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diff --git a/doc/bird.html b/doc/bird.html new file mode 100644 index 0000000..2401ede --- /dev/null +++ b/doc/bird.html @@ -0,0 +1,200 @@ +<HTML><HEAD><TITLE>Bird</TITLE></HEAD><BODY> + +<!-- 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 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later. + + --> + +<TEX t="Insert nice, hand-generated title page here"> + +<h1>Introduction</h1> + +<p>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 <A +HREF="fixme">gated</A> 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. + +<h2>About this documentation</h2> + +<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. + +<h1>Bird configuration</h1> + +<p>Bird is configured using text configuration file. At startup, bird reads <TT file>bird.conf</TT> +(unless -c command line parameter is given). Really simple configuration file might look like this: + +<PRE conf> + +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; +} +</PRE> + +<p>You can find example of more complicated configuration file in <TT file>doc/bird.conf.example</TT>. + +<h1>Filters</h1> + +<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. + +<p pgm>You can find sources of filters language in <TT file>filter/</TT> directory. <TT +file>filter/config.Y</TT> contains filter gramar, and basically translates source from user into +tree of <TT c>f_inst</TT> structures. These trees are later interpreted using code in <TT +file>filter/filter.c</TT>. Filters internally work with values/variables in <TT c>struct f_val</TT>, +which contains type of value and value. + +<p>Filter basically looks like this: + +<PRE filt> +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"; +} +</PRE> + +<p>As you can see, filter has a header, list of local variables, and body. Header consists of <TT +filt>filter</TT> keyword, followed by (unique) name of filter. List of local variables consists of +pairs <TT filt><I>type name</I>;</TT>, where each pair defines one local variable. Body consists of +<TT filt> { <I>statments</I> }</TT>. Statements are terminated by <TT filt>;</TT>. You can group +several statments into one by <TT filt>{ <I>statments</I> }</TT> construction, that is usefull if +you want to make bigger block of code conditional. + +<h2>Variables</h2> + +<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). + +<DL filt> + <DT>bool + <DD>this is boolean type, it can have only two values, <TT filt>TRUE</TT> and <TT + filt>FALSE</TT>. Boolean is not compatible with integer and is the only type you can use + in if statments. + + <DT>int + <DD>this is common integer, you can expect it to store signed values from -2000000000 to + +2000000000. + + <DT>pair + <DD>this is pair of two short integers. Each component can have values from 0 to + 65535. Constant of this type is written as <TT filt>(1234,5678)</TT>. + + <DT>string + <DD>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 <TT + filt>"This is string constant"</TT>. + + <DT>ip + <DD>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 + <TT filt>1.2.3.4</TT>. You can apply special operator <TT filt>.mask(<I>num</I>)</TT> + on values of type ip. It masks out all but first <TT filt><I>num</I></TT> bits from ip + address. So <TT filt>1.2.3.4.mask(8) = 1.0.0.0</TT> is true. + + <DT>prefix + <DD>this type can hold ip address, prefix len pair. Prefixes are written as <TT filt><I>ip + address</I>/<I>px len</I></TT>. There are two special operators on prefix: <TT + filt>.ip</TT>, which separates ip address from the pair, and <TT filt>.len</TT>, which + separates prefix len from the pair. + + <DT>set int|ip|prefix|pair + <DD>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</TT> looks like <TT filt> + [ 1, 2, 5..7 ]</TT>. 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} ]</TT>. + + <DT>enum + <DD>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. +</DL> + +<h1>Protocols</h1> + +<h2>Rip</h2> + +<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. 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 15, 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>. + +<h3>Configuration</h3> + +<p>In addition to options generic to other protocols, rip supports following options: + +<DL conf> + <DT>port <I>number</I> + <DD>selects IP port to operate on, default 520. + + <DT>authentication <I>none|password|md5</I> + <DD>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 { }</TT><FIXME: add reference to that section> section. +</DL> + +<pre conf> + +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; }; +} +</pre> + +</BODY></HTML> |