Network Working Group Padma Pillay-Esnault Internet Draft Juniper Networks Expiration Date:June 2001 December 2000 OSPF Refresh and flooding reduction in stable topologies draft-pillay-esnault-ospf-flooding-03.txt Status 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. 1. Abstract This document describes extension to the OSPF protocol [1] to optimize flooding of Link State Advertisements (LSA) in stable topologies. The current behavior of OSPF requires that all LSA be refreshed every 30 minutes regardless of the stability of the network except for Do Not Age (DNA) LSA [2]. This document proposes to generalize the use of DNA LSA so as to reduce protocol traffic in stable networks. Pillay-Esnault [Page 1] Internet Draft draft-pillay-esnault-ospf-flooding-03.txt November 1999 2. Motivation The explosive growth of IP based networks has placed the focus on the scalability of the Interior Gateway Protocols such as OSPF. The networks using OSPF are larger everyday and will continue to expand to accommodate the demand to connect to the Internet or intra nets. Internet Service Providers and users having large networks have noticed of a non negligible protocol traffic even when their network topology was stable. By design OSPF requires LSA to be refreshed as they expire after 3600 seconds. Some implementations have tried to improve the flooding by reducing its frequency to refresh from 30 minutes to around 50 minutes or so. This solution presents the advantage of cutting down the amount of refresh traffic but will require at least one refresh before the LSA expires. This document proposes to overcome the LSA expiration by implementing the generalization of DO NOT AGE LSA use. By reducing considerably the traffic overhead in stable topologies OSPF will scale better. 3. Changes in the existing implementation. The existing OSPF Demand Circuit feature [2] provides the premise of the Do Not Age LSA implementation. The goal here is to reduce refreshing and flooding of already known and unchanged information. To achieve this, the Link State Advertisements will now be flooded over all interfaces with the higher bit set thus making them DO NOT AGE LSAs. The LSA originator can then set the refresh rate to what ever it is configured to. It can be configured for periodic refresh over extended periods (days, weeks or months) or even never at all. All the routers should implement the DoNotAge bit as defined by Section 2 of RFC 1793. 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 [Ref1]. The enhancement rely heavily on the Demand Circuit mechanism and come at the same costs as described in [2] section 6. Pillay-Esnault [Page 2] Internet Draft draft-pillay-esnault-ospf-flooding-03.txt November 1999 5. Acknowledgments The author would like to thank Jean-Michel Esnault, Barry Friedman, Thomas Kramer, Peter Psenak and Henk Smit for their helpful comments on this work. 6. References [1] RFC 2328 OSPF Version 2. J. Moy. April 1998. (Format: TXT=447367 bytes) (Obsoletes RFC2178) (Also STD0054) (Status: STANDARD) [2] RFC 1793 Extending OSPF to Support Demand Circuits. J. Moy. April 1995. (Format: TXT=78728 bytes) (Status: PROPOSED STANDARD) 7. Authors' Addresses Padma Pillay-Esnault Juniper Networks 1194 N, Mathilda Avenue Sunnyvale, CA 94089-1206 Email: padma@juniper.net Pillay-Esnault [Page 3]