Users Guide

Open Shortest Path First (OSPFv2)

Open Shortest Path First (OSPFv2) is supported on Dell Networking OS.

OSPF protocol standards are listed in the Standards Compliance chapter.

Topics:

• Protocol Overview

• Implementing OSPF with Dell Networking OS

• Configuration Information

• Configuration Task List for OSPFv3 (OSPF for IPv6)

Protocol Overview

OSPF routing is a link-state routing protocol that calls for the sending of link-state advertisements (LSAs) to all

other routers within the same autonomous system (AS) areas.

Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. As OSPF

routers accumulate link-state information, they use the shortest path first (SPF) algorithm to calculate the

shortest path to each node.

OSPF routers initially exchange HELLO messages to set up adjacencies with neighbor routers. The HELLO

process is used to establish adjacencies between routers of the AS. It is not required that every router within

the AS areas establish adjacencies. If two routers on the same subnet agree to become neighbors through the

HELLO process, they begin to exchange network topology information in the form of LSAs.

In OSPFv2 neighbors on broadcast and NBMA links are identified by their interface addresses, while neighbors

on other types of links are identified by RID.

Autonomous System (AS) Areas

OSPF operates in a type of hierarchy.

The largest entity within the hierarchy is the autonomous system (AS), which is a collection of networks under

a common administration that share a common routing strategy. OSPF is an intra-AS (interior gateway)

routing protocol, although it can receive routes from and sending routes to other ASs.

You can divide an AS into a number of areas, which are groups of contiguous networks and attached hosts.

Routers with multiple interfaces can participate in multiple areas. These routers, called area border routers

(ABRs), maintain separate databases for each area. Areas are a logical grouping of OSPF routers identified by

an integer or dotted-decimal number.

Areas allow you to further organize your routers within in the AS. One or more areas are required within the

AS. Areas are valuable in that they allow sub-networks to "hide" within the AS, thus minimizing the size of the

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