OSPF Overview

In an Open Shortest Path First (OSPF) network, the network topology is distributed among the nodes of the autonomous system (AS) and is regularly updated through the exchange of link-state advertisements (LSAs). As a result, OSPF is known as a link-state protocol. Because topology changes are flooded throughout the network, every node maintains the same copy of the network map in its local topological database. Packets are then routed based on the shared topology using the shortest path first (SPF) algorithm.

This overview contains the following topics:

• Link-State Advertisements
• Role of the Designated Router
• Path Cost Metrics
• Areas and Area Border Routers
• Role of the Backbone Area
• Stub Areas and Not-So-Stubby Areas

Note: The J-series Services Router supports both OSPF version 2 and OSPF version 3. In this guide, the term OSPF refers to both versions of the protocol.