Commit 8fd12e6b authored by Ondřej Filip's avatar Ondřej Filip

OSPF user documentation added.

parent 2e9b2421
......@@ -877,6 +877,193 @@ protocol kernel { # Secondary routing table
<p>Open Shortest Path First (OSPF) is quite complex interior gateway
protocol. Today's version for IPv4 is 2 and it's defined in RFC 2328<htmlurl
url="">. It's based on
link-state of SPF technology. Each router maintains a database
describing the Autonomous System's topology. Each participating router has
has an identical database and all routers run the exact same algorithm
calculatin shortest path tree with themselves as roots, in parallel.
OSPF chooses the least cost path as the best path. In OSPF, the
Autonomous System can be splitted into more areas. Topology
of such area is hidden to the rest of the Autonomous System. This enables
a reduction in routing traffic as well as protection other areas from bad
routing data. Unfortunatelly multiple OSPF areas are not fully supported
in this version of BIRD. Another very important feature of OSPF is that
it can keep routing information from other protocols (like static or BGP)
in it's link-state database as external routes. Each external route can
be tagged by the advertising router, enabling the passing of additional
information between routers on the boundary of the Autonomous System.
<p>OSPF quickly detects topological changes in the Autonomous System (such
as router interface failures) and calculates new loop-free routes after a
period of convergence. This period of convergence is short and involves
a minimum of routing traffic.
<p>Each router joined in OSPF periodically sends hello messages out
all its interfaces. This allows neighbors to be discovered dynamically.
Then the neighbors exchange theirs parts of database. And keep it
identical flooding updates. Flooding proces is reliable and ensures
that each routes detects the change.
protocol ospf <name> {
rfc1583compat bool;
area <id> {
stub <bool>;
tick <num>;
interface <interface>
cost <num>;
hello <num>;
retransmit <num>;
priority <num>;
wait <num>;
dead count <num>;
type [broadcast|nonbroadcast|pointopoint];
authetication [none|simple];
password "<text>";
neighbors {
<tag>rfc1583compat <M>bool</M></tag>
This option can disable or enable compatibility of routing table
calculation with RFC 1583<htmlurl
url="">. Default
value is no.
<tag>area <M>id</M></tag>
This specifies area id of configured OSPF area. It can be written
as a number or as an IPv4 number. The most important area is
the backbone (area id 0) to which every other area must be connected.
<tag>stub <M>bool</M></tag>
No external routes are flooded into stub area. Default value is no.
<tag>tick <M>num</M></tag>
The routing table calculation is not processed when any single
change comes. To lower the CPU utilization it's processed late
in periodical interval. The default value is 7.
<tag>interface <M>interface</M></tag>
This mean that specified interface (or interface pattern) belongs
to actual area.
<tag>cost <M>num</M></tag>
Specifies output cost of interface. Default value is 10.
<tag>hello <M>num</M></tag>
Specifies interval between sending hello messages. Beware, all
router on the same network has to have the same hello interval.
Default value is 10.
<tag>retransmit <M>num</M></tag>
Specifies interval between retransmiting unacknoledged update.
Default value is 5.
<tag>priority <M>num</M></tag>
On every multiple access network (like e.g ethernet) Designed
and Backup Designed router is elected. These routers have some
special functions in flooding process. Higher priority rices
preferences in elections. Routers with priority 0 are not
eligible. Default value is 1.
<tag>wait <M>num</M></tag>
After start, router waits specified interval between starting
election and building adjacency. Default value is 40.
<tag>dead count <M>num</M></tag>
When router does not receive any message from neighbor in
<dead count>*<hello> seconds, it will declare neighbor down.
<tag>type <M>broadcast</M><tag>
BIRD detects a type of connected network. However, sometimes is
necessary to change it. On broadcast networks are flooding
and hello messages sent using multicasting. (Single
packet to all neighbors.)
<tag>type <M>nonbroadcast</M></tag>
On nonbroadcast network are packets sent to each neighbor
separately because of lack of multicast messages.
<tag>type <M>pointopoint</M></tag>
Pointopoint network connects just 2 routers together. No election
is provided there, this reduces a number of sent messages.
<tag>authetication <M>none</M></tag>
No passwords are sent in OSPF's packets. This is default value.
<tag>authetication <M>simple</M></tag>
In every packet is sent an 8 bytes long password. Received packets
without this password are ignored. This autentication mechanism is
very weak.
<tag>password <M>text</M></tag>
An 8 bytes long password used for authentication.
A set of neighbors to which hello messages on nonbroadcast networks
are sent.
<p>OSPF defines 3 route attributes. Each internal route has a metric. External
routes uses metric type 1 or metric type 2. Metric type one is comparable
with internal metric. Metric type 2 is always longer then metric type 1
or internal metric. Each external route can also carry a tag. Tag is
32 bits long number and it's used for exporting routes to other protocols
in link-state it has no funtion.
protocol ospf MyOSPF {
area {
tick 8;
interface "eth*" {
cost 11;
hello 15;
priority 100;
retransmit 7;
authentication simple;
password "aaa";
interface "ppp*" {
cost 100;
area 120 {
stub yes;
interface "-arc0" , "arc*" {
type nonbroadcast;
authentication none;
wait 50;
dead count 6;
neighbors {;;;
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