Statistics
| Branch: | Revision:

iof-bird-daemon / doc / bird.sgml @ 080ed4d8

History | View | Annotate | Download (144 KB)

1
<!doctype birddoc system>
2

    
3
<!--
4
	BIRD documentation
5

    
6
This documentation can have 4 forms: sgml (this is master copy), html,
7
ASCII text and dvi/postscript (generated from sgml using
8
sgmltools). You should always edit master copy.
9

    
10
This is a slightly modified linuxdoc dtd.  Anything in <descrip> tags is considered definition of
11
configuration primitives, <cf> is fragment of configuration within normal text, <m> is
12
"meta" information within fragment of configuration - something in config which is not keyword.
13

    
14
    (set-fill-column 100)
15

    
16
    Copyright 1999,2000 Pavel Machek <pavel@ucw.cz>, distribute under GPL version 2 or later.
17

    
18
 -->
19

    
20
<book>
21

    
22
<title>BIRD User's Guide
23
<author>
24
Ondrej Filip <it/&lt;feela@network.cz&gt;/,
25
Pavel Machek <it/&lt;pavel@ucw.cz&gt;/,
26
Martin Mares <it/&lt;mj@ucw.cz&gt;/,
27
Ondrej Zajicek <it/&lt;santiago@crfreenet.org&gt;/
28
</author>
29

    
30
<abstract>
31
This document contains user documentation for the BIRD Internet Routing Daemon project.
32
</abstract>
33

    
34
<!-- Table of contents -->
35
<toc>
36

    
37
<!-- Begin the document -->
38

    
39
<chapt>Introduction
40

    
41
<sect>What is BIRD
42

    
43
<p><label id="intro">
44
The name `BIRD' is actually an acronym standing for `BIRD Internet Routing Daemon'.
45
Let's take a closer look at the meaning of the name:
46

    
47
<p><em/BIRD/: Well, we think we have already explained that. It's an acronym standing
48
for `BIRD Internet Routing Daemon', you remember, don't you? :-)
49

    
50
<p><em/Internet Routing/: It's a program (well, a daemon, as you are going to discover in a moment)
51
which works as a dynamic router in an Internet type network (that is, in a network running either
52
the IPv4 or the IPv6 protocol). Routers are devices which forward packets between interconnected
53
networks in order to allow hosts not connected directly to the same local area network to
54
communicate with each other. They also communicate with the other routers in the Internet to discover
55
the topology of the network which allows them to find optimal (in terms of some metric) rules for
56
forwarding of packets (which are called routing tables) and to adapt themselves to the
57
changing conditions such as outages of network links, building of new connections and so on. Most of
58
these routers are costly dedicated devices running obscure firmware which is hard to configure and
59
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 
60
computer to act as a router and forward packets belonging to the other hosts, but only according to
61
a statically configured table.
62

    
63
<p>A <em/Routing Daemon/ is in UNIX terminology a non-interactive program running on
64
background which does the dynamic part of Internet routing, that is it communicates
65
with the other routers, calculates routing tables and sends them to the OS kernel
66
which does the actual packet forwarding. There already exist other such routing
67
daemons: routed (RIP only), GateD (non-free), Zebra<HTMLURL URL="http://www.zebra.org">
68
and MRTD<HTMLURL URL="http://sourceforge.net/projects/mrt">, but their capabilities are
69
limited and they are relatively hard to configure and maintain.
70

    
71
<p>BIRD is an Internet Routing Daemon designed to avoid all of these shortcomings,
72
to support all the routing technology used in the today's Internet or planned to be
73
used in near future and to have a clean extensible architecture allowing new routing
74
protocols to be incorporated easily. Among other features, BIRD supports:
75

    
76
<itemize>
77
	<item>both IPv4 and IPv6 protocols
78
	<item>multiple routing tables
79
	<item>the Border Gateway Protocol (BGPv4)
80
	<item>the Routing Information Protocol (RIPv2)
81
	<item>the Open Shortest Path First protocol (OSPFv2, OSPFv3)
82
	<item>the Router Advertisements for IPv6 hosts
83
	<item>a virtual protocol for exchange of routes between different routing tables on a single host
84
	<item>a command-line interface allowing on-line control and inspection
85
		of status of the daemon
86
	<item>soft reconfiguration (no need to use complex online commands
87
		to change the configuration, just edit the configuration file
88
		and notify BIRD to re-read it and it will smoothly switch itself
89
		to the new configuration, not disturbing routing protocols
90
		unless they are affected by the configuration changes)
91
	<item>a powerful language for route filtering
92
</itemize>
93

    
94
<p>BIRD has been developed at the Faculty of Math and Physics, Charles University, Prague,
95
Czech Republic as a student project. It can be freely distributed under the terms of the GNU General
96
Public License.
97

    
98
<p>BIRD has been designed to work on all UNIX-like systems. It has
99
been developed and tested under Linux 2.0 to 2.6, and then ported to
100
FreeBSD, NetBSD and OpenBSD, porting to other systems (even non-UNIX
101
ones) should be relatively easy due to its highly modular
102
architecture.
103

    
104
<p>BIRD supports either IPv4 or IPv6 protocol, but have to be compiled
105
separately for each one. Therefore, a dualstack router would run two
106
instances of BIRD (one for IPv4 and one for IPv6), with completely
107
separate setups (configuration files, tools ...).
108

    
109
<sect>Installing BIRD
110

    
111
<p>On a recent UNIX system with GNU development tools (GCC, binutils, m4, make) and Perl, installing BIRD should be as easy as:
112

    
113
<code>
114
        ./configure
115
        make
116
        make install
117
        vi /usr/local/etc/bird.conf
118
	bird
119
</code>
120

    
121
<p>You can use <tt>./configure --help</tt> to get a list of configure
122
options. The most important ones are:
123
<tt/--enable-ipv6/ which enables building of an IPv6 version of BIRD,
124
<tt/--with-protocols=/ to produce a slightly smaller BIRD executable by configuring out routing protocols you don't use, and
125
<tt/--prefix=/ to install BIRD to a place different from.
126
<file>/usr/local</file>.
127

    
128
<sect>Running BIRD
129

    
130
<p>You can pass several command-line options to bird:
131

    
132
<descrip>
133
	<tag>-c <m/config name/</tag>
134
	use given configuration file instead of <it/prefix/<file>/etc/bird.conf</file>.
135

    
136
	<tag>-d</tag>
137
	enable debug messages and run bird in foreground.
138

    
139
	<tag>-D <m/filename of debug log/</tag>
140
	log debugging information to given file instead of stderr.
141

    
142
	<tag>-p</tag>
143
	just parse the config file and exit. Return value is zero if the config file is valid,
144
	nonzero if there are some errors.
145

    
146
	<tag>-s <m/name of communication socket/</tag>
147
	use given filename for a socket for communications with the client, default is <it/prefix/<file>/var/run/bird.ctl</file>.
148

    
149
	<tag>-P <m/name of PID file/</tag>
150
	create a PID file with given filename</file>.
151

    
152
	<tag>-u <m/user/</tag>
153
	drop privileges and use that user ID, see the next section for details.
154

    
155
	<tag>-g <m/group/</tag>
156
	use that group ID, see the next section for details.
157

    
158
	<tag>-f</tag>
159
	run bird in foreground.
160
</descrip>
161

    
162
<p>BIRD writes messages about its work to log files or syslog (according to config).
163

    
164
<sect>Privileges
165

    
166
<p>BIRD, as a routing daemon, uses several privileged operations (like
167
setting routing table and using raw sockets). Traditionally, BIRD is
168
executed and runs with root privileges, which may be prone to security
169
problems. The recommended way is to use a privilege restriction
170
(options <cf/-u/, <cf/-g/). In that case BIRD is executed with root
171
privileges, but it changes its user and group ID to an unprivileged
172
ones, while using Linux capabilities to retain just required
173
privileges (capabilities CAP_NET_*). Note that the control socket is
174
created before the privileges are dropped, but the config file is read
175
after that. The privilege restriction is not implemented in BSD port
176
of BIRD.
177

    
178
<p>A nonprivileged user (as an argument to <cf/-u/ options) may be the
179
user <cf/nobody/, but it is suggested to use a new dedicated user
180
account (like <cf/bird/). The similar considerations apply for
181
the group option, but there is one more condition -- the users
182
in the same group can use <file/birdc/ to control BIRD.
183

    
184
<p>Finally, there is a possibility to use external tools to run BIRD in
185
an environment with restricted privileges. This may need some
186
configuration, but it is generally easy -- BIRD needs just the
187
standard library, privileges to read the config file and create the
188
control socket and the CAP_NET_* capabilities.
189

    
190
<chapt>About routing tables
191

    
192
<p>BIRD has one or more routing tables which may or may not be
193
synchronized with OS kernel and which may or may not be synchronized with
194
each other (see the Pipe protocol). Each routing table contains a list of
195
known routes. Each route consists of:
196

    
197
<itemize>
198
	<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)
199
	<item>preference of this route
200
	<item>IP address of router which told us about this route
201
	<item>IP address of router we should forward the packets to
202
	using this route
203
	<item>other attributes common to all routes
204
	<item>dynamic attributes defined by protocols which may or
205
	may not be present (typically protocol metrics)
206
</itemize>
207

    
208
Routing table maintains multiple entries
209
for a network, but at most one entry for one network and one
210
protocol. The entry with the highest preference is used for routing (we
211
will call such an entry the <it/selected route/). If
212
there are more entries with the same preference and they are from the same
213
protocol, the protocol decides (typically according to metrics). If they aren't,
214
an internal ordering is used to break the tie. You can
215
get the list of route attributes in the Route attributes section.
216

    
217
<p>Each protocol is connected to a routing table through two filters
218
which can accept, reject and modify the routes. An <it/export/
219
filter checks routes passed from the routing table to the protocol,
220
an <it/import/ filter checks routes in the opposite direction.
221
When the routing table gets a route from a protocol, it recalculates
222
the selected route and broadcasts it to all protocols connected to
223
the table. The protocols typically send the update to other routers
224
in the network. Note that although most protocols are interested 
225
in receiving just selected routes, some protocols (e.g. the <cf/Pipe/
226
protocol) receive and process all entries in routing tables (accepted
227
by filters).
228

    
229
<p><label id="dsc-sorted">Usually, a routing table just chooses a
230
selected route from a list of entries for one network. But if the
231
<cf/sorted/ option is activated, these lists of entries are kept
232
completely sorted (according to preference or some protocol-dependent
233
metric).
234

    
235
This is needed for some features of some protocols
236
(e.g. <cf/secondary/ option of BGP protocol, which allows to accept
237
not just a selected route, but the first route (in the sorted list)
238
that is accepted by filters), but it is incompatible with some other
239
features (e.g. <cf/deterministic med/ option of BGP protocol, which
240
activates a way of choosing selected route that cannot be described
241
using comparison and ordering). Minor advantage is that routes are
242
shown sorted in <cf/show route/, minor disadvantage is that it is
243
slightly more computationally expensive.
244

    
245

    
246
<chapt>Configuration
247

    
248
<sect>Introduction
249

    
250
<p>BIRD is configured using a text configuration file. Upon startup, BIRD reads <it/prefix/<file>/etc/bird.conf</file> (unless the
251
<tt/-c/ command line option is given). Configuration may be changed at user's request: if you modify
252
the config file and then signal BIRD with <tt/SIGHUP/, it will adjust to the new
253
config. Then there's the client
254
which allows you to talk with BIRD in an extensive way.
255

    
256
<p>In the config, everything on a line after <cf/#/ or inside <cf>/*
257
*/</cf> is a comment, whitespace characters are treated as a single space. If there's a variable number of options, they are grouped using
258
the <cf/{ }/ brackets. Each option is terminated by a <cf/;/. Configuration
259
is case sensitive. There are two ways how to name symbols (like protocol names, filter names, constats etc.). You can either use
260
a simple string starting with a letter followed by any combination of letters and numbers (e.g. "R123", "myfilter", "bgp5") or you
261
can enclose the name into apostrophes (<cf/'/) and than you can use any combination of numbers, letters. hyphens, dots and colons
262
(e.g. "'1:strange-name'", "'-NAME-'", "'cool::name'").
263

    
264
<p>Here is an example of a simple config file. It enables
265
synchronization of routing tables with OS kernel, scans for 
266
new network interfaces every 10 seconds and runs RIP on all network interfaces found.
267

    
268

    
269
<code>
270
protocol kernel {
271
	persist;		# Don't remove routes on BIRD shutdown
272
	scan time 20;		# Scan kernel routing table every 20 seconds
273
	export all;		# Default is export none
274
}
275

    
276
protocol device {
277
	scan time 10;		# Scan interfaces every 10 seconds
278
}
279

    
280
protocol rip {
281
	export all;
282
	import all;
283
	interface "*";
284
}
285
</code>
286

    
287

    
288
<sect>Global options
289

    
290
<p><descrip>
291
	<tag>include "<m/filename/"</tag> 
292
	This statement causes inclusion of a new file. The maximal depth is set to 5.
293

    
294
	<tag><label id="dsc-log">log "<m/filename/"|syslog [name <m/name/]|stderr all|{ <m/list of classes/ }</tag> 
295
	Set logging of messages having the given class (either <cf/all/ or <cf/{
296
	error, trace }/ etc.) into selected destination (a file specified as a filename string,
297
	syslog with optional name argument, or the stderr output). Classes are:
298
	<cf/info/, <cf/warning/, <cf/error/ and <cf/fatal/ for messages about local problems,
299
	<cf/debug/ for debugging messages, 
300
	<cf/trace/ when you want to know what happens in the network, 
301
	<cf/remote/ for messages about misbehavior of remote machines, 
302
	<cf/auth/ about authentication failures,
303
	<cf/bug/ for internal BIRD bugs. You may specify more than one <cf/log/ line to establish logging to multiple
304
	destinations. Default: log everything to the system log.
305

    
306
	<tag>debug protocols all|off|{ states, routes, filters, interfaces, events, packets }</tag>
307
	Set global defaults of protocol debugging options. See <cf/debug/ in the following section. Default: off.
308

    
309
	<tag>debug commands <m/number/</tag>
310
	Control logging of client connections (0 for no logging, 1 for
311
	logging of connects and disconnects, 2 and higher for logging of
312
	all client commands). Default: 0.
313

    
314
	<tag>mrtdump "<m/filename/"</tag>
315
	Set MRTdump file name. This option must be specified to allow MRTdump feature.
316
	Default: no dump file.
317

    
318
	<tag>mrtdump protocols all|off|{ states, messages }</tag>
319
	Set global defaults of MRTdump options. See <cf/mrtdump/ in the following section.
320
	Default: off.
321

    
322
	<tag>filter <m/name local variables/{ <m/commands/ }</tag> Define a filter. You can learn more about filters
323
	in the following chapter. 
324

    
325
	<tag>function <m/name/ (<m/parameters/) <m/local variables/ { <m/commands/ }</tag> Define a function. You can learn more
326
	about functions in the following chapter.
327
 
328
	<tag>protocol rip|ospf|bgp|... [<m/name/ [from <m/name2/]] { <m>protocol options</m> }</tag>
329
	Define a protocol instance called <cf><m/name/</cf> (or with a name like "rip5" generated
330
	automatically if you don't specify any <cf><m/name/</cf>). You can learn more about
331
	configuring protocols in their own chapters. When <cf>from <m/name2/</cf> expression is
332
	used, initial protocol options are taken from protocol or template <cf><m/name2/</cf>
333
	You can run more than one instance of most protocols (like RIP or BGP). By default, no
334
	instances are configured.
335

    
336
	<tag>template rip|bgp|... [<m/name/ [from <m/name2/]] { <m>protocol options</m> }</tag>
337
	Define a protocol template instance called <cf><m/name/</cf> (or with a name like "bgp1"
338
	generated automatically if you don't specify any <cf><m/name/</cf>). Protocol templates can
339
	be used to group common options when many similarly configured protocol instances are to be
340
	defined. Protocol instances (and other templates) can use templates by using <cf/from/
341
	expression and the name of the template. At the moment templates (and <cf/from/ expression)
342
	are not implemented for OSPF protocol.
343

    
344
	<tag>define <m/constant/ = <m/expression/</tag>
345
	Define a constant. You can use it later in every place you could use a value of the same type.
346
	Besides, there are some predefined numeric constants based on /etc/iproute2/rt_* files.
347
	A list of defined constants can be seen (together with other symbols) using 'show symbols' command.
348

    
349
	<tag>router id <m/IPv4 address/</tag>
350
 	Set BIRD's router ID. It's a world-wide unique identification
351
	of your router, usually one of router's IPv4 addresses.
352
	Default: in IPv4 version, the lowest IP address of a
353
	non-loopback interface. In IPv6 version, this option is
354
	mandatory.
355

    
356
	<tag>router id from [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...]</tag>
357
	Set BIRD's router ID based on an IP address of an interface
358
	specified by an interface pattern. The option is applicable
359
	for IPv4 version only. See <ref id="dsc-iface" name="interface">
360
	section for detailed description of interface patterns.
361

    
362
	<tag>listen bgp [address <m/address/] [port <m/port/] [dual]</tag>
363
	This option allows to specify address and port where BGP
364
	protocol should listen. It is global option as listening
365
	socket is common to all BGP instances. Default is to listen on
366
	all addresses (0.0.0.0) and port 179. In IPv6 mode, option
367
	<cf/dual/ can be used to specify that BGP socket should accept
368
	both IPv4 and IPv6 connections (but even in that case, BIRD
369
	would accept IPv6 routes only). Such behavior was default in
370
	older versions of BIRD.
371

    
372
	<tag>timeformat route|protocol|base|log "<m/format1/" [<m/limit/ "<m/format2/"]</tag>
373
	This option allows to specify a format of date/time used by
374
	BIRD.  The first argument specifies for which purpose such
375
	format is used. <cf/route/ is a format used in 'show route'
376
	command output, <cf/protocol/ is used in 'show protocols'
377
	command output, <cf/base/ is used for other commands and
378
	<cf/log/ is used in a log file.
379

    
380
	"<m/format1/" is a format string using <it/strftime(3)/
381
	notation (see <it/man strftime/ for details). <m/limit> and
382
	"<m/format2/" allow to specify the second format string for
383
	times in past deeper than <m/limit/ seconds. There are few
384
	shorthands: <cf/iso long/ is a ISO 8601 date/time format
385
	(YYYY-MM-DD hh:mm:ss) that can be also specified using <cf/"%F
386
	%T"/. <cf/iso short/ is a variant of ISO 8601 that uses just
387
	the time format (hh:mm:ss) for near times (up to 20 hours in
388
	the past) and the date format (YYYY-MM-DD) for far times. This
389
	is a shorthand for <cf/"%T" 72000 "%F"/.
390

    
391
	By default, BIRD uses the <cf/iso short/ format for <cf/route/ and
392
	<cf/protocol/ times, and the <cf/iso long/ format for <cf/base/ and
393
	<cf/log/ times.
394

    
395
	In pre-1.4.0 versions, BIRD used an short, ad-hoc format for
396
	<cf/route/ and <cf/protocol/ times, and a <cf/iso long/ similar format
397
	(DD-MM-YYYY hh:mm:ss) for <cf/base/ and <cf/log/. These timeformats
398
	could be set by <cf/old short/ and <cf/old long/ compatibility
399
	shorthands.
400

    
401
	<tag>table <m/name/ [sorted]</tag>
402
	Create a new routing table. The default routing table is
403
	created implicitly, other routing tables have to be added by
404
	this command. Option <cf/sorted/ can be used to enable
405
	sorting of routes, see <ref id="dsc-sorted" name="sorted table">
406
	description for details.
407

    
408
	<tag>roa table <m/name/ [ { roa table options ... } ]</tag>
409
	Create a new ROA (Route Origin Authorization) table. ROA
410
	tables can be used to validate route origination of BGP
411
	routes. A ROA table contains ROA entries, each consist of a
412
	network prefix, a max prefix length and an AS number. A ROA
413
	entry specifies prefixes which could be originated by that AS
414
	number. ROA tables could be filled with data from RPKI (RFC
415
	6480) or from public databases like Whois. ROA tables are 
416
	examined by <cf/roa_check()/ operator in filters.
417

    
418
	Currently, there is just one option,
419
	<cf>roa <m/prefix/ max <m/num/ as <m/num/</cf>, which
420
	can be used to populate the ROA table with static ROA
421
	entries. The option may be used multiple times. Other entries
422
	can be added dynamically by <cf/add roa/ command.
423

    
424
	<tag>eval <m/expr/</tag>
425
	Evaluates given filter expression. It is used by us for	testing of filters.
426
</descrip>
427

    
428
<sect>Protocol options
429

    
430
<p>For each protocol instance, you can configure a bunch of options.
431
Some of them (those described in this section) are generic, some are
432
specific to the protocol (see sections talking about the protocols).
433

    
434
<p>Several options use a <cf><m/switch/</cf> argument. It can be either
435
<cf/on/, <cf/yes/ or a numeric expression with a non-zero value for the
436
option to be enabled or <cf/off/, <cf/no/ or a numeric expression evaluating
437
to zero to disable it. An empty <cf><m/switch/</cf> is equivalent to <cf/on/
438
("silence means agreement").
439

    
440
<descrip>
441
	<tag>preference <m/expr/</tag> Sets the preference of routes generated by this protocol. Default: protocol dependent.
442

    
443
	<tag>disabled <m/switch/</tag> Disables the protocol. You can change the disable/enable status from the command
444
	line interface without needing to touch the configuration. Disabled protocols are not activated. Default: protocol is enabled.
445

    
446
	<tag>debug all|off|{ states, routes, filters, interfaces, events, packets }</tag>
447
	Set protocol debugging options. If asked, each protocol is capable of
448
	writing trace messages about its work to the log (with category
449
	<cf/trace/). You can either request printing of <cf/all/ trace messages
450
	or only of the types selected: <cf/states/ for protocol state changes
451
	(protocol going up, down, starting, stopping etc.),
452
	<cf/routes/ for routes exchanged with the routing table,
453
	<cf/filters/ for details on route filtering,
454
	<cf/interfaces/ for interface change events sent to the protocol,
455
	<cf/events/ for events internal to the protocol and
456
	<cf/packets/ for packets sent and received by the protocol. Default: off.
457

    
458
	<tag>mrtdump all|off|{ states, messages }</tag>
459
	Set protocol MRTdump flags. MRTdump is a standard binary
460
	format for logging information from routing protocols and
461
	daemons.  These flags control what kind of information is
462
	logged from the protocol to the MRTdump file (which must be
463
	specified by global <cf/mrtdump/ option, see the previous
464
	section). Although these flags are similar to flags of
465
	<cf/debug/ option, their meaning is different and
466
	protocol-specific. For BGP protocol, <cf/states/ logs BGP
467
	state changes and <cf/messages/ logs received BGP messages.
468
	Other protocols does not support MRTdump yet.
469

    
470
	<tag>router id <m/IPv4 address/</tag>
471
	This option can be used to override global router id for a
472
	given protocol. Default: uses global router id.
473

    
474
	<tag>import all | none | filter <m/name/ | filter { <m/filter commands/ } | where <m/filter expression/</tag> 
475
	Specify a filter to be used for filtering routes coming from
476
	the protocol to the routing table. <cf/all/ is shorthand for
477
	<cf/where true/ and <cf/none/ is shorthand for
478
	<cf/where false/. Default: <cf/all/.
479

    
480
	<tag>export <m/filter/</tag>
481
	This is similar to the <cf>import</cf> keyword, except that it
482
	works in the direction from the routing table to the protocol.
483
	Default: <cf/none/.
484

    
485
	<tag>import keep filtered <m/switch/</tag>
486
	Usually, if an import filter rejects a route, the route is
487
	forgotten. When this option is active, these routes are
488
	kept in the routing table, but they are hidden and not
489
	propagated to other protocols. But it is possible to show them
490
	using <cf/show route filtered/. Note that this option does not
491
	work for the pipe protocol. Default: off.
492

    
493
	<tag><label id="import-limit">import limit [<m/number/ | off ] [action warn | block | restart | disable]</tag>
494
	Specify an import route limit (a maximum number of routes
495
	imported from the protocol) and optionally the action to be
496
	taken when the limit is hit. Warn action just prints warning
497
	log message. Block action discards new routes coming from the
498
	protocol. Restart and disable actions shut the protocol down
499
	like appropriate commands. Disable is the default action if an
500
	action is not explicitly specified. Note that limits are reset
501
	during protocol reconfigure, reload or restart. Default: <cf/off/.
502

    
503
	<tag>receive limit [<m/number/ | off ] [action warn | block | restart | disable]</tag>
504
	Specify an receive route limit (a maximum number of routes
505
	received from the protocol and remembered). It works almost
506
	identically to <cf>import limit</cf> option, the only
507
	difference is that if <cf/import keep filtered/ option is
508
	active, filtered routes are counted towards the limit and
509
	blocked routes are forgotten, as the main purpose of the
510
	receive limit is to protect routing tables from
511
	overflow. Import limit, on the contrary, counts accepted
512
	routes only and routes blocked by the limit are handled like
513
	filtered routes. Default: <cf/off/.
514

    
515
	<tag>export limit [ <m/number/ | off ] [action warn | block | restart | disable]</tag>
516
	Specify an export route limit, works similarly to
517
	the <cf>import limit</cf> option, but for the routes exported
518
	to the protocol. This option is experimental, there are some
519
	problems in details of its behavior -- the number of exported
520
	routes can temporarily exceed the limit without triggering it
521
	during protocol reload, exported routes counter ignores route
522
	blocking and block action also blocks route updates of already
523
	accepted routes -- and these details will probably change in
524
	the future. Default: <cf/off/.
525

    
526
	<tag>description "<m/text/"</tag>
527
	This is an optional description of the protocol. It is
528
	displayed as a part of the output of 'show route all' command.
529

    
530
	<tag>table <m/name/</tag>
531
	Connect this protocol to a non-default routing table.
532
</descrip>
533

    
534
<p>There are several options that give sense only with certain protocols:
535

    
536
<descrip>
537
	<tag><label id="dsc-iface">interface [-] [ "<m/mask/" ] [ <m/prefix/ ] [, ...] [ { <m/option/ ; [...] } ]</tag>
538

    
539
	Specifies a set of interfaces on which the protocol is activated with
540
	given interface-specific options. A set of interfaces specified by one
541
	interface option is described using an interface pattern. The
542
	interface pattern consists of a sequence of clauses (separated by
543
	commas), each clause may contain a mask, a prefix, or both of them. An
544
	interface matches the clause if its name matches the mask (if
545
	specified) and its address matches the prefix (if specified). Mask is
546
	specified as shell-like pattern. For IPv6, the prefix part of a clause
547
	is generally ignored and interfaces are matched just by their name.
548

    
549
	An interface matches the pattern if it matches any of its
550
	clauses. If the clause begins with <cf/-/, matching interfaces are
551
	excluded. Patterns are parsed left-to-right, thus
552
	<cf/interface "eth0", -"eth*", "*";/ means eth0 and all
553
	non-ethernets.
554

    
555
	An interface option can be used more times with different
556
	interfaces-specific options, in that case for given interface
557
	the first matching interface option is used.
558
	
559
	This option is allowed in Direct, OSPF, RIP and RAdv protocols,
560
	but in OSPF protocol it is used in <cf/area/ subsection.
561

    
562
	Default: none.
563

    
564
	Examples:
565

    
566
	<cf>interface "*" { type broadcast; };</cf> - start the protocol on all interfaces with
567
	<cf>type broadcast</cf> option.
568

    
569
	<cf>interface "eth1", "eth4", "eth5" { type ptp; };</cf> - start the protocol
570
	on enumerated interfaces with <cf>type ptp</cf> option.
571
	
572
	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all
573
	interfaces that have address from 192.168.0.0/16, but not
574
	from 192.168.1.0/24.
575

    
576
	<cf>interface -192.168.1.0/24, 192.168.0.0/16;</cf> - start the protocol on all
577
	interfaces that have address from 192.168.0.0/16, but not
578
	from 192.168.1.0/24.
579

    
580
	<cf>interface "eth*" 192.168.1.0/24;</cf> - start the protocol on all
581
	ethernet interfaces that have address from 192.168.1.0/24.
582

    
583
	<tag><label id="dsc-prio">tx class|dscp <m/num/</tag>
584
        This option specifies the value of ToS/DS/Class field in IP
585
        headers of the outgoing protocol packets. This may affect how the
586
        protocol packets are processed by the network relative to the
587
        other network traffic. With <cf/class/ keyword, the value
588
        (0-255) is used for the whole ToS/Class octet (but two bits
589
        reserved for ECN are ignored). With <cf/dscp/ keyword, the
590
        value (0-63) is used just for the DS field in the
591
        octet. Default value is 0xc0 (DSCP 0x30 - CS6).
592

    
593
	<tag>tx priority <m/num/</tag>
594
        This option specifies the local packet priority. This may
595
        affect how the protocol packets are processed in the local TX
596
        queues. This option is Linux specific. Default value is 7
597
        (highest priority, privileged traffic).
598

    
599
	<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>
600
	Specifies a password that can be used by the protocol. Password option can
601
	be used more times to specify more passwords. If more passwords are
602
	specified, it is a protocol-dependent decision which one is really
603
	used. Specifying passwords does not mean that authentication is
604
	enabled, authentication can be enabled by separate, protocol-dependent
605
	<cf/authentication/ option.
606
	
607
	This option is allowed in OSPF and RIP protocols. BGP has also
608
	<cf/password/ option, but it is slightly different and described
609
	separately.
610

    
611
	Default: none.
612
</descrip>
613

    
614
<p>Password option can contain section with some (not necessary all) password sub-options:
615

    
616
<descrip>
617
	<tag>id <M>num</M></tag>
618
	 ID of the password, (0-255). If it's not used, BIRD will choose
619
	 ID based on an order of the password item in the interface. For
620
	 example, second password item in one interface will have default
621
	 ID 2. ID is used by some routing protocols to identify which
622
	 password was used to authenticate protocol packets.
623

    
624
	<tag>generate from "<m/time/"</tag>
625
	 The start time of the usage of the password for packet signing.
626
	 The format of <cf><m/time/</cf> is <tt>dd-mm-yyyy HH:MM:SS</tt>.
627

    
628
	<tag>generate to "<m/time/"</tag>
629
	 The last time of the usage of the password for packet signing.
630

    
631
	<tag>accept from "<m/time/"</tag>
632
	 The start time of the usage of the password for packet verification.
633

    
634
	<tag>accept to "<m/time/"</tag>
635
	 The last time of the usage of the password for packet verification.
636
</descrip>
637

    
638
<chapt>Remote control
639

    
640
<p>You can use the command-line client <file>birdc</file> to talk with
641
a running BIRD. Communication is done using a <file/bird.ctl/ UNIX
642
domain socket (unless changed with the <tt/-s/ option given to both
643
the server and the client). The commands can perform simple actions
644
such as enabling/disabling of protocols, telling BIRD to show various
645
information, telling it to show routing table filtered by filter, or
646
asking BIRD to reconfigure. Press <tt/?/ at any time to get online
647
help. Option <tt/-r/ can be used to enable a restricted mode of BIRD
648
client, which allows just read-only commands (<cf/show .../). Option
649
<tt/-v/ can be passed to the client, to make it dump numeric return
650
codes along with the messages. You do not necessarily need to use
651
<file/birdc/ to talk to BIRD, your own applications could do that, too
652
-- the format of communication between BIRD and <file/birdc/ is stable
653
(see the programmer's documentation).
654

    
655
<p>There is also lightweight variant of BIRD client called
656
<file/birdcl/, which does not support command line editing and history
657
and has minimal dependencies. This is useful for running BIRD in
658
resource constrained environments, where Readline library (required
659
for regular BIRD client) is not available.
660

    
661
<p>Many commands have the <m/name/ of the protocol instance as an argument.
662
This argument can be omitted if there exists only a single instance.
663

    
664
<p>Here is a brief list of supported functions:
665

    
666
<descrip>
667
	<tag>show status</tag>
668
	Show router status, that is BIRD version, uptime and time from last reconfiguration.
669

    
670
	<tag>show protocols [all]</tag>
671
	Show list of protocol instances along with tables they are connected to and protocol status, possibly giving verbose information, if <cf/all/ is specified.
672

    
673
	<tag>show ospf interface [<m/name/] ["<m/interface/"]</tag>
674
	Show detailed information about OSPF interfaces.
675

    
676
	<tag>show ospf neighbors [<m/name/] ["<m/interface/"]</tag>
677
	Show a list of OSPF neighbors and a state of adjacency to them.
678

    
679
	<tag>show ospf state [all] [<m/name/]</tag>
680
	Show detailed information about OSPF areas based on a content
681
	of the link-state database. It shows network topology, stub
682
	networks, aggregated networks and routers from other areas and
683
	external routes. The command shows information about reachable
684
	network nodes, use option <cf/all/ to show information about
685
	all network nodes in the link-state database.
686

    
687
	<tag>show ospf topology [all] [<m/name/]</tag>
688
	Show a topology of OSPF areas based on a content of the
689
	link-state database.  It is just a stripped-down version of
690
	'show ospf state'.
691

    
692
	<tag>show ospf lsadb [global | area <m/id/ | link] [type <m/num/] [lsid <m/id/] [self | router <m/id/] [<m/name/] </tag>
693
	Show contents of an OSPF LSA database. Options could be used to filter entries.
694

    
695
	<tag>show static [<m/name/]</tag>
696
	Show detailed information about static routes.
697

    
698
	<tag>show interfaces [summary]</tag>
699
	Show the list of interfaces. For each interface, print its type, state, MTU and addresses assigned. 
700

    
701
	<tag>show symbols [table|filter|function|protocol|template|roa|<m/symbol/]</tag>
702
	Show the list of symbols defined in the configuration (names of protocols, routing tables etc.).
703

    
704
	<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>
705
	Show contents of a routing table (by default of the main one or
706
        the table attached to a respective protocol),
707
	that is routes, their metrics and (in case the <cf/all/ switch is given)
708
	all their attributes.
709

    
710
	<p>You can specify a <m/prefix/ if you want to print routes for a
711
	specific network. If you use <cf>for <m/prefix or IP/</cf>, you'll get
712
	the entry which will be used for forwarding of packets to the given
713
	destination. By default, all routes for each network are printed with
714
	the selected one at the top, unless <cf/primary/ is given in which case
715
	only the selected route is shown.
716

    
717
	<p>You can also ask for printing only routes processed and accepted by
718
	a given filter (<cf>filter <m/name/</cf> or <cf>filter { <m/filter/ }
719
	</cf> or matching a given condition (<cf>where <m/condition/</cf>).
720
	The <cf/export/ and <cf/preexport/ switches ask for printing of entries
721
	that are exported to the specified protocol. With <cf/preexport/, the
722
	export filter of the protocol is skipped.
723

    
724
	<p>You can also select just routes added by a specific protocol.
725
	<cf>protocol <m/p/</cf>.
726

    
727
	<p>If BIRD is configured to keep filtered routes (see <cf/import keep filtered/
728
	option), you can show them instead of routes by using <cf/filtered/ switch.
729

    
730
	<p>The <cf/stats/ switch requests showing of route statistics (the
731
	number of networks, number of routes before and after filtering). If
732
	you use <cf/count/ instead, only the statistics will be printed.
733

    
734
	<tag>show roa [<m/prefix/ | in <m/prefix/ | for <m/prefix/] [as <m/num/] [table <m/t/>]</tag>
735
	Show contents of a ROA table (by default of the first one).
736
	You can specify a <m/prefix/ to print ROA entries for a
737
	specific network. If you use <cf>for <m/prefix/</cf>, you'll
738
	get all entries relevant for route validation of the network
739
	prefix; i.e., ROA entries whose prefixes cover the network
740
	prefix. Or you can use <cf>in <m/prefix/</cf> to get ROA entries
741
	covered by the network prefix. You could also use <cf/as/ option
742
	to show just entries for given AS.
743

    
744
	<tag>add roa <m/prefix/ max <m/num/] as <m/num/ [table <m/t/>]</tag>
745
	Add a new ROA entry to a ROA table. Such entry is called
746
	<it/dynamic/ compared to <it/static/ entries specified in the
747
	config file. These dynamic entries survive reconfiguration.
748

    
749
	<tag>delete roa <m/prefix/ max <m/num/] as <m/num/ [table <m/t/>]</tag>
750
	Delete the specified ROA entry from a ROA table. Only dynamic
751
	ROA entries (i.e., the ones added by <cf/add roa/ command) can
752
	be deleted.
753

    
754
	<tag>flush roa [table <m/t/>]</tag>
755
	Remove all dynamic ROA entries from a ROA table.
756

    
757
	<tag>configure [soft] ["<m/config file/"] [timeout [<m/num/]]</tag>
758
	Reload configuration from a given file. BIRD will smoothly
759
	switch itself to the new configuration, protocols are
760
	reconfigured if possible, restarted otherwise. Changes in
761
	filters usually lead to restart of affected protocols.
762

    
763
	If <cf/soft/ option is used, changes in filters does not cause
764
	BIRD to restart affected protocols, therefore already accepted
765
	routes (according to old filters) would be still propagated,
766
	but new routes would be processed according to the new
767
	filters.
768

    
769
	If <cf/timeout/ option is used, config timer is activated. The
770
	new configuration could be either confirmed using
771
	<cf/configure confirm/ command, or it will be reverted to the
772
	old one when the config timer expires. This is useful for cases
773
	when reconfiguration breaks current routing and a router becames
774
	inaccessible for an administrator. The config timeout expiration is
775
	equivalent to <cf/configure undo/ command. The timeout duration
776
	could be specified, default is 300 s.
777

    
778
	<tag>configure confirm</tag>
779
	Deactivate the config undo timer and therefore confirm the current
780
	configuration.
781

    
782
	<tag>configure undo</tag>
783
	Undo the last configuration change and smoothly switch back to
784
	the previous (stored) configuration. If the last configuration
785
	change was soft, the undo change is also soft. There is only
786
	one level of undo, but in some specific cases when several
787
	reconfiguration requests are given immediately in a row and
788
	the intermediate ones are skipped then the undo also skips them back.
789

    
790
	<tag>configure check ["<m/config file/"]</tag>
791
	Read and parse given config file, but do not use it. useful
792
	for checking syntactic and some semantic validity of an config
793
	file.
794

    
795
	<tag>enable|disable|restart <m/name/|"<m/pattern/"|all</tag>
796
	Enable, disable or restart a given protocol instance,
797
	instances matching the <cf><m/pattern/</cf> or
798
	<cf/all/ instances.
799

    
800
	<tag>reload [in|out] <m/name/|"<m/pattern/"|all</tag>
801
	
802
	Reload a given protocol instance, that means re-import routes
803
	from the protocol instance and re-export preferred routes to
804
	the instance. If <cf/in/ or <cf/out/ options are used, the
805
	command is restricted to one direction (re-import or
806
	re-export).
807

    
808
	This command is useful if appropriate filters have changed but
809
	the protocol instance was not restarted (or reloaded),
810
	therefore it still propagates the old set of routes. For example
811
	when <cf/configure soft/ command was used to change filters.
812

    
813
	Re-export always succeeds, but re-import is protocol-dependent
814
	and might fail (for example, if BGP neighbor does not support
815
	route-refresh extension). In that case, re-export is also
816
	skipped. Note that for the pipe protocol, both directions are
817
	always reloaded together (<cf/in/ or <cf/out/ options are
818
	ignored in that case).
819

    
820
	<tag/down/
821
	Shut BIRD down.
822

    
823
	<tag>debug <m/protocol/|<m/pattern/|all all|off|{ states | routes | filters | events | packets }</tag>
824
	Control protocol debugging.
825

    
826
	<tag>dump resources|sockets|interfaces|neighbors|attributes|routes|protocols</tag>
827
	Dump contents of internal data structures to the debugging output.
828

    
829
	<tag>echo all|off|{ <m/list of log classes/ } [ <m/buffer-size/ ]</tag>
830
	Control echoing of log messages to the command-line output.
831
	See <ref id="dsc-log" name="log option"> for a list of log classes.
832

    
833
	<tag>eval <m/expr/</tag>
834
	Evaluate given expression.
835

    
836
</descrip>
837

    
838
<chapt>Filters
839

    
840
<sect>Introduction
841

    
842
<p>BIRD contains a simple programming language. (No, it can't yet read mail :-). There are
843
two objects in this language: filters and functions. Filters are interpreted by BIRD core when a route is
844
being passed between protocols and routing tables. The filter language contains control structures such
845
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>. 
846

    
847
<p>Filter gets the route, looks at its attributes and
848
modifies some of them if it wishes. At the end, it decides whether to
849
pass the changed route through (using <cf/accept/) or whether to <cf/reject/ it. A simple filter looks
850
like this:
851

    
852
<code>
853
filter not_too_far
854
int var;
855
{
856
	if defined( rip_metric ) then
857
		var = rip_metric;
858
	else {
859
		var = 1;
860
		rip_metric = 1;
861
	}
862
	if rip_metric &gt; 10 then
863
		reject "RIP metric is too big";
864
	else
865
		accept "ok";
866
}
867
</code>
868

    
869
<p>As you can see, a filter has a header, a list of local variables, and a body. The header consists of
870
the <cf/filter/ keyword followed by a (unique) name of filter. The list of local variables consists of
871
<cf><M>type name</M>;</cf> pairs where each pair defines one local variable. The body consists of
872
<cf> { <M>statements</M> }</cf>. Each <m/statement/ is terminated by a <cf/;/. You can group
873
several statements to a single compound statement by using braces (<cf>{ <M>statements</M> }</cf>) which is useful if
874
you want to make a bigger block of code conditional.
875

    
876
<p>BIRD supports functions, so that you don't have to repeat the same blocks of code over and
877
over. Functions can have zero or more parameters and they can have local variables. Recursion is not allowed. Function definitions
878
look like this:
879

    
880
<code>
881
function name ()
882
int local_variable;
883
{
884
	local_variable = 5;
885
}
886

    
887
function with_parameters (int parameter)
888
{
889
	print parameter;
890
}
891
</code>
892

    
893
<p>Unlike in C, variables are declared after the <cf/function/ line, but before the first <cf/{/. You can't declare
894
variables in nested blocks. Functions are called like in C: <cf>name();
895
with_parameters(5);</cf>. Function may return values using the <cf>return <m/[expr]/</cf>
896
command. Returning a value exits from current function (this is similar to C).
897

    
898
<p>Filters are declared in a way similar to functions except they can't have explicit
899
parameters. They get a route table entry as an implicit parameter, it is also passed automatically 
900
to any functions called. The filter must terminate with either
901
<cf/accept/ or <cf/reject/ statement. If there's a runtime error in filter, the route
902
is rejected. 
903

    
904
<p>A nice trick to debug filters is to use <cf>show route filter
905
<m/name/</cf> from the command line client. An example session might look
906
like:
907

    
908
<code>
909
pavel@bug:~/bird$ ./birdc -s bird.ctl
910
BIRD 0.0.0 ready.
911
bird> show route
912
10.0.0.0/8         dev eth0 [direct1 23:21] (240)
913
195.113.30.2/32    dev tunl1 [direct1 23:21] (240)
914
127.0.0.0/8        dev lo [direct1 23:21] (240)
915
bird> show route ?
916
show route [<prefix>] [table <t>] [filter <f>] [all] [primary]...
917
bird> show route filter { if 127.0.0.5 &tilde; net then accept; }
918
127.0.0.0/8        dev lo [direct1 23:21] (240)
919
bird>
920
</code>
921

    
922
<sect>Data types
923

    
924
<p>Each variable and each value has certain type. Booleans, integers and enums are
925
incompatible with each other (that is to prevent you from shooting in the foot).
926

    
927
<descrip>
928
	<tag/bool/ This is a boolean type, it can have only two values,
929
	  <cf/true/ and <cf/false/. Boolean is the only type you can use in
930
	  <cf/if/ statements.
931

    
932
	<tag/int/ This is a general integer type. It is an unsigned 32bit type;
933
	  i.e., you can expect it to store values from 0 to 4294967295.
934
	  Overflows are not checked. You can use <cf/0x1234/ syntax to write
935
	  hexadecimal values.
936

    
937
	<tag/pair/ This is a pair of two short integers. Each component can have
938
	  values from 0 to 65535. Literals of this type are written as
939
	  <cf/(1234,5678)/. The same syntax can also be used to construct a pair
940
	  from two arbitrary integer expressions (for example <cf/(1+2,a)/).
941

    
942
	<tag/quad/ This is a dotted quad of numbers used to represent router IDs
943
	  (and others).  Each component can have a value from 0 to 255. Literals
944
	  of this type are written like IPv4 addresses.
945

    
946
	<tag/string/ This is a string of characters. There are no ways to modify
947
	  strings in filters. You can pass them between functions, assign them
948
	  to variables of type <cf/string/, print such variables, use standard
949
	  string comparison operations (e.g. <cf/=, !=, &lt;, &gt;, &lt;=,
950
	  &gt;=/), but you can't concatenate two strings. String literals are
951
	  written as <cf/"This is a string constant"/. Additionaly matching
952
	  <cf/&tilde;/ operator could be used to match a string value against a
953
	  shell pattern (represented also as a string).
954

    
955
	<tag/ip/ This type can hold a single IP address. Depending on the
956
	  compile-time configuration of BIRD you are using, it is either an IPv4
957
	  or IPv6 address. IP addresses are written in the standard notation
958
	  (<cf/10.20.30.40/ or <cf/fec0:3:4::1/). You can apply special
959
	  operator <cf>.mask(<M>num</M>)</cf> on values of type ip. It masks out
960
	  all but first <cf><M>num</M></cf> bits from the IP address. So
961
	  <cf/1.2.3.4.mask(8) = 1.0.0.0/ is true.
962

    
963
	<tag/prefix/ This type can hold a network prefix consisting of IP
964
	  address and prefix length. Prefix literals are written
965
	  as <cf><M>ipaddress</M>/<M>pxlen</M></cf>, or
966
	  <cf><m>ipaddress</m>/<m>netmask</m></cf>. There are two special
967
	  operators on prefixes: <cf/.ip/ which extracts the IP address from the
968
	  pair, and <cf/.len/, which separates prefix length from the
969
	  pair. So <cf>1.2.0.0/16.pxlen = 16</cf> is true.
970

    
971
	<tag/ec/ This is a specialized type used to represent BGP extended
972
	  community values. It is essentially a 64bit value, literals of this
973
	  type are usually written as <cf>(<m/kind/, <m/key/, <m/value/)</cf>,
974
	  where <cf/kind/ is a kind of extended community (e.g. <cf/rt/ /
975
	  <cf/ro/ for a route target / route origin communities), the format and
976
	  possible values of <cf/key/ and <cf/value/ are usually integers, but
977
	  it depends on the used kind. Similarly to pairs, ECs can be
978
	  constructed using expressions for <cf/key/ and <cf/value/ parts,
979
	  (e.g. <cf/(ro, myas, 3*10)/, where <cf/myas/ is an integer variable).
980
 
981
	<tag/int|pair|quad|ip|prefix|ec|enum set/ Filters recognize four types
982
	  of sets. Sets are similar to strings: you can pass them around but you
983
	  can't modify them. Literals of type <cf>int set</cf> look like <cf> [
984
	  1, 2, 5..7 ]</cf>. As you can see, both simple values and ranges are
985
	  permitted in sets.
986

    
987
	  For pair sets, expressions like <cf/(123,*)/ can be used to denote ranges (in
988
	  that case <cf/(123,0)..(123,65535)/). You can also use <cf/(123,5..100)/ for range
989
	  <cf/(123,5)..(123,100)/. You can also use <cf/*/ and <cf/a..b/ expressions
990
	  in the first part of a pair, note that such expressions are translated to a set
991
	  of intervals, which may be memory intensive. E.g. <cf/(*,4..20)/ is translated to
992
	  <cf/(0,4..20), (1,4..20), (2,4..20), ... (65535, 4..20)/.
993

    
994
	  EC sets use similar expressions like pair sets, e.g. <cf/(rt, 123, 10..20)/ 
995
	  or <cf/(ro, 123, *)/. Expressions requiring the translation (like  <cf/(rt, *, 3)/)
996
	  are not allowed (as they usually have 4B range for ASNs).
997

    
998
	  You can also use expressions for int, pair and EC set values. However it must
999
	  be possible to evaluate these expressions before daemon boots. So you can use
1000
	  only constants inside them. E.g.
1001
	<code>
1002
	 define one=1;
1003
	 define myas=64500;
1004
	 int set odds;
1005
	 pair set ps;
1006
	 ec set es;
1007

    
1008
	 odds = [ one, 2+1, 6-one, 2*2*2-1, 9, 11 ];
1009
	 ps = [ (1,one+one), (3,4)..(4,8), (5,*), (6,3..6), (7..9,*) ];
1010
	 es = [ (rt, myas, 3*10), (rt, myas+one, 0..16*16*16-1), (ro, myas+2, *) ];
1011
	</code>
1012

    
1013
	  Sets of prefixes are special: their literals does not allow ranges, but allows
1014
	  prefix patterns that are written as <cf><M>ipaddress</M>/<M>pxlen</M>{<M>low</M>,<M>high</M>}</cf>.
1015
	  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> if 
1016
	  the first <cf>min(len1, len2)</cf> bits of <cf/ip1/ and <cf/ip2/ are identical and <cf>len1 &lt;= ip1 &lt;= len2</cf>.
1017
	  A valid prefix pattern has to satisfy <cf>low &lt;= high</cf>, but <cf/pxlen/ is not constrained by <cf/low/
1018
	  or <cf/high/. Obviously, a prefix matches a prefix set literal if it matches any prefix pattern in the
1019
	  prefix set literal.
1020

    
1021
	  There are also two shorthands for prefix patterns: <cf><m>address</m>/<m/len/+</cf> is a shorthand for
1022
	  <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), 
1023
	  that means network prefix <cf><m>address</m>/<m/len/</cf> and all its subnets. <cf><m>address</m>/<m/len/-</cf>
1024
	  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>
1025
	  and all its supernets (network prefixes that contain it).
1026

    
1027
	  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
1028
	  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
1029
	  <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
1030
	  IP address) whose prefix length is 20 to 24, <cf>[ 1.2.3.4/32- ]</cf> matches any prefix that contains IP address
1031
	  <cf>1.2.3.4</cf>. <cf>1.2.0.0/16 &tilde; [ 1.0.0.0/8{15,17} ]</cf> is true,
1032
	  but <cf>1.0.0.0/16 &tilde; [ 1.0.0.0/8- ]</cf> is false.
1033

    
1034
	  Cisco-style patterns like <cf>10.0.0.0/8 ge 16 le 24</cf> can be expressed
1035
	  in BIRD as <cf>10.0.0.0/8{16,24}</cf>, <cf>192.168.0.0/16 le 24</cf> as 
1036
	  <cf>192.168.0.0/16{16,24}</cf> and <cf>192.168.0.0/16 ge 24</cf> as
1037
	  <cf>192.168.0.0/16{24,32}</cf>.
1038

    
1039
	<tag/enum/
1040
	  Enumeration types are fixed sets of possibilities. You can't define your own
1041
	  variables of such type, but some route attributes are of enumeration
1042
	  type. Enumeration types are incompatible with each other.
1043

    
1044
	<tag/bgppath/
1045
	  BGP path is a list of autonomous system numbers. You can't write literals of this type.
1046
	  There are several special operators on bgppaths:
1047

    
1048
	  <cf><m/P/.first</cf> returns the first ASN (the neighbor ASN) in path <m/P/.
1049

    
1050
          <cf><m/P/.last</cf> returns the last ASN (the source ASN) in path <m/P/.
1051

    
1052
	  Both <cf/first/ and <cf/last/ return zero if there is no appropriate ASN,
1053
          for example if the path contains an AS set element as the first (or the last) part.
1054

    
1055
          <cf><m/P/.len</cf> returns the length of path <m/P/.
1056

    
1057
          <cf>prepend(<m/P/,<m/A/)</cf> prepends ASN <m/A/ to path
1058
          <m/P/ and returns the result.
1059

    
1060
          <cf>delete(<m/P/,<m/A/)</cf> deletes all instances of ASN
1061
	  <m/A/ from from path <m/P/ and returns the result.
1062
	  <m/A/ may also be an integer set, in that case the
1063
	  operator deletes all ASNs from path <m/P/ that are also
1064
	  members of set <m/A/.
1065

    
1066
          <cf>filter(<m/P/,<m/A/)</cf> deletes all ASNs from path
1067
	  <m/P/ that are not members of integer set <m/A/.
1068
	  I.e., <cf/filter/ do the same as <cf/delete/ with inverted
1069
	  set <m/A/.
1070

    
1071
          Statement <cf><m/P/ = prepend(<m/P/, <m/A/);</cf> can be shortened to
1072
          <cf><m/P/.prepend(<m/A/);</cf> if <m/P/ is appropriate route attribute
1073
          (for example <cf/bgp_path/). Similarly for <cf/delete/ and <cf/filter/.
1074

    
1075
	<tag/bgpmask/
1076
	  BGP masks are patterns used for BGP path matching
1077
	  (using <cf>path &tilde; [= 2 3 5 * =]</cf> syntax). The masks
1078
	  resemble wildcard patterns as used by UNIX shells. Autonomous
1079
	  system numbers match themselves, <cf/*/ matches any (even empty)
1080
	  sequence of arbitrary AS numbers and <cf/?/ matches one arbitrary AS number.
1081
	  For example, if <cf>bgp_path</cf> is 4 3 2 1, then:
1082
	  <tt>bgp_path &tilde; [= * 4 3 * =]</tt> is true, but 
1083
	  <tt>bgp_path &tilde; [= * 4 5 * =]</tt> is false.
1084
	  BGP mask expressions can also contain integer expressions enclosed in parenthesis
1085
	  and integer variables, for example <tt>[= * 4 (1+2) a =]</tt>.
1086
	  There is also old syntax that uses / .. / instead of [= .. =] and ? instead of *.
1087

    
1088
	<tag/clist/
1089
	  Clist is similar to a set, except that unlike other sets, it
1090
	  can be modified. The type is used for community list (a set
1091
	  of pairs) and for cluster list (a set of quads). There exist
1092
	  no literals of this type. There are three special operators on
1093
	  clists:
1094

    
1095
	  <cf><m/C/.len</cf> returns the length of clist <m/C/.
1096

    
1097
          <cf>add(<m/C/,<m/P/)</cf> adds pair (or quad) <m/P/ to clist
1098
	  <m/C/ and returns the result.  If item <m/P/ is already in
1099
	  clist <m/C/, it does nothing. <m/P/ may also be a clist,
1100
	  in that case all its members are added; i.e., it works as clist union.
1101

    
1102
          <cf>delete(<m/C/,<m/P/)</cf> deletes pair (or quad)
1103
	  <m/P/ from clist <m/C/ and returns the result.  If clist
1104
	  <m/C/ does not contain item <m/P/, it does nothing.
1105
	  <m/P/ may also be a pair (or quad) set, in that case the
1106
	  operator deletes all items from clist <m/C/ that are also
1107
	  members of set <m/P/. Moreover, <m/P/ may also be a clist,
1108
	  which works analogously; i.e., it works as clist difference.
1109

    
1110
          <cf>filter(<m/C/,<m/P/)</cf> deletes all items from clist
1111
	  <m/C/ that are not members of pair (or quad) set <m/P/.
1112
	  I.e., <cf/filter/ do the same as <cf/delete/ with inverted
1113
	  set <m/P/. <m/P/ may also be a clist, which works analogously;
1114
	  i.e., it works as clist intersection.
1115

    
1116
          Statement <cf><m/C/ = add(<m/C/, <m/P/);</cf> can be shortened to
1117
          <cf><m/C/.add(<m/P/);</cf> if <m/C/ is appropriate route
1118
          attribute (for example <cf/bgp_community/). Similarly for
1119
          <cf/delete/ and <cf/filter/.
1120

    
1121
	<tag/eclist/
1122
	  Eclist is a data type used for BGP extended community lists.
1123
	  Eclists are very similar to clists, but they are sets of ECs
1124
	  instead of pairs. The same operations (like <cf/add/,
1125
	  <cf/delete/, or <cf/&tilde;/ membership operator) can be
1126
	  used to modify or test eclists, with ECs instead of pairs as
1127
	  arguments.
1128
</descrip>
1129

    
1130
<sect>Operators
1131

    
1132
<p>The filter language supports common integer operators <cf>(+,-,*,/)</cf>, parentheses <cf/(a*(b+c))/, comparison
1133
<cf/(a=b, a!=b, a&lt;b, a&gt;=b)/. Logical operations include unary not (<cf/!/), and (<cf/&amp;&amp;/) and or (<cf/&verbar;&verbar;/). 
1134
Special operators include <cf/&tilde;/ for "is element of a set" operation - it can be
1135
used on element and set of elements of the same type (returning true if element is contained in the given set), or
1136
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
1137
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 number and bgppath (returning true if the number is in the path) or on bgppath and int (number) set (returning true if any ASN from the path is in the set) or on pair/quad and clist (returning true if the pair/quad is element of the clist) or on clist and pair/quad set (returning true if there is an element of the clist that is also a member of the pair/quad set).
1138

    
1139
<p>There is one operator related to ROA infrastructure -
1140
<cf/roa_check()/. It examines a ROA table and does RFC 6483 route
1141
origin validation for a given network prefix. The basic usage
1142
is <cf>roa_check(<m/table/)</cf>, which checks current route (which
1143
should be from BGP to have AS_PATH argument) in the specified ROA
1144
table and returns ROA_UNKNOWN if there is no relevant ROA, ROA_VALID
1145
if there is a matching ROA, or ROA_INVALID if there are some relevant
1146
ROAs but none of them match. There is also an extended variant
1147
<cf>roa_check(<m/table/, <m/prefix/, <m/asn/)</cf>, which allows to
1148
specify a prefix and an ASN as arguments.
1149

    
1150

    
1151
<sect>Control structures
1152

    
1153
<p>Filters support two control structures: conditions and case switches. 
1154

    
1155
<p>Syntax of a condition is: <cf>if
1156
<M>boolean expression</M> then <M>command1</M>; else <M>command2</M>;</cf> and you can use <cf>{
1157
<M>command_1</M>; <M>command_2</M>; <M>...</M> }</cf> instead of either command. The <cf>else</cf>
1158
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.
1159

    
1160
<p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else: |
1161
<m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after
1162
<cf>case</cf> can be of any type which can be on the left side of the &tilde; operator and anything that could
1163
be a member of a set is allowed before <cf/:/. Multiple commands are allowed without <cf/{}/ grouping.
1164
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.
1165

    
1166
<p>Here is example that uses <cf/if/ and <cf/case/ structures:
1167

    
1168
<code>
1169
case arg1 {
1170
	2: print "two"; print "I can do more commands without {}";
1171
	3 .. 5: print "three to five";
1172
	else: print "something else";
1173
}
1174

    
1175
if 1234 = i then printn "."; else { 
1176
  print "not 1234"; 
1177
  print "You need {} around multiple commands"; 
1178
}
1179
</code>
1180

    
1181
<sect>Route attributes
1182

    
1183
<p>A filter is implicitly passed a route, and it can access its
1184
attributes just like it accesses variables. Attempts to access undefined
1185
attribute result in a runtime error; you can check if an attribute is
1186
defined by using the <cf>defined( <m>attribute</m> )</cf> operator.
1187
One notable exception to this rule are attributes of clist type, where
1188
undefined value is regarded as empty clist for most purposes.
1189

    
1190
<descrip>
1191
	<tag><m/prefix/ net</tag>
1192
	Network the route is talking about. Read-only. (See the chapter about routing tables.)
1193

    
1194
	<tag><m/enum/ scope</tag>
1195
	The scope of the route. Possible values: <cf/SCOPE_HOST/ for
1196
	routes local to this host, <cf/SCOPE_LINK/ for those specific
1197
	for a physical link, <cf/SCOPE_SITE/ and
1198
	<cf/SCOPE_ORGANIZATION/ for private routes and
1199
	<cf/SCOPE_UNIVERSE/ for globally visible routes. This
1200
	attribute is not interpreted by BIRD and can be used to mark
1201
	routes in filters. The default value for new routes is
1202
	<cf/SCOPE_UNIVERSE/.
1203

    
1204
	<tag><m/int/ preference</tag>
1205
	Preference of the route. Valid values are 0-65535. (See the chapter about routing tables.)
1206

    
1207
	<tag><m/ip/ from</tag>
1208
	The router which the route has originated from.
1209
	
1210
	<tag><m/ip/ gw</tag>
1211
	Next hop packets routed using this route should be forwarded to.
1212

    
1213
	<tag><m/string/ proto</tag>
1214
	The name of the protocol which the route has been imported from. Read-only.
1215

    
1216
	<tag><m/enum/ source</tag>
1217
	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_EXT1/, <cf/RTS_OSPF_EXT2/, <cf/RTS_BGP/, <cf/RTS_PIPE/.
1218

    
1219
	<tag><m/enum/ cast</tag>
1220
	Route type (Currently <cf/RTC_UNICAST/ for normal routes,
1221
	<cf/RTC_BROADCAST/, <cf/RTC_MULTICAST/, <cf/RTC_ANYCAST/ will
1222
	be used in the future for broadcast, multicast and anycast
1223
	routes). Read-only.
1224

    
1225
	<tag><m/enum/ dest</tag>
1226
	Type of destination the packets should be sent to
1227
	(<cf/RTD_ROUTER/ for forwarding to a neighboring router,
1228
	<cf/RTD_DEVICE/ for routing to a directly-connected network,
1229
	<cf/RTD_MULTIPATH/ for multipath destinations,
1230
	<cf/RTD_BLACKHOLE/ for packets to be silently discarded,
1231
	<cf/RTD_UNREACHABLE/, <cf/RTD_PROHIBIT/ for packets that
1232
	should be returned with ICMP host unreachable / ICMP
1233
	administratively prohibited messages). Can be changed, but
1234
	only to <cf/RTD_BLACKHOLE/, <cf/RTD_UNREACHABLE/ or
1235
	<cf/RTD_PROHIBIT/.
1236

    
1237
	<tag><m/string/ ifname</tag>
1238
	Name of the outgoing interface. Sink routes (like blackhole,
1239
	unreachable or prohibit) and multipath routes have no interface
1240
	associated with them, so <cf/ifname/ returns an empty string for
1241
	such routes. Read-only.
1242

    
1243
	<tag><m/int/ ifindex</tag>
1244
	Index of the outgoing interface. System wide index of the
1245
	interface. May be used for interface matching, however
1246
	indexes might change on interface creation/removal. Zero is
1247
	returned for routes with undefined outgoing
1248
	interfaces. Read-only.
1249

    
1250
	<tag><m/int/ igp_metric</tag>
1251
	The optional attribute that can be used to specify a distance
1252
	to the network for routes that do not have a native protocol
1253
	metric attribute (like <cf/ospf_metric1/ for OSPF routes). It
1254
	is used mainly by BGP to compare internal distances to boundary
1255
	routers (see below). It is also used when the route is exported
1256
	to OSPF as a default value for OSPF type 1 metric.
1257
</descrip>
1258

    
1259
<p>There also exist some protocol-specific attributes which are described in the corresponding protocol sections.
1260

    
1261
<sect>Other statements
1262

    
1263
<p>The following statements are available:
1264

    
1265
<descrip>
1266
	<tag><m/variable/ = <m/expr/</tag> Set variable to a given value.
1267

    
1268
	<tag>accept|reject [ <m/expr/ ]</tag> Accept or reject the route, possibly printing <cf><m>expr</m></cf>.
1269

    
1270
	<tag>return <m/expr/</tag> Return <cf><m>expr</m></cf> from the current function, the function ends at this point.
1271

    
1272
	<tag>print|printn <m/expr/ [<m/, expr.../]</tag>
1273
	Prints given expressions; useful mainly while debugging
1274
	filters. The <cf/printn/ variant does not terminate the line.
1275

    
1276
	<tag>quitbird</tag>
1277
	Terminates BIRD. Useful when debugging the filter interpreter.
1278
</descrip>
1279

    
1280
<chapt>Protocols
1281

    
1282
<sect><label id="sect-bfd">BFD
1283

    
1284
<sect1>Introduction
1285

    
1286
<p>Bidirectional Forwarding Detection (BFD) is not a routing protocol itself, it
1287
is an independent tool providing liveness and failure detection. Routing
1288
protocols like OSPF and BGP use integrated periodic "hello" messages to monitor
1289
liveness of neighbors, but detection times of these mechanisms are high (e.g. 40
1290
seconds by default in OSPF, could be set down to several seconds). BFD offers
1291
universal, fast and low-overhead mechanism for failure detection, which could be
1292
attached to any routing protocol in an advisory role.
1293

    
1294
<p>BFD consists of mostly independent BFD sessions. Each session monitors an
1295
unicast bidirectional path between two BFD-enabled routers. This is done by
1296
periodically sending control packets in both directions. BFD does not handle
1297
neighbor discovery, BFD sessions are created on demand by request of other
1298
protocols (like OSPF or BGP), which supply appropriate information like IP
1299
addresses and associated interfaces. When a session changes its state, these
1300
protocols are notified and act accordingly (e.g. break an OSPF adjacency when
1301
the BFD session went down).
1302

    
1303
<p>BIRD implements basic BFD behavior as defined in
1304
RFC 5880<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5880.txt">
1305
(some advanced features like the echo mode or authentication are not implemented),
1306
IP transport for BFD as defined in
1307
RFC 5881<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5881.txt"> and
1308
RFC 5883<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5883.txt">
1309
and interaction with client protocols as defined in
1310
RFC 5882<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5882.txt">.
1311

    
1312
<p>Note that BFD implementation in BIRD is currently a new feature in
1313
development, expect some rough edges and possible UI and configuration changes
1314
in the future. Also note that we currently support at most one protocol instance.
1315

    
1316
<sect1>Configuration
1317

    
1318
<p>BFD configuration consists mainly of multiple definitions of interfaces.
1319
Most BFD config options are session specific. When a new session is requested
1320
and dynamically created, it is configured from one of these definitions. For
1321
sessions to directly connected neighbors, <cf/interface/ definitions are chosen
1322
based on the interface associated with the session, while <cf/multihop/
1323
definition is used for multihop sessions. If no definition is relevant, the
1324
session is just created with the default configuration. Therefore, an empty BFD
1325
configuration is often sufficient.
1326

    
1327
<p>Note that to use BFD for other protocols like OSPF or BGP, these protocols
1328
also have to be configured to request BFD sessions, usually by <cf/bfd/ option.
1329

    
1330
<p>Some of BFD session options require <m/time/ value, which has to be specified
1331
with the appropriate unit: <m/num/ <cf/s/|<cf/ms/|<cf/us/. Although microseconds
1332
are allowed as units, practical minimum values are usually in order of tens of
1333
milliseconds.
1334

    
1335
<code>
1336
protocol bfd [&lt;name&gt;] {
1337
	interface &lt;interface pattern&gt; {
1338
		interval &lt;time&gt;;
1339
		min rx interval &lt;time&gt;;
1340
		min tx interval &lt;time&gt;;
1341
		idle tx interval &lt;time&gt;;
1342
		multiplier &lt;num&gt;;
1343
		passive &lt;switch&gt;;
1344
	};
1345
	multihop {
1346
		interval &lt;time&gt;;
1347
		min rx interval &lt;time&gt;;
1348
		min tx interval &lt;time&gt;;
1349
		idle tx interval &lt;time&gt;;
1350
		multiplier &lt;num&gt;;
1351
		passive &lt;switch&gt;;
1352
	};
1353
	neighbor &lt;ip&gt; [dev "&lt;interface&gt;"] [local &lt;ip&gt;] [multihop &lt;switch&gt;];
1354
}
1355
</code>
1356

    
1357
<descrip>
1358
	<tag>interface <m/pattern [, ...]/  { <m/options/ }</tag>
1359
	Interface definitions allow to specify options for sessions associated
1360
	with such interfaces and also may contain interface specific options.
1361
	See <ref id="dsc-iface" name="interface"> common option for a detailed
1362
	description of interface patterns. Note that contrary to the behavior of
1363
	<cf/interface/ definitions of other protocols, BFD protocol would accept
1364
	sessions (in default configuration) even on interfaces not covered by
1365
	such definitions.
1366

    
1367
	<tag>multihop { <m/options/ }</tag>
1368
	Multihop definitions allow to specify options for multihop BFD sessions,
1369
	in the same manner as <cf/interface/ definitions are used for directly
1370
	connected sessions. Currently only one such definition (for all multihop
1371
	sessions) could be used.
1372

    
1373
	<tag>neighbor <m/ip/ [dev "<m/interface/"] [local <m/ip/] [multihop <m/switch/]</tag>
1374
	BFD sessions are usually created on demand as requested by other
1375
	protocols (like OSPF or BGP). This option allows to explicitly add
1376
	a BFD session to the specified neighbor regardless of such requests.
1377
	
1378
	The session is identified by the IP address of the neighbor, with
1379
	optional specification of used interface and local IP.  By default
1380
	the neighbor must be directly connected, unless the the session is
1381
	configured as multihop. Note that local IP must be specified for
1382
	multihop sessions.
1383
</descrip>
1384

    
1385
<p>Session specific options (part of <cf/interface/ and <cf/multihop/ definitions):
1386

    
1387
<descrip>
1388
	<tag>interval <m/time/</tag>
1389
	BFD ensures availability of the forwarding path associated with the
1390
	session by periodically sending BFD control packets in both
1391
	directions. The rate of such packets is controlled by two options,
1392
	<cf/min rx interval/ and <cf/min tx interval/ (see below). This option
1393
	is just a shorthand to set both of these options together.
1394

    
1395
	<tag>min rx interval <m/time/</tag>
1396
	This option specifies the minimum RX interval, which is announced to the
1397
	neighbor and used there to limit the neighbor's rate of generated BFD
1398
	control packets. Default: 10 ms.
1399

    
1400
	<tag>min tx interval <m/time/</tag>
1401
	This option specifies the desired TX interval, which controls the rate
1402
	of generated BFD control packets (together with <cf/min rx interval/
1403
	announced by the neighbor). Note that this value is used only if the BFD
1404
	session is up, otherwise the value of <cf/idle tx interval/ is used
1405
	instead. Default: 100 ms.
1406

    
1407
	<tag>idle tx interval <m/time/</tag>
1408
	In order to limit unnecessary traffic in cases where a neighbor is not
1409
	available or not running BFD, the rate of generated BFD control packets
1410
	is lower when the BFD session is not up. This option specifies the
1411
	desired TX interval in such cases instead of <cf/min tx interval/.
1412
	Default: 1 s.
1413

    
1414
	<tag>multiplier <m/num/</tag>
1415
	Failure detection time for BFD sessions is based on established rate of
1416
	BFD control packets (<cf>min rx/tx interval</cf>) multiplied by this
1417
	multiplier, which is essentially (ignoring jitter) a number of missed
1418
	packets after which the session is declared down. Note that rates and
1419
	multipliers could be different in each direction of a BFD session.
1420
	Default: 5.
1421

    
1422
	<tag>passive <m/switch/</tag>
1423
	Generally, both BFD session endpoinds try to establish the session by
1424
	sending control packets to the other side. This option allows to enable
1425
	passive mode, which means that the router does not send BFD packets
1426
	until it has received one from the other side. Default: disabled.
1427
</descrip>
1428

    
1429
<sect1>Example
1430

    
1431
<p><code>
1432
protocol bfd {
1433
	interface "eth*" {
1434
		min rx interval 20 ms;
1435
		min tx interval 50 ms;
1436
		idle tx interval 300 ms;
1437
	};
1438
	interface "gre*" {
1439
		interval 200 ms;
1440
		multiplier 10;
1441
		passive;
1442
	};
1443
	multihop {
1444
		interval 200 ms;
1445
		multiplier 10;
1446
	};
1447

    
1448
	neighbor 192.168.1.10;
1449
	neighbor 192.168.2.2 dev "eth2";
1450
	neighbor 192.168.10.1 local 192.168.1.1 multihop;
1451
}
1452
</code>
1453

    
1454
<sect>BGP
1455

    
1456
<p>The Border Gateway Protocol is the routing protocol used for backbone
1457
level routing in the today's Internet. Contrary to the other protocols, its convergence
1458
doesn't rely on all routers following the same rules for route selection,
1459
making it possible to implement any routing policy at any router in the
1460
network, the only restriction being that if a router advertises a route,
1461
it must accept and forward packets according to it.
1462

    
1463
<p>BGP works in terms of autonomous systems (often abbreviated as
1464
AS). Each AS is a part of the network with common management and
1465
common routing policy. It is identified by a unique 16-bit number
1466
(ASN).  Routers within each AS usually exchange AS-internal routing
1467
information with each other using an interior gateway protocol (IGP,
1468
such as OSPF or RIP). Boundary routers at the border of the AS
1469
communicate global (inter-AS) network reachability information with
1470
their neighbors in the neighboring AS'es via exterior BGP (eBGP) and
1471
redistribute received information to other routers in the AS via
1472
interior BGP (iBGP).
1473

    
1474
<p>Each BGP router sends to its neighbors updates of the parts of its
1475
routing table it wishes to export along with complete path information
1476
(a list of AS'es the packet will travel through if it uses the particular
1477
route) in order to avoid routing loops.
1478

    
1479
<p>BIRD supports all requirements of the BGP4 standard as defined in
1480
RFC 4271<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4271.txt">
1481
It also supports the community attributes
1482
(RFC 1997<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1997.txt">),
1483
capability negotiation
1484
(RFC 3392<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3392.txt">),
1485
MD5 password authentication
1486
(RFC 2385<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2385.txt">),
1487
extended communities
1488
(RFC 4360<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4360.txt">),
1489
route reflectors 
1490
(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
1491
multiprotocol extensions
1492
(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
1493
4B AS numbers 
1494
(RFC 4893<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4893.txt">),
1495
and 4B AS numbers in extended communities
1496
(RFC 5668<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc5668.txt">).
1497

    
1498

    
1499
For IPv6, it uses the standard multiprotocol extensions defined in
1500
RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
1501
including changes described in the
1502
latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
1503
and applied to IPv6 according to
1504
RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
1505

    
1506
<sect1>Route selection rules
1507

    
1508
<p>BGP doesn't have any simple metric, so the rules for selection of an optimal
1509
route among multiple BGP routes with the same preference are a bit more complex
1510
and they are implemented according to the following algorithm. It starts the first
1511
rule, if there are more "best" routes, then it uses the second rule to choose
1512
among them and so on.
1513

    
1514
<itemize>
1515
	<item>Prefer route with the highest Local Preference attribute.
1516
	<item>Prefer route with the shortest AS path.
1517
	<item>Prefer IGP origin over EGP and EGP origin over incomplete.
1518
	<item>Prefer the lowest value of the Multiple Exit Discriminator.
1519
	<item>Prefer routes received via eBGP over ones received via iBGP.
1520
	<item>Prefer routes with lower internal distance to a boundary router.
1521
	<item>Prefer the route with the lowest value of router ID of the
1522
	advertising router.
1523
</itemize>
1524

    
1525
<sect1>IGP routing table
1526

    
1527
<p>BGP is mainly concerned with global network reachability and with
1528
routes to other autonomous systems. When such routes are redistributed
1529
to routers in the AS via BGP, they contain IP addresses of a boundary
1530
routers (in route attribute NEXT_HOP). BGP depends on existing IGP
1531
routing table with AS-internal routes to determine immediate next hops
1532
for routes and to know their internal distances to boundary routers
1533
for the purpose of BGP route selection. In BIRD, there is usually
1534
one routing table used for both IGP routes and BGP routes.
1535

    
1536
<sect1>Configuration
1537

    
1538
<p>Each instance of the BGP corresponds to one neighboring router.
1539
This allows to set routing policy and all the other parameters differently
1540
for each neighbor using the following configuration parameters:
1541

    
1542
<descrip>
1543
	<tag>local [<m/ip/] as <m/number/</tag> Define which AS we are part
1544
	of. (Note that contrary to other IP routers, BIRD is able to act as a
1545
	router located in multiple AS'es simultaneously, but in such cases you
1546
	need to tweak the BGP paths manually in the filters to get consistent
1547
	behavior.) Optional <cf/ip/ argument specifies a source address,
1548
	equivalent to the <cf/source address/ option (see below).  This
1549
	parameter is mandatory.
1550

    
1551
	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router this
1552
	instance will be talking to and what AS it's located in. In case the
1553
	neighbor is in the same AS as we are, we automatically switch to iBGP.
1554
	This parameter is mandatory.
1555

    
1556
	<tag>direct</tag> Specify that the neighbor is directly connected. The
1557
	IP address of the neighbor must be from a directly reachable IP range
1558
	(i.e. associated with one of your router's interfaces), otherwise the
1559
	BGP session wouldn't start but it would wait for such interface to
1560
	appear. The alternative is the <cf/multihop/ option.  Default: enabled
1561
	for eBGP.
1562

    
1563
	<tag>multihop [<m/number/]</tag> Configure multihop BGP session to a
1564
	neighbor that isn't directly connected.  Accurately, this option should
1565
	be used if the configured neighbor IP address does not match with any
1566
	local network subnets. Such IP address have to be reachable through
1567
	system routing table.  The alternative is the <cf/direct/ option. For
1568
	multihop BGP it is recommended to explicitly configure the source
1569
	address to have it stable. Optional <cf/number/ argument can be used to
1570
	specify the number of hops (used for TTL). Note that the number of
1571
	networks (edges) in a path is counted; i.e., if two BGP speakers are
1572
	separated by one router, the number of hops is 2. Default: enabled for
1573
	iBGP.
1574

    
1575
	<tag>source address <m/ip/</tag> Define local address we
1576
	should use for next hop calculation and as a source address
1577
	for the BGP session. Default: the address of the local
1578
	end of the interface our neighbor is connected to.
1579

    
1580
	<tag>next hop self</tag> Avoid calculation of the Next Hop
1581
	attribute and always advertise our own source address as a
1582
	next hop.  This needs to be used only occasionally to
1583
	circumvent misconfigurations of other routers.  Default:
1584
	disabled.
1585

    
1586
	<tag>next hop keep</tag> Forward the received Next Hop
1587
	attribute even in situations where the local address should be
1588
	used instead, like when the route is sent to an interface with
1589
	a different subnet. Default: disabled.
1590

    
1591
	<tag>missing lladdr self|drop|ignore</tag>Next Hop attribute
1592
	in BGP-IPv6 sometimes contains just the global IPv6 address,
1593
	but sometimes it has to contain both global and link-local
1594
	IPv6 addresses. This option specifies what to do if BIRD have
1595
	to send both addresses but does not know link-local address.
1596
	This situation might happen when routes from other protocols
1597
	are exported to BGP, or when improper updates are received
1598
	from BGP peers.  <cf/self/ means that BIRD advertises its own
1599
	local address instead. <cf/drop/ means that BIRD skips that
1600
	prefixes and logs error. <cf/ignore/ means that BIRD ignores
1601
	the problem and sends just the global address (and therefore
1602
	forms improper BGP update). Default: <cf/self/, unless BIRD
1603
	is configured as a route server (option <cf/rs client/), in
1604
	that case default is <cf/ignore/, because route servers usually
1605
	do not forward packets themselves.
1606

    
1607
	<tag>gateway direct|recursive</tag>For received routes, their
1608
	<cf/gw/ (immediate next hop) attribute is computed from
1609
	received <cf/bgp_next_hop/ attribute. This option specifies
1610
	how it is computed. Direct mode means that the IP address from
1611
	<cf/bgp_next_hop/ is used if it is directly reachable,
1612
	otherwise the neighbor IP address is used. Recursive mode
1613
	means that the gateway is computed by an IGP routing table
1614
	lookup for the IP address from <cf/bgp_next_hop/. Recursive
1615
	mode is the behavior specified by the BGP standard. Direct
1616
	mode is simpler, does not require any routes in a routing
1617
	table, and was used in older versions of BIRD, but does not
1618
	handle well nontrivial iBGP setups and multihop.  Recursive
1619
	mode is incompatible with <ref id="dsc-sorted" name="sorted
1620
	tables">. Default: <cf/direct/ for direct sessions,
1621
	<cf/recursive/ for multihop sessions.
1622

    
1623
	<tag>igp table <m/name/</tag> Specifies a table that is used
1624
	as an IGP routing table. Default: the same as the table BGP is
1625
	connected to.
1626

    
1627
	<tag>bfd <M>switch</M></tag>
1628
	BGP could use BFD protocol as an advisory mechanism for neighbor
1629
	liveness and failure detection. If enabled, BIRD setups a BFD session
1630
	for the BGP neighbor and tracks its liveness by it. This has an
1631
	advantage of an order of magnitude lower detection times in case of
1632
	failure. Note that BFD protocol also has to be configured, see
1633
	<ref id="sect-bfd" name="BFD"> section for details. Default: disabled.
1634

    
1635
	<tag>ttl security <m/switch/</tag> Use GTSM (RFC 5082 - the
1636
	generalized TTL security mechanism). GTSM protects against
1637
	spoofed packets by ignoring received packets with a smaller
1638
	than expected TTL. To work properly, GTSM have to be enabled
1639
	on both sides of a BGP session. If both <cf/ttl security/ and
1640
	<cf/multihop/ options are enabled, <cf/multihop/ option should
1641
	specify proper hop value to compute expected TTL. Kernel
1642
	support required: Linux: 2.6.34+ (IPv4), 2.6.35+ (IPv6), BSD:
1643
	since long ago, IPv4 only. Note that full (ICMP protection,
1644
	for example) RFC 5082 support is provided by Linux
1645
	only. Default: disabled.
1646
	
1647
	<tag>password <m/string/</tag> Use this password for MD5 authentication
1648
	of BGP sessions. Default: no authentication. Password has to be set by
1649
	external utility (e.g. setkey(8)) on BSD systems.
1650

    
1651
	<tag>passive <m/switch/</tag> Standard BGP behavior is both
1652
        initiating outgoing connections and accepting incoming
1653
        connections. In passive mode, outgoing connections are not
1654
        initiated. Default: off.
1655

    
1656
	<tag>rr client</tag> Be a route reflector and treat the neighbor as
1657
	a route reflection client. Default: disabled.
1658

    
1659
	<tag>rr cluster id <m/IPv4 address/</tag> Route reflectors use cluster id
1660
	to avoid route reflection loops. When there is one route reflector in a cluster
1661
	it usually uses its router id as a cluster id, but when there are more route
1662
	reflectors in a cluster, these need to be configured (using this option) to
1663
	use a common cluster id. Clients in a cluster need not know their cluster
1664
	id and this option is not allowed for them. Default: the same as router id.
1665

    
1666
	<tag>rs client</tag> Be a route server and treat the neighbor
1667
	as a route server client. A route server is used as a
1668
	replacement for full mesh EBGP routing in Internet exchange
1669
	points in a similar way to route reflectors used in IBGP routing.
1670
	BIRD does not implement obsoleted RFC 1863, but uses ad-hoc implementation,
1671
	which behaves like plain EBGP but reduces modifications to advertised route
1672
	attributes to be transparent (for example does not prepend its AS number to
1673
	AS PATH attribute and keeps MED attribute). Default: disabled.
1674

    
1675
	<tag>secondary <m/switch/</tag> Usually, if an export filter
1676
	rejects a selected route, no other route is propagated for
1677
	that network. This option allows to try the next route in
1678
	order until one that is accepted is found or all routes for
1679
	that network are rejected. This can be used for route servers
1680
	that need to propagate different tables to each client but do
1681
	not want to have these tables explicitly (to conserve memory).
1682
	This option requires that the connected routing table is
1683
	<ref id="dsc-sorted" name="sorted">. Default: off.
1684

    
1685
	<tag>add paths <m/switch/|rx|tx</tag>
1686
	Standard BGP can propagate only one path (route) per destination network
1687
	(usually the selected one). This option controls the add-path protocol
1688
	extension, which allows to advertise any number of paths to a
1689
	destination. Note that to be active, add-path has to be enabled on both
1690
	sides of the BGP session, but it could be enabled separately for RX and
1691
	TX direction. When active, all available routes accepted by the export
1692
	filter are advertised to the neighbor. Default: off.
1693

    
1694
	<tag>allow local as [<m/number/]</tag> 
1695
	BGP prevents routing loops by rejecting received routes with
1696
	the local AS number in the AS path. This option allows to
1697
	loose or disable the check. Optional <cf/number/ argument can
1698
	be used to specify the maximum number of local ASNs in the AS
1699
	path that is allowed for received routes. When the option is
1700
	used without the argument, the check is completely disabled
1701
	and you should ensure loop-free behavior by some other means.
1702
	Default: 0 (no local AS number allowed).
1703

    
1704
	<tag>enable route refresh <m/switch/</tag> When BGP speaker
1705
	changes its import filter, it has to re-examine all routes
1706
	received from its neighbor against the new filter. As these
1707
	routes might not be available, there is a BGP protocol
1708
	extension Route Refresh (specified in RFC 2918) that allows
1709
	BGP speaker to request re-advertisement of all routes from its
1710
	neighbor. This option specifies whether BIRD advertises this
1711
	capability and accepts such requests. Even when disabled, BIRD
1712
	can send route refresh requests. Default: on.
1713

    
1714
	<tag>interpret communities <m/switch/</tag> RFC 1997 demands
1715
	that BGP speaker should process well-known communities like
1716
	no-export (65535, 65281) or no-advertise (65535, 65282). For
1717
	example, received route carrying a no-adverise community
1718
	should not be advertised to any of its neighbors. If this
1719
	option is enabled (which is by default), BIRD has such
1720
	behavior automatically (it is evaluated when a route is
1721
	exported to the BGP protocol just before the export filter).
1722
	Otherwise, this integrated processing of well-known
1723
	communities is disabled. In that case, similar behavior can be
1724
	implemented in the export filter.  Default: on.
1725

    
1726
	<tag>enable as4 <m/switch/</tag> BGP protocol was designed to use 2B AS numbers
1727
	and was extended later to allow 4B AS number. BIRD supports 4B AS extension,
1728
	but by disabling this option it can be persuaded not to advertise it and
1729
	to maintain old-style sessions with its neighbors. This might be useful for
1730
	circumventing bugs in neighbor's implementation of 4B AS extension.
1731
	Even when disabled (off), BIRD behaves internally as AS4-aware BGP router.
1732
	Default: on.
1733

    
1734
	<tag>capabilities <m/switch/</tag> Use capability advertisement
1735
	to advertise optional capabilities. This is standard behavior
1736
	for newer BGP implementations, but there might be some older
1737
	BGP implementations that reject such connection attempts.
1738
	When disabled (off), features that request it (4B AS support)
1739
	are also disabled. Default: on, with automatic fallback to
1740
	off when received capability-related error.
1741

    
1742
	<tag>advertise ipv4 <m/switch/</tag> Advertise IPv4 multiprotocol capability.
1743
	This is not a correct behavior according to the strict interpretation
1744
	of RFC 4760, but it is widespread and required by some BGP
1745
	implementations (Cisco and Quagga). This option is relevant
1746
	to IPv4 mode with enabled capability advertisement only. Default: on.
1747

    
1748
	<tag>route limit <m/number/</tag> The maximal number of routes
1749
	that may be imported from the protocol. If the route limit is
1750
	exceeded, the connection is closed with an error. Limit is currently implemented as
1751
	<cf/import limit <m/number/ action restart/. This option is obsolete and it is
1752
        replaced by <ref id="import-limit" name="import limit option">.  Default: no limit.
1753

    
1754
	<tag>disable after error <m/switch/</tag> When an error is encountered (either
1755
	locally or by the other side), disable the instance automatically
1756
	and wait for an administrator to fix the problem manually. Default: off.
1757

    
1758
	<tag>hold time <m/number/</tag> Time in seconds to wait for a Keepalive
1759
	message from the other side before considering the connection stale.
1760
	Default: depends on agreement with the neighboring router, we prefer
1761
	240 seconds if the other side is willing to accept it.
1762

    
1763
	<tag>startup hold time <m/number/</tag> Value of the hold timer used
1764
	before the routers have a chance to exchange open messages and agree
1765
	on the real value. Default: 240 seconds.
1766

    
1767
	<tag>keepalive time <m/number/</tag> Delay in seconds between sending
1768
	of two consecutive Keepalive messages. Default: One third of the hold time.
1769

    
1770
	<tag>connect retry time <m/number/</tag> Time in seconds to wait before
1771
	retrying a failed attempt to connect. Default: 120 seconds.
1772

    
1773
	<tag>start delay time <m/number/</tag> Delay in seconds between protocol
1774
	startup and the first attempt to connect. Default: 5 seconds.
1775

    
1776
	<tag>error wait time <m/number/,<m/number/</tag> Minimum and maximum delay in seconds between a protocol
1777
	failure (either local or reported by the peer) and automatic restart.
1778
	Doesn't apply when <cf/disable after error/ is configured. If consecutive
1779
	errors happen, the delay is increased exponentially until it reaches the maximum. Default: 60, 300.
1780

    
1781
	<tag>error forget time <m/number/</tag> Maximum time in seconds between two protocol
1782
	failures to treat them as a error sequence which makes the <cf/error wait time/
1783
	increase exponentially. Default: 300 seconds.
1784

    
1785
	<tag>path metric <m/switch/</tag> Enable comparison of path lengths
1786
	when deciding which BGP route is the best one. Default: on.
1787

    
1788
	<tag>med metric <m/switch/</tag> Enable comparison of MED
1789
	attributes (during best route selection) even between routes
1790
	received from different ASes.  This may be useful if all MED
1791
	attributes contain some consistent metric, perhaps enforced in
1792
	import filters of AS boundary routers. If this option is
1793
	disabled, MED attributes are compared only if routes are
1794
	received from the same AS (which is the standard behavior).
1795
	Default: off.
1796

    
1797
	<tag>deterministic med <m/switch/</tag> BGP route selection
1798
	algorithm is often viewed as a comparison between individual
1799
	routes (e.g. if a new route appears and is better than the
1800
	current best one, it is chosen as the new best one). But the
1801
	proper route selection, as specified by RFC 4271, cannot be
1802
	fully implemented in that way. The problem is mainly in
1803
	handling the MED attribute. BIRD, by default, uses an
1804
	simplification based on individual route comparison, which in
1805
	some cases may lead to temporally dependent behavior (i.e. the
1806
	selection is dependent on the order in which routes appeared).
1807
	This option enables a different (and slower) algorithm
1808
	implementing proper RFC 4271 route selection, which is
1809
	deterministic. Alternative way how to get deterministic
1810
	behavior is to use <cf/med metric/ option. This option is
1811
	incompatible with <ref id="dsc-sorted" name="sorted tables">.
1812
	Default: off.
1813

    
1814
	<tag>igp metric <m/switch/</tag> Enable comparison of internal
1815
 	distances to boundary routers during best route selection. Default: on.
1816

    
1817
	<tag>prefer older <m/switch/</tag> Standard route selection algorithm
1818
	breaks ties by comparing router IDs. This changes the behavior
1819
	to prefer older routes (when both are external and from different
1820
	peer). For details, see RFC 5004. Default: off.
1821

    
1822
	<tag>default bgp_med <m/number/</tag> Value of the Multiple Exit
1823
	Discriminator to be used during route selection when the MED attribute
1824
	is missing. Default: 0.
1825

    
1826
	<tag>default bgp_local_pref <m/number/</tag> A default value
1827
	for the Local Preference attribute. It is used when a new
1828
	Local Preference attribute is attached to a route by the BGP
1829
	protocol itself (for example, if a route is received through
1830
	eBGP and therefore does not have such attribute). Default: 100
1831
	(0 in pre-1.2.0 versions of BIRD).
1832
</descrip>
1833

    
1834
<sect1>Attributes
1835

    
1836
<p>BGP defines several route attributes. Some of them (those marked with `<tt/I/' in the
1837
table below) are available on internal BGP connections only, some of them (marked
1838
with `<tt/O/') are optional.
1839

    
1840
<descrip>
1841
	<tag>bgppath <cf/bgp_path/</tag> Sequence of AS numbers describing the AS path
1842
	the packet will travel through when forwarded according to the particular route.
1843
	In case of internal BGP it doesn't contain the number of the local AS.
1844

    
1845
	<tag>int <cf/bgp_local_pref/ [I]</tag> Local preference value used for
1846
	selection among multiple BGP routes (see the selection rules above). It's
1847
	used as an additional metric which is propagated through the whole local AS.
1848

    
1849
	<tag>int <cf/bgp_med/ [O]</tag> The Multiple Exit Discriminator of the route
1850
	is an optional attribute which is used on external (inter-AS) links to
1851
	convey to an adjacent AS the optimal entry point into the local AS.
1852
	The received attribute is also propagated over internal BGP links.
1853
	The attribute value is zeroed when a route is exported to an external BGP
1854
	instance to ensure that the attribute received from a neighboring AS is
1855
	not propagated to other neighboring ASes. A new value might be set in
1856
	the export filter of an external BGP instance.
1857
	See RFC 4451<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4451.txt">
1858
	for further discussion of BGP MED attribute.
1859

    
1860
	<tag>enum <cf/bgp_origin/</tag> Origin of the route: either <cf/ORIGIN_IGP/
1861
	if the route has originated in an interior routing protocol or
1862
	<cf/ORIGIN_EGP/ if it's been imported from the <tt>EGP</tt> protocol
1863
	(nowadays it seems to be obsolete) or <cf/ORIGIN_INCOMPLETE/ if the origin
1864
	is unknown.
1865

    
1866
	<tag>ip <cf/bgp_next_hop/</tag> Next hop to be used for forwarding of packets
1867
	to this destination. On internal BGP connections, it's an address of the
1868
	originating router if it's inside the local AS or a boundary router the
1869
	packet will leave the AS through if it's an exterior route, so each BGP
1870
	speaker within the AS has a chance to use the shortest interior path
1871
	possible to this point.
1872

    
1873
	<tag>void <cf/bgp_atomic_aggr/ [O]</tag> This is an optional attribute
1874
	which carries no value, but the sole presence of which indicates that the route
1875
	has been aggregated from multiple routes by some router on the path from
1876
	the originator.
1877

    
1878
<!-- we don't handle aggregators right since they are of a very obscure type
1879
	<tag>bgp_aggregator</tag>
1880
-->
1881
	<tag>clist <cf/bgp_community/ [O]</tag> List of community values associated
1882
	with the route. Each such value is a pair (represented as a <cf/pair/ data
1883
	type inside the filters) of 16-bit integers, the first of them containing the number of the AS which defines
1884
	the community and the second one being a per-AS identifier. There are lots
1885
	of uses of the community mechanism, but generally they are used to carry
1886
	policy information like "don't export to USA peers". As each AS can define
1887
	its own routing policy, it also has a complete freedom about which community
1888
	attributes it defines and what will their semantics be.
1889

    
1890
	<tag>eclist <cf/bgp_ext_community/ [O]</tag> List of extended community
1891
	values associated with the route. Extended communities have similar usage
1892
	as plain communities, but they have an extended range (to allow 4B ASNs)
1893
	and a nontrivial structure with a type field. Individual community values are
1894
	represented using an <cf/ec/ data type inside the filters.
1895

    
1896
	<tag>quad <cf/bgp_originator_id/ [I, O]</tag> This attribute is created by the
1897
	route reflector when reflecting the route and contains the router ID of the
1898
	originator of the route in the local AS.
1899

    
1900
	<tag>clist <cf/bgp_cluster_list/ [I, O]</tag> This attribute contains a list
1901
	of cluster IDs of route reflectors. Each route reflector prepends its
1902
	cluster ID when reflecting the route.
1903
</descrip>
1904

    
1905
<sect1>Example
1906

    
1907
<p><code>
1908
protocol bgp {
1909
	local as 65000;			     # Use a private AS number
1910
	neighbor 198.51.100.130 as 64496;    # Our neighbor ...
1911
	multihop;			     # ... which is connected indirectly
1912
	export filter {			     # We use non-trivial export rules
1913
		if source = RTS_STATIC then { # Export only static routes
1914
		        # Assign our community
1915
			bgp_community.add((65000,64501));
1916
			# Artificially increase path length
1917
			# by advertising local AS number twice
1918
			if bgp_path ~ [= 65000 =] then
1919
				bgp_path.prepend(65000);
1920
			accept;
1921
		}
1922
		reject;
1923
	};
1924
	import all;
1925
	source address 198.51.100.14;	# Use a non-standard source address
1926
}
1927
</code>
1928

    
1929
<sect>Device
1930

    
1931
<p>The Device protocol is not a real routing protocol.  It doesn't generate
1932
any routes and it only serves as a module for getting information about network
1933
interfaces from the kernel.
1934

    
1935
<p>Except for very unusual circumstances, you probably should include
1936
this protocol in the configuration since almost all other protocols
1937
require network interfaces to be defined for them to work with.
1938

    
1939
<sect1>Configuration
1940

    
1941
<p><descrip>
1942
	<tag>scan time <m/number/</tag> Time in seconds between two scans
1943
	of the network interface list. On systems where we are notified about
1944
	interface status changes asynchronously (such as newer versions of
1945
	Linux), we need to scan the list only in order to avoid confusion by lost
1946
	notification messages, so the default time is set to a large value.
1947

    
1948
	<tag>primary  [ "<m/mask/" ] <m/prefix/</tag>
1949
	If a network interface has more than one network address, BIRD
1950
	has to choose one of them as a primary one. By default, BIRD
1951
	chooses the lexicographically smallest address as the primary
1952
	one.
1953

    
1954
	This option allows to specify which network address should be
1955
	chosen as a primary one. Network addresses that match
1956
	<m/prefix/ are preferred to non-matching addresses. If more
1957
	<cf/primary/ options are used, the first one has the highest
1958
	preference. If "<m/mask/" is specified, then such
1959
	<cf/primary/ option is relevant only to matching network
1960
	interfaces.
1961

    
1962
	In all cases, an address marked by operating system as
1963
	secondary cannot be chosen as the primary one. 
1964
</descrip>
1965

    
1966
<p>As the Device protocol doesn't generate any routes, it cannot have
1967
any attributes. Example configuration looks like this:
1968

    
1969
<p><code>
1970
protocol device {
1971
	scan time 10;		# Scan the interfaces often
1972
	primary "eth0" 192.168.1.1;
1973
	primary 192.168.0.0/16;
1974
}
1975
</code>
1976

    
1977
<sect>Direct
1978

    
1979
<p>The Direct protocol is a simple generator of device routes for all the
1980
directly connected networks according to the list of interfaces provided
1981
by the kernel via the Device protocol.
1982

    
1983
<p>The question is whether it is a good idea to have such device
1984
routes in BIRD routing table. OS kernel usually handles device routes
1985
for directly connected networks by itself so we don't need (and don't
1986
want) to export these routes to the kernel protocol. OSPF protocol
1987
creates device routes for its interfaces itself and BGP protocol is
1988
usually used for exporting aggregate routes. Although there are some
1989
use cases that use the direct protocol (like abusing eBGP as an IGP
1990
routing protocol), in most cases it is not needed to have these device
1991
routes in BIRD routing table and to use the direct protocol.
1992

    
1993
<p>There is one notable case when you definitely want to use the
1994
direct protocol -- running BIRD on BSD systems. Having high priority
1995
device routes for directly connected networks from the direct protocol
1996
protects kernel device routes from being overwritten or removed by IGP
1997
routes during some transient network conditions, because a lower
1998
priority IGP route for the same network is not exported to the kernel
1999
routing table. This is an issue on BSD systems only, as on Linux
2000
systems BIRD cannot change non-BIRD route in the kernel routing table.
2001

    
2002
<p>The only configurable thing about direct is what interfaces it watches:
2003

    
2004
<p><descrip>
2005
	<tag>interface <m/pattern [, ...]/</tag> By default, the Direct
2006
	protocol will generate device routes for all the interfaces
2007
	available. If you want to restrict it to some subset of interfaces
2008
	(for example if you're using multiple routing tables for policy
2009
	routing and some of the policy domains don't contain all interfaces),
2010
	just use this clause.
2011
</descrip>
2012

    
2013
<p>Direct device routes don't contain any specific attributes.
2014

    
2015
<p>Example config might look like this:
2016

    
2017
<p><code>
2018
protocol direct {
2019
	interface "-arc*", "*";		# Exclude the ARCnets
2020
}
2021
</code>
2022

    
2023
<sect>Kernel
2024

    
2025
<p>The Kernel protocol is not a real routing protocol. Instead of communicating
2026
with other routers in the network, it performs synchronization of BIRD's routing
2027
tables with the OS kernel. Basically, it sends all routing table updates to the kernel
2028
and from time to time it scans the kernel tables to see whether some routes have
2029
disappeared (for example due to unnoticed up/down transition of an interface)
2030
or whether an `alien' route has been added by someone else (depending on the
2031
<cf/learn/ switch, such routes are either ignored or accepted to our
2032
table).
2033

    
2034
<p>Unfortunately, there is one thing that makes the routing table
2035
synchronization a bit more complicated. In the kernel routing table
2036
there are also device routes for directly connected networks. These
2037
routes are usually managed by OS itself (as a part of IP address
2038
configuration) and we don't want to touch that.  They are completely
2039
ignored during the scan of the kernel tables and also the export of
2040
device routes from BIRD tables to kernel routing tables is restricted
2041
to prevent accidental interference. This restriction can be disabled using
2042
<cf/device routes/ switch.
2043

    
2044
<p>If your OS supports only a single routing table, you can configure
2045
only one instance of the Kernel protocol. If it supports multiple
2046
tables (in order to allow policy routing; such an OS is for example
2047
Linux), you can run as many instances as you want, but each of them
2048
must be connected to a different BIRD routing table and to a different
2049
kernel table.
2050

    
2051
<p>Because the kernel protocol is partially integrated with the
2052
connected routing table, there are two limitations - it is not
2053
possible to connect more kernel protocols to the same routing table
2054
and changing route destination/gateway in an export
2055
filter of a kernel protocol does not work. Both limitations can be
2056
overcome using another routing table and the pipe protocol.
2057

    
2058
<sect1>Configuration
2059

    
2060
<p><descrip>
2061
	<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
2062
	routing tables when it exits (instead of cleaning them up).
2063
	<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
2064
	kernel routing table.
2065
	<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
2066
	routing tables by other routing daemons or by the system administrator.
2067
	This is possible only on systems which support identification of route
2068
	authorship.
2069

    
2070
	<tag>device routes <m/switch/</tag> Enable export of device
2071
	routes to the kernel routing table. By default, such routes
2072
	are rejected (with the exception of explicitly configured
2073
	device routes from the static protocol) regardless of the
2074
	export filter to protect device routes in kernel routing table
2075
	(managed by OS itself) from accidental overwriting or erasing.
2076

    
2077
	<tag>kernel table <m/number/</tag> Select which kernel table should
2078
	this particular instance of the Kernel protocol work with. Available
2079
	only on systems supporting multiple routing tables.
2080
</descrip>
2081

    
2082
<sect1>Attributes
2083

    
2084
<p>The Kernel protocol defines several attributes. These attributes
2085
are translated to appropriate system (and OS-specific) route attributes.
2086
We support these attributes:
2087

    
2088
<descrip>
2089
	<tag>int <cf/krt_source/</tag> The original source of the imported
2090
	kernel route.  The value is system-dependent. On Linux, it is
2091
	a value of the protocol field of the route. See
2092
	/etc/iproute2/rt_protos for common values.  On BSD, it is
2093
	based on STATIC and PROTOx flags. The attribute is read-only.
2094

    
2095
	<tag>int <cf/krt_metric/</tag> The kernel metric of
2096
	the route.  When multiple same routes are in a kernel routing
2097
	table, the Linux kernel chooses one with lower metric.
2098

    
2099
	<tag>ip <cf/krt_prefsrc/</tag> (Linux) The preferred source address.
2100
 	Used in source address selection for outgoing packets. Have to
2101
 	be one of IP addresses of the router.
2102

    
2103
	<tag>int <cf/krt_realm/</tag> (Linux) The realm of the route. Can be
2104
	used for traffic classification.
2105
</descrip>
2106

    
2107
<sect1>Example
2108

    
2109
<p>A simple configuration can look this way:
2110

    
2111
<p><code>
2112
protocol kernel {
2113
	export all;
2114
}
2115
</code>
2116

    
2117
<p>Or for a system with two routing tables:
2118

    
2119
<p><code>
2120
protocol kernel {		# Primary routing table
2121
	learn;			# Learn alien routes from the kernel
2122
	persist;		# Don't remove routes on bird shutdown
2123
	scan time 10;		# Scan kernel routing table every 10 seconds
2124
	import all;
2125
	export all;
2126
}
2127

    
2128
protocol kernel {		# Secondary routing table
2129
	table auxtable;
2130
	kernel table 100;
2131
	export all;
2132
}
2133
</code>
2134

    
2135
<sect>OSPF
2136

    
2137
<sect1>Introduction
2138

    
2139
<p>Open Shortest Path First (OSPF) is a quite complex interior gateway
2140
protocol. The current IPv4 version (OSPFv2) is defined in RFC
2141
2328<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt"> and
2142
the current IPv6 version (OSPFv3) is defined in RFC 5340<htmlurl
2143
url="ftp://ftp.rfc-editor.org/in-notes/rfc5340.txt">  It's a link state
2144
(a.k.a. shortest path first) protocol -- each router maintains a
2145
database describing the autonomous system's topology. Each participating
2146
router has an identical copy of the database and all routers run the
2147
same algorithm calculating a shortest path tree with themselves as a
2148
root. OSPF chooses the least cost path as the best path.
2149

    
2150
<p>In OSPF, the autonomous system can be split to several areas in order
2151
to reduce the amount of resources consumed for exchanging the routing
2152
information and to protect the other areas from incorrect routing data.
2153
Topology of the area is hidden to the rest of the autonomous system.
2154

    
2155
<p>Another very important feature of OSPF is that
2156
it can keep routing information from other protocols (like Static or BGP)
2157
in its link state database as external routes. Each external route can
2158
be tagged by the advertising router, making it possible to pass additional
2159
information between routers on the boundary of the autonomous system.
2160

    
2161
<p>OSPF quickly detects topological changes in the autonomous system (such
2162
as router interface failures) and calculates new loop-free routes after a short
2163
period of convergence. Only a minimal amount of 
2164
routing traffic is involved.
2165

    
2166
<p>Each router participating in OSPF routing periodically sends Hello messages
2167
to all its interfaces. This allows neighbors to be discovered dynamically.
2168
Then the neighbors exchange theirs parts of the link state database and keep it
2169
identical by flooding updates. The flooding process is reliable and ensures
2170
that each router detects all changes.
2171

    
2172
<sect1>Configuration
2173

    
2174
<p>In the main part of configuration, there can be multiple definitions of
2175
OSPF areas, each with a different id. These definitions includes many other
2176
switches and multiple definitions of interfaces. Definition of interface
2177
may contain many switches and constant definitions and list of neighbors
2178
on nonbroadcast networks.
2179

    
2180
<code>
2181
protocol ospf &lt;name&gt; {
2182
	rfc1583compat &lt;switch&gt;;
2183
	stub router &lt;switch&gt;;
2184
	tick &lt;num&gt;;
2185
	ecmp &lt;switch&gt; [limit &lt;num&gt;];
2186
	area &lt;id&gt; {
2187
		stub;
2188
		nssa;
2189
		summary &lt;switch&gt;;
2190
		default nssa &lt;switch&gt;;
2191
		default cost &lt;num&gt;;
2192
		default cost2 &lt;num&gt;;
2193
		translator &lt;switch&gt;;
2194
		translator stability &lt;num&gt;;
2195

    
2196
                networks {
2197
			&lt;prefix&gt;;
2198
			&lt;prefix&gt; hidden;
2199
		}
2200
                external {
2201
			&lt;prefix&gt;;
2202
			&lt;prefix&gt; hidden;
2203
			&lt;prefix&gt; tag &lt;num&gt;;
2204
		}
2205
		stubnet &lt;prefix&gt;;
2206
		stubnet &lt;prefix&gt; {
2207
			hidden &lt;switch&gt;;
2208
			summary &lt;switch&gt;;
2209
			cost &lt;num&gt;;
2210
		}
2211
		interface &lt;interface pattern&gt; [instance &lt;num&gt;] {
2212
			cost &lt;num&gt;;
2213
			stub &lt;switch&gt;;
2214
			hello &lt;num&gt;;
2215
			poll &lt;num&gt;;
2216
			retransmit &lt;num&gt;;
2217
			priority &lt;num&gt;;
2218
			wait &lt;num&gt;;
2219
			dead count &lt;num&gt;;
2220
			dead &lt;num&gt;;
2221
			rx buffer [normal|large|&lt;num&gt;];
2222
			type [broadcast|bcast|pointopoint|ptp|
2223
				nonbroadcast|nbma|pointomultipoint|ptmp];
2224
			strict nonbroadcast &lt;switch&gt;;
2225
			real broadcast &lt;switch&gt;;
2226
			ptp netmask &lt;switch&gt;;
2227
			check link &lt;switch&gt;;
2228
			bfd &lt;switch&gt;;
2229
			ecmp weight &lt;num&gt;;
2230
			ttl security [&lt;switch&gt;; | tx only]
2231
			tx class|dscp &lt;num&gt;;
2232
			tx priority &lt;num&gt;;
2233
			authentication [none|simple|cryptographic];
2234
			password "&lt;text&gt;";
2235
			password "&lt;text&gt;" {
2236
				id &lt;num&gt;;
2237
				generate from "&lt;date&gt;";
2238
				generate to "&lt;date&gt;";
2239
				accept from "&lt;date&gt;";
2240
				accept to "&lt;date&gt;";
2241
			};
2242
			neighbors {
2243
				&lt;ip&gt;;
2244
				&lt;ip&gt; eligible;
2245
			};
2246
		};
2247
		virtual link &lt;id&gt; [instance &lt;num&gt;] {
2248
			hello &lt;num&gt;;
2249
			retransmit &lt;num&gt;;
2250
			wait &lt;num&gt;;
2251
			dead count &lt;num&gt;;
2252
			dead &lt;num&gt;;
2253
			authentication [none|simple|cryptographic];
2254
			password "&lt;text&gt;";
2255
		};
2256
	};
2257
}
2258
</code>
2259

    
2260
<descrip>
2261
	<tag>rfc1583compat <M>switch</M></tag>
2262
	 This option controls compatibility of routing table
2263
	 calculation with RFC 1583<htmlurl
2264
	 url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
2265
	 value is no.
2266

    
2267
	<tag>stub router <M>switch</M></tag>
2268
	 This option configures the router to be a stub router, i.e.,
2269
	 a router that participates in the OSPF topology but does not
2270
	 allow transit traffic. In OSPFv2, this is implemented by
2271
	 advertising maximum metric for outgoing links, as suggested
2272
	 by RFC 3137<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc3137.txt">.
2273
	 In OSPFv3, the stub router behavior is announced by clearing
2274
	 the R-bit in the router LSA. Default value is no.
2275

    
2276
	<tag>tick <M>num</M></tag>
2277
	 The routing table calculation and clean-up of areas' databases
2278
         is not performed when a single link state
2279
	 change arrives. To lower the CPU utilization, it's processed later
2280
	 at periodical intervals of <m/num/ seconds. The default value is 1.
2281

    
2282
	<tag>ecmp <M>switch</M> [limit <M>number</M>]</tag>
2283
	 This option specifies whether OSPF is allowed to generate
2284
	 ECMP (equal-cost multipath) routes. Such routes are used when
2285
	 there are several directions to the destination, each with
2286
	 the same (computed) cost. This option also allows to specify
2287
	 a limit on maximal number of nexthops in one route. By
2288
	 default, ECMP is disabled.  If enabled, default value of the
2289
	 limit is 16.
2290

    
2291
	<tag>area <M>id</M></tag>
2292
	 This defines an OSPF area with given area ID (an integer or an IPv4
2293
	 address, similarly to a router ID). The most important area is
2294
	 the backbone (ID 0) to which every other area must be connected.
2295

    
2296
	<tag>stub</tag>
2297
	 This option configures the area to be a stub area. External
2298
	 routes are not flooded into stub areas. Also summary LSAs can be
2299
	 limited in stub areas (see option <cf/summary/).
2300
	 By default, the area is not a stub area.
2301

    
2302
	<tag>nssa</tag>
2303
	 This option configures the area to be a NSSA (Not-So-Stubby
2304
	 Area). NSSA is a variant of a stub area which allows a
2305
	 limited way of external route propagation. Global external
2306
	 routes are not propagated into a NSSA, but an external route
2307
	 can be imported into NSSA as a (area-wide) NSSA-LSA (and
2308
	 possibly translated and/or aggregated on area boundary).
2309
	 By default, the area is not NSSA.
2310

    
2311
	<tag>summary <M>switch</M></tag>
2312
	 This option controls propagation of summary LSAs into stub or
2313
	 NSSA areas. If enabled, summary LSAs are propagated as usual,
2314
	 otherwise just the default summary route (0.0.0.0/0) is
2315
	 propagated (this is sometimes called totally stubby area). If
2316
	 a stub area has more area boundary routers, propagating
2317
	 summary LSAs could lead to more efficient routing at the cost
2318
	 of larger link state database. Default value is no.
2319

    
2320
	<tag>default nssa <M>switch</M></tag>
2321
 	 When <cf/summary/ option is enabled, default summary route is
2322
	 no longer propagated to the NSSA. In that case, this option
2323
	 allows to originate default route as NSSA-LSA to the NSSA.
2324
	 Default value is no.
2325

    
2326
	<tag>default cost <M>num</M></tag>
2327
	 This option controls the cost of a default route propagated to
2328
	 stub and NSSA areas. Default value is 1000.
2329

    
2330
	<tag>default cost2 <M>num</M></tag>
2331
	 When a default route is originated as NSSA-LSA, its cost
2332
	 can use either type 1 or type 2 metric. This option allows
2333
	 to specify the cost of a default route in type 2 metric.
2334
	 By default, type 1 metric (option <cf/default cost/) is used.
2335

    
2336
	<tag>translator <M>switch</M></tag>
2337
	 This option controls translation of NSSA-LSAs into external
2338
	 LSAs. By default, one translator per NSSA is automatically
2339
	 elected from area boundary routers. If enabled, this area
2340
	 boundary router would unconditionally translate all NSSA-LSAs
2341
	 regardless of translator election. Default value is no.
2342

    
2343
	<tag>translator stability <M>num</M></tag>
2344
	 This option controls the translator stability interval (in
2345
	 seconds). When the new translator is elected, the old one
2346
	 keeps translating until the interval is over. Default value
2347
	 is 40.
2348

    
2349
	<tag>networks { <m/set/ }</tag>
2350
         Definition of area IP ranges. This is used in summary LSA origination.
2351
	 Hidden networks are not propagated into other areas.
2352

    
2353
	<tag>external { <m/set/ }</tag>
2354
         Definition of external area IP ranges for NSSAs. This is used
2355
	 for NSSA-LSA translation. Hidden networks are not translated
2356
	 into external LSAs. Networks can have configured route tag.
2357

    
2358
	<tag>stubnet <m/prefix/ { <m/options/ }</tag>
2359
	 Stub networks are networks that are not transit networks
2360
	 between OSPF routers. They are also propagated through an
2361
	 OSPF area as a part of a link state database. By default,
2362
	 BIRD generates a stub network record for each primary network
2363
	 address on each OSPF interface that does not have any OSPF
2364
	 neighbors, and also for each non-primary network address on
2365
	 each OSPF interface. This option allows to alter a set of
2366
	 stub networks propagated by this router. 
2367

    
2368
	 Each instance of this option adds a stub network with given
2369
	 network prefix to the set of propagated stub network, unless
2370
	 option <cf/hidden/ is used. It also suppresses default stub
2371
	 networks for given network prefix. When option
2372
	 <cf/summary/ is used, also default stub networks that are
2373
	 subnetworks of given stub network are suppressed. This might
2374
	 be used, for example, to aggregate generated stub networks.
2375
	 
2376
	<tag>interface <M>pattern</M> [instance <m/num/]</tag>
2377
	 Defines that the specified interfaces belong to the area being defined.
2378
	 See <ref id="dsc-iface" name="interface"> common option for detailed description.
2379
	 In OSPFv3, you can specify instance ID for that interface
2380
	 description, so it is possible to have several instances of
2381
	 that interface with different options or even in different areas.
2382

    
2383
	<tag>virtual link <M>id</M> [instance <m/num/]</tag>
2384
	 Virtual link to router with the router id. Virtual link acts
2385
         as a point-to-point interface belonging to backbone. The
2386
         actual area is used as transport area. This item cannot be in
2387
         the backbone. In OSPFv3, you could also use several virtual
2388
         links to one destination with different instance IDs.
2389

    
2390
	<tag>cost <M>num</M></tag>
2391
	 Specifies output cost (metric) of an interface. Default value is 10.
2392

    
2393
	<tag>stub <M>switch</M></tag>
2394
	 If set to interface it does not listen to any packet and does not send
2395
	 any hello. Default value is no.
2396

    
2397
	<tag>hello <M>num</M></tag>
2398
	 Specifies interval in seconds between sending of Hello messages. Beware, all
2399
	 routers on the same network need to have the same hello interval.
2400
	 Default value is 10.
2401

    
2402
	<tag>poll <M>num</M></tag>
2403
	 Specifies interval in seconds between sending of Hello messages for
2404
	 some neighbors on NBMA network. Default value is 20.
2405

    
2406
	<tag>retransmit <M>num</M></tag>
2407
	 Specifies interval in seconds between retransmissions of unacknowledged updates.
2408
	 Default value is 5.
2409

    
2410
        <tag>priority <M>num</M></tag>
2411
	 On every multiple access network (e.g., the Ethernet) Designed Router
2412
	 and Backup Designed router are elected. These routers have some
2413
	 special functions in the flooding process. Higher priority increases
2414
	 preferences in this election. Routers with priority 0 are not
2415
	 eligible. Default value is 1.
2416

    
2417
	<tag>wait <M>num</M></tag>
2418
	 After start, router waits for the specified number of seconds between starting
2419
	 election and building adjacency. Default value is 40.
2420
	 
2421
	<tag>dead count <M>num</M></tag>
2422
	 When the router does not receive any messages from a neighbor in
2423
	 <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
2424

    
2425
	<tag>dead <M>num</M></tag>
2426
	 When the router does not receive any messages from a neighbor in
2427
	 <m/dead/ seconds, it will consider the neighbor down. If both directives
2428
	 <m/dead count/ and <m/dead/ are used, <m/dead/ has precendence.
2429

    
2430
	<tag>rx buffer <M>num</M></tag>
2431
	 This sets the size of buffer used for receiving packets. The buffer should
2432
	 be bigger than maximal size of any packets. Value NORMAL (default)
2433
	 means 2*MTU, value LARGE means maximal allowed packet - 65535.
2434

    
2435
	<tag>type broadcast|bcast</tag>
2436
	 BIRD detects a type of a connected network automatically, but
2437
	 sometimes it's convenient to force use of a different type
2438
	 manually. On broadcast networks (like ethernet), flooding
2439
	 and Hello messages are sent using multicasts (a single packet
2440
	 for all the neighbors). A designated router is elected and it
2441
	 is responsible for synchronizing the link-state databases and
2442
	 originating network LSAs. This network type cannot be used on
2443
	 physically NBMA networks and on unnumbered networks (networks
2444
	 without proper IP prefix).
2445

    
2446
	<tag>type pointopoint|ptp</tag>
2447
	 Point-to-point networks connect just 2 routers together. No
2448
	 election is performed and no network LSA is originated, which
2449
	 makes it simpler and faster to establish. This network type
2450
	 is useful not only for physically PtP ifaces (like PPP or
2451
	 tunnels), but also for broadcast networks used as PtP links.
2452
	 This network type cannot be used on physically NBMA networks.
2453

    
2454
	<tag>type nonbroadcast|nbma</tag>
2455
	 On NBMA networks, the packets are sent to each neighbor
2456
	 separately because of lack of multicast capabilities.
2457
	 Like on broadcast networks, a designated router is elected,
2458
	 which plays a central role in propagation of LSAs.
2459
	 This network type cannot be used on unnumbered networks.
2460

    
2461
	<tag>type pointomultipoint|ptmp</tag>
2462
	 This is another network type designed to handle NBMA
2463
	 networks. In this case the NBMA network is treated as a
2464
	 collection of PtP links. This is useful if not every pair of
2465
	 routers on the NBMA network has direct communication, or if
2466
	 the NBMA network is used as an (possibly unnumbered) PtP
2467
	 link.
2468

    
2469
	<tag>strict nonbroadcast <M>switch</M></tag>
2470
	 If set, don't send hello to any undefined neighbor. This switch
2471
	 is ignored on other than NBMA or PtMP networks. Default value is no.
2472

    
2473
	<tag>real broadcast <m/switch/</tag>
2474
	 In <cf/type broadcast/ or <cf/type ptp/ network
2475
	 configuration, OSPF packets are sent as IP multicast
2476
	 packets. This option changes the behavior to using
2477
	 old-fashioned IP broadcast packets. This may be useful as a
2478
	 workaround if IP multicast for some reason does not work or
2479
	 does not work reliably. This is a non-standard option and
2480
	 probably is not interoperable with other OSPF
2481
	 implementations. Default value is no.
2482

    
2483
	<tag>ptp netmask <m/switch/</tag>
2484
	 In <cf/type ptp/ network configurations, OSPFv2
2485
	 implementations should ignore received netmask field in hello
2486
	 packets and should send hello packets with zero netmask field
2487
	 on unnumbered PtP links. But some OSPFv2 implementations
2488
	 perform netmask checking even for PtP links. This option
2489
	 specifies whether real netmask will be used in hello packets
2490
	 on <cf/type ptp/ interfaces. You should ignore this option
2491
	 unless you meet some compatibility problems related to this
2492
	 issue. Default value is no for unnumbered PtP links, yes
2493
	 otherwise.
2494

    
2495
	<tag>check link <M>switch</M></tag>
2496
	 If set, a hardware link state (reported by OS) is taken into
2497
	 consideration. When a link disappears (e.g. an ethernet cable is
2498
	 unplugged), neighbors are immediately considered unreachable
2499
	 and only the address of the iface (instead of whole network
2500
	 prefix) is propagated. It is possible that some hardware
2501
	 drivers or platforms do not implement this feature. Default value is no.
2502

    
2503
	<tag>bfd <M>switch</M></tag>
2504
	OSPF could use BFD protocol as an advisory mechanism for neighbor
2505
	liveness and failure detection. If enabled, BIRD setups a BFD session
2506
	for each OSPF neighbor and tracks its liveness by it. This has an
2507
	advantage of an order of magnitude lower detection times in case of
2508
	failure. Note that BFD protocol also has to be configured, see
2509
	<ref id="sect-bfd" name="BFD"> section for details. Default value is no.
2510

    
2511
	<tag>ttl security [<m/switch/ | tx only]</tag>
2512
	 TTL security is a feature that protects routing protocols
2513
	 from remote spoofed packets by using TTL 255 instead of TTL 1
2514
	 for protocol packets destined to neighbors. Because TTL is
2515
	 decremented when packets are forwarded, it is non-trivial to
2516
	 spoof packets with TTL 255 from remote locations. Note that
2517
	 this option would interfere with OSPF virtual links.
2518

    
2519
	 If this option is enabled, the router will send OSPF packets
2520
	 with TTL 255 and drop received packets with TTL less than
2521
	 255. If this option si set to <cf/tx only/, TTL 255 is used
2522
	 for sent packets, but is not checked for received
2523
	 packets. Default value is no.
2524

    
2525
	<tag>tx class|dscp|priority <m/num/</tag>
2526
         These options specify the ToS/DiffServ/Traffic class/Priority
2527
         of the outgoing OSPF packets. See <ref id="dsc-prio" name="tx
2528
         class"> common option for detailed description.
2529

    
2530
	<tag>ecmp weight <M>num</M></tag>
2531
	 When ECMP (multipath) routes are allowed, this value specifies
2532
	 a relative weight used for nexthops going through the iface.
2533
	 Allowed values are 1-256. Default value is 1.
2534

    
2535
	<tag>authentication none</tag>
2536
	 No passwords are sent in OSPF packets. This is the default value.
2537

    
2538
	<tag>authentication simple</tag>
2539
	 Every packet carries 8 bytes of password. Received packets
2540
	 lacking this password are ignored. This authentication mechanism is
2541
	 very weak.
2542

    
2543
	<tag>authentication cryptographic</tag>
2544
	 16-byte long MD5 digest is appended to every packet. For the digest
2545
         generation 16-byte long passwords are used. Those passwords are 
2546
         not sent via network, so this mechanism is quite secure.
2547
         Packets can still be read by an attacker.
2548

    
2549
	<tag>password "<M>text</M>"</tag>
2550
	 An 8-byte or 16-byte password used for authentication.
2551
	 See <ref id="dsc-pass" name="password"> common option for detailed description.
2552

    
2553
	<tag>neighbors { <m/set/ } </tag>
2554
	 A set of neighbors to which Hello messages on NBMA or PtMP
2555
	 networks are to be sent. For NBMA networks, some of them
2556
	 could be marked as eligible. In OSPFv3, link-local addresses
2557
	 should be used, using global ones is possible, but it is
2558
	 nonstandard and might be problematic. And definitely,
2559
	 link-local and global addresses should not be mixed.
2560

    
2561
</descrip>
2562

    
2563
<sect1>Attributes
2564

    
2565
<p>OSPF defines four route attributes. Each internal route has a <cf/metric/.
2566
Metric is ranging from 1 to infinity (65535).
2567
External routes use <cf/metric type 1/ or <cf/metric type 2/.
2568
A <cf/metric of type 1/ is comparable with internal <cf/metric/, a
2569
<cf/metric of type 2/ is always longer
2570
than any <cf/metric of type 1/ or any <cf/internal metric/.
2571
<cf/Internal metric/ or <cf/metric of type 1/ is stored in attribute
2572
<cf/ospf_metric1/, <cf/metric type 2/ is stored in attribute <cf/ospf_metric2/.
2573
If you specify both metrics only metric1 is used.
2574

    
2575
Each external route can also carry attribute <cf/ospf_tag/ which is a
2576
32-bit integer which is used when exporting routes to other protocols;
2577
otherwise, it doesn't affect routing inside the OSPF domain at all.
2578
The fourth attribute <cf/ospf_router_id/ is a router ID of the router
2579
advertising that route/network. This attribute is read-only. Default
2580
is <cf/ospf_metric2 = 10000/ and <cf/ospf_tag = 0/.
2581

    
2582
<sect1>Example
2583

    
2584
<p>
2585

    
2586
<code>
2587
protocol ospf MyOSPF {
2588
        rfc1583compat yes;
2589
        tick 2;
2590
	export filter {
2591
		if source = RTS_BGP then {
2592
			ospf_metric1 = 100;
2593
			accept;
2594
		}
2595
		reject;
2596
	};
2597
	area 0.0.0.0 {
2598
		interface "eth*" {
2599
			cost 11;
2600
			hello 15;
2601
			priority 100;
2602
			retransmit 7;
2603
			authentication simple;
2604
			password "aaa";
2605
		};
2606
		interface "ppp*" {
2607
			cost 100;
2608
			authentication cryptographic;
2609
			password "abc" {
2610
				id 1;
2611
				generate to "22-04-2003 11:00:06";
2612
				accept from "17-01-2001 12:01:05";
2613
			};
2614
			password "def" {
2615
				id 2;
2616
				generate to "22-07-2005 17:03:21";
2617
				accept from "22-02-2001 11:34:06";
2618
			};
2619
		};
2620
		interface "arc0" {
2621
			cost 10;
2622
			stub yes;
2623
		};
2624
		interface "arc1";
2625
	};
2626
	area 120 {
2627
		stub yes;
2628
		networks {
2629
			172.16.1.0/24;
2630
			172.16.2.0/24 hidden;
2631
		}
2632
		interface "-arc0" , "arc*" {
2633
			type nonbroadcast;
2634
			authentication none;
2635
			strict nonbroadcast yes;
2636
			wait 120;
2637
			poll 40;
2638
			dead count 8;
2639
			neighbors {
2640
				192.168.120.1 eligible;
2641
				192.168.120.2;
2642
				192.168.120.10;
2643
			};
2644
		};
2645
	};
2646
}
2647
</code>
2648

    
2649
<sect>Pipe
2650

    
2651
<sect1>Introduction
2652

    
2653
<p>The Pipe protocol serves as a link between two routing tables, allowing routes to be
2654
passed from a table declared as primary (i.e., the one the pipe is connected to using the
2655
<cf/table/ configuration keyword) to the secondary one (declared using <cf/peer table/)
2656
and vice versa, depending on what's allowed by the filters. Export filters control export
2657
of routes from the primary table to the secondary one, import filters control the opposite
2658
direction.
2659

    
2660
<p>The Pipe protocol may work in the transparent mode mode or in the opaque mode.
2661
In the transparent mode, the Pipe protocol retransmits all routes from
2662
one table to the other table, retaining their original source and
2663
attributes.  If import and export filters are set to accept, then both
2664
tables would have the same content. The transparent mode is the default mode.
2665

    
2666
<p>In the opaque mode, the Pipe protocol retransmits optimal route
2667
from one table to the other table in a similar way like other
2668
protocols send and receive routes. Retransmitted route will have the
2669
source set to the Pipe protocol, which may limit access to protocol
2670
specific route attributes. This mode is mainly for compatibility, it
2671
is not suggested for new configs. The mode can be changed by
2672
<tt/mode/ option.
2673

    
2674
<p>The primary use of multiple routing tables and the Pipe protocol is for policy routing,
2675
where handling of a single packet doesn't depend only on its destination address, but also
2676
on its source address, source interface, protocol type and other similar parameters.
2677
In many systems (Linux being a good example), the kernel allows to enforce routing policies
2678
by defining routing rules which choose one of several routing tables to be used for a packet
2679
according to its parameters. Setting of these rules is outside the scope of BIRD's work
2680
(on Linux, you can use the <tt/ip/ command), but you can create several routing tables in BIRD,
2681
connect them to the kernel ones, use filters to control which routes appear in which tables
2682
and also you can employ the Pipe protocol for exporting a selected subset of one table to
2683
another one.
2684

    
2685
<sect1>Configuration
2686

    
2687
<p><descrip>
2688
	<tag>peer table <m/table/</tag> Defines secondary routing table to connect to. The
2689
	primary one is selected by the <cf/table/ keyword.
2690

    
2691
	<tag>mode opaque|transparent</tag> Specifies the mode for the pipe to work in. Default is transparent.
2692
</descrip>
2693

    
2694
<sect1>Attributes
2695

    
2696
<p>The Pipe protocol doesn't define any route attributes.
2697

    
2698
<sect1>Example
2699

    
2700
<p>Let's consider a router which serves as a boundary router of two different autonomous
2701
systems, each of them connected to a subset of interfaces of the router, having its own
2702
exterior connectivity and wishing to use the other AS as a backup connectivity in case
2703
of outage of its own exterior line.
2704

    
2705
<p>Probably the simplest solution to this situation is to use two routing tables (we'll
2706
call them <cf/as1/ and <cf/as2/) and set up kernel routing rules, so that packets having
2707
arrived from interfaces belonging to the first AS will be routed according to <cf/as1/
2708
and similarly for the second AS. Thus we have split our router to two logical routers,
2709
each one acting on its own routing table, having its own routing protocols on its own
2710
interfaces. In order to use the other AS's routes for backup purposes, we can pass
2711
the routes between the tables through a Pipe protocol while decreasing their preferences
2712
and correcting their BGP paths to reflect the AS boundary crossing.
2713

    
2714
<code>
2715
table as1;				# Define the tables
2716
table as2;
2717

    
2718
protocol kernel kern1 {			# Synchronize them with the kernel
2719
	table as1;
2720
	kernel table 1;
2721
}
2722

    
2723
protocol kernel kern2 {
2724
	table as2;
2725
	kernel table 2;
2726
}
2727

    
2728
protocol bgp bgp1 {			# The outside connections
2729
	table as1;
2730
	local as 1;
2731
	neighbor 192.168.0.1 as 1001;
2732
	export all;
2733
	import all;
2734
}
2735

    
2736
protocol bgp bgp2 {
2737
	table as2;
2738
	local as 2;
2739
	neighbor 10.0.0.1 as 1002;
2740
	export all;
2741
	import all;
2742
}
2743

    
2744
protocol pipe {				# The Pipe
2745
	table as1;
2746
	peer table as2;
2747
	export filter {
2748
		if net ~ [ 1.0.0.0/8+] then {	# Only AS1 networks
2749
			if preference>10 then preference = preference-10;
2750
			if source=RTS_BGP then bgp_path.prepend(1);
2751
			accept;
2752
		}
2753
		reject;
2754
	};
2755
	import filter {
2756
		if net ~ [ 2.0.0.0/8+] then {	# Only AS2 networks
2757
			if preference>10 then preference = preference-10;
2758
			if source=RTS_BGP then bgp_path.prepend(2);
2759
			accept;
2760
		}
2761
		reject;
2762
	};
2763
}
2764
</code>
2765

    
2766
<sect>RAdv
2767

    
2768
<sect1>Introduction
2769

    
2770
<p>The RAdv protocol is an implementation of Router Advertisements,
2771
which are used in the IPv6 stateless autoconfiguration. IPv6 routers
2772
send (in irregular time intervals or as an answer to a request)
2773
advertisement packets to connected networks. These packets contain
2774
basic information about a local network (e.g. a list of network
2775
prefixes), which allows network hosts to autoconfigure network
2776
addresses and choose a default route. BIRD implements router behavior
2777
as defined in
2778
RFC 4861<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4861.txt">
2779
and also the DNS extensions from
2780
RFC 6106<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc6106.txt">.
2781

    
2782
<sect1>Configuration
2783

    
2784
<p>There are several classes of definitions in RAdv configuration --
2785
interface definitions, prefix definitions and DNS definitions:
2786

    
2787
<descrip>
2788
	<tag>interface <m/pattern [, ...]/  { <m/options/ }</tag>
2789
	Interface definitions specify a set of interfaces on which the
2790
	protocol is activated and contain interface specific options.
2791
	See <ref id="dsc-iface" name="interface"> common options for
2792
	detailed description.
2793

    
2794
	<tag>prefix <m/prefix/ { <m/options/ }</tag>
2795
	Prefix definitions allow to modify a list of advertised
2796
	prefixes. By default, the advertised prefixes are the same as
2797
	the network prefixes assigned to the interface. For each
2798
	network prefix, the matching prefix definition is found and
2799
	its options are used. If no matching prefix definition is
2800
	found, the prefix is used with default options.
2801

    
2802
	Prefix definitions can be either global or interface-specific.
2803
	The second ones are part of interface options. The prefix
2804
	definition matching is done in the first-match style, when
2805
	interface-specific definitions are processed before global
2806
	definitions. As expected, the prefix definition is matching if
2807
	the network prefix is a subnet of the prefix in prefix
2808
	definition.
2809

    
2810
	<tag>rdnss { <m/options/ }</tag>
2811
	RDNSS definitions allow to specify a list of advertised
2812
	recursive DNS servers together with their options. As options
2813
	are seldom necessary, there is also a short variant <cf>rdnss
2814
	<m/address/</cf> that just specifies one DNS server. Multiple
2815
	definitions are cumulative. RDNSS definitions may also be
2816
	interface-specific when used inside interface options. By
2817
	default, interface uses both global and interface-specific
2818
	options, but that can be changed by <cf/rdnss local/ option.
2819

    
2820
	<tag>dnssl { <m/options/ }</tag>
2821
	DNSSL definitions allow to specify a list of advertised DNS
2822
	search domains together with their options. Like <cf/rdnss/
2823
	above, multiple definitions are cumulative, they can be used
2824
	also as interface-specific options and there is a short
2825
	variant <cf>dnssl <m/domain/</cf> that just specifies one DNS
2826
        search domain.
2827

    
2828
	<label id="dsc-trigger"> <tag>trigger <m/prefix/</tag>
2829
	RAdv protocol could be configured to change its behavior based
2830
	on availability of routes. When this option is used, the
2831
	protocol waits in suppressed state until a <it/trigger route/
2832
	(for the specified network) is exported to the protocol, the
2833
	protocol also returnsd to suppressed state if the
2834
	<it/trigger route/ disappears. Note that route export depends
2835
	on specified export filter, as usual. This option could be
2836
	used, e.g., for handling failover in multihoming scenarios.
2837

    
2838
	During suppressed state, router advertisements are generated,
2839
	but with some fields zeroed. Exact behavior depends on which
2840
	fields are zeroed, this can be configured by
2841
	<cf/sensitive/ option for appropriate fields. By default, just
2842
	<cf/default lifetime/ (also called <cf/router lifetime/) is
2843
	zeroed, which means hosts cannot use the router as a default
2844
	router. <cf/preferred lifetime/ and <cf/valid lifetime/ could
2845
	also be configured as <cf/sensitive/ for a prefix, which would
2846
	cause autoconfigured IPs to be deprecated or even removed.
2847
</descrip>
2848

    
2849
<p>Interface specific options:
2850

    
2851
<descrip>
2852
	<tag>max ra interval <m/expr/</tag>
2853
	Unsolicited router advertisements are sent in irregular time
2854
	intervals. This option specifies the maximum length of these
2855
	intervals, in seconds. Valid values are 4-1800. Default: 600
2856

    
2857
	<tag>min ra interval <m/expr/</tag>
2858
	This option specifies the minimum length of that intervals, in
2859
	seconds. Must be at least 3 and at most 3/4 * <cf/max ra interval/.
2860
	Default: about 1/3 * <cf/max ra interval/.
2861

    
2862
	<tag>min delay <m/expr/</tag>
2863
	The minimum delay between two consecutive router advertisements,
2864
	in seconds. Default: 3
2865

    
2866
	<tag>managed <m/switch/</tag>
2867
	This option specifies whether hosts should use DHCPv6 for
2868
	IP address configuration. Default: no
2869

    
2870
	<tag>other config <m/switch/</tag>
2871
	This option specifies whether hosts should use DHCPv6 to
2872
	receive other configuration information. Default: no
2873

    
2874
	<tag>link mtu <m/expr/</tag>
2875
	This option specifies which value of MTU should be used by
2876
	hosts. 0 means unspecified. Default: 0
2877

    
2878
	<tag>reachable time <m/expr/</tag>
2879
	This option specifies the time (in milliseconds) how long
2880
	hosts should assume a neighbor is reachable (from the last
2881
	confirmation). Maximum is 3600000, 0 means unspecified.
2882
	Default 0.
2883

    
2884
	<tag>retrans timer <m/expr/</tag>
2885
	This option specifies the time (in milliseconds) how long
2886
	hosts should wait before retransmitting Neighbor Solicitation
2887
	messages. 0 means unspecified. Default 0.
2888

    
2889
	<tag>current hop limit <m/expr/</tag>
2890
	This option specifies which value of Hop Limit should be used
2891
	by hosts. Valid values are 0-255, 0 means unspecified. Default: 64
2892

    
2893
	<tag>default lifetime <m/expr/ [sensitive <m/switch/]</tag>
2894
	This option specifies the time (in seconds) how long (after
2895
	the receipt of RA) hosts may use the router as a default
2896
	router. 0 means do not use as a default router. For
2897
	<cf/sensitive/ option, see <ref id="dsc-trigger" name="trigger">.
2898
	Default: 3 * <cf/max ra interval/, <cf/sensitive/ yes.
2899

    
2900
	<tag>rdnss local <m/switch/</tag>
2901
	Use only local (interface-specific) RDNSS definitions for this
2902
	interface. Otherwise, both global and local definitions are
2903
	used. Could also be used to disable RDNSS for given interface
2904
	if no local definitons are specified. Default: no.
2905

    
2906
	<tag>dnssl local <m/switch/</tag>
2907
	Use only local DNSSL definitions for this interface. See
2908
	<cf/rdnss local/ option above. Default: no.
2909
</descrip>
2910

    
2911

    
2912
<p>Prefix specific options:
2913

    
2914
<descrip>
2915
	<tag>skip <m/switch/</tag>
2916
	This option allows to specify that given prefix should not be
2917
	advertised. This is useful for making exceptions from a
2918
	default policy of advertising all prefixes. Note that for
2919
	withdrawing an already advertised prefix it is more useful to
2920
	advertise it with zero valid lifetime. Default: no
2921

    
2922
	<tag>onlink <m/switch/</tag>
2923
	This option specifies whether hosts may use the advertised
2924
	prefix for onlink determination. Default: yes
2925

    
2926
	<tag>autonomous <m/switch/</tag>
2927
	This option specifies whether hosts may use the advertised
2928
	prefix for stateless autoconfiguration. Default: yes
2929

    
2930
	<tag>valid lifetime <m/expr/ [sensitive <m/switch/]</tag>
2931
	This option specifies the time (in seconds) how long (after
2932
	the receipt of RA) the prefix information is valid, i.e.,
2933
	autoconfigured IP addresses can be assigned and hosts with
2934
	that IP addresses are considered directly reachable. 0 means
2935
	the prefix is no longer valid. For <cf/sensitive/ option, see
2936
	<ref id="dsc-trigger" name="trigger">. Default: 86400 (1 day), <cf/sensitive/ no.
2937

    
2938
	<tag>preferred lifetime <m/expr/ [sensitive <m/switch/]</tag>
2939
	This option specifies the time (in seconds) how long (after
2940
	the receipt of RA) IP addresses generated from the prefix
2941
	using stateless autoconfiguration remain preferred. For
2942
	<cf/sensitive/ option, see <ref id="dsc-trigger" name="trigger">.
2943
	Default: 14400 (4 hours), <cf/sensitive/ no.
2944
</descrip>
2945

    
2946

    
2947
<p>RDNSS specific options:
2948

    
2949
<descrip>
2950
	<tag>ns <m/address/</tag>
2951
	This option specifies one recursive DNS server. Can be used
2952
	multiple times for multiple servers. It is mandatory to have
2953
	at least one <cf/ns/ option in <cf/rdnss/ definition.
2954

    
2955
	<tag>lifetime [mult] <m/expr/</tag>
2956
	This option specifies the time how long the RDNSS information
2957
        may be used by clients after the receipt of RA. It is
2958
        expressed either in seconds or (when <cf/mult/ is used) in
2959
        multiples of <cf/max ra interval/. Note that RDNSS information
2960
        is also invalidated when <cf/default lifetime/ expires. 0
2961
        means these addresses are no longer valid DNS servers.
2962
	Default: 3 * <cf/max ra interval/.
2963
</descrip>
2964

    
2965

    
2966
<p>DNSSL specific options:
2967

    
2968
<descrip>
2969
	<tag>domain <m/address/</tag>
2970
	This option specifies one DNS search domain. Can be used
2971
	multiple times for multiple domains. It is mandatory to have
2972
	at least one <cf/domain/ option in <cf/dnssl/ definition.
2973

    
2974
	<tag>lifetime [mult] <m/expr/</tag>
2975
	This option specifies the time how long the DNSSL information
2976
        may be used by clients after the receipt of RA. Details are
2977
	the same as for RDNSS <cf/lifetime/ option above.
2978
	Default: 3 * <cf/max ra interval/.
2979
</descrip>
2980

    
2981

    
2982
<sect1>Example
2983

    
2984
<p><code>
2985
protocol radv {
2986
	interface "eth2" {
2987
		max ra interval 5;	# Fast failover with more routers
2988
		managed yes;		# Using DHCPv6 on eth2
2989
		prefix ::/0 {
2990
			autonomous off;	# So do not autoconfigure any IP
2991
		};
2992
	};
2993

    
2994
	interface "eth*";		# No need for any other options
2995

    
2996
	prefix 2001:0DB8:1234::/48 {
2997
		preferred lifetime 0;	# Deprecated address range
2998
	};
2999

    
3000
	prefix 2001:0DB8:2000::/48 {
3001
		autonomous off;		# Do not autoconfigure
3002
	};
3003

    
3004
	rdnss 2001:0DB8:1234::10;	# Short form of RDNSS
3005

    
3006
	rdnss {
3007
		lifetime mult 10;
3008
		ns 2001:0DB8:1234::11;
3009
		ns 2001:0DB8:1234::12;
3010
	};
3011

    
3012
	dnssl {
3013
		lifetime 3600;
3014
		domain "abc.com";
3015
		domain "xyz.com";
3016
	};
3017
}
3018
</code>
3019

    
3020
<sect>RIP
3021

    
3022
<sect1>Introduction
3023

    
3024
<p>The RIP protocol (also sometimes called Rest In Pieces) is a simple protocol, where each router broadcasts (to all its neighbors)
3025
distances to all networks it can reach. When a router hears distance to another network, it increments
3026
it and broadcasts it back. Broadcasts are done in regular intervals. Therefore, if some network goes
3027
unreachable, routers keep telling each other that its distance is the original distance plus 1 (actually, plus
3028
interface metric, which is usually one). After some time, the distance reaches infinity (that's 15 in
3029
RIP) and all routers know that network is unreachable. RIP tries to minimize situations where
3030
counting to infinity is necessary, because it is slow. Due to infinity being 16, you can't use
3031
RIP on networks where maximal distance is higher than 15 hosts. You can read more about RIP at <HTMLURL
3032
URL="http://www.ietf.org/html.charters/rip-charter.html" name="http://www.ietf.org/html.charters/rip-charter.html">. Both IPv4  
3033
(RFC 1723<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc1723.txt">)
3034
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
3035
not currently supported. RIPv4 MD5 authentication (RFC 2082<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2082.txt">) is supported.
3036

    
3037
<p>RIP is a very simple protocol, and it has a lot of shortcomings. Slow
3038
convergence, big network load and inability to handle larger networks
3039
makes it pretty much obsolete. (It is still usable on very small networks.)
3040

    
3041
<sect1>Configuration
3042

    
3043
<p>In addition to options common for all to other protocols, RIP supports the following ones:
3044

    
3045
<descrip>
3046
	<tag/authentication none|plaintext|md5/ selects authentication method to be used. <cf/none/ means that
3047
	  packets are not authenticated at all, <cf/plaintext/ means that a plaintext password is embedded
3048
	  into each packet, and <cf/md5/ means that packets are authenticated using a MD5 cryptographic
3049
	  hash. If you set authentication to not-none, it is a good idea to add <cf>password</cf>
3050
	  section. Default: none.
3051

    
3052
	<tag>honor always|neighbor|never </tag>specifies when should requests for dumping routing table
3053
	  be honored. (Always, when sent from a  host on a directly connected
3054
	  network or never.) Routing table updates are honored only from
3055
	  neighbors, that is not configurable. Default: never.
3056
</descrip>
3057

    
3058
<p>There are some options that can be specified per-interface:
3059

    
3060
<descrip>
3061
	<tag>metric <m/num/</tag>
3062
	  This option specifies the metric of the interface. Valid
3063

    
3064
	<tag>mode multicast|broadcast|quiet|nolisten|version1</tag>
3065
	  This option selects the mode for RIP to work in. If nothing is
3066
	  specified, RIP runs in multicast mode. <cf/version1/ is
3067
	  currently equivalent to <cf/broadcast/, and it makes RIP talk
3068
	  to a broadcast address even through multicast mode is
3069
	  possible. <cf/quiet/ option means that RIP will not transmit
3070
	  any periodic messages to this interface and <cf/nolisten/
3071
	  means that RIP will send to this interface butnot listen to it.
3072

    
3073
	<tag>ttl security [<m/switch/ | tx only]</tag>
3074
	 TTL security is a feature that protects routing protocols
3075
	 from remote spoofed packets by using TTL 255 instead of TTL 1
3076
	 for protocol packets destined to neighbors. Because TTL is
3077
	 decremented when packets are forwarded, it is non-trivial to
3078
	 spoof packets with TTL 255 from remote locations.
3079

    
3080
	 If this option is enabled, the router will send RIP packets
3081
	 with TTL 255 and drop received packets with TTL less than
3082
	 255. If this option si set to <cf/tx only/, TTL 255 is used
3083
	 for sent packets, but is not checked for received
3084
	 packets. Such setting does not offer protection, but offers
3085
	 compatibility with neighbors regardless of whether they use
3086
	 ttl security.
3087

    
3088
	 Note that for RIPng, TTL security is a standard behavior
3089
	 (required by RFC 2080), but BIRD uses <cf/tx only/ by
3090
	 default, for compatibility with older versions. For IPv4 RIP,
3091
	 default value is no.
3092

    
3093
	<tag>tx class|dscp|priority <m/num/</tag>
3094
          These options specify the ToS/DiffServ/Traffic class/Priority
3095
          of the outgoing RIP packets. See <ref id="dsc-prio" name="tx
3096
          class"> common option for detailed description.
3097
</descrip>
3098

    
3099
<p>The following options generally override behavior specified in RFC. If you use any of these
3100
options, BIRD will no longer be RFC-compliant, which means it will not be able to talk to anything
3101
other than equally configured BIRD. I have warned you.
3102

    
3103
<descrip>
3104
	<tag>port <M>number</M></tag>
3105
	  selects IP port to operate on, default 520. (This is useful when testing BIRD, if you
3106
	  set this to an address &gt;1024, you will not need to run bird with UID==0).
3107

    
3108
	<tag>infinity <M>number</M></tag>
3109
	  selects the value of infinity, default is 16. Bigger values will make protocol convergence
3110
	  even slower.
3111

    
3112
	<tag>period <M>number</M>
3113
	  </tag>specifies the number of seconds between periodic updates. Default is 30 seconds. A lower
3114
	  number will mean faster convergence but bigger network
3115
	  load. Do not use values lower than 12.
3116

    
3117
	<tag>timeout time <M>number</M>
3118
	  </tag>specifies how old route has to be to be considered unreachable. Default is 4*<cf/period/.
3119

    
3120
	<tag>garbage time <M>number</M>
3121
	  </tag>specifies how old route has to be to be discarded. Default is 10*<cf/period/.
3122
</descrip>
3123

    
3124
<sect1>Attributes
3125

    
3126
<p>RIP defines two route attributes:
3127

    
3128
<descrip>
3129
	<tag>int <cf/rip_metric/</tag> RIP metric of the route (ranging from 0 to <cf/infinity/).
3130
	When routes from different RIP instances are available and all of them have the same
3131
	preference, BIRD prefers the route with lowest <cf/rip_metric/.
3132
	When importing a non-RIP route, the metric defaults to 5.
3133

    
3134
	<tag>int <cf/rip_tag/</tag> RIP route tag: a 16-bit number which can be used
3135
	to carry additional information with the route (for example, an originating AS number
3136
	in case of external routes). When importing a non-RIP route, the tag defaults to 0.
3137
</descrip>
3138

    
3139
<sect1>Example
3140

    
3141
<p><code>
3142
protocol rip MyRIP_test {
3143
        debug all;
3144
        port 1520;
3145
        period 12;
3146
        garbage time 60;
3147
        interface "eth0" { metric 3; mode multicast; };
3148
	interface "eth*" { metric 2; mode broadcast; };
3149
        honor neighbor;
3150
        authentication none;
3151
        import filter { print "importing"; accept; };
3152
        export filter { print "exporting"; accept; };
3153
}
3154
</code>
3155

    
3156
<sect>Static
3157

    
3158
<p>The Static protocol doesn't communicate with other routers in the network,
3159
but instead it allows you to define routes manually. This is often used for
3160
specifying how to forward packets to parts of the network which don't use
3161
dynamic routing at all and also for defining sink routes (i.e., those
3162
telling to return packets as undeliverable if they are in your IP block,
3163
you don't have any specific destination for them and you don't want to send
3164
them out through the default route to prevent routing loops).
3165

    
3166
<p>There are five types of static routes: `classical' routes telling
3167
to forward packets to a neighboring router, multipath routes
3168
specifying several (possibly weighted) neighboring routers, device
3169
routes specifying forwarding to hosts on a directly connected network,
3170
recursive routes computing their nexthops by doing route table lookups
3171
for a given IP and special routes (sink, blackhole etc.) which specify
3172
a special action to be done instead of forwarding the packet.
3173

    
3174
<p>When the particular destination is not available (the interface is down or
3175
the next hop of the route is not a neighbor at the moment), Static just
3176
uninstalls the route from the table it is connected to and adds it again as soon
3177
as the destination becomes adjacent again.
3178

    
3179
<p>The Static protocol does not have many configuration options. The
3180
definition of the protocol contains mainly a list of static routes:
3181

    
3182
<descrip>
3183
	<tag>route <m/prefix/ via <m/ip/</tag> Static route through
3184
	a neighboring router.
3185
	<tag>route <m/prefix/ multipath via <m/ip/ [weight <m/num/] [via ...]</tag>
3186
	Static multipath route. Contains several nexthops (gateways), possibly
3187
 	with their weights.
3188
	<tag>route <m/prefix/ via <m/"interface"/</tag> Static device
3189
	route through an interface to hosts on a directly connected network.
3190
	<tag>route <m/prefix/ recursive <m/ip/</tag> Static recursive route,
3191
	its nexthop depends on a route table lookup for given IP address.
3192
	<tag>route <m/prefix/ blackhole|unreachable|prohibit</tag> Special routes
3193
	specifying to silently drop the packet, return it as unreachable or return
3194
	it as administratively prohibited. First two targets are also known
3195
	as <cf/drop/ and <cf/reject/.
3196

    
3197
	<tag>check link <m/switch/</tag>
3198
	If set, hardware link states of network interfaces are taken
3199
	into consideration.  When link disappears (e.g. ethernet cable
3200
	is unplugged), static routes directing to that interface are
3201
	removed. It is possible that some hardware drivers or
3202
	platforms do not implement this feature. Default: off.
3203

    
3204
	<tag>igp table <m/name/</tag> Specifies a table that is used
3205
	for route table lookups of recursive routes. Default: the
3206
	same table as the protocol is connected to.
3207
</descrip>
3208

    
3209
<p>Static routes have no specific attributes.
3210

    
3211
<p>Example static config might look like this:
3212

    
3213
<p><code>
3214
protocol static {
3215
	table testable;			 # Connect to a non-default routing table
3216
	route 0.0.0.0/0 via 198.51.100.130; # Default route
3217
	route 10.0.0.0/8 multipath	 # Multipath route
3218
		via 198.51.100.10 weight 2
3219
		via 198.51.100.20
3220
		via 192.0.2.1;
3221
	route 203.0.113.0/24 unreachable; # Sink route
3222
	route 10.2.0.0/24 via "arc0";	 # Secondary network
3223
}
3224
</code>
3225

    
3226
<chapt>Conclusions
3227

    
3228
<sect>Future work
3229

    
3230
<p>Although BIRD supports all the commonly used routing protocols,
3231
there are still some features which would surely deserve to be
3232
implemented in future versions of BIRD:
3233

    
3234
<itemize>
3235
<item>Opaque LSA's
3236
<item>Route aggregation and flap dampening
3237
<item>Multipath routes
3238
<item>Multicast routing protocols
3239
<item>Ports to other systems
3240
</itemize>
3241

    
3242
<sect>Getting more help
3243

    
3244
<p>If you use BIRD, you're welcome to join the bird-users mailing list
3245
(<HTMLURL URL="mailto:bird-users@bird.network.cz" name="bird-users@bird.network.cz">)
3246
where you can share your experiences with the other users and consult
3247
your problems with the authors. To subscribe to the list, just send a
3248
<tt/subscribe bird-users/ command in a body of a mail to
3249
(<HTMLURL URL="mailto:majordomo@bird.network.cz" name="majordomo@bird.network.cz">).
3250
The home page of BIRD can be found at <HTMLURL URL="http://bird.network.cz/" name="http://bird.network.cz/">.
3251

    
3252
<p>BIRD is a relatively young system and it probably contains some
3253
bugs. You can report any problems to the bird-users list and the authors
3254
will be glad to solve them, but before you do so,
3255
please make sure you have read the available documentation and that you are running the latest version (available at <HTMLURL
3256
URL="ftp://bird.network.cz/pub/bird" name="bird.network.cz:/pub/bird">). (Of course, a patch
3257
which fixes the bug is always welcome as an attachment.)
3258

    
3259
<p>If you want to understand what is going inside, Internet standards are
3260
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">).
3261

    
3262
<p><it/Good luck!/
3263

    
3264
</book>
3265

    
3266
<!--
3267
LocalWords:  GPL IPv GateD BGPv RIPv OSPFv Linux sgml html dvi sgmltools Pavel
3268
LocalWords:  linuxdoc dtd descrip config conf syslog stderr auth ospf bgp Mbps
3269
LocalWords:  router's eval expr num birdc ctl UNIX if's enums bool int ip GCC
3270
LocalWords:  len ipaddress pxlen netmask enum bgppath bgpmask clist gw md eth
3271
LocalWords:  RTS printn quitbird iBGP AS'es eBGP RFC multiprotocol IGP Machek
3272
LocalWords:  EGP misconfigurations keepalive pref aggr aggregator BIRD's RTC
3273
LocalWords:  OS'es AS's multicast nolisten misconfigured UID blackhole MRTD MTU
3274
LocalWords:  uninstalls ethernets IP binutils ANYCAST anycast dest RTD ICMP rfc
3275
LocalWords:  compat multicasts nonbroadcast pointopoint loopback sym stats
3276
LocalWords:  Perl SIGHUP dd mm yy HH MM SS EXT IA UNICAST multihop Discriminator txt
3277
LocalWords:  proto wildcard Ondrej Filip
3278
-->