BIRD User's Guide <author> Ondrej Filip <it/<feela@network.cz>/, Pavel Machek <it/<pavel@ucw.cz>/, Martin Mares <it/<mj@ucw.cz>/, Ondrej Zajicek <it/<santiago@crfreenet.org>/ </author> <abstract> This document contains user documentation for the BIRD Internet Routing Daemon project. </abstract>  <toc>  <chapt>Introduction <sect>What is BIRD <label id="intro"> The name `BIRD' is actually an acronym standing for `BIRD Internet Routing Daemon'. Let's take a closer look at the meaning of the name: <em/BIRD/: Well, we think we have already explained that. It's an acronym standing for `BIRD Internet Routing Daemon', you remember, don't you? :-) <em/Internet Routing/: It's a program (well, a daemon, as you are going to discover in a moment) which works as a dynamic router in an Internet type network (that is, in a network running either the IPv4 or the IPv6 protocol). Routers are devices which forward packets between interconnected networks in order to allow hosts not connected directly to the same local area network to communicate with each other. They also communicate with the other routers in the Internet to discover the topology of the network which allows them to find optimal (in terms of some metric) rules for forwarding of packets (which are called routing tables) and to adapt themselves to the changing conditions such as outages of network links, building of new connections and so on. Most of these routers are costly dedicated devices running obscure firmware which is hard to configure and not open to any changes (on the other hand, their special hardware design allows them to keep up with lots of high-speed network interfaces, better than general-purpose computer does). Fortunately, most operating systems of the UNIX family allow an ordinary computer to act as a router and forward packets belonging to the other hosts, but only according to a statically configured table. A <em/Routing Daemon/ is in UNIX terminology a non-interactive program running on background which does the dynamic part of Internet routing, that is it communicates with the other routers, calculates routing tables and sends them to the OS kernel which does the actual packet forwarding. There already exist other such routing daemons: routed (RIP only), GateD (non-free), Zebra<HTMLURL URL="http://www.zebra.org"> and MRTD<HTMLURL URL="http://sourceforge.net/projects/mrt">, but their capabilities are limited and they are relatively hard to configure and maintain. BIRD is an Internet Routing Daemon designed to avoid all of these shortcomings, to support all the routing technology used in the today's Internet or planned to be used in near future and to have a clean extensible architecture allowing new routing protocols to be incorporated easily. Among other features, BIRD supports: <itemize> <item>both IPv4 and IPv6 protocols <item>multiple routing tables <item>the Border Gateway Protocol (BGPv4) <item>the Routing Information Protocol (RIPv2) <item>the Open Shortest Path First protocol (OSPFv2) <item>a virtual protocol for exchange of routes between different routing tables on a single host <item>a command-line interface allowing on-line control and inspection of status of the daemon <item>soft reconfiguration (no need to use complex online commands to change the configuration, just edit the configuration file and notify BIRD to re-read it and it will smoothly switch itself to the new configuration, not disturbing routing protocols unless they are affected by the configuration changes) <item>a powerful language for route filtering </itemize> BIRD has been developed at the Faculty of Math and Physics, Charles University, Prague, Czech Republic as a student project. It can be freely distributed under the terms of the GNU General Public License. BIRD has been designed to work on all UNIX-like systems. It has been developed and tested under Linux 2.0 to 2.4, and then ported to FreeBSD and NetBSD, porting to other systems (even non-UNIX ones) should be relatively easy due to its highly modular architecture. <sect>Installing BIRD On a recent UNIX system with GNU development tools (GCC, binutils, m4, make) and Perl, installing BIRD should be as easy as: <code> ./configure make make install vi /usr/local/etc/bird.conf bird </code> You can use <tt>./configure --help</tt> to get a list of configure options. The most important ones are: <tt/--enable-ipv6/ which enables building of an IPv6 version of BIRD, <tt/--with-protocols=/ to produce a slightly smaller BIRD executable by configuring out routing protocols you don't use, and <tt/--prefix=/ to install BIRD to a place different from. <file>/usr/local</file>. <sect>Running BIRD You can pass several command-line options to bird: <descrip> <tag>-c <m/config name/</tag> use given configuration file instead of <it/prefix/<file>/etc/bird.conf</file>. <tag>-d</tag> enable debug messages and run bird in foreground. <tag>-D <m/filename of debug log/</tag> log debugging information to given file instead of stderr. <tag>-p</tag> just parse the config file and exit. Return value is zero if the config file is valid, nonzero if there are some errors. <tag>-s <m/name of communication socket/</tag> use given filename for a socket for communications with the client, default is <it/prefix/<file>/var/run/bird.ctl</file>. </descrip> BIRD writes messages about its work to log files or syslog (according to config). <chapt>About routing tables BIRD has one or more routing tables which may or may not be synchronized with OS kernel and which may or may not be synchronized with each other (see the Pipe protocol). Each routing table contains a list of known routes. Each route consists of: <itemize> <item>network prefix this route is for (network address and prefix length -- the number of bits forming the network part of the address; also known as a netmask) <item>preference of this route <item>IP address of router which told us about this route <item>IP address of router we should forward the packets to using this route <item>other attributes common to all routes <item>dynamic attributes defined by protocols which may or may not be present (typically protocol metrics) </itemize> Routing table maintains multiple entries for a network, but at most one entry for one network and one protocol. The entry with the highest preference is used for routing (we will call such an entry the <it/selected route/). If there are more entries with the same preference and they are from the same protocol, the protocol decides (typically according to metrics). If they aren't, an internal ordering is used to break the tie. You can get the list of route attributes in the Route attributes section. Each protocol is connected to a routing table through two filters which can accept, reject and modify the routes. An <it/export/ filter checks routes passed from the routing table to the protocol, an <it/import/ filter checks routes in the opposite direction. When the routing table gets a route from a protocol, it recalculates the selected route and broadcasts it to all protocols connected to the table. The protocols typically send the update to other routers in the network. <chapt>Configuration <sect>Introduction BIRD is configured using a text configuration file. Upon startup, BIRD reads <it/prefix/<file>/etc/bird.conf</file> (unless the <tt/-c/ command line option is given). Configuration may be changed at user's request: if you modify the config file and then signal BIRD with <tt/SIGHUP/, it will adjust to the new config. Then there's the client which allows you to talk with BIRD in an extensive way. In the config, everything on a line after <cf/#/ or inside <cf>/* */</cf> is a comment, whitespace characters are treated as a single space. If there's a variable number of options, they are grouped using the <cf/{ }/ brackets. Each option is terminated by a <cf/;/. Configuration is case sensitive. Here is an example of a simple config file. It enables synchronization of routing tables with OS kernel, scans for new network interfaces every 10 seconds and runs RIP on all network interfaces found. <code> protocol kernel { persist; # Don't remove routes on BIRD shutdown scan time 20; # Scan kernel routing table every 20 seconds export all; # Default is export none } protocol device { scan time 10; # Scan interfaces every 10 seconds } protocol rip { export all; import all; interface "*"; } </code> <sect>Global options <descrip> <tag>log "<m/filename/"|syslog|stderr all|{ <m/list of classes/ }</tag> Set logging of messages having the given class (either <cf/all/ or <cf/{ error, trace }/ etc.) into selected destination. Classes are: <cf/info/, <cf/warning/, <cf/error/ and <cf/fatal/ for messages about local problems, <cf/debug/ for debugging messages, <cf/trace/ when you want to know what happens in the network, <cf/remote/ for messages about misbehavior of remote machines, <cf/auth/ about authentication failures, <cf/bug/ for internal BIRD bugs. You may specify more than one <cf/log/ line to establish logging to multiple destinations. Default: log everything to the system log. <tag>debug protocols all|off|{ states, routes, filters, interfaces, events, packets }</tag> Set global defaults of protocol debugging options. See <cf/debug/ in the following section. Default: off. <tag>debug commands <m/number/</tag> Control logging of client connections (0 for no logging, 1 for logging of connects and disconnects, 2 and higher for logging of all client commands). Default: 0. <tag>filter <m/name local variables/{ <m/commands/ }</tag> Define a filter. You can learn more about filters in the following chapter. <tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag> Define a function. You can learn more about functions in the following chapter. <tag>protocol rip|ospf|bgp|... <m/[name]/ { <m>protocol options</m> }</tag> Define a protocol instance called <cf><m/name/</cf> (or with a name like "rip5" generated automatically if you don't specify any <cf><m/name/</cf>). You can learn more about configuring protocols in their own chapters. You can run more than one instance of most protocols (like RIP or BGP). By default, no instances are configured. <tag>define <m/constant/ = (<m/expression/)|<m/number/|<m/IP address/</tag> Define a constant. You can use it later in every place you could use a simple integer or an IP address. <tag>router id <m/IPv4 address/</tag> Set BIRD's router ID. It's a world-wide unique identification of your router, usually one of router's IPv4 addresses. Default: in IPv4 version, the lowest IP address of a non-loopback interface. In IPv6 version, this option is mandatory. <tag>listen bgp [address <m/address/] [port <m/port/] [v6only]</tag> This option allows to specify address and port where BGP protocol should listen. It is global option as listening socket is common to all BGP instances. Default is to listen on all addresses (0.0.0.0) and port 179. In IPv6 mode, option <cf/v6only/ can be used to specify that BGP socket should listen to IPv6 connections only. This is needed if you want to run both bird and bird6 on the same port. <tag>table <m/name/</tag> Create a new routing table. The default routing table is created implicitly, other routing tables have to be added by this command. <tag>eval <m/expr/</tag> Evaluates given filter expression. It is used by us for testing of filters. </descrip> <sect>Protocol options For each protocol instance, you can configure a bunch of options. Some of them (those described in this section) are generic, some are specific to the protocol (see sections talking about the protocols). Several options use a <cf><m/switch/</cf> argument. It can be either <cf/on/, <cf/yes/ or a numeric expression with a non-zero value for the option to be enabled or <cf/off/, <cf/no/ or a numeric expression evaluating to zero to disable it. An empty <cf><m/switch/</cf> is equivalent to <cf/on/ ("silence means agreement"). <descrip> <tag>preference <m/expr/</tag> Sets the preference of routes generated by this protocol. Default: protocol dependent. <tag>disabled <m/switch/</tag> Disables the protocol. You can change the disable/enable status from the command line interface without needing to touch the configuration. Disabled protocols are not activated. Default: protocol is enabled. <tag>debug all|off|{ states, routes, filters, interfaces, events, packets }</tag> Set protocol debugging options. If asked, each protocol is capable of writing trace messages about its work to the log (with category <cf/trace/). You can either request printing of <cf/all/ trace messages or only of the types selected: <cf/states/ for protocol state changes (protocol going up, down, starting, stopping etc.), <cf/routes/ for routes exchanged with the routing table, <cf/filters/ for details on route filtering, <cf/interfaces/ for interface change events sent to the protocol, <cf/events/ for events internal to the protocol and <cf/packets/ for packets sent and received by the protocol. Default: off. <tag>router id <m/IPv4 address/</tag> This option can be used to override global router id for a given protocol. This option is not yet implemented for OSPF protocol. Default: uses global router id. <tag>import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag> Specify a filter to be used for filtering routes coming from the protocol to the routing table. <cf/all/ is shorthand for <cf/where true/ and <cf/none/ is shorthand for <cf/where false/. Default: <cf/all/. <tag>export <m/filter/</tag> This is similar to the <cf>import</cf> keyword, except that it works in the direction from the routing table to the protocol. Default: <cf/none/. <tag>description "<m/text/"</tag> This is an optional description of the protocol. It is displayed as a part of the output of 'show route all' command. <tag>table <m/name/</tag> Connect this protocol to a non-default routing table. </descrip> There are several options that give sense only with certain protocols: <descrip> <tag><label id="dsc-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...] [ { <m/option/ ; [...] } ]</tag> Specifies a set of interfaces on which the protocol is activated with given interface-specific options. A set of interfaces specified by one interface option is described using an interface pattern. The interface pattern consists of a sequence of clauses (separted by commas), each clause may contain a mask, a prefix, or both of them. An interface matches the clause if its name matches the mask (if specified) and its address matches the prefix (if specified). Mask is specified as shell-like pattern. An interface matches the pattern if it matches any of its clauses. If the clause begins with <cf/-/, matching interfaces are excluded. Patterns are parsed left-to-right, thus <cf/interface "eth0", -"eth*", "*";/ means eth0 and all non-ethernets. An interface option can be used more times with different interfaces-specific options, in that case for given interface the first matching interface option is used. This option is allowed in Direct, OSPF and RIP protocols, but in OSPF protocol it is used in <cf/area/ subsection. Default: none. Examples: <cf>interface "*" { type broadcast; };</cf> - start the protocol on all interfaces with <cf>type broadcast</cf> option. <cf>interface "eth1", "eth4", "eth5" { type pointopoint; };</cf> - start the protocol on enumerated interfaces with <cf>type pointopoint</cf> option. <cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all interfaces that have address from 192.168.0.0/16, but not from 192.168.1.0/24. <cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all interfaces that have address from 192.168.0.0/16, but not from 192.168.1.0/24. <cf>interface "eth*" 192.168.1.0/24;</cf> - start the protocol on all ethernet interfaces that have address from 192.168.1.0/24. <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> Specifies a password that can be used by the protocol. Password option can be used more times to specify more passwords. If more passwords are specified, it is a protocol-dependent decision which one is really used. Specifying passwords does not mean that authentication is enabled, authentication can be enabled by separate, protocol-dependent <cf/authentication/ option. This option is allowed in OSPF and RIP protocols. BGP has also <cf/password/ option, but it is slightly different and described separately. Default: none. </descrip> Password option can contain section with some (not necessary all) password sub-options: <descrip> <tag>id <M>num</M></tag> ID of the password, (0-255). If it's not used, BIRD will choose ID based on an order of the password item in the interface. For example, second password item in one interface will have default ID 2. ID is used by some routing protocols to identify which password was used to authenticate protocol packets. <tag>generate from "<m/time/"</tag> The start time of the usage of the password for packet signing. The format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>. <tag>generate to "<m/time/"</tag> The last time of the usage of the password for packet signing. <tag>accept from "<m/time/"</tag> The start time of the usage of the password for packet verification. <tag>accept to "<m/time/"</tag> The last time of the usage of the password for packet verification. </descrip> <chapt>Remote control You can use the command-line client <file>birdc</file> to talk with a running BIRD. Communication is done using a <file/bird.ctl/ UNIX domain socket (unless changed with the <tt/-s/ option given to both the server and the client). The commands can perform simple actions such as enabling/disabling of protocols, telling BIRD to show various information, telling it to show routing table filtered by filter, or asking BIRD to reconfigure. Press <tt/?/ at any time to get online help. Option <tt/-v/ can be passed to the client, to make it dump numeric return codes along with the messages. You do not necessarily need to use <file/birdc/ to talk to BIRD, your own applications could do that, too -- the format of communication between BIRD and <file/birdc/ is stable (see the programmer's documentation). Many commands have the <m/name/ of the protocol instance as an argument. This argument can be omitted if there exists only a single instance. Here is a brief list of supported functions: <descrip> <tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag> Dump contents of internal data structures to the debugging output. <tag>show status</tag> Show router status, that is BIRD version, uptime and time from last reconfiguration. <tag>show protocols [all]</tag> Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified. <tag>show ospf interface [<m/name/] ["<m/interface/"]</tag> Show detailed information about OSPF interfaces. <tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag> Show a list of OSPF neighbors and a state of adjacency to them. <tag>show ospf state [<m/name/]</tag> Show detailed information about OSPF areas based on a content of link-state database. It shows network topology, aggregated networks and routers from other areas and external routes. <tag>show ospf topology [<m/name/]</tag> Show a topology of OSPF areas based on a content of link-state database. It is just a stripped-down version of 'show ospf state'. <tag>show static [<m/name/]</tag> Show detailed information about static routes. <tag>show interfaces [summary]</tag> Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. <tag>show symbols</tag> Show the list of symbols defined in the configuration (names of protocols, routing tables etc.). <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> Show contents of a routing table (by default of the main one), that is routes, their metrics and (in case the <cf/all/ switch is given) all their attributes. You can specify a <m/prefix/ if you want to print routes for a specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get the entry which will be used for forwarding of packets to the given destination. By default, all routes for each network are printed with the selected one at the top, unless <cf/primary/ is given in which case only the selected route is shown. You can also ask for printing only routes processed and accepted by a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ } </cf> or matching a given condition (<cf>where <m/condition/</cf>). The <cf/export/ and <cf/preexport/ switches ask for printing of entries that are exported to the specified protocol. With <cf/preexport/, the export filter of the protocol is skipped. You can also select just routes added by a specific protocol. <cf>protocol <m/p/</cf>. The <cf/stats/ switch requests showing of route statistics (the number of networks, number of routes before and after filtering). If you use <cf/count/ instead, only the statistics will be printed. <tag>configure [soft] ["<m/config file/"]</tag> Reload configuration from a given file. BIRD will smoothly switch itself to the new configuration, protocols are reconfigured if possible, restarted otherwise. Changes in filters usualy lead to restart of affected protocols. If <cf/soft/ option is used, changes in filters does not cause BIRD to restart affected protocols, therefore already accepted routes (according to old filters) would be still propagated, but new routes would be processed according to the new filters. <tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag> Enable, disable or restart a given protocol instance, instances matching the <cf><m/pattern/</cf> or <cf/all/ instances. <tag>reload [in|out] <m/name/|"<m/pattern/"|all</tag> Reload a given protocol instance, that means re-import routes from the protocol instance and re-export preferred routes to the instance. If <cf/in/ or <cf/out/ options are used, the command is restricted to one direction (re-import or re-export). This command is useful if appropriate filters have changed but the protocol instance was not restarted (or reloaded), therefore it still propagates the old set of routes. For example when <cf/configure soft/ command was used to change filters. Re-export always succeeds, but re-import is protocol-dependent and might fail (for example, if BGP neighbor does not support route-refresh extension). In that case, re-export is also skipped. Note that for the pipe protocol, both directions are always reloaded together (<cf/in/ or <cf/out/ options are ignored in that case). <tag/down/ Shut BIRD down. <tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag> Control protocol debugging. </descrip> <chapt>Filters <sect>Introduction BIRD contains a simple programming language. (No, it can't yet read mail :-). There are two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is being passed between protocols and routing tables. The filter language contains control structures such as if's and switches, but it allows no loops. An example of a filter using many features can be found in <file>filter/test.conf</file>. Filter gets the route, looks at its attributes and modifies some of them if it wishes. At the end, it decides whether to pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks like this: <code> filter not_too_far int var; { if defined( rip_metric ) then var = rip_metric; else { var = 1; rip_metric = 1; } if rip_metric > 10 then reject "RIP metric is too big"; else accept "ok"; } </code> As you can see, a filter has a header, a list of local variables, and a body. The header consists of the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of <cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of <cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if you want to make a bigger block of code conditional. BIRD supports functions, so that you don't have to repeat the same blocks of code over and over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions look like this: <code> function name () int local_variable; { local_variable = 5; } function with_parameters (int parameter) { print parameter; } </code> Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare variables in nested blocks. Functions are called like in C: <cf>name(); with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf> command. Returning a value exits from current function (this is similar to C). Filters are declared in a way similar to functions except they can't have explicit parameters. They get a route table entry as an implicit parameter, it is also passed automatically to any functions called. The filter must terminate with either <cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route is rejected. A nice trick to debug filters is to use <cf>show route filter <m/name/</cf> from the command line client. An example session might look like: <code> pavel@bug:~/bird$ ./birdc -s bird.ctl BIRD 0.0.0 ready. bird> show route 10.0.0.0/8 dev eth0 [direct1 23:21] (240) 195.113.30.2/32 dev tunl1 [direct1 23:21] (240) 127.0.0.0/8 dev lo [direct1 23:21] (240) bird> show route ? show route [<prefix>] [table <t>] [filter <f>] [all] [primary]... bird> show route filter { if 127.0.0.5 ˜ net then accept; } 127.0.0.0/8 dev lo [direct1 23:21] (240) bird> </code> <sect>Data types Each variable and each value has certain type. Booleans, integers and enums are incompatible with each other (that is to prevent you from shooting in the foot). <descrip> <tag/bool/ This is a boolean type, it can have only two values, <cf/true/ and <cf/false/. Boolean is the only type you can use in <cf/if/ statements. <tag/int/ This is a general integer type, you can expect it to store signed values from -2000000000 to +2000000000. Overflows are not checked. You can use <cf/0x1234/ syntax to write hexadecimal values. <tag/pair/ This is a pair of two short integers. Each component can have values from 0 to 65535. Literals of this type are written as <cf/(1234,5678)/. The same syntax can also be used to construct a pair from two arbitrary integer expressions (for example <cf/(1+2,a)/). <tag/string/ This is a string of characters. There are no ways to modify strings in filters. You can pass them between functions, assign them to variables of type <cf/string/, print such variables, but you can't concatenate two strings. String literals are written as <cf/"This is a string constant"/. <tag/ip/ This type can hold a single IP address. Depending on the compile-time configuration of BIRD you are using, it is either an IPv4 or IPv6 address. IP addresses are written in the standard notation (<cf/10.20.30.40/ or <cf/fec0:3:4::1/). You can apply special operator <cf>.mask(<M>num</M>)</cf> on values of type ip. It masks out all but first <cf><M>num</M></cf> bits from the IP address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true. <tag/prefix/ This type can hold a network prefix consisting of IP address and prefix length. Prefix literals are written as <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special operators on prefixes: <cf/.ip/ which extracts the IP address from the pair, and <cf/.len/, which separates prefix length from the pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true. <tag/int|ip|prefix|pair|enum set/ Filters recognize four types of sets. Sets are similar to strings: you can pass them around but you can't modify them. Literals of type <cf>set int</cf> look like <cf> [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in sets. Sets of prefixes are special: their literals does not allow ranges, but allows prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>. Prefix <cf><m>ip1</m>/<m>len1</m></cf> matches prefix pattern <cf><m>ip2</m>/<m>len2</m>{<m>l</m>,<m>h</m>}</cf> iff the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 <= ip1 <= len2</cf>. A valid prefix pattern has to satisfy <cf>low <= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/ or <cf/high/. Obviously, a prefix matches a prefix set literal iff it matches any prefix pattern in the prefix set literal. There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for <cf><m>address</m>/<m/len/{<m/len/,<m/maxlen/}</cf> (where <cf><m>maxlen</m></cf> is 32 for IPv4 and 128 for IPv6), that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf> is a shorthand for <cf><m>address</m>/<m/len/{0,<m/len/}</cf>, that means network prefix <cf><m>address</m>/<m/len/</cf> and all its supernets (network prefixes that contain it). For example, <cf>[ 1.0.0.0/8, 2.0.0.0/8+, 3.0.0.0/8-, 4.0.0.0/8{16,24} ]</cf> matches prefix <cf>1.0.0.0/8</cf>, all subprefixes of <cf>2.0.0.0/8</cf>, all superprefixes of <cf>3.0.0.0/8</cf> and prefixes <cf/4.X.X.X/ whose prefix length is 16 to 24. <cf>[ 0.0.0.0/0{20,24} ]</cf> matches all prefixes (regardless of IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 ˜ [ 1.0.0.0/8{15,17} ]</cf> is true, but <cf>1.0.0.0/16 ˜ [ 1.0.0.0/8- ]</cf> is false. Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as <cf>192.168.0.0/16{24,32}</cf>. <tag/enum/ Enumeration types are fixed sets of possibilities. You can't define your own variables of such type, but some route attributes are of enumeration type. Enumeration types are incompatible with each other. <tag/bgppath/ BGP path is a list of autonomous system numbers. You can't write literals of this type. There are several special operators on bgppaths: <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/. <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/. Both <cf/first/ and <cf/last/ return zero if there is no appropriate ASN, for example if the path contains an AS set element as the first (or the last) part. <cf><m/P/.len</cf> returns the length of path <m/P/. <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path <m/P/ and returns the result. Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute (for example <cf/bgp_path/). <tag/bgpmask/ BGP masks are patterns used for BGP path matching (using <cf>path ˜ [= 2 3 5 * =]</cf> syntax). The masks resemble wildcard patterns as used by UNIX shells. Autonomous system numbers match themselves, <cf/*/ matches any (even empty) sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number. For example, if <cf>bgp_path</cf> is 4 3 2 1, then: <tt>bgp_path ˜ [= * 4 3 * =]</tt> is true, but <tt>bgp_path ˜ [= * 4 5 * =]</tt> is false. BGP mask expressions can also contain integer expressions enclosed in parenthesis and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>. There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *. <tag/clist/ Community list is similar to set of pairs, except that unlike other sets, it can be modified. There exist no literals of this type. There are two special operators on clists: <cf>add(<m/C/,<m/P/)</cf> adds pair <m/P/ to clist <m/C/ and returns the result. <cf>delete(<m/C/,<m/P/)</cf> deletes pair <m/P/ from clist <m/C/ and returns the result. Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route attribute (for example <cf/bgp_community/). Similarly for <cf/delete/. </descrip> <sect>Operators The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison <cf/(a=b, a!=b, a<b, a>=b)/. Logical operations include unary not (<cf/!/), and (<cf/&&/) and or (<cf/||/). Special operators include <cf/˜/ for "is element of a set" operation - it can be used on element and set of elements of the same type (returning true if element is contained in the given set), or on two strings (returning true if first string matches a shell-like pattern stored in second string) or on IP and prefix (returning true if IP is within the range defined by that prefix), or on prefix and prefix (returning true if first prefix is more specific than second one) or on bgppath and bgpmask (returning true if the path matches the mask) or on pair and clist (returning true if the community is element of the community list). <sect>Control structures Filters support two control structures: conditions and case switches. Syntax of a condition is: <cf>if <M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{ <M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf> clause may be omitted. If the <cf><m>boolean expression</m></cf> is true, <cf><m>command1</m></cf> is executed, otherwise <cf><m>command2</m></cf> is executed. The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else | <m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after <cf>case</cf> can be of any type which can be on the left side of the ˜ operator and anything that could be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping. If <cf><m/expr/</cf> matches one of the <cf/:/ clauses, statements between it and next <cf/:/ statement are executed. If <cf><m/expr/</cf> matches neither of the <cf/:/ clauses, the statements after <cf/else:/ are executed. Here is example that uses <cf/if/ and <cf/case/ structures: <code> case arg1 { 2: print "two"; print "I can do more commands without {}"; 3 .. 5: print "three to five"; else: print "something else"; } if 1234 = i then printn "."; else { print "not 1234"; print "You need {} around multiple commands"; } </code> <sect>Route attributes A filter is implicitly passed a route, and it can access its attributes just like it accesses variables. Attempts to access undefined attribute result in a runtime error; you can check if an attribute is defined by using the <cf>defined( <m>attribute</m> )</cf> operator. <descrip> <tag><m/prefix/ net</tag> Network the route is talking about. Read-only. (See the chapter about routing tables.) <tag><m/enum/ scope</tag> Address scope of the network (<cf/SCOPE_HOST/ for addresses local to this host, <cf/SCOPE_LINK/ for those specific for a physical link, <cf/SCOPE_SITE/ and <cf/SCOPE_ORGANIZATION/ for private addresses, <cf/SCOPE_UNIVERSE/ for globally visible addresses). <tag><m/int/ preference</tag> Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.) <tag><m/ip/ from</tag> The router which the route has originated from. Read-only. <tag><m/ip/ gw</tag> Next hop packets routed using this route should be forwarded to. <tag><m/string/ proto</tag> The name of the protocol which the route has been imported from. Read-only. <tag><m/enum/ source</tag> what protocol has told me about this route. Possible values: <cf/RTS_DUMMY/, <cf/RTS_STATIC/, <cf/RTS_INHERIT/, <cf/RTS_DEVICE/, <cf/RTS_STATIC_DEVICE/, <cf/RTS_REDIRECT/, <cf/RTS_RIP/, <cf/RTS_OSPF/, <cf/RTS_OSPF_IA/, <cf/RTS_OSPF_EXT/, <cf/RTS_BGP/, <cf/RTS_PIPE/. <tag><m/enum/ cast</tag> Route type (<cf/RTC_UNICAST/ for normal routes, <cf/RTC_BROADCAST/, <cf/RTC_MULTICAST/, <cf/RTC_ANYCAST/ for broadcast, multicast and anycast routes). Read-only. <tag><m/enum/ dest</tag> Type of destination the packets should be sent to (<cf/RTD_ROUTER/ for forwarding to a neighboring router, <cf/RTD_NETWORK/ for routing to a directly-connected network, <cf/RTD_BLACKHOLE/ for packets to be silently discarded, <cf/RTD_UNREACHABLE/, <cf/RTD_PROHIBIT/ for packets that should be returned with ICMP host unreachable / ICMP administratively prohibited messages). Read-only. </descrip> There also exist some protocol-specific attributes which are described in the corresponding protocol sections. <sect>Other statements The following statements are available: <descrip> <tag><m/variable/ = <m/expr/</tag> Set variable to a given value. <tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>. <tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point. <tag>print|printn <m/expr/ [<m/, expr.../]</tag> Prints given expressions; useful mainly while debugging filters. The <cf/printn/ variant does not terminate the line. <tag>quitbird</tag> Terminates BIRD. Useful when debugging the filter interpreter. </descrip> <chapt>Protocols <sect>BGP The Border Gateway Protocol is the routing protocol used for backbone level routing in the today's Internet. Contrary to the other protocols, its convergence doesn't rely on all routers following the same rules for route selection, making it possible to implement any routing policy at any router in the network, the only restriction being that if a router advertises a route, it must accept and forward packets according to it. BGP works in terms of autonomous systems (often abbreviated as AS). Each AS is a part of the network with common management and common routing policy. It is identified by a unique 16-bit number. Routers within each AS usually communicate with each other using either a interior routing protocol (such as OSPF or RIP) or an interior variant of BGP (called iBGP). Boundary routers at the border of the AS communicate with their peers in the neighboring AS'es via exterior BGP (eBGP). Each BGP router sends to its neighbors updates of the parts of its routing table it wishes to export along with complete path information (a list of AS'es the packet will travel through if it uses the particular route) in order to avoid routing loops. BIRD supports all requirements of the BGP4 standard as defined in RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt"> It also supports the community attributes (RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">), capability negotiation (RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">), MD5 password authentication (RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">), route reflectors (RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">), multiprotocol extensions (RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">), and 4B AS numbers (RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">). For IPv6, it uses the standard multiprotocol extensions defined in RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt"> including changes described in the latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt"> and applied to IPv6 according to RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">. <sect1>Route selection rules BGP doesn't have any simple metric, so the rules for selection of an optimal route among multiple BGP routes with the same preference are a bit more complex and they are implemented according to the following algorithm. It starts the first rule, if there are more "best" routes, then it uses the second rule to choose among them and so on. <itemize> <item>Prefer route with the highest Local Preference attribute. <item>Prefer route with the shortest AS path. <item>Prefer IGP origin over EGP and EGP over incomplete. <item>Prefer the lowest value of the Multiple Exit Discriminator. <item>Prefer internal routes over external ones. <item>Prefer the route with the lowest value of router ID of the advertising router. </itemize> <sect1>Configuration Each instance of the BGP corresponds to one neighboring router. This allows to set routing policy and all the other parameters differently for each neighbor using the following configuration parameters: <descrip> <tag>local as <m/number/</tag> Define which AS we are part of. (Note that contrary to other IP routers, BIRD is able to act as a router located in multiple AS'es simultaneously, but in such cases you need to tweak the BGP paths manually in the filters to get consistent behavior.) This parameter is mandatory. <tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router this instance will be talking to and what AS it's located in. Unless you use the <cf/multihop/ clause, it must be directly connected to one of your router's interfaces. In case the neighbor is in the same AS as we are, we automatically switch to iBGP. This parameter is mandatory. <tag>multihop <m/number/ via <m/ip/</tag> Configure multihop BGP to a neighbor which is connected at most <m/number/ hops far and to which we should route via our direct neighbor with address <m/ip/. Default: switched off. <tag>next hop self</tag> Avoid calculation of the Next Hop attribute and always advertise our own source address (see below) as a next hop. This needs to be used only occasionally to circumvent misconfigurations of other routers. Default: disabled. <tag>missing lladdr self|drop|ignore</tag>Next Hop attribute in BGP-IPv6 sometimes contains just the global IPv6 address, but sometimes it has to contain both global and link-local IPv6 addresses. This option specifies what to do if BIRD have to send both addresses but does not know link-local address. This situation might happen when routes from other protocols are exported to BGP, or when improper updates are received from BGP peers. <cf/self/ means that BIRD advertises its own local address instead. <cf/drop/ means that BIRD skips that prefixes and logs error. <cf/ignore/ means that BIRD ignores the problem and sends just the global address (and therefore forms improper BGP update). Default: <cf/self/, unless BIRD is configured as a route server (option <cf/rs client/), in that case default is <cf/drop/, because route servers usually does not forward packets ifselves. <tag>source address <m/ip/</tag> Define local address we should use for next hop calculation. Default: the address of the local end of the interface our neighbor is connected to. <tag>password <m/string/</tag> Use this password for MD5 authentication of BGP sessions. Default: no authentication. Password has to be set by external utility (e.g. setkey(8)) on BSD systems. <tag>passive <m/switch/</tag> Standard BGP behavior is both initiating outgoing connections and accepting incoming connections. In passive mode, outgoing connections are not initiated. Default: off. <tag>rr client</tag> Be a route reflector and treat the neighbor as a route reflection client. Default: disabled. <tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id to avoid route reflection loops. When there is one route reflector in a cluster it usually uses its router id as a cluster id, but when there are more route reflectors in a cluster, these need to be configured (using this option) to use a common cluster id. Clients in a cluster need not know their cluster id and this option is not allowed for them. Default: the same as router id. <tag>rs client</tag> Be a route server and treat the neighbor as a route server client. A route server is used as a replacement for full mesh EBGP routing in Internet exchange points in a similar way to route reflectors used in IBGP routing. BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation, which behaves like plain EBGP but reduces modifications to advertised route attributes to be transparent (for example does not prepend its AS number to AS PATH attribute and keep MED attribute). Default: disabled. <tag>enable route refresh <m/switch/</tag> When BGP speaker changes its import filter, it has to re-examine all routes received from its neighbor against the new filter. As these routes might not be available, there is a BGP protocol extension Route Refresh (specified in RFC 2918) that allows BGP speaker to request re-advertisment of all routes from its neighbor. This option specifies whether BIRD advertises this capability and accepts such requests. Even when disabled, BIRD can send route refresh requests. Default: on. <tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers and was extended later to allow 4B AS number. BIRD supports 4B AS extension, but by disabling this option it can be persuaded not to advertise it and to maintain old-style sessions with its neighbors. This might be useful for circumventing bugs in neighbor's implementation of 4B AS extension. Even when disabled (off), BIRD behaves internally as AS4-aware BGP router. Default: on. <tag>capabilities <m/switch/</tag> Use capability advertisement to advertise optional capabilities. This is standard behavior for newer BGP implementations, but there might be some older BGP implementations that reject such connection attempts. When disabled (off), features that request it (4B AS support) are also disabled. Default: on, with automatic fallback to off when received capability-related error. <tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability. This is not a correct behavior according to the strict interpretation of RFC 4760, but it is widespread and required by some BGP implementations (Cisco and Quagga). This option is relevant to IPv4 mode with enabled capability advertisement only. Default: on. <tag>route limit <m/number/</tag> The maximal number of routes that may be imported from the protocol. If the route limit is exceeded, the connection is closed with error. Default: no limit. <tag>disable after error <m/switch/</tag> When an error is encountered (either locally or by the other side), disable the instance automatically and wait for an administrator to fix the problem manually. Default: off. <tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive message from the other side before considering the connection stale. Default: depends on agreement with the neighboring router, we prefer 240 seconds if the other side is willing to accept it. <tag>startup hold time <m/number/</tag> Value of the hold timer used before the routers have a chance to exchange open messages and agree on the real value. Default: 240 seconds. <tag>keepalive time <m/number/</tag> Delay in seconds between sending of two consecutive Keepalive messages. Default: One third of the hold time. <tag>connect retry time <m/number/</tag> Time in seconds to wait before retrying a failed attempt to connect. Default: 120 seconds. <tag>start delay time <m/number/</tag> Delay in seconds between protocol startup and the first attempt to connect. Default: 5 seconds. <tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol failure (either local or reported by the peer) and automatic restart. Doesn't apply when <cf/disable after error/ is configured. If consecutive errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300. <tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol failures to treat them as a error sequence which makes the <cf/error wait time/ increase exponentially. Default: 300 seconds. <tag>path metric <m/switch/</tag> Enable comparison of path lengths when deciding which BGP route is the best one. Default: on. <tag>prefer older <m/switch/</tag> Standard route selection algorithm breaks ties by comparing router IDs. This changes the behavior to prefer older routes (when both are external and from different peer). For details, see RFC 5004. Default: off. <tag>default bgp_med <m/number/</tag> Value of the Multiple Exit Discriminator to be used during route selection when the MED attribute is missing. Default: 0. <tag>default bgp_local_pref <m/number/</tag> Value of the Local Preference to be used during route selection when the Local Preference attribute is missing. Default: 0. </descrip> <sect1>Attributes BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the table below) are available on internal BGP connections only, some of them (marked with `<tt/O/') are optional. <descrip> <tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path the packet will travel through when forwarded according to the particular route. In case of internal BGP it doesn't contain the number of the local AS. <tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for selection among multiple BGP routes (see the selection rules above). It's used as an additional metric which is propagated through the whole local AS. <tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route is an optional attribute which is used on on external (inter-AS) links to convey to an adjacent AS the optimal entry point into the local AS. The received attribute may be also propagated over internal BGP links (and this is default behavior). The attribute value is zeroed when a route is exported from a routing table to a BGP instance to ensure that the attribute received from a neighboring AS is not propagated to other neighboring ASes. A new value might be set in the export filter of a BGP instance. See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt"> for further discussion of BGP MED attribute. <tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/ if the route has originated in an interior routing protocol or <cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol (nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin is unknown. <tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets to this destination. On internal BGP connections, it's an address of the originating router if it's inside the local AS or a boundary router the packet will leave the AS through if it's an exterior route, so each BGP speaker within the AS has a chance to use the shortest interior path possible to this point. <tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute which carries no value, but the sole presence of which indicates that the route has been aggregated from multiple routes by some router on the path from the originator.  <tag>clist <cf/bgp_community/ [O]</tag> List of community values associated with the route. Each such value is a pair (represented as a <cf/pair/ data type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines the community and the second one being a per-AS identifier. There are lots of uses of the community mechanism, but generally they are used to carry policy information like "don't export to USA peers". As each AS can define its own routing policy, it also has a complete freedom about which community attributes it defines and what will their semantics be. </descrip> <sect1>Example <code> protocol bgp { local as 65000; # Use a private AS number neighbor 62.168.0.130 as 5588; # Our neighbor ... multihop 20 via 62.168.0.13; # ... which is connected indirectly export filter { # We use non-trivial export rules if source = RTS_STATIC then { # Export only static routes # Assign our community bgp_community.add((65000,5678)); # Artificially increase path length # by advertising local AS number twice if bgp_path ~ [= 65000 =] then bgp_path.prepend(65000); accept; } reject; }; import all; source address 62.168.0.1; # Use a non-standard source address } </code> <sect>Device The Device protocol is not a real routing protocol. It doesn't generate any routes and it only serves as a module for getting information about network interfaces from the kernel. Except for very unusual circumstances, you probably should include this protocol in the configuration since almost all other protocols require network interfaces to be defined for them to work with. <sect1>Configuration <descrip> <tag>scan time <m/number/</tag> Time in seconds between two scans of the network interface list. On systems where we are notified about interface status changes asynchronously (such as newer versions of Linux), we need to scan the list only in order to avoid confusion by lost notification messages, so the default time is set to a large value. <tag>primary [ "<m/mask/" ] <m/prefix/</tag> If a network interface has more than one network address, BIRD has to choose one of them as a primary one, because some routing protocols (for example OSPFv2) suppose there is only one network address per interface. By default, BIRD chooses the lexicographically smallest address as the primary one. This option allows to specify which network address should be chosen as a primary one. Network addresses that match <m/prefix/ are preferred to non-matching addresses. If more <cf/primary/ options are used, the first one has the highest preference. If "<m/mask/" is specified, then such <cf/primary/ option is relevant only to matching network interfaces. In all cases, an address marked by operating system as secondary cannot be chosen as the primary one. </descrip> As the Device protocol doesn't generate any routes, it cannot have any attributes. Example configuration looks like this: <code> protocol device { scan time 10; # Scan the interfaces often primary "eth0" 192.168.1.1; primary 192.168.0.0/16; } </code> <sect>Direct The Direct protocol is a simple generator of device routes for all the directly connected networks according to the list of interfaces provided by the kernel via the Device protocol. It's highly recommended to include this protocol in your configuration unless you want to use BIRD as a route server or a route reflector, that is on a machine which doesn't forward packets itself and only participates in distribution of routing information. The only configurable thing about direct is what interfaces it watches: <descrip> <tag>interface <m/pattern [, ...]/</tag> By default, the Direct protocol will generate device routes for all the interfaces available. If you want to restrict it to some subset of interfaces (for example if you're using multiple routing tables for policy routing and some of the policy domains don't contain all interfaces), just use this clause. </descrip> Direct device routes don't contain any specific attributes. Example config might look like this: <code> protocol direct { interface "-arc*", "*"; # Exclude the ARCnets } </code> <sect>Kernel The Kernel protocol is not a real routing protocol. Instead of communicating the with other routers in the network, it performs synchronization of BIRD's routing tables with the OS kernel. Basically, it sends all routing table updates to the kernel and from time to time it scans the kernel tables to see whether some routes have disappeared (for example due to unnoticed up/down transition of an interface) or whether an `alien' route has been added by someone else (depending on the <cf/learn/ switch, such routes are either deleted or accepted to our table). If your OS supports only a single routing table, you can configure only one instance of the Kernel protocol. If it supports multiple tables (in order to allow policy routing; such an OS is for example Linux 2.2), you can run as many instances as you want, but each of them must be connected to a different BIRD routing table and to a different kernel table. <sect1>Configuration <descrip> <tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the routing tables when it exits (instead of cleaning them up). <tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the kernel routing table. <tag>learn <m/switch/</tag> Enable learning of routes added to the kernel routing tables by other routing daemons or by the system administrator. This is possible only on systems which support identification of route authorship. <tag>kernel table <m/number/</tag> Select which kernel table should this particular instance of the Kernel protocol work with. Available only on systems supporting multiple routing tables. </descrip> The Kernel protocol doesn't define any route attributes. A simple configuration can look this way: <code> protocol kernel { import all; export all; } </code> Or for a system with two routing tables: <code> protocol kernel { # Primary routing table learn; # Learn alien routes from the kernel persist; # Don't remove routes on bird shutdown scan time 10; # Scan kernel routing table every 10 seconds import all; export all; } protocol kernel { # Secondary routing table table auxtable; kernel table 100; export all; } </code> <sect>OSPF <sect1>Introduction Open Shortest Path First (OSPF) is a quite complex interior gateway protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link state (a.k.a. shortest path first) protocol -- each router maintains a database describing the autonomous system's topology. Each participating router has an identical copy of the database and all routers run the same algorithm calculating a shortest path tree with themselves as a root. OSPF chooses the least cost path as the best path. (OSPFv3 - OSPF for IPv6 is not supported yet.) In OSPF, the autonomous system can be split to several areas in order to reduce the amount of resources consumed for exchanging the routing information and to protect the other areas from incorrect routing data. Topology of the area is hidden to the rest of the autonomous system. Another very important feature of OSPF is that it can keep routing information from other protocols (like Static or BGP) in its link state database as external routes. Each external route can be tagged by the advertising router, making it possible to pass additional information between routers on the boundary of the autonomous system. OSPF quickly detects topological changes in the autonomous system (such as router interface failures) and calculates new loop-free routes after a short period of convergence. Only a minimal amount of routing traffic is involved. Each router participating in OSPF routing periodically sends Hello messages to all its interfaces. This allows neighbors to be discovered dynamically. Then the neighbors exchange theirs parts of the link state database and keep it identical by flooding updates. The flooding process is reliable and ensures that each router detects all changes. <sect1>Configuration In the main part of configuration, there can be multiple definitions of OSPF area witch different id included. These definitions includes many other switches and multiple definitions of interfaces. Definition of interface may contain many switches and constant definitions and list of neighbors on nonbroadcast networks. <code> protocol ospf <name> { rfc1583compat <switch>; tick <num>; area <id> { stub cost <num>; networks { <prefix>; <prefix> hidden; } stubnet <prefix>; stubnet <prefix> { hidden <switch>; summary <switch>; cost <num>; } interface <interface pattern> { cost <num>; stub <switch>; hello <num>; poll <num>; retransmit <num>; priority <num>; wait <num>; dead count <num>; dead <num>; rx buffer [normal|large|<num>]; type [broadcast|nonbroadcast|pointopoint]; strict nonbroadcast <switch>; authentication [none|simple|cryptographics]; password "<text>"; password "<text>" { id <num>; generate from "<date>"; generate to "<date>"; accept from "<date>"; accept to "<date>"; }; neighbors { <ip>; <ip> eligible; }; }; virtual link <id> { hello <num>; retransmit <num>; wait <num>; dead count <num>; dead <num>; authentication [none|simple]; password "<text>"; }; }; } </code> <descrip> <tag>rfc1583compat <M>switch</M></tag> This option controls compatibility of routing table calculation with RFC 1583<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default value is no. <tag>area <M>id</M></tag> This defines an OSPF area with given area ID (an integer or an IPv4 address, similarly to a router ID). The most important area is the backbone (ID 0) to which every other area must be connected. <tag>stub cost <M>num</M></tag> No external (except default) routes are flooded into stub areas. Setting this value marks area stub with defined cost of default route. Default value is no. (Area is not stub.) <tag>tick <M>num</M></tag> The routing table calculation and clean-up of areas' databases is not performed when a single link state change arrives. To lower the CPU utilization, it's processed later at periodical intervals of <m/num/ seconds. The default value is 1. <tag>networks { <m/set/ }</tag> Definition of area IP ranges. This is used in summary lsa origination. Hidden networks are not propagated into other areas. <tag>stubnet <m/prefix/ { <m/options/ }</tag> Stub networks are networks that are not transit networks between OSPF routers. They are also propagated through an OSPF area as a part of a link state database. By default, BIRD generates a stub network record for each primary network address on each OSPF interface that does not have any OSPF neighbors, and also for each non-primary network address on each OSPF interface. This option allows to alter a set of stub networks propagated by this router. Each instance of this option adds a stub network with given network prefix to the set of propagated stub network, unless option <cf/hidden/ is used. It also suppresses default stub networks for given network prefix. When option <cf/summary/ is used, also default stub networks that are subnetworks of given stub network are suppressed. This might be used, for example, to aggregate generated stub networks. <tag>interface <M>pattern</M></tag> Defines that the specified interfaces belong to the area being defined. See <ref id="dsc-iface" name="interface"> common option for detailed description. <tag>virtual link <M>id</M></tag> Virtual link to router with the router id. Virtual link acts as a point-to-point interface belonging to backbone. The actual area is used as transport area. This item cannot be in the backbone. <tag>cost <M>num</M></tag> Specifies output cost (metric) of an interface. Default value is 10. <tag>stub <M>switch</M></tag> If set to interface it does not listen to any packet and does not send any hello. Default value is no. <tag>hello <M>num</M></tag> Specifies interval in seconds between sending of Hello messages. Beware, all routers on the same network need to have the same hello interval. Default value is 10. <tag>poll <M>num</M></tag> Specifies interval in seconds between sending of Hello messages for some neighbors on NBMA network. Default value is 20. <tag>retransmit <M>num</M></tag> Specifies interval in seconds between retransmissions of unacknowledged updates. Default value is 5. <tag>priority <M>num</M></tag> On every multiple access network (e.g., the Ethernet) Designed Router and Backup Designed router are elected. These routers have some special functions in the flooding process. Higher priority increases preferences in this election. Routers with priority 0 are not eligible. Default value is 1. <tag>wait <M>num</M></tag> After start, router waits for the specified number of seconds between starting election and building adjacency. Default value is 40. <tag>dead count <M>num</M></tag> When the router does not receive any messages from a neighbor in <m/dead count/*<m/hello/ seconds, it will consider the neighbor down. <tag>dead <M>num</M></tag> When the router does not receive any messages from a neighbor in <m/dead/ seconds, it will consider the neighbor down. If both directives <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence. <tag>rx buffer <M>num</M></tag> This sets the size of buffer used for receiving packets. The buffer should be bigger than maximal size of any packets. Value NORMAL (default) means 2*MTU, value LARGE means maximal allowed packet - 65536. <tag>type broadcast</tag> BIRD detects a type of a connected network automatically, but sometimes it's convenient to force use of a different type manually. On broadcast networks, flooding and Hello messages are sent using multicasts (a single packet for all the neighbors). <tag>type pointopoint</tag> Point-to-point networks connect just 2 routers together. No election is performed there which reduces the number of messages sent. <tag>type nonbroadcast</tag> On nonbroadcast networks, the packets are sent to each neighbor separately because of lack of multicast capabilities. <tag>strict nonbroadcast <M>switch</M></tag> If set, don't send hello to any undefined neighbor. This switch is ignored on on any non-NBMA network. Default is No. <tag>authentication none</tag> No passwords are sent in OSPF packets. This is the default value. <tag>authentication simple</tag> Every packet carries 8 bytes of password. Received packets lacking this password are ignored. This authentication mechanism is very weak. <tag>authentication cryptographic</tag> 16-byte long MD5 digest is appended to every packet. For the digest generation 16-byte long passwords are used. Those passwords are not sent via network, so this mechanismus is quite secure. Packets can still be read by an attacker. <tag>password "<M>text</M>"</tag> An 8-byte or 16-byte password used for authentication. See <ref id="dsc-pass" name="password"> common option for detailed description. <tag>neighbors { <m/set/ } </tag> A set of neighbors to which Hello messages on nonbroadcast networks are to be sent. Some of them could be marked as eligible. </descrip> <sect1>Attributes OSPF defines three route attributes. Each internal route has a <cf/metric/ Metric is ranging from 1 to infinity (65535). External routes use <cf/metric type 1/ or <cf/metric type 2/. A <cf/metric of type 1/ is comparable with internal <cf/metric/, a <cf/metric of type 2/ is always longer than any <cf/metric of type 1/ or any <cf/internal metric/. If you specify both metrics only metric1 is used. Each external route can also carry a <cf/tag/ which is a 32-bit integer which is used when exporting routes to other protocols; otherwise, it doesn't affect routing inside the OSPF domain at all. Default is <cf/metric of type 2 = 10000/ and <cf/tag = 0/. <sect1>Example <code> protocol ospf MyOSPF { rfc1583compat yes; tick 2; export filter { if source = RTS_BGP then { ospf_metric1 = 100; accept; } reject; }; area 0.0.0.0 { interface "eth*" { cost 11; hello 15; priority 100; retransmit 7; authentication simple; password "aaa"; }; interface "ppp*" { cost 100; authentication cryptographic; password "abc" { id 1; generate to "22-04-2003 11:00:06"; accept from "17-01-2001 12:01:05"; }; password "def" { id 2; generate to "22-07-2005 17:03:21"; accept from "22-02-2001 11:34:06"; }; }; interface "arc0" { cost 10; stub yes; }; interface "arc1"; }; area 120 { stub yes; networks { 172.16.1.0/24; 172.16.2.0/24 hidden; } interface "-arc0" , "arc*" { type nonbroadcast; authentication none; strict nonbroadcast yes; wait 120; poll 40; dead count 8; neighbors { 192.168.120.1 eligible; 192.168.120.2; 192.168.120.10; }; }; }; } </code> <sect>Pipe <sect1>Introduction The Pipe protocol serves as a link between two routing tables, allowing routes to be passed from a table declared as primary (i.e., the one the pipe is connected to using the <cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/) and vice versa, depending on what's allowed by the filters. Export filters control export of routes from the primary table to the secondary one, import filters control the opposite direction. The Pipe protocol may work in the opaque mode or in the transparent mode. In the opaque mode, the Pipe protocol retransmits optimal route from one table to the other table in a similar way like other protocols send and receive routes. Retransmitted route will have the source set to the Pipe protocol, which may limit access to protocol specific route attributes. The opaque mode is a default mode. In transparent mode, the Pipe protocol retransmits all routes from one table to the other table, retaining their original source and attributes. If import and export filters are set to accept, then both tables would have the same content. The mode can be set by <tt/mode/ option. The primary use of multiple routing tables and the Pipe protocol is for policy routing, where handling of a single packet doesn't depend only on its destination address, but also on its source address, source interface, protocol type and other similar parameters. In many systems (Linux being a good example), the kernel allows to enforce routing policies by defining routing rules which choose one of several routing tables to be used for a packet according to its parameters. Setting of these rules is outside the scope of BIRD's work (on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD, connect them to the kernel ones, use filters to control which routes appear in which tables and also you can employ the Pipe protocol for exporting a selected subset of one table to another one. <sect1>Configuration <descrip> <tag>peer table <m/table/</tag> Defines secondary routing table to connect to. The primary one is selected by the <cf/table/ keyword. <tag>mode opaque|transparent</tag> Specifies the mode for the pipe to work in. Default is opaque. </descrip> <sect1>Attributes The Pipe protocol doesn't define any route attributes. <sect1>Example Let's consider a router which serves as a boundary router of two different autonomous systems, each of them connected to a subset of interfaces of the router, having its own exterior connectivity and wishing to use the other AS as a backup connectivity in case of outage of its own exterior line. Probably the simplest solution to this situation is to use two routing tables (we'll call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having arrived from interfaces belonging to the first AS will be routed according to <cf/as1/ and similarly for the second AS. Thus we have split our router to two logical routers, each one acting on its own routing table, having its own routing protocols on its own interfaces. In order to use the other AS's routes for backup purposes, we can pass the routes between the tables through a Pipe protocol while decreasing their preferences and correcting their BGP paths to reflect the AS boundary crossing. <code> table as1; # Define the tables table as2; protocol kernel kern1 { # Synchronize them with the kernel table as1; kernel table 1; } protocol kernel kern2 { table as2; kernel table 2; } protocol bgp bgp1 { # The outside connections table as1; local as 1; neighbor 192.168.0.1 as 1001; export all; import all; } protocol bgp bgp2 { table as2; local as 2; neighbor 10.0.0.1 as 1002; export all; import all; } protocol pipe { # The Pipe table as1; peer table as2; export filter { if net ~ [ 1.0.0.0/8+] then { # Only AS1 networks if preference>10 then preference = preference-10; if source=RTS_BGP then bgp_path.prepend(1); accept; } reject; }; import filter { if net ~ [ 2.0.0.0/8+] then { # Only AS2 networks if preference>10 then preference = preference-10; if source=RTS_BGP then bgp_path.prepend(2); accept; } reject; }; } </code> <sect>RIP <sect1>Introduction The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors) distances to all networks it can reach. When a router hears distance to another network, it increments it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in RIP) and all routers know that network is unreachable. RIP tries to minimize situations where counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4 (RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">) and IPv6 (RFC 2080<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2080.txt">) versions of RIP are supported by BIRD, historical RIPv1 (RFC 1058<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1058.txt">)is not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported. RIP is a very simple protocol, and it has a lot of shortcomings. Slow convergence, big network load and inability to handle larger networks makes it pretty much obsolete in IPv4 world. (It is still usable on very small networks.) It is widely used in IPv6 networks, because there are no good implementations of OSPFv3. <sect1>Configuration In addition to options common for all to other protocols, RIP supports the following ones: <descrip> <tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf> section. Default: none. <tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table be honored. (Always, when sent from a host on a directly connected network or never.) Routing table updates are honored only from neighbors, that is not configurable. Default: never. </descrip> There are two options that can be specified per-interface. First is <cf>metric</cf>, with default one. Second is <cf>mode multicast|broadcast|quiet|nolisten|version1</cf>, it selects mode for rip to work in. If nothing is specified, rip runs in multicast mode. <cf>version1</cf> is currently equivalent to <cf>broadcast</cf>, and it makes RIP talk to a broadcast address even through multicast mode is possible. <cf>quiet</cf> option means that RIP will not transmit any periodic messages to this interface and <cf>nolisten</cf> means that RIP will send to this interface but not listen to it. The following options generally override behavior specified in RFC. If you use any of these options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything other than equally configured BIRD. I have warned you. <descrip> <tag>port <M>number</M></tag> selects IP port to operate on, default 520. (This is useful when testing BIRD, if you set this to an address >1024, you will not need to run bird with UID==0). <tag>infinity <M>number</M></tag> selects the value of infinity, default is 16. Bigger values will make protocol convergence even slower. <tag>period <M>number</M> </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower number will mean faster convergence but bigger network load. Do not use values lower than 10. <tag>timeout time <M>number</M> </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/. <tag>garbage time <M>number</M> </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/. </descrip> <sect1>Attributes RIP defines two route attributes: <descrip> <tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/). When routes from different RIP instances are available and all of them have the same preference, BIRD prefers the route with lowest <cf/rip_metric/. When importing a non-RIP route, the metric defaults to 5. <tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used to carry additional information with the route (for example, an originating AS number in case of external routes). When importing a non-RIP route, the tag defaults to 0. </descrip> <sect1>Example <code> protocol rip MyRIP_test { debug all; port 1520; period 10; garbage time 60; interface "eth0" { metric 3; mode multicast; }; interface "eth*" { metric 2; mode broadcast; }; honor neighbor; authentication none; import filter { print "importing"; accept; }; export filter { print "exporting"; accept; }; } </code> <sect>Static The Static protocol doesn't communicate with other routers in the network, but instead it allows you to define routes manually. This is often used for specifying how to forward packets to parts of the network which don't use dynamic routing at all and also for defining sink routes (i.e., those telling to return packets as undeliverable if they are in your IP block, you don't have any specific destination for them and you don't want to send them out through the default route to prevent routing loops). There are three types of static routes: `classical' routes telling to forward packets to a neighboring router, device routes specifying forwarding to hosts on a directly connected network and special routes (sink, blackhole etc.) which specify a special action to be done instead of forwarding the packet. When the particular destination is not available (the interface is down or the next hop of the route is not a neighbor at the moment), Static just uninstalls the route from the table it is connected to and adds it again as soon as the destination becomes adjacent again. The Static protocol has no configuration options. Instead, the definition of the protocol contains a list of static routes: <descrip> <tag>route <m/prefix/ via <m/ip/</tag> Static route through a neighboring router. <tag>route <m/prefix/ via <m/"interface"/</tag> Static device route through an interface to hosts on a directly connected network. <tag>route <m/prefix/ drop|reject|prohibit</tag> Special routes specifying to drop the packet, return it as unreachable or return it as administratively prohibited. </descrip> Static routes have no specific attributes. Example static config might look like this: <code> protocol static { table testable; # Connect to a non-default routing table route 0.0.0.0/0 via 62.168.0.13; # Default route route 62.168.0.0/25 reject; # Sink route route 10.2.0.0/24 via "arc0"; # Secondary network } </code> <chapt>Conclusions <sect>Future work Although BIRD supports all the commonly used routing protocols, there are still some features which would surely deserve to be implemented in future versions of BIRD: <itemize> <item>OSPF for IPv6 networks <item>OSPF NSSA areas and opaque LSA's <item>Route aggregation and flap dampening <item>Generation of IPv6 router advertisements <item>Multipath routes <item>Multicast routing protocols <item>Ports to other systems </itemize> <sect>Getting more help If you use BIRD, you're welcome to join the bird-users mailing list (<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">) where you can share your experiences with the other users and consult your problems with the authors. To subscribe to the list, just send a <tt/subscribe bird-users/ command in a body of a mail to (<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">). The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">. BIRD is a relatively young system and it probably contains some bugs. You can report any problems to the bird-users list and the authors will be glad to solve them, but before you do so, please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch which fixes the bug is always welcome as an attachment.) If you want to understand what is going inside, Internet standards are a good and interesting reading. You can get them from <HTMLURL URL="ftp://ftp.rfc-editor.org/" name="ftp.rfc-editor.org"> (or a nicely sorted version from <HTMLURL URL="ftp://atrey.karlin.mff.cuni.cz/pub/rfc" name="atrey.karlin.mff.cuni.cz:/pub/rfc">). <it/Good luck!/ </book>