Network Working Group Padma Pillay-Esnault Internet Draft Juniper Networks June 2003 Category: Informational Expires: December 2003 OSPF Refresh and Flooding Reduction in Stable Topologies draft-pillay-esnault-ospf-flooding-07.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. 1. Abstract This document describes an extension to the OSPF protocol to reduce periodic flooding of Link State Advertisements in stable topologies. The OSPF current behavior requires that all LSAs other than DoNotAge LSAs to be refreshed every 30 minutes. This document proposes to generalize the use of DoNotAge LSAs to reduce protocol traffic in stable topologies Pillay-Esnault [Page 1] Internet Draft OSPF Refresh and Flooding Reduction March 2003 2. Motivation 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 having 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. 3. 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, they will flood their self-originated LSAs with the DoNotAge bit set. Hence, self-originated LSAs do not have to be reflooded every 30 minutes and the reflooding 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 both as 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. Pillay-Esnault [Page 2] Internet Draft OSPF Refresh and Flooding Reduction March 2003 4. 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 which 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 capability 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. 5. 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]. 6. Intellectual Property Considerations The IETF has been notified by Cisco Systems of intellectual property rights claimed in regard to some or all of the specifications contained in this document. For more information please refer to the IETF web page http://www.ietf.org/ietf/IPR/CISCO-OSPF-REFRESH.txt 7. 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. 8. Normative References [1] RFC 2328 OSPF Version 2. J. Moy. April 1998. [2] RFC 1793 Extending OSPF to Support Demand Circuits. J. Moy. April 1995. Pillay-Esnault [Page 3] Internet Draft OSPF Refresh and Flooding Reduction March 2003 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 Indicates that the router has flooding reduction feature enabled. By default, it 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 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 reflooding of self-originated LSAs that have not changed. Pillay-Esnault [Page 4] Internet Draft OSPF Refresh and Flooding Reduction March 2003 9. Authors' Addresses Padma Pillay-Esnault Juniper Networks 1194 N, Mathilda Avenue Sunnyvale, CA 94089-1206 Email: padma@juniper.net Pillay-Esnault [Page 5]