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OSPF Version 2 (RFC1247) Disclosure Number: IPCOM000002063D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2019-Feb-11

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10.17487/RFC1247: DOI


This memo documents version 2 of the OSPF protocol. OSPF is a link- state based routing protocol. [STANDARDS-TRACK]

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Network Working Group J. Moy Request for Comments: 1247 Proteon, Inc. Obsoletes: RFC 1131 July 1991

OSPF Version 2

Status of this Memo

This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the ‘‘IAB Official Protocol Standards’’ for the standardization state and status of this protocol. Distribution of this memo is unlimited.


This memo documents version 2 of the OSPF protocol. OSPF is a link- state based routing protocol. It is designed to be run internal to a single Autonomous System. Each OSPF router maintains an identical database describing the Autonomous System’s topology. From this database, a routing table is calculated by constructing a shortest-path tree.

OSPF recalculates routes quickly in the face of topological changes, utilizing a minimum of routing protocol traffic. OSPF provides support for equal-cost multipath. Separate routes can be calculated for each IP type of service. An area routing capability is provided, enabling an additional level of routing protection and a reduction in routing protocol traffic. In addition, all OSPF routing protocol exchanges are authenticated.

Version 1 of the OSPF protocol was documented in RFC 1131. The differences between the two versions are explained in Appendix F.

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1. Introduction

This document is a specification of the Open Shortest Path First (OSPF) internet routing protocol. OSPF is classified as an Internal Gateway Protocol (IGP). This means that it distributes routing information between routers belonging to a single Autonomous System. The OSPF protocol is based on SPF or link-state technology. This is a departure

[Moy] [Page 1]

RFC 1247 OSPF Version 2 July 1991

from the Bellman-Ford base used by traditional internet routing protocols.

The OSPF protocol was developed by the OSPF working group of the Internet Engineering Task Force. It has been designed expressly for the internet environment, including explicit support for IP subnetting, TOS-based routing and the tagging of externally-derived routing information. OSPF also provides for the authentication of routing updates, and utilizes IP multicast when sending/receiving the updates. In addition, much work has been done to produce a protocol that responds quickly to topology changes, yet involves small amounts of routing protocol traffic.

The author would like to thank Rob Coltun, Milo Medin, Mike Petry and the rest of the OSPF working group for the ideas and support they have given to this project.

1.1 Protocol overview

OSPF routes IP packets based solely on the destination IP address and IP Type of Service found in the IP packet header. IP packets are routed "as is" -- they are not encapsulated in any further protocol headers as they transit the Autonomous System. OSPF is a dynamic routing protocol. It quickly detects topological changes in the AS (such as route...