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OSPF Restart Signaling
RFC 4812

Document type: RFC - Informational (March 2007; Errata)
Was draft-nguyen-ospf-restart (individual in rtg area)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 4812 (Informational)
Responsible AD: Bill Fenner
Send notices to: lhnguyen@cisco.com, ospf-chairs@tools.ietf.org

Network Working Group                                          L. Nguyen
Request for Comments: 4812                                        A. Roy
Category: Informational                                    Cisco Systems
                                                                A. Zinin
                                                          Alcatel-Lucent
                                                              March 2007

                         OSPF Restart Signaling

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   OSPF is a link-state intra-domain routing protocol used in IP
   networks.  Routers find new and detect unreachable neighbors via the
   Hello subprotocol.  Hello OSPF packets are also used to ensure two-
   way connectivity within time.  When a router restarts its OSPF
   software, it may not know its neighbors.  If such a router sends a
   Hello packet on an interface, its neighbors are going to reset the
   adjacency, which may not be desirable in certain conditions.

   This memo describes a vendor-specific mechanism that allows OSPF
   routers to inform their neighbors about the restart process.  Note
   that this mechanism requires support from neighboring routers.  The
   mechanism described in this document was proposed before Graceful
   OSPF Restart, as described in RFC 3623, came into existence.  It is
   implemented/supported by at least one major vendor and is currently
   deployed in the field.  The purpose of this document is to capture
   the details of this mechanism for public use.  This mechanism is not
   an IETF standard.

Nguyen, et al.                Experimental                      [Page 1]
RFC 4812                 OSPF Restart Signaling               March 2007

Table of Contents

   1. Introduction ....................................................2
   2. Proposed Solution ...............................................2
      2.1. Sending Hello Packets with the RS-bit Set ..................3
      2.2. Receiving Hello Packets with the RS-Bit Set ................3
      2.3. Ensuring Topology Stability ................................4
   3. Backward Compatibility ..........................................4
   4. Security Considerations .........................................4
   5. IANA Considerations .............................................4
   6. References ......................................................5
      6.1. Normative References .......................................5
      6.2. Informative References .....................................5
   Appendix A.  Acknowledgements ......................................6

1.  Introduction

   While performing a graceful restart of OSPF software [RFC3623],
   routers need to prevent their neighbors from resetting their
   adjacencies.  However, after a reload, routers may not be aware of
   the neighbors they had adjacencies with in their previous
   incarnations.  If such a router sends a Hello packet on an interface
   and this packet does not list some neighbors, those neighbors will
   reset the adjacency with the restarting router.

   This document describes a technique that allows restarting routers to
   inform their neighbors that they may not know about some neighbors
   yet and the absence of some router IDs in the Hello packets should be
   ignored.

2.  Proposed Solution

   With this Restart Signaling Solution, a new bit, called RS (restart
   signal), is introduced into the Extended Options (EO) TLV in the
   Link-Local Signaling (LLS) block (see [RFC4813]).  The value of this
   bit is 0x00000002; see Figure 1 below.

   +---+---+---+---+---+---+---+- -+---+---+---+---+---+---+---+---+
   | * | * | * | * | * | * | * |...| * | * | * | * | * | * | RS| LR|
   +---+---+---+---+---+---+---+- -+---+---+---+---+---+---+---+---+

                  Figure 1.  Bits in Extended Options TLV

   For a definition of the LR-bit, see [RFC4811].

Nguyen, et al.                Experimental                      [Page 2]
RFC 4812                 OSPF Restart Signaling               March 2007

2.1.  Sending Hello Packets with the RS-bit Set

   OSPF routers should set the RS-bit in the EO-TLV attached to a Hello
   packet when it is not known that all neighbors are listed in this
   packet, but the restarting router wants them to preserve their
   adjacencies.  The RS-bit must not be set in Hello packets longer than
   RouterDeadInterval seconds.

2.2.  Receiving Hello Packets with the RS-Bit Set

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