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diff --git a/doc/bird.sgml b/doc/bird.sgml new file mode 100644 index 00000000..4b744d0c --- /dev/null +++ b/doc/bird.sgml @@ -0,0 +1,314 @@ +<!doctype linuxdoc system> + +<!-- + Bird documentation + + This is bird documentation system. It looks like html, but it is _not_ html: nonstandard + extensions are in use in order to auto-generate nice tex source. Use TT tag to markup short + texts that should be rendered in fixed-space font, and further specify what kind of text this + is. Currently TT file and TT conf are being used. For multi-line texts, use PRE section, again + with option saying what kind of section this is. Use DL conf for definition of configuration + keywords. + + (set-fill-column 100) + + Copyright 1999,2000 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later. + + --> + +<article> + +<title>Bird +<author> +Pavel Machek <tt/pavel@ucw.cz/ + +<date>2000 +<abstract> +This document contains documentation for Basic Internet Routing Daemon +</abstract> + +<!-- Table of contents --> +<toc> + +<!-- Begin the document --> + +<sect>Introduction + +<sect1>What is bird + +<p><label id="intro"> +You may wonder what 'bird' means. It is acronym of 'Basic Internet Routing Daemon', and we think +that's cool name. Its task is similar to what firmware of Cisco routers does, or what gated +(<HTMLURL URL="fixme">) does. However, you can not run Cisco's firmware on "normal" computer +and gated is really hard to configure and comes under wrong license. Bird is being developed on +Charles University, Prague, and can be freely distributed under terms of GNU General Public +License. Bird is designed to run on unix and unix-like systems, it is primarily developed on Linux. + +<sect1>About this documentation + +<p>This documentation can have 4 forms: extended html (this is master copy), html with stripped +extensions, ascii text (generated from html) and dvi/postscript (generated from html using +html2latex and latex). You should always edit master copy; if you do so be sure to read comment at +beggining of file. If you want to view documentation, you can either launch your www browser at +master copy (and hope that browser does not have incompatible extensions from our), or you can +generate nice printed copy. + +<sect1>Configuration + +<p>Bird is configured using text configuration file. At startup, bird reads <file/bird.conf/ +(unless -c command line parameter is given). Really simple configuration file might look like this: + +<cf> + +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; +} +</cf> + +<p>You can find example of more complicated configuration file in <file>doc/bird.conf.example</file>. + +<sect>Filters + +<sect1>Introduction + +<p>Bird contains rather simple programming language. (No, it can not yet read mail :-). There are +two objects in this language: filters and functions. Filters are called by bird core when route is +being passed between protocol and main routing table, and filters may call functions. Functions may +call other functions but recursion is not allowed. Filter language contains control structures such +as if's and switches, but it allows no loops. Filters are +interpretted. Filter using many features can be found in <file>filter/test.conf</file>. + +<p>There's one strange thing with filter language: it does not permit you to create loops. There's +no equivalent of while() or for() command, and recursive functions are not permitted. + +<p pgm>You can find sources of filters language in +<file>filter/</file> directory. <file>filter/config.Y</file> contains +filter gramar, and basically translates source from user into tree of +<TT c>f_inst</cf> structures. These trees are later interpreted using +code in <file>filter/filter.c</file>. Filters internally work with +values/variables in <TT c>struct f_val</cf>, which contains type of +value and value. + +<p>Filter basically looks like this: + +<cf> +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"; +} +</cf> + +<p>As you can see, filter has a header, list of local variables, and body. Header consists of <cf/filter/ keyword, followed by (unique) name of filter. List of local variables consists of +pairs <cf><I>type name</I>;</cf>, where each pair defines one local variable. Body consists of +<cf> { <I>statments</I> }</cf>. Statements are terminated by <cf/;/. You can group +several statments into one by <cf>{ <I>statments</I> }</cf> construction, that is usefull if +you want to make bigger block of code conditional. + +<sect1>Data types + +<p>Each variable and each value has certain type. Unlike C, filters distinguish between integers and +booleans (that is to prevent you from shooting in the foot). + +<descrip> + <tag/bool/ this is boolean type, it can have only two values, + <cf/TRUE/ and <cf/FALSE/. Boolean is not compatible with + integer and is the only type you can use in if statments. + + <tag/int/ this is common integer, you can expect it to store + signed values from -2000000000 to +2000000000. + + <tag/pair/ this is pair of two short integers. Each component + can have values from 0 to 65535. Constant of this type is + written as <cf/(1234,5678)/. + + <tag/string/ this is string of characters. There are no ways to modify strings in filters. You can + pass them between functions, assign to variable of type string, print such variables, but + you can not concatenate two strings (for example). String constants are written as <cf/ + "This is string constant". + + <tag/ip/ this type can hold single ip address. Depending on version of bird you are using, it + can be ipv4 or ipv6 address. Ipv4 addresses addresses are written (as you would expect) as + <cf/1.2.3.4/. You can apply special operator <cf>.mask(<I>num</I>)</cf> + on values of type ip. It masks out all but first <cf><I>num</I></cf> bits from ip + address. So <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true. + + <tag/prefix/ this type can hold ip address, prefix len + pair. Prefixes are written as <cf><I>ip address</I>/<I>px + len</I></cf>. There are two special operators on prefix: + <cf/.ip/, which separates ip address from the pair, and + <cf/.len/, which separates prefix len from the pair. + + <tag/set int|ip|prefix|pair/ + filters know four types of sets. Sets are similar to strings: you can pass them around + but you can not modify them. Constant of type <TT filt>set int</cf> looks like <TT filt> + [ 1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are permitted in + sets. Sets of prefixes are special: you can specify which prefixes should match them by + using <TT filt>[ 1.0.0.0/8+, 2.0.0.0/8-, 3.0.0.0/8{5,6} ]</cf>. 3.0.0.0/8{5,6} matches + prefixes 3.X.X.X, whose prefixlength is 5 to 6. 3.0.0.0/8+ is shorthand for 3.0.0.0/{0,8}, + 3.0.0.0/8- is shorthand for 3.0.0.0/{0,7}. + + <tag/enum/ + enumerational types are halfway-internal in the bird. You can not define your own + variable of enumerational type, but some pre-defined variables are of enumerational + type. Enumerational types are incompatible with each other, again, its for your + protection. +</descrip> + +<sect1>Operations + +<p>Filter language supports common integer operations (+,-,*,/), parenthesis (a*(b+c)), comparation +(a=b, a!=b, a<b, a>=b). Special operators include ~ for "in" operation. In operation can be +used on element and set of that elements, or on ip and prefix, or on prefix and prefix. Its result +is true if element is in given set or if ip adress is inside given prefix. + +<sect1>Functions + +<p>Bird supports functions, so that you don't have to repeat same blocks of code over and +over. Functions can have zero or more parameters, and can have local variables. Function basically +looks like this: + +<cf> +function name () +int local_variable; +{ + local_variable = 5; +} + +function with_parameters (int parameter) +{ + print parameter; +} +</cf> + +<p>Unlike C, variables are declared after function line but before first {. You can not declare +variables in nested blocks. Functions are called like in C: <cf>name(); with_parameters(5);</cf>. + +<p>Filters are declared in similar way to functions, except they can not have explicit +parameters. They get route table entry as implicit parameter. + +<sect1>Control structures + +<p>Filters support two control structures: if/then/else and +case. Syntax of if/then/else is <cf>if <I>expression</I> then +<I>command</I>; else <I>command</I>;<TT> and you can use <cf>{ +<I>command_1</I>; <I>command_2</I>; <I>...</I> }</cf> instead of one +or both commands. <cf>else</cf> clause may be ommited. Case is +used like this: + +<cf> + case <I>argument</I> { + 2: print "dva"; print "jeste jednou dva"; + 3 .. 5: print "tri az pet"; + else: print "neco jineho"; + } +</cf> + +where <I>argument</I> is any argument that can be on the left side of ~ operator, and anything that +could be member of set is allowed before :. Multiple commands are allowed without {} grouping. If +argument matches neither of : clauses, else: clause is used. (Case is actually implemented as set +matching, internally.) + +<sect>Protocols + +<sect1>Rip + +<sect2>Introduction + +<p>Rip protocol (sometimes called Rest In Pieces) is simple protocol, where each router broadcasts +distances to all networks he can reach. When router hears distance to other 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 distance is old distance plus 1 (actually, plus +interface metric, which is usually one). After some time, 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 neccessary, because it is slow. Due to infinity being 16, you can not use +rip on networks where maximal distance is bigger than 15 hosts. You can read more about rip at <A +HREF="fixme">rfc1234</A>. + +<sect2>Configuration + +<p>In addition to options generic to other protocols, rip supports following options: + +<descrip> + <tag/authentication none|password|md5/ + selects authenticaion method to use. None means that packets are not authenticated at + all, password means that plaintext password is embedded into each packet, and md5 means + that packets are authenticated using md5 cryptographics hash. See <A + HREF="fixme">rfc1234</A>. If you set authentication to non-none, it is good idea to add + <TT conf>passwords { }</cf> section. +</descrip> + +<p>There are two options that can be specified per-interface. First is <cf>metric</cf>, with +default one. Second is <cf>mode broadcast|quiet|nolisten|version1</cf>, it selects mode for +rip to work in. If nothing is specified, rip runs in multicasts mode. <cf>version1</cf> is +currently equivalent to <cf>broadcast</cf>, and it makes rip talk at broadcast address even +through multicast mode is possible. <cf>quiet</cf> option means that rip will not transmit +periodic messages onto this interface and <cf>nolisten</cf> means that rip will talk to this +interface but not listen on it. + +<p>Following options generally override specified behaviour from rfc. If you use any of these +options, bird will no longer be rfc-compatible, which means it will not be able to talk to anything +other than equally (mis-)configured bird. I warned you. + +<descrip> + <tag>port <I>number</I></tag> + selects IP port to operate on, default 520. (This is usefull when testing bird, if you + set this to address >1024, you will not need to run bird with uid==0). + + <tag>infinity <I>number</I></tag> + select value of infinity, default 16. Bigger values will make protocol convergence + even slower. + + <tag>period <I>number</I> + </tag>specifies number of seconds between periodic updates. Default is 30 seconds. Lower + number will mean faster convergence but bigger network load. + + <tag>timeouttime <I>number</I> + </tag>specifies how old route has to be to be considered unreachable. Default is 4*period. + + <tag>garbagetime <I>number</I> + </tag>specifies how old route has to be to be discarded. Default is 10*period. +</descrip> + +<p>In addition, rip defines two filter variables, both of type it. <cf>rip_metric</cf> is rip +metric of current route, <cf>rip_tag</cf> is tag of current route. + +<cf> + +protocol rip MyRIP_test { + debug all; + port 1520; + period 7; + garbagetime 60; + interface "*"; + honour neighbour; + passwords { password "ahoj" from 0 to 10; + password "nazdar" from 10; + } + authentication none; + import filter { print "importing"; accept; }; + export filter { print "exporting"; accept; }; +} +</cf> + +</article> |