Avaya C360 - Manual (Page 167)

OSPF (Open Shortest Path First) Configuration
Issue 1 July 2006 167
OSPF (Open Shortest Path First) Configuration
OSPF Overview
OSPF is a routing protocol developed for IP networks based on the shortest path first or
link-state algorithm. It was introduced to overcome the limitations of RIP in increasingly complex
network designs.
OSPF is based on the cost of a particular path. In contrast, RIP uses hops as a path criterion.
Also, updates are sent on a "need to know" basis rather than every 30 seconds as with RIP.
The advantage of shortest path first algorithms is that they result in smaller more frequent
updates everywhere. They converge quickly, thus preventing such problems as routing loops
and Count-to-Infinity (when routers continuously increment the hop count to a particular
network). This stabilizes the network.
The disadvantage of shortest path first algorithms is that they require a lot of CPU power and
memory.
Routers use link-state algorithms to send routing information to all nodes in an internetwork by
calculating the shortest path to each node. This calculation is based on a topography of the
Internet constructed by each node. Each router sends that portion of the routing table (keeps
track of routes to particular network destinations) that describes the state of its own links, and it
also sends the complete routing structure (topography).
The C360 supports the OSPF routing protocol. The C360 can serve as an OSPF Autonomous
System Boundary Router (ASBR) by configuration of route redistribution. The C360 can be
installed in the OSPF backbone area (area 0.0.0.0) or in any OSPF area that is part of a multiple
areas network. However, the C360 cannot be configured to be an OSPF area border router
itself.
The C360 supports the equal-cost multipath (ECMP) feature which allows load balancing by
splitting traffic between several equivalent paths.
While OSPF can be activated with default values for each interface using a single command,
many of the OSPF parameters are configurable.
For a detailed description of OSPF, refer to the OSPF standards and published literature.