OSPF Working Group R. Ogier Internet-Draft June 19, 2006 Expires: December 19, 2006 OSPF Database Exchange Summary List Optimization draft-ogier-ospf-dbex-opt-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on December 19, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document describes a backward compatible optimization for the Database Exchange process in OSPFv2 and OSPFv3. In this optimization, a router does not list an LSA in Database Description packets sent to a neighbor, if the same or a more recent instance of the LSA was listed in a Database Description packet already received from the neighbor. This optimization reduces Database Description overhead by about 50% in large networks. This optimization does not affect synchronization, since it only omits unnecessary information from Database Description packets. Ogier Expires December 19, 2006 [Page 1] Internet-Draft MANET Extension of OSPF June 2006 1. Introduction In OSPFv2 [RFC2328] and OSPFv3 [RFC2740], when two neighboring routers become adjacent, they synchronize their link-state databases via the Database Exchange process. Each router sends the other router a set of Database Description (DD) packets that describes the router's link-state database for the area. This is done by listing each LSA (i.e., including the header of each LSA) in one of the sent DD packets. This procedure allows each router to determine whether the other router has newer LSA instances that should be requested via Link State Request packets. The proposed optimization simply observes that it is not necessary for a router (master or slave) to list an LSA in a DD packet if it knows the neighbor already has an instance of the LSA that is the same or more recent (and therefore will not request the LSA). To avoid listing such LSAs in DD packets, when an LSA is listed in a DD packet received from the neighbor, and the Database summary list for the neighbor has an instance of the LSA that is the same or less recent than the one received, the LSA is removed from the summary list. The proposed optimization, called the Database Exchange summary list optimization, does not affect synchronization, since the LSAs that are omitted from DD packets are unnecessary. The optimization is fully backward compatible with OSPF. The optimization reduces Database Description overhead by about 50% in large networks, since it reduces the total number of LSA headers exchanged by about one- half when the two routers are already nearly synchronized. The optimization is especially beneficially in large networks with limited bandwidth, such as large mobile ad hoc networks. 2. Specification of Proposed Optimization The Database Exchange summary list optimization is defined by modifying Section 10.6 (Receiving Database Description Packets) of RFC 2328 as follows. The second-to-last paragraph of Section 10.6 is replaced with the following augmented paragraph: When the router accepts a received Database Description Packet as the next in sequence the packet contents are processed as follows. For each LSA listed, the LSA's LS type is checked for validity. If the LS type is unknown (e.g., not one of the LS types 1-5 defined by this specification), or if this is an AS- external-LSA (LS type = 5) and the neighbor is associated with a stub area, generate the neighbor event SeqNumberMismatch and stop processing the packet. Otherwise, the router looks up the LSA in its database to see whether it also Ogier Expires December 19, 2006 [Page 2] Internet-Draft MANET Extension of OSPF June 2006 has an instance of the LSA. If it does not, or if the database copy is less recent (see Section 13.1), the LSA is put on the Link state request list so that it can be requested (immediately or at some later time) in Link State Request Packets. The router also looks up the LSA in the Database summary list for the neighbor. If the Database summary list contains an instance of the LSA that is the same or less recent than the one listed in the received packet, the LSA is removed from the Database summary list. 3. Security Considerations This document does not raise any new security concerns. 4. IANA Considerations This document proposes a simple backward compatible optimization for OSPFv2 and OSPFv3, which does not require any new number assignment. 5. Normative References [RFC2328] J. Moy. "OSPF Version 2", RFC 2328, April 1998. [RFC2740] R. Coltun, D. Ferguson, and J. Moy. "OSPF for IPv6", RFC 2740, December 1999. Author's Address Richard G. Ogier Email: rich.ogier@earthlink.net Ogier Expires December 19, 2006 [Page 3] Internet-Draft MANET Extension of OSPF June 2006 Intellectual Property Statement 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. 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Disclaimer of Validity 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. Copyright Statement Copyright (C) The Internet Society (2006). 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. Ogier Expires December 19, 2006 [Page 4]