the first of them containing the number of the AS which
1978
	defines the community and the second one being a per-AS identifier.
1979
	There are lots of uses of the community mechanism, but generally they
1980
	are used to carry policy information like "don't export to USA peers".
1981
	As each AS can define its own routing policy, it also has a complete
1982
	freedom about which community attributes it defines and what will their
1983
	semantics be.
1984

    
1985
	<tag>eclist <cf/bgp_ext_community/ [O]</tag>
1986
	List of extended community values associated with the route. Extended
1987
	communities have similar usage as plain communities, but they have an
1988
	extended range (to allow 4B ASNs) and a nontrivial structure with a type
1989
	field. Individual community values are represented using an <cf/ec/ data
1990
	type inside the filters.
1991

    
1992
	<tag>quad <cf/bgp_originator_id/ [I, O]</tag>
1993
	This attribute is created by the route reflector when reflecting the
1994
	route and contains the router ID of the originator of the route in the
1995
	local AS.
1996

    
1997
	<tag>clist <cf/bgp_cluster_list/ [I, O]</tag>
1998
	This attribute contains a list of cluster IDs of route reflectors. Each
1999
	route reflector prepends its cluster ID when reflecting the route.
2000
</descrip>
2001

    
2002
<sect1>Example
2003

    
2004
<p><code>
2005
protocol bgp {
2006
	local as 65000;			     # Use a private AS number
2007
	neighbor 198.51.100.130 as 64496;    # Our neighbor ...
2008
	multihop;			     # ... which is connected indirectly
2009
	export filter {			     # We use non-trivial export rules
2010
		if source = RTS_STATIC then { # Export only static routes
2011
		        # Assign our community
2012
			bgp_community.add((65000,64501));
2013
			# Artificially increase path length
2014
			# by advertising local AS number twice
2015
			if bgp_path ~ [= 65000 =] then
2016
				bgp_path.prepend(65000);
2017
			accept;
2018
		}
2019
		reject;
2020
	};
2021
	import all;
2022
	source address 198.51.100.14;	# Use a non-standard source address
2023
}
2024
</code>
2025

    
2026

    
2027
<sect>Device
2028

    
2029
<p>The Device protocol is not a real routing protocol. It doesn't generate any
2030
routes and it only serves as a module for getting information about network
2031
interfaces from the kernel.
2032

    
2033
<p>Except for very unusual circumstances, you probably should include this
2034
protocol in the configuration since almost all other protocols require network
2035
interfaces to be defined for them to work with.
2036

    
2037
<sect1>Configuration
2038

    
2039
<p><descrip>
2040

    
2041
	<tag>scan time <m/number/</tag>
2042

    
2043
	Time in seconds between two scans of the network interface list. On
2044
	systems where we are notified about interface status changes
2045
	asynchronously (such as newer versions of Linux), we need to scan the
2046
	list only in order to avoid confusion by lost notification messages,
2047
	so the default time is set to a large value.
2048

    
2049
	<tag>primary [ "<m/mask/" ] <m/prefix/</tag>
2050
	If a network interface has more than one network address, BIRD has to
2051
	choose one of them as a primary one. By default, BIRD chooses the
2052
	lexicographically smallest address as the primary one.
2053

    
2054
	This option allows to specify which network address should be chosen as
2055
	a primary one. Network addresses that match <m/prefix/ are preferred to
2056
	non-matching addresses. If more <cf/primary/ options are used, the first
2057
	one has the highest preference. If "<m/mask/" is specified, then such
2058
	<cf/primary/ option is relevant only to matching network interfaces.
2059

    
2060
	In all cases, an address marked by operating system as secondary cannot
2061
	be chosen as the primary one.
2062
</descrip>
2063

    
2064
<p>As the Device protocol doesn't generate any routes, it cannot have
2065
any attributes. Example configuration looks like this:
2066

    
2067
<p><code>
2068
protocol device {
2069
	scan time 10;		# Scan the interfaces often
2070
	primary "eth0" 192.168.1.1;
2071
	primary 192.168.0.0/16;
2072
}
2073
</code>
2074

    
2075

    
2076
<sect>Direct
2077

    
2078
<p>The Direct protocol is a simple generator of device routes for all the
2079
directly connected networks according to the list of interfaces provided by the
2080
kernel via the Device protocol.
2081

    
2082
<p>The question is whether it is a good idea to have such device routes in BIRD
2083
routing table. OS kernel usually handles device routes for directly connected
2084
networks by itself so we don't need (and don't want) to export these routes to
2085
the kernel protocol. OSPF protocol creates device routes for its interfaces
2086
itself and BGP protocol is usually used for exporting aggregate routes. Although
2087
there are some use cases that use the direct protocol (like abusing eBGP as an
2088
IGP routing protocol), in most cases it is not needed to have these device
2089
routes in BIRD routing table and to use the direct protocol.
2090

    
2091
<p>There is one notable case when you definitely want to use the direct protocol
2092
-- running BIRD on BSD systems. Having high priority device routes for directly
2093
connected networks from the direct protocol protects kernel device routes from
2094
being overwritten or removed by IGP routes during some transient network
2095
conditions, because a lower priority IGP route for the same network is not
2096
exported to the kernel routing table. This is an issue on BSD systems only, as
2097
on Linux systems BIRD cannot change non-BIRD route in the kernel routing table.
2098

    
2099
<p>The only configurable thing about direct is what interfaces it watches:
2100

    
2101
<p><descrip>
2102
	<tag>interface <m/pattern [, ...]/</tag>
2103
	By default, the Direct protocol will generate device routes for all the
2104
	interfaces available. If you want to restrict it to some subset of
2105
	interfaces or addresses (e.g. if you're using multiple routing tables
2106
	for policy routing and some of the policy domains don't contain all
2107
	interfaces), just use this clause. See <ref id="dsc-iface" name="interface">
2108
	common option for detailed description. The Direct protocol uses
2109
	extended interface clauses.
2110
</descrip>
2111

    
2112
<p>Direct device routes don't contain any specific attributes.
2113

    
2114
<p>Example config might look like this:
2115

    
2116
<p><code>
2117
protocol direct {
2118
	interface "-arc*", "*";		# Exclude the ARCnets
2119
}
2120
</code>
2121

    
2122

    
2123
<sect>Kernel
2124

    
2125
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
2126
with other routers in the network, it performs synchronization of BIRD's routing
2127
tables with the OS kernel. Basically, it sends all routing table updates to the
2128
kernel and from time to time it scans the kernel tables to see whether some
2129
routes have disappeared (for example due to unnoticed up/down transition of an
2130
interface) or whether an `alien' route has been added by someone else (depending
2131
on the <cf/learn/ switch, such routes are either ignored or accepted to our
2132
table).
2133

    
2134
<p>Unfortunately, there is one thing that makes the routing table synchronization
2135
a bit more complicated. In the kernel routing table there are also device routes
2136
for directly connected networks. These routes are usually managed by OS itself
2137
(as a part of IP address configuration) and we don't want to touch that. They
2138
are completely ignored during the scan of the kernel tables and also the export
2139
of device routes from BIRD tables to kernel routing tables is restricted to
2140
prevent accidental interference. This restriction can be disabled using
2141
<cf/device routes/ switch.
2142

    
2143
<p>If your OS supports only a single routing table, you can configure only one
2144
instance of the Kernel protocol. If it supports multiple tables (in order to
2145
allow policy routing; such an OS is for example Linux), you can run as many
2146
instances as you want, but each of them must be connected to a different BIRD
2147
routing table and to a different kernel table.
2148

    
2149
<p>Because the kernel protocol is partially integrated with the connected
2150
routing table, there are two limitations - it is not possible to connect more
2151
kernel protocols to the same routing table and changing route destination
2152
(gateway) in an export filter of a kernel protocol does not work. Both
2153
limitations can be overcome using another routing table and the pipe protocol.
2154

    
2155
<sect1>Configuration
2156

    
2157
<p><descrip>
2158
	<tag>persist <m/switch/</tag>
2159
	Tell BIRD to leave all its routes in the routing tables when it exits
2160
	(instead of cleaning them up).
2161

    
2162
	<tag>scan time <m/number/</tag>
2163
	Time in seconds between two consecutive scans of the kernel routing
2164
	table.
2165

    
2166
	<tag>learn <m/switch/</tag>
2167
	Enable learning of routes added to the kernel routing tables by other
2168
	routing daemons or by the system administrator. This is possible only on
2169
	systems which support identification of route authorship.
2170

    
2171
	<tag>device routes <m/switch/</tag>
2172
	Enable export of device routes to the kernel routing table. By default,
2173
	such routes are rejected (with the exception of explicitly configured
2174
	device routes from the static protocol) regardless of the export filter
2175
	to protect device routes in kernel routing table (managed by OS itself)
2176
	from accidental overwriting or erasing.
2177

    
2178
	<tag>kernel table <m/number/</tag>
2179
	Select which kernel table should this particular instance of the Kernel
2180
	protocol work with. Available only on systems supporting multiple
2181
	routing tables.
2182

    
2183
	<tag>graceful restart <m/switch/</tag>
2184
	Participate in graceful restart recovery. If this option is enabled and
2185
	a graceful restart recovery is active, the Kernel protocol will defer
2186
	synchronization of routing tables until the end of the recovery. Note
2187
	that import of kernel routes to BIRD is not affected.
2188
</descrip>
2189

    
2190
<sect1>Attributes
2191

    
2192
<p>The Kernel protocol defines several attributes. These attributes are
2193
translated to appropriate system (and OS-specific) route attributes. We support
2194
these attributes:
2195

    
2196
<descrip>
2197
	<tag>int <cf/krt_source/</tag>
2198
	The original source of the imported kernel route. The value is
2199
	system-dependent. On Linux, it is a value of the protocol field of the
2200
	route. See /etc/iproute2/rt_protos for common values. On BSD, it is
2201
	based on STATIC and PROTOx flags. The attribute is read-only.
2202

    
2203
	<tag>int <cf/krt_metric/</tag>
2204
	The kernel metric of the route. When multiple same routes are in a
2205
	kernel routing table, the Linux kernel chooses one with lower metric.
2206

    
2207
	<tag>ip <cf/krt_prefsrc/</tag> (Linux)
2208
	The preferred source address. Used in source address selection for
2209
 	outgoing packets. Have to be one of IP addresses of the router.
2210

    
2211
	<tag>int <cf/krt_realm/</tag> (Linux)
2212
	The realm of the route. Can be used for traffic classification.
2213
</descrip>
2214

    
2215
<sect1>Example
2216

    
2217
<p>A simple configuration can look this way:
2218

    
2219
<p><code>
2220
protocol kernel {
2221
	export all;
2222
}
2223
</code>
2224

    
2225
<p>Or for a system with two routing tables:
2226

    
2227
<p><code>
2228
protocol kernel {		# Primary routing table
2229
	learn;			# Learn alien routes from the kernel
2230
	persist;		# Don't remove routes on bird shutdown
2231
	scan time 10;		# Scan kernel routing table every 10 seconds
2232
	import all;
2233
	export all;
2234
}
2235

    
2236
protocol kernel {		# Secondary routing table
2237
	table auxtable;
2238
	kernel table 100;
2239
	export all;
2240
}
2241
</code>
2242

    
2243

    
2244
<sect>OSPF
2245

    
2246
<sect1>Introduction
2247

    
2248
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
2249
protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328
2250
<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">
2251
and the current IPv6 version (OSPFv3) is defined in RFC 5340
2252
<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt">
2253
It's a link state (a.k.a. shortest path first) protocol -- each router maintains
2254
a database describing the autonomous system's topology. Each participating
2255
router has an identical copy of the database and all routers run the same
2256
algorithm calculating a shortest path tree with themselves as a root. OSPF
2257
chooses the least cost path as the best path.
2258

    
2259
<p>In OSPF, the autonomous system can be split to several areas in order to
2260
reduce the amount of resources consumed for exchanging the routing information
2261
and to protect the other areas from incorrect routing data. Topology of the area
2262
is hidden to the rest of the autonomous system.
2263

    
2264
<p>Another very important feature of OSPF is that it can keep routing information
2265
from other protocols (like Static or BGP) in its link state database as external
2266
routes. Each external route can be tagged by the advertising router, making it
2267
possible to pass additional information between routers on the boundary of the
2268
autonomous system.
2269

    
2270
<p>OSPF quickly detects topological changes in the autonomous system (such as
2271
router interface failures) and calculates new loop-free routes after a short
2272
period of convergence. Only a minimal amount of routing traffic is involved.
2273

    
2274
<p>Each router participating in OSPF routing periodically sends Hello messages
2275
to all its interfaces. This allows neighbors to be discovered dynamically. Then
2276
the neighbors exchange theirs parts of the link state database and keep it
2277
identical by flooding updates. The flooding process is reliable and ensures that
2278
each router detects all changes.
2279

    
2280
<sect1>Configuration
2281

    
2282
<p>In the main part of configuration, there can be multiple definitions of OSPF
2283
areas, each with a different id. These definitions includes many other switches
2284
and multiple definitions of interfaces. Definition of interface may contain many
2285
switches and constant definitions and list of neighbors on nonbroadcast
2286
networks.
2287

    
2288
<code>
2289
protocol ospf &lt;name&gt; {
2290
	rfc1583compat &lt;switch&gt;;
2291
	stub router &lt;switch&gt;;
2292
	tick &lt;num&gt;;
2293
	ecmp &lt;switch&gt; [limit &lt;num&gt;];
2294
	area &lt;id&gt; {
2295
		stub;
2296
		nssa;
2297
		summary &lt;switch&gt;;
2298
		default nssa &lt;switch&gt;;
2299
		default cost &lt;num&gt;;
2300
		default cost2 &lt;num&gt;;
2301
		translator &lt;switch&gt;;
2302
		translator stability &lt;num&gt;;
2303

    
2304
                networks {
2305
			&lt;prefix&gt;;
2306
			&lt;prefix&gt; hidden;
2307
		}
2308
                external {
2309
			&lt;prefix&gt;;
2310
			&lt;prefix&gt; hidden;
2311
			&lt;prefix&gt; tag &lt;num&gt;;
2312
		}
2313
		stubnet &lt;prefix&gt;;
2314
		stubnet &lt;prefix&gt; {
2315
			hidden &lt;switch&gt;;
2316
			summary &lt;switch&gt;;
2317
			cost &lt;num&gt;;
2318
		}
2319
		interface &lt;interface pattern&gt; [instance &lt;num&gt;] {
2320
			cost &lt;num&gt;;
2321
			stub &lt;switch&gt;;
2322
			hello &lt;num&gt;;
2323
			poll &lt;num&gt;;
2324
			retransmit &lt;num&gt;;
2325
			priority &lt;num&gt;;
2326
			wait &lt;num&gt;;
2327
			dead count &lt;num&gt;;
2328
			dead &lt;num&gt;;
2329
			secondary &lt;switch&gt;;
2330
			rx buffer [normal|large|&lt;num&gt;];
2331
			tx length &lt;num&gt;;
2332
			type [broadcast|bcast|pointopoint|ptp|
2333
				nonbroadcast|nbma|pointomultipoint|ptmp];
2334
			strict nonbroadcast &lt;switch&gt;;
2335
			real broadcast &lt;switch&gt;;
2336
			ptp netmask &lt;switch&gt;;
2337
			check link &lt;switch&gt;;
2338
			bfd &lt;switch&gt;;
2339
			ecmp weight &lt;num&gt;;
2340
			ttl security [&lt;switch&gt;; | tx only]
2341
			tx class|dscp &lt;num&gt;;
2342
			tx priority &lt;num&gt;;
2343
			authentication [none|simple|cryptographic];
2344
			password "&lt;text&gt;";
2345
			password "&lt;text&gt;" {
2346
				id &lt;num&gt;;
2347
				generate from "&lt;date&gt;";
2348
				generate to "&lt;date&gt;";
2349
				accept from "&lt;date&gt;";
2350
				accept to "&lt;date&gt;";
2351
			};
2352
			neighbors {
2353
				&lt;ip&gt;;
2354
				&lt;ip&gt; eligible;
2355
			};
2356
		};
2357
		virtual link &lt;id&gt; [instance &lt;num&gt;] {
2358
			hello &lt;num&gt;;
2359
			retransmit &lt;num&gt;;
2360
			wait &lt;num&gt;;
2361
			dead count &lt;num&gt;;
2362
			dead &lt;num&gt;;
2363
			authentication [none|simple|cryptographic];
2364
			password "&lt;text&gt;";
2365
		};
2366
	};
2367
}
2368
</code>
2369

    
2370
<descrip>
2371
	<tag>rfc1583compat <M>switch</M></tag>
2372
	This option controls compatibility of routing table calculation with
2373
	RFC 1583 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">.
2374
	Default	value is no.
2375

    
2376
	<tag>stub router <M>switch</M></tag>
2377
	This option configures the router to be a stub router, i.e., a router
2378
	that participates in the OSPF topology but does not allow transit
2379
	traffic. In OSPFv2, this is implemented by advertising maximum metric
2380
	for outgoing links, as suggested by
2381
	RFC 3137 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3137.txt">.
2382
	In OSPFv3, the stub router behavior is announced by clearing the R-bit
2383
	in the router LSA. Default value is no.
2384

    
2385
	<tag>tick <M>num</M></tag>
2386
	The routing table calculation and clean-up of areas' databases is not
2387
	performed when a single link state change arrives. To lower the CPU
2388
	utilization, it's processed later at periodical intervals of <m/num/
2389
	seconds. The default value is 1.
2390

    
2391
	<tag>ecmp <M>switch</M> [limit <M>number</M>]</tag>
2392
	This option specifies whether OSPF is allowed to generate ECMP
2393
	(equal-cost multipath) routes. Such routes are used when there are
2394
	several directions to the destination, each with the same (computed)
2395
	cost. This option also allows to specify a limit on maximal number of
2396
	nexthops in one route. By default, ECMP is disabled. If enabled,
2397
	default	value of the limit is 16.
2398

    
2399
	<tag>area <M>id</M></tag>
2400
	This defines an OSPF area with given area ID (an integer or an IPv4
2401
	address, similarly to a router ID). The most important area is the
2402
	backbone (ID 0) to which every other area must be connected.
2403

    
2404
	<tag>stub</tag>
2405
	This option configures the area to be a stub area. External routes are
2406
	not flooded into stub areas. Also summary LSAs can be limited in stub
2407
	areas (see option <cf/summary/). By default, the area is not a stub
2408
	area.
2409

    
2410
	<tag>nssa</tag>
2411
	This option configures the area to be a NSSA (Not-So-Stubby Area). NSSA
2412
	is a variant of a stub area which allows a limited way of external route
2413
	propagation. Global external routes are not propagated into a NSSA, but
2414
	an external route can be imported into NSSA as a (area-wide) NSSA-LSA
2415
	(and possibly translated and/or aggregated on area boundary). By
2416
	default, the area is not NSSA.
2417

    
2418
	<tag>summary <M>switch</M></tag>
2419
	This option controls propagation of summary LSAs into stub or NSSA
2420
	areas. If enabled, summary LSAs are propagated as usual, otherwise just
2421
	the default summary route (0.0.0.0/0) is propagated (this is sometimes
2422
	called totally stubby area). If a stub area has more area boundary
2423
	routers, propagating summary LSAs could lead to more efficient routing
2424
	at the cost of larger link state database. Default value is no.
2425

    
2426
	<tag>default nssa <M>switch</M></tag>
2427
	When <cf/summary/ option is enabled, default summary route is no longer
2428
	propagated to the NSSA. In that case, this option allows to originate
2429
	default route as NSSA-LSA to the NSSA. Default value is no.
2430

    
2431
	<tag>default cost <M>num</M></tag>
2432
	This option controls the cost of a default route propagated to stub and
2433
	NSSA areas. Default value is 1000.
2434

    
2435
	<tag>default cost2 <M>num</M></tag>
2436
	When a default route is originated as NSSA-LSA, its cost can use either
2437
	type 1 or type 2 metric. This option allows to specify the cost of a
2438
	default route in type 2 metric. By default, type 1 metric (option
2439
	<cf/default cost/) is used.
2440

    
2441
	<tag>translator <M>switch</M></tag>
2442
	This option controls translation of NSSA-LSAs into external LSAs. By
2443
	default, one translator per NSSA is automatically elected from area
2444
	boundary routers. If enabled, this area boundary router would
2445
	unconditionally translate all NSSA-LSAs regardless of translator
2446
	election. Default value is no.
2447

    
2448
	<tag>translator stability <M>num</M></tag>
2449
	This option controls the translator stability interval (in seconds).
2450
	When the new translator is elected, the old one keeps translating until
2451
	the interval is over. Default value is 40.
2452

    
2453
	<tag>networks { <m/set/ }</tag>
2454
	Definition of area IP ranges. This is used in summary LSA origination.
2455
	Hidden networks are not propagated into other areas.
2456

    
2457
	<tag>external { <m/set/ }</tag>
2458
	Definition of external area IP ranges for NSSAs. This is used for
2459
	NSSA-LSA translation. Hidden networks are not translated into external
2460
	LSAs. Networks can have configured route tag.
2461

    
2462
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
2463
	Stub networks are networks that are not transit networks between OSPF
2464
	routers. They are also propagated through an OSPF area as a part of a
2465
	link state database. By default, BIRD generates a stub network record
2466
	for each primary network address on each OSPF interface that does not
2467
	have any OSPF neighbors, and also for each non-primary network address
2468
	on each OSPF interface. This option allows to alter a set of stub
2469
	networks propagated by this router.
2470

    
2471
	Each instance of this option adds a stub network with given network
2472
	prefix to the set of propagated stub network, unless option <cf/hidden/
2473
	is used. It also suppresses default stub networks for given network
2474
	prefix. When option <cf/summary/ is used, also default stub networks
2475
	that are subnetworks of given stub network are suppressed. This might be
2476
	used, for example, to aggregate generated stub networks.
2477
	 
2478
	<tag>interface <M>pattern</M> [instance <m/num/]</tag>
2479
	Defines that the specified interfaces belong to the area being defined.
2480
	See <ref id="dsc-iface" name="interface"> common option for detailed
2481
	description. In OSPFv2, extended interface clauses are used, because
2482
	OSPFv2 handles each network prefix as a separate virtual interface. In
2483
	OSPFv3, you can specify instance ID for that interface description, so
2484
	it is possible to have several instances of that interface with
2485
	different options or even in different areas.
2486

    
2487
	<tag>virtual link <M>id</M> [instance <m/num/]</tag>
2488
	Virtual link to router with the router id. Virtual link acts as a
2489
	point-to-point interface belonging to backbone. The actual area is used
2490
	as transport area. This item cannot be in the backbone. In OSPFv3, you
2491
	could also use several virtual links to one destination with different
2492
	instance IDs.
2493

    
2494
	<tag>cost <M>num</M></tag>
2495
	Specifies output cost (metric) of an interface. Default value is 10.
2496

    
2497
	<tag>stub <M>switch</M></tag>
2498
	If set to interface it does not listen to any packet and does not send
2499
	any hello. Default value is no.
2500

    
2501
	<tag>hello <M>num</M></tag>
2502
	Specifies interval in seconds between sending of Hello messages. Beware,
2503
	all routers on the same network need to have the same hello interval.
2504
	Default value is 10.
2505

    
2506
	<tag>poll <M>num</M></tag>
2507
	Specifies interval in seconds between sending of Hello messages for some
2508
	neighbors on NBMA network. Default value is 20.
2509

    
2510
	<tag>retransmit <M>num</M></tag>
2511
	Specifies interval in seconds between retransmissions of unacknowledged
2512
	updates. Default value is 5.
2513

    
2514
	<tag>priority <M>num</M></tag>
2515
	On every multiple access network (e.g., the Ethernet) Designed Router
2516
	and Backup Designed router are elected. These routers have some special
2517
	functions in the flooding process. Higher priority increases preferences
2518
	in this election. Routers with priority 0 are not eligible. Default
2519
	value is 1.
2520

    
2521
	<tag>wait <M>num</M></tag>
2522
	After start, router waits for the specified number of seconds between
2523
	starting election and building adjacency. Default value is 40.
2524
	 
2525
	<tag>dead count <M>num</M></tag>
2526
	When the router does not receive any messages from a neighbor in
2527
	<m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
2528

    
2529
	<tag>dead <M>num</M></tag>
2530
	When the router does not receive any messages from a neighbor in
2531
	<m/dead/ seconds, it will consider the neighbor down. If both directives
2532
	<cf/dead count/ and <cf/dead/ are used, <cf/dead/ has precendence.
2533

    
2534
	<tag>secondary <M>switch</M></tag>
2535
	On BSD systems, older versions of BIRD supported OSPFv2 only for the
2536
	primary IP address of an interface, other IP ranges on the interface
2537
	were handled as stub networks. Since v1.4.1, regular operation on
2538
	secondary IP addresses is supported, but disabled by default for
2539
	compatibility. This option allows to enable it. The option is a
2540
	transitional measure, will be removed in the next major release as the
2541
	behavior will be changed. On Linux systems, the option is irrelevant, as
2542
	operation on non-primary addresses is already the regular behavior.
2543

    
2544
	<tag>rx buffer <M>num</M></tag>
2545
	This option allows to specify the size of buffers used for packet
2546
	processing. The buffer size should be bigger than maximal size of any
2547
	packets. By default, buffers are dynamically resized as needed, but a
2548
	fixed value could be specified. Value <cf/large/ means maximal allowed
2549
	packet size - 65535.
2550

    
2551
	<tag>tx length <M>num</M></tag>
2552
	Transmitted OSPF messages that contain large amount of information are
2553
	segmented to separate OSPF packets to avoid IP fragmentation. This
2554
	option specifies the soft ceiling for the length of generated OSPF
2555
	packets. Default value is the MTU of the network interface. Note that
2556
	larger OSPF packets may still be generated if underlying OSPF messages
2557
	cannot be splitted (e.g. when one large LSA is propagated).
2558

    
2559
	<tag>type broadcast|bcast</tag>
2560
	BIRD detects a type of a connected network automatically, but sometimes
2561
	it's convenient to force use of a different type manually. On broadcast
2562
	networks (like ethernet), flooding and Hello messages are sent using
2563
	multicasts (a single packet for all the neighbors). A designated router
2564
	is elected and it is responsible for synchronizing the link-state
2565
	databases and originating network LSAs. This network type cannot be used
2566
	on physically NBMA networks and on unnumbered networks (networks without
2567
	proper IP prefix).
2568

    
2569
	<tag>type pointopoint|ptp</tag>
2570
	Point-to-point networks connect just 2 routers together. No election is
2571
	performed and no network LSA is originated, which makes it simpler and
2572
	faster to establish. This network type is useful not only for physically
2573
	PtP ifaces (like PPP or tunnels), but also for broadcast networks used
2574
	as PtP links. This network type cannot be used on physically NBMA
2575
	networks.
2576

    
2577
	<tag>type nonbroadcast|nbma</tag>
2578
	On NBMA networks, the packets are sent to each neighbor separately
2579
	because of lack of multicast capabilities. Like on broadcast networks,
2580
	a designated router is elected, which plays a central role in propagation
2581
	of LSAs. This network type cannot be used on unnumbered networks.
2582

    
2583
	<tag>type pointomultipoint|ptmp</tag>
2584
	This is another network type designed to handle NBMA networks. In this
2585
	case the NBMA network is treated as a collection of PtP links. This is
2586
	useful if not every pair of routers on the NBMA network has direct
2587
	communication, or if the NBMA network is used as an (possibly
2588
	unnumbered) PtP link.
2589

    
2590
	<tag>strict nonbroadcast <M>switch</M></tag>
2591
	If set, don't send hello to any undefined neighbor. This switch is
2592
	ignored on other than NBMA or PtMP networks. Default value is no.
2593

    
2594
	<tag>real broadcast <m/switch/</tag>
2595
	In <cf/type broadcast/ or <cf/type ptp/ network configuration, OSPF
2596
	packets are sent as IP multicast packets. This option changes the
2597
	behavior to using old-fashioned IP broadcast packets. This may be useful
2598
	as a workaround if IP multicast for some reason does not work or does
2599
	not work reliably. This is a non-standard option and probably is not
2600
	interoperable with other OSPF implementations. Default value is no.
2601

    
2602
	<tag>ptp netmask <m/switch/</tag>
2603
	In <cf/type ptp/ network configurations, OSPFv2 implementations should
2604
	ignore received netmask field in hello packets and should send hello
2605
	packets with zero netmask field on unnumbered PtP links. But some OSPFv2
2606
	implementations perform netmask checking even for PtP links. This option
2607
	specifies whether real netmask will be used in hello packets on <cf/type
2608
 	ptp/ interfaces. You should ignore this option unless you meet some
2609
	compatibility problems related to this issue. Default value is no for
2610
	unnumbered PtP links, yes otherwise.
2611

    
2612
	<tag>check link <M>switch</M></tag>
2613
	If set, a hardware link state (reported by OS) is taken into consideration.
2614
	When a link disappears (e.g. an ethernet cable is unplugged), neighbors
2615
	are immediately considered unreachable and only the address of the iface
2616
	(instead of whole network prefix) is propagated. It is possible that
2617
	some hardware drivers or platforms do not implement this feature.
2618
	Default value is no.
2619

    
2620
	<tag>bfd <M>switch</M></tag>
2621
	OSPF could use BFD protocol as an advisory mechanism for neighbor
2622
	liveness and failure detection. If enabled, BIRD setups a BFD session
2623
	for each OSPF neighbor and tracks its liveness by it. This has an
2624
	advantage of an order of magnitude lower detection times in case of
2625
	failure. Note that BFD protocol also has to be configured, see
2626
	<ref id="sect-bfd" name="BFD"> section for details. Default value is no.
2627

    
2628
	<tag>ttl security [<m/switch/ | tx only]</tag>
2629
	TTL security is a feature that protects routing protocols from remote
2630
	spoofed packets by using TTL 255 instead of TTL 1 for protocol packets
2631
	destined to neighbors. Because TTL is decremented when packets are
2632
	forwarded, it is non-trivial to spoof packets with TTL 255 from remote
2633
	locations. Note that this option would interfere with OSPF virtual
2634
	links.
2635

    
2636
	If this option is enabled, the router will send OSPF packets with TTL
2637
	255 and drop received packets with TTL less than 255. If this option si
2638
	set to <cf/tx only/, TTL 255 is used for sent packets, but is not
2639
	checked for received packets. Default value is no.
2640

    
2641
	<tag>tx class|dscp|priority <m/num/</tag>
2642
	These options specify the ToS/DiffServ/Traffic class/Priority of the
2643
	outgoing OSPF packets. See <ref id="dsc-prio" name="tx class"> common
2644
	option for detailed description.
2645

    
2646
	<tag>ecmp weight <M>num</M></tag>
2647
	When ECMP (multipath) routes are allowed, this value specifies a
2648
	relative weight used for nexthops going through the iface. Allowed
2649
	values are 1-256. Default value is 1.
2650

    
2651
	<tag>authentication none</tag>
2652
	No passwords are sent in OSPF packets. This is the default value.
2653

    
2654
	<tag>authentication simple</tag>
2655
	Every packet carries 8 bytes of password. Received packets lacking this
2656
	password are ignored. This authentication mechanism is very weak.
2657

    
2658
	<tag>authentication cryptographic</tag>
2659
	16-byte long MD5 digest is appended to every packet. For the digest
2660
	generation 16-byte long passwords are used. Those passwords are not sent
2661
	via network, so this mechanism is quite secure. Packets can still be
2662
	read by an attacker.
2663

    
2664
	<tag>password "<M>text</M>"</tag>
2665
	An 8-byte or 16-byte password used for authentication. See
2666
	<ref id="dsc-pass" name="password"> common option for detailed
2667
	description.
2668

    
2669
	<tag>neighbors { <m/set/ } </tag>
2670
	A set of neighbors to which Hello messages on NBMA or PtMP networks are
2671
	to be sent. For NBMA networks, some of them could be marked as eligible.
2672
	In OSPFv3, link-local addresses should be used, using global ones is
2673
	possible, but it is nonstandard and might be problematic. And definitely,
2674
	link-local and global addresses should not be mixed.
2675
</descrip>
2676

    
2677
<sect1>Attributes
2678

    
2679
<p>OSPF defines four route attributes. Each internal route has a <cf/metric/.
2680

    
2681
<p>Metric is ranging from 1 to infinity (65535). External routes use
2682
<cf/metric type 1/ or <cf/metric type 2/. A <cf/metric of type 1/ is comparable
2683
with internal <cf/metric/, a <cf/metric of type 2/ is always longer than any
2684
<cf/metric of type 1/ or any <cf/internal metric/. <cf/Internal metric/ or
2685
<cf/metric of type 1/ is stored in attribute <cf/ospf_metric1/, <cf/metric type
2686
2/ is stored in attribute <cf/ospf_metric2/. If you specify both metrics only
2687
metric1 is used.
2688

    
2689
<p>Each external route can also carry attribute <cf/ospf_tag/ which is a 32-bit
2690
integer which is used when exporting routes to other protocols; otherwise, it
2691
doesn't affect routing inside the OSPF domain at all. The fourth attribute
2692
<cf/ospf_router_id/ is a router ID of the router advertising that route /
2693
network. This attribute is read-only. Default is <cf/ospf_metric2 = 10000/ and
2694
<cf/ospf_tag = 0/.
2695

    
2696
<sect1>Example
2697

    
2698
<p><code>
2699
protocol ospf MyOSPF {
2700
	rfc1583compat yes;
2701
	tick 2;
2702
	export filter {
2703
		if source = RTS_BGP then {
2704
			ospf_metric1 = 100;
2705
			accept;
2706
		}
2707
		reject;
2708
	};
2709
	area 0.0.0.0 {
2710
		interface "eth*" {
2711
			cost 11;
2712
			hello 15;
2713
			priority 100;
2714
			retransmit 7;
2715
			authentication simple;
2716
			password "aaa";
2717
		};
2718
		interface "ppp*" {
2719
			cost 100;
2720
			authentication cryptographic;
2721
			password "abc" {
2722
				id 1;
2723
				generate to "22-04-2003 11:00:06";
2724
				accept from "17-01-2001 12:01:05";
2725
			};
2726
			password "def" {
2727
				id 2;
2728
				generate to "22-07-2005 17:03:21";
2729
				accept from "22-02-2001 11:34:06";
2730
			};
2731
		};
2732
		interface "arc0" {
2733
			cost 10;
2734
			stub yes;
2735
		};
2736
		interface "arc1";
2737
	};
2738
	area 120 {
2739
		stub yes;
2740
		networks {
2741
			172.16.1.0/24;
2742
			172.16.2.0/24 hidden;
2743
		}
2744
		interface "-arc0" , "arc*" {
2745
			type nonbroadcast;
2746
			authentication none;
2747
			strict nonbroadcast yes;
2748
			wait 120;
2749
			poll 40;
2750
			dead count 8;
2751
			neighbors {
2752
				192.168.120.1 eligible;
2753
				192.168.120.2;
2754
				192.168.120.10;
2755
			};
2756
		};
2757
	};
2758
}
2759
</code>
2760

    
2761

    
2762
<sect>Pipe
2763

    
2764
<sect1>Introduction
2765

    
2766
<p>The Pipe protocol serves as a link between two routing tables, allowing
2767
routes to be passed from a table declared as primary (i.e., the one the pipe is
2768
connected to using the <cf/table/ configuration keyword) to the secondary one
2769
(declared using <cf/peer table/) and vice versa, depending on what's allowed by
2770
the filters. Export filters control export of routes from the primary table to
2771
the secondary one, import filters control the opposite direction.
2772

    
2773
<p>The Pipe protocol may work in the transparent mode mode or in the opaque
2774
mode. In the transparent mode, the Pipe protocol retransmits all routes from
2775
one table to the other table, retaining their original source and attributes.
2776
If import and export filters are set to accept, then both tables would have
2777
the same content. The transparent mode is the default mode.
2778

    
2779
<p>In the opaque mode, the Pipe protocol retransmits optimal route from one
2780
table to the other table in a similar way like other protocols send and receive
2781
routes. Retransmitted route will have the source set to the Pipe protocol, which
2782
may limit access to protocol specific route attributes. This mode is mainly for
2783
compatibility, it is not suggested for new configs. The mode can be changed by
2784
<tt/mode/ option.
2785

    
2786
<p>The primary use of multiple routing tables and the Pipe protocol is for
2787
policy routing, where handling of a single packet doesn't depend only on its
2788
destination address, but also on its source address, source interface, protocol
2789
type and other similar parameters. In many systems (Linux being a good example),
2790
the kernel allows to enforce routing policies by defining routing rules which
2791
choose one of several routing tables to be used for a packet according to its
2792
parameters. Setting of these rules is outside the scope of BIRD's work (on
2793
Linux, you can use the <tt/ip/ command), but you can create several routing
2794
tables in BIRD, connect them to the kernel ones, use filters to control which
2795
routes appear in which tables and also you can employ the Pipe protocol for
2796
exporting a selected subset of one table to another one.
2797

    
2798
<sect1>Configuration
2799

    
2800
<p><descrip>
2801
	<tag>peer table <m/table/</tag>
2802
	Defines secondary routing table to connect to. The primary one is
2803
	selected by the <cf/table/ keyword.
2804

    
2805
	<tag>mode opaque|transparent</tag>
2806
	Specifies the mode for the pipe to work in. Default is transparent.
2807
</descrip>
2808

    
2809
<sect1>Attributes
2810

    
2811
<p>The Pipe protocol doesn't define any route attributes.
2812

    
2813
<sect1>Example
2814

    
2815
<p>Let's consider a router which serves as a boundary router of two different
2816
autonomous systems, each of them connected to a subset of interfaces of the
2817
router, having its own exterior connectivity and wishing to use the other AS as
2818
a backup connectivity in case of outage of its own exterior line.
2819

    
2820
<p>Probably the simplest solution to this situation is to use two routing tables
2821
(we'll call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that
2822
packets having arrived from interfaces belonging to the first AS will be routed
2823
according to <cf/as1/ and similarly for the second AS. Thus we have split our
2824
router to two logical routers, each one acting on its own routing table, having
2825
its own routing protocols on its own interfaces. In order to use the other AS's
2826
routes for backup purposes, we can pass the routes between the tables through a
2827
Pipe protocol while decreasing their preferences and correcting their BGP paths
2828
to reflect the AS boundary crossing.
2829

    
2830
<code>
2831
table as1;				# Define the tables
2832
table as2;
2833

    
2834
protocol kernel kern1 {			# Synchronize them with the kernel
2835
	table as1;
2836
	kernel table 1;
2837
}
2838

    
2839
protocol kernel kern2 {
2840
	table as2;
2841
	kernel table 2;
2842
}
2843

    
2844
protocol bgp bgp1 {			# The outside connections
2845
	table as1;
2846
	local as 1;
2847
	neighbor 192.168.0.1 as 1001;
2848
	export all;
2849
	import all;
2850
}
2851

    
2852
protocol bgp bgp2 {
2853
	table as2;
2854
	local as 2;
2855
	neighbor 10.0.0.1 as 1002;
2856
	export all;
2857
	import all;
2858
}
2859

    
2860
protocol pipe {				# The Pipe
2861
	table as1;
2862
	peer table as2;
2863
	export filter {
2864
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
2865
			if preference>10 then preference = preference-10;
2866
			if source=RTS_BGP then bgp_path.prepend(1);
2867
			accept;
2868
		}
2869
		reject;
2870
	};
2871
	import filter {
2872
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
2873
			if preference>10 then preference = preference-10;
2874
			if source=RTS_BGP then bgp_path.prepend(2);
2875
			accept;
2876
		}
2877
		reject;
2878
	};
2879
}
2880
</code>
2881

    
2882

    
2883
<sect>RAdv
2884

    
2885
<sect1>Introduction
2886

    
2887
<p>The RAdv protocol is an implementation of Router Advertisements, which are
2888
used in the IPv6 stateless autoconfiguration. IPv6 routers send (in irregular
2889
time intervals or as an answer to a request) advertisement packets to connected
2890
networks. These packets contain basic information about a local network (e.g. a
2891
list of network prefixes), which allows network hosts to autoconfigure network
2892
addresses and choose a default route. BIRD implements router behavior as defined
2893
in RFC 4861<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4861.txt">
2894
and also the DNS extensions from
2895
RFC 6106<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc6106.txt">.
2896

    
2897
<sect1>Configuration
2898

    
2899
<p>There are several classes of definitions in RAdv configuration -- interface
2900
definitions, prefix definitions and DNS definitions:
2901

    
2902
<descrip>
2903
	<tag>interface <m/pattern [, ...]/ { <m/options/ }</tag>
2904
	Interface definitions specify a set of interfaces on which the
2905
	protocol is activated and contain interface specific options.
2906
	See <ref id="dsc-iface" name="interface"> common options for
2907
	detailed description.
2908

    
2909
	<tag>prefix <m/prefix/ { <m/options/ }</tag>
2910
	Prefix definitions allow to modify a list of advertised prefixes. By
2911
	default, the advertised prefixes are the same as the network prefixes
2912
	assigned to the interface. For each network prefix, the matching prefix
2913
	definition is found and its options are used. If no matching prefix
2914
	definition is found, the prefix is used with default options.
2915

    
2916
	Prefix definitions can be either global or interface-specific. The
2917
	second ones are part of interface options. The prefix definition
2918
	matching is done in the first-match style, when interface-specific
2919
	definitions are processed before global definitions. As expected, the
2920
	prefix definition is matching if the network prefix is a subnet of the
2921
	prefix in prefix definition.
2922

    
2923
	<tag>rdnss { <m/options/ }</tag>
2924
	RDNSS definitions allow to specify a list of advertised recursive DNS
2925
	servers together with their options. As options are seldom necessary,
2926
	there is also a short variant <cf>rdnss <m/address/</cf> that just
2927
	specifies one DNS server. Multiple definitions are cumulative. RDNSS
2928
	definitions may also be interface-specific when used inside interface
2929
	options. By default, interface uses both global and interface-specific
2930
	options, but that can be changed by <cf/rdnss local/ option.
2931

    
2932
	<tag>dnssl { <m/options/ }</tag>
2933
	DNSSL definitions allow to specify a list of advertised DNS search
2934
	domains together with their options. Like <cf/rdnss/ above, multiple
2935
	definitions are cumulative, they can be used also as interface-specific
2936
	options and there is a short variant <cf>dnssl <m/domain/</cf> that just
2937
	specifies one DNS search domain.
2938

    
2939
	<label id="dsc-trigger"> <tag>trigger <m/prefix/</tag>
2940
	RAdv protocol could be configured to change its behavior based on
2941
	availability of routes. When this option is used, the protocol waits in
2942
	suppressed state until a <it/trigger route/ (for the specified network)
2943
	is exported to the protocol, the protocol also returnsd to suppressed
2944
	state if the <it/trigger route/ disappears. Note that route export
2945
	depends on specified export filter, as usual. This option could be used,
2946
	e.g., for handling failover in multihoming scenarios.
2947

    
2948
	During suppressed state, router advertisements are generated, but with
2949
	some fields zeroed. Exact behavior depends on which fields are zeroed,
2950
	this can be configured by <cf/sensitive/ option for appropriate
2951
	fields. By default, just <cf/default lifetime/ (also called <cf/router
2952
	lifetime/) is zeroed, which means hosts cannot use the router as a
2953
	default router. <cf/preferred lifetime/ and <cf/valid lifetime/ could
2954
	also be configured as <cf/sensitive/ for a prefix, which would cause
2955
	autoconfigured IPs to be deprecated or even removed.
2956
</descrip>
2957

    
2958
<p>Interface specific options:
2959

    
2960
<descrip>
2961
	<tag>max ra interval <m/expr/</tag>
2962
	Unsolicited router advertisements are sent in irregular time intervals.
2963
	This option specifies the maximum length of these intervals, in seconds.
2964
	Valid values are 4-1800. Default: 600
2965

    
2966
	<tag>min ra interval <m/expr/</tag>
2967
	This option specifies the minimum length of that intervals, in seconds.
2968
	Must be at least 3 and at most 3/4 * <cf/max ra interval/. Default:
2969
	about 1/3 * <cf/max ra interval/.
2970

    
2971
	<tag>min delay <m/expr/</tag>
2972
	The minimum delay between two consecutive router advertisements, in
2973
	seconds. Default: 3
2974

    
2975
	<tag>managed <m/switch/</tag>
2976
	This option specifies whether hosts should use DHCPv6 for IP address
2977
	configuration. Default: no
2978

    
2979
	<tag>other config <m/switch/</tag>
2980
	This option specifies whether hosts should use DHCPv6 to receive other
2981
	configuration information. Default: no
2982

    
2983
	<tag>link mtu <m/expr/</tag>
2984
	This option specifies which value of MTU should be used by hosts. 0
2985
	means unspecified. Default: 0
2986

    
2987
	<tag>reachable time <m/expr/</tag>
2988
	This option specifies the time (in milliseconds) how long hosts should
2989
	assume a neighbor is reachable (from the last confirmation). Maximum is
2990
	3600000, 0 means unspecified. Default 0.
2991

    
2992
	<tag>retrans timer <m/expr/</tag>
2993
	This option specifies the time (in milliseconds) how long hosts should
2994
	wait before retransmitting Neighbor Solicitation messages. 0 means
2995
	unspecified. Default 0.
2996

    
2997
	<tag>current hop limit <m/expr/</tag>
2998
	This option specifies which value of Hop Limit should be used by
2999
	hosts. Valid values are 0-255, 0 means unspecified. Default: 64
3000

    
3001
	<tag>default lifetime <m/expr/ [sensitive <m/switch/]</tag>
3002
	This option specifies the time (in seconds) how long (after the receipt
3003
	of RA) hosts may use the router as a default router. 0 means do not use
3004
	as a default router. For <cf/sensitive/ option, see <ref id="dsc-trigger" name="trigger">.
3005
	Default: 3 * <cf/max ra	interval/, <cf/sensitive/ yes.
3006

    
3007
	<tag>rdnss local <m/switch/</tag>
3008
	Use only local (interface-specific) RDNSS definitions for this
3009
	interface. Otherwise, both global and local definitions are used. Could
3010
	also be used to disable RDNSS for given interface if no local definitons
3011
	are specified. Default: no.
3012

    
3013
	<tag>dnssl local <m/switch/</tag>
3014
	Use only local DNSSL definitions for this interface. See <cf/rdnss local/
3015
	option above. Default: no.
3016
</descrip>
3017

    
3018

    
3019
<p>Prefix specific options:
3020

    
3021
<descrip>
3022
	<tag>skip <m/switch/</tag>
3023
	This option allows to specify that given prefix should not be
3024
	advertised. This is useful for making exceptions from a default policy
3025
	of advertising all prefixes. Note that for withdrawing an already
3026
	advertised prefix it is more useful to advertise it with zero valid
3027
	lifetime. Default: no
3028

    
3029
	<tag>onlink <m/switch/</tag>
3030
	This option specifies whether hosts may use the advertised prefix for
3031
	onlink determination. Default: yes
3032

    
3033
	<tag>autonomous <m/switch/</tag>
3034
	This option specifies whether hosts may use the advertised prefix for
3035
	stateless autoconfiguration. Default: yes
3036

    
3037
	<tag>valid lifetime <m/expr/ [sensitive <m/switch/]</tag>
3038
	This option specifies the time (in seconds) how long (after the
3039
	receipt of RA) the prefix information is valid, i.e., autoconfigured
3040
	IP addresses can be assigned and hosts with that IP addresses are
3041
	considered directly reachable. 0 means the prefix is no longer
3042
	valid. For <cf/sensitive/ option, see <ref id="dsc-trigger" name="trigger">.
3043
	Default: 86400 (1 day), <cf/sensitive/ no.
3044

    
3045
	<tag>preferred lifetime <m/expr/ [sensitive <m/switch/]</tag>
3046
	This option specifies the time (in seconds) how long (after the
3047
	receipt of RA) IP addresses generated from the prefix using stateless
3048
	autoconfiguration remain preferred. For <cf/sensitive/ option,
3049
	see <ref id="dsc-trigger" name="trigger">. Default: 14400 (4 hours),
3050
	<cf/sensitive/ no.
3051
</descrip>
3052

    
3053

    
3054
<p>RDNSS specific options:
3055

    
3056
<descrip>
3057
	<tag>ns <m/address/</tag>
3058
	This option specifies one recursive DNS server. Can be used multiple
3059
	times for multiple servers. It is mandatory to have at least one
3060
	<cf/ns/ option in <cf/rdnss/ definition.
3061

    
3062
	<tag>lifetime [mult] <m/expr/</tag>
3063
	This option specifies the time how long the RDNSS information may be
3064
	used by clients after the receipt of RA. It is expressed either in
3065
	seconds or (when <cf/mult/ is used) in multiples of <cf/max ra
3066
	interval/. Note that RDNSS information is also invalidated when
3067
	<cf/default lifetime/ expires. 0 means these addresses are no longer
3068
	valid DNS servers. Default: 3 * <cf/max ra interval/.
3069
</descrip>
3070

    
3071

    
3072
<p>DNSSL specific options:
3073

    
3074
<descrip>
3075
	<tag>domain <m/address/</tag>
3076
	This option specifies one DNS search domain. Can be used multiple times
3077
	for multiple domains. It is mandatory to have at least one <cf/domain/
3078
	option in <cf/dnssl/ definition.
3079

    
3080
	<tag>lifetime [mult] <m/expr/</tag>
3081
	This option specifies the time how long the DNSSL information may be
3082
	used by clients after the receipt of RA. Details are the same as for
3083
	RDNSS <cf/lifetime/ option above. Default: 3 * <cf/max ra interval/.
3084
</descrip>
3085

    
3086

    
3087
<sect1>Example
3088

    
3089
<p><code>
3090
protocol radv {
3091
	interface "eth2" {
3092
		max ra interval 5;	# Fast failover with more routers
3093
		managed yes;		# Using DHCPv6 on eth2
3094
		prefix ::/0 {
3095
			autonomous off;	# So do not autoconfigure any IP
3096
		};
3097
	};
3098

    
3099
	interface "eth*";		# No need for any other options
3100

    
3101
	prefix 2001:0DB8:1234::/48 {
3102
		preferred lifetime 0;	# Deprecated address range
3103
	};
3104

    
3105
	prefix 2001:0DB8:2000::/48 {
3106
		autonomous off;		# Do not autoconfigure
3107
	};
3108

    
3109
	rdnss 2001:0DB8:1234::10;	# Short form of RDNSS
3110

    
3111
	rdnss {
3112
		lifetime mult 10;
3113
		ns 2001:0DB8:1234::11;
3114
		ns 2001:0DB8:1234::12;
3115
	};
3116

    
3117
	dnssl {
3118
		lifetime 3600;
3119
		domain "abc.com";
3120
		domain "xyz.com";
3121
	};
3122
}
3123
</code>
3124

    
3125

    
3126
<sect>RIP
3127

    
3128
<sect1>Introduction
3129

    
3130
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol,
3131
where each router broadcasts (to all its neighbors) distances to all networks it
3132
can reach. When a router hears distance to another network, it increments it and
3133
broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some
3134
network goes unreachable, routers keep telling each other that its distance is
3135
the original distance plus 1 (actually, plus interface metric, which is usually
3136
one). After some time, the distance reaches infinity (that's 15 in RIP) and all
3137
routers know that network is unreachable. RIP tries to minimize situations where
3138
counting to infinity is necessary, because it is slow. Due to infinity being 16,
3139
you can't use RIP on networks where maximal distance is higher than 15
3140
hosts. You can read more about RIP at
3141
<HTMLURL URL="http://www.ietf.org/html.charters/rip-charter.html"
3142
name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4
3143
(RFC 1723 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">) and IPv6
3144
(RFC 2080 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2080.txt">) versions
3145
of RIP are supported by BIRD, historical RIPv1
3146
(RFC 1058 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1058.txt">) is not
3147
currently supported. RIPv4 MD5 authentication
3148
(RFC 2082 <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is
3149
supported.
3150

    
3151
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
3152
convergence, big network load and inability to handle larger networks makes it
3153
pretty much obsolete. It is still usable on very small networks.
3154

    
3155
<sect1>Configuration
3156

    
3157
<p>In addition to options common for all to other protocols, RIP supports the
3158
following ones:
3159

    
3160
<descrip>
3161
	<tag>authentication none|plaintext|md5</tag>
3162
	Selects authentication method to be used. <cf/none/ means that packets
3163
	are not authenticated at all, <cf/plaintext/ means that a plaintext
3164
	password is embedded into each packet, and <cf/md5/ means that packets
3165
	are authenticated using a MD5 cryptographic hash. If you set
3166
	authentication to not-none, it is a good idea to add <cf>password</cf>
3167
	section. Default: none.
3168

    
3169
	<tag>honor always|neighbor|never</tag>
3170
	Specifies when should requests for dumping routing table be honored.
3171
	(Always, when sent from a host on a directly connected network or
3172
	never.) Routing table updates are honored only from neighbors, that is
3173
	not configurable. Default: never.
3174
</descrip>
3175

    
3176
<p>There are some options that can be specified per-interface:
3177

    
3178
<descrip>
3179
	<tag>metric <m/num/</tag>
3180
	This option specifies the metric of the interface. Valid
3181

    
3182
	<tag>mode multicast|broadcast|quiet|nolisten|version1</tag>
3183
	This option selects the mode for RIP to use on the interface. If nothing
3184
	is specified, RIP runs in multicast mode. <cf/version1/ is currently
3185
	equivalent to <cf/broadcast/, and it makes RIP talk to a broadcast
3186
	address even through multicast mode is possible. <cf/quiet/ option means
3187
	that RIP will not transmit any periodic messages to this interface and
3188
	<cf/nolisten/ means that RIP will send to this interface butnot listen
3189
	to it.
3190

    
3191
	<tag>ttl security [<m/switch/ | tx only]</tag>
3192
	TTL security is a feature that protects routing protocols from remote
3193
	spoofed packets by using TTL 255 instead of TTL 1 for protocol packets
3194
	destined to neighbors. Because TTL is decremented when packets are
3195
	forwarded, it is non-trivial to spoof packets with TTL 255 from remote
3196
	locations.
3197

    
3198
	If this option is enabled, the router will send RIP packets with TTL 255
3199
	and drop received packets with TTL less than 255. If this option si set
3200
	to <cf/tx only/, TTL 255 is used for sent packets, but is not checked
3201
	for received packets. Such setting does not offer protection, but offers
3202
	compatibility with neighbors regardless of whether they use ttl
3203
	security.
3204

    
3205
	Note that for RIPng, TTL security is a standard behavior (required by
3206
	RFC 2080), but BIRD uses <cf/tx only/ by default, for compatibility with
3207
	older versions. For IPv4 RIP, default value is no.
3208

    
3209
	<tag>tx class|dscp|priority <m/num/</tag>
3210
	These options specify the ToS/DiffServ/Traffic class/Priority of the
3211
	outgoing RIP packets. See <ref id="dsc-prio" name="tx class"> common
3212
	option for detailed description.
3213
</descrip>
3214

    
3215
<p>The following options generally override behavior specified in RFC. If you
3216
use any of these options, BIRD will no longer be RFC-compliant, which means it
3217
will not be able to talk to anything other than equally configured BIRD. I have
3218
warned you.
3219

    
3220
<descrip>
3221
	<tag>port <M>number</M></tag>
3222
	Selects IP port to operate on, default 520. (This is useful when testing
3223
	BIRD, if you set this to an address &gt;1024, you will not need to run
3224
	bird with UID==0).
3225

    
3226
	<tag>infinity <M>number</M></tag>
3227
	Selects the value of infinity, default is 16. Bigger values will make
3228
	protocol convergence even slower.
3229

    
3230
	<tag>period <M>number</M></tag>
3231
	Specifies the number of seconds between periodic updates. Default is 30
3232
	seconds. A lower number will mean faster convergence but bigger network
3233
	load. Do not use values lower than 12.
3234

    
3235
	<tag>timeout time <M>number</M></tag>
3236
	Specifies how old route has to be to be considered unreachable.
3237
	Default is 4*<cf/period/.
3238

    
3239
	<tag>garbage time <M>number</M></tag>
3240
	Specifies how old route has to be to be discarded. Default is
3241
	10*<cf/period/.
3242
</descrip>
3243

    
3244
<sect1>Attributes
3245

    
3246
<p>RIP defines two route attributes:
3247

    
3248
<descrip>
3249
	<tag>int <cf/rip_metric/</tag>
3250
	RIP metric of the route (ranging from 0 to <cf/infinity/).  When routes
3251
	from different RIP instances are available and all of them have the same
3252
	preference, BIRD prefers the route with lowest <cf/rip_metric/. When
3253
	importing a non-RIP route, the metric defaults to 5.
3254

    
3255
	<tag>int <cf/rip_tag/</tag>
3256
	RIP route tag: a 16-bit number which can be used to carry additional
3257
	information with the route (for example, an originating AS number in
3258
	case of external routes). When importing a non-RIP route, the tag
3259
	defaults to 0.
3260
</descrip>
3261

    
3262
<sect1>Example
3263

    
3264
<p><code>
3265
protocol rip MyRIP_test {
3266
        debug all;
3267
        port 1520;
3268
        period 12;
3269
        garbage time 60;
3270
        interface "eth0" { metric 3; mode multicast; };
3271
	interface "eth*" { metric 2; mode broadcast; };
3272
        honor neighbor;
3273
        authentication none;
3274
        import filter { print "importing"; accept; };
3275
        export filter { print "exporting"; accept; };
3276
}
3277
</code>
3278

    
3279

    
3280
<sect>Static
3281

    
3282
<p>The Static protocol doesn't communicate with other routers in the network,
3283
but instead it allows you to define routes manually. This is often used for
3284
specifying how to forward packets to parts of the network which don't use
3285
dynamic routing at all and also for defining sink routes (i.e., those telling to
3286
return packets as undeliverable if they are in your IP block, you don't have any
3287
specific destination for them and you don't want to send them out through the
3288
default route to prevent routing loops).
3289

    
3290
<p>There are five types of static routes: `classical' routes telling to forward
3291
packets to a neighboring router, multipath routes specifying several (possibly
3292
weighted) neighboring routers, device routes specifying forwarding to hosts on a
3293
directly connected network, recursive routes computing their nexthops by doing
3294
route table lookups for a given IP and special routes (sink, blackhole etc.)
3295
which specify a special action to be done instead of forwarding the packet.
3296

    
3297
<p>When the particular destination is not available (the interface is down or
3298
the next hop of the route is not a neighbor at the moment), Static just
3299
uninstalls the route from the table it is connected to and adds it again as soon
3300
as the destination becomes adjacent again.
3301

    
3302
<p>The Static protocol does not have many configuration options. The definition
3303
of the protocol contains mainly a list of static routes:
3304

    
3305
<descrip>
3306
	<tag>route <m/prefix/ via <m/ip/</tag>
3307
	Static route through a neighboring router.
3308

    
3309
	<tag>route <m/prefix/ multipath via <m/ip/ [weight <m/num/] [via ...]</tag>
3310
	Static multipath route. Contains several nexthops (gateways), possibly
3311
 	with their weights.
3312

    
3313
	<tag>route <m/prefix/ via <m/"interface"/</tag>
3314
	Static device route through an interface to hosts on a directly
3315
	connected network.
3316

    
3317
	<tag>route <m/prefix/ recursive <m/ip/</tag>
3318
	Static recursive route, its nexthop depends on a route table lookup for
3319
	given IP address.
3320

    
3321
	<tag>route <m/prefix/ blackhole|unreachable|prohibit</tag>
3322
	Special routes specifying to silently drop the packet, return it as
3323
	unreachable or return it as administratively prohibited. First two
3324
	targets are also known as <cf/drop/ and <cf/reject/.
3325

    
3326
	<tag>check link <m/switch/</tag>
3327
	If set, hardware link states of network interfaces are taken into
3328
	consideration.  When link disappears (e.g. ethernet cable is unplugged),
3329
	static routes directing to that interface are removed. It is possible
3330
	that some hardware drivers or platforms do not implement this feature.
3331
	Default: off.
3332

    
3333
	<tag>igp table <m/name/</tag>
3334
	Specifies a table that is used for route table lookups of recursive
3335
	routes. Default: the same table as the protocol is connected to.
3336
</descrip>
3337

    
3338
<p>Static routes have no specific attributes.
3339

    
3340
<p>Example static config might look like this:
3341

    
3342
<p><code>
3343
protocol static {
3344
	table testable;			 # Connect to a non-default routing table
3345
	route 0.0.0.0/0 via 198.51.100.130; # Default route
3346
	route 10.0.0.0/8 multipath	 # Multipath route
3347
		via 198.51.100.10 weight 2
3348
		via 198.51.100.20
3349
		via 192.0.2.1;
3350
	route 203.0.113.0/24 unreachable; # Sink route
3351
	route 10.2.0.0/24 via "arc0";	 # Secondary network
3352
}
3353
</code>
3354

    
3355

    
3356
<chapt>Conclusions
3357

    
3358
<sect>Future work
3359

    
3360
<p>Although BIRD supports all the commonly used routing protocols, there are
3361
still some features which would surely deserve to be implemented in future
3362
versions of BIRD:
3363

    
3364
<itemize>
3365
<item>Opaque LSA's
3366
<item>Route aggregation and flap dampening
3367
<item>Multipath routes
3368
<item>Multicast routing protocols
3369
<item>Ports to other systems
3370
</itemize>
3371

    
3372

    
3373
<sect>Getting more help
3374

    
3375
<p>If you use BIRD, you're welcome to join the bird-users mailing list
3376
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
3377
where you can share your experiences with the other users and consult
3378
your problems with the authors. To subscribe to the list, just send a
3379
<tt/subscribe bird-users/ command in a body of a mail to
3380
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
3381
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
3382

    
3383
<p>BIRD is a relatively young system and it probably contains some bugs. You can
3384
report any problems to the bird-users list and the authors will be glad to solve
3385
them, but before you do so, please make sure you have read the available
3386
documentation and that you are running the latest version (available at
3387
<HTMLURL URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">).
3388
(Of course, a patch which fixes the bug is always welcome as an attachment.)
3389

    
3390
<p>If you want to understand what is going inside, Internet standards are a good
3391
and interesting reading. You can get them from
3392
<HTMLURL URL="ftp://ftp.rfc-editor.org/" name="ftp.rfc-editor.org"> (or a
3393
nicely sorted version from <HTMLURL URL="ftp://atrey.karlin.mff.cuni.cz/pub/rfc"
3394
name="atrey.karlin.mff.cuni.cz:/pub/rfc">).
3395

    
3396
<p><it/Good luck!/
3397

    
3398
</book>
3399

    
3400
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3401
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