OSPF Out-of-Band Link State Database (LSDB) Resynchronization
RFC 4811

 
Document Type RFC - Informational (March 2007; No errata)
Was draft-nguyen-ospf-oob-resync (individual in rtg area)
Last updated 2013-03-02
Stream IETF
Formats plain text pdf html
Stream WG state (None)
Consensus Unknown
Document shepherd No shepherd assigned
IESG IESG state RFC 4811 (Informational)
Telechat date
Responsible AD Bill Fenner
Send notices to lhnguyen@cisco.com, ospf-chairs@ietf.org
Network Working Group                                          L. Nguyen
Request for Comments: 4811                                        A. Roy
Category: Informational                                    Cisco Systems
                                                                A. Zinin
                                                          Alcatel-Lucent
                                                              March 2007

     OSPF Out-of-Band Link State Database (LSDB) Resynchronization

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.  Link State Database (LSDB) synchronization in OSPF is
   achieved via two methods -- initial LSDB synchronization when an OSPF
   router has just been connected to the network and asynchronous
   flooding that ensures continuous LSDB synchronization in the presence
   of topology changes after the initial procedure was completed.  It
   may sometime be necessary for OSPF routers to resynchronize their
   LSDBs.  The OSPF standard, however, does not allow routers to do so
   without actually changing the topology view of the network.

   This memo describes a vendor-specific mechanism to perform such a
   form of out-of-band LSDB synchronization.  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.               Informational                      [Page 1]
RFC 4811        OSPF Out-of-Band LSDB Resynchronization       March 2007

Table of Contents

   1. Introduction ....................................................2
   2. Proposed Solution ...............................................2
      2.1. The LR-Bit .................................................3
      2.2. OSPF Neighbor Data Structure ...............................3
      2.3. Hello Packets ..............................................4
      2.4. DBD Packets ................................................4
      2.5. Neighbor State Treatment ...................................7
      2.6. Initiating OOB LSDB Resynchronization ......................7
   3. Backward Compatibility ..........................................7
   4. Security Considerations .........................................7
   5. IANA Considerations .............................................7
   6. References ......................................................8
      6.1. Normative References .......................................8
      6.2. Informative References .....................................8
   Appendix A.  Acknowledgements ......................................9

1.  Introduction

   According to the OSPF standard [RFC2328], after two OSPF routers have
   established an adjacency (the neighbor Finite State Machines (FSMs)
   have reached Full state), routers announce the adjacency states in
   their router-Link State Advertisements (LSAs).  Asynchronous flooding
   algorithm ensures that routers' LSDBs stay in sync in the presence of
   topology changes.  However, if routers need (for some reason) to
   resynchronize their LSDBs, they cannot do that without actually
   putting the neighbor FSMs into the ExStart state.  This effectively
   causes the adjacencies to be removed from the router-LSAs, which may
   not be acceptable if the desire is to prevent routing table flaps
   during database resynchronization.  In this document, we provide the
   means for so-called out-of-band (OOB) LSDB resynchronization.

   The described mechanism can be used in a number of situations
   including those where the routers are picking up the adjacencies
   after a reload.  The process of adjacency preemption is outside the
   scope of this document.  Only the details related to LSDB
   resynchronization are mentioned herein.

2.  Proposed Solution

   With this Out-of-Band Resynchronization Solution, the format of the
   OSPF Database Description (DBD) packet is changed to include a new
   R-bit indicating OOB LSDB resynchronization.  All DBD packets sent
   during the OOB resynchronization procedure are sent with the R-bit
   set.

Nguyen, et al.               Informational                      [Page 2]
RFC 4811        OSPF Out-of-Band LSDB Resynchronization       March 2007
Show full document text