Network Working Group L. NguyenInternet-DraftRequest for Comments: 4812 A. RoyIntended status:Category: Informational Cisco SystemsExpires: April 29, 2007A. Zinin AlcatelOctober 26, 2006February 2007 OSPF Restart Signalingdraft-nguyen-ospf-restart-06.txtStatus ofthisThis MemoBy 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 ofThis memo provides information for the InternetEngineering 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.community. Itis inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The listdoes not specify an Internet standard ofcurrent Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The listany kind. Distribution ofInternet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 29, 2007.this memo is unlimited. Copyright Notice Copyright (C) TheInternet Society (2006). AbstractIETF Trust (2007). Abstract OSPF is a link-state intra-domain routing protocol used in IP networks. Routers find new and detect unreachable neighbors via the 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 ahelloHello packet on an interface, its neighbors are going to reset the adjacency, which may not be desirable in certain conditions. This memo describes avendor specificvendor-specific mechanism that allows OSPF routers to inform their neighbors about the restart process. Note that this mechanism requires support from neighboring routers. The mechanism described in this document was proposed before Graceful OSPFRestart [RFC3623]Restart, as described in RFC 3623, came into existence. It isimplemented/ supportedimplemented/supported by at least one major vendor and is currently deployed in the field. The purpose of this document is to capture the details of this mechanism for public use. This mechanism is not an IETF standard. Table of Contents 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4....................................................2 2. Proposed Solution. . . . . . . . . . . . . . . . . . . . . . 5...............................................2 2.1. Sending Hello Packets with the RS-bitset . . . . . . . . 5Set ..................3 2.2. Receiving Hello Packets withRS-bit set . . . . . . . . . 5the RS-Bit Set ................3 2.3.Insuring topology stability . . . . . . . . . . . . . . . 6Ensuring Topology Stability ................................4 3. Backward Compatibility. . . . . . . . . . . . . . . . . . . . 7..........................................4 4. Security Considerations. . . . . . . . . . . . . . . . . . . 8.........................................4 5. IANA Considerations. . . . . . . . . . . . . . . . . . . . . 9.............................................4 6. References. . . . . . . . . . . . . . . . . . . . . . . . . . 10......................................................5 6.1. Normative References. . . . . . . . . . . . . . . . . . . 10.......................................5 6.2. Informative References. . . . . . . . . . . . . . . . . . 10.....................................5 Appendix A.Acknowledgments . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 13Acknowledgements ......................................6 1. Introduction While performing a graceful restart of OSPF software[OSPF],[RFC3623], routers need to prevent their neighbors from resetting 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 the 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 somerouter-IDsrouter IDs in the Hello packets should be ignored.1.1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [RFC2119].2. Proposed Solution With this Restart Signaling Solution,Aa new bit, called RS (restart signal), is introduced into the Extended Options (EO) TLV in theLLSLink-Local Signaling (LLS) block (see[LLS]).[RFC4813]). The value of this bit is 0x00000002; see Figure 1 below. +---+---+---+---+---+---+---+- -+---+---+---+---+---+---+---+---+ | * | * | * | * | * | * | * |...| * | * | * | * | * | * | RS| LR| +---+---+---+---+---+---+---+- -+---+---+---+---+---+---+---+---+ Figure 1. Bits in Extended Options TLV For a definition of theLR bit,LR-bit, see[OOB].[RFC4811]. 2.1. Sending Hello Packets with the RS-bitsetSet OSPF routers should set the RS-bit in the EO-TLV attached to a Hello packet when it is not known that all neighbors are listed in this packet, but the restarting router wants them to preserve their adjacencies. The RS-bit must not be set in Hello packets longer than RouterDeadInterval seconds. 2.2. Receiving Hello Packets withRS-bit setthe RS-Bit Set When an OSPF router receives a Hellopacket,packet containing the LLS block with the EO-TLVwhichthat 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 Section 10.5 of [RFC2328]), provided that the neighborFSMFinite State Machine (FSM) for this neighbor is in the Full state. The router should also send a unicast Hello back to the sender in reply to a Hello packet withRS bitRS-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 theRS bitRS-bit is clear in it. Two additional fields are introduced in the neighbor data structure: RestartState flag and ResyncTimeout timer. RestartState flag indicates that a Hello packet with the RS-bit set has been received and the local router expects its neighbor to go through theLSDBLink State Database (LSDB) resynchronization procedure using[OOB].[RFC4811]. ResyncTimeout is asingle- shotsingle-shot timer limiting the delay between the first seen Hello packet with the RS-bit set and initialization of the LSDB resynchronization procedure. The length of ResyncTimeout timer is RouterDeadInterval seconds. When a Hello packet with the RS-bit set is received and RestartState flag is not set for the neighbor, the router sets RestartState flag and starts ResyncTimeout timer. If ResyncTimeout expires, RestartState flag is cleared and a 1-WayReceived event is generated for the neighbor. If, while ResyncTimeout timer is running, the neighbor starts LSDB resynchronization procedure using[OOB],[RFC4811], ResyncTimeout timer iscancelled.canceled. The router also clears RestartState flag on completion of the LSDB resynchronization process. Two or more routers on the same segment cannot have Hello packets with the RS-bit set at the same time, as can be the case when two or more routers restart at about the same time. In such a scenario, the routers should clear the RestartState flag, cancel the ResyncTimeout timer, and generate a 1-WayReceived event. 2.3.Insuring topology stabilityEnsuring Topology Stability Under certaincircumstancescircumstances, it might be desirable to stop announcing the restarting router as fully adjacent if this may lead to possible routing loops. In order to provide this functionality, a configurable option is provided on the neighboring routers that instructs the OSPF process to follow the logics described below. When an OSPF router schedules a routing table calculation due to a change in the contents of its LSDB, it should also reset all adjacencies with restarting routers (those with RestartState set to TRUE) by clearing the RestartState neighbor flags, canceling ResyncTimeout timers (if running), and generating the 1-WayReceived events for the neighbor FSMs. 3. Backward Compatibility 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 the OSPF protocol. 5. IANA Considerations Please refer to the "IANA Considerations" section of[LLS][RFC4813] for more information on the Extended Options bit definitions. 6. References 6.1. Normative References[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate Requirement Levels", RFC 2119, March 1997.[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC3623] Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF Restart", RFC 3623, November 2003. 6.2. Informative References[LLS][RFC4813] Friedman, B., Nguyen, L., Roy, A., Yeung, D., and A. Zinin, "OSPFLink-localLink-Local Signaling",Work in progress , October 2006. [OOB]RFC 4813, February 2007. [RFC4811] Nguyen, L., Roy, A., and A. Zinin, "OSPFOut-of-band LSDB resynchronization", Work in progress , October 2006.Out-of-Band Link State Database (LSDB) Resynchronization", RFC 4811, February 2007. Appendix A. Acknowledgments The authors would like to thank John Moy, Russ White, Don Slice, and Alvaro Retana for their valuable comments. Authors' Addresses Liem Nguyen Cisco Systems 225 West Tasman Drive San Jose, CA 95134 USAEmail:EMail: lhnguyen@cisco.com Abhay Roy Cisco Systems 225 West Tasman Drive San Jose, CA 95134 USAEmail:EMail: akr@cisco.com Alex Zinin Alcatel Sunnyvale, CA USAEmail:EMail: zinin@psg.com Full Copyright Statement Copyright (C) TheInternet Society (2006).IETF Trust (2007). 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. 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