Administrator's Guide v4.1.1 Manual

Configuring OSPF
● OSPF overview............................................................................................................. 583
● Configuring OSPF......................................................................................................... 591
OSPF overview
Open Shortest Path First (OSPF) is a link-state routing protocol that uses link-state advertisements
(LSAs) to update neighboring routers about a router’s interfaces. Each router maintains an identical
area-topology database to determine the shortest path to any neighboring router.
OSPF is built upon a hierarchy of network components and areas. The highest level of the hierarchy is
the Autonomous System (AS). An autonomous system is defined as a number of networks, all of which
share the same routing and administration characteristics. A backbone area forms the core of the
network, connecting all other areas. Details of these and other OSPF components are provided below.
Autonomous System
An AS can be divided into multiple areas as shown in the figure below. Each area represents a
collection of contiguous networks and hosts (refer to OSPF areas on page 586). Areas limit the
amount of advertisements sent (called flooding) within the network. An area is represented in OSPF by
either an IP address or a number.
Network OS Administrator’s Guide
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