Commit c8c0f624 authored by Pavel Machek's avatar Pavel Machek

This is first version of documentation. Be sure to take a close look

at it, and it would be very nice if you wrote at least introductions
to your chapters...
parent 60d7d10e
<!-- This is bird documentation system. It looks like html, but it is _not_ html: nonstandard
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Copyright 1999 Pavel Machek <>, distribute under GPL version 2 or later.
<TEX t="Insert nice, hand-generated title page here">
<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;
<p>You can find example of more complicated configuration file in <TT file>doc/bird.conf.example</TT>.
<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 &gt; 10 then
reject "RIP metric is too big";
accept "ok";
<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.
<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>
<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.
<DD>this is common integer, you can expect it to store signed values from -2000000000 to
<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>.
<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>.
<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></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> =</TT> is true.
<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>[,,{5,6} ]</TT>.
<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
<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>.
<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.
<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; };
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