< draft-ietf-6man-impatient-nud-01.txt		draft-ietf-6man-impatient-nud-02.txt >
	6MAN WG E. Nordmark		6MAN WG E. Nordmark
	Internet-Draft Cisco Systems, Inc.		Internet-Draft Cisco Systems, Inc.
	Updates: 4861 (if approved) I. Gashinsky		Updates: 4861 (if approved) I. Gashinsky
	Expires: September 13, 2012 Yahoo!		Expires: January 2, 2013 Yahoo!
	March 12, 2012		Jul 2012
	Neighbor Unreachability Detection is too impatient		Neighbor Unreachability Detection is too impatient
	draft-ietf-6man-impatient-nud-01.txt		draft-ietf-6man-impatient-nud-02.txt
	Abstract		Abstract
	IPv6 Neighbor Discovery includes Neighbor Unreachability Detection.		IPv6 Neighbor Discovery includes Neighbor Unreachability Detection.
	That function is very useful when a host has an alternative, for		That function is very useful when a host has an alternative, for
	instance multiple default routers, since it allows the host to switch		instance multiple default routers, since it allows the host to switch
	to the alternative in short time. This time is 3 seconds after the		to the alternative in short time. This time is 3 seconds after the
	node starts probing by default. However, if there are no		node starts probing by default. However, if there are no
	alternatives, this is far too impatient. This document specifies		alternatives, this is far too impatient. This document specifies
	relaxed rules for Neighbor Discovery retransmissions that allows an		relaxed rules for Neighbor Discovery retransmissions that allows an
	skipping to change at page 1, line 39 ¶		skipping to change at page 1, line 39 ¶
	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 September 13, 2012.		This Internet-Draft will expire on January 2, 2013.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 IETF Trust and the persons identified as the		Copyright (c) 2012 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 3, line 34 ¶		skipping to change at page 3, line 34 ¶
	However, when there is no alternative there are several benefits in		However, when there is no alternative there are several benefits in
	making NUD try probing for a longer time. One of those benefits is		making NUD try probing for a longer time. One of those benefits is
	to be more robust against transient failures, such as spanning tree		to be more robust against transient failures, such as spanning tree
	reconvergence and other layer 2 issues that can take many seconds to		reconvergence and other layer 2 issues that can take many seconds to
	resolve. Marking the NCE as unreachable in that case causes		resolve. Marking the NCE as unreachable in that case causes
	additional multicast on the network. Assuming there are IP packets		additional multicast on the network. Assuming there are IP packets
	to send, the lack of an NCE will result in multicast Neighbor		to send, the lack of an NCE will result in multicast Neighbor
	Solicitations every second instead of the unicast Neighbor		Solicitations every second instead of the unicast Neighbor
	Solicitations that NUD sends.		Solicitations that NUD sends.
	As a result IPv6 is operationally more brittle than IPv4. For IPv4		As a result IPv6 Neighbor Discovery is operationally more brittle
	there is no mandatory time limit on the retransmission behavior for		than IPv4 ARP. For IPv4 there is no mandatory time limit on the
	ARP [RFC0826] which allows implementors to pick more robust schemes.		retransmission behavior for ARP [RFC0826] which allows implementors
			to pick more robust schemes.
	The following constant values in [RFC4861] seem to have been made		The following constant values in [RFC4861] seem to have been made
	part of IPv6 conformance testing: MAX_MULTICAST_SOLICIT,		part of IPv6 conformance testing: MAX_MULTICAST_SOLICIT,
	MAX_UNICAST_SOLICIT, and RETRANS_TIMER. While such strict		MAX_UNICAST_SOLICIT, and RETRANS_TIMER. While such strict
	conformance testing seems consistent with [RFC4861], it means that we		conformance testing seems consistent with [RFC4861], it means that we
	need to update the standard if we want to allow IPv6 Neighbor		need to update the standard if we want to allow IPv6 Neighbor
	Discovery to be as operationally robust as ARP.		Discovery to be as robust as ARP.
	This document updates RFC 4861 to relax the retransmission rules.		This document updates RFC 4861 to relax the retransmission rules.
	Additional motivations for making IPv6 Neighbor Discovery as robust		Additional motivations for making IPv6 Neighbor Discovery more robust
	as ARP are covered in [I-D.gashinsky-v6nd-enhance].		in the face of degenerate conditions are covered in [RFC6583].
	2. Definition Of Terms		2. Definition Of Terms
	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].
	3. Protocol Updates		3. Protocol Updates
	Giving up after three packets spaced one second apart is only		Giving up after three packets spaced one second apart is only
	REQUIRED when there is an alternative, such as an additional default		REQUIRED when there is an alternative, such as an additional default
	route or a redirect.		route or a redirect.
	If implementations transmit more than MAX_*CAST_SOLICIT packets it		If implementations transmit more than MAX_*CAST_SOLICIT packets it
	SHOULD use (binary) exponential backoff of the retransmit timer.		SHOULD use (binary) exponential backoff of the retransmit timer.
	This is to avoid any significant load due to a steady background		This is to avoid any significant load due to a steady background
	level of retransmissions from implementations that try for a long		level of retransmissions from implementations that try for a long
	time.		time.
	However, even if there is no alternative, the protocol needs to be		Even if there is no alternative, the protocol needs to be able to
	able to handle the case when the link-layer address of the		handle the case when the link-layer address of the destination has
	destination has changed by switching to multicast Neighbor		changed by switching to multicast Neighbor Solicitations at some
	Solicitations at some point in time.		point in time.
	In order to capture all the cases above this document introduces a		In order to capture all the cases above this document introduces a
	new UNREACHABLE state in the conceptual model described in [RFC4861].		new UNREACHABLE state in the conceptual model described in [RFC4861].
	A NCE in the UNREACHABLE state retains the link-layer address, and		A NCE in the UNREACHABLE state retains the link-layer address, and
	IPv6 packets continue to be sent to that link-layer address. But in		IPv6 packets continue to be sent to that link-layer address. But in
	the UNREACHABLE state the NUD Neighbor Solicitations are multicast,		the UNREACHABLE state the NUD Neighbor Solicitations are multicast,
	using a timeout that follows a (binary) exponential backoff.		using a timeout that follows a (binary) exponential backoff.
	In the places where RFC4861 says to to discard/delete the NCE after N		In the places where RFC4861 says to to discard/delete the NCE after N
	probes (Section 7.3, 7.3.3 and Appendix C) we will instead transition		probes (Section 7.3, 7.3.3 and Appendix C) we will instead transition
	skipping to change at page 5, line 46 ¶		skipping to change at page 5, line 46 ¶
	That needs to be replaced by:		That needs to be replaced by:
	PROBE Retransmit timeout, Double timeout UNREACHABLE		PROBE Retransmit timeout, Double timeout UNREACHABLE
	N or more Send multicast NS		N or more Send multicast NS
	retransmissions.		retransmissions.
	UNREACHABLE Retransmit timeout Double timeout UNREACHABLE		UNREACHABLE Retransmit timeout Double timeout UNREACHABLE
	Send multicast NS		Send multicast NS
	The binary exponential backoff SHOULD be clamped at some reasonable		The binary exponential backoff SHOULD be clamped at some reasonable
	maximum retransmit timeout, such as 60 seconds. And if there is no		maximum retransmit timeout, such as 60 seconds. If there is no IPv6
	IPv6 packets sent using the UNREACHABLE NCE, then it makes sense to		packets sent using the UNREACHABLE NCE, then it makes sense to stop
	stop the retransmits of the multicast NS until either the NCE is		the retransmits of the multicast NS until either the NCE is garbage
	garbage collected, or there are IPv6 packets sent using the NCE. In		collected or there are IPv6 packets sent using the NCE. The
	essence the multicast NS and associated binary exponential backoff		multicast NS and associated binary exponential backoff can be applied
	can be conditioned on the continued use of the NCE to send IPv6		on the condition of the continued use of the NCE to send IPv6 packets
	packets to the recorded link-layer address.		to the recorded link-layer address.
	A node MAY unicast the first few Neighbor Solicitation messages while		A node MAY unicast the first few Neighbor Solicitation messages while
	in UNREACHABLE state, but it MUST switch to multicast Neighbor		in UNREACHABLE state, but it MUST switch to multicast Neighbor
	Solicitations. Otherwise it would not detect a link-layer address		Solicitations. Otherwise it would not detect a link-layer address
	change for the target.		change for the target.
	4. Example Algorithm		4. Example Algorithm
	This section is NOT normative, but specifies a simple implementation		This section is NOT normative, but specifies a simple implementation
	which conforms with this document. The implementation is described		which conforms with this document. The implementation is described
	skipping to change at page 7, line 21 ¶		skipping to change at page 7, line 21 ¶
	configure are BACKOFF_MULTIPLE, MAX_UNICAST_SOLICIT and		configure are BACKOFF_MULTIPLE, MAX_UNICAST_SOLICIT and
	MAX_MULTICAST_SOLICIT.		MAX_MULTICAST_SOLICIT.
	It would be useful to have a maximum value for		It would be useful to have a maximum value for
	($BACKOFF_MULTIPLE^$solicit_attempt_num)*$RetransTimer so that the		($BACKOFF_MULTIPLE^$solicit_attempt_num)*$RetransTimer so that the
	retransmissions are not too far apart. A value 60 seconds is		retransmissions are not too far apart. A value 60 seconds is
	consistent with DHCP.		consistent with DHCP.
	5. Acknowledgements		5. Acknowledgements
	The comments from Thomas Narten and Philip Homburg have helped		The comments from Thomas Narten, Philip Homburg, and Joel Jaeggli
	improve this draft.		have helped improve this draft.
	6. Security Considerations		6. Security Considerations
	Relaxing the retransmission behavior for NUD has no impact on		Relaxing the retransmission behavior for NUD is belived to have no
	security. In particular, it doesn't impact applying Secure Neighbor		impact on security. In particular, it doesn't impact the application
	Discovery [RFC3971].		Secure Neighbor Discovery [RFC3971].
	7. IANA Considerations		7. IANA Considerations
	This are no IANA considerations for this document.		This are no IANA considerations for this document.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	skipping to change at page 8, line 7 ¶		skipping to change at page 8, line 7 ¶
	[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure		[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
	Neighbor Discovery (SEND)", RFC 3971, March 2005.		Neighbor Discovery (SEND)", RFC 3971, March 2005.
	[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,		[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
	"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,		"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
	September 2007.		September 2007.
	8.2. Informative References		8.2. Informative References
	[I-D.gashinsky-v6nd-enhance]
	Kumari, W., "Operational Neighbor Discovery Problems and
	Enhancements.", draft-gashinsky-v6nd-enhance-00 (work in
	progress), June 2011.
	[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or		[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
	converting network protocol addresses to 48.bit Ethernet		converting network protocol addresses to 48.bit Ethernet
	address for transmission on Ethernet hardware", STD 37,		address for transmission on Ethernet hardware", STD 37,
	RFC 826, November 1982.		RFC 826, November 1982.
			[RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
			Neighbor Discovery Problems", RFC 6583, March 2012.
	Authors' Addresses		Authors' Addresses
	Erik Nordmark		Erik Nordmark
	Cisco Systems, Inc.		Cisco Systems, Inc.
	510 McCarthy Blvd.		510 McCarthy Blvd.
	Milpitas, CA, 95035		Milpitas, CA, 95035
	USA		USA
	Phone: +1 408 527 6625		Phone: +1 408 527 6625
	Email: nordmark@cisco.com		Email: nordmark@cisco.com
End of changes. 12 change blocks.
	31 lines changed or deleted		30 lines changed or added
This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/