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Spelling and style corrections to the OSPF section.

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Martin Mares 2000-06-07 13:54:24 +00:00
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@ -879,34 +879,38 @@ protocol kernel { # Secondary routing table
<sect1>Introduction <sect1>Introduction
<p>Open Shortest Path First (OSPF) is quite complex interior gateway <p>Open Shortest Path First (OSPF) is a quite complex interior gateway
protocol. Today's version for IPv4 is 2 and it's defined in RFC 2328<htmlurl protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328
url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's based on <htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
link-state of SPF technology. Each router maintains a database state (a.k.a. shortest path first) protocol -- Each router maintains a database
describing the Autonomous System's topology. Each participating router has describing the autonomous system's topology. Each participating router
has an identical database and all routers run the exact same algorithm has an identical copy of the database and all routers run the same algorithm
calculatin shortest path tree with themselves as roots, in parallel. calculating a shortest path tree with themselves as a root.
OSPF chooses the least cost path as the best path. In OSPF, the OSPF choses the least cost path as the best path.
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 <p>In OSPF, the autonomous system can be split to several areas in order
to reduce the amount of resources consumed for exchanging the routing
information and to protect the other areas from incorrect routing data.
Topology of the area is hidden to the rest of the autonomous system.
Unfortunatelly multiple OSPF areas are not yet fully supported
by this version of BIRD and neither is the IPv6 version (OSPFv3).
<p>Another very important feature of OSPF is that
it can keep routing information from other protocols (like Static or BGP)
in its link state database as external routes. Each external route can
be tagged by the advertising router, making possible to pass 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 as router interface failures) and calculates new loop-free routes after a
period of convergence. This period of convergence is short and involves period of convergence. This period is short and involves only minimal
a minimum of routing traffic. routing traffic.
<p>Each router joined in OSPF periodically sends hello messages out <p>Each router participating in OSPF routing periodically sends Hello messages
all its interfaces. This allows neighbors to be discovered dynamically. to all its interfaces. This allows neighbors to be discovered dynamically.
Then the neighbors exchange theirs parts of database. And keep it Then the neighbors exchange theirs parts of the link state database and keep it
identical flooding updates. Flooding proces is reliable and ensures identical by flooding updates. The flooding process is reliable and ensures
that each routes detects the change. that each router detects all changes.
<sect1>Configuration <sect1>Configuration
@ -914,11 +918,11 @@ that each routes detects the change.
<code> <code>
protocol ospf &lt;name&gt; { protocol ospf &lt;name&gt; {
rfc1583compat bool; rfc1583compat &lt;bool&gt;;
area &lt;id&gt; { area &lt;id&gt; {
stub &lt;bool&gt;; stub &lt;bool&gt;;
tick &lt;num&gt;; tick &lt;num&gt;;
interface &lt;interface&gt; interface &lt;interface pattern&gt;
{ {
cost &lt;num&gt;; cost &lt;num&gt;;
hello &lt;num&gt;; hello &lt;num&gt;;
@ -939,93 +943,92 @@ protocol ospf &lt;name&gt; {
<descrip> <descrip>
<tag>rfc1583compat <M>bool</M></tag> <tag>rfc1583compat <M>bool</M></tag>
This option can disable or enable compatibility of routing table This option controls compatibility of routing table
calculation with RFC 1583<htmlurl calculation with RFC 1583<htmlurl
url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default url="ftp://ftp.rfc-editor.org/in-notes/rfc1583.txt">. Default
value is no. value is no.
<tag>area <M>id</M></tag> <tag>area <M>id</M></tag>
This specifies area id of configured OSPF area. It can be written This defines an OSPF area with given area ID (an integer or an IPv4
as a number or as an IPv4 number. The most important area is address, similarly to a router ID).
the backbone (area id 0) to which every other area must be connected. The most important area is
the backbone (ID 0) to which every other area must be connected.
<tag>stub <M>bool</M></tag> <tag>stub <M>bool</M></tag>
No external routes are flooded into stub area. Default value is no. No external routes are flooded into stub areas. Default value is no.
<tag>tick <M>num</M></tag> <tag>tick <M>num</M></tag>
The routing table calculation is not processed when any single The routing table calculation is not performed when a single link state
change comes. To lower the CPU utilization it's processed late change arrives. To lower the CPU utilization, it's processed later
in periodical interval. The default value is 7. at periodical intervals of <m/num/ seconds. The default value is 7.
<tag>interface <M>interface</M></tag> <tag>interface <M>pattern</M></tag>
This mean that specified interface (or interface pattern) belongs Defines that the specified interfaces belong to the area being defined.
to actual area.
<tag>cost <M>num</M></tag> <tag>cost <M>num</M></tag>
Specifies output cost of interface. Default value is 10. Specifies output cost (metric) of an interface. Default value is 10.
<tag>hello <M>num</M></tag> <tag>hello <M>num</M></tag>
Specifies interval between sending hello messages. Beware, all Specifies interval in seconds between sending of Hello messages. Beware, all
router on the same network has to have the same hello interval. routers on the same network need to have the same hello interval.
Default value is 10. Default value is 10.
<tag>retransmit <M>num</M></tag> <tag>retransmit <M>num</M></tag>
Specifies interval between retransmiting unacknoledged update. Specifies interval in seconds between retransmissions of unacknoledged updates.
Default value is 5. Default value is 5.
<tag>priority <M>num</M></tag> <tag>priority <M>num</M></tag>
On every multiple access network (like e.g ethernet) Designed On every multiple access network (e.g., the Ethernet) Designed Router
and Backup Designed router is elected. These routers have some and Backup Designed router are elected. These routers have some
special functions in flooding process. Higher priority rices special functions in the flooding process. Higher priority increases
preferences in elections. Routers with priority 0 are not preferences in this election. Routers with priority 0 are not
eligible. Default value is 1. eligible. Default value is 1.
<tag>wait <M>num</M></tag> <tag>wait <M>num</M></tag>
After start, router waits specified interval between starting After start, router waits for the specified number of seconds between starting
election and building adjacency. Default value is 40. election and building adjacency. Default value is 40.
<tag>dead count <M>num</M></tag> <tag>dead count <M>num</M></tag>
When router does not receive any message from neighbor in When the router does not receive any messages from a neighbor in
<m/dead count/*<m/hello/ seconds, it will declare neighbor down. <m/dead count/*<m/hello/ seconds, it will consider the neighbor down.
<tag>type <M>broadcast</M></tag> <tag>type broadcast</tag>
BIRD detects a type of connected network. However, sometimes is BIRD detects a type of a connected network automatically, but sometimes it's
necessary to change it. On broadcast networks are flooding convenient to force use of a different type manually.
and hello messages sent using multicasting. (Single On broadcast networks, flooding and Hello messages are sent using multicasts (a single packet for all the neighbors).
packet to all neighbors.)
<tag>type <M>nonbroadcast</M></tag> <tag>type nonbroadcast</tag>
On nonbroadcast network are packets sent to each neighbor On nonbroadcast networks, the packets are sent to each neighbor
separately because of lack of multicast messages. separately because of lack of multicast capabilities.
<tag>type <M>pointopoint</M></tag> <tag>type pointopoint</tag>
Pointopoint network connects just 2 routers together. No election Point-to-point networks connect just 2 routers together. No election
is provided there, this reduces a number of sent messages. is performed there which reduces the number of messages sent.
<tag>authetication <M>none</M></tag> <tag>authetication none</tag>
No passwords are sent in OSPF's packets. This is default value. No passwords are sent in OSPF packets. This is the default value.
<tag>authetication <M>simple</M></tag> <tag>authetication simple</tag>
In every packet is sent an 8 bytes long password. Received packets Every packet carries 8 bytes of password. Received packets
without this password are ignored. This autentication mechanism is lacking this password are ignored. This autentication mechanism is
very weak. very weak.
<tag>password <M>text</M></tag> <tag>password <M>text</M></tag>
An 8 bytes long password used for authentication. An 8-byte password used for authentication.
<tag>neighbors</tag> <tag>neighbors</tag>
A set of neighbors to which hello messages on nonbroadcast networks A set of neighbors to which Hello messages on nonbroadcast networks
are sent. are to be sent.
</descrip> </descrip>
<sect1>Attributes <sect1>Attributes
<p>OSPF defines 3 route attributes. Each internal route has a metric. External <p>OSPF defines three route attributes. Each internal route has a metric. External
routes uses metric type 1 or metric type 2. Metric type one is comparable routes use metric type 1 or metric type 2. A metric of type 1 is comparable
with internal metric. Metric type 2 is always longer then metric type 1 with internal metrics, a metric of type 2 is always longer than any metric of type 1
or internal metric. Each external route can also carry a tag. Tag is or any internal metric. Each external route can also carry a tag which is
32 bits long number and it's used for exporting routes to other protocols a 32-bit integer which is used when exporting routes to other protocols; otherwise,
in link-state it has no funtion. it doesn't affect routing inside the OSPF domain at all.
<sect1>Example <sect1>Example