Network Working Group                                             J. Moy
Request for Comments: 1583                                 Proteon, Inc.
Obsoletes: 1247                                               March 1994
Category: Standards Track


                             OSPF Version 2



Status of this Memo

    This document specifies an Internet standards track protocol for the
    Internet community, and requests discussion and suggestions for
    improvements.  Please refer to the current edition of the "Internet
    Official Protocol Standards" (STD 1) for the standardization state
    and status of this protocol.  Distribution of this memo is
    unlimited.

Abstract

    This memo documents version 2 of the OSPF protocol.  OSPF is a
    link-state 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.

    OSPF Version 2 was originally documented in RFC 1247. The
    differences between RFC 1247 and this memo are explained in Appendix
    E. The differences consist of bug fixes and clarifications, and are
    backward-compatible in nature. Implementations of RFC 1247 and of
    this memo will interoperate.

    Please send comments to ospf@gated.cornell.edu.









 
RFC 1583                     OSPF Version 2                   March 1994


Table of Contents

    1       Introduction ........................................... 5
    1.1     Protocol Overview ...................................... 5
    1.2     Definitions of commonly used terms ..................... 6
    1.3     Brief history of link-state routing technology ......... 9
    1.4     Organization of this document .......................... 9
    2       The Topological Database .............................. 10
    2.1     The shortest-path tree ................................ 13
    2.2     Use of external routing information ................... 16
    2.3     Equal-cost multipath .................................. 20
    2.4     TOS-based routing ..................................... 20
    3       Splitting the AS into Areas ........................... 21
    3.1     The backbone of the Autonomous System ................. 22
    3.2     Inter-area routing .................................... 22
    3.3     Classification of routers ............................. 23
    3.4     A sample area configuration ........................... 24
    3.5     IP subnetting support ................................. 30
    3.6     Supporting stub areas ................................. 31
    3.7     Partitions of areas ................................... 32
    4       Functional Summary .................................... 34
    4.1     Inter-area routing .................................... 35
    4.2     AS external routes .................................... 35
    4.3     Routing protocol packets .............................. 35
    4.4     Basic implementation requirements ..................... 38
    4.5     Optional OSPF capabilities ............................ 39
    5       Protocol data structures .............................. 41
    6       The Area Data Structure ............................... 42
    7       Bringing Up Adjacencies ............................... 45
    7.1     The Hello Protocol .................................... 45
    7.2     The Synchronization of Databases ...................... 46
    7.3     The Designated Router ................................. 47
    7.4     The Backup Designated Router .......................... 48
    7.5     The graph of adjacencies .............................. 49
    8       Protocol Packet Processing ............................ 50
    8.1     Sending protocol packets .............................. 51
    8.2     Receiving protocol packets ............................ 53
    9       The Interface Data Structure .......................... 55
    9.1     Interface states ...................................... 58
    9.2     Events causing interface state changes ................ 61