draft-ietf-bfd-seamless-base-01.txt		draft-ietf-bfd-seamless-base-02.txt
	Internet Engineering Task Force N. Akiya		Internet Engineering Task Force N. Akiya
	Internet-Draft C. Pignataro		Internet-Draft C. Pignataro
	Updates: 5880 (if approved) D. Ward		Updates: 5880 (if approved) D. Ward
	Intended status: Standards Track Cisco Systems		Intended status: Standards Track Cisco Systems
	Expires: December 28, 2014 M. Bhatia		Expires: February 2, 2015 M. Bhatia
	Ionos Networks		Ionos Networks
	P. K. Santosh		P. K. Santosh
	Juniper Networks		Juniper Networks
	June 26, 2014		August 1, 2014
	Seamless Bidirectional Forwarding Detection (S-BFD)		Seamless Bidirectional Forwarding Detection (S-BFD)
	draft-ietf-bfd-seamless-base-01		draft-ietf-bfd-seamless-base-02
	Abstract		Abstract
	This document defines a simplified mechanism to use Bidirectional		This document defines a simplified mechanism to use Bidirectional
	Forwarding Detection (BFD) with large portions of negotiation aspects		Forwarding Detection (BFD) with large portions of negotiation aspects
	eliminated, thus providing benefits such as quick provisioning as		eliminated, thus providing benefits such as quick provisioning as
	well as improved control and flexibility to network nodes initiating		well as improved control and flexibility to network nodes initiating
	the path monitoring.		the path monitoring.
	This document updates RFC5880.		This document updates RFC5880.
	skipping to change at page 1, line 47		skipping to change at page 1, line 47
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on December 28, 2014.		This Internet-Draft will expire on February 2, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 25		skipping to change at page 2, line 25
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Seamless BFD Overview . . . . . . . . . . . . . . . . . . . . 4		3. Seamless BFD Overview . . . . . . . . . . . . . . . . . . . . 4
	4. S-BFD UDP Port . . . . . . . . . . . . . . . . . . . . . . . 5		4. S-BFD Discriminators . . . . . . . . . . . . . . . . . . . . 5
	5. S-BFD Discriminators . . . . . . . . . . . . . . . . . . . . 5		4.1. Discriminator Pools . . . . . . . . . . . . . . . . . . . 5
	6. Reflector BFD Session . . . . . . . . . . . . . . . . . . . . 6		4.2. S-BFD Discriminator Uniqueness . . . . . . . . . . . . . 6
	7. State Variables . . . . . . . . . . . . . . . . . . . . . . . 7		5. Reflector BFD Session . . . . . . . . . . . . . . . . . . . . 7
	7.1. New State Variables . . . . . . . . . . . . . . . . . . . 7		6. State Variables . . . . . . . . . . . . . . . . . . . . . . . 7
	7.2. State Variable Initialization and Maintenance . . . . . . 7		6.1. New State Variables . . . . . . . . . . . . . . . . . . . 7
	8. S-BFD Procedures . . . . . . . . . . . . . . . . . . . . . . 7		6.2. State Variable Initialization and Maintenance . . . . . . 8
	8.1. Initiator Procedures . . . . . . . . . . . . . . . . . . 7		7. S-BFD Procedures . . . . . . . . . . . . . . . . . . . . . . 8
	8.1.1. SBFDInitiator State Machine . . . . . . . . . . . . . 8		7.1. S-BFD Packet Demultiplexing . . . . . . . . . . . . . . . 8
	8.1.2. Details of S-BFD Packet Sent by SBFDInitiator . . . . 9		7.2. Initiator Procedures . . . . . . . . . . . . . . . . . . 8
	8.2. Responder Procedures . . . . . . . . . . . . . . . . . . 9		7.2.1. SBFDInitiator State Machine . . . . . . . . . . . . . 9
	8.2.1. Responder Demultiplexing . . . . . . . . . . . . . . 10		7.2.2. Details of S-BFD Packet Sent by SBFDInitiator . . . . 10
	8.2.2. Details of S-BFD Packet Sent by SBFDReflector . . . . 10		7.3. Responder Procedures . . . . . . . . . . . . . . . . . . 10
	8.3. Diagnostic Values . . . . . . . . . . . . . . . . . . . . 10		7.3.1. Responder Demultiplexing . . . . . . . . . . . . . . 10
	8.4. The Poll Sequence . . . . . . . . . . . . . . . . . . . . 11		7.3.2. Details of S-BFD Packet Sent by SBFDReflector . . . . 11
	8.5. Control Plane Independent (C) . . . . . . . . . . . . . . 11		7.4. Diagnostic Values . . . . . . . . . . . . . . . . . . . . 11
	8.6. Additional SBFDInitiator Behaviors . . . . . . . . . . . 11		7.5. The Poll Sequence . . . . . . . . . . . . . . . . . . . . 11
	8.7. Additional SBFDReflector Behaviors . . . . . . . . . . . 12		7.6. Control Plane Independent (C) . . . . . . . . . . . . . . 11
	9. Scaling Aspect . . . . . . . . . . . . . . . . . . . . . . . 12		7.7. Additional SBFDInitiator Behaviors . . . . . . . . . . . 12
	10. Co-existence with Traditional BFD . . . . . . . . . . . . . . 12		7.8. Additional SBFDReflector Behaviors . . . . . . . . . . . 12
	11. BFD Echo . . . . . . . . . . . . . . . . . . . . . . . . . . 12		8. Scaling Aspect . . . . . . . . . . . . . . . . . . . . . . . 13
	12. Security Considerations . . . . . . . . . . . . . . . . . . . 13		9. Co-existence with Classical BFD Sessions . . . . . . . . . . 13
	13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14		10. S-BFD Echo Function . . . . . . . . . . . . . . . . . . . . . 13
	14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14		11. Security Considerations . . . . . . . . . . . . . . . . . . . 14
	15. Contributing Authors . . . . . . . . . . . . . . . . . . . . 14		12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
	16. References . . . . . . . . . . . . . . . . . . . . . . . . . 15		13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
	16.1. Normative References . . . . . . . . . . . . . . . . . . 15		14. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15
	16.2. Informative References . . . . . . . . . . . . . . . . . 15		15. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
			15.1. Normative References . . . . . . . . . . . . . . . . . . 16
			15.2. Informative References . . . . . . . . . . . . . . . . . 16
	Appendix A. Loop Problem . . . . . . . . . . . . . . . . . . . . 16		Appendix A. Loop Problem . . . . . . . . . . . . . . . . . . . . 16
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
	1. Introduction		1. Introduction
	Bidirectional Forwarding Detection (BFD), [RFC5880] and related		Bidirectional Forwarding Detection (BFD), [RFC5880] and related
	documents, has efficiently generalized the failure detection		documents, has efficiently generalized the failure detection
	mechanism for multiple protocols and applications. There are some		mechanism for multiple protocols and applications. There are some
	improvements which can be made to better fit existing technologies.		improvements which can be made to better fit existing technologies.
	There is a possibility of evolving BFD to better fit new		There is a possibility of evolving BFD to better fit new
	technologies. This document focuses on several aspects of BFD in		technologies. This document focuses on several aspects of BFD in
	order to further improve efficiency, to expand failure detection		order to further improve efficiency, to expand failure detection
	coverage and to allow BFD usage for wider scenarios. This document		coverage and to allow BFD usage for wider scenarios. This document
	extends BFD to provide solutions to use cases listed in		extends BFD to provide solutions to use cases listed in
	[I-D.ietf-bfd-seamless-use-case].		[I-D.ietf-bfd-seamless-use-case].
	One key aspect of the mechanism described in this document eliminates		One key aspect of the mechanism described in this document eliminates
	the time between a network node wanting to perform a connectivity		the time between a network node wanting to perform a continuity test
	test and completing the connectivity test. In traditional BFD terms,		and completing the continuity test. In traditional BFD terms, the
	the initial state changes from DOWN to UP is virtually nonexistent.		initial state changes from DOWN to UP are virtually nonexistent.
	Removal of this seam (i.e. time delay) in BFD provides applications a		Removal of this seam (i.e. time delay) in BFD provides applications a
	smooth and continuous operational experience. Therefore, "Seamless		smooth and continuous operational experience. Therefore, "Seamless
	BFD" (S-BFD) has been chosen as the name for this mechanism.		BFD" (S-BFD) has been chosen as the name for this mechanism.
	2. Terminology		2. Terminology
	The reader is expected to be familiar with the BFD, IP and MPLS		The reader is expected to be familiar with the BFD, IP and MPLS
	terminologies and protocol constructs. This section describes		terminologies and protocol constructs. This section describes
	several new terminologies introduced by S-BFD.		several new terminologies introduced by S-BFD.
			o Classical BFD - BFD session types based on [RFC5880].
	o S-BFD - Seamless BFD.		o S-BFD - Seamless BFD.
	o S-BFD packet - a BFD control packet on the well-known S-BFD port.		o S-BFD packet - a BFD control packet destined to or sourced from
			the well-known S-BFD port.
	o Entity - a function on a network node that S-BFD mechanism allows		o Entity - a function on a network node that S-BFD mechanism allows
	remote network nodes to perform connectivity test to. An entity		remote network nodes to perform continuity test to. An entity can
	can be abstract (ex: reachability) or specific (ex: IP addresses,		be abstract (ex: reachability) or specific (ex: IP addresses,
	router-IDs, functions).		router-IDs, functions).
	o SBFDInitiator - an S-BFD session on a network node that performs a		o SBFDInitiator - an S-BFD session on a network node that performs a
	connectivity test to a remote entity by sending S-BFD packets.		continuity test to a remote entity by sending S-BFD packets.
	o SBFDReflector - an S-BFD session on a network node that listens		o SBFDReflector - an S-BFD session on a network node that listens
	for incoming S-BFD packets to local entities and generates		for incoming S-BFD packets to local entities and generates
	response S-BFD packets.		response S-BFD packets.
	o Reflector BFD session - synonymous with SBFDReflector.		o Reflector BFD session - synonymous with SBFDReflector.
	o S-BFD discriminator - a BFD discriminator allocated for a local		o S-BFD discriminator - a BFD discriminator allocated for a local
	entity and is being listened by an SBFDReflector.		entity and is being listened by an SBFDReflector.
	skipping to change at page 4, line 47		skipping to change at page 5, line 4
	session. Allocated S-BFD discriminators may be advertised by		session. Allocated S-BFD discriminators may be advertised by
	applications (ex: OSPF/IS-IS). Required result is that applications,		applications (ex: OSPF/IS-IS). Required result is that applications,
	on other network nodes, possess the knowledge of the mapping from		on other network nodes, possess the knowledge of the mapping from
	remote entities to S-BFD discriminators. The reflector BFD session		remote entities to S-BFD discriminators. The reflector BFD session
	is to, upon receiving an S-BFD packet targeted to one of local S-BFD		is to, upon receiving an S-BFD packet targeted to one of local S-BFD
	discriminator values, transmit a response S-BFD packet back to the		discriminator values, transmit a response S-BFD packet back to the
	initiator.		initiator.
	Once above setup is complete, any network nodes, having the knowledge		Once above setup is complete, any network nodes, having the knowledge
	of the mapping from a remote entity to an S-BFD discriminator, can		of the mapping from a remote entity to an S-BFD discriminator, can
	quickly perform a connectivity test to the remote entity by simply		quickly perform a continuity test to the remote entity by simply
	sending S-BFD packets with corresponding S-BFD discriminator value in		sending S-BFD packets with corresponding S-BFD discriminator value in
	the "your discriminator" field.		the "your discriminator" field.
	For example:		For example:
	<------- IS-IS Network ------->		<------- IS-IS Network ------->
	+---------+		+---------+
	| |		| |
	A---------B---------C---------D		A---------B---------C---------D
	skipping to change at page 5, line 26		skipping to change at page 5, line 29
	BFD Discrim BFD Discrim		BFD Discrim BFD Discrim
	123 456		123 456
	Figure 2: S-BFD for IS-IS Network		Figure 2: S-BFD for IS-IS Network
	The IS-IS with SystemID xxx (node A) allocates an S-BFD discriminator		The IS-IS with SystemID xxx (node A) allocates an S-BFD discriminator
	123, and advertises the S-BFD discriminator 123 in an IS-IS TLV. The		123, and advertises the S-BFD discriminator 123 in an IS-IS TLV. The
	IS-IS with SystemID yyy (node D) allocates an S-BFD discriminator		IS-IS with SystemID yyy (node D) allocates an S-BFD discriminator
	456, and advertises the S-BFD discriminator 456 in an IS-IS TLV. A		456, and advertises the S-BFD discriminator 456 in an IS-IS TLV. A
	reflector BFD session is created on both network nodes (node A and		reflector BFD session is created on both network nodes (node A and
	node D). When network node A wants to check the connectivity to		node D). When network node A wants to check the reachability to
	network node D, node A can send an S-BFD packet, destined to node D,		network node D, node A can send an S-BFD packet, destined to node D,
	with "your discriminator" field set to 456. When the reflector BFD		with "your discriminator" field set to 456. When the reflector BFD
	session on node D receives this S-BFD packet, then response S-BFD		session on node D receives this S-BFD packet, then response S-BFD
	packet is sent back to node A, which allows node A to complete the		packet is sent back to node A, which allows node A to complete the
	connectivity test.		continuity test.
	4. S-BFD UDP Port		4. S-BFD Discriminators
	S-BFD functions on a well-known UDP port: TBD1.		4.1. Discriminator Pools
	5. S-BFD Discriminators		This document defines following suggestions for discriminator
			management on SBFDInitiator and SBFDReflector sessions, to minimize
			the collision between required S-BFD discriminators on a local
			device.
	Locally allocated S-BFD discriminator values for entities may be		o SBFDInitiator is to allocate a discriminator from the BFD
	arbitrary allocated or derived from values provided by applications.		discriminator pool. If the system also supports classical BFD
	These values may be protocol IDs (ex: System-ID, Router-ID) or		that runs on [RFC5880], then the BFD discriminator pool SHOULD be
	network targets (ex: IP address). To minimize the collision of		shared by SBFDInitiator sessions and classical BFD sessions.
	discriminator values between BFD and S-BFD, it is RECOMMENDED that
	discriminator pool be separate for BFD and S-BFD. Even when		o SBFDReflector is to allocate a discriminator from the S-BFD
	employing the separate discriminator pool approach, collision is		discriminator pool. The S-BFD discriminator pool SHOULD be a
	still possible between one S-BFD application to another S-BFD		separate pool than the BFD discriminator pool.
	application, that may be using different values and algorithms to
	derive S-BFD discriminator values. If the two applications are using		Remainder of this subsection describes the reasons for above
	S-BFD for a same purpose (ex: network reachability), then the		suggestions.
			Locally allocated S-BFD discriminator values for entities, listened
			by SBFDReflector sessions, may be arbitrary allocated or derived from
			values provided by applications. These values may be protocol IDs
			(ex: System-ID, Router-ID) or network targets (ex: IP address). To
			avoid derived S-BFD discriminator values already being assigned to
			other BFD sessions (i.e. SBFDInitiator sessions and classical BFD
			sessions), it is RECOMMENDED that discriminator pool for
			SBFDReflector sessions be separate from other BFD sessions.
			Even when following the separate discriminator pool approach,
			collision is still possible between one S-BFD application to another
			S-BFD application, that may be using different values and algorithms
			to derive S-BFD discriminator values. If the two applications are
			using S-BFD for a same purpose (ex: network reachability), then the
	colliding S-BFD discriminator value can be shared. If the two		colliding S-BFD discriminator value can be shared. If the two
	applications are using S-BFD for a different purpose, then the		applications are using S-BFD for a different purpose, then the
	collision must be addressed. How such collisions are addressed is		collision must be addressed. How such collisions are addressed is
	outside the scope of this document.		outside the scope of this document.
			4.2. S-BFD Discriminator Uniqueness
	One important characteristics of an S-BFD discriminator is that it		One important characteristics of an S-BFD discriminator is that it
	MUST be unique within an administrative domain. If multiple network		MUST be unique within an administrative domain. If multiple network
	nodes allocated a same S-BFD discriminator value, then S-BFD packets		nodes allocated a same S-BFD discriminator value, then S-BFD packets
	falsely terminating on a wrong network node can result in a reflector		falsely terminating on a wrong network node can result in a reflector
	BFD session to generate a response back, due to "your discriminator"		BFD session to generate a response back, due to "your discriminator"
	matching. This is clearly not desirable. If only IP based S-BFD is		matching. This is clearly not desirable. If only IP based S-BFD is
	considered, then it is possible for the reflector BFD session to		considered, then it is possible for the reflector BFD session to
	require demultiplexing of incoming S-BFD packets with combination of		require demultiplexing of incoming S-BFD packets with combination of
	destination IP address and "your discriminator". Then S-BFD		destination IP address and "your discriminator". Then S-BFD
	discriminator only has to be unique within a local node. However,		discriminator only has to be unique within a local node. However,
	S-BFD is a generic mechanism defined to run on wide range of		S-BFD is a generic mechanism defined to run on wide range of
	environments: IP, MPLS, etc. For other transports like MPLS, because		environments: IP, MPLS, etc. For other transports like MPLS, because
	of the need to use non-routable IP destination address, it is not		of the need to use non-routable IP destination address, it is not
	possible for reflector BFD session to demultiplex using IP		possible for reflector BFD session to demultiplex using IP
	destination address. With PHP, there may not be any incoming label		destination address. With PHP, there may not be any incoming label
	stack to aid in demultiplexing either. Thus, S-BFD imposes a		stack to aid in demultiplexing either. Thus, S-BFD imposes a
	requirement that S-BFD discriminators MUST be unique within an		requirement that S-BFD discriminators MUST be unique within an
	administrative domain.		administrative domain.
	6. Reflector BFD Session		5. Reflector BFD Session
	Each network node creates one or more reflector BFD sessions. This		Each network node creates one or more reflector BFD sessions. This
	reflector BFD session is a session which transmits S-BFD packets in		reflector BFD session is a session which transmits S-BFD packets in
	response to received S-BFD packets with "your discriminator" having		response to received S-BFD packets with "your discriminator" having
	S-BFD discriminators allocated for local entities. Specifically,		S-BFD discriminators allocated for local entities. Specifically,
	this reflector BFD session is to have following characteristics:		this reflector BFD session is to have following characteristics:
	o MUST NOT transmit any S-BFD packets based on local timer expiry.		o MUST NOT transmit any S-BFD packets based on local timer expiry.
	o MUST transmit an S-BFD packet in response to a received S-BFD		o MUST transmit an S-BFD packet in response to a received S-BFD
	skipping to change at page 7, line 5		skipping to change at page 7, line 32
	One reflector BFD session may be responsible for handling received		One reflector BFD session may be responsible for handling received
	S-BFD packets targeted to all locally allocated S-BFD discriminators,		S-BFD packets targeted to all locally allocated S-BFD discriminators,
	or few reflector BFD sessions may each be responsible for subset of		or few reflector BFD sessions may each be responsible for subset of
	locally allocated S-BFD discriminators. This policy is a local		locally allocated S-BFD discriminators. This policy is a local
	matter, and is outside the scope of this document.		matter, and is outside the scope of this document.
	Note that incoming S-BFD packets may be IPv4, IPv6 or MPLS based.		Note that incoming S-BFD packets may be IPv4, IPv6 or MPLS based.
	How such S-BFD packets reach an appropriate reflector BFD session is		How such S-BFD packets reach an appropriate reflector BFD session is
	also a local matter, and is outside the scope of this document.		also a local matter, and is outside the scope of this document.
	7. State Variables		6. State Variables
	S-BFD introduces new state variables, and modifies the usage of		S-BFD introduces new state variables, and modifies the usage of
	existing ones.		existing ones.
	7.1. New State Variables		6.1. New State Variables
	A new state variable is added to the base specification in support of		A new state variable is added to the base specification in support of
	S-BFD.		S-BFD.
	o bfd.SessionType: The type of this session. Allowable values are:		o bfd.SessionType: The type of this session. Allowable values are:
	* SBFDInitiator - an S-BFD session on a network node that		* SBFDInitiator - an S-BFD session on a network node that
	performs a connectivity test to a target entity by sending		performs a continuity test to a target entity by sending S-BFD
	S-BFD packets.		packets.
	* SBFDReflector - an S-BFD session on a network node that listens		* SBFDReflector - an S-BFD session on a network node that listens
	for incoming S-BFD packets to local entities and generates		for incoming S-BFD packets to local entities and generates
	response S-BFD packets.		response S-BFD packets.
	bfd.SessionType variable MUST be initialized to the appropriate type		bfd.SessionType variable MUST be initialized to the appropriate type
	when an S-BFD session is created.		when an S-BFD session is created.
	7.2. State Variable Initialization and Maintenance		6.2. State Variable Initialization and Maintenance
	Some state variables defined in section 6.8.1 of the BFD base		Some state variables defined in section 6.8.1 of the BFD base
	specification need to be initialized or manipulated differently		specification need to be initialized or manipulated differently
	depending on the session type. Ed-Note: Anything else?.		depending on the session type.
	o bfd.DemandMode: This variable MUST be initialized to 1 for session		o bfd.DemandMode: This variable MUST be initialized to 1 for session
	type SBFDInitiator, and MUST be initialized to 0 for session type		type SBFDInitiator, and MUST be initialized to 0 for session type
	SBFDReflector.		SBFDReflector.
	8. S-BFD Procedures		7. S-BFD Procedures
	8.1. Initiator Procedures		7.1. S-BFD Packet Demultiplexing
			Received BFD control packet MUST first be demultiplexed with
			information from the lower layer (ex: destination UDP port,
			associated channel type). If the packet is determined to be for an
			SBFDReflector, then the packet MUST be looked up to locate a
			corresponding SBFDReflector session based on the value from the "your
			discriminator" field in the table describing S-BFD discriminators.
			If the packet is determined not to be for SBFDReflector, then the
			packet MUST be looked up to locate a corresponding SBFDInitiator
			session or classical BFD session based on the value from the "your
			discriminator" field in the table describing BFD discriminators. If
			the located session is a SBFDInitiator, then destination of the
			packet (i.e. destination IP address) SHOULD be validated to be for
			self.
			Details of the initial BFD control packet demultiplexing are
			described in relevant S-BFD data plane documents.
			7.2. Initiator Procedures
	S-BFD packets transmitted by an SBFDInitiator MUST set "your		S-BFD packets transmitted by an SBFDInitiator MUST set "your
	discriminator" field to an S-BFD discriminator corresponding to the		discriminator" field to an S-BFD discriminator corresponding to the
	remote entity.		remote entity.
	S-BFD packets transmitted by an SBFDInitiator MUST NOT set "my		Every SBFDInitiator MUST have a locally unique "my discriminator"
	discriminator" field to an S-BFD discriminator allocated for a local		allocated from the BFD discriminator pool.
	entity (and is being monitored by a local SBFDReflector). This is to
	prevent incoming response S-BFD packets, from a remote SBFDReflector,
	having "your discriminator" as a S-BFD discriminator of a local
	entity. Every SBFDInitiator is to have a unique "my discriminator",
	and SHOULD be allocated from the BFD discriminator pool if the
	implementation employs the approach of having separate discriminator
	pools for BFD and S-BFD.
	Below ASCII art describes high level concept of connectivity test		Below ASCII art describes high level concept of continuity test using
	using S-BFD. R2 allocates XX as the S-BFD discriminator for its		S-BFD. R2 allocates XX as the S-BFD discriminator for its network
	network reachability purpose, and advertises XX to neighbors. ASCII		reachability purpose, and advertises XX to neighbors. ASCII art
	art shows R1 and R4 performing a connectivity test to R2.		shows R1 and R4 performing a continuity test to R2.
	+--- md=50/yd=XX (ping) ----+		+--- md=50/yd=XX (ping) ----+
	| |		| |
	|+-- md=XX/yd=50 (pong) --+ |		|+-- md=XX/yd=50 (pong) --+ |
	|| | |		|| | |
	|v | v		|v | v
	R1 ==================== R2[*] ========= R3 ========= R4		R1 ==================== R2[*] ========= R3 ========= R4
	| ^ |^		| ^ |^
	| | ||		| | ||
	| +-- md=60/yd=XX (ping) --+|		| +-- md=60/yd=XX (ping) --+|
	| |		| |
	+---- md=XX/yd=60 (pong) ---+		+---- md=XX/yd=60 (pong) ---+
	[*] Reflector BFD session on R2.		[*] Reflector BFD session on R2.
	=== Links connecting network nodes.		=== Links connecting network nodes.
	--- S-BFD packet traversal.		--- S-BFD packet traversal.
	Figure 3: S-BFD Connectivity Test		Figure 3: S-BFD Continuity Test
	8.1.1. SBFDInitiator State Machine		7.2.1. SBFDInitiator State Machine
	An SBFDInitiator may be a persistent session on the initiator with a		An SBFDInitiator may be a persistent session on the initiator with a
	timer for S-BFD packet transmissions. An SBFDInitiator may also be a		timer for S-BFD packet transmissions (stateful SBFDInitiator). An
	module, a script or a tool on the initiator that transmits one or		SBFDInitiator may also be a module, a script or a tool on the
	more S-BFD packets "when needed". For transient SBFDInitiators, the		initiator that transmits one or more S-BFD packets "when needed"
	BFD state machine described in [RFC5880] may not be applicable. For		(stateless SBFDInitiator). For stateless SBFDInitiators, a complete
	persistent SBFDInitiators, the states and the state machine described		BFD state machine may not be applicable. For stateful
	in [RFC5880] will function but are more than necessary. The		SBFDInitiators, the states and the state machine described in
	following diagram provides an optimized state machine for persistent		[RFC5880] will not function due to SBFDReflector session only sending
	SBFDInitiators. The notation on each arc represents the state of the		UP and ADMINDOWN states (i.e. SBFDReflector session does not send
	SBFDInitiator (as received in the State field in the S-BFD packet) or		INIT state). The following diagram provides the RECOMMENDED state
	indicates the expiration of the Detection Timer.		machine for stateful SBFDInitiators. The notation on each arc
			represents the state of the SBFDInitiator (as received in the State
			field in the S-BFD packet) or indicates the expiration of the
			Detection Timer.
	+--+		+--+
	ADMIN DOWN, | |		ADMIN DOWN, | |
	TIMER | V		TIMER | V
	+------+ UP +------+		+------+ UP +------+
	| |-------------------->| |----+		| |-------------------->| |----+
	| DOWN | | UP | | UP		| DOWN | | UP | | UP
	| |<--------------------| |<---+		| |<--------------------| |<---+
	+------+ ADMIN DOWN, +------+		+------+ ADMIN DOWN, +------+
	TIMER		TIMER
	Figure 4: SBFDInitiator FSM		Figure 4: SBFDInitiator FSM
	Note that the above state machine is different from the base BFD		Note that the above state machine is different from the base BFD
	specification[RFC5880]. This is because the Init state is no longer		specification[RFC5880]. This is because the INIT state is no longer
	applicable for the SBFDInitiator. Another important difference is		applicable for the SBFDInitiator. Another important difference is
	the transition of the state machine from the Down state to the Up		the transition of the state machine from the DOWN state to the UP
	state when a packet with State Up is received by the initiator. The		state when a packet with State UP is received by the SBFDInitiator.
	definitions of the states and the events have the same meaning as in		The definitions of the states and the events have the same meaning as
	the base BFD specification [RFC5880].		in the base BFD specification [RFC5880].
	8.1.2. Details of S-BFD Packet Sent by SBFDInitiator		7.2.2. Details of S-BFD Packet Sent by SBFDInitiator
	S-BFD packets sent by an SBFDInitiator is to have following contents:		S-BFD packets sent by an SBFDInitiator is to have following contents:
	o Well-known UDP destination port assigned for S-BFD.
	o UDP source port as per described in [RFC5881], [RFC5883],
	[RFC5884] and [RFC5885].
	o "my discriminator" assigned by local node.		o "my discriminator" assigned by local node.
	o "your discriminator" corresponding to a remote entity.		o "your discriminator" corresponding to a remote entity.
	o "State" MUST be set to a value describing local state.		o "State" MUST be set to a value describing local state.
	o "Desired Min TX Interval" MUST be set to a value describing local		o "Desired Min TX Interval" MUST be set to a value describing local
	desired minimum transmit interval.		desired minimum transmit interval.
	o "Required Min RX Interval" MUST be zero.		o "Required Min RX Interval" MUST be zero.
	o "Required Min Echo RX Interval" SHOULD be zero.		o "Required Min Echo RX Interval" SHOULD be zero.
	o "Detection Multiplier" MUST be set to a value describing locally		o "Detection Multiplier" MUST be set to a value describing locally
	used multiplier value.		used multiplier value.
	o Demand (D) bit MUST be set.		o Demand (D) bit MUST be set.
	8.2. Responder Procedures		7.3. Responder Procedures
	A network node which receives S-BFD packets transmitted by an		A network node which receives S-BFD packets transmitted by an
	initiator is referred as responder. The responder, upon reception of		initiator is referred as responder. The responder, upon reception of
	S-BFD packets, is to perform necessary relevant validations described		S-BFD packets, is to perform necessary relevant validations described
	in [RFC5880], [RFC5881], [RFC5883], [RFC5884] and [RFC5885].		in [RFC5880], [RFC5881], [RFC5883], [RFC5884] and [RFC5885].
	8.2.1. Responder Demultiplexing		7.3.1. Responder Demultiplexing
	A BFD control packet received by a resonder is considered an S-BFD		When a responder receives an S-BFD packet, if the value in the "your
	packet if the packet is on the well-known S-BFD port. When a
	responder receives an S-BFD packet, if the value in the "your
	discriminator" field is not one of S-BFD discriminators allocated for		discriminator" field is not one of S-BFD discriminators allocated for
	local entities, then this packet MUST NOT be considered for this		local entities, then this packet MUST NOT be considered for this
	mechanism. If the value in the "your discriminator" field is one of		mechanism. If the value in the "your discriminator" field is one of
	S-BFD discriminators allocated for local entities, then the packet is		S-BFD discriminators allocated for local entities, then the packet is
	determined to be handled by a reflector BFD session responsible for		determined to be handled by a reflector BFD session responsible for
	the S-BFD discriminator. If the packet was determined to be		the S-BFD discriminator. If the packet was determined to be
	processed further for this mechanism, then chosen reflector BFD		processed further for this mechanism, then chosen reflector BFD
	session is to transmit a response BFD control packet using procedures		session is to transmit a response BFD control packet using procedures
	described in Section 8.2.2, unless prohibited by local policies (ex:		described in Section 7.3.2, unless prohibited by local policies (ex:
	administrative, security, rate-limiter, etc).		administrative, security, rate-limiter, etc).
	8.2.2. Details of S-BFD Packet Sent by SBFDReflector		7.3.2. Details of S-BFD Packet Sent by SBFDReflector
	S-BFD packets sent by an SBFDReflector is to have following contents:		S-BFD packets sent by an SBFDReflector is to have following contents:
	o Well-known UDP destination port assigned for S-BFD.
	o UDP source port as described in [RFC5881], [RFC5883], [RFC5884]
	and [RFC5885].
	o "my discriminator" MUST be copied from received "your		o "my discriminator" MUST be copied from received "your
	discriminator".		discriminator".
	o "your discriminator" MUST be copied from received "my		o "your discriminator" MUST be copied from received "my
	discriminator".		discriminator".
	o "State" MUST be UP or ADMINDOWN. Clarification of reflector BFD		o "State" MUST be UP or ADMINDOWN. Clarification of reflector BFD
	session state is described in Section 8.7.		session state is described in Section 7.8.
	o "Desired Min TX Interval" MUST be copied from received "Desired		o "Desired Min TX Interval" MUST be copied from received "Desired
	Min TX Interval".		Min TX Interval".
	o "Required Min RX Interval" MUST be set to a value describing how		o "Required Min RX Interval" MUST be set to a value describing how
	many incoming control packets this reflector BFD session can		many incoming control packets this reflector BFD session can
	handle. Further details are described in Section 8.7.		handle. Further details are described in Section 7.8.
	o "Required Min Echo RX Interval" SHOULD be set to zero.		o "Required Min Echo RX Interval" SHOULD be set to zero.
	o "Detection Multiplier" MUST be copied from received "Detection		o "Detection Multiplier" MUST be copied from received "Detection
	Multiplier".		Multiplier".
	o Demand (D) bit MUST be cleared.		o Demand (D) bit MUST be cleared.
	8.3. Diagnostic Values		7.4. Diagnostic Values
	Diagnostic value in both directions MAY be set to a certain value, to		Diagnostic value in both directions MAY be set to a certain value, to
	attempt to communicate further information to both ends. However,		attempt to communicate further information to both ends. However,
	details of such are outside the scope of this specification.		details of such are outside the scope of this specification.
	8.4. The Poll Sequence		7.5. The Poll Sequence
	Poll sequence MAY be used in both directions. The Poll sequence MUST		Poll sequence MAY be used in both directions. The Poll sequence MUST
	operate in accordance with [RFC5880]. An SBFDReflector MAY use the		operate in accordance with [RFC5880]. An SBFDReflector MAY use the
	Poll sequence to slow down that rate at which S-BFD packets are		Poll sequence to slow down that rate at which S-BFD packets are
	generated from an SBFDInitiator. This is done by the SBFDReflector		generated from an SBFDInitiator. This is done by the SBFDReflector
	using procedures described in Section 8.7 and setting the Poll (P)		using procedures described in Section 7.8 and setting the Poll (P)
	bit in the reflected S-BFD packet. The SBFDInitiator is to then send		bit in the reflected S-BFD packet. The SBFDInitiator is to then send
	the next S-BFD packet with the Final (F) bit set. If an		the next S-BFD packet with the Final (F) bit set. If an
	SBFDReflector receives an S-BFD packet with Poll (P) bit set, then		SBFDReflector receives an S-BFD packet with Poll (P) bit set, then
	the SBFDReflector MUST respond with an S-BFD packet with Poll (P) bit		the SBFDReflector MUST respond with an S-BFD packet with Poll (P) bit
	cleared and Final (F) bit set.		cleared and Final (F) bit set.
	8.5. Control Plane Independent (C)		7.6. Control Plane Independent (C)
	Control plane independent (C) bit for an SBFDInitiator sending S-BFD		Control plane independent (C) bit for an SBFDInitiator sending S-BFD
	packets to a reflector BFD session MUST work according to [RFC5880].		packets to a reflector BFD session MUST work according to [RFC5880].
	Reflector BFD session also MUST work according to [RFC5880].		Reflector BFD session also MUST work according to [RFC5880].
	Specifically, if reflector BFD session implementation does not share		Specifically, if reflector BFD session implementation does not share
	fate with control plane, then response S-BFD packets transmitted MUST		fate with control plane, then response S-BFD packets transmitted MUST
	have control plane independent (C) bit set. If reflector BFD session		have control plane independent (C) bit set. If reflector BFD session
	implementation shares fate with control plane, then response S-BFD		implementation shares fate with control plane, then response S-BFD
	packets transmitted MUST NOT have control plane independent (C) bit		packets transmitted MUST NOT have control plane independent (C) bit
	set.		set.
	8.6. Additional SBFDInitiator Behaviors		7.7. Additional SBFDInitiator Behaviors
	o If the SBFDInitiator receives a valid S-BFD packet in response to		o If the SBFDInitiator receives a valid S-BFD packet in response to
	transmitted S-BFD packet to a remote entity, then the		transmitted S-BFD packet to a remote entity, then the
	SBFDInitiator SHOULD conclude that S-BFD packet reached the		SBFDInitiator SHOULD conclude that S-BFD packet reached the
	intended remote entity.		intended remote entity.
	o When a sufficient number of S-BFD packets have not arrived as they		o When a sufficient number of S-BFD packets have not arrived as they
	should, the SBFDInitiator SHOULD declare loss of connectivity to		should, the SBFDInitiator SHOULD declare loss of reachability to
	the remote entity. The criteria for declaring loss of		the remote entity. The criteria for declaring loss of
	connectivity and the action that would be triggered as a result		reachability and the action that would be triggered as a result
	are outside the scope of this document.		are outside the scope of this document.
	o Relating to above bullet item, it is critical for an		o Relating to above bullet item, it is critical for an
	implementation to understand the latency to/from the reflector BFD		implementation to understand the latency to/from the reflector BFD
	session on the responder. In other words, for very first S-BFD		session on the responder. In other words, for very first S-BFD
	packet transmitted by the SBFDInitiator, an implementation MUST		packet transmitted by the SBFDInitiator, an implementation MUST
	NOT expect response S-BFD packet to be received for time		NOT expect response S-BFD packet to be received for time
	equivalent to sum of latencies: initiator to responder and		equivalent to sum of latencies: initiator to responder and
	responder back to initiator.		responder back to initiator.
	o If the SBFDInitiator receives an S-BFD packet with Demand (D) bit		o If the SBFDInitiator receives an S-BFD packet with Demand (D) bit
	set, the packet MUST be discarded.		set, the packet MUST be discarded.
	8.7. Additional SBFDReflector Behaviors		7.8. Additional SBFDReflector Behaviors
	o S-BFD packets transmitted by the SBFDReflector MUST have "Required		o S-BFD packets transmitted by the SBFDReflector MUST have "Required
	Min RX Interval" set to a value which expresses how many incoming		Min RX Interval" set to a value which expresses how many incoming
	S-BFD packets this SBFDReflector can handle. The SBFDReflector		S-BFD packets this SBFDReflector can handle. The SBFDReflector
	can control how fast SBFInitiators will be sending S-BFD packets		can control how fast SBFInitiators will be sending S-BFD packets
	to self by ensuring "Required Min RX Interval" indicates a value		to self by ensuring "Required Min RX Interval" indicates a value
	based on the current load.		based on the current load.
	o If the SBFDReflector wishes to communicate to some or all		o If the SBFDReflector wishes to communicate to some or all
	SBFDInitiators that monitored local entity is "temporarily out of		SBFDInitiators that monitored local entity is "temporarily out of
	service", then S-BFD packets with "state" set to ADMINDOWN are		service", then S-BFD packets with "state" set to ADMINDOWN are
	sent to those SBFDInitiators. The SBFDInitiators, upon reception		sent to those SBFDInitiators. The SBFDInitiators, upon reception
	of such packets, MUST NOT conclude loss of connectivity to		of such packets, MUST NOT conclude loss of reachability to
	corresponding remote entity, and MUST back off packet transmission		corresponding remote entity, and MUST back off packet transmission
	interval for the remote entity to an interval no faster than 1		interval for the remote entity to an interval no faster than 1
	second. If the SBFDReflector is generating a response S-BFD		second. If the SBFDReflector is generating a response S-BFD
	packet for a local entity that is in service, then "state" in		packet for a local entity that is in service, then "state" in
	response BFD control packets MUST be set to UP.		response BFD control packets MUST be set to UP.
	o If an SBFDReflector receives an S-BFD packet with Demand (D) bit		o If an SBFDReflector receives an S-BFD packet with Demand (D) bit
	cleared, the packet MUST be discarded.		cleared, the packet MUST be discarded.
	9. Scaling Aspect		8. Scaling Aspect
	This mechanism brings forth one noticeable difference in terms of		This mechanism brings forth one noticeable difference in terms of
	scaling aspect: number of SBFDReflector. This specification		scaling aspect: number of SBFDReflector. This specification
	eliminates the need for egress nodes to have fully active BFD		eliminates the need for egress nodes to have fully active BFD
	sessions when only one side desires to perform connectivity tests.		sessions when only one side desires to perform continuity tests.
	With introduction of reflector BFD concept, egress no longer is		With introduction of reflector BFD concept, egress no longer is
	required to create any active BFD session per path/LSP/function		required to create any active BFD session per path/LSP/function
	basis. Due to this, total number of BFD sessions in a network is		basis. Due to this, total number of BFD sessions in a network is
	reduced.		reduced.
	10. Co-existence with Traditional BFD		9. Co-existence with Classical BFD Sessions
	This mechanism has no issues being deployed with traditional BFDs		Initial packet demultiplexing requirement is described in
	([RFC5881], [RFC5883], [RFC5884] and [RFC5885]) because S-BFD		Section 7.1. Because of this, S-BFD mechanism can co-exist with
	discriminators which allow this mechanism to function are explicitly		classical BFD sessions.
	reserved and separate UDP port values are used with S-BFD.
	11. BFD Echo		10. S-BFD Echo Function
	BFD echo is outside the scope of this document.		The concept of the S-BFD Echo function is similar to the BFD Echo
			function described in [RFC5880], packets are self-generated and self-
			terminated after traversing a link/path. S-BFD echo packets are
			expected to u-turn on the target node in the data plane and MUST NOT
			be processed by any reflector BFD sessions on the target node.
	12. Security Considerations		When using the S-BFD Echo function, it is RECOMMENDED that:
	Same security considerations as [RFC5880], [RFC5881], [RFC5883],		o Both S-BFD packets (with BFD control header) and S-BFD echo
	[RFC5884] and [RFC5885] apply to this document.		packets (implementation specific) be sent.
	Additionally, implementing the following measures will strengthen		o Both S-BFD packets and S-BFD echo packets have the same semantics
	security aspects of the mechanism described by this document.		in the forward direction to reach the target node.
	o Implementations MUST provide filtering capability based on source		In other words, it is not preferable to send just S-BFD echo packets.
	IP addresses of received S-BFD packets: [RFC2827].		There are two reason behind this suggestion:
	o Implementations MUST NOT act on received S-BFD packets containing		o S-BFD packets can verify reachability to intended target node,
	Martian addresses as source IP addresses.		which allows one to conclude that S-BFD echo packets are u-turning
			on the expected target node.
	o Implementations MUST ensure that response S-BFD packets generated		o S-BFD packets can detect when the target node is going out of
	to the initiator by the SBFDReflector have a reachable target (ex:		service (i.e. via receiving back ADMINDOWN state).
	destination IP address).
			Implementations MAY set "Required Min Echo RX Interval" field to
			indicate the rate which SBFDInitiator is sending S-BFD Echo packets
			(in ping) or the rate which SBFDReflector wants SBFDInitiators to
			send S-BFD Echo packets (in pong). However, this is likely more than
			necessary for the S-BFD Echo function to operate. Therefore, it is
			RECOMMENDED that "Required Min Echo RX Interval" field simply be set
			to zero in both directions.
			Additionally, following aspects are left as implementation details,
			and are outside the scope of this document:
			o Format of the S-BFD Echo packet (ex: data beyond UDP header).
			o Procedures on when and how to use the S-BFD Echo function.
			11. Security Considerations
			Same security considerations as [RFC5880], [RFC5881], [RFC5883],
			[RFC5884] and [RFC5885] apply to this document. Additionally,
			implementing the following measures will strengthen security aspects
			of the mechanism described by this document:
	o SBFDInitiator MAY pick crypto sequence number based on		o SBFDInitiator MAY pick crypto sequence number based on
	authentication mode configured.		authentication mode configured.
	o SBFDReflector MUST NOT look at the crypto sequence number before		o SBFDReflector MUST NOT look at the crypto sequence number before
	accepting the packet.		accepting the packet.
	o SBFDReflector MAY look at the Key ID		o SBFDReflector MAY look at the Key ID
	[I-D.ietf-bfd-generic-crypto-auth] in the incoming packet and		[I-D.ietf-bfd-generic-crypto-auth] in the incoming packet and
	verify the authentication data.		verify the authentication data.
	skipping to change at page 14, line 10		skipping to change at page 15, line 14
	o SBFDReflector are not susceptible to replay attacks as they always		o SBFDReflector are not susceptible to replay attacks as they always
	respond to S-BFD packets irrespective of the sequence number		respond to S-BFD packets irrespective of the sequence number
	carried.		carried.
	o An attacker cannot impersonate the responder since the		o An attacker cannot impersonate the responder since the
	SBFDInitiator will only accept S-BFD packets that come with the		SBFDInitiator will only accept S-BFD packets that come with the
	sequence number that it had originally used when sending the S-BFD		sequence number that it had originally used when sending the S-BFD
	packet.		packet.
	13. IANA Considerations		12. IANA Considerations
	A new value TBD1 is requested from the "Service Name and Transport
	Protocol Port Number Registry". The requested registry entry is:
	Service Name (REQUIRED)		No action is required by IANA for this document.
	s-bfd
	Transport Protocol(s) (REQUIRED)
	udp
	Assignee (REQUIRED)
	IESG <iesg@ietf.org>
	Contact (REQUIRED)
	BFD Chairs <bfd-chairs@tools.ietf.org>
	Description (REQUIRED)
	Seamless Bidirectional Forwarding Detection (S-BFD)
	Reference (REQUIRED)
	draft-ietf-bfd-seamless-base
	Port Number (OPTIONAL)
	TBD1 (Requesting 7784)
	14. Acknowledgements		13. Acknowledgements
	Authors would like to thank Jeffrey Haas for performing thorough		Authors would like to thank Jeffrey Haas, Greg Mirsky and Marc
	reviews and providing number of suggestions. Authors would like to		Binderberger for performing thorough reviews and providing number of
	thank Girija Raghavendra Rao, Marc Binderberger, Les Ginsberg,		suggestions. Authors would like to thank Girija Raghavendra Rao, Les
	Srihari Raghavan, Vanitha Neelamegam and Vengada Prasad Govindan from		Ginsberg, Srihari Raghavan, Vanitha Neelamegam and Vengada Prasad
	Cisco Systems for providing valuable comments. Authors would also		Govindan from Cisco Systems for providing valuable comments. Authors
	like to thank John E. Drake for providing comments and suggestions.		would also like to thank John E. Drake and Pablo Frank for providing
			comments and suggestions.
	15. Contributing Authors		14. Contributing Authors
	Tarek Saad		Tarek Saad
	Cisco Systems		Cisco Systems
	Email: tsaad@cisco.com		Email: tsaad@cisco.com
	Siva Sivabalan		Siva Sivabalan
	Cisco Systems		Cisco Systems
	Email: msiva@cisco.com		Email: msiva@cisco.com
	Nagendra Kumar		Nagendra Kumar
	skipping to change at page 15, line 4		skipping to change at page 15, line 41
	Cisco Systems		Cisco Systems
	Email: tsaad@cisco.com		Email: tsaad@cisco.com
	Siva Sivabalan		Siva Sivabalan
	Cisco Systems		Cisco Systems
	Email: msiva@cisco.com		Email: msiva@cisco.com
	Nagendra Kumar		Nagendra Kumar
	Cisco Systems		Cisco Systems
	Email: naikumar@cisco.com		Email: naikumar@cisco.com
	Mallik Mudigonda		Mallik Mudigonda
	Cisco Systems		Cisco Systems
	Email: mmudigon@cisco.com		Email: mmudigon@cisco.com
	Sam Aldrin		Sam Aldrin
	Huawei Technologies		Huawei Technologies
	Email: aldrin.ietf@gmail.com		Email: aldrin.ietf@gmail.com
	16. References		15. References
	16.1. Normative References
	[I-D.ietf-bfd-seamless-use-case]		15.1. Normative References
	Aldrin, S., Bhatia, M., Mirsky, G., Kumar, N., and S.
	Matsushima, "Seamless Bidirectional Forwarding Detection
	(BFD) Use Case", draft-ietf-bfd-seamless-use-case-00 (work
	in progress), June 2014.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection		[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
	(BFD)", RFC 5880, June 2010.		(BFD)", RFC 5880, June 2010.
	[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection		[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
	(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June		(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
	2010.		2010.
	[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection		[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
	(BFD) for Multihop Paths", RFC 5883, June 2010.		(BFD) for Multihop Paths", RFC 5883, June 2010.
	[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,		[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
	"Bidirectional Forwarding Detection (BFD) for MPLS Label		"Bidirectional Forwarding Detection (BFD) for MPLS Label
	Switched Paths (LSPs)", RFC 5884, June 2010.		Switched Paths (LSPs)", RFC 5884, June 2010.
	16.2. Informative References		15.2. Informative References
	[I-D.ietf-bfd-generic-crypto-auth]		[I-D.ietf-bfd-generic-crypto-auth]
	Bhatia, M., Manral, V., Zhang, D., and M. Jethanandani,		Bhatia, M., Manral, V., Zhang, D., and M. Jethanandani,
	"BFD Generic Cryptographic Authentication", draft-ietf-		"BFD Generic Cryptographic Authentication", draft-ietf-
	bfd-generic-crypto-auth-06 (work in progress), April 2014.		bfd-generic-crypto-auth-06 (work in progress), April 2014.
	[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:		[I-D.ietf-bfd-seamless-use-case]
	Defeating Denial of Service Attacks which employ IP Source		Aldrin, S., Bhatia, M., Mirsky, G., Kumar, N., and S.
	Address Spoofing", BCP 38, RFC 2827, May 2000.		Matsushima, "Seamless Bidirectional Forwarding Detection
			(BFD) Use Case", draft-ietf-bfd-seamless-use-case-00 (work
			in progress), June 2014.
	[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding		[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
	Detection (BFD) for the Pseudowire Virtual Circuit		Detection (BFD) for the Pseudowire Virtual Circuit
	Connectivity Verification (VCCV)", RFC 5885, June 2010.		Connectivity Verification (VCCV)", RFC 5885, June 2010.
	Appendix A. Loop Problem		Appendix A. Loop Problem
	Consider a scenario where we have two nodes and both are S-BFD		Consider a scenario where we have two nodes and both are S-BFD
	capable.		capable.
	skipping to change at page 16, line 51		skipping to change at page 17, line 37
	Solutions		Solutions
	The current proposals to avoid the loop problem are:		The current proposals to avoid the loop problem are:
	o Overload "D" bit (Demand mode bit): Initiator always sets the 'D'		o Overload "D" bit (Demand mode bit): Initiator always sets the 'D'
	bit and reflector clears it. This way we can identify if a		bit and reflector clears it. This way we can identify if a
	received packet was a reflected packet and avoid reflecting it		received packet was a reflected packet and avoid reflecting it
	back. However this changes the interpretation of 'D' bit.		back. However this changes the interpretation of 'D' bit.
	o Use of State field in the BFD control packets: Initiator will		o Use of State field in the BFD control packets: Initiator will
	always send packets with State set to "DOWN" and reflector will		always send packets with State set to DOWN and reflector will send
	send back packets with state field set to "UP. Reflectors will		back packets with state field set to UP. Reflectors will never
	never reflect any received packets with state as "UP". However		reflect any received packets with state as UP. However the only
	the only issue is the use of state field differently i.e. state in		issue is the use of state field differently i.e. state in the
	the S-BFD control packet from initiator does not reflect the local		S-BFD control packet from initiator does not reflect the local
	state which is anyway not significant at reflector.		state which is anyway not significant at reflector.
	o Use of local discriminator as My Disc at reflector: Reflector will		o Use of local discriminator as My Disc at reflector: Reflector will
	always fill in My Discriminator with a locally allocated		always fill in My Discriminator with a locally allocated
	discriminator value (not reserved discriminators) and will not		discriminator value (not reserved discriminators) and will not
	copy it from the received packet.		copy it from the received packet.
	Authors' Addresses		Authors' Addresses
	Nobo Akiya		Nobo Akiya
End of changes. 76 change blocks.
	186 lines changed or deleted		224 lines changed or added
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