GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc4136

Network Working Group P. Pillay-Esnault Request for Comments: 4136 Cisco Systems Category: Informational July 2005

      OSPF Refresh and Flooding Reduction in Stable Topologies

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 Internet Society (2005).

Abstract

 This document describes an extension to the OSPF protocol to reduce
 periodic flooding of Link State Advertisements (LSAs) in stable
 topologies.
 Current OSPF behavior requires that all LSAs, except DoNotAge LSAs,
 to be refreshed every 30 minutes.  This document proposes to
 generalize the use of DoNotAge LSAs in order to reduce protocol
 traffic in stable topologies.

1. Introduction

 The explosive growth of IP-based networks has placed focus on the
 scalability of Interior Gateway Protocols such as OSPF.  Networks
 using OSPF are growing every day and will continue to expand to
 accommodate the demand for connections to the Internet or intranets.
 Internet Service Providers and users that have large networks have
 noticed non-negligible protocol traffic, even when their network
 topologies were stable.
 OSPF requires every LSA to be refreshed every 1800 seconds or else
 they will expire when they reach 3600 seconds [1].
 This document proposes to overcome the LSA expiration by generalizing
 the use of DoNotAge LSAs.  This technique will facilitate OSPF
 scaling by reducing OSPF traffic overhead in stable topologies.

Pillay-Esnault Informational [Page 1] RFC 4136 OSPF Refresh and Flooding Reduction July 2005

2. Changes in the Existing Implementation

 This enhancement relies on the implementation of the DoNotAge bit and
 the Indication-LSA.  The details of the implementation of the
 DoNotAge bit and the Indication-LSA are specified in "Extending OSPF
 to Support Demand Circuits" [2].
 Flooding-reduction-capable routers will continue to send hellos to
 their neighbors and keep aging their self-originated LSAs in their
 database.  However, these routers will flood their self-originated
 LSAs with the DoNotAge bit set.  Thus, self-originated LSAs do not
 have to be re-flooded every 30 minutes and the re-flooding interval
 can be extended to the configured forced-flooding interval.  As in
 normal OSPF operation, any change in the contents of the LSA will
 cause a reoriginated LSA to be flooded with the DoNotAge bit set.
 This will reduce protocol traffic overhead while allowing changes to
 be flooded immediately.
 Flooding-reduction-capable routers will flood received non-self-
 originated LSAs with the DoNotAge bit set on all normal or flooding-
 reduction-only interfaces within the LSA's flooding scope.  If an
 interface is configured as both flooding-reduction-capable and
 Demand-Circuit, then the flooding is done if and only if the contents
 of the LSA have changed.  This allows LSA flooding for unchanged LSAs
 to be periodically forced by the originating router.

3. Backward Compatibility

 Routers supporting the demand circuit extensions [2] will be able to
 correctly process DoNotAge LSAs flooded by routers supporting the
 flooding reduction capability described herein.  These routers will
 also suppress flooding DoNotAge LSAs on interfaces configured as
 demand circuits.  However, they will also flood DoNotAge LSAs on
 interfaces that are not configured as demand circuits.
 When there are routers in the OSPF routing domain, stub area, or NSSA
 area, that do not support the demand circuit extensions [2] then the
 use of these flooding reduction capabilities will be subject to the
 demand circuit interoperability constraints articulated in section
 2.5 of "Extending OSPF to Support Demand Circuits" [2].  This implies
 that detection of an LSA, with the DC bit clear, will result in the
 re-origination of self-originated DoNotAge LSAs with the DoNotAge
 clear and purging of non-self-originated DoNotAge LSAs.

Pillay-Esnault Informational [Page 2] RFC 4136 OSPF Refresh and Flooding Reduction July 2005

4. Security Considerations

 This memo does not create any new security issues for the OSPF
 protocol.  Security considerations for the base OSPF protocol are
 covered in [1].

5. Acknowledgments

 The author would like to thank Jean-Michel Esnault, Barry Friedman,
 Thomas Kramer, Acee Lindem, Peter Psenak, Henk Smit, and Alex Zinin
 for their helpful comments on this work.

6. Normative References

 [1] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
 [2] Moy, J., "Extending OSPF to Support Demand Circuits", RFC 1793,
     April 1995.

Pillay-Esnault Informational [Page 3] RFC 4136 OSPF Refresh and Flooding Reduction July 2005

A. Configurable Parameters

 This memo defines new configuration parameters for the flooding
 reduction feature.  The feature must be enabled by configuration on a
 router and is, by default, off.
  flooding-reduction <all | list of interfaces> Indicates that the
     router has the flooding reduction feature enabled.  By default,
     this parameter applies to all interfaces running under the OSPF
     instance to which it applies.  The feature can be enabled on a
     subset of explicitly specified interfaces.
  flooding-interval <n minutes> Indicates the interval in minutes for
     the periodic flooding of self-originated LSAs.  By default, this
     value is 30 minutes as per [1].  The minimum value is also 30
     minutes.  A value of infinity will prevent re-flooding of self-
     originated LSAs that have not changed.

Author's Address

 Padma Pillay-Esnault
 Cisco Systems
 170 W. Tasman Drive
 San Jose, CA  95134
 EMail: ppe@cisco.com

Pillay-Esnault Informational [Page 4] RFC 4136 OSPF Refresh and Flooding Reduction July 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at ietf-
 ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Pillay-Esnault Informational [Page 5]

/data/webs/external/dokuwiki/data/pages/rfc/rfc4136.txt · Last modified: 2005/07/28 17:31 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki