ADC 3 Configuring OSPF

ADC Telecommunications, Inc.

298 CHAPTER 14: CONFIGURING IP

Configuring OSPF

Open Shortest Path First (OSPF) is a link-state-based interior gateway

protocol. With link-state routing protocols, routers maintain a link-state

database that contains current information on the state of each

communications link in the network topology. This information enables

routers to determine the best routes to each destination network within a

single autonomous system of networks.

The Cuda 12000 supports OSPF version 2 as defined in RFC 1583.

Configuring OSPF consists of the following tasks:

■Configuring OSPF Global Parameters

■Adding OSPF Areas

■Removing OSPF Areas

■Configuring OSPF on IP Interfaces

■Configuring OSPF Virtual Interfaces

■Removing OSPF Virtual Interfaces

Before you can effectively perform these tasks, you need to understand

certain concepts about OSPF.

In an OSPF environment, routers exchange link-state advertisements (LSAs)

which contain topology information, and they store these LSAs in link-state

databases. OSPF ensures that all routers have identical databases and the

same topology information.

Link-state databases include router addresses, links and their associated

costs, and network addresses. Routers use the link-state database and

Dijkstra’s algorithm (algorithm used to calculate best routes) to choose the

best route.

Link-state database size increases in proportion to network size. This causes

several problems. Demand for router resources, such as memory and CPU

time, can increase significantly. It also takes longer to calculate link costs for

more links and generate large routing tables that large networks require.