Network Working Group Alex Zinin Internet Draft Abhay Roy Expiration Date: July 2001 Liem Nguyen File name: draft-ietf-ospf-restart-00.txt Cisco Systems November 2000 OSPF Restart Signaling draft-ietf-ospf-restart-00.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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "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. Abstract OSPF is a link-state intra-domain routing protocol used in IP networks. Routers find new and detect unreachable neighbors via Hello subprotocol. Hello OSPF packets are also used to ensure two-way connectivity within time. When a router restarts its OSPF software, it may not know its neighbors. If such a router sends a hello packet on an interface, its neighbors are going to reset the adjacency, which may not be desirable in certain conditions. This memo provides a mechanism that allows OSPF routers to inform their neighbors about the restart process. Note that this mechanism requires support from neighboring routers. 1 Motivation Zinin, Roy, Nguyen [Page 1]
INTERNET DRAFT OSPF Restart Signaling November 2000 While performing a graceful restart of OSPF software [OSPF], routers need to prevent their neigbors from reseting their adjacencies. However, after a reload, routers may not be aware of the neighbors they had adjacencies with in their previous incarnations. If such a router sends a Hello packet on an interface and this packet does not list some neighbors, those neighbors will reset the adjacency with restarting router. This document describes a technique that allows restarting routers to inform their neighbors that they may not know about some neighbors yet and the absence of some router-IDs in the Hello packets should be ignored. 2 Proposed solution A new bit, called RS (restart signal) is introduced into Extended Options TLV in the LLS block (see [LLS]). The value of this bit is TBD (temporarily used value is 0x00000002, see Figure 1 below). +---+---+---+---+---+---+---+- -+---+---+---+---+---+---+---+---+ | * | * | * | * | * | * | * |...| * | * | * | * | * | * | RS| OR| +---+---+---+---+---+---+---+- -+---+---+---+---+---+---+---+---+ Figure 1. Bits in Extended Options TLV OSPF routers should set the RS-bit in the EO-TLV attached to a Hello packet when this is not clear that all neighbors are listed in this packet, but the restarting router wants them to preserve their adjacencies. The RS-bit may not be set in Hello packets longer than RouterDeadInterval seconds. For a definition of the OR bit, see [OOB]. 2.2 Receiving Hello Packets with RS-bit set When an OSPF router receives a Hello packet, containing the LLS block with the EO-TLV which has the RS-bit set, the router should skip the two-way connectivity check with the announcing neighbor (i.e., the router should not generate a 1-WayReceived event for the neighbor if it does not find its own router ID in the list of neighbors as described in 10.5 of [OSPF]), provided that the neighbor FSM for this neighbor is in the Full state. It is also recommended that a unicast Hello is sent back to the sender in reply to a Hello packet with RS bit set. This is to speed up learning of previously known neighbors. When sending such a reply packet, care must be taken to ensure that the RS bit is clear in it. Zinin, Roy, Nguyen [Page 2]
INTERNET DRAFT OSPF Restart Signaling November 2000 3 Compatibility Issues The described technique requires cooperation from neighboring routers. However, if neighbors do not support this technique, they will just reset the adjacency. 4 Security Considerations The described technique does not introduce any new security issues into OSPF protocol. 5 Acknowledgements The authors would like to thank Russ White, Don Slice, and Alvaro Retana for their valuable comments. 6 References [OSPF]J. Moy. OSPF version 2. Technical Report RFC 2328, Internet Engineering Task Force, 1998. ftp://ftp.isi.edu/in- notes/rfc2328.txt. [LLS] Zinin, Friedman, Roy, Nguyen, Yeung, "OSPF Link-local Signal- ing", draft-ietf-ospf-lls-00.txt, Work in progress. [OOB] Zinin, Roy, Nguyen, "OSPF Out-of-band LSDB resynchronization", draft-ietf-ospf-oob-resync-00.txt, Work in progress. 7 Authors' addresses Alex Zinin Abhay Roy Cisco Systems Cisco Systems 150 W. Tasman Dr. 170 W. Tasman Dr. San Jose,CA 95134 San Jose,CA 95134 USA USA E-mail: azinin@cisco.com E-mail: akr@cisco.com Liem Nguyen 7025 Kit Creek Rd. Research Triangle Park, NC 27709 USA e-mail: lhnguyen@cisco.com Zinin, Roy, Nguyen [Page 3]
