--- 1/draft-ietf-bfd-v4v6-1hop-04.txt 2006-06-14 22:12:25.000000000 +0200 +++ 2/draft-ietf-bfd-v4v6-1hop-05.txt 2006-06-14 22:12:25.000000000 +0200 @@ -1,19 +1,19 @@ Network Working Group D. Katz Internet Draft Juniper Networks D. Ward Cisco Systems -Expires: April, 2006 October, 2005 +Expires: December, 2006 June, 2006 BFD for IPv4 and IPv6 (Single Hop) - draft-ietf-bfd-v4v6-1hop-04.txt + draft-ietf-bfd-v4v6-1hop-05.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 @@ -26,45 +26,45 @@ 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 Copyright Notice - Copyright (C) The Internet Society (2005). All Rights Reserved. + Copyright (C) The Internet Society (2006). All Rights Reserved. Abstract This document describes the use of the Bidirectional Forwarding - Detection protocol over IPv4 and IPv6 for single IP hops. It further - describes the use of BFD with OSPFv2, OSPFv3, and IS-IS. Comments on - this draft should be directed to rtg-bfd@ietf.org. + Detection protocol over IPv4 and IPv6 for single IP hops. Comments + on this draft should be directed to rtg-bfd@ietf.org. Conventions used in this document 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 RFC-2119 [KEYWORDS]. 1. Introduction One very desirable application for BFD [BFD] is to track IPv4 and IPv6 connectivity between directly-connected systems. This could be - used to supplement the detection mechanisms in IS-IS and OSPF, or to - monitor router-host connectivity, among other applications. + used to supplement the detection mechanisms in routing protocols, or + to monitor router-host connectivity, among other applications. This document describes the particulars necessary to use BFD in this - environment, and describes how BFD can be used in conjunction OSPFv2 - [OSPFv2], OSPFv3 [OSPFv3], and IS-IS [ISIS]. + environment. Interactions between BFD and other protocols and system + functions are described in the BFD Generic Applications document + [BFD-GENERIC]. 2. Applications and Limitations This application of BFD can be used by any pair of systems communicating via IPv4 and/or IPv6 across a single IP hop that can be associated with an incoming interface. This includes, but is not limited to, physical media, virtual circuits, and tunnels. Each BFD session between a pair of systems MUST traverse a separate path in both directions. @@ -173,236 +173,43 @@ address changes, the local system MUST NOT use that address as the destination in outgoing BFD Control packets; rather it MUST continue to use the address configured at session creation. An implementation MAY notify the application that the neighbor's source address has changed, so that the application might choose to change the destination address or take some other action. Note that the TTL/Hop Count check described in section 5 (or the use of authentication) precludes the BFD packets from having come from any source other than the immediate neighbor. -7. BFD for use with OSPFv2, OSPFv3, and IS-IS - - The two versions of OSPF, as well as IS-IS, all suffer from an - architectural limitation, namely that their Hello protocols are - limited in the granularity of their failure detection times. In - particular, OSPF has a minimum detection time of two seconds, and IS- - IS has a minimum detection time of one second. - - BFD MAY be used to achieve arbitrarily small detection times for - these protocols by supplementing the Hello protocols used in each - case. - - It should be noted that the purpose of using BFD in this context is - not to replace the adjacency timeout mechanism, nor is it to - demonstrate that the network is fully functional for the use of the - routing protocol, but is simply to advise the routing protocol that - there are problems forwarding the data protocol for which the routing - protocol is calculating routes. - -7.1. Session Establishment - - The mechanism by which a BFD session is established in this - environment is outside the scope of this specification. An obvious - choice would be to use the discovery mechanism inherent in the Hello - protocols in OSPF and IS-IS to bootstrap the establishment of a BFD - session. - - Any BFD sessions established to support OSPF and IS-IS across a - single IP hop MUST operate in accordance with the rest of this - document. - - If multiple routing protocols wish to establish BFD sessions with the - same remote system for the same data protocol, all MUST share a - single BFD session. - -7.2. Session Parameters - - The setting of the various timing parameters and modes in this - application are outside the scope of this specification. - - Note that all protocols sharing a session will operate using the same - parameters. The mechanism for choosing the parameters among those - desired by the various protocols are outside the scope of this - specification. - -7.3. Interactions with OSPF and IS-IS without Graceful Restart - - Slightly different mechanisms are used if the routing protocol - supports the routing of multiple data protocols, depending on whether - the routing protocol supports separate topologies for each data - protocol. With a shared topology, if one of the data protocols fails - (as signalled by the associated BFD session), it is necessary to - consider the path to have failed for all data protocols, since there - is otherwise no way for the routing protocol to turn away traffic for - the failed protocol (and such traffic would be black holed - indefinitely.) - - With individual routing topologies for each data protocol, only the - failed data protocol needs to be rerouted around the failed path. - - Therefore, when a BFD session transitions from Up to Down, action - SHOULD be taken in the routing protocol to signal the lack of - connectivity for the data protocol (IPv4 or IPv6) over which BFD is - running. If only one data protocol is being advertised in the - routing protocol Hello, or if multiple protocols are being advertised - but the protocols must share a common topology, a Hello protocol - timeout SHOULD be emulated for the associated OSPF neighbors and/or - IS-IS adjacencies. - - If multiple data protocols are advertised in the routing protocol - Hello, and the routing protocol supports different topologies for - each data protocol, the failing data protocol SHOULD no longer be - advertised in Hello packets in order to signal a lack of connectivity - for that protocol. - - Note that it is possible in some failure scenarios for the network to - be in a state such that the IGP comes up, but the BFD session cannot - be established, and, more particularly, data cannot be forwarded. To - avoid this situation, it would be beneficial to not allow the IGP to - establish a neighbor/adjacency. However, this would preclude the - operation of the IGP in an environment in which not all systems - support BFD. - - Therefore, if a BFD session is not in Up state (possibly because the - remote system does not support BFD), it is OPTIONAL to preclude the - establishment of an OSPF neighbor or an IS-IS adjacency. The choice - of whether to do so SHOULD be controlled by means outside the scope - of this specification, such as configuration or other mechanisms. If - an OSPF neighbor or IS-IS adjacency is established but the - corresponding BFD session is not in Up state (implying that the - neighbor does not support BFD) implementations MAY raise the BFD - transmit interval beyond the minimum of one second in order to - minimize extraneous traffic. - -7.4. Interactions with OSPF and IS-IS with Graceful Restart - - The Graceful Restart functions in OSPF [OSPF-GRACE] and IS-IS [ISIS- - GRACE] are predicated on the existence of a separate forwarding plane - that does not necessarily share fate with the control plane in which - the routing protocols operate. In particular, the assumption is that - the forwarding plane can continue to function while the protocols - restart and sort things out. - - BFD implementations announce via the Control Plane Independent (C) - bit whether or not BFD shares fate with the control plane. This - information is used to determine the actions to be taken in - conjunction with Graceful Restart. - - If BFD does not share its fate with the control plane on either - system, it can be used to determine whether Graceful Restart is NOT - viable (the forwarding plane is not operating.) In this situation, - if a BFD session fails while graceful restart is taking place, and - BFD is independent of the control plane on the local system, and the - remote system has been transmitting BFD Control packets with the C - bit set, the graceful restart SHOULD be aborted and the topology - change made visible to the network as outlined in section 7.3. - - If BFD shares its fate with the control plane on either system - (either the local system shares fate with the control plane, or the - remote system is transmitting BFD packets with the C bit set to - zero), it is not useful during graceful restart, as the BFD session - is likely to fail regardless of the state of the forwarding plane. - The action to take in this case depends on the capabilities of the - IGP. - -7.4.1. OSPF Graceful Restart With Control Plane Fate Sharing - - OSPF has a "planned" restart mechanism, in which the restarting - system notifies its neighbors that it is about to perform a restart. - In this situation, if a BFD session fails while the neighbor is - performing a graceful restart, the graceful restart SHOULD be allowed - to complete and the topology change should not be made visible to the - network as outlined in section 7.3. - - For unplanned restarts (in which the neighbor has not notified the - local system of its intention to restart), the OSPF Graceful Restart - specification allows a Graceful Restart to take place if the system - restarts prior to the expiration of the OSPF neighbor relationship. - In this case, the BFD Detection Time is likely to expire prior to the - restart, and the neighbor relationship SHOULD be torn down. In the - unlikely event that the system restarts quickly enough, and the - system chooses to attempt a Graceful Restart, the graceful restart - SHOULD be allowed to complete and the topology change should not be - made visible to the network as outlined in section 7.3. - -7.4.2. ISIS Graceful Restart With Control Plane Fate Sharing - - ISIS Graceful Restart does not signal a "planned" restart; its - mechanism does not begin until after the system has restarted. If - the BFD session expires prior to the restart of the system, there is - no way for the neighbors to know that a Graceful Restart will take - place. - - If a planned restart is about to place, the restarting system MAY - change the BFD timing parameters on a temporary basis in such a way - as to make the Detection Time greater than or equal to the ISIS - adjacency timeout. This will provide the restarting system the same - opportunity to enter Graceful Restart as it would have without BFD. - - In this case, the restarted system SHOULD avoid sending any BFD - Control packets until there is a high likelihood that its neighbors - know it is performing a Graceful Restart, since the neighbors will - tear down their BFD sessions when those sessions restart. - - In any case, if a BFD session fails while the neighbor is known to be - performing a Graceful Restart, the Graceful Restart SHOULD be allowed - to complete and the topology change should not be made visible to the - network as outlined in section 7.3. - - If the BFD session fails, and it is not known whether the neighbor is - performing a Graceful Restart, the BFD session failure SHOULD be made - visible to the network as outlined in section 7.3. - -7.5. OSPF Virtual Links - - If it is desired to use BFD for failure detction of OSPF Virtual - Links, the mechanism described in [BFD-MULTI] MUST be used, since - OSPF Virtual Links may traverse an arbitrary number of hops. BFD - Authentication SHOULD be used and is strongly encouraged. - -8. BFD for use with Tunnels +7. BFD for use with Tunnels A number of mechanisms are available to tunnel IPv4 and IPv6 over arbitrary topologies. If the tunnel mechanism does not decrement the TTL or hop count of the network protocol carried within, the mechanism described in this document may be used to provide liveness detection for the tunnel. The BFD Authentication mechanism SHOULD be used and is strongly encouraged. Normative References [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", - draft-ietf-bfd-base-04.txt, October, 2005. + draft-ietf-bfd-base-05.txt, June, 2006. - [BFD-MULTI] Katz, D., and Ward, D., "BFD for Multihop Paths", draft- - ietf-bfd-multihop-03.txt, July, 2005. + [BFD-GENERIC] Katz, D., and Ward, D., "Generic Application of BFD", + draft-ietf-bfd-generic-02.txt, June, 2006. [GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism (GTSM)", RFC 3682, February 2004. - [ISIS] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual - environments", RFC 1195, December 1990. - - [ISIS-GRACE] Shand, M., and Ginsberg, L., "Restart signaling for IS- - IS", RFC 3847, July 2004. - [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. - [OSPFv2] Moy, J., "OSPF Version 2", RFC 2328, April 1998. - - [OSPFv3] Coltun, R., et al, "OSPF for IPv6", RFC 2740, December 1999. - - [OSPF-GRACE] Moy, J., et al, "Graceful OSPF Restart", RFC 3623, - November 2003. - Security Considerations In this application, the use of TTL=255 on transmit and receive is viewed as supplying equivalent security characteristics to other protocols used in the infrastructure, as it is not trivially spoofable. The security implications of this mechanism are further discussed in [GTSM]. The security implications of the use of BFD Authentication are discussed in [BFD]. @@ -429,23 +236,22 @@ Dave Ward Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA Phone: +1-408-526-4000 Email: dward@cisco.com Changes from the previous draft - Text was added to point out that implementations may raise the BFD - transmit interval above the minimum if it appears that the neighbor - does not support BFD. All other changes are editorial in nature. + Application-specific information was moved to the Generic draft. All + other changes are purely editorial in nature. IPR Disclaimer 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 @@ -459,30 +265,30 @@ http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Full Copyright Notice - Copyright (C) The Internet Society (2005). + 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. 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. - This document expires in April, 2006. + This document expires in December, 2006.