3Com 10014299 manual Ospf Overview, Displaying and Debugging Ospf, Ospf Configuration Example

29 CONFIGURING OSPF

	This chapter covers the following topics:
	■	OSPF Overview
	■	Configuring OSPF
	■ Displaying and Debugging OSPF
	■	OSPF Configuration Example
OSPF Overview	Open Shortest Path First (OSPF) is an autonomous, link-state-based internal

routing protocol developed by Internet Engineering Task Force (IETF). The current version is version 2 (RFC1583), which features the following:

■ Applicable range — Supports networks of various sizes and hundreds of routers.

■ Fast convergence — Sends an update message immediately after the topological structure of the network is changed, so the change can be synchronized in the autonomous system.

■ No self-loop — OSPF calculates the route with the shortest path tree algorithm through the collected link status. This algorithm ensures that no self-loop route is generated.

■ Area division — An AS network can be divided into areas and the routing information between the areas is further abstracted, reducing the bandwidth occupation in the network.

■ Equivalent route ----support multiple equivalent routes to the same destination

address.

■ Route level --- the four levels of routes according to different priorities: intra-area routes, inter-area routes, external route class 1 and external route class 2.

■ Authentication ---- support interface-based message authentication to ensure

the security of the route computation.

■ Multicast ---packets are transmitted and received with multicast address on multicasting link layer, greatly reducing interference to other netw ork devices.

The entire network is composed of multiple autonomous systems (AS). The link state of an AS is collected and transmitted to determine and propagate the route dynamically and then synchronize the information of the AS. Each system is divided into areas. If a router port is allocated to multiple areas, it is an area boundary router (ABR) since it is located at the boundary and connected with multiple areas. Routing information of another area can be learned from the ABR. All ABRs and the routers between them form a backbone area, tagged with