Spelling and style corrections to the OSPF section.
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doc/bird.sgml
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doc/bird.sgml
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@ -879,34 +879,38 @@ protocol kernel { # Secondary routing table
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<sect1>Introduction
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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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<p>Open Shortest Path First (OSPF) is a 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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protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328
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url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's based on
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<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
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link-state of SPF technology. Each router maintains a database
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state (a.k.a. shortest path first) protocol -- Each router maintains a database
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describing the Autonomous System's topology. Each participating router has
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describing the autonomous system's topology. Each participating router
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has an identical database and all routers run the exact same algorithm
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has an identical copy of the database and all routers run the same algorithm
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calculatin shortest path tree with themselves as roots, in parallel.
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calculating a shortest path tree with themselves as a root.
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OSPF chooses the least cost path as the best path. In OSPF, the
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OSPF choses the least cost path as the best path.
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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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<p>In OSPF, the autonomous system can be split to several areas in order
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to reduce the amount of resources consumed for exchanging the routing
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information and to protect the other areas from incorrect routing data.
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Topology of the area is hidden to the rest of the autonomous system.
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Unfortunatelly multiple OSPF areas are not yet fully supported
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by this version of BIRD and neither is the IPv6 version (OSPFv3).
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<p>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 its link state database as external routes. Each external route can
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be tagged by the advertising router, making possible to pass 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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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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period of convergence. This period is short and involves only minimal
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a minimum of routing traffic.
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routing traffic.
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<p>Each router joined in OSPF periodically sends hello messages out
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<p>Each router participating in OSPF routing periodically sends Hello messages
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all its interfaces. This allows neighbors to be discovered dynamically.
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to 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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Then the neighbors exchange theirs parts of the link state database and keep it
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identical flooding updates. Flooding proces is reliable and ensures
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identical by flooding updates. The flooding process is reliable and ensures
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that each routes detects the change.
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that each router detects all changes.
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<sect1>Configuration
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<sect1>Configuration
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@ -914,11 +918,11 @@ that each routes detects the change.
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<code>
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<code>
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protocol ospf <name> {
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protocol ospf <name> {
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rfc1583compat bool;
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rfc1583compat <bool>;
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area <id> {
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area <id> {
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stub <bool>;
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stub <bool>;
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tick <num>;
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tick <num>;
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interface <interface>
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interface <interface pattern>
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{
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{
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cost <num>;
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cost <num>;
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hello <num>;
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hello <num>;
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@ -939,93 +943,92 @@ protocol ospf <name> {
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<descrip>
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<descrip>
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<tag>rfc1583compat <M>bool</M></tag>
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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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This option controls compatibility of routing table
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calculation with RFC 1583<htmlurl
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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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url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
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value is no.
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value is no.
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<tag>area <M>id</M></tag>
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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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This defines an OSPF area with given area ID (an integer or an IPv4
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as a number or as an IPv4 number. The most important area is
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address, similarly to a router ID).
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the backbone (area id 0) to which every other area must be connected.
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The most important area is
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the backbone (ID 0) to which every other area must be connected.
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<tag>stub <M>bool</M></tag>
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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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No external routes are flooded into stub areas. Default value is no.
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<tag>tick <M>num</M></tag>
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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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The routing table calculation is not performed when a single link state
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change comes. To lower the CPU utilization it's processed late
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change arrives. To lower the CPU utilization, it's processed later
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in periodical interval. The default value is 7.
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at periodical intervals of <m/num/ seconds. The default value is 7.
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<tag>interface <M>interface</M></tag>
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<tag>interface <M>pattern</M></tag>
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This mean that specified interface (or interface pattern) belongs
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Defines that the specified interfaces belong to the area being defined.
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to actual area.
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<tag>cost <M>num</M></tag>
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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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Specifies output cost (metric) of an interface. Default value is 10.
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<tag>hello <M>num</M></tag>
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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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Specifies interval in seconds between sending of Hello messages. Beware, all
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router on the same network has to have the same hello interval.
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routers on the same network need to have the same hello interval.
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Default value is 10.
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Default value is 10.
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<tag>retransmit <M>num</M></tag>
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<tag>retransmit <M>num</M></tag>
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Specifies interval between retransmiting unacknoledged update.
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Specifies interval in seconds between retransmissions of unacknoledged updates.
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Default value is 5.
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Default value is 5.
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<tag>priority <M>num</M></tag>
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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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On every multiple access network (e.g., the Ethernet) Designed Router
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and Backup Designed router is elected. These routers have some
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and Backup Designed router are elected. These routers have some
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special functions in flooding process. Higher priority rices
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special functions in the flooding process. Higher priority increases
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preferences in elections. Routers with priority 0 are not
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preferences in this election. Routers with priority 0 are not
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eligible. Default value is 1.
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eligible. Default value is 1.
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<tag>wait <M>num</M></tag>
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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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After start, router waits for the specified number of seconds between starting
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election and building adjacency. Default value is 40.
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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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<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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When the router does not receive any messages from a neighbor in
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<m/dead count/*<m/hello/ seconds, it will declare neighbor down.
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<m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
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<tag>type <M>broadcast</M></tag>
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<tag>type broadcast</tag>
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BIRD detects a type of connected network. However, sometimes is
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BIRD detects a type of a connected network automatically, but sometimes it's
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necessary to change it. On broadcast networks are flooding
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convenient to force use of a different type manually.
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and hello messages sent using multicasting. (Single
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On broadcast networks, flooding and Hello messages are sent using multicasts (a single packet for all the neighbors).
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packet to all neighbors.)
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<tag>type <M>nonbroadcast</M></tag>
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<tag>type nonbroadcast</tag>
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On nonbroadcast network are packets sent to each neighbor
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On nonbroadcast networks, the packets are sent to each neighbor
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separately because of lack of multicast messages.
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separately because of lack of multicast capabilities.
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<tag>type <M>pointopoint</M></tag>
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<tag>type pointopoint</tag>
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Pointopoint network connects just 2 routers together. No election
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Point-to-point networks connect just 2 routers together. No election
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is provided there, this reduces a number of sent messages.
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is performed there which reduces the number of messages sent.
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<tag>authetication <M>none</M></tag>
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<tag>authetication none</tag>
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No passwords are sent in OSPF's packets. This is default value.
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No passwords are sent in OSPF packets. This is the default value.
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<tag>authetication <M>simple</M></tag>
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<tag>authetication simple</tag>
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In every packet is sent an 8 bytes long password. Received packets
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Every packet carries 8 bytes of password. Received packets
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without this password are ignored. This autentication mechanism is
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lacking this password are ignored. This autentication mechanism is
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very weak.
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very weak.
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<tag>password <M>text</M></tag>
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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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An 8-byte password used for authentication.
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<tag>neighbors</tag>
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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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A set of neighbors to which Hello messages on nonbroadcast networks
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are sent.
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are to be sent.
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</descrip>
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</descrip>
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<sect1>Attributes
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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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<p>OSPF defines three 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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routes use metric type 1 or metric type 2. A metric of type 1 is comparable
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with internal metric. Metric type 2 is always longer then metric type 1
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with internal metrics, a metric of type 2 is always longer than any metric of type 1
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or internal metric. Each external route can also carry a tag. Tag is
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or any internal metric. Each external route can also carry a tag which is
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32 bits long number and it's used for exporting routes to other protocols
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a 32-bit integer which is used when exporting routes to other protocols; otherwise,
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in link-state it has no funtion.
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it doesn't affect routing inside the OSPF domain at all.
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<sect1>Example
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<sect1>Example
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