draft-ietf-bfd-intervals-02.txt		draft-ietf-bfd-intervals-03.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: January 28, 2015 G. Mirsky		Expires: February 17, 2015 G. Mirsky
	Ericsson		Ericsson
	July 27, 2014		August 16, 2014
	Common Interval Support in BFD		Common Interval Support in BFD
	draft-ietf-bfd-intervals-02		draft-ietf-bfd-intervals-03
	Abstract		Abstract
	Some BFD implementations may be restricted to only support several		BFD requires that messages are transmitted at regular intervals and
	interval values. When such BFD implementations speak to each other,		provides a way to negotiate the interval used by BFD peers. Some BFD
	there is a possibility of two sides not being able to find a common		implementations may be restricted to only support several interval
	interval value to run BFD sessions.		values. When such BFD implementations speak to each other, there is
			a possibility of two sides not being able to find a common 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
	the defined intervals. This solves the problem of finding an		the defined intervals. This solves the problem of finding an
	interval value that both BFD speakers can support while allowing a		interval value that both BFD speakers can support while allowing a
	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
	skipping to change at page 1, line 48		skipping to change at page 2, line 4
	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 February 17, 2015.
	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 . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. The problem with few supported intervals . . . . . . . . . . 3		2. The problem with few supported intervals . . . . . . . . . . 3
	3. Well-defined, common intervals . . . . . . . . . . . . . . . 3		3. Well-defined, common intervals . . . . . . . . . . . . . . . 4
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 4		5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
	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 . . . . . . . . . . . . . . . . . . . . . . . 7		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	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
	small compared to 25 percent jitter.		small compared to 25 percent jitter.
	In the meantime requests exist for very fast interval values, down to		In the meantime requests exist for very fast interval values, down to
	3.3msec for MPLS-TP. At the same time the requested scale for the		3.3msec for MPLS-TP. At the same time the requested scale for the
	number of BFD sessions in increasing. Both requirements have driven		number of BFD sessions is increasing. Both requirements have driven
	vendors to use Network Processors (NP), FPGAs or other hardware-based		vendors to use Network Processors (NP), FPGAs or other hardware-based
	solutions to offload the periodic packet transmission and the timeout		solutions to offload the periodic packet transmission and the timeout
	detection in the receive direction. A potential problem with this		detection in the receive direction. A potential problem with this
	hardware-based BFD is the granularity of the interval timers.		hardware-based BFD is the granularity of the interval timers.
	Depending on the implementation only a few intervals may be		Depending on the implementation only a few intervals may be
	supported, which can cause interoperability problems. This document		supported, which can cause interoperability problems. This document
	proposes a set of interval values that should be supported by all		proposes a set of interval values that should be supported by all
	implementations. Details are laid out in the following sections.		implementations. Details are laid out in the following sections.
	2. The problem with few supported intervals		2. The problem with few supported intervals
	Let's assume vendor "A" supports 10msec, 100msec and 1sec interval		Let's assume vendor "A" supports 10msec, 100msec and 1sec interval
	timers in hardware. Vendor "B" supports every value from 20msec		timers in hardware. Vendor "B" supports every value from 20msec
	onward, with a granularity of 1msec. For a BFD session "A" tries to		onward, with a granularity of 1msec. For a BFD session "A" tries to
	skipping to change at page 4, line 19		skipping to change at page 4, line 26
	The proposed set of Common interval values is: 3.3msec, 10msec,		The proposed set of Common interval values is: 3.3msec, 10msec,
	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 the
	exact a timer value must be implemented. Supporting an interval		precision with which a timer value must be implemented. Supporting
	value means to advertise this value in the DesiredMinTxInterval and/		an interval value means to advertise this value in the
	or RequiredMinRxInterval field of the BFD packets and to provide		DesiredMinTxInterval and/or RequiredMinRxInterval field of the BFD
	timers that are reasonably close. [RFC5880] defines safety margins		packets and to provide timers that are reasonably close. [RFC5880]
	for the timers by defining a jitter range.		defines safety margins 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
	vendor "A" and "B" are free to support additional values outside of		vendor "A" and "B" are free to support additional values outside of
	the common set.		the common set.
	4. IANA Considerations		4. IANA Considerations
	No request to IANA.		No request to IANA.
	5. Security Considerations		5. Security Considerations
	This document does not introduce any additional security issues.		This document does not introduce any additional security concerns.
			The security considerations described in the BFD documents, [RFC5880]
			and others, apply to devices implementing the BFD protocol,
			regardless of whether or not the common interval set is implemented.
	6. Acknowledgements		6. Acknowledgements
	We would like to thank Sylvain Masse and Anca Zamfir for bringing up		We would like to thank Sylvain Masse and Anca Zamfir for bringing up
	the discussion about the Poll sequence, and Jeffrey Haas helped		the discussion about the Poll sequence, and Jeffrey Haas helped
	finding the fine line between "exact" and "pedantic".		finding the fine line between "exact" and "pedantic".
	7. References		7. References
	7.1. Normative References		7.1. Normative References
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