< draft-carpenter-6man-ug-00.txt		draft-carpenter-6man-ug-01.txt >
	6MAN B. Carpenter		6MAN B. Carpenter
	Internet-Draft Univ. of Auckland		Internet-Draft Univ. of Auckland
	Intended status: Informational S. Jiang		Updates: 4291 (if approved) S. Jiang
	Expires: August 4, 2013 Huawei Technologies Co., Ltd		Intended status: Standards Track Huawei Technologies Co., Ltd
	January 31, 2013		Expires: August 25, 2013 February 21, 2013
	The U and G bits in IPv6 Interface Identifiers		The U and G bits in IPv6 Interface Identifiers
	draft-carpenter-6man-ug-00		draft-carpenter-6man-ug-01
	Abstract		Abstract
	The IPv6 addressing architecture defines a method by which the		The IPv6 addressing architecture defines a method by which the
	Universal and Group bits of an IEEE link-layer address are mapped		Universal and Group bits of an IEEE link-layer address are mapped
	into an IPv6 unicast interface identifier. This document clarifies		into an IPv6 unicast interface identifier. This document clarifies
	the status of those bits for interface identifiers that are not		the status of those bits for interface identifiers that are not
	derived from an IEEE link-layer address.		derived from an IEEE link-layer address, and updates RFC 4291
			accordingly.
	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 August 4, 2013.		This Internet-Draft will expire on August 25, 2013.
	Copyright Notice		Copyright Notice
	Copyright (c) 2013 IETF Trust and the persons identified as the		Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
			1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3		2. Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Proposed solution . . . . . . . . . . . . . . . . . . . . . . . 5		3. Usefulness of the U and G Bits . . . . . . . . . . . . . . . . 5
	4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5		4. Clarification of Specifications . . . . . . . . . . . . . . . . 6
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5		5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
	7. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 6		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6		8. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 7
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 6		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
	8.2. Informative References . . . . . . . . . . . . . . . . . . 6		9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7		9.2. Informative References . . . . . . . . . . . . . . . . . . 8
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
	1. Introduction		1. Introduction
	NOTE IN DRAFT: This version is in the form of a discussion document,		According to the IPv6 addressing architecture [RFC4291], when a 64-
	but the proposal included uses normative language. If the WG wishes		bit IPv6 unicast Interface Identifier (IID) is formed on the basis of
	to proceed with it, the authors suggest to make it a formal		an IEEE EUI-64 address, usually itself expanded from a 48-bit MAC
	standards-track update of the IPv6 addressing architecture.		address, a particular format must be used:
	According to the IPv6 addressing architecture [RFC4291], when an IPv6
	unicast Interface Identifier (IID) is formed on the basis of an IEEE
	EUI-64 address, usually itself expanded from a 48-bit MAC address, a
	particular format must be used:
	"For all unicast addresses, except those that start with the binary		"For all unicast addresses, except those that start with the binary
	value 000, Interface IDs are required to be 64 bits long and to be		value 000, Interface IDs are required to be 64 bits long and to be
	constructed in Modified EUI-64 format."		constructed in Modified EUI-64 format."
	The specification assumes that that the normal case is to transform		The specification assumes that that the normal case is to transform
	an Ethernet-style address into an IID, preserving the semantics of		an Ethernet-style address into an IID, preserving the information
	two bits in particular:		provided by two bits in particular:
	o The "u" bit in an IEEE address is set to 0 to indicate universal		o The "u" bit in an IEEE address is set to 0 to indicate universal
	scope (implying uniqueness) or to 1 to indicate local scope		scope (implying uniqueness) or to 1 to indicate local scope
	(without implying uniqueness). In an IID this bit is inverted,		(without implying uniqueness). In an IID this bit is inverted,
	i.e., 1 for universal scope and 0 for local scope. According to		i.e., 1 for universal scope and 0 for local scope. According to
	[RFC5342], the reason for this was "to make it easier for network		[RFC5342], the reason for this was "to make it easier for network
	operators to type in local-scope identifiers".		operators to type in local-scope identifiers".
	o The "g" bit in an IEEE address is set to 1 to indicate group		o The "g" bit in an IEEE address is set to 1 to indicate group
	addressing (link-layer multicast). This value is supposed to be		addressing (link-layer multicast). The value of this bit is
	preserved in an IID.		preserved in an IID.
			This document discusses problems observed with the "u" and "g" bits
			as a result of the above requirements. It then discusses the
			usefulness of the two bits, and updates RFC 4291 accordingly.
			1.1. Terminology
	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 [RFC2119].		document are to be interpreted as described in [RFC2119].
	2. Problem statement		2. Problem statement
	Various new forms of IID have been defined or proposed, such as		In addition to IIDs formed from IEEE EUI-64 addresses, various new
	temporary addresses [RFC4941], Cryptographically Generated Addresses		forms of IID have been defined or proposed, such as temporary
	(CGAs) [RFC3972], stable privacy addresses		addresses [RFC4941], Cryptographically Generated Addresses (CGAs)
	[I-D.ietf-6man-stable-privacy-addresses], or mapped addresses		[RFC3972], Hash-Based Addresses (HBAs) [RFC5535], stable privacy
	[I-D.ietf-softwire-4rd]. In each case, the question of how to set		addresses [I-D.ietf-6man-stable-privacy-addresses], or mapped
	and interpret the "u" and "g" bits has been debated. For example,		addresses for 4rd [I-D.ietf-softwire-4rd]. In each case, the
	RFC 3972 specifies that they are zero in CGAs.		question of how to set the "u" and "g" bits has to be decided. For
			example, RFC 3972 specifies that they are both zero in CGAs, and the
	NOTE IN DRAFT: Are there other examples we should include? Are we		same applies to HBAs. On the other hand, RFC 4941 specifies that "u"
	sure that no IID format defines semantics for u/g?		must be zero but leaves "g" variable.
	The question underlying these repeated debates is: do these bits have
	any usefulness as currently defined? Section 2.2.1 of RFC 5342
	discusses the mechanics of the bit allocations but does not explain
	the purpose or value of these bits in an IID. There is an IANA
	registry for reserved IID values [RFC5453] but again there is no
	explanation of the purpose of the "u" and "g" bits.
	Another case where the "u" and "g" bits are specified is in the		Another case where the "u" and "g" bits are specified is in the
	Reserved IPv6 Subnet Anycast Address format [RFC2526], which states		Reserved IPv6 Subnet Anycast Address format [RFC2526], which states
	that "for interface identifiers in EUI-64 format, the universal/local		that "for interface identifiers in EUI-64 format, the universal/local
	bit in the interface identifier MUST be set to 0" (i.e., local) and		bit in the interface identifier MUST be set to 0" (i.e., local) and
	requires that "g" bit to be set to 1. However, the text neither		requires that "g" bit to be set to 1. However, the text neither
	states nor implies any semantics for these bits in anycast addresses.		states nor implies any semantics for these bits in anycast addresses.
			These cases illustrate that the statement quoted above from RFC 4291
			requiring "Modified EUI-64 format" is rather meaningless when applied
			to forms of IID that are not in fact based on an underlying EUI-64
			address. In practice, the IETF has chosen to assign some 64-bit IIDs
			that have nothing to do with EUI-64.
			A particular case is that of /127 prefixes for point-to-point links
			between routers, as standardised by [RFC6164]. The addresses on
			these links are undoubtedly global unicast addresses, but they do not
			have a 64-bit IID. The bits in the positions named "u" and "g" in
			such an IID have no special significance and their values are not
			specified.
			Each time a new IID format is proposed, the question arises whether
			these bits have any meaning. Section 2.2.1 of RFC 5342 discusses the
			mechanics of the bit allocations but does not explain the purpose or
			usefulness of these bits in an IID. There is an IANA registry for
			reserved IID values [RFC5453] but again there is no explanation of
			the purpose of the "u" and "g" bits.
	There was a presumption when IPv6 was designed and the IID format was		There was a presumption when IPv6 was designed and the IID format was
	first specified that a universally unique IID might prove to be very		first specified that a universally unique IID might prove to be very
	useful, for example to contribute to solving the multihoming problem.		useful, for example to contribute to solving the multihoming problem.
	Indeed, the addressing architecture [RFC4291] states this explicitly:		Indeed, the addressing architecture [RFC4291] states this explicitly:
	"The use of the universal/local bit in the Modified EUI-64 format		"The use of the universal/local bit in the Modified EUI-64 format
	identifier is to allow development of future technology that can take		identifier is to allow development of future technology that can take
	advantage of interface identifiers with universal scope."		advantage of interface identifiers with universal scope."
	However, this has not so far proved to be the case. Also, there is		However, this has not so far proved to be the case. Also, there is
	evidence from the field that IEEE MAC addresses with "u" = 0 are		evidence from the field that IEEE MAC addresses with "u" = 0 are
	sometime incorrectly assigned to multiple MAC interfaces. Once		sometime incorrectly assigned to multiple MAC interfaces. Firstly,
	transformed into IID format (with "u" = 1) these identifiers would		there are recurrent reports of manufacturers assigning the same MAC
	purport to be universally unique but would in fact be ambiguous.		address to multiple devices. Secondly, significant re-use of the
	Also, ILNP, the currently specified multihoming solution that might		same virtual MAC address is reported in virtual machine environments.
	be expected to benefit from universally unique IIDs in modified		Once transformed into IID format (with "u" = 1) these identifiers
	EUI-64 format does not in fact rely on them; it uses its own format,		would purport to be universally unique but would in fact be
	defined as a Node Identifier [RFC6741]. We can conclude that the "u"		ambiguous. This has no known harmful effect as long as the
	bit in IIDs has no semantic value. In the case of an IID created		replicated MAC addresses and IIDs are used on different layer 2
	from a MAC address according to RFC 4941, its value is determined by		links. If they are used on the same link, of course there will be a
	the MAC address, but that is all.		problem, to be detected by duplicate address detection [RFC4862], but
			such a problem can usually only be resolved by human intervention.
	The "g" bit in an IID has no meaning in IPv6. If an IID is for some		The conclusion from this is that the "u" bit is not a reliable
	reason created from a MAC group address, the bit will be set, but		indicator of universal uniqueness.
	that is all. Both the "u" and the "g" bit are meaningless in the
	format of an IPv6 multicast group ID [RFC3306], [RFC3307].
	The problem caused by the above is the confusion and distraction		We note that Identifier-Locator Network Protocol (ILNP), a
	caused each time that a new form of IID is proposed. Since the bits		multihoming solution that might be expected to benefit from
	concerned appear to have no useful semantics, this is wasteful.		universally unique IIDs in modified EUI-64 format, does not in fact
			rely on them. ILNP uses its own format, defined as a Node Identifier
			[RFC6741]. ILNP does have the constraint that Node Identifiers must
			be unique within a given site, but as we have just shown, the state
			of the "u" bit does not in any way guarantee this.
	3. Proposed solution		Thus, we can conclude that the value of the "u" bit in IIDs has no
			particular meaning. In the case of an IID created from a MAC address
			according to RFC 4291, its value is determined by the MAC address,
			but that is all.
	It should be noted that IIDs known or guessed to have been created		An IPv6 IID should not be created from a MAC group address, so the
	according to RFC 4941 could be transformed back into MAC addresses,		"g" bit will normally be zero, but this value also has no particular
	for example during fault diagnosis. For that reason, keeping the "u"		meaning. Additionally, the "u" and the "g" bits are both meaningless
	and "g" bits in the IID has operational value. Therefore, the EUI-64		in the format of an IPv6 multicast group ID [RFC3306], [RFC3307].
	to IPv6 IID transformation defined in RFC 4941 MUST be used for all
	cases where an IID is derived from a MAC address.
	However, for all forms of IID that are not derived from an EUI-64 MAC		None of the above implies that there is a problem with using the "u"
	address (or an equivalent form of link-layer address), it is not		and "g" bits in MAC addresses as part of the process of generating
	required to set the "u" and "g" bits in any particular way. These		IIDs from MAC addresses, or with specifying their values in other
	bits have no semantics in an IID. Specifications of other forms of		methods of generating IIDs. What it does imply is that, after an IID
	IID MUST specify how they should be set, without defining any		is generated by any method, no reliable deductions can be made from
	semantics for them.		the state of the "u" and "g" bits; in other words, these bits have no
			useful semantics in an IID.
	The statement about future technology quoted above from RFC 4941 is		Once this is recognised, we can avoid the problematic confusion
	obsolete.		caused by these bits each time that a new form of IID is proposed.
			3. Usefulness of the U and G Bits
			Given that the "u" and "g" bits do not have a reliable meaning in an
			IID, it is relevant to consider what usefulness they do have.
			If an IID is known or guessed to have been created according to RFC
			4291, it could be transformed back into a MAC address. This can be
			very helpful during operational fault diagnosis. For that reason,
			mapping the IEEE "u" and "g" bits into the IID has operational
			usefulness. However, it should be stressed that "u" = "g" = 0 does
			not prove that an IID was formed from a MAC address; on the contrary,
			it might equally result from another method. With other methods,
			there is no reverse transformation available.
			To the extent that each method of IID creation specifies the values
			of the "u" and "g" bits, and that each new method is carefully
			designed in the light of its predecessors, these bits tend to reduce
			the chances of duplicate IIDs.
			4. Clarification of Specifications
			This section describes clarifications to the IPv6 specifications that
			result from the above discussion. Their aim is to reduce confusion
			while retaining the useful aspects of the "u" and "g" bits in IIDs.
			The EUI-64 to IID transformation defined in the IPv6 addressing
			architecture [RFC4291] MUST be used for all cases where an IPv6 IID
			is derived from an IEEE MAC or EUI-64 address. With any other form
			of link layer address, an equivalent transformation SHOULD be used.
			However, the resulting "u" and "g" bits in an IID have no semantics;
			in other words, they have opaque values. In fact, the whole IID
			should be viewed as opaque by third parties.
			Specifications of other forms of 64-bit IID will either specify
			explicitly how the "u" and "g" bits are set, or will simply include
			them as part of a field within the IID. In either case, a semantic
			meaning for these bits MUST NOT be defined.
			In the following statement in section 2.5.1 of the IPv6 addressing
			architecture [RFC4291], the reference to "Modified EUI-64 format"
			applies only to cases where there is an underlying IEEE address:
			"For all unicast addresses, except those that start with the binary
			value 000, Interface IDs are required to be 64 bits long and to be
			constructed in Modified EUI-64 format."
			The following statement in section 2.5.1 of the IPv6 addressing
			architecture [RFC4291] is hereby obsoleted:
			"The use of the universal/local bit in the Modified EUI-64 format
			identifier is to allow development of future technology that can take
			advantage of interface identifiers with universal scope."
	As far as is known, no existing implementation will be affected by		As far as is known, no existing implementation will be affected by
	these changes. The benefit is that future design discussions are		these changes. The benefit is that future design discussions are
	simplified.		simplified.
	4. Security Considerations		5. Security Considerations
	No new security exposures or issues are raised by this document.		No new security exposures or issues are raised by this document.
	5. IANA Considerations		6. IANA Considerations
	This document requests no immediate action by IANA. However, in		This document requests no immediate action by IANA. However, the
	considering future proposed additions to the registry of reserved IID		following should be noted when considering future proposed additions
	values [RFC5453], no special consideration is needed of the "u" and		to the registry of reserved IID values, which requires Standards
	"g" bits, since they have no special meaning.		Action according to [RFC5453]. A reserved IID, or a range of
			reserved IIDs, will most likely specify values for both "u" and "g",
			since they are among the high-order bits. At the present time, none
			of the known methods of generating IIDs will generate "u" = "g" = 1.
			Reserved IIDs with "u" = "g" = 1 are therefore unlikely to collide
			with automatically generated IIDs.
	6. Acknowledgements		7. Acknowledgements
	Valuable comments were received from ... and other participants in		Valuable comments were received from Remi Despres, Fernando Gont,
	the 6MAN working group.		Brian Haberman, Joel Halpern, Ray Hunter, Mark Smith, and other
			participants in the 6MAN working group.
	Brian Carpenter was a visitor at the Computer Laboratory, Cambridge		Brian Carpenter was a visitor at the Computer Laboratory, Cambridge
	University during part of this work.		University during part of this work.
	This document was produced using the xml2rfc tool [RFC2629].		This document was produced using the xml2rfc tool [RFC2629].
	7. Change log [RFC Editor: Please remove]		8. Change log [RFC Editor: Please remove]
			draft-carpenter-6man-ug-01: numerous clarifications following WG
			comments, discussed DAD, added new section on the usefulness of the
			u/g bits, expanded IANA considerations, set intended status,
			2013-02-21.
	draft-carpenter-6man-ug-00: original version, 2013-01-31.		draft-carpenter-6man-ug-00: original version, 2013-01-31.
	8. References		9. References
	8.1. Normative References		9.1. Normative References
	[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.
	[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing		[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
	Architecture", RFC 4291, February 2006.		Architecture", RFC 4291, February 2006.
	[RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage		[RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage
	for IEEE 802 Parameters", BCP 141, RFC 5342,		for IEEE 802 Parameters", BCP 141, RFC 5342,
	September 2008.		September 2008.
	[RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers",		[RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers",
	RFC 5453, February 2009.		RFC 5453, February 2009.
	8.2. Informative References		9.2. Informative References
	[I-D.ietf-6man-stable-privacy-addresses]		[I-D.ietf-6man-stable-privacy-addresses]
	Gont, F., "A method for Generating Stable Privacy-Enhanced		Gont, F., "A method for Generating Stable Privacy-Enhanced
	Addresses with IPv6 Stateless Address Autoconfiguration		Addresses with IPv6 Stateless Address Autoconfiguration
	(SLAAC)", draft-ietf-6man-stable-privacy-addresses-03		(SLAAC)", draft-ietf-6man-stable-privacy-addresses-03
	(work in progress), January 2013.		(work in progress), January 2013.
	[I-D.ietf-softwire-4rd]		[I-D.ietf-softwire-4rd]
	Jiang, S., Despres, R., Penno, R., Lee, Y., Chen, G., and		Jiang, S., Despres, R., Penno, R., Lee, Y., Chen, G., and
	M. Chen, "IPv4 Residual Deployment via IPv6 - a Stateless		M. Chen, "IPv4 Residual Deployment via IPv6 - a Stateless
	skipping to change at page 7, line 8 ¶		skipping to change at page 8, line 37 ¶
	[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6		[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
	Multicast Addresses", RFC 3306, August 2002.		Multicast Addresses", RFC 3306, August 2002.
	[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast		[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
	Addresses", RFC 3307, August 2002.		Addresses", RFC 3307, August 2002.
	[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",		[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
	RFC 3972, March 2005.		RFC 3972, March 2005.
			[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
			Address Autoconfiguration", RFC 4862, September 2007.
	[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy		[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
	Extensions for Stateless Address Autoconfiguration in		Extensions for Stateless Address Autoconfiguration in
	IPv6", RFC 4941, September 2007.		IPv6", RFC 4941, September 2007.
			[RFC5535] Bagnulo, M., "Hash-Based Addresses (HBA)", RFC 5535,
			June 2009.
			[RFC6164] Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
			L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
			Router Links", RFC 6164, April 2011.
	[RFC6741] Atkinson,, RJ., "Identifier-Locator Network Protocol		[RFC6741] Atkinson,, RJ., "Identifier-Locator Network Protocol
	(ILNP) Engineering Considerations", RFC 6741,		(ILNP) Engineering Considerations", RFC 6741,
	November 2012.		November 2012.
	Authors' Addresses		Authors' Addresses
	Brian Carpenter		Brian Carpenter
	Department of Computer Science		Department of Computer Science
	University of Auckland		University of Auckland
	PB 92019		PB 92019
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