draft-ietf-bfd-intervals-01.txt		draft-ietf-bfd-intervals-02.txt
	Internet Engineering Task Force N. Akiya		Internet Engineering Task Force N. Akiya
	Internet-Draft M. Binderberger		Internet-Draft M. Binderberger
	Intended status: Informational Cisco Systems		Intended status: Informational Cisco Systems
	Expires: December 13, 2014 G. Mirsky		Expires: January 28, 2015 G. Mirsky
	Ericsson		Ericsson
	June 11, 2014		July 27, 2014
	Common Interval Support in BFD		Common Interval Support in BFD
	draft-ietf-bfd-intervals-01		draft-ietf-bfd-intervals-02
	Abstract		Abstract
	Some BFD implementations may be restricted to only support several		Some BFD implementations may be restricted to only support several
	interval values. When such BFD implementations speak to each other,		interval values. When such BFD implementations speak to each other,
	there is a possibility of two sides not being able to find a common		there is a possibility of two sides not being able to find a common
	interval value to run BFD sessions.		interval value to run BFD sessions.
	This document defines a small set of interval values for BFD that we		This document defines a small set of interval values for BFD that we
	call "Common intervals", and recommends implementations to support		call "Common intervals", and recommends implementations to support
	skipping to change at page 1, line 34		skipping to change at page 1, line 34
	simplified implementation as seen for hardware-based BFD. It does		simplified implementation as seen for hardware-based BFD. It does
	not restrict an implementation from supporting more intervals in		not restrict an implementation from supporting more intervals in
	addition to the Common intervals.		addition to the Common intervals.
	Requirements Language		Requirements Language
	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 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	Status of this Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	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 13, 2014.		This Internet-Draft will expire on January 28, 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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	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 . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. The problem with few supported intervals . . . . . . . . . . . 3		2. The problem with few supported intervals . . . . . . . . . . 3
	3. Well-defined, common intervals . . . . . . . . . . . . . . . . 4		3. Well-defined, common intervals . . . . . . . . . . . . . . . 3
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5		5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	7.1. Normative References . . . . . . . . . . . . . . . . . . . 5		7.1. Normative References . . . . . . . . . . . . . . . . . . 5
	7.2. Informative References . . . . . . . . . . . . . . . . . . 5		7.2. Informative References . . . . . . . . . . . . . . . . . 5
	Appendix A. Why some intervals are in the common set . . . . . . . 5		Appendix A. Why some intervals are in the common set . . . . . . 5
	Appendix B. Timer adjustment with non-identical interval sets . . 6		Appendix B. Timer adjustment with non-identical interval sets . 6
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
	1. Introduction		1. Introduction
	The standard [RFC5880] describes how to calculate the transmission		The standard [RFC5880] describes how to calculate the transmission
	interval and the detection time. It does not make any statement		interval and the detection time. It does not make any statement
	though how to solve a situation where one BFD speaker cannot support		though how to solve a situation where one BFD speaker cannot support
	the calculated value. In practice this may not been a problem as		the calculated value. In practice this may not been a problem as
	long as software-implemented timers have been used and as long as the		long as software-implemented timers have been used and as long as the
	granularity of such timers was small compared to the interval values		granularity of such timers was small compared to the interval values
	being supported, i.e. as long as the error in the timer interval was		being supported, i.e. as long as the error in the timer interval was
	skipping to change at page 4, line 40		skipping to change at page 4, line 21
	20msec, 50msec, 100msec and 1sec.		20msec, 50msec, 100msec and 1sec.
	In addition support for 10sec interval together with multiplier		In addition support for 10sec interval together with multiplier
	values up to 255 is recommended to support graceful restart.		values up to 255 is recommended to support graceful restart.
	The adjustment is always towards larger, i.e. slower, interval values		The adjustment is always towards larger, i.e. slower, interval values
	when the initial interval proposed by the peer is not supported.		when the initial interval proposed by the peer is not supported.
	This document is not adding new requirements with respect to how		This document is not adding new requirements with respect to how
	exact a timer value must be implemented. Supporting an interval		exact a timer value must be implemented. Supporting an interval
	value means to advertise this value in the DesiredMinTxInterval		value means to advertise this value in the DesiredMinTxInterval and/
	and/or RequiredMinRxInterval field of the BFD packets and to provide		or RequiredMinRxInterval field of the BFD packets and to provide
	timers that are reasonably close. [RFC5880] defines safety margins		timers that are reasonably close. [RFC5880] defines safety margins
	for the timers by defining a jitter range.		for the timers by defining a jitter range.
	How is the "Common interval set" used exactly? In the example above,		How is the "Common interval set" used exactly? In the example above,
	vendor "A" has a fastest interval of 10msec and thus would be		vendor "A" has a fastest interval of 10msec and thus would be
	required to support all intervals in the common set that are equal or		required to support all intervals in the common set that are equal or
	larger than 10msec, i.e. it would support 10msec, 20msec, 50msec,		larger than 10msec, i.e. it would support 10msec, 20msec, 50msec,
	100msec, 1sec. Vendor "B" has a fastest interval of 20msec and thus		100msec, 1sec. Vendor "B" has a fastest interval of 20msec and thus
	would need to support 20msec, 50msec, 100msec and 1sec. As long as		would need to support 20msec, 50msec, 100msec and 1sec. As long as
	this requirement is met for the common set of values, then both		this requirement is met for the common set of values, then both
	skipping to change at page 5, line 38		skipping to change at page 5, line 21
	[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.
	7.2. Informative References		7.2. Informative References
	[G.8013_Y.1731]		[G.8013_Y.1731]
	ITU-T G.8013/Y.1731, "ITU-T OAM functions and mechanisms		ITU-T G.8013/Y.1731, "ITU-T OAM functions and mechanisms
	for Ethernet based network", November 2013.		for Ethernet based network", November 2013.
			[GR-253-CORE]
			Telcordia Technologies, Inc., "Synchronous Optical Network
			(SONET) Transport Systems: Common Generic Criteria",
			October 2009.
	Appendix A. Why some intervals are in the common set		Appendix A. Why some intervals are in the common set
	The list of common interval values is trying to balance various		The list of common interval values is trying to balance various
	objectives. The list should not contain too many values as more		objectives. The list should not contain too many values as more
	timers may increase the implementation costs. On the other hand less		timers may increase the implementation costs. On the other hand less
	values produces larger gaps and adjustment jumps. More values in the		values produces larger gaps and adjustment jumps. More values in the
	lower interval range is thus seen as critical to support customer		lower interval range is thus seen as critical to support customer
	needs for fast detection in setups with multiple vendors.		needs for fast detection in setups with multiple vendors.
	o 3.3msec: required by MPLS-TP		o 3.3msec: required by MPLS-TP, adopting the detection time of
			10msec from [GR-253-CORE].
	o 10msec: general consensus is to support 10msec.		o 10msec: general consensus is to support 10msec. Multiple vendors
			plan to or do already implement 10msec.
	o 20msec: basically avoids a larger gap in this critical interval		o 20msec: basically avoids a larger gap in this critical interval
	region. Still allows 50-60msec detect and restore (with		region. Still allows 50-60msec detect and restore (with
	multiplier of 2) and covers existing software-based		multiplier of 2) and covers existing software-based
	implementations.		implementations.
	o 50msec: widely deployed interval. Supporting this value reflects		o 50msec: widely deployed interval. Supporting this value reflects
	reality of many BFD implementations today.		reality of many BFD implementations today.
	o 100msec: similar to 10msec this value allows the reuse of		o 100msec: similar to 10msec this value allows the reuse of
End of changes. 10 change blocks.
	21 lines changed or deleted		28 lines changed or added
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