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OSPF Version 2
RFC 2328

Document type: RFC - Internet Standard (April 1998; Errata)
Obsoletes RFC 2178
Also Known As STD 54
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
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IESG State: RFC 2328 (Internet Standard)
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Network Working Group                                             J. Moy
Request for Comments: 2328                   Ascend Communications, Inc.
STD: 54                                                       April 1998
Obsoletes: 2178
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.

Copyright Notice

    Copyright (C) The Internet Society (1998).  All Rights Reserved.

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.  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.

    The differences between this memo and RFC 2178 are explained in
    Appendix G. All differences are backward-compatible in nature.

Moy                         Standards Track                     [Page 1]
RFC 2328                     OSPF Version 2                   April 1998

    Implementations of this memo and of RFCs 2178, 1583, and 1247 will
    interoperate.

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

Table of Contents

    1        Introduction ........................................... 6
    1.1      Protocol Overview ...................................... 6
    1.2      Definitions of commonly used terms ..................... 8
    1.3      Brief history of link-state routing technology ........ 11
    1.4      Organization of this document ......................... 12
    1.5      Acknowledgments ....................................... 12
    2        The link-state database: organization and calculations  13
    2.1      Representation of routers and networks ................ 13
    2.1.1    Representation of non-broadcast networks .............. 15
    2.1.2    An example link-state database ........................ 18
    2.2      The shortest-path tree ................................ 21
    2.3      Use of external routing information ................... 23
    2.4      Equal-cost multipath .................................. 26
    3        Splitting the AS into Areas ........................... 26
    3.1      The backbone of the Autonomous System ................. 27
    3.2      Inter-area routing .................................... 27
    3.3      Classification of routers ............................. 28
    3.4      A sample area configuration ........................... 29
    3.5      IP subnetting support ................................. 35
    3.6      Supporting stub areas ................................. 37
    3.7      Partitions of areas ................................... 38
    4        Functional Summary .................................... 40
    4.1      Inter-area routing .................................... 41
    4.2      AS external routes .................................... 41
    4.3      Routing protocol packets .............................. 42
    4.4      Basic implementation requirements ..................... 43
    4.5      Optional OSPF capabilities ............................ 46
    5        Protocol data structures .............................. 47
    6        The Area Data Structure ............................... 49
    7        Bringing Up Adjacencies ............................... 52
    7.1      The Hello Protocol .................................... 52
    7.2      The Synchronization of Databases ...................... 53
    7.3      The Designated Router ................................. 54
    7.4      The Backup Designated Router .......................... 56
    7.5      The graph of adjacencies .............................. 56

Moy                         Standards Track                     [Page 2]
RFC 2328                     OSPF Version 2                   April 1998

    8        Protocol Packet Processing ............................ 58
    8.1      Sending protocol packets .............................. 58

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