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Chapter 12 Avaya P330 Layer 3 Features
132 Avaya P334T-ML User’s Guide
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 P330 supports the OSPF routing protocol. The P330 can serve as an OSPF
Autonomous System Boundary Router (ASBR) by configuration of route
redistribution. The P330 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 P330 cannot
be configured to be an OSPF area border router itself.
The P330 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.