mirror of
https://gitlab.nic.cz/labs/bird.git
synced 2024-12-22 09:41:54 +00:00
201 lines
8.4 KiB
HTML
201 lines
8.4 KiB
HTML
<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>
|