Explanation of an OSPF Area (168515)


The information in this article applies to:

  • Microsoft Windows NT Server 4.0
  • Microsoft Routing and Remote Access Service Update for Windows NT Server 4.0
This article was previously published under Q168515

SUMMARY

An Autonomous System (AS) in an Open Shortest Path First (OSPF) routed network can be broken up into areas. An OSPF area, based on the same concept as IP subnets, consists of a group of networks logically linked and sharing a single link state database (LSDB).

MORE INFORMATION

Routers within a single area maintain the same LSDB and communicate this information to each other by flooding the area with link state advertisements (LSA).

A router that is connected to more than one area is called an area border router (ABR). ABRs are most commonly used to connect tie areas together by being connected its own area and the backbone area. An area border router advertises a summary of its area information to other area border routers using summary advertisements. This area topology significantly reduces the amount of traffic between routers. It also reduces the size of the LSDB within an area. Since the LSDB is used to calculate the SPF, this size reduction can be a significant performance enhancement on the router.

Area ID's are 32-bit numbers and in dotted decimal notation. The area ID is in no way related to the IP address of a network. However, it is possible to logically associate these numbers for administrative convenience.
Modification Type:MajorLast Reviewed:8/10/2001
Keywords:kbnetwork KB168515
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