Network Working Group Padma Pillay-Esnault Internet Draft Juniper Networks March 2003 Expires: October 2003 OSPF Refresh and Flooding Reduction in Stable Topologies draft-pillay-esnault-ospf-flooding-05.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 eliminate or reduce periodic flooding of Link State Advertisements in stable topologies. The current behavior of OSPF requires that all LSAs be refreshed every 30 minutes regardless of the stability of the network except for DoNotAge LSAs. 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 heavily on the OSPF Demand Circuit extension. The details of the implementation of the DC-bit, DoNotAge bit and the Indication-LSA are specified in "Extending OSPF to Support Demand Circuits" [2]. The flooding reduction capable routers will continue to send hellos to their neighbors and keep their aging self-originated LSAs in their database. However, they will flood their self-originated LSAs with the DoNotAge bit set. Hence, self-originated LSAs need not be reflooded unless there is change in the contents of the LSA. This will reduce the protocol traffic overhead while allowing changes to be flooded immediately. 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 DoNotLSAs 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. Configuration of the flooding reduction capable routers Implementations of this flooding reduction capability must provide a knob to activate/deactivate the feature and by default it should be disabled. The flooding reduction capability can be enabled globally or on selected interfaces. It should be also possible to specify a forced flooding interval of unchanged self-originated LSAs. 6. 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]. Pillay-Esnault [Page 3] Internet Draft OSPF Refresh and Flooding Reduction March 2003 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. 9. Authors' Addresses Padma Pillay-Esnault Juniper Networks 1194 N, Mathilda Avenue Sunnyvale, CA 94089-1206 Email: padma@juniper.net Pillay-Esnault [Page 4]