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diff --git a/doc/bird.sgml b/doc/bird.sgml index 32c28ea7..2bdbed0d 100644 --- a/doc/bird.sgml +++ b/doc/bird.sgml @@ -877,6 +877,193 @@ protocol kernel { # Secondary routing table <sect>OSPF +<sect1>Introduction + +<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="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. 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. + +<sect1>Configuration + +<p> + +<code> +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 { + <ip>; + }; + }; + }; +} +</code> + +<descrip> + <tag>rfc1583compat <M>bool</M></tag> + This option can disable or enable compatibility of routing table + calculation with RFC 1583<htmlurl + url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. 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. + + <tag>neighbors</tag> + A set of neighbors to which hello messages on nonbroadcast networks + are sent. +</descrip> + +<sect1>Attributes + +<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. + +<sect1>Example + +<p> + +<code> +protocol ospf MyOSPF { + area 0.0.0.0 { + 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 { + 192.168.120.1; + 192.168.120.2; + 192.168.120.10; + }; + }; + }; +} +</code> + <sect>Pipe <sect1>Introduction |