Network Working Group Padma Pillay-Esnault Internet Draft Juniper Networks January 2003 Category: Standards Track Expires: June 2003 OSPF Refresh and Flooding Reduction in Stable Topologies draft-pillay-esnault-ospf-flooding-04.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 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 so as to reduce protocol traffic in stable topologies. Pillay-Esnault Standards Track [Page 1] Internet Draft OSPF Refresh and Flooding Reduction January 2003 2. Motivation The explosive growth of IP based networks has placed the focus on the scalability of the Interior Gateway Protocols such as OSPF. Networks using OSPF are larger everyday and will continue to expand to accommodate the demand to connect to the Internet or intranets. Internet Service Providers and users having large networks have noticed non-negligible protocol traffic even when their network topology was 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 but will flood their Link State Advertisements (LSAs) with the DoNotAge bit set. This will reduce the protocol traffic overhead while allowing changes to be flooded immediately. Pillay-Esnault Standards Track [Page 2] Internet Draft OSPF Refresh and Flooding Reduction January 2003 4. Deployment 4.1 Routers supporting the OSPF Demand Circuit capability. All routers supporting OSPF Demand Circuit will be able to interoperate with the routers supporting the flooding reduction. For routers supporting OSPF Demand Circuits but do NOT support the new Flooding Reduction capability but have to interoperate with routers having the Flooding Reduction capability there are two possibilities: (1) Demand Circuit is not configured In this case, the router older implementation will send its LSAs without the DoNotAge bit set and it will need to refresh its LSAs periodically. It will however receive DoNotAge LSAs from the flooding reduction capable routers and will keep them as such in its own database. (2) Demand Circuit is configured All DC routers will set the DoNotAge bit on their own LSAs and will suppress hellos. The flooding reduction capable routers will run as DC as well. 4.2 Router not supporting the OSPF Demand Circuit capability. For routers that do not support OSPF Demand Circuit Feature have no knowledge how to handle DoNotAge LSAs and the LSAs with the DoNotAge bit set will appear as expired LSAs in their own database. The DCbitless LSAs must be used here to detect the presence of those routers not supporting the OSPF Demand Circuit and indication LSAs will be use as described in [2] to inform other routers of the presence of routers incapable to handling DoNotAge LSAs. In the presence of routers not supporting DC-bit, the Flooding Reduction capable routers must flush all the DoNotAge LSAs and revert to sending normal aging LSAs. 5. Configuration of the Flooding Reduction capable routers The implementations of Flooding Reduction capability must provide a knob to activate/deactivate the feature and by default it should be disabled. It should be also possible to specify a forced periodic refresh interval of Link State Advertisements. Pillay-Esnault Standards Track [Page 3] Internet Draft OSPF Refresh and Flooding Reduction January 2003 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]. 7. 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. 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 Standards Track [Page 4] Internet Draft OSPF Refresh and Flooding Reduction January 2003 IPR Notice The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Pillay-Esnault Standards Track [Page 5] Internet Draft OSPF Refresh and Flooding Reduction January 2003 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Pillay-Esnault Standards Track [Page 6]