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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
<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>Open Shortest Path First (OSPF) is a quite complex interior gateway
protocol. The current IPv4 version (OSPFv2) is defined in RFC 2328
<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2328.txt">. It's a link
state (a.k.a. shortest path first) protocol -- Each router maintains a database
describing the autonomous system's topology. Each participating router
has an identical copy of the database and all routers run the same algorithm
calculating a shortest path tree with themselves as a root.
OSPF choses the least cost path as the best path.
<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
period of convergence. This period of convergence is short and involves
a minimum of routing traffic.
period of convergence. This period is short and involves only minimal
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.
<p>Each router participating in OSPF routing periodically sends Hello messages
to all its interfaces. This allows neighbors to be discovered dynamically.
Then the neighbors exchange theirs parts of the link state database and keep it
identical by flooding updates. The flooding process is reliable and ensures
that each router detects all changes.
<sect1>Configuration
@ -914,11 +918,11 @@ that each routes detects the change.
<code>
protocol ospf &lt;name&gt; {
rfc1583compat bool;
rfc1583compat &lt;bool&gt;;
area &lt;id&gt; {
stub &lt;bool&gt;;
tick &lt;num&gt;;
interface &lt;interface&gt;
interface &lt;interface pattern&gt;
{
cost &lt;num&gt;;
hello &lt;num&gt;;
@ -939,93 +943,92 @@ protocol ospf &lt;name&gt; {
<descrip>
<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
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.
This defines an OSPF area with given area ID (an integer or an IPv4
address, similarly to a router ID).
The most important area is
the backbone (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.
No external routes are flooded into stub areas. 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.
The routing table calculation is not performed when a single link state
change arrives. To lower the CPU utilization, it's processed later
at periodical intervals of <m/num/ seconds. The default value is 7.
<tag>interface <M>interface</M></tag>
This mean that specified interface (or interface pattern) belongs
to actual area.
<tag>interface <M>pattern</M></tag>
Defines that the specified interfaces belong to the area being defined.
<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>
Specifies interval between sending hello messages. Beware, all
router on the same network has to have the same hello interval.
Specifies interval in seconds between sending of Hello messages. Beware, all
routers on the same network need to have the same hello interval.
Default value is 10.
<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.
<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
On every multiple access network (e.g., the Ethernet) Designed Router
and Backup Designed router are elected. These routers have some
special functions in the flooding process. Higher priority increases
preferences in this election. 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
After start, router waits for the specified number of seconds 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
<m/dead count/*<m/hello/ seconds, it will declare neighbor down.
When the router does not receive any messages from a neighbor in
<m/dead count/*<m/hello/ seconds, it will consider the 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 broadcast</tag>
BIRD detects a type of a connected network automatically, but sometimes it's
convenient to force use of a different type manually.
On broadcast networks, flooding and Hello messages are sent using multicasts (a single packet for all the 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 nonbroadcast</tag>
On nonbroadcast networks, the packets are sent to each neighbor
separately because of lack of multicast capabilities.
<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>type pointopoint</tag>
Point-to-point networks connect just 2 routers together. No election
is performed there which reduces the number of messages sent.
<tag>authetication <M>none</M></tag>
No passwords are sent in OSPF's packets. This is default value.
<tag>authetication none</tag>
No passwords are sent in OSPF packets. This is the 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
<tag>authetication simple</tag>
Every packet carries 8 bytes of password. Received packets
lacking this password are ignored. This autentication mechanism is
very weak.
<tag>password <M>text</M></tag>
An 8 bytes long password used for authentication.
An 8-byte password used for authentication.
<tag>neighbors</tag>
A set of neighbors to which hello messages on nonbroadcast networks
are sent.
A set of neighbors to which Hello messages on nonbroadcast networks
are to be 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.
<p>OSPF defines three route attributes. Each internal route has a metric. External
routes use metric type 1 or metric type 2. A metric of type 1 is comparable
with internal metrics, a metric of type 2 is always longer than any metric of type 1
or any internal metric. Each external route can also carry a tag which is
a 32-bit integer which is used when exporting routes to other protocols; otherwise,
it doesn't affect routing inside the OSPF domain at all.
<sect1>Example