OSPF user documentation added.
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Ondrej Filip
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doc/bird.sgml
187
doc/bird.sgml
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@ -877,6 +877,193 @@ protocol kernel { # Secondary routing table
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<sect>OSPF
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<sect1>Introduction
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<p>Open Shortest Path First (OSPF) is quite complex interior gateway
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protocol. Today's version for IPv4 is 2 and it's defined in RFC 2328<htmlurl
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url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's based on
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link-state of SPF technology. Each router maintains a database
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describing the Autonomous System's topology. Each participating router has
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has an identical database and all routers run the exact same algorithm
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calculatin shortest path tree with themselves as roots, in parallel.
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OSPF chooses the least cost path as the best path. In OSPF, the
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Autonomous System can be splitted into more areas. Topology
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of such area is hidden to the rest of the Autonomous System. This enables
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a reduction in routing traffic as well as protection other areas from bad
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routing data. Unfortunatelly multiple OSPF areas are not fully supported
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in this version of BIRD. Another very important feature of OSPF is that
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it can keep routing information from other protocols (like static or BGP)
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in it's link-state database as external routes. Each external route can
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be tagged by the advertising router, enabling the passing of additional
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information between routers on the boundary of the Autonomous System.
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<p>OSPF quickly detects topological changes in the Autonomous System (such
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as router interface failures) and calculates new loop-free routes after a
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period of convergence. This period of convergence is short and involves
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a minimum of routing traffic.
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<p>Each router joined in OSPF periodically sends hello messages out
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all its interfaces. This allows neighbors to be discovered dynamically.
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Then the neighbors exchange theirs parts of database. And keep it
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identical flooding updates. Flooding proces is reliable and ensures
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that each routes detects the change.
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<sect1>Configuration
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<p>
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<code>
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protocol ospf <name> {
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rfc1583compat bool;
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area <id> {
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stub <bool>;
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tick <num>;
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interface <interface>
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{
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cost <num>;
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hello <num>;
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retransmit <num>;
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priority <num>;
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wait <num>;
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dead count <num>;
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type [broadcast|nonbroadcast|pointopoint];
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authetication [none|simple];
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password "<text>";
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neighbors {
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<ip>;
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};
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};
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};
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}
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</code>
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<descrip>
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<tag>rfc1583compat <M>bool</M></tag>
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This option can disable or enable compatibility of routing table
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calculation with RFC 1583<htmlurl
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url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
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value is no.
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<tag>area <M>id</M></tag>
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This specifies area id of configured OSPF area. It can be written
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as a number or as an IPv4 number. The most important area is
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the backbone (area id 0) to which every other area must be connected.
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<tag>stub <M>bool</M></tag>
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No external routes are flooded into stub area. Default value is no.
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<tag>tick <M>num</M></tag>
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The routing table calculation is not processed when any single
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change comes. To lower the CPU utilization it's processed late
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in periodical interval. The default value is 7.
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<tag>interface <M>interface</M></tag>
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This mean that specified interface (or interface pattern) belongs
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to actual area.
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<tag>cost <M>num</M></tag>
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Specifies output cost of interface. Default value is 10.
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<tag>hello <M>num</M></tag>
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Specifies interval between sending hello messages. Beware, all
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router on the same network has to have the same hello interval.
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Default value is 10.
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<tag>retransmit <M>num</M></tag>
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Specifies interval between retransmiting unacknoledged update.
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Default value is 5.
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<tag>priority <M>num</M></tag>
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On every multiple access network (like e.g ethernet) Designed
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and Backup Designed router is elected. These routers have some
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special functions in flooding process. Higher priority rices
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preferences in elections. Routers with priority 0 are not
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eligible. Default value is 1.
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<tag>wait <M>num</M></tag>
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After start, router waits specified interval between starting
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election and building adjacency. Default value is 40.
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<tag>dead count <M>num</M></tag>
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When router does not receive any message from neighbor in
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<dead count>*<hello> seconds, it will declare neighbor down.
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<tag>type <M>broadcast</M><tag>
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BIRD detects a type of connected network. However, sometimes is
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necessary to change it. On broadcast networks are flooding
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and hello messages sent using multicasting. (Single
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packet to all neighbors.)
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<tag>type <M>nonbroadcast</M></tag>
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On nonbroadcast network are packets sent to each neighbor
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separately because of lack of multicast messages.
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<tag>type <M>pointopoint</M></tag>
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Pointopoint network connects just 2 routers together. No election
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is provided there, this reduces a number of sent messages.
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<tag>authetication <M>none</M></tag>
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No passwords are sent in OSPF's packets. This is default value.
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<tag>authetication <M>simple</M></tag>
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In every packet is sent an 8 bytes long password. Received packets
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without this password are ignored. This autentication mechanism is
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very weak.
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<tag>password <M>text</M></tag>
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An 8 bytes long password used for authentication.
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<tag>neighbors</tag>
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A set of neighbors to which hello messages on nonbroadcast networks
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are sent.
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</descrip>
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<sect1>Attributes
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<p>OSPF defines 3 route attributes. Each internal route has a metric. External
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routes uses metric type 1 or metric type 2. Metric type one is comparable
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with internal metric. Metric type 2 is always longer then metric type 1
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or internal metric. Each external route can also carry a tag. Tag is
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32 bits long number and it's used for exporting routes to other protocols
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in link-state it has no funtion.
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<sect1>Example
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<p>
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<code>
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protocol ospf MyOSPF {
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area 0.0.0.0 {
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tick 8;
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interface "eth*" {
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cost 11;
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hello 15;
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priority 100;
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retransmit 7;
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authentication simple;
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password "aaa";
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};
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interface "ppp*" {
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cost 100;
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};
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};
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area 120 {
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stub yes;
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interface "-arc0" , "arc*" {
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type nonbroadcast;
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authentication none;
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wait 50;
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dead count 6;
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neighbors {
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192.168.120.1;
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192.168.120.2;
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192.168.120.10;
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};
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};
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};
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}
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</code>
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<sect>Pipe
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<sect1>Introduction
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