draft-ietf-6man-ipv6-subnet-model-00.txt		draft-ietf-6man-ipv6-subnet-model-01.txt
	Network Working Group H. Singh		Network Working Group H. Singh
	Internet-Draft W. Beebee		Internet-Draft W. Beebee
	Intended status: Standards Track Cisco Systems, Inc.		Intended status: Standards Track Cisco Systems, Inc.
	Expires: November 8, 2008 E. Nordmark		Expires: January 11, 2009 E. Nordmark
	Sun Microsystems		Sun Microsystems
	May 7, 2008		July 10, 2008
	IPv6 Subnet Model: the Relationship between Links and Subnet Prefixes		IPv6 Subnet Model: the Relationship between Links and Subnet Prefixes
	draft-ietf-6man-ipv6-subnet-model-00		draft-ietf-6man-ipv6-subnet-model-01
	Status of this Memo		Status of this Memo
	By submitting this Internet-Draft, each author represents that any		By submitting this Internet-Draft, each author represents that any
	applicable patent or other IPR claims of which he or she is aware		applicable patent or other IPR claims of which he or she is aware
	have been or will be disclosed, and any of which he or she becomes		have been or will be disclosed, and any of which he or she becomes
	aware will be disclosed, in accordance with Section 6 of BCP 79.		aware will be disclosed, in accordance with Section 6 of BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	skipping to change at page 1, line 36		skipping to change at page 1, line 36
	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."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt.
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	This Internet-Draft will expire on November 8, 2008.		This Internet-Draft will expire on January 11, 2009.
	Abstract		Abstract
	IPv6 specifies a model of a subnet that is different than the IPv4		IPv6 specifies a model of a subnet that is different than the IPv4
	subnet model. The subtlety of the differences has resulted in		subnet model. The subtlety of the differences has resulted in
	incorrect implementations that do not interoperate. This document		incorrect implementations that do not interoperate. This document
	spells out the most important difference; that an IPv6 address isn't		spells out the most important difference; that an IPv6 address isn't
	automatically associated with an IPv6 on-link prefix.		automatically associated with an IPv6 on-link prefix.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Host Behavior Rules . . . . . . . . . . . . . . . . . . . . . . 4		2. Host Behavior and Rules . . . . . . . . . . . . . . . . . . . . 4
	3. Observed Incorrect Implementation Behavior . . . . . . . . . . 5		3. Observed Incorrect Implementation Behavior . . . . . . . . . . 5
	4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 5		4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5		5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 6		8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
	8.2. Informative References . . . . . . . . . . . . . . . . . . 6		8.2. Informative References . . . . . . . . . . . . . . . . . . 6
			Appendix A. CHANGE HISTORY . . . . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
	Intellectual Property and Copyright Statements . . . . . . . . . . 8		Intellectual Property and Copyright Statements . . . . . . . . . . 9
	1. Introduction		1. Introduction
	IPv4 implementations associate a netmask when an IPv4 address is		IPv4 implementations typically associate a netmask with an address
	assigned to an interface. That netmask together with the IPv4		when an IPv4 address is assigned to an interface. That netmask
	address designates an on-link prefix. Addresses that match this		together with the IPv4 address designates an on-link prefix.
	prefix are viewed as on-link i.e., traffic to these addresses is not		Addresses that are covered by this prefix are viewed as on-link i.e.,
	sent to a router. See section 3.3.1 in [RFC1122]. Further, note		traffic to these addresses is not sent to a router. See section
	that implementations of IPv4 point-to-point interfaces might not have		3.3.1 in [RFC1122]. Prior to the deployment of CIDR, an address's
	an associated IPv4 subnet prefix.		netmask could be derived directly from the address. In the absence
			of specifying a specific netmask when assigning a address, some
			implementations would fall back to deriving the netmask from the
			class of the address.
	The behavior of IPv6 as specified in Neighbor Discovery [RFC4861] is		The behavior of IPv6 as specified in Neighbor Discovery [RFC4861] is
	quite different. The on-link determination is separate from the		quite different. The on-link determination is separate from the
	address assignment. A host can have IPv6 addresses without any		address assignment. A host can have IPv6 addresses without any
	related on-link prefixes or have on-link prefixes that are not		related on-link prefixes or have on-link prefixes that are not
	related to any IPv6 addresses that are assigned to the host. Any		related to any IPv6 addresses that are assigned to the host. Any
	assigned address on an interface should initially be considered as		assigned address on an interface should initially be considered as
	having no internal structure as shown in [RFC4291].		having no internal structure as shown in [RFC4291].
	In IPv6, by default, a host treats only the link-local prefix as on-		In IPv6, by default, a host treats only the link-local prefix as on-
	link.		link.
	The reception of a Prefix Information Option (PIO) with the L-bit set		The reception of a Prefix Information Option (PIO) with the L-bit set
	[RFC4861] and a non-zero valid lifetime creates an entry (or updates		[RFC4861] and a non-zero valid lifetime creates an entry (or updates
	the valid lifetime for an existing entry) in the Prefix List. All		the valid lifetime for an existing entry) in the Prefix List. All
	the prefixes that are on the Prefix List, i.e., have not yet timed		the prefixes that are on the Prefix List, i.e., have not yet timed
	out, are on-link.		out, are on-link.
	In addition to the Prefix List, individual addresses are on-link if		The on-link definition in the Terminology section of [RFC4861]
	they are the target of a Redirect Message indicating on-link, or the		defines the complete list of cases where an address is considered on-
	source of a valid Neighbor Solicitation or Neighbor Advertisement		link. Note, in particular, that Redirect Messages can also indicate
	message. Note that Redirect Messages can also indicate an address is		an address is off-link. Individual address entries can be expired by
	off-link. Individual address entries can be expired by the Neighbor		the Neighbor Unreachability Detection mechanism.
	Unreachability Detection mechanism.
	A host only performs address resolution for IPv6 addresses that are		A host only performs address resolution for IPv6 addresses that are
	on-link. Packets to any other address are sent to a default router.		on-link. Packets to any other address are sent to a default router.
	If there is no default router, then the node should send an ICMPv6		If there is no default router, then the node should send an ICMPv6
	Destination Unreachable indication as specified in [RFC4861] - more		Destination Unreachable indication as specified in [RFC4861] - more
	details are provided in the Host Behavior Rules section. (Note that		details are provided in the Host Behavior Rules section. (Note that
	RFC 4861 changed the behavior when the Default Router List is empty.		RFC 4861 changed the behavior when the Default Router List is empty.
	The behavior in the old version of Neighbor Discovery [RFC2461] was		The behavior in the old version of Neighbor Discovery [RFC2461] was
	different when there were no default routers.)		different when there were no default routers.)
	Failure of host implementations to correctly implement the IPv6		Failure of host implementations to correctly implement the IPv6
	subnet model can result in lack of IPv6 connectivity. See the		subnet model can result in lack of IPv6 connectivity. See the
	Observed Incorrect Implementation Behavior section for details.		Observed Incorrect Implementation Behavior section for details.
	Host behavior is clarified in the Host Behavior Rules section.		Host behavior is clarified in the Host Behavior Rules section.
			Finally, this document mainly restates and clarifies [RFC4861].
	Finally, this document merely restates and clarifies [RFC4861].		2. Host Behavior and Rules
	2. Host Behavior Rules
	A correctly implemented IPv6 host MUST adhere to the following rules:		A correctly implemented IPv6 host MUST adhere to the following rules:
	1. By default only the link-local prefix is on-link.		1. By default only the link-local prefix is on-link.
	2. The configuration of an IPv6 address, whether through IPv6		2. The configuration of an IPv6 address, whether through IPv6
	stateless address autoconfiguration [RFC4862], DHCPv6 [RFC3315],		stateless address autoconfiguration [RFC4862], DHCPv6 [RFC3315],
	or manual configuration MUST NOT imply that any prefix is on-		or manual configuration MUST NOT implicitely cause a prefix
	link. A host is explicitly told that prefixes or addresses are		derived from that address to be treated as on-link. A host
	on-link through the means specified in [RFC4861]. Note that this		considers a prefix to be on-link only through explicit means,
	requirement for manually configured addresses is not explicitly		such as those specified in the on-link definition in the
	mentioned in [RFC4861].		Terminology section of [RFC4861] or via manual configuration.
			Note that the requirement for manually configured addresses is
			not explicitly mentioned in [RFC4861].
	3. On-link determination SHOULD NOT persist across IPv6 interface		3. If on-link determination persists across IPv6 interface
	initializations. Note that section 5.7 of [RFC4862] describes		initializations, then lack of IPv6 connectivity can result. For
	the use of stable storage for addresses acquired with stateless		example, a host receives an RA from a router with on-link prefix
	address autoconfiguration with a note that the Preferred and		A. The host reboots. During the reboot, the router sends out
	Valid Lifetimes must be retained if this approach is used.		prefix A with on-link bit set and a zero lifetime to indicate a
	However no RFC suggests or recommends retaining the on-link		renumbering. The host misses the renumbering. The host comes
	prefixes.		online. Then, the router sends an RA with no PIO. The host uses
			cached on-link prefix A and issues NS's instead of sending
			traffic to a default router. The "Observed Incorrect
			Implementation Behavior" section below describes how this can
			result in lack of IPv6 connectivity.
	4. In the absence of other sources of on-link information, including		4. In the absence of other sources of on-link information, including
	Redirects, if the RA advertises a prefix with the on-link(L) bit		Redirects, if the RA advertises a prefix with the on-link(L) bit
	set and later the Valid Lifetime expires, the host MUST then		set and later the Valid Lifetime expires, the host MUST then
	consider addresses of the prefix to be off-link, as specified by		consider addresses of the prefix to be off-link, as specified by
	the PIO paragraph of section 6.3.4 of [RFC4861].		the PIO paragraph of section 6.3.4 of [RFC4861].
	5. Newer implementations, which are compliant with [RFC4861] MUST		5. Newer implementations, which are compliant with [RFC4861] MUST
	adhere to the following rules. Older implementations, which are		adhere to the following rules. Older implementations, which are
	compliant with [RFC2461] but not [RFC4861] may remain as is. If		compliant with [RFC2461] but not [RFC4861] may remain as is. If
	skipping to change at page 4, line 49		skipping to change at page 5, line 8
	on-link information about any address or prefix:		on-link information about any address or prefix:
	1. The host MUST NOT assume that all destinations are on-link.		1. The host MUST NOT assume that all destinations are on-link.
	2. The host MUST NOT perform address resolution for non-link-		2. The host MUST NOT perform address resolution for non-link-
	local addresses.		local addresses.
	3. Since the host cannot assume the destination is on-link, and		3. Since the host cannot assume the destination is on-link, and
	off-link traffic cannot be sent to a default router (since		off-link traffic cannot be sent to a default router (since
	the Default Router List is empty), address resolution cannot		the Default Router List is empty), address resolution cannot
	be performed. This case is analogous to the behavior		be performed. This case is specified in the last paragraph
	specified in the last paragraph of section 7.2.2 of		of section 4 of [RFC4943]: when there is no route to
	[RFC4861]: when address resolution fails, the host SHOULD		destination, the host should send an ICMPv6 Destination
	send an ICMPv6 Destination Unreachable indication as		Unreachable indication (for example, a locally delivered
	specified in [RFC4861]. The specified behavior MAY be		error message) as specified in the Terminology section of
	extended to cover this case where address resolution cannot		[RFC4861].
	be performed.
	On-link information concerning particular addresses and prefixes		On-link information concerning particular addresses and prefixes
	can make those specific addresses and prefixes on-link, but does		can make those specific addresses and prefixes on-link, but does
	not change the default behavior mentioned above for addresses and		not change the default behavior mentioned above for addresses and
	prefixes not specified. [RFC4943] provides justification for		prefixes not specified. [RFC4943] provides justification for
	these rules.		these rules.
	3. Observed Incorrect Implementation Behavior		3. Observed Incorrect Implementation Behavior
	One incorrect implementation behavior illustrates the severe		One incorrect implementation behavior illustrates the severe
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	4. Conclusion		4. Conclusion
	This document clarifies and summarizes the relationship between links		This document clarifies and summarizes the relationship between links
	and subnet prefixes described in [RFC4861]. Configuration of an IPv6		and subnet prefixes described in [RFC4861]. Configuration of an IPv6
	address does not imply the existence of corresponding on-link		address does not imply the existence of corresponding on-link
	prefixes. One should also look at API considerations for prefix		prefixes. One should also look at API considerations for prefix
	length as described in last paragraph of section 4.2 of [RFC4903].		length as described in last paragraph of section 4.2 of [RFC4903].
	5. Security Considerations		5. Security Considerations
	As this document merely restates and clarifies [RFC4861], it does not		This document mainly restates and clarifies [RFC4861]. It does not
	introduce any new security issues.		introduce any new security issues.
	6. IANA Considerations		6. IANA Considerations
	None.		None.
	7. Acknowledgements		7. Acknowledgements
	Thanks (in alphabetical order) to Adeel Ahmed, Jari Arkko, Ralph		Thanks (in alphabetical order) to Adeel Ahmed, Jari Arkko, Ralph
	Droms, Alun Evans, Dave Forster, Prashanth Krishnamurthy, Suresh		Droms, Alun Evans, Dave Forster, Prashanth Krishnamurthy, Suresh
	skipping to change at page 7, line 5		skipping to change at page 7, line 9
	[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless		[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
	Address Autoconfiguration", RFC 4862, September 2007.		Address Autoconfiguration", RFC 4862, September 2007.
	[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,		[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
	June 2007.		June 2007.
	[RFC4943] Roy, S., Durand, A., and J. Paugh, "IPv6 Neighbor		[RFC4943] Roy, S., Durand, A., and J. Paugh, "IPv6 Neighbor
	Discovery On-Link Assumption Considered Harmful",		Discovery On-Link Assumption Considered Harmful",
	RFC 4943, September 2007.		RFC 4943, September 2007.
			Appendix A. CHANGE HISTORY
			[NOTE TO RFC EDITOR: PLEASE REMOVE THIS SECTION UPON PUBLICATION.]
			Changes in draft-ietf-6man-ipv6-subnet-model-01.txt since -00.txt
			are:
			o Changed Introduction section to remove any mention of src address
			of ND message as a means for on-link determination. Also reworded
			first paragrpah of Introduction section.
			o Reworded bullet 2 of section 2 and added text to clarify on-link
			definition.
			o Added text to bullet 3 of section 2 to make explicit that this is
			a new rule.
			o Reworded bullet 5 of section 2 to clearly explain where ICMPv6
			Destination Unreachable is sent to.
	Authors' Addresses		Authors' Addresses
	Hemant Singh		Hemant Singh
	Cisco Systems, Inc.		Cisco Systems, Inc.
	1414 Massachusetts Ave.		1414 Massachusetts Ave.
	Boxborough, MA 01719		Boxborough, MA 01719
	USA		USA
	Phone: +1 978 936 1622		Phone: +1 978 936 1622
	Email: shemant@cisco.com		Email: shemant@cisco.com
End of changes. 17 change blocks.
	43 lines changed or deleted		70 lines changed or added
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