draft-ietf-bfd-v4v6-1hop-04.txt		draft-ietf-bfd-v4v6-1hop-05.txt
	Network Working Group D. Katz		Network Working Group D. Katz
	Internet Draft Juniper Networks		Internet Draft Juniper Networks
	D. Ward		D. Ward
	Cisco Systems		Cisco Systems
	Expires: April, 2006 October, 2005		Expires: December, 2006 June, 2006
	BFD for IPv4 and IPv6 (Single Hop)		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		Status of this Memo
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	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2005). All Rights Reserved.		Copyright (C) The Internet Society (2006). All Rights Reserved.
	Abstract		Abstract
	This document describes the use of the Bidirectional Forwarding		This document describes the use of the Bidirectional Forwarding
	Detection protocol over IPv4 and IPv6 for single IP hops. It further		Detection protocol over IPv4 and IPv6 for single IP hops. Comments
	describes the use of BFD with OSPFv2, OSPFv3, and IS-IS. Comments on		on this draft should be directed to rtg-bfd@ietf.org.
	this draft should be directed to rtg-bfd@ietf.org.
	Conventions used in this document		Conventions used in this document
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC-2119 [KEYWORDS].		document are to be interpreted as described in RFC-2119 [KEYWORDS].
	1. Introduction		1. Introduction
	One very desirable application for BFD [BFD] is to track IPv4 and		One very desirable application for BFD [BFD] is to track IPv4 and
	IPv6 connectivity between directly-connected systems. This could be		IPv6 connectivity between directly-connected systems. This could be
	used to supplement the detection mechanisms in IS-IS and OSPF, or to		used to supplement the detection mechanisms in routing protocols, or
	monitor router-host connectivity, among other applications.		to monitor router-host connectivity, among other applications.
	This document describes the particulars necessary to use BFD in this		This document describes the particulars necessary to use BFD in this
	environment, and describes how BFD can be used in conjunction OSPFv2		environment. Interactions between BFD and other protocols and system
	[OSPFv2], OSPFv3 [OSPFv3], and IS-IS [ISIS].		functions are described in the BFD Generic Applications document
			[BFD-GENERIC].
	2. Applications and Limitations		2. Applications and Limitations
	This application of BFD can be used by any pair of systems		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		communicating via IPv4 and/or IPv6 across a single IP hop that can be
	associated with an incoming interface. This includes, but is not		associated with an incoming interface. This includes, but is not
	limited to, physical media, virtual circuits, and tunnels.		limited to, physical media, virtual circuits, and tunnels.
	Each BFD session between a pair of systems MUST traverse a separate		Each BFD session between a pair of systems MUST traverse a separate
	path in both directions.		path in both directions.
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	address changes, the local system MUST NOT use that address as the		address changes, the local system MUST NOT use that address as the
	destination in outgoing BFD Control packets; rather it MUST continue		destination in outgoing BFD Control packets; rather it MUST continue
	to use the address configured at session creation. An implementation		to use the address configured at session creation. An implementation
	MAY notify the application that the neighbor's source address has		MAY notify the application that the neighbor's source address has
	changed, so that the application might choose to change the		changed, so that the application might choose to change the
	destination address or take some other action. Note that the TTL/Hop		destination address or take some other action. Note that the TTL/Hop
	Count check described in section 5 (or the use of authentication)		Count check described in section 5 (or the use of authentication)
	precludes the BFD packets from having come from any source other than		precludes the BFD packets from having come from any source other than
	the immediate neighbor.		the immediate neighbor.
	7. BFD for use with OSPFv2, OSPFv3, and IS-IS		7. BFD for use with Tunnels
	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
	A number of mechanisms are available to tunnel IPv4 and IPv6 over		A number of mechanisms are available to tunnel IPv4 and IPv6 over
	arbitrary topologies. If the tunnel mechanism does not decrement the		arbitrary topologies. If the tunnel mechanism does not decrement the
	TTL or hop count of the network protocol carried within, the		TTL or hop count of the network protocol carried within, the
	mechanism described in this document may be used to provide liveness		mechanism described in this document may be used to provide liveness
	detection for the tunnel. The BFD Authentication mechanism SHOULD be		detection for the tunnel. The BFD Authentication mechanism SHOULD be
	used and is strongly encouraged.		used and is strongly encouraged.
	Normative References		Normative References
	[BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection",		[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-		[BFD-GENERIC] Katz, D., and Ward, D., "Generic Application of BFD",
	ietf-bfd-multihop-03.txt, July, 2005.		draft-ietf-bfd-generic-02.txt, June, 2006.
	[GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism		[GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism
	(GTSM)", RFC 3682, February 2004.		(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		[KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", RFC 2119, March 1997.		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		Security Considerations
	In this application, the use of TTL=255 on transmit and receive is		In this application, the use of TTL=255 on transmit and receive is
	viewed as supplying equivalent security characteristics to other		viewed as supplying equivalent security characteristics to other
	protocols used in the infrastructure, as it is not trivially		protocols used in the infrastructure, as it is not trivially
	spoofable. The security implications of this mechanism are further		spoofable. The security implications of this mechanism are further
	discussed in [GTSM].		discussed in [GTSM].
	The security implications of the use of BFD Authentication are		The security implications of the use of BFD Authentication are
	discussed in [BFD].		discussed in [BFD].
	skipping to change at page 11, line 23		skipping to change at page 7, line 23
	Dave Ward		Dave Ward
	Cisco Systems		Cisco Systems
	170 W. Tasman Dr.		170 W. Tasman Dr.
	San Jose, CA 95134 USA		San Jose, CA 95134 USA
	Phone: +1-408-526-4000		Phone: +1-408-526-4000
	Email: dward@cisco.com		Email: dward@cisco.com
	Changes from the previous draft		Changes from the previous draft
	Text was added to point out that implementations may raise the BFD		Application-specific information was moved to the Generic draft. All
	transmit interval above the minimum if it appears that the neighbor		other changes are purely editorial in nature.
	does not support BFD. All other changes are editorial in nature.
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