< draft-ietf-shim6-proto-09.txt		draft-ietf-shim6-proto-10.txt >
	SHIM6 WG E. Nordmark		SHIM6 WG E. Nordmark
	Internet-Draft Sun Microsystems		Internet-Draft Sun Microsystems
	Expires: April 3, 2008 M. Bagnulo		Expires: August 17, 2008 M. Bagnulo
	UC3M		UC3M
	October 2007		February 14, 2008
	Shim6: Level 3 Multihoming Shim Protocol for IPv6		Shim6: Level 3 Multihoming Shim Protocol for IPv6
	draft-ietf-shim6-proto-09.txt		draft-ietf-shim6-proto-10.txt
	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 35 ¶		skipping to change at page 1, line 35 ¶
	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 April 3, 2008.		This Internet-Draft will expire on August 17, 2008.
	Copyright Notice		Copyright Notice
	Copyright (C) The IETF Trust (2007).		Copyright (C) The IETF Trust (2008).
	Abstract		Abstract
	This document defines the Shim6 protocol, a layer 3 shim for		This document defines the Shim6 protocol, a layer 3 shim for
	providing locator agility below the transport protocols, so that		providing locator agility below the transport protocols, so that
	multihoming can be provided for IPv6 with failover and load sharing		multihoming can be provided for IPv6 with failover and load sharing
	properties, without assuming that a multihomed site will have a		properties, without assuming that a multihomed site will have a
	provider independent IPv6 address prefix which is announced in the		provider independent IPv6 address prefix which is announced in the
	global IPv6 routing table. The hosts in a site which has multiple		global IPv6 routing table. The hosts in a site which has multiple
	provider allocated IPv6 address prefixes, will use the Shim6 protocol		provider allocated IPv6 address prefixes, will use the Shim6 protocol
	skipping to change at page 2, line 28 ¶		skipping to change at page 2, line 28 ¶
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
	1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 5		1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	1.2. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 6		1.2. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 6
	1.3. Locators as Upper-layer IDentifiers (ULID) . . . . . . . 6		1.3. Locators as Upper-layer IDentifiers (ULID) . . . . . . . 6
	1.4. IP Multicast . . . . . . . . . . . . . . . . . . . . . . 7		1.4. IP Multicast . . . . . . . . . . . . . . . . . . . . . . 7
	1.5. Renumbering Implications . . . . . . . . . . . . . . . . 8		1.5. Renumbering Implications . . . . . . . . . . . . . . . . 8
	1.6. Placement of the shim . . . . . . . . . . . . . . . . . . 9		1.6. Placement of the shim . . . . . . . . . . . . . . . . . . 9
	1.7. Traffic Engineering . . . . . . . . . . . . . . . . . . . 11		1.7. Traffic Engineering . . . . . . . . . . . . . . . . . . . 11
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 12		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 13
	2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 12		2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 13
	2.2. Notational Conventions . . . . . . . . . . . . . . . . . 15		2.2. Notational Conventions . . . . . . . . . . . . . . . . . 16
	3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 16		3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 17
	4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 18		4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 19
	4.1. Context Tags . . . . . . . . . . . . . . . . . . . . . . 20		4.1. Context Tags . . . . . . . . . . . . . . . . . . . . . . 21
	4.2. Context Forking . . . . . . . . . . . . . . . . . . . . . 20		4.2. Context Forking . . . . . . . . . . . . . . . . . . . . . 21
	4.3. API Extensions . . . . . . . . . . . . . . . . . . . . . 21		4.3. API Extensions . . . . . . . . . . . . . . . . . . . . . 22
	4.4. Securing Shim6 . . . . . . . . . . . . . . . . . . . . . 21		4.4. Securing Shim6 . . . . . . . . . . . . . . . . . . . . . 22
	4.5. Overview of Shim Control Messages . . . . . . . . . . . . 22		4.5. Overview of Shim Control Messages . . . . . . . . . . . . 23
	4.6. Extension Header Order . . . . . . . . . . . . . . . . . 23		4.6. Extension Header Order . . . . . . . . . . . . . . . . . 24
	5. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 25		5. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 26
	5.1. Common Shim6 Message Format . . . . . . . . . . . . . . . 25		5.1. Common Shim6 Message Format . . . . . . . . . . . . . . . 26
	5.2. Payload Extension Header Format . . . . . . . . . . . . . 26		5.2. Payload Extension Header Format . . . . . . . . . . . . . 27
	5.3. Common Shim6 Control header . . . . . . . . . . . . . . . 26		5.3. Common Shim6 Control header . . . . . . . . . . . . . . . 27
	5.4. I1 Message Format . . . . . . . . . . . . . . . . . . . . 28		5.4. I1 Message Format . . . . . . . . . . . . . . . . . . . . 29
	5.5. R1 Message Format . . . . . . . . . . . . . . . . . . . . 29		5.5. R1 Message Format . . . . . . . . . . . . . . . . . . . . 30
	5.6. I2 Message Format . . . . . . . . . . . . . . . . . . . . 31		5.6. I2 Message Format . . . . . . . . . . . . . . . . . . . . 32
	5.7. R2 Message Format . . . . . . . . . . . . . . . . . . . . 33		5.7. R2 Message Format . . . . . . . . . . . . . . . . . . . . 34
	5.8. R1bis Message Format . . . . . . . . . . . . . . . . . . 34		5.8. R1bis Message Format . . . . . . . . . . . . . . . . . . 35
	5.9. I2bis Message Format . . . . . . . . . . . . . . . . . . 36		5.9. I2bis Message Format . . . . . . . . . . . . . . . . . . 37
	5.10. Update Request Message Format . . . . . . . . . . . . . . 38		5.10. Update Request Message Format . . . . . . . . . . . . . . 39
	5.11. Update Acknowledgement Message Format . . . . . . . . . . 39		5.11. Update Acknowledgement Message Format . . . . . . . . . . 40
	5.12. Keepalive Message Format . . . . . . . . . . . . . . . . 40		5.12. Keepalive Message Format . . . . . . . . . . . . . . . . 41
	5.13. Probe Message Format . . . . . . . . . . . . . . . . . . 41		5.13. Probe Message Format . . . . . . . . . . . . . . . . . . 42
	5.14. Error Message Format . . . . . . . . . . . . . . . . . . 41		5.14. Error Message Format . . . . . . . . . . . . . . . . . . 42
	5.15. Option Formats . . . . . . . . . . . . . . . . . . . . . 42		5.15. Option Formats . . . . . . . . . . . . . . . . . . . . . 43
	5.15.1. Responder Validator Option Format . . . . . . . . . 45		5.15.1. Responder Validator Option Format . . . . . . . . . 46
	5.15.2. Locator List Option Format . . . . . . . . . . . . . 45		5.15.2. Locator List Option Format . . . . . . . . . . . . . 46
	5.15.3. Locator Preferences Option Format . . . . . . . . . 47		5.15.3. Locator Preferences Option Format . . . . . . . . . 48
	5.15.4. CGA Parameter Data Structure Option Format . . . . . 49		5.15.4. CGA Parameter Data Structure Option Format . . . . . 50
	5.15.5. CGA Signature Option Format . . . . . . . . . . . . 49		5.15.5. CGA Signature Option Format . . . . . . . . . . . . 50
	5.15.6. ULID Pair Option Format . . . . . . . . . . . . . . 50		5.15.6. ULID Pair Option Format . . . . . . . . . . . . . . 51
	5.15.7. Forked Instance Identifier Option Format . . . . . . 51		5.15.7. Forked Instance Identifier Option Format . . . . . . 52
	5.15.8. Keepalive Timeout Option Format . . . . . . . . . . 51		5.15.8. Keepalive Timeout Option Format . . . . . . . . . . 52
	6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 52		6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 53
	6.1. Conceptual Data Structures . . . . . . . . . . . . . . . 52		6.1. Conceptual Data Structures . . . . . . . . . . . . . . . 53
	6.2. Context States . . . . . . . . . . . . . . . . . . . . . 54		6.2. Context STATES . . . . . . . . . . . . . . . . . . . . . 55
	7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . . 56		7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . . 57
	7.1. Uniqueness of Context Tags . . . . . . . . . . . . . . . 56		7.1. Uniqueness of Context Tags . . . . . . . . . . . . . . . 57
	7.2. Locator Verification . . . . . . . . . . . . . . . . . . 56		7.2. Locator Verification . . . . . . . . . . . . . . . . . . 57
	7.3. Normal context establishment . . . . . . . . . . . . . . 57		7.3. Normal context establishment . . . . . . . . . . . . . . 58
	7.4. Concurrent context establishment . . . . . . . . . . . . 57		7.4. Concurrent context establishment . . . . . . . . . . . . 58
	7.5. Context recovery . . . . . . . . . . . . . . . . . . . . 59		7.5. Context recovery . . . . . . . . . . . . . . . . . . . . 60
	7.6. Context confusion . . . . . . . . . . . . . . . . . . . . 61		7.6. Context confusion . . . . . . . . . . . . . . . . . . . . 62
	7.7. Sending I1 messages . . . . . . . . . . . . . . . . . . . 62		7.7. Sending I1 messages . . . . . . . . . . . . . . . . . . . 63
	7.8. Retransmitting I1 messages . . . . . . . . . . . . . . . 63		7.8. Retransmitting I1 messages . . . . . . . . . . . . . . . 64
	7.9. Receiving I1 messages . . . . . . . . . . . . . . . . . . 63		7.9. Receiving I1 messages . . . . . . . . . . . . . . . . . . 64
	7.10. Sending R1 messages . . . . . . . . . . . . . . . . . . . 64		7.10. Sending R1 messages . . . . . . . . . . . . . . . . . . . 65
	7.10.1. Generating the R1 Validator . . . . . . . . . . . . 65		7.10.1. Generating the R1 Validator . . . . . . . . . . . . 66
	7.11. Receiving R1 messages and sending I2 messages . . . . . . 65		7.11. Receiving R1 messages and sending I2 messages . . . . . . 66
	7.12. Retransmitting I2 messages . . . . . . . . . . . . . . . 66		7.12. Retransmitting I2 messages . . . . . . . . . . . . . . . 67
	7.13. Receiving I2 messages . . . . . . . . . . . . . . . . . . 66		7.13. Receiving I2 messages . . . . . . . . . . . . . . . . . . 68
	7.14. Sending R2 messages . . . . . . . . . . . . . . . . . . . 68		7.14. Sending R2 messages . . . . . . . . . . . . . . . . . . . 69
	7.15. Match for Context Confusion . . . . . . . . . . . . . . . 68		7.15. Match for Context Confusion . . . . . . . . . . . . . . . 70
	7.16. Receiving R2 messages . . . . . . . . . . . . . . . . . . 69		7.16. Receiving R2 messages . . . . . . . . . . . . . . . . . . 70
	7.17. Sending R1bis messages . . . . . . . . . . . . . . . . . 70		7.17. Sending R1bis messages . . . . . . . . . . . . . . . . . 71
	7.17.1. Generating the R1bis Validator . . . . . . . . . . . 71		7.17.1. Generating the R1bis Validator . . . . . . . . . . . 72
	7.18. Receiving R1bis messages and sending I2bis messages . . . 71		7.18. Receiving R1bis messages and sending I2bis messages . . . 72
	7.19. Retransmitting I2bis messages . . . . . . . . . . . . . . 72		7.19. Retransmitting I2bis messages . . . . . . . . . . . . . . 73
	7.20. Receiving I2bis messages and sending R2 messages . . . . 72		7.20. Receiving I2bis messages and sending R2 messages . . . . 74
	8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 75		8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 76
	9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . . 77		9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . . 79
	10. Updating the Peer . . . . . . . . . . . . . . . . . . . . . . 78		10. Updating the Peer . . . . . . . . . . . . . . . . . . . . . . 80
	10.1. Sending Update Request messages . . . . . . . . . . . . . 78		10.1. Sending Update Request messages . . . . . . . . . . . . . 80
	10.2. Retransmitting Update Request messages . . . . . . . . . 78		10.2. Retransmitting Update Request messages . . . . . . . . . 80
	10.3. Newer Information While Retransmitting . . . . . . . . . 79		10.3. Newer Information While Retransmitting . . . . . . . . . 81
	10.4. Receiving Update Request messages . . . . . . . . . . . . 79		10.4. Receiving Update Request messages . . . . . . . . . . . . 81
	10.5. Receiving Update Acknowledgement messages . . . . . . . . 81		10.5. Receiving Update Acknowledgement messages . . . . . . . . 83
	11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . . 83		11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . . 85
	11.1. Sending ULP Payload after a Switch . . . . . . . . . . . 83		11.1. Sending ULP Payload after a Switch . . . . . . . . . . . 85
	12. Receiving Packets . . . . . . . . . . . . . . . . . . . . . . 85		12. Receiving Packets . . . . . . . . . . . . . . . . . . . . . . 87
	12.1. Receiving payload without extension headers . . . . . . . 85		12.1. Receiving payload without extension headers . . . . . . . 87
	12.2. Receiving Payload Extension Headers . . . . . . . . . . . 85		12.2. Receiving Payload Extension Headers . . . . . . . . . . . 87
	12.3. Receiving Shim Control messages . . . . . . . . . . . . . 86		12.3. Receiving Shim Control messages . . . . . . . . . . . . . 88
	12.4. Context Lookup . . . . . . . . . . . . . . . . . . . . . 86		12.4. Context Lookup . . . . . . . . . . . . . . . . . . . . . 88
	13. Initial Contact . . . . . . . . . . . . . . . . . . . . . . . 89		13. Initial Contact . . . . . . . . . . . . . . . . . . . . . . . 91
	14. Protocol constants . . . . . . . . . . . . . . . . . . . . . 90		14. Protocol constants . . . . . . . . . . . . . . . . . . . . . 92
	15. Implications Elsewhere . . . . . . . . . . . . . . . . . . . 91		15. Implications Elsewhere . . . . . . . . . . . . . . . . . . . 93
	15.1. Congestion Control Considerations . . . . . . . . . . . . 91		15.1. Congestion Control Considerations . . . . . . . . . . . . 93
	15.2. Middle-boxes considerations . . . . . . . . . . . . . . . 91		15.2. Middle-boxes considerations . . . . . . . . . . . . . . . 93
	15.3. Other considerations . . . . . . . . . . . . . . . . . . 92		15.3. Operation and Management Considerations . . . . . . . . . 94
	16. Security Considerations . . . . . . . . . . . . . . . . . . . 94		15.4. Other considerations . . . . . . . . . . . . . . . . . . 95
	17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 97		16. Security Considerations . . . . . . . . . . . . . . . . . . . 97
	18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 99		17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 101
	Appendix A. Possible Protocol Extensions . . . . . . . . . . 100		18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 103
	Appendix B. Simplified State Machine . . . . . . . . . . . . 102		Appendix A. Possible Protocol Extensions . . . . . . . . . . 104
	Appendix B.1. Simplified State Machine diagram . . . . . . . . 107		Appendix B. Simplified STATE Machine . . . . . . . . . . . . 106
	Appendix C. Context Tag Reuse . . . . . . . . . . . . . . . . 109		Appendix B.1. Simplified STATE Machine diagram . . . . . . . . 111
	Appendix C.1. Context Recovery . . . . . . . . . . . . . . . . 109		Appendix C. Context Tag Reuse . . . . . . . . . . . . . . . . 113
	Appendix C.2. Context Confusion . . . . . . . . . . . . . . . . 109		Appendix C.1. Context Recovery . . . . . . . . . . . . . . . . 113
	Appendix C.3. Three Party Context Confusion . . . . . . . . . . 110		Appendix C.2. Context Confusion . . . . . . . . . . . . . . . . 113
	Appendix D. Design Alternatives . . . . . . . . . . . . . . . 111		Appendix C.3. Three Party Context Confusion . . . . . . . . . . 114
	Appendix D.1. Context granularity . . . . . . . . . . . . . . . 111		Appendix D. Design Alternatives . . . . . . . . . . . . . . . 115
			Appendix D.1. Context granularity . . . . . . . . . . . . . . . 115
	Appendix D.2. Demultiplexing of data packets in Shim6		Appendix D.2. Demultiplexing of data packets in Shim6
	communications . . . . . . . . . . . . . . . . . 111		communications . . . . . . . . . . . . . . . . . 115
	Appendix D.2.1. Flow-label . . . . . . . . . . . . . . . . . . . 112		Appendix D.2.1. Flow-label . . . . . . . . . . . . . . . . . . . 116
	Appendix D.2.2. Extension Header . . . . . . . . . . . . . . . . 114		Appendix D.2.2. Extension Header . . . . . . . . . . . . . . . . 118
	Appendix D.3. Context Loss Detection . . . . . . . . . . . . . 115		Appendix D.3. Context Loss Detection . . . . . . . . . . . . . 119
	Appendix D.4. Securing locator sets . . . . . . . . . . . . . . 117		Appendix D.4. Securing locator sets . . . . . . . . . . . . . . 121
	Appendix D.5. ULID-pair context establishment exchange . . . . 120		Appendix D.5. ULID-pair context establishment exchange . . . . 124
	Appendix D.6. Updating locator sets . . . . . . . . . . . . . . 121		Appendix D.6. Updating locator sets . . . . . . . . . . . . . . 125
	Appendix D.7. State Cleanup . . . . . . . . . . . . . . . . . . 121		Appendix D.7. State Cleanup . . . . . . . . . . . . . . . . . . 125
	Appendix E. Change Log . . . . . . . . . . . . . . . . . . . 124		Appendix E. Change Log . . . . . . . . . . . . . . . . . . . 128
	19. References . . . . . . . . . . . . . . . . . . . . . . . . . 130		19. References . . . . . . . . . . . . . . . . . . . . . . . . . 135
	19.1. Normative References . . . . . . . . . . . . . . . . . . 130		19.1. Normative References . . . . . . . . . . . . . . . . . . 135
	19.2. Informative References . . . . . . . . . . . . . . . . . 130		19.2. Informative References . . . . . . . . . . . . . . . . . 135
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 132		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 137
	Intellectual Property and Copyright Statements . . . . . . . . . 133		Intellectual Property and Copyright Statements . . . . . . . . . 138
	1. Introduction		1. Introduction
	This document describes a layer 3 shim approach and protocol for		This document describes a layer 3 shim approach and protocol for
	providing locator agility below the transport protocols, so that		providing locator agility below the transport protocols, so that
	multihoming can be provided for IPv6 with failover and load sharing		multihoming can be provided for IPv6 with failover and load sharing
	properties [11], without assuming that a multihomed site will have a		properties [11], without assuming that a multihomed site will have a
	provider independent IPv6 address which is announced in the global		provider independent IPv6 address which is announced in the global
	IPv6 routing table. The hosts in a site which has multiple provider		IPv6 routing table. The hosts in a site which has multiple provider
	allocated IPv6 address prefixes, will use the Shim6 protocol		allocated IPv6 address prefixes, will use the Shim6 protocol
	skipping to change at page 9, line 8 ¶		skipping to change at page 9, line 8 ¶
	ULID (or at least the prefix on which it is based) is reassigned to		ULID (or at least the prefix on which it is based) is reassigned to
	another site while it is still being used (with another locator) for		another site while it is still being used (with another locator) for
	existing communication.		existing communication.
	In the worst case we could end up with two separate hosts using the		In the worst case we could end up with two separate hosts using the
	same ULID while both of them are communicating with the same host.		same ULID while both of them are communicating with the same host.
	This potential source for confusion is avoided requiring that any		This potential source for confusion is avoided requiring that any
	communication using a ULID MUST be terminated when the ULID becomes		communication using a ULID MUST be terminated when the ULID becomes
	invalid (due to the underlying prefix becoming invalid). This		invalid (due to the underlying prefix becoming invalid). This
	behaviour can be accomplished by explicitly discarding the shim state		behavior can be accomplished by explicitly discarding the shim state
	when the ULID becomes invalid. The context recovery mechanism will		when the ULID becomes invalid. The context recovery mechanism will
	then make the peer aware that the context is gone, and that the ULID		then make the peer aware that the context is gone, and that the ULID
	is no longer present at the same locator(s).		is no longer present at the same locator(s).
	1.6. Placement of the shim		1.6. Placement of the shim
	-----------------------		-----------------------
	| Transport Protocols |		| Transport Protocols |
	-----------------------		-----------------------
	skipping to change at page 9, line 42 ¶		skipping to change at page 9, line 42 ¶
	The proposal uses a multihoming shim layer within the IP layer, i.e.,		The proposal uses a multihoming shim layer within the IP layer, i.e.,
	below the ULPs, as shown in Figure 1, in order to provide ULP		below the ULPs, as shown in Figure 1, in order to provide ULP
	independence. The multihoming shim layer behaves as if it is		independence. The multihoming shim layer behaves as if it is
	associated with an extension header, which would be placed after any		associated with an extension header, which would be placed after any
	routing-related headers in the packet (such as any hop-by-hop		routing-related headers in the packet (such as any hop-by-hop
	options, or routing header). However, when the locator pair is the		options, or routing header). However, when the locator pair is the
	ULID pair there is no data that needs to be carried in an extension		ULID pair there is no data that needs to be carried in an extension
	header, thus none is needed in that case.		header, thus none is needed in that case.
	Layering AH and ESP above the multihoming shim means that IPsec can		Layering AH and ESP above the multihoming shim means that for a
	be made to be unaware of locator changes the same way that transport		native implementation of IPsec, IPsec can be made to be unaware of
	protocols can be unaware. Thus the IPsec security associations		locator changes the same way that transport protocols can be unaware.
	remain stable even though the locators are changing. This means that
	the IP addresses specified in the selectors should be the ULIDs.		A "bump-in-the-stack" or "bump-in-the-wire" IPsec implementation is
			layered in the same place as the application of IPsec in security
			gateways. In that case there might be separate security associations
			for different locators.
	Layering the fragmentation header above the multihoming shim makes		Layering the fragmentation header above the multihoming shim makes
	reassembly robust in the case that there is broken multi-path routing		reassembly robust in the case that there is broken multi-path routing
	which results in using different paths, hence potentially different		which results in using different paths, hence potentially different
	source locators, for different fragments. Thus, effectively the		source locators, for different fragments. Thus, effectively the
	multihoming shim layer is placed between the IP endpoint sublayer,		multihoming shim layer is placed between the IP endpoint sublayer,
	which handles fragmentation, reassembly, and IPsec, and the IP		which handles fragmentation, reassembly, and IPsec, and the IP
	routing sublayer, which selects which next hop and interface to use		routing sublayer, which selects which next hop and interface to use
	for sending out packets.		for sending out packets.
	skipping to change at page 11, line 9 ¶		skipping to change at page 11, line 12 ¶
	Conceptually, one could view this approach as if both ULIDs and		Conceptually, one could view this approach as if both ULIDs and
	locators are being present in every packet, and with a header		locators are being present in every packet, and with a header
	compression mechanism applied that removes the need for the ULIDs to		compression mechanism applied that removes the need for the ULIDs to
	be carried in the packets once the compression state has been		be carried in the packets once the compression state has been
	established. In order for the receiver to recreate a packet with the		established. In order for the receiver to recreate a packet with the
	correct ULIDs there is a need to include some "compression tag" in		correct ULIDs there is a need to include some "compression tag" in
	the data packets. This serves to indicate the correct context to use		the data packets. This serves to indicate the correct context to use
	for decompression when the locator pair in the packet is insufficient		for decompression when the locator pair in the packet is insufficient
	to uniquely identify the context.		to uniquely identify the context.
			There are different types of interactions between the Shim6 layer and
			other protocols. Those intereactions are influenced by the usage of
			the addresses that these other protocols do and the impact of the
			Shim6 mapping on these usages. A detailed analysis of the
			interactions of different portocols, including SCTP, MIP and HIP can
			be found in [19]. Moreover, some applications may need to have a
			richer interaction with the Shim6 sub-layer. In order to enable
			that, a API [23] has been defined to enable greater control and
			information exchange for those applications that need it.
	1.7. Traffic Engineering		1.7. Traffic Engineering
	At the time of this writing it is not clear what requirements for		At the time of this writing it is not clear what requirements for
	traffic engineering make sense for the Shim6 protocol, since the		traffic engineering make sense for the Shim6 protocol, since the
	requirements must both result in some useful behavior as well as be		requirements must both result in some useful behavior as well as be
	implementable using a host-to-host locator agility mechanism like		implementable using a host-to-host locator agility mechanism like
	Shim6.		Shim6.
	Inherent in a scalable multihoming mechanism that separates the		Inherent in a scalable multihoming mechanism that separates the
	locator function of the IP address from identifying function of the		locator function of the IP address from identifying function of the
	skipping to change at page 11, line 32 ¶		skipping to change at page 11, line 45 ¶
	initial ULID, which automatically becomes the initial locator. In		initial ULID, which automatically becomes the initial locator. In
	the case of Shim6 this is performed by applying RFC 3484 address		the case of Shim6 this is performed by applying RFC 3484 address
	selection.		selection.
	This is quite different than the common case of IPv4 multihoming		This is quite different than the common case of IPv4 multihoming
	where the site has a single IP address prefix, since in that case the		where the site has a single IP address prefix, since in that case the
	peer performs no destination address selection.		peer performs no destination address selection.
	Thus in "single prefix multihoming" the site, and in many cases its		Thus in "single prefix multihoming" the site, and in many cases its
	upstream ISPs, can use BGP to exert some control of the ingress path		upstream ISPs, can use BGP to exert some control of the ingress path
	used to reach the site. This capability can't easily be recreated in		used to reach the site. This capability does not by itself exist
	"multiple prefix multihoming" such as Shim6.		"multiple prefix multihoming" such as Shim6. It is conceivable that
			extensions allowing site or provider guidance of host-based
			mechanisms could be developed. But t should be noted that traffic
			engineering via BGP, MPLS or other similar techniques can still be
			applied for traffic on each individual prefix; Shim6 does not remove
			the capability for this. It does provide some additional
			capabilities for hosts to choose between prefixes.
			These capabilities also carry some risk for non-optimal behaviour
			when more than one mechanism attempts to correct problems at the same
			time. However, it should be noted that this is not necessarily a
			situation brought about by Shim6. A more constrained form of this
			capability already exists in IPv6 itself via its support of multiple
			prefixes and address selection rules for starting new communications.
			Even IPv4 hosts with multiple interfaces may have limited
			capabilities to choose interfaces on which they communicate.
			Similarly, upper layers may choose different addresses.
			In general, it is expected that Shim6 is applicable in relatively
			small sites and individual hosts where BGP-style traffic engineering
			operations are unavailable, unlikely or, if run with provider
			independent addressing, might even be harmful considering the growth
			rates in the global routing table.
	The protocol provides a placeholder, in the form of the Locator		The protocol provides a placeholder, in the form of the Locator
	Preferences option, which can be used by hosts to express priority		Preferences option, which can be used by hosts to express priority
	and weight values for each locator. This is intentionally made		and weight values for each locator. This option is merely a place
	identical to the DNS SRV [6] specification of priority and weight, so		holder when it comes to providing traffic engineering; in order to
	that DNS SRV records can be used for initial contact and the shim for		use this in a large site there would have to be a mechanism by which
	failover, and they can use the same way to describe the preferences.		the host can find out what preference values to use, either
	But the Locator Preference option is merely a place holder when it		statically (e.g., some new DHCPv6 option) or dynamically.
	comes to providing traffic engineering; in order to use this in a
	large site there would have to be a mechanism by which the host can
	find out what preference values to use, either statically (e.g., some
	new DHCPv6 option) or dynamically.
	Thus traffic engineering is listed as a possible extension in		Thus traffic engineering is listed as a possible extension in
	Appendix A.		Appendix A.
	2. Terminology		2. 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 RFC 2119 [1].		document are to be interpreted as described in RFC 2119 [1].
	skipping to change at page 15, line 20 ¶		skipping to change at page 16, line 20 ¶
	Ls(A) is the locator set for A, which consists of the locators L1(A),		Ls(A) is the locator set for A, which consists of the locators L1(A),
	L2(A), ... Ln(A). The locator set in not ordered in any particular		L2(A), ... Ln(A). The locator set in not ordered in any particular
	way other than maybe what is returned by the DNS.		way other than maybe what is returned by the DNS.
	ULID(A) is an upper-layer ID for A. In this proposal, ULID(A) is		ULID(A) is an upper-layer ID for A. In this proposal, ULID(A) is
	always one member of A's locator set.		always one member of A's locator set.
	CT(A) is a context tag assigned by A.		CT(A) is a context tag assigned by A.
			STATE (in uppercase) refers to the the specific state of the state
			machine described in Section 6.2
	This document also makes use of internal conceptual variables to		This document also makes use of internal conceptual variables to
	describe protocol behavior and external variables that an		describe protocol behavior and external variables that an
	implementation must allow system administrators to change. The		implementation must allow system administrators to change. The
	specific variable names, how their values change, and how their		specific variable names, how their values change, and how their
	settings influence protocol behavior are provided to demonstrate		settings influence protocol behavior are provided to demonstrate
	protocol behavior. An implementation is not required to have them in		protocol behavior. An implementation is not required to have them in
	the exact form described here, so long as its external behavior is		the exact form described here, so long as its external behavior is
	consistent with that described in this document. See Section 6 for a		consistent with that described in this document. See Section 6 for a
	description of the conceptual data structures.		description of the conceptual data structures.
	skipping to change at page 16, line 18 ¶		skipping to change at page 17, line 18 ¶
	handling path failures independently of the number of IP addresses		handling path failures independently of the number of IP addresses
	(locators) available to the two communicating hosts, and		(locators) available to the two communicating hosts, and
	independently of which host detects the failure condition.		independently of which host detects the failure condition.
	Consider, for example, the case in which both A and B have active		Consider, for example, the case in which both A and B have active
	Shim6 state and where A has only one locator while B has multiple		Shim6 state and where A has only one locator while B has multiple
	locators. In this case, it might be that B is trying to send a		locators. In this case, it might be that B is trying to send a
	packet to A, and has detected a failure condition with the current		packet to A, and has detected a failure condition with the current
	locator pair. Since B has multiple locators it presumably has		locator pair. Since B has multiple locators it presumably has
	multiple ISPs, and consequently likely has alternate egress paths		multiple ISPs, and consequently likely has alternate egress paths
	toward A. However, B cannot vary the destination address (i.e., A's		toward A. B cannot vary the destination address (i.e., A's locator),
	locator), since A has only one locator.		since A has only one locator. However, B may need to vary the source
			address in order to ensure packet delivery.
	The above scenario leads to the assumption that a host should be able
	to cause different egress paths from its site to be used. The most
	reasonable approach to accomplish this is to have the host use
	different source addresses and have the source address affect the
	selection of the site egress. The details of how this can be
	accomplished is beyond the scope of this document, but without this
	capability the ability of the shim to try different "paths" by trying
	different locator pairs will have limited utility.
	The above assumption applies whether or not the ISPs perform ingress		In many cases normal operation of IP routing may cause the packets to
	filtering.		follow a path towards the correct (currently operational) egress. In
			some cases it is possible that a path may be selected based on the
			source address, implying that B will need to select a source address
			corresponding to the currently operating egress. The details of how
			routing can be accomplished is beyond the scope of this document
	In addition, when the site's ISPs perform ingress filtering based on		Also, when the site's ISPs perform ingress filtering based on packet
	packet source addresses, Shim6 assumes that packets sent with		source addresses, Shim6 assumes that packets sent with different
	different source and destination combinations have a reasonable		source and destination combinations have a reasonable chance of
	chance of making it through the relevant ISP's ingress filters. This		making it through the relevant ISP's ingress filters. This can be
	can be accomplished in several ways (all outside the scope of this		accomplished in several ways (all outside the scope of this
	document), such as having the ISPs relax their ingress filters, or		document), such as having the ISPs relax their ingress filters, or
	selecting the egress such that it matches the IP source address		selecting the egress such that it matches the IP source address
	prefix.		prefix. In the case that one egress path has failed but another is
			operating correctly, it may be necessary for the packet's source
	Further discussion of this issue is captured in [16].		(node B in the previous paragraph) to select a source address that
			corresponds to the operational egress, in order to pass the ISP's
			ingress filters.
	The Shim6 approach assumes that there are no IPv6-to-IPv6 NATs on the		The Shim6 approach assumes that there are no IPv6-to-IPv6 NATs on the
	paths, i.e., that the two ends can exchange their own notion of their		paths, i.e., that the two ends can exchange their own notion of their
	IPv6 addresses and that those addresses will also make sense to their		IPv6 addresses and that those addresses will also make sense to their
	peer.		peer.
	The security of the Shim6 protocol relies on the usage of Hash Based		The security of the Shim6 protocol relies on the usage of Hash Based
	Addresses (HBA) [4] and/or Cryptographically Generated Addresses		Addresses (HBA) [4] and/or Cryptographically Generated Addresses
	(CGA) [2]. In the case that HBAs are used, all the addresses		(CGA) [2]. In the case that HBAs are used, all the addresses
	assigned to the host that are included in the Shim6 protocol (either		assigned to the host that are included in the Shim6 protocol (either
	skipping to change at page 21, line 39 ¶		skipping to change at page 22, line 39 ¶
	Several API extensions have been discussed for Shim6, but their		Several API extensions have been discussed for Shim6, but their
	actual specification is out of scope for this document. The simplest		actual specification is out of scope for this document. The simplest
	one would be to add a socket option to be able to have traffic bypass		one would be to add a socket option to be able to have traffic bypass
	the shim (not create any state, and not use any state created by		the shim (not create any state, and not use any state created by
	other traffic). This could be an IPV6_DONTSHIM socket option. Such		other traffic). This could be an IPV6_DONTSHIM socket option. Such
	an option would be useful for protocols, such as DNS, where the		an option would be useful for protocols, such as DNS, where the
	application has its own failover mechanism (multiple NS records in		application has its own failover mechanism (multiple NS records in
	the case of DNS) and using the shim could potentially add extra		the case of DNS) and using the shim could potentially add extra
	latency with no added benefits.		latency with no added benefits.
	Some other API extensions are discussed in Appendix A		Some other API extensions are discussed in Appendix A. The actual
			API extensions are defined in [23].
	4.4. Securing Shim6		4.4. Securing Shim6
	The mechanisms are secured using a combination of techniques:		The mechanisms are secured using a combination of techniques:
	o The HBA technique [4] for verifying the locators to prevent an		o The HBA technique [4] for verifying the locators to prevent an
	attacker from redirecting the packet stream to somewhere else.		attacker from redirecting the packet stream to somewhere else.
	o Requiring a Reachability Probe+Reply /defined in [5]) before a new		o Requiring a Reachability Probe+Reply /defined in [5]) before a new
	locator is used as the destination, in order to prevent 3rd party		locator is used as the destination, in order to prevent 3rd party
	skipping to change at page 22, line 31 ¶		skipping to change at page 23, line 31 ¶
	result is that through this technique, the Shim6 protocol is		result is that through this technique, the Shim6 protocol is
	protected against off-path attackers.		protected against off-path attackers.
	4.5. Overview of Shim Control Messages		4.5. Overview of Shim Control Messages
	The Shim6 context establishment is accomplished using four messages;		The Shim6 context establishment is accomplished using four messages;
	I1, R1, I2, R2. Normally they are sent in that order from initiator		I1, R1, I2, R2. Normally they are sent in that order from initiator
	and responder, respectively. Should both ends attempt to set up		and responder, respectively. Should both ends attempt to set up
	context state at the same time (for the same ULID pair), then their		context state at the same time (for the same ULID pair), then their
	I1 messages might cross in flight, and result in an immediate R2		I1 messages might cross in flight, and result in an immediate R2
	message. [The names of these messages are borrowed from HIP [19].]		message. [The names of these messages are borrowed from HIP [20].]
	R1bis and I2bis messages are defined, which are used to recover a		R1bis and I2bis messages are defined, which are used to recover a
	context after it has been lost. A R1bis message is sent when a Shim6		context after it has been lost. A R1bis message is sent when a Shim6
	control or Payload extension header arrives and there is no matching		control or Payload extension header arrives and there is no matching
	context state at the receiver. When such a message is received, it		context state at the receiver. When such a message is received, it
	will result in the re-creation of the Shim6 context using the I2bis		will result in the re-creation of the Shim6 context using the I2bis
	and R2 messages.		and R2 messages.
	The peers' lists of locators are normally exchanged as part of the		The peers' lists of locators are normally exchanged as part of the
	context establishment exchange. But the set of locators might be		context establishment exchange. But the set of locators might be
	skipping to change at page 42, line 42 ¶		skipping to change at page 43, line 42 ¶
	| 1 | Critical Option not recognized |		| 1 | Critical Option not recognized |
	| | |		| | |
	| 2 | Locator verification method failed (Pointer to the |		| 2 | Locator verification method failed (Pointer to the |
	| | inconsistent Verification method octet) |		| | inconsistent Verification method octet) |
	| | |		| | |
	| 3 | Locator List Generation number out of sync. |		| 3 | Locator List Generation number out of sync. |
	| | |		| | |
	| 4 | Error in the number of locators in a Locator Preference |		| 4 | Error in the number of locators in a Locator Preference |
	| | option |		| | option |
	| | |		| | |
	| 120-127 | Reserved for debugging pruposes |		| 120-127 | Reserved for debugging purposes |
	+---------+---------------------------------------------------------+		+---------+---------------------------------------------------------+
	Table 2		Table 2
	5.15. Option Formats		5.15. Option Formats
	The format of the options is a snapshot of the current HIP option		The format of the options is a snapshot of the current HIP option
	format [19]. However, there is no intention to track any changes to		format [20]. However, there is no intention to track any changes to
	the HIP option format, nor is there an intent to use the same name		the HIP option format, nor is there an intent to use the same name
	space for the option type values. But using the same format will		space for the option type values. But using the same format will
	hopefully make it easier to import HIP capabilities into Shim6 as		hopefully make it easier to import HIP capabilities into Shim6 as
	extensions to Shim6, should this turn out to be useful.		extensions to Shim6, should this turn out to be useful.
	All of the TLV parameters have a length (including Type and Length		All of the TLV parameters have a length (including Type and Length
	fields) which is a multiple of 8 bytes. When needed, padding MUST be		fields) which is a multiple of 8 bytes. When needed, padding MUST be
	added to the end of the parameter so that the total length becomes a		added to the end of the parameter so that the total length becomes a
	multiple of 8 bytes. This rule ensures proper alignment of data. If		multiple of 8 bytes. This rule ensures proper alignment of data. If
	padding is added, the Length field MUST NOT include the padding. Any		padding is added, the Length field MUST NOT include the padding. Any
	skipping to change at page 54, line 5 ¶		skipping to change at page 55, line 5 ¶
	o Reachability state for the locator pairs as specified in [5].		o Reachability state for the locator pairs as specified in [5].
	o During pair exploration, information about the probe messages that		o During pair exploration, information about the probe messages that
	have been sent and received as specified in [5].		have been sent and received as specified in [5].
	o During context establishment phase, Init Nonce, Responder Nonce,		o During context establishment phase, Init Nonce, Responder Nonce,
	Responder Validator and timers related to the different packets		Responder Validator and timers related to the different packets
	sent (I1,I2, R2), as described in Section 7		sent (I1,I2, R2), as described in Section 7
	6.2. Context States		6.2. Context STATES
	The states that are used to describe the Shim6 protocol are as		The STATES that are used to describe the Shim6 protocol are as
	follows:		follows:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| State | Explanation |		| STATE | Explanation |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| IDLE | State machine start |		| IDLE | State machine start |
	| | |		| | |
	| I1-SENT | Initiating context establishment exchange |		| I1-SENT | Initiating context establishment exchange |
	| | |		| | |
	| I2-SENT | Waiting to complete context establishment |		| I2-SENT | Waiting to complete context establishment |
	| | exchange |		| | exchange |
	| | |		| | |
	| I2BIS-SENT | Potential context loss detected |		| I2BIS-SENT | Potential context loss detected |
	| | |		| | |
	| | |		| | |
	| ESTABLISHED | SHIM context established |		| ESTABLISHED | SHIM context established |
	| | |		| | |
	| E-FAILED | Context establishment exchange failed |		| E-FAILED | Context establishment exchange failed |
	| | |		| | |
	| NO-SUPPORT | ICMP Unrecognized Next Header type |		| NO-SUPPORT | ICMP Unrecognized Next Header type |
	| | (type 4, code 1) received indicating |		| | (type 4, code 1) received indicating |
	| | that Shim6 is not supported |		| | that Shim6 is not supported |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	In addition, in each of the aforementioned states, the following		In addition, in each of the aforementioned STATES, the following
	state information is stored:		state information is stored:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| State | Information |		| STATE | Information |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| IDLE | None |		| IDLE | None |
	| | |		| | |
	| I1-SENT | ULID(peer), ULID(local), [FII], CT(local), |		| I1-SENT | ULID(peer), ULID(local), [FII], CT(local), |
	| | INIT nonce, Lp(local), Lp(peer), Ls(local) |		| | INIT nonce, Lp(local), Lp(peer), Ls(local) |
	| | |		| | |
	| I2-SENT | ULID(peer), ULID(local), [FII], CT(local), |		| I2-SENT | ULID(peer), ULID(local), [FII], CT(local), |
	| | INIT nonce, RESP nonce, Lp(local), Lp(peer),|		| | INIT nonce, RESP nonce, Lp(local), Lp(peer),|
	| | Ls(local), Responder Validator |		| | Ls(local), Responder Validator |
	| | |		| | |
	skipping to change at page 56, line 31 ¶		skipping to change at page 57, line 31 ¶
	demultiplexed based solely on the context tag value (without using		demultiplexed based solely on the context tag value (without using
	the locators), the context tag MUST be unique for each context.		the locators), the context tag MUST be unique for each context.
	It is important that context tags are hard to guess for off-path		It is important that context tags are hard to guess for off-path
	attackers. Therefore, if an implementation uses structure in the		attackers. Therefore, if an implementation uses structure in the
	context tag to facilitate efficient lookups, at least 30 bits of the		context tag to facilitate efficient lookups, at least 30 bits of the
	context tag MUST be unstructured and populated by random or pseudo-		context tag MUST be unstructured and populated by random or pseudo-
	random bits.		random bits.
	In addition, in order to minimize the reuse of context tags, the host		In addition, in order to minimize the reuse of context tags, the host
	SHOULD randomly cycle through the unstrucutred tag name space		SHOULD randomly cycle through the unstructured tag name space
	reserved for randomly assigned context tag values,(e.g. following the		reserved for randomly assigned context tag values,(e.g. following the
	guidelines described in [13]).		guidelines described in [13]).
	7.2. Locator Verification		7.2. Locator Verification
	The peer's locators might need to be verified during context		The peer's locators might need to be verified during context
	establishment as well as when handling locator updates in Section 10.		establishment as well as when handling locator updates in Section 10.
	There are two separate aspects of locator verification. One is to		There are two separate aspects of locator verification. One is to
	verify that the locator is tied to the ULID, i.e., that the host		verify that the locator is tied to the ULID, i.e., that the host
	skipping to change at page 62, line 42 ¶		skipping to change at page 63, line 42 ¶
	7.7. Sending I1 messages		7.7. Sending I1 messages
	When the shim layer decides to setup a context for a ULID pair, it		When the shim layer decides to setup a context for a ULID pair, it
	starts by allocating and initializing the context state for its end.		starts by allocating and initializing the context state for its end.
	As part of this it assigns a random context tag to the context that		As part of this it assigns a random context tag to the context that
	is not being used as CT(local) by any other context . In the case		is not being used as CT(local) by any other context . In the case
	that a new API is used and the ULP requests a forked context, the		that a new API is used and the ULP requests a forked context, the
	Forked Instance Identifier value will be set to a non-zero value.		Forked Instance Identifier value will be set to a non-zero value.
	Otherwise, the FII value is zero. Then the initiator can send an I1		Otherwise, the FII value is zero. Then the initiator can send an I1
	message and set the context state to I1-SENT. The I1 message MUST		message and set the context STATE to I1-SENT. The I1 message MUST
	include the ULID pair; normally in the IPv6 source and destination		include the ULID pair; normally in the IPv6 source and destination
	fields. But if the ULID pair for the context is not used as locator		fields. But if the ULID pair for the context is not used as locator
	pair for the I1 message, then a ULID option MUST be included in the		pair for the I1 message, then a ULID option MUST be included in the
	I1 message. In addition, if a Forked Instance Identifier value is		I1 message. In addition, if a Forked Instance Identifier value is
	non-zero, the I1 message MUST include a Context Instance Identifier		non-zero, the I1 message MUST include a Context Instance Identifier
	option containing the correspondent value.		option containing the correspondent value.
	7.8. Retransmitting I1 messages		7.8. Retransmitting I1 messages
	If the host does not receive an I2 or R2 message in response to the		If the host does not receive an I2 or R2 message in response to the
	skipping to change at page 63, line 50 ¶		skipping to change at page 64, line 50 ¶
	Upon the reception of an I1 message, the host extracts the ULID pair		Upon the reception of an I1 message, the host extracts the ULID pair
	and the Forked Instance Identifier from the message. If there is no		and the Forked Instance Identifier from the message. If there is no
	ULID-pair option, then the ULID pair is taken from the source and		ULID-pair option, then the ULID pair is taken from the source and
	destination fields in the IPv6 header. If there is no FII option in		destination fields in the IPv6 header. If there is no FII option in
	the message, then the FII value is taken to be zero.		the message, then the FII value is taken to be zero.
	Next the host looks for an existing context which matches the ULID		Next the host looks for an existing context which matches the ULID
	pair and the FII.		pair and the FII.
	If no state is found (i.e., the state is IDLE), then the host replies		If no state is found (i.e., the STATE is IDLE), then the host replies
	with a R1 message as specified below.		with a R1 message as specified below.
	If such a context exists in ESTABLISHED state, the host verifies that		If such a context exists in ESTABLISHED STATE, the host verifies that
	the locator of the Initiator is included in Ls(peer) (This check is		the locator of the Initiator is included in Ls(peer) (This check is
	unnecessary if there is no ULID-pair option in the I1 message).		unnecessary if there is no ULID-pair option in the I1 message).
	If the state exists in ESTABLISHED state and the locators do not fall		If the state exists in ESTABLISHED STATE and the locators do not fall
	in the locator sets, then the host replies with a R1 message as		in the locator sets, then the host replies with a R1 message as
	specified below. This completes the I1 processing, with the context		specified below. This completes the I1 processing, with the context
	state being unchanged.		STATE being unchanged.
	If the state exists in ESTABLISHED state and the locators do fall in		If the state exists in ESTABLISHED STATE and the locators do fall in
	the sets, then the host compares CT(peer) for the context with the CT		the sets, then the host compares CT(peer) for the context with the CT
	contained in the I1 message.		contained in the I1 message.
	o If the context tags match, then this probably means that the R2		o If the context tags match, then this probably means that the R2
	message was lost and this I1 is a retransmission. In this case,		message was lost and this I1 is a retransmission. In this case,
	the host replies with a R2 message containing the information		the host replies with a R2 message containing the information
	available for the existent context.		available for the existent context.
	o If the context tags do not match, then it probably means that the		o If the context tags do not match, then it probably means that the
	Initiator has lost the context information for this context and it		Initiator has lost the context information for this context and it
	is trying to establish a new one for the same ULID-pair. In this		is trying to establish a new one for the same ULID-pair. In this
	case, the host replies with a R1 message as specified below. This		case, the host replies with a R1 message as specified below. This
	completes the I1 processing, with the context state being		completes the I1 processing, with the context STATE being
	unchanged.		unchanged.
	If the state exists in other state (I1-SENT, I2-SENT, I2BIS-SENT), we		If the state exists in other STATE (I1-SENT, I2-SENT, I2BIS-SENT), we
	are in the situation of Concurrent context establishment described in		are in the situation of Concurrent context establishment described in
	Section 7.4. In this case, the host leaves CT(peer) unchanged, and		Section 7.4. In this case, the host leaves CT(peer) unchanged, and
	replies with a R2 message. This completes the I1 processing, with		replies with a R2 message. This completes the I1 processing, with
	the context state being unchanged.		the context STATE being unchanged.
	7.10. Sending R1 messages		7.10. Sending R1 messages
	When the host needs to send a R1 message in response to the I1		When the host needs to send a R1 message in response to the I1
	message, it copies the Initiator Nonce from the I1 message to the R1		message, it copies the Initiator Nonce from the I1 message to the R1
	message, generates a Responder Nonce and calculates a Responder		message, generates a Responder Nonce and calculates a Responder
	Validator option as suggested in the following section. No state is		Validator option as suggested in the following section. No state is
	created on the host in this case.(Note that the information used to		created on the host in this case.(Note that the information used to
	generate the R1 reply message is either contained in the received I1		generate the R1 reply message is either contained in the received I1
	message or it is global information that is not associated with the		message or it is global information that is not associated with the
	particular requested context (the S and the Responder nonce values)).		particular requested context (the S and the Responder nonce values)).
	When the host needs to send a R2 message in response to the I1		When the host needs to send a R2 message in response to the I1
	message, it copies the Initiator Nonce from the I1 message to the R2		message, it copies the Initiator Nonce from the I1 message to the R2
	message, and otherwise follows the normal rules for forming an R2		message, and otherwise follows the normal rules for forming an R2
	message (see Section 7.14).		message (see Section 7.14).
	7.10.1. Generating the R1 Validator		7.10.1. Generating the R1 Validator
	One way for the responder to properly generate validators is to		As it is stated in Section 5.15.1, the Validator generation mechanism
	maintain a single secret (S) and a running counter (C) for the		is a local choice since the validator is generated and verified by
	Responder Nonce that is incremented in fixed periods of time (this		the same node i.e. the responder. However, in order to provide the
	allows the Responder to verify the age of a Responder Nonce,		required protection, the Validator needs to be generated fullflling
	independently of the context in which it is used).		the conditions described in Section 5.15.1. One way for the
			responder to properly generate validators is to maintain a single
			secret (S) and a running counter (C) for the Responder Nonce that is
			incremented in fixed periods of time (this allows the Responder to
			verify the age of a Responder Nonce, independently of the context in
			which it is used).
	In the case the validator is generated to be included in a R1		When the validator is generated to be included in a R1 message, that
	message, for each I1 message. The responder use the current counter		is sent in respose to a specific I1 message, the responder can
	C value as the Responder Nonce, and use the following information		perform the following procedure to generate the validator value:
	concatenated as input to the one-way function:
			First, the responder uses the current counter C value as the
			Responder Nonce.
			Second, it uses the following information (concatenated) as input to
			the one-way function:
	o The secret S		o The secret S
	o That Responder Nonce		o That Responder Nonce
	o The Initiator Context Tag from the I1 message		o The Initiator Context Tag from the I1 message
	o The ULIDs from the I1 message		o The ULIDs from the I1 message
	o The locators from the I1 message (strictly only needed if they are		o The locators from the I1 message (strictly only needed if they are
	different from the ULIDs)		different from the ULIDs)
	o The forked instance identifier if such option was included in the		o The forked instance identifier if such option was included in the
	I1 message		I1 message
	and then the output of the hash function is used as the validator		Third, it uses the output of the hash function as the validator value
	octet string.		included in the R1 message.
	7.11. Receiving R1 messages and sending I2 messages		7.11. Receiving R1 messages and sending I2 messages
	A host MUST silently discard any received R1 messages that do not		A host MUST silently discard any received R1 messages that do not
	satisfy all of the following validity checks in addition to those		satisfy all of the following validity checks in addition to those
	specified in Section 12.3:		specified in Section 12.3:
	o The Hdr Ext Len field is at least 1, i.e., the length is at least		o The Hdr Ext Len field is at least 1, i.e., the length is at least
	16 octets.		16 octets.
	Upon the reception of an R1 message, the host extracts the Initiator		Upon the reception of an R1 message, the host extracts the Initiator
	Nonce and the Locator Pair from the message (the latter from the		Nonce and the Locator Pair from the message (the latter from the
	source and destination fields in the IPv6 header). Next the host		source and destination fields in the IPv6 header). Next the host
	looks for an existing context which matches the Initiator Nonce and		looks for an existing context which matches the Initiator Nonce and
	where the locators are contained in Ls(peer) and Ls(local),		where the locators are contained in Ls(peer) and Ls(local),
	respectively. If no such context is found, then the R1 message is		respectively. If no such context is found, then the R1 message is
	silently discarded.		silently discarded.
	If such a context is found, then the host looks at the state:		If such a context is found, then the host looks at the STATE:
	o If the state is I1-SENT, then it sends an I2 message as specified		o If the STATE is I1-SENT, then it sends an I2 message as specified
	below.		below.
	o In any other state (I2-SENT, I2BIS-SENT, ESTABLISHED) then the		o In any other STATE (I2-SENT, I2BIS-SENT, ESTABLISHED) then the
	host has already sent an I2 message then this is probably a reply		host has already sent an I2 message then this is probably a reply
	to a retransmitted I1 message, so this R1 message MUST be silently		to a retransmitted I1 message, so this R1 message MUST be silently
	discarded.		discarded.
	When the host sends an I2 message, then it includes the Responder		When the host sends an I2 message, then it includes the Responder
	Validator option that was in the R1 message. The I2 message MUST		Validator option that was in the R1 message. The I2 message MUST
	include the ULID pair; normally in the IPv6 source and destination		include the ULID pair; normally in the IPv6 source and destination
	fields. If a ULID-pair option was included in the I1 message then it		fields. If a ULID-pair option was included in the I1 message then it
	MUST be included in the I2 message as well. In addition, if the		MUST be included in the I2 message as well. In addition, if the
	Forked Instance Identifier value for this context is non-zero, the I2		Forked Instance Identifier value for this context is non-zero, the I2
	message MUST contain a Forked Instance Identifier Option carrying		message MUST contain a Forked Instance Identifier Option carrying
	this value. Besides, the I2 message contains an Initiator Nonce.		this value. Besides, the I2 message contains an Initiator Nonce.
	This is not required to be the same than the one included in the		This is not required to be the same than the one included in the
	previous I1 message.		previous I1 message.
	The I2 message may also include the Initiator's locator list. If		The I2 message may also include the Initiator's locator list. If
	this is the the case, then it must also include the CGA Parameter		this is the the case, then it must also include the CGA Parameter
	Data Structure. If CGA (and not HBA) is used to verify one or more		Data Structure. If CGA (and not HBA) is used to verify one or more
	fo the locators included in the locator list, then Initiator must		of the locators included in the locator list, then Initiator must
	also include a CGA signature option containing the signature.		also include a CGA signature option containing the signature.
	When the I2 message has been sent, the state is set to I2-SENT.		When the I2 message has been sent, the STATE is set to I2-SENT.
	7.12. Retransmitting I2 messages		7.12. Retransmitting I2 messages
	If the initiator does not receive an R2 message after I2_TIMEOUT time		If the initiator does not receive an R2 message after I2_TIMEOUT time
	after sending an I2 message it MAY retransmit the I2 message, using		after sending an I2 message it MAY retransmit the I2 message, using
	binary exponential backoff and randomized timers. The Responder		binary exponential backoff and randomized timers. The Responder
	Validator option might have a limited lifetime, that is, the peer		Validator option might have a limited lifetime, that is, the peer
	might reject Responder Validator options that are older than		might reject Responder Validator options that are older than
	VALIDATOR_MIN_LIFETIME to avoid replay attacks. In the case that the		VALIDATOR_MIN_LIFETIME to avoid replay attacks. In the case that the
	initiator decides not to retransmit I2 messages or in the case that		initiator decides not to retransmit I2 messages or in the case that
	the initiator still does not recieve an R2 message after		the initiator still does not receive an R2 message after
	retransmitting I2 messages I2_RETRIES_MAX times, the initiator SHOULD		retransmitting I2 messages I2_RETRIES_MAX times, the initiator SHOULD
	fall back to retransmitting the I1 message.		fall back to retransmitting the I1 message.
	7.13. Receiving I2 messages		7.13. Receiving I2 messages
	A host MUST silently discard any received I2 messages that do not		A host MUST silently discard any received I2 messages that do not
	satisfy all of the following validity checks in addition to those		satisfy all of the following validity checks in addition to those
	specified in Section 12.3:		specified in Section 12.3:
	o The Hdr Ext Len field is at least 2, i.e., the length is at least		o The Hdr Ext Len field is at least 2, i.e., the length is at least
	skipping to change at page 67, line 27 ¶		skipping to change at page 68, line 37 ¶
	If a CGA Parameter Data Structure (PDS) is included in the message,		If a CGA Parameter Data Structure (PDS) is included in the message,
	then the host MUST verify if the actual PDS contained in the message		then the host MUST verify if the actual PDS contained in the message
	corresponds to the ULID(peer).		corresponds to the ULID(peer).
	If any of the above verifications fails, then the host silently		If any of the above verifications fails, then the host silently
	discards the message and it has completed the I2 processing.		discards the message and it has completed the I2 processing.
	If all the above verifications are successful, then the host proceeds		If all the above verifications are successful, then the host proceeds
	to look for a context state for the Initiator. The host looks for a		to look for a context state for the Initiator. The host looks for a
	context with the extracted ULID pair and FII. If none exist then		context with the extracted ULID pair and FII. If none exist then
	state of the (non-existing) context is viewed as being IDLE, thus the		STATE of the (non-existing) context is viewed as being IDLE, thus the
	actions depend on the state as follows:		actions depend on the STATE as follows:
	o If the state is IDLE (i.e., the context does not exist) the host		o If the STATE is IDLE (i.e., the context does not exist) the host
	allocates a context tag (CT(local)), creates the context state for		allocates a context tag (CT(local)), creates the context state for
	the context, and sets its state to ESTABLISHED. It records		the context, and sets its STATE to ESTABLISHED. It records
	CT(peer), and the peer's locator set as well as its own locator		CT(peer), and the peer's locator set as well as its own locator
	set in the context. It SHOULD perform the HBA/CGA verification of		set in the context. It SHOULD perform the HBA/CGA verification of
	the peer's locator set at this point in time, as specified in		the peer's locator set at this point in time, as specified in
	Section 7.2. Then the host sends an R2 message back as specified		Section 7.2. Then the host sends an R2 message back as specified
	below.		below.
	o If the state is I1-SENT, then the host verifies if the source		o If the STATE is I1-SENT, then the host verifies if the source
	locator is included in Ls(peer) or, it is included in the Locator		locator is included in Ls(peer) or, it is included in the Locator
	List contained in the I2 message and the HBA/CGA verification for		List contained in the I2 message and the HBA/CGA verification for
	this specific locator is successful		this specific locator is successful
	* If this is not the case, then the message is silently discarded		* If this is not the case, then the message is silently discarded
	and the context state remains unchanged.		and the context STATE remains unchanged.
	* If this is the case, then the host updates the context		* If this is the case, then the host updates the context
	information (CT(peer), Ls(peer)) with the data contained in the		information (CT(peer), Ls(peer)) with the data contained in the
	I2 message and the host MUST send a R2 message back as		I2 message and the host MUST send a R2 message back as
	specified below. Note that before updating Ls(peer)		specified below. Note that before updating Ls(peer)
	information, the host SHOULD perform the HBA/CGA validation of		information, the host SHOULD perform the HBA/CGA validation of
	the peer's locator set at this point in time as specified in		the peer's locator set at this point in time as specified in
	Section 7.2. The host moves to ESTABLISHED state.		Section 7.2. The host moves to ESTABLISHED STATE.
	o If the state is ESTABLISHED, I2-SENT, or I2BIS-SENT, then the host		o If the STATE is ESTABLISHED, I2-SENT, or I2BIS-SENT, then the host
	verifies if the source locator is included in Ls(peer) or, it is		verifies if the source locator is included in Ls(peer) or, it is
	included in the Locator List contained in the I2 message and the		included in the Locator List contained in the I2 message and the
	HBA/CGA verification for this specific locator is successful		HBA/CGA verification for this specific locator is successful
	* If this is not the case, then the message is silently discarded		* If this is not the case, then the message is silently discarded
	and the context state remains unchanged.		and the context STATE remains unchanged.
	* If this is the case, then the host updates the context		* If this is the case, then the host updates the context
	information (CT(peer), Ls(peer)) with the data contained in the		information (CT(peer), Ls(peer)) with the data contained in the
	I2 message and the host MUST send a R2 message back as		I2 message and the host MUST send a R2 message back as
	specified in Section 7.14. Note that before updating Ls(peer)		specified in Section 7.14. Note that before updating Ls(peer)
	information, the host SHOULD perform the HBA/CGA validation of		information, the host SHOULD perform the HBA/CGA validation of
	the peer's locator set at this point in time as specified in		the peer's locator set at this point in time as specified in
	Section 7.2. The context state remains unchanged.		Section 7.2. The context STATE remains unchanged.
	7.14. Sending R2 messages		7.14. Sending R2 messages
	Before the host sends the R2 message it MUST look for a possible		Before the host sends the R2 message it MUST look for a possible
	context confusion i.e. where it would end up with multiple contexts		context confusion i.e. where it would end up with multiple contexts
	using the same CT(peer) for the same peer host. See Section 7.15.		using the same CT(peer) for the same peer host. See Section 7.15.
	When the host needs to send an R2 message, the host forms the message		When the host needs to send an R2 message, the host forms the message
	its context tag, copies the Initiator Nonce from the triggering		its context tag, copies the Initiator Nonce from the triggering
	message (I2, I2bis, or I1). In addition, it may include alternative		message (I2, I2bis, or I1). In addition, it may include alternative
	skipping to change at page 69, line 8 ¶		skipping to change at page 70, line 18 ¶
	When the host receives an I2, I2bis, or R2 it MUST look for a		When the host receives an I2, I2bis, or R2 it MUST look for a
	possible context confusion i.e. where it would end up with multiple		possible context confusion i.e. where it would end up with multiple
	contexts using the same CT(peer) for the same peer host. This can		contexts using the same CT(peer) for the same peer host. This can
	happen when it has received the above messages since they create a		happen when it has received the above messages since they create a
	new context with a new CT(peer). Same issue applies when CT(peer) is		new context with a new CT(peer). Same issue applies when CT(peer) is
	updated for an existing context.		updated for an existing context.
	The host takes CT(peer) for the newly created or updated context, and		The host takes CT(peer) for the newly created or updated context, and
	looks for other contexts which:		looks for other contexts which:
	o Are in state ESTABLISHED or I2BIS-SENT.		o Are in STATE ESTABLISHED or I2BIS-SENT.
	o Have the same CT(peer).		o Have the same CT(peer).
	o Where Ls(peer) has at least one locator in common with the newly		o Where Ls(peer) has at least one locator in common with the newly
	created or updated context.		created or updated context.
	If such a context is found, then the host checks if the ULID pair or		If such a context is found, then the host checks if the ULID pair or
	the Forked Instance Identifier different than the ones in the newly		the Forked Instance Identifier different than the ones in the newly
	created or updated context:		created or updated context:
	o If either or both are different, then the peer is reusing the		o If either or both are different, then the peer is reusing the
	context tag for the creation of a context with different ULID pair		context tag for the creation of a context with different ULID pair
	or FII, which is an indication that the peer has lost the original		or FII, which is an indication that the peer has lost the original
	context. In this case, we are in the Context confusion situation,		context. In this case, we are in the Context confusion situation,
	and the host MUST NOT use the old context to send any packets. It		and the host MUST NOT use the old context to send any packets. It
	MAY just discard the old context (after all, the peer has		MAY just discard the old context (after all, the peer has
	discarded it), or it MAY attempt to re-establish the old context		discarded it), or it MAY attempt to re-establish the old context
	by sending a new I1 message and moving its state to I1-SENT. In		by sending a new I1 message and moving its STATE to I1-SENT. In
	any case, once that this situation is detected, the host MUST NOT		any case, once that this situation is detected, the host MUST NOT
	keep two contexts with overlapping Ls(peer) locator sets and the		keep two contexts with overlapping Ls(peer) locator sets and the
	same context tag in ESTABLISHED state, since this would result in		same context tag in ESTABLISHED STATE, since this would result in
	demultiplexing problems on the peer.		demultiplexing problems on the peer.
	o If both are the same, then this context is actually the context		o If both are the same, then this context is actually the context
	that is created or updated, hence there is no confusion.		that is created or updated, hence there is no confusion.
	7.16. Receiving R2 messages		7.16. Receiving R2 messages
	A host MUST silently discard any received R2 messages that do not		A host MUST silently discard any received R2 messages that do not
	satisfy all of the following validity checks in addition to those		satisfy all of the following validity checks in addition to those
	specified in Section 12.3:		specified in Section 12.3:
	o The Hdr Ext Len field is at least 1, i.e., the length is at least		o The Hdr Ext Len field is at least 1, i.e., the length is at least
	16 octets.		16 octets.
	Upon the reception of an R2 message, the host extracts the Initiator		Upon the reception of an R2 message, the host extracts the Initiator
	Nonce and the Locator Pair from the message (the latter from the		Nonce and the Locator Pair from the message (the latter from the
	source and destination fields in the IPv6 header). Next the host		source and destination fields in the IPv6 header). Next the host
	looks for an existing context which matches the Initiator Nonce and		looks for an existing context which matches the Initiator Nonce and
	where the locators are Lp(peer) and Lp(local), respectively. Based		where the locators are Lp(peer) and Lp(local), respectively. Based
	on the state:		on the STATE:
	o If no such context is found, i.e., the state is IDLE, then the		o If no such context is found, i.e., the STATE is IDLE, then the
	message is silently dropped.		message is silently dropped.
	o If state is I1-SENT, I2-SENT, or I2BIS-SENT then the host performs		o If STATE is I1-SENT, I2-SENT, or I2BIS-SENT then the host performs
	the following actions: If a CGA Parameter Data Structure (PDS) is		the following actions: If a CGA Parameter Data Structure (PDS) is
	included in the message, then the host MUST verify that the actual		included in the message, then the host MUST verify that the actual
	PDS contained in the message corresponds to the ULID(peer) as		PDS contained in the message corresponds to the ULID(peer) as
	specified in Section 7.2. If the verification fails, then the		specified in Section 7.2. If the verification fails, then the
	message is silently dropped. If the verification succeeds, then		message is silently dropped. If the verification succeeds, then
	the host records the information from the R2 message in the		the host records the information from the R2 message in the
	context state; it records the peer's locator set and CT(peer).		context state; it records the peer's locator set and CT(peer).
	The host SHOULD perform the HBA/CGA verification of the peer's		The host SHOULD perform the HBA/CGA verification of the peer's
	locator set at this point in time, as specified in Section 7.2.		locator set at this point in time, as specified in Section 7.2.
	The host sets its state to ESTABLISHED.		The host sets its STATE to ESTABLISHED.
	o If the state is ESTABLISHED, the R2 message is silently ignored,		o If the STATE is ESTABLISHED, the R2 message is silently ignored,
	(since this is likely to be a reply to a retransmitted I2		(since this is likely to be a reply to a retransmitted I2
	message).		message).
	Before the host completes the R2 processing it MUST look for a		Before the host completes the R2 processing it MUST look for a
	possible context confusion i.e. where it would end up with multiple		possible context confusion i.e. where it would end up with multiple
	contexts using the same CT(peer) for the same peer host. See		contexts using the same CT(peer) for the same peer host. See
	Section 7.15.		Section 7.15.
	7.17. Sending R1bis messages		7.17. Sending R1bis messages
	skipping to change at page 71, line 16 ¶		skipping to change at page 72, line 27 ¶
	is computed as suggested in the next section.		is computed as suggested in the next section.
	7.17.1. Generating the R1bis Validator		7.17.1. Generating the R1bis Validator
	One way for the responder to properly generate validators is to		One way for the responder to properly generate validators is to
	maintain a single secret (S) and a running counter C for the		maintain a single secret (S) and a running counter C for the
	Responder Nonce that is incremented in fixed periods of time (this		Responder Nonce that is incremented in fixed periods of time (this
	allows the Responder to verify the age of a Responder Nonce,		allows the Responder to verify the age of a Responder Nonce,
	independently of the context in which it is used).		independently of the context in which it is used).
	In the case the validator is generated to be included in a R1bis		When the validator is generated to be included in a R1bis message,
	message, for each received payload extension header or control		that is sent in respose to a specific controls packet or packet
	message, the responder use the counter C value as the Responder		containing the Shim6 payload extension header message, the responder
	Nonce, and use the following information concatenated as input to the		can perform the following procedure to generate the validator value:
	one-way function:
			First, the responder uses the counter C value as the Responder Nonce.
			Second, it uses the following information (concatenated) as input to
			the one-way function:
	o The secret S		o The secret S
	o That Responder Nonce		o That Responder Nonce
	o The Receiver Context tag included in the received packet		o The Receiver Context tag included in the received packet
	o The locators from the received packet		o The locators from the received packet
	and then the output of the hash function is used as the validator		Third, it uses the output of the hash function as the validator
	octet string.		string.
	7.18. Receiving R1bis messages and sending I2bis messages		7.18. Receiving R1bis messages and sending I2bis messages
	A host MUST silently discard any received R1bis messages that do not		A host MUST silently discard any received R1bis messages that do not
	satisfy all of the following validity checks in addition to those		satisfy all of the following validity checks in addition to those
	specified in Section 12.3:		specified in Section 12.3:
	o The Hdr Ext Len field is at least 1, i.e., the length is at least		o The Hdr Ext Len field is at least 1, i.e., the length is at least
	16 octets.		16 octets.
	Upon the reception of an R1bis message, the host extracts the Packet		Upon the reception of an R1bis message, the host extracts the Packet
	Context Tag and the Locator Pair from the message (the latter from		Context Tag and the Locator Pair from the message (the latter from
	the source and destination fields in the IPv6 header). Next the host		the source and destination fields in the IPv6 header). Next the host
	looks for an existing context where the Packet Context Tag matches		looks for an existing context where the Packet Context Tag matches
	CT(peer) and where the locators match Lp(peer) and Lp(local),		CT(peer) and where the locators match Lp(peer) and Lp(local),
	respectively.		respectively.
	o If no such context is not found, i.e., the state is IDLE, then the		o If no such context is not found, i.e., the STATE is IDLE, then the
	R1bis message is silently discarded.		R1bis message is silently discarded.
	o If the state is I1-SENT, I2-SENT, or I2BIS-SENT, then the R1bis		o If the STATE is I1-SENT, I2-SENT, or I2BIS-SENT, then the R1bis
	message is silently discarded.		message is silently discarded.
	o If the state is ESTABLISHED, then we are in the case where the		o If the STATE is ESTABLISHED, then we are in the case where the
	peer has lost the context and the goal is to try to re-establish		peer has lost the context and the goal is to try to re-establish
	it. For that, the host leaves CT(peer) unchanged in the context		it. For that, the host leaves CT(peer) unchanged in the context
	state, transitions to I2BIS-SENT state, and sends a I2bis message,		state, transitions to I2BIS-SENT STATE, and sends a I2bis message,
	including the computed Responder Validator option, the Packet		including the computed Responder Validator option, the Packet
	Context Tag, and the Responder Nonce received in the R1bis		Context Tag, and the Responder Nonce received in the R1bis
	message. This I2bis message is sent using the locator pair		message. This I2bis message is sent using the locator pair
	included in the R1bis message. In the case that this locator pair		included in the R1bis message. In the case that this locator pair
	differs from the ULID pair defined for this context, then an ULID		differs from the ULID pair defined for this context, then an ULID
	option MUST be included in the I2bis message. In addition, if the		option MUST be included in the I2bis message. In addition, if the
	Forked Instance Identifier for this context is non-zero, then a		Forked Instance Identifier for this context is non-zero, then a
	Forked Instance Identifier option carrying the instance identifier		Forked Instance Identifier option carrying the instance identifier
	value for this context MUST be included in the I2bis message. The		value for this context MUST be included in the I2bis message. The
	I2bis message may also include a locator list. If this is the the		I2bis message may also include a locator list. If this is the the
	case, then it must also include the CGA Parameter Data Structure.		case, then it must also include the CGA Parameter Data Structure.
	If CGA (and not HBA) is used to verify one or more fo the locators		If CGA (and not HBA) is used to verify one or more of the locators
	included in the locator list, then Initiator must also include a		included in the locator list, then Initiator must also include a
	CGA signature option containing the signature.		CGA signature option containing the signature.
	7.19. Retransmitting I2bis messages		7.19. Retransmitting I2bis messages
	If the initiator does not receive an R2 message after I2bis_TIMEOUT		If the initiator does not receive an R2 message after I2bis_TIMEOUT
	time after sending an I2bis message it MAY retransmit the I2bis		time after sending an I2bis message it MAY retransmit the I2bis
	message, using binary exponential backoff and randomized timers. The		message, using binary exponential backoff and randomized timers. The
	Responder Validator option might have a limited lifetime, that is,		Responder Validator option might have a limited lifetime, that is,
	the peer might reject Responder Validator options that are older than		the peer might reject Responder Validator options that are older than
	VALIDATOR_MIN_LIFETIME to avoid replay attacks. In the case that the		VALIDATOR_MIN_LIFETIME to avoid replay attacks. In the case that the
	initiator decides not to retransmit I2bis messages or in the case		initiator decides not to retransmit I2bis messages or in the case
	that the initiator still does not recieve an R2 message after		that the initiator still does not receive an R2 message after
	retransmitting I2bis messages I2bis_RETRIES_MAX times, the initiator		retransmitting I2bis messages I2bis_RETRIES_MAX times, the initiator
	SHOULD fallback to retransmitting the I1 message.		SHOULD fallback to retransmitting the I1 message.
	7.20. Receiving I2bis messages and sending R2 messages		7.20. Receiving I2bis messages and sending R2 messages
	A host MUST silently discard any received I2bis messages that do not		A host MUST silently discard any received I2bis messages that do not
	satisfy all of the following validity checks in addition to those		satisfy all of the following validity checks in addition to those
	specified in Section 12.3:		specified in Section 12.3:
	o The Hdr Ext Len field is at least 3, i.e., the length is at least		o The Hdr Ext Len field is at least 3, i.e., the length is at least
	skipping to change at page 73, line 22 ¶		skipping to change at page 74, line 37 ¶
	If a CGA Parameter Data Structure (PDS) is included in the message,		If a CGA Parameter Data Structure (PDS) is included in the message,
	then the host MUST verify if the actual PDS contained in the message		then the host MUST verify if the actual PDS contained in the message
	corresponds to the ULID(peer).		corresponds to the ULID(peer).
	If any of the above verifications fails, then the host silently		If any of the above verifications fails, then the host silently
	discard the message and it has completed the I2bis processing.		discard the message and it has completed the I2bis processing.
	If both verifications are successful, then the host proceeds to look		If both verifications are successful, then the host proceeds to look
	for a context state for the Initiator. The host looks for a context		for a context state for the Initiator. The host looks for a context
	with the extracted ULID pair and FII. If none exist then state of		with the extracted ULID pair and FII. If none exist then STATE of
	the (non-existing) context is viewed as being IDLE, thus the actions		the (non-existing) context is viewed as being IDLE, thus the actions
	depend on the state as follows:		depend on the STATE as follows:
	o If the state is IDLE (i.e., the context does not exist) the host		o If the STATE is IDLE (i.e., the context does not exist) the host
	allocates a context tag (CT(local)), creates the context state for		allocates a context tag (CT(local)), creates the context state for
	the context, and sets its state to ESTABLISHED. The host SHOULD		the context, and sets its STATE to ESTABLISHED. The host SHOULD
	NOT use the Packet Context Tag in the I2bis message for CT(local);		NOT use the Packet Context Tag in the I2bis message for CT(local);
	instead it should pick a new random context tag just as when it		instead it should pick a new random context tag just as when it
	processes an I2 message. It records CT(peer), and the peer's		processes an I2 message. It records CT(peer), and the peer's
	locator set as well as its own locator set in the context. It		locator set as well as its own locator set in the context. It
	SHOULD perform the HBA/CGA verification of the peer's locator set		SHOULD perform the HBA/CGA verification of the peer's locator set
	at this point in time as specified in Section 7.2. Then the host		at this point in time as specified in Section 7.2. Then the host
	sends an R2 message back as specified in Section 7.14.		sends an R2 message back as specified in Section 7.14.
	o If the state is I1-SENT, then the host verifies if the source		o If the STATE is I1-SENT, then the host verifies if the source
	locator is included in Ls(peer) or, it is included in the Locator		locator is included in Ls(peer) or, it is included in the Locator
	List contained in the I2 message and the HBA/CGA verification for		List contained in the I2 message and the HBA/CGA verification for
	this specific locator is successful		this specific locator is successful
	* If this is not the case, then the message is silently		* If this is not the case, then the message is silently
	discarded. The the context state remains unchanged.		discarded. The the context STATE remains unchanged.
	* If this is the case, then the host updates the context		* If this is the case, then the host updates the context
	information (CT(peer), Ls(peer)) with the data contained in the		information (CT(peer), Ls(peer)) with the data contained in the
	I2 message and the host MUST send a R2 message back as		I2 message and the host MUST send a R2 message back as
	specified below. Note that before updating Ls(peer)		specified below. Note that before updating Ls(peer)
	information, the host SHOULD perform the HBA/CGA validation of		information, the host SHOULD perform the HBA/CGA validation of
	the peer's locator set at this point in time as specified in		the peer's locator set at this point in time as specified in
	Section 7.2. The host moves to ESTABLISHED state.		Section 7.2. The host moves to ESTABLISHED STATE.
	o If the state is ESTABLISHED, I2-SENT, or I2BIS-SENT, then the host		o If the STATE is ESTABLISHED, I2-SENT, or I2BIS-SENT, then the host
	verifies if the source locator is included in Ls(peer) or, it is		whther at least one of the two following conditions hold: i) if
	included in the Locator List contained in the I2 message and the		the source locator is included in Ls(peer) or, ii) if the source
	HBA/CGA verification for this specific locator is successful		locator is included in the Locator List contained in the I2
			message and the HBA/CGA verification for this specific locator is
			successful
	* If this is not the case, then the message is silently		* If none of the two aforementioned conditions hold, then the
	discarded. The the context state remains unchanged.		message is silently discarded. The the context STATE remains
			unchanged.
	* If this is the case, then the host updates the context		* If at least one of the two aforementioned conditions hold, then
	information (CT(peer), Ls(peer)) with the data contained in the		the host updates the context information (CT(peer), Ls(peer))
	I2 message and the host MUST send a R2 message back as		with the data contained in the I2 message and the host MUST
	specified in Section 7.14. Note that before updating Ls(peer)		send a R2 message back as specified in Section 7.14. Note that
	information, the host SHOULD perform the HBA/CGA validation of		before updating Ls(peer) information, the host SHOULD perform
	the peer's locator set at this point in time as specified in		the HBA/CGA validation of the peer's locator set at this point
	Section 7.2. The context state remains unchanged.		in time as specified in Section 7.2. The context STATE remains
			unchanged.
	8. Handling ICMP Error Messages		8. Handling ICMP Error Messages
	The routers in the path as well as the destination might generate		The routers in the path as well as the destination might generate
	various ICMP error messages, such as host unreachable, packet too		various ICMP error messages, such as destination unreachable, packet
	big, and Unrecognized Next Header type. It is critical that these		too big, and Unrecognized Next Header type. In some cases, it is
	packets make it back up to the ULPs so that they can take appropriate		critical that these packets make it back up to the ULPs so that they
	action.		can take appropriate action. In other cases, it is probably the best
			option to process these packets locally at the Shim6 layer and not
			inform to the ULP.
	This is an implementation issue in the sense that the mechanism is		This is an implementation issue in the sense that the mechanism is
	completely local to the host itself. But the issue of how ICMP		completely local to the host itself. But the issue of how ICMP
	errors are correctly dispatched to the ULP on the host are important,		errors are correctly dispatched to the ULP on the host are important,
	hence this section specifies the issue.		hence this section specifies the issue.
			The main issue to be consider is whether the reported error can be
			solved by the Shim6 layer or not. In some cases, it is clear that
			the shim6 layer cannot do anything to solve the problem reported by
			the ICMP error e.g. Port unreachable, Packet too big error. In
			these cases, the Shim6 layer should pass these messages to the ULP.
			However, in some other cases, the reported error can be solved by the
			Shim6 layer. For instance, in many of the cases, the Destination
			unreachable error will be solved by the Shim6 layer by changing the
			communication path. In this case, it maynot make sense to pass the
			ICMP error to the ULP, since the problem will be solved by the Shim6
			layer. Nevertheless, it is not clear whether the Shim6 will be able
			to actually solve the problem, since it may be the case that there is
			no communication path available. So the basic guideline to handle
			this situation is: if the Shim6 layer cannot do anything to solve the
			problem reported in the ICMP error, then pass the error to the ULP as
			described below. If the Shim6 layer can try to solve the problem, it
			may make sense to not pass the error to the ULP. This, on the other
			hand, may be implementations specific, meaning that depending what is
			the response of the ULP to the ICMP error, it may be more or less
			critical to actually passing or not the ICMP errors back. In other
			words, if the response of a given ULP to the reception of an ICMP
			error is to close the communication, it is very important that the
			Shim6 layer does not passes the ICMP error unless it is certain that
			there is no alternative path available. If the response of the ULP
			is simply to ignore ICMP error, it may make sense to always pass the
			ICMP errors to the ULP. In any case, we reccommend that the Shim6
			layer provides a configuration interface, so it is possible to
			configure how to process the different ICMP error messages. Below,
			we provide some guidelines on how to process the different ICMP
			errors.
			The following ICMP error messages should be processed by the Shim6
			layer and not passed to the ULP: ICMP error Destiantion unreachable
			with codes 0 (No route to destination), 1 (Communication with
			destination administratively prohibited), 2 (Beyond scope of source
			address), 3 (Address unreachable), 5 (Source address failed ingress/
			egress policy), 6 (Reject route to destination), ICMP Time exceeded
			error, ICMP Parameter problem error with the paramter that caused the
			error being a Shim6 paramter.
			The following ICMP error messages report problems that cannot be
			addressed by the Shim6 layer and that should be passed to the ULP (as
			described below): ICMP Packet too big error, ICMP Destination
			Unreachable with Code 4 (Port unreachable) ICMP Paramenter problem
			(if the paramter that caused the problem is not a Shim6 parameter).
	+--------------+		+--------------+
	| IPv6 Header |		| IPv6 Header |
	| |		| |
	+--------------+		+--------------+
	| ICMPv6 |		| ICMPv6 |
	| Header |		| Header |
	- - +--------------+ - -		- - +--------------+ - -
	| IPv6 Header |		| IPv6 Header |
	| src, dst as | Can be dispatched		| src, dst as | Can be dispatched
	IPv6 | sent by ULP | unmodified to ULP		IPv6 | sent by ULP | unmodified to ULP
	skipping to change at page 75, line 50 ¶		skipping to change at page 77, line 49 ¶
	When the ULP packets are sent without the payload extension header,		When the ULP packets are sent without the payload extension header,
	that is, while the initial locators=ULIDs are working, this		that is, while the initial locators=ULIDs are working, this
	introduces no new concerns; an implementation's existing mechanism		introduces no new concerns; an implementation's existing mechanism
	for delivering these errors to the ULP will work. See Figure 30.		for delivering these errors to the ULP will work. See Figure 30.
	But when the shim on the transmitting side inserts the payload		But when the shim on the transmitting side inserts the payload
	extension header and replaces the ULIDs in the IP address fields with		extension header and replaces the ULIDs in the IP address fields with
	some other locators, then an ICMP error coming back will have a		some other locators, then an ICMP error coming back will have a
	"packet in error" which is not a packet that the ULP sent. Thus the		"packet in error" which is not a packet that the ULP sent. Thus the
	implementation will have to apply the reverse mapping to the "packet		implementation will have to apply the reverse mapping to the "packet
	in error" before passing the ICMP error up to the ULP. See		in error" before passing the ICMP error up to the ULP, including the
	Figure 31.		ICMP extensions defined in [25]. See Figure 31.
	+--------------+		+--------------+
	| IPv6 Header |		| IPv6 Header |
	| |		| |
	+--------------+		+--------------+
	| ICMPv6 |		| ICMPv6 |
	| Header |		| Header |
	- - +--------------+ - -		- - +--------------+ - -
	| IPv6 Header |		| IPv6 Header |
	| src, dst as | Needs to be		| src, dst as | Needs to be
	skipping to change at page 78, line 35 ¶		skipping to change at page 80, line 35 ¶
	in the same Update Request or in some future Update Request, will use		in the same Update Request or in some future Update Request, will use
	that generation number to make sure the preferences get applied to		that generation number to make sure the preferences get applied to
	the correct version of the locator list.		the correct version of the locator list.
	The host picks a random Request Nonce for each update, and keeps the		The host picks a random Request Nonce for each update, and keeps the
	same nonce for any retransmissions of the Update Request. The nonce		same nonce for any retransmissions of the Update Request. The nonce
	is used to match the acknowledgement with the request.		is used to match the acknowledgement with the request.
	The UPDATE message can also include a CGA Parameter Data Structure		The UPDATE message can also include a CGA Parameter Data Structure
	(this is needed if the CGA PDS was not previously exchanged,). If		(this is needed if the CGA PDS was not previously exchanged,). If
	CGA (and not HBA) is used to verify one or more fo the locators		CGA (and not HBA) is used to verify one or more of the locators
	included in the locator list, then a CGA signature option containing		included in the locator list, then a CGA signature option containing
	the signature must also be included in the UPDATE message.		the signature must also be included in the UPDATE message.
	10.2. Retransmitting Update Request messages		10.2. Retransmitting Update Request messages
	If the host does not receive an Update Acknowledgement R2 message in		If the host does not receive an Update Acknowledgement R2 message in
	response to the Update Request message after UPDATE_TIMEOUT time,		response to the Update Request message after UPDATE_TIMEOUT time,
	then it needs to retransmit the Update Request message. The		then it needs to retransmit the Update Request message. The
	retransmissions should use a retransmission timer with binary		retransmissions should use a retransmission timer with binary
	exponential backoff to avoid creating congestion issues for the		exponential backoff to avoid creating congestion issues for the
	skipping to change at page 80, line 19 ¶		skipping to change at page 82, line 19 ¶
	case, the sender of the Update Request has a stale context which		case, the sender of the Update Request has a stale context which
	happens to match the CT(local) for this context. In this case the		happens to match the CT(local) for this context. In this case the
	host MUST send a R1bis message, and otherwise ignore the Update		host MUST send a R1bis message, and otherwise ignore the Update
	Request message.		Request message.
	If a CGA Parameter Data Structure (PDS) is included in the message,		If a CGA Parameter Data Structure (PDS) is included in the message,
	then the host MUST verify if the actual PDS contained in the packet		then the host MUST verify if the actual PDS contained in the packet
	corresponds to the ULID(peer). If this verification fails, the		corresponds to the ULID(peer). If this verification fails, the
	message is silently discarded.		message is silently discarded.
	Then, depending on the state of the context:		Then, depending on the STATE of the context:
	o If ESTABLISHED: Proceed to process message.		o If ESTABLISHED: Proceed to process message.
	o If I1-SENT, discard the message and stay in I1-SENT.		o If I1-SENT, discard the message and stay in I1-SENT.
	o If I2-SENT, then send I2 and proceed to process the message.		o If I2-SENT, then send I2 and proceed to process the message.
	o If I2BIS-SENT, then send I2bis and proceed to process the message.		o If I2BIS-SENT, then send I2bis and proceed to process the message.
	The verification issues for the locators carried in the Locator		The verification issues for the locators carried in the Locator
	skipping to change at page 81, line 41 ¶		skipping to change at page 83, line 41 ¶
	as specified in Section 7.17.		as specified in Section 7.17.
	Since context tags can be reused, the host MUST verify that the IPv6		Since context tags can be reused, the host MUST verify that the IPv6
	source address field is part of Ls(peer) and that the IPv6		source address field is part of Ls(peer) and that the IPv6
	destination address field is part of Ls(local). If this is not the		destination address field is part of Ls(local). If this is not the
	case, the sender of the Update Acknowledgement has a stale context		case, the sender of the Update Acknowledgement has a stale context
	which happens to match the CT(local) for this context. In this case		which happens to match the CT(local) for this context. In this case
	the host MUST send a R1bis message, and otherwise ignore the Update		the host MUST send a R1bis message, and otherwise ignore the Update
	Acknowledgement message.		Acknowledgement message.
	Then, depending on the state of the context:		Then, depending on the STATE of the context:
	o If ESTABLISHED: Proceed to process message.		o If ESTABLISHED: Proceed to process message.
	o If I1-SENT, discard the message and stay in I1-SENT.		o If I1-SENT, discard the message and stay in I1-SENT.
	o If I2-SENT, then send R2 and proceed to process the message.		o If I2-SENT, then send R2 and proceed to process the message.
	o If I2BIS-SENT, then send R2 and proceed to process the message.		o If I2BIS-SENT, then send R2 and proceed to process the message.
	If the Request Nonce doesn't match the Nonce for the last sent Update		If the Request Nonce doesn't match the Nonce for the last sent Update
	skipping to change at page 83, line 14 ¶		skipping to change at page 85, line 14 ¶
	11. Sending ULP Payloads		11. Sending ULP Payloads
	When there is no context state for the ULID pair on the sender, there		When there is no context state for the ULID pair on the sender, there
	is no effect on how ULP packets are sent. If the host is using some		is no effect on how ULP packets are sent. If the host is using some
	heuristic for determining when to perform a deferred context		heuristic for determining when to perform a deferred context
	establishment, then the host might need to do some accounting (count		establishment, then the host might need to do some accounting (count
	the number of packets sent and received) even before there is a ULID-		the number of packets sent and received) even before there is a ULID-
	pair context.		pair context.
	If the context is not in ESTABLISHED or I2BIS-SENT state, then it		If the context is not in ESTABLISHED or I2BIS-SENT STATE, then it
	there is also no effect on how the ULP packets are sent. Only in the		there is also no effect on how the ULP packets are sent. Only in the
	ESTABLISHED and I2BIS-SENT states does the host have CT(peer) and		ESTABLISHED and I2BIS-SENT STATES does the host have CT(peer) and
	Ls(peer) set.		Ls(peer) set.
	If there is a ULID-pair context for the ULID pair, then the sender		If there is a ULID-pair context for the ULID pair, then the sender
	needs to verify whether context uses the ULIDs as locators, that is,		needs to verify whether context uses the ULIDs as locators, that is,
	whether Lp(peer) == ULID(peer) and Lp(local) == ULID(local).		whether Lp(peer) == ULID(peer) and Lp(local) == ULID(local).
	If this is the case, then packets can be sent unmodified by the shim.		If this is the case, then packets can be sent unmodified by the shim.
	If it is not the case, then the logic in Section 11.1 will need to be		If it is not the case, then the logic in Section 11.1 will need to be
	used.		used.
	skipping to change at page 85, line 8 ¶		skipping to change at page 87, line 8 ¶
	header.		header.
	The inserted Shim6 Payload extension header includes the peer's		The inserted Shim6 Payload extension header includes the peer's
	context tag. It takes on the next header value from the preceding		context tag. It takes on the next header value from the preceding
	extension header, since that extension header will have a next header		extension header, since that extension header will have a next header
	value of Shim6.		value of Shim6.
	12. Receiving Packets		12. Receiving Packets
	The receive side of the communication can receive packets associated		The receive side of the communication can receive packets associated
	to a Shim6 context with or without the Shim6 extenson header. In		to a Shim6 context with or without the Shim6 extension header. In
	case that the ULID pair is being used as locator pair, the packets		case that the ULID pair is being used as locator pair, the packets
	received will not have the Shim6 extension header and will be		received will not have the Shim6 extension header and will be
	processed by the Shim6 layer as described below. If the received		processed by the Shim6 layer as described below. If the received
	packet does carry the Shim6 extension header, as in normal IPv6		packet does carry the Shim6 extension header, as in normal IPv6
	receive side packet processing the receiver parses the (extension)		receive side packet processing the receiver parses the (extension)
	headers in order. Should it find a Shim6 extension header it will		headers in order. Should it find a Shim6 extension header it will
	look at the "P" field in that header. If this bit is zero, then the		look at the "P" field in that header. If this bit is zero, then the
	packet must be passed to the Shim6 payload handling for rewriting.		packet must be passed to the Shim6 payload handling for rewriting.
	Otherwise, the packet is passed to the Shim6 control handling.		Otherwise, the packet is passed to the Shim6 control handling.
	12.1. Receiving payload without extension headers		12.1. Receiving payload without extension headers
	The receiver extracts the IPv6 source and destination fields, and		The receiver extracts the IPv6 source and destination fields, and
	uses this to find a ULID-pair context, such that the IPv6 address		uses this to find a ULID-pair context, such that the IPv6 address
	fields match the ULID(local) and ULID(peer). If such a context is		fields match the ULID(local) and ULID(peer). If such a context is
	found, the context appears not to be quiescent and this should be		found, the context appears not to be quiescent and this should be
	remembered in order to avoid tearing down the context and for		remembered in order to avoid tearing down the context and for
	reachability detection porpuses as described in [5]. The host		reachability detection purposes as described in [5]. The host
	continues with the normal processing of the IP packet.		continues with the normal processing of the IP packet.
	12.2. Receiving Payload Extension Headers		12.2. Receiving Payload Extension Headers
	The receiver extracts the context tag from the payload extension		The receiver extracts the context tag from the payload extension
	header, and uses this to find a ULID-pair context. If no context is		header, and uses this to find a ULID-pair context. If no context is
	found, the receiver SHOULD generate a R1bis message (see		found, the receiver SHOULD generate a R1bis message (see
	Section 7.17).		Section 7.17).
	Then, depending on the state of the context:		Then, depending on the STATE of the context:
	o If ESTABLISHED: Proceed to process message.		o If ESTABLISHED: Proceed to process message.
	o If I1-SENT, discard the message and stay in I1-SENT.		o If I1-SENT, discard the message and stay in I1-SENT.
	o If I2-SENT, then send I2 and proceed to process the message.		o If I2-SENT, then send I2 and proceed to process the message.
	o If I2BIS-SENT, then send I2bis and proceed to process the message.		o If I2BIS-SENT, then send I2bis and proceed to process the message.
	With the context in hand, the receiver can now replace the IP address		With the context in hand, the receiver can now replace the IP address
	skipping to change at page 86, line 37 ¶		skipping to change at page 88, line 37 ¶
	is generated and sent back. The Pointer field is set to point at the		is generated and sent back. The Pointer field is set to point at the
	first octet of the shim message type.		first octet of the shim message type.
	All the control messages can contain any options with C=0. If there		All the control messages can contain any options with C=0. If there
	is any option in the message with C=1 that isn't known to the host,		is any option in the message with C=1 that isn't known to the host,
	then the host MUST send a Shim6 Error Message with Error Code=1, with		then the host MUST send a Shim6 Error Message with Error Code=1, with
	the Pointer field referencing the first octet of the Option Type.		the Pointer field referencing the first octet of the Option Type.
	12.4. Context Lookup		12.4. Context Lookup
	We assume that each shim context has its own state machine. We		We assume that each shim context has its own STATE machine. We
	assume that a dispatcher delivers incoming packets to the state		assume that a dispatcher delivers incoming packets to the STATE
	machine that it belongs to. Here we describe the rules used for the		machine that it belongs to. Here we describe the rules used for the
	dispatcher to deliver packets to the correct shim context state		dispatcher to deliver packets to the correct shim context STATE
	machine.		machine.
	There is one state machine per context identified that is		There is one STATE machine per context identified that is
	conceptually identified by ULID pair and Forked Instance Identifier		conceptually identified by ULID pair and Forked Instance Identifier
	(which is zero by default), or identified by CT(local). However, the		(which is zero by default), or identified by CT(local). However, the
	detailed lookup rules are more complex, especially during context		detailed lookup rules are more complex, especially during context
	establishment.		establishment.
	Clearly, if the required context is not established, it will be in		Clearly, if the required context is not established, it will be in
	IDLE state.		IDLE STATE.
	During context establishment, the context is identified as follows:		During context establishment, the context is identified as follows:
	o I1 packets: Deliver to the context associated with the ULID pair		o I1 packets: Deliver to the context associated with the ULID pair
	and the Forked Instance Identifier.		and the Forked Instance Identifier.
	o I2 packets: Deliver to the context associated with the ULID pair		o I2 packets: Deliver to the context associated with the ULID pair
	and the Forked Instance Identifier.		and the Forked Instance Identifier.
	o R1 packets: Deliver to the context with the locator pair included		o R1 packets: Deliver to the context with the locator pair included
	skipping to change at page 90, line 29 ¶		skipping to change at page 92, line 29 ¶
	I2_RETRIES_MAX = 2		I2_RETRIES_MAX = 2
	I2bis_TIMEOUT = 4 seconds		I2bis_TIMEOUT = 4 seconds
	I2bis_RETRIES_MAX = 2		I2bis_RETRIES_MAX = 2
	VALIDATOR_MIN_LIFETIME = 30 seconds		VALIDATOR_MIN_LIFETIME = 30 seconds
	UPDATE_TIMEOUT = 4 seconds		UPDATE_TIMEOUT = 4 seconds
			MAX_UPDATE_TIMEOUT = 120 seconds
	The retransmit timers (I1_TIMEOUT, I2_TIMEOUT, UPDATE_TIMEOUT) are		The retransmit timers (I1_TIMEOUT, I2_TIMEOUT, UPDATE_TIMEOUT) are
	subject to binary exponential backoff, as well as randomization		subject to binary exponential backoff, as well as randomization
	across a range of 0.5 and 1.5 times the nominal (backed off) value.		across a range of 0.5 and 1.5 times the nominal (backed off) value.
	This removes any risk of synchronization between lots of hosts		This removes any risk of synchronization between lots of hosts
	performing independent shim operations at the same time.		performing independent shim operations at the same time.
	The randomization is applied after the binary exponential backoff.		The randomization is applied after the binary exponential backoff.
	Thus the first retransmission would happen based on a uniformly		Thus the first retransmission would happen based on a uniformly
	distributed random number in the range [0.5*4, 1.5*4] seconds, the		distributed random number in the range [0.5*4, 1.5*4] seconds, the
	second retransmission [0.5*8, 1.5*8] seconds after the first one,		second retransmission [0.5*8, 1.5*8] seconds after the first one,
	skipping to change at page 91, line 14 ¶		skipping to change at page 93, line 14 ¶
	15. Implications Elsewhere		15. Implications Elsewhere
	15.1. Congestion Control Considerations		15.1. Congestion Control Considerations
	When the locator pair currently used for exchanging packets in a		When the locator pair currently used for exchanging packets in a
	Shim6 context becomes unreachable, the Shim6 layer will divert the		Shim6 context becomes unreachable, the Shim6 layer will divert the
	communication through an alternative locator pair, which in most		communication through an alternative locator pair, which in most
	cases will result in redirecting the packet flow through an		cases will result in redirecting the packet flow through an
	alternative network path. In this case, it recommended that the		alternative network path. In this case, it recommended that the
	Shim6 follows the recommendation defined in [20] and it informs the		Shim6 follows the recommendation defined in [21] and it informs the
	upper layers about the path change, in order to allow the congestion		upper layers about the path change, in order to allow the congestion
	control mechanisms of the upper layers to react accordingly.		control mechanisms of the upper layers to react accordingly.
	15.2. Middle-boxes considerations		15.2. Middle-boxes considerations
	Data packets belonging to a Shim6 context carrying the Shim6 Payload		Data packets belonging to a Shim6 context carrying the Shim6 Payload
	Header contain alternative locators other than the ULIDs in the		Header contain alternative locators other than the ULIDs in the
	source and destination address fields of the IPv6 header. On the		source and destination address fields of the IPv6 header. On the
	other hand, the upper layers of the peers involved in the		other hand, the upper layers of the peers involved in the
	communication operate on the ULID pair presented by the Shim6 layer		communication operate on the ULID pair presented by the Shim6 layer
	to them, rather on the locator pair contained in the IPv6 header of		to them, rather on the locator pair contained in the IPv6 header of
	the actual packets. It should be noted that the Shim6 layer does not		the actual packets. It should be noted that the Shim6 layer does not
	modify the data packets, but because a constant ULID pair is		modify the data packets, but because a constant ULID pair is
	presented to upper layers irrespective of the locator pair changes,		presented to upper layers irrespective of the locator pair changes,
	the relation between the upper layer header (such as TCP, UDP, ICMP,		the relation between the upper layer header (such as TCP, UDP, ICMP,
	ESP, etc) and the IPv6 header is modified. In particular, when the		ESP, etc) and the IPv6 header is modified. In particular, when the
	Shim6 Extension header is present in the packet, if those data		Shim6 Extension header is present in the packet, if those data
	packets are TCP, UDP or ICMP packets, the presudoheader used for the		packets are TCP, UDP or ICMP packets, the pseudoheader used for the
	checksum calculation will contain the ULID pair, rather than the		checksum calculation will contain the ULID pair, rather than the
	locator pair contained in the data packet.		locator pair contained in the data packet.
	It is possible that some firewalls or other middle boxes try to		It is possible that some firewalls or other middle boxes try to
	verify the validity of upper layer sanity checks of the packet on the		verify the validity of upper layer sanity checks of the packet on the
	fly. If they do that based on the actual source and destination		fly. If they do that based on the actual source and destination
	addresses contained in the IPv6 header without considering the Shim6		addresses contained in the IPv6 header without considering the Shim6
	context information (in particular without replacing the locator pair		context information (in particular without replacing the locator pair
	by the ULID pair used by the Shim6 context) such verifications may		by the ULID pair used by the Shim6 context) such verifications may
	fail. Those middle-boxes need to be updated in order to be able to		fail. Those middle-boxes need to be updated in order to be able to
	skipping to change at page 92, line 29 ¶		skipping to change at page 94, line 29 ¶
	failure (those using the Shim6 payload extension header with a TCP		failure (those using the Shim6 payload extension header with a TCP
	packet inside it). Thus stateful firewalls that are modified to pass		packet inside it). Thus stateful firewalls that are modified to pass
	Shim6 messages should also be modified to pass the payload extension		Shim6 messages should also be modified to pass the payload extension
	header, so that the shim can use the alternate locators to recover		header, so that the shim can use the alternate locators to recover
	from failures. This presumably implies that the firewall needs to		from failures. This presumably implies that the firewall needs to
	track the set of locators in use by looking at the Shim6 control		track the set of locators in use by looking at the Shim6 control
	exchanges. Such firewalls might even want to verify the locators		exchanges. Such firewalls might even want to verify the locators
	using the HBA/CGA verification themselves, which they can do without		using the HBA/CGA verification themselves, which they can do without
	modifying any of the Shim6 packets they pass through.		modifying any of the Shim6 packets they pass through.
	15.3. Other considerations		15.3. Operation and Management Considerations
			This section considers some aspects related to the operations and
			management of the Shim6 protocol.
			Deployment of th Shim6 protocol: The Shim6 protocol is a host based
			solution, so, in order to be deployed, the stacks of the hosts using
			the Shim6 protocol need to be updated to support it. This enables an
			incremental deployment of the protocol, since it does not requires a
			flag day for the deployment, just single host updates. If the Shim6
			solution will be deployed in a site, host can be gradually updated to
			support the solution. Moreover, for supporting the Shim6 protocol,
			only end hosts need to be updated and no router changes are required.
			However, it should be noted that in order to benefit from the Shim6
			protocol, both ends of a communication should support the protocol,
			meaning that both hosts must be updated to be able to use the Shim6
			protocol. Nevertheless, the Shim6 protocol uses a deferred context
			setup capability, that allows to establish normal IPv6 communications
			and later on, if both endpoints are Shim6-capable, protect the
			communication with the Shim6 protocol. This has an important
			deployment benefit, since Shim6 enabled nodes can perfectly talk to
			non-Shim6 capable nodes wihtout introducing any problem in the
			communication.
			Configuration of Shim6-capable nodes: The Shim6 protocol itself does
			not requires any spcific configuration to provide its basic features.
			The Shim6 protocol is designed to provide a default service to upper
			layers that should satisfy general applications. Th Shim6 layer
			would automatically attempt to protect long lived communications, by
			triggering the establishment of the Shim6 context using some
			predefined heuristics. Of course, if some special tunning is
			required by some applications, this may required additional
			configuration. Similar considerations apply to a site attempting to
			perform some forms of traffic engineering using different preferences
			for different locators.
			Address and prefix configuration: The Shim6 protocol assumes that in
			a multihomed site multiple prefixes will be available. Such
			configuration can increase the operation work in a network. However,
			it should be noted that the capability of having multiupl prefixes in
			a site and multiple addresses assigned to an interface is an IPv6
			capability that goes beyond the Shim6 case and it is expected to be
			widely used. So, even though this is the case for Shim6, we consider
			that the implications of such a configuration is beyond the
			particular case of Shim6 and must be addressed for the generic IPv6
			case. Nevertheless, Shim6 also assumes the usage of CGA/HBA
			addresses by Shim6 hosts. this implies that Shim6 capable hosts
			should configure addresses using HBA/CGA generation mechanims.
			Additional consideration about this issue can be found at [19]
			15.4. Other considerations
	The general Shim6 approach, as well as the specifics of this proposed		The general Shim6 approach, as well as the specifics of this proposed
	solution, has implications elsewhere, including:		solution, has implications elsewhere, including:
	o Applications that perform referrals, or callbacks using IP		o Applications that perform referrals, or callbacks using IP
	addresses as the 'identifiers' can still function in limited ways,		addresses as the 'identifiers' can still function in limited ways,
	as described in [18]. But in order for such applications to be		as described in [18]. But in order for such applications to be
	able to take advantage of the multiple locators for redundancy,		able to take advantage of the multiple locators for redundancy,
	the applications need to be modified to either use fully qualified		the applications need to be modified to either use fully qualified
	domain names as the 'identifiers', or they need to pass all the		domain names as the 'identifiers', or they need to pass all the
	skipping to change at page 93, line 13 ¶		skipping to change at page 96, line 14 ¶
	does not overload the flow label as a context tag; the in-path		does not overload the flow label as a context tag; the in-path
	devices need to know about the use of the new locators even though		devices need to know about the use of the new locators even though
	the flow label stays the same.		the flow label stays the same.
	o MTU implications. The path MTU mechanisms we use are robust		o MTU implications. The path MTU mechanisms we use are robust
	against different packets taking different paths through the		against different packets taking different paths through the
	Internet, by computing a minimum over the recently observed path		Internet, by computing a minimum over the recently observed path
	MTUs. When Shim6 fails over from using one locator pair to		MTUs. When Shim6 fails over from using one locator pair to
	another pair, this means that packets might travel over a		another pair, this means that packets might travel over a
	different path through the Internet, hence the path MTU might be		different path through the Internet, hence the path MTU might be
	quite different. Perhaps such a path change would be a good hint		quite different. In order to deal with this changes in the MTU,
	to the path MTU mechanism to try a larger MTU?		the usage of Packetization Layer Path MTU Discovery as defined in
			[24] is reccommended.
	The fact that the shim will add an 8 octet Payload Extension		The fact that the shim will add an 8 octet Payload Extension
	header to the ULP packets after a locator switch, can also affect		header to the ULP packets after a locator switch, can also affect
	the usable path MTU for the ULPs. In this case the MTU change is		the usable path MTU for the ULPs. In this case the MTU change is
	local to the sending host, thus conveying the change to the ULPs		local to the sending host, thus conveying the change to the ULPs
	is an implementation matter.		is an implementation matter. By conveying the information to the
			transport layer, it can adapt and reduce the MSS accordingly.
	16. Security Considerations		16. Security Considerations
	This document satisfies the concerns specified in [15] as follows:		This document satisfies the concerns specified in [15] as follows:
	o The HBA [2] and CGA technique [4] for verifying the locators to		o The HBA [2] and CGA technique [4] for verifying the locators to
	prevent an attacker from redirecting the packet stream to		prevent an attacker from redirecting the packet stream to
	somewhere else. The minimum acceptable key length for public keys		somewhere else, preventing threats described in sections 4.1.1,
	used in the generation of CGAs SHOULD be 1024 bits. Any		4.1.2, 4.1.3 and 4.2 of [15]. These two approaches provide a
	implementation should follow prudent cryptographic practice in		similar level of protection but they provide different
	determining the appropriate key lengths.		functionality with a different computational cost. The HBA
			mechanism relies on the capability of generating all the addresses
			of a multihomed host as an unalterable set of intrinsically bound
			IPv6 addresses, known as an HBA set. In this approach, addresses
			incorporate a cryptographic one-way hash of the prefix-set
			available into the interface identifier part. The result is that
			the binding between all the available addresses is encoded within
			the addresses themselves, providing hijacking protection. Any
			peer using the shim protocol node can efficiently verify that the
			alternative addresses proposed for continuing the communication
			are bound to the initial address through a simple hash
			calculation. In a CGA based approach the address used as ULID is
			a CGA that contains a hash of a public key in its interface
			identifier. The result is a secure binding between the ULID and
			the associated key pair. This allows each peer to use the
			corresponding private key to sign the shim messages that convey
			locator set information. The trust chain in this case is the
			following: the ULID used for the communication is securely bound
			to the key pair because it contains the hash of the public key,
			and the locator set is bound to the public key through the
			signature. Any of these two mechanisms HBA and CGA provide time-
			shifted attack protection (as described in section 4.1.2 of [15]),
			since the ULID is securely bound to a locator set that can only be
			defined by the owner of the ULID. The minimum acceptable key
			length for RSA keys used in the generation of CGAs MUST be at
			least 1024 bits. Any implementation should follow prudent
			cryptographic practice in determining the appropriate key lengths.
	o Requiring a Reachability Probe+Reply before a new locator is used		o 3rd party flooding attacks described in section 4.3 of [15] are
	as the destination, in order to prevent 3rd party flooding		prevented by requiring a Shim6 peer to perform a successful
	attacks.		Reachability probe + reply exchange before accepting a new locator
			for use as a packet destination..
	o The first message does not create any state on the responder.		o The first message does not create any state on the responder.
	Essentially a 3-way exchange is required before the responder		Essentially a 3-way exchange is required before the responder
	creates any state. This means that a state-based DoS attack		creates any state. This means that a state-based DoS attack
	(trying to use up all of memory on the responder) at least		(trying to use up all of memory on the responder) at least
	requires the attacker to create state, consuming his own resources		requires the attacker to create state, consuming his own resources
	and also it provides an IPv6 address that the attacker was using.		and also it provides an IPv6 address that the attacker was using.
	o The context establishment messages use nonces to prevent replay		o The context establishment messages use nonces to prevent replay
	attacks, and to prevent off-path attackers from interfering with		attacks as described in section 4.1.4 of [15], and to prevent off-
	the establishment.		path attackers from interfering with the establishment.
	o Every control message of the Shim6 protocol, past the context		o Every control message of the Shim6 protocol, past the context
	establishment, carry the context tag assigned to the particular		establishment, carry the context tag assigned to the particular
	context. This implies that an attacker needs to discover that		context. This implies that an attacker needs to discover that
	context tag before being able to spoof any Shim6 control message.		context tag before being able to spoof any Shim6 control message
	Such discovery probably requires to be along the path in order to		as described in section 4.4 of [15]. Such discovery probably
	be sniff the context tag value. The result is that through this		requires to be along the path in order to be sniff the context tag
	technique, the Shim6 protocol is protected against off-path		value. The result is that through this technique, the Shim6
	attackers.		protocol is protected against off-path attackers.
	Interaction with IPsec		Interaction with IPsec
	The Shim6 sub-layer is implemented below the IPsec layer within the		The Shim6 sub-layer is implemented below the IPsec layer within the
	IP layer. This deserves some additional considerations for a couple		IP layer. This deserves some additional considerations for a couple
	of specific cases: First, it should be noted that the Shim6 approach		of specific cases: First, it should be noted that the Shim6 approach
	does not preclude using IPsec tunnels on Shim6 packets within the		does not preclude using IPsec tunnels on Shim6 packets within the
	network transit path. Second, in case that IPsec is implemented as		network transit path. Second, in case that IPsec is implemented as
	Bump-In-The-Wire (BITW) [3], either the shim MUST be disabled, or the		Bump-In-The-Wire (BITW) [3], either the shim MUST be disabled, or the
	shim MUST also be implemented as Bump-In-The-Wire, in order to		shim MUST also be implemented as Bump-In-The-Wire, in order to
	satisfy the requirement that IPsec is layered above the shim.		satisfy the requirement that IPsec is layered above the shim.
			If a shim6 node has some protected and some unprotected interfaces
			[RFC 4301] for the purposes of IPsec, then it MUST treat the locator
			sets for the protected and unprotected interfaces as separate locator
			sets and not intermix them. This ensures that shim6 will never
			failover from using a protected interface to using an unprotected
			interface and vice versa.
			The same constraint applies to shim6 hosts which have interfaces
			attached to networks where there are different security
			considerations, for instance a host with some interfaces attached to
			the public Internet and some interfaces attached to an intranet.
			In a "bump-in-the-stack" (BITS) IPsec implementation, IPsec is
			implemented "underneath" an existing implementation of an IP protocol
			stack, between the native IP and the local network drivers. In that
			case it is not possible to make IPsec benefit from the failover
			capabilities of shim6; when shim6 fails over to a different locator
			pair then the BITS IPsec would end up using a different (and possibly
			establish a new) security association for that pair of IP addresses.
			Same thing applies to a "bump-in-the-wire" (BITW) IPsec
			implementation. In those cases shim6 and IPsec still work, but it is
			less efficient to have to use separate security associations as a
			result of a shim6 failover.
			In order for a BITS and BITW IPsec implementation on a host as well
			as a security gateway to be able to look at the same selectors before
			and after a failover, their implementation needs to skip the SHIM6
			extension header to find the selectors for the next layer protocols
			(e.g., TCP, UDP, Stream Control Transmission Protocol (SCTP))
	Some of the residual threats in this proposal are:		Some of the residual threats in this proposal are:
	o An attacker which arrives late on the path (after the context has		o An attacker which arrives late on the path (after the context has
	been established) can use the R1bis message to cause one peer to		been established) can use the R1bis message to cause one peer to
	recreate the context, and at that point in time the attacker can		recreate the context, and at that point in time the attacker can
	observe all of the exchange. But this doesn't seem to open any		observe all of the exchange. But this doesn't seem to open any
	new doors for the attacker since such an attacker can observe the		new doors for the attacker since such an attacker can observe the
	context tags that are being used, and once known it can use those		context tags that are being used, and once known it can use those
	to send bogus messages.		to send bogus messages.
	skipping to change at page 98, line 49 ¶		skipping to change at page 102, line 49 ¶
	| 0 | Unknown Shim6 message type |		| 0 | Unknown Shim6 message type |
	| | |		| | |
	| 1 | Critical Option not recognized |		| 1 | Critical Option not recognized |
	| | |		| | |
	| 2 | Locator verification method failed |		| 2 | Locator verification method failed |
	| | |		| | |
	| 3 | Locator List Generation number out of sync |		| 3 | Locator List Generation number out of sync |
	| | |		| | |
	| 4 | Error in the number of locators |		| 4 | Error in the number of locators |
	| | |		| | |
	| 120-127 | Reserved for debugging pruposes |		| 120-127 | Reserved for debugging purposes |
	+------------+--------------------------------------------+		+------------+--------------------------------------------+
	18. Acknowledgements		18. Acknowledgements
	Over the years many people active in the multi6 and shim6 WGs have		Over the years many people active in the multi6 and shim6 WGs have
	contributed ideas a suggestions that are reflected in this		contributed ideas a suggestions that are reflected in this
	specification. Special thanks to the careful comments from Geoff		specification. Special thanks to the careful comments from Sam
	Huston, Shinta Sugimoto, Pekka Savola, Dave Meyer, Deguang Le, Jari		Hartman, Cullen Jennings, Magnus Nystrom, Stephen Kent, Geoff Huston,
	Arkko, Iljitsch van Beijnum, Jim Bound, Brian Carpenter, Sebastien		Shinta Sugimoto, Pekka Savola, Dave Meyer, Deguang Le, Jari Arkko,
	Barre, Matthijs Mekking, Dave Thaler, Bob Braden Wesley Eddy and Tom		Iljitsch van Beijnum, Jim Bound, Brian Carpenter, Sebastien Barre,
			Matthijs Mekking, Dave Thaler, Bob Braden Wesley Eddy and Tom
	Henderson on earlier versions of this document.		Henderson on earlier versions of this document.
	Appendix A. Possible Protocol Extensions		Appendix A. Possible Protocol Extensions
	During the development of this protocol, several issues have been		During the development of this protocol, several issues have been
	brought up as important one to address, but are ones that do not need		brought up as important one to address, but are ones that do not need
	to be in the base protocol itself but can instead be done as		to be in the base protocol itself but can instead be done as
	extensions to the protocol. The key ones are:		extensions to the protocol. The key ones are:
	o As stated in the assumptions in Section 3, the in order for the		o As stated in the assumptions in Section 3, the in order for the
	Shim6 protocol to be able to recover from a wide range of		Shim6 protocol to be able to recover from a wide range of
	failures, for instance when one of the communicating hosts is		failures, for instance when one of the communicating hosts is
	singly-homed, and cope with a site's ISPs that do ingress		single-homed, and cope with a site's ISPs that do ingress
	filtering based on the source IPv6 address, there is a need for		filtering based on the source IPv6 address, there is a need for
	the host to be able to influence the egress selection from its		the host to be able to influence the egress selection from its
	site. Further discussion of this issue is captured in [16].		site. Further discussion of this issue is captured in [16].
	o Is there need for keeping the list of locators private between the		o Is there need for keeping the list of locators private between the
	two communicating endpoints? We can potentially accomplish that		two communicating endpoints? We can potentially accomplish that
	when using CGA but not with HBA, but it comes at the cost of doing		when using CGA but not with HBA, but it comes at the cost of doing
	some public key encryption and decryption operations as part of		some public key encryption and decryption operations as part of
	the context establishment. The suggestion is to leave this for a		the context establishment. The suggestion is to leave this for a
	future extension to the protocol.		future extension to the protocol.
	skipping to change at page 100, line 37 ¶		skipping to change at page 104, line 37 ¶
	o Defining some form of end-to-end "compression" mechanism that		o Defining some form of end-to-end "compression" mechanism that
	removes the need for including the Shim6 Payload extension header		removes the need for including the Shim6 Payload extension header
	when the locator pair is not the ULID pair.		when the locator pair is not the ULID pair.
	o Supporting the dynamic setting of locator preferences on a site-		o Supporting the dynamic setting of locator preferences on a site-
	wide basis, and use the Locator Preference option in the Shim6		wide basis, and use the Locator Preference option in the Shim6
	protocol to convey these preferences to remote communicating		protocol to convey these preferences to remote communicating
	hosts. This could mirror the DNS SRV record's notion of priority		hosts. This could mirror the DNS SRV record's notion of priority
	and weight.		and weight.
	o Potentially recommend that more application protocols use DNS SRV
	records to allow a site some influence on load spreading for the
	initial contact (before the Shim6 context establishment) as well
	as for traffic which does not use the shim.
	o Specifying APIs for the ULPs to be aware of the locators the shim		o Specifying APIs for the ULPs to be aware of the locators the shim
	is using, and be able to influence the choice of locators		is using, and be able to influence the choice of locators
	(controlling preferences as well as triggering a locator pair		(controlling preferences as well as triggering a locator pair
	switch). This includes providing APIs the ULPs can use to fork a		switch). This includes providing APIs the ULPs can use to fork a
	shim context.		shim context.
	o Whether it is feasible to relax the suggestions for when context		o Whether it is feasible to relax the suggestions for when context
	state is removed, so that one can end up with an asymmetric		state is removed, so that one can end up with an asymmetric
	distribution of the context state and still get (most of) the shim		distribution of the context state and still get (most of) the shim
	benefits. For example, the busy server would go through the		benefits. For example, the busy server would go through the
	skipping to change at page 102, line 5 ¶		skipping to change at page 106, line 5 ¶
	o ULP specified timers for the reachability detection mechanism		o ULP specified timers for the reachability detection mechanism
	(which can be useful particularly when there are forked contexts).		(which can be useful particularly when there are forked contexts).
	o Pre-verify some "backup" locator pair, so that the failover time		o Pre-verify some "backup" locator pair, so that the failover time
	can be shorter.		can be shorter.
	o Study how Shim6 and Mobile IPv6 might interact. There existing an		o Study how Shim6 and Mobile IPv6 might interact. There existing an
	initial draft on this topic [17].		initial draft on this topic [17].
	Appendix B. Simplified State Machine		Appendix B. Simplified STATE Machine
	The states are defined in Section 6.2. The intent is that the		The STATES are defined in Section 6.2. The intent is that the
	stylized description below be consistent with the textual description		stylized description below be consistent with the textual description
	in the specification, but should they conflict, the textual		in the specification, but should they conflict, the textual
	description is normative.		description is normative.
	The following table describes the possible actions in state IDLE and		The following table describes the possible actions in STATE IDLE and
	their respective triggers:		their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Receive I1 | Send R1 and stay in IDLE |		| Receive I1 | Send R1 and stay in IDLE |
	| | |		| | |
	| Heuristics trigger | Send I1 and move to I1-SENT |		| Heuristics trigger | Send I1 and move to I1-SENT |
	| a new context | |		| a new context | |
	| establishment | |		| establishment | |
	skipping to change at page 103, line 4 ¶		skipping to change at page 107, line 4 ¶
	| | If fail, stay in IDLE |		| | If fail, stay in IDLE |
	| | |		| | |
	| R1, R1bis, R2 | N/A (This context lacks the required info |		| R1, R1bis, R2 | N/A (This context lacks the required info |
	| | for the dispatcher to deliver them) |		| | for the dispatcher to deliver them) |
	| | |		| | |
	| Receive payload | Send R1bis and stay in IDLE |		| Receive payload | Send R1bis and stay in IDLE |
	| extension header | |		| extension header | |
	| or other control | |		| or other control | |
	| packet | |		| packet | |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	The following table describes the possible actions in state I1-SENT		The following table describes the possible actions in STATE I1-SENT
	and their respective triggers:		and their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Receive R1, verify | If successful, send I2 and move to I2-SENT |		| Receive R1, verify | If successful, send I2 and move to I2-SENT |
	| INIT nonce | |		| INIT nonce | |
	| | If fail, discard and stay in I1-SENT |		| | If fail, discard and stay in I1-SENT |
	| | |		| | |
	| Receive I1 | Send R2 and stay in I1-SENT |		| Receive I1 | Send R2 and stay in I1-SENT |
	skipping to change at page 104, line 4 ¶		skipping to change at page 108, line 4 ¶
	| unknown error | |		| unknown error | |
	| | |		| | |
	| R1bis | N/A (Dispatcher doesn't deliver since |		| R1bis | N/A (Dispatcher doesn't deliver since |
	| | CT(peer) is not set) |		| | CT(peer) is not set) |
	| | |		| | |
	| Receive Payload or | Discard and stay in I1-SENT |		| Receive Payload or | Discard and stay in I1-SENT |
	| extension header | |		| extension header | |
	| or other control | |		| or other control | |
	| packet | |		| packet | |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	The following table describes the possible actions in state I2-SENT		The following table describes the possible actions in STATE I2-SENT
	and their respective triggers:		and their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Receive R2, verify | If successful move to ESTABLISHED |		| Receive R2, verify | If successful move to ESTABLISHED |
	| INIT nonce | |		| INIT nonce | |
	| | If fail, stay in I2-SENT |		| | If fail, stay in I2-SENT |
	| | |		| | |
	| Receive I1 | Send R2 and stay in I2-SENT |		| Receive I1 | Send R2 and stay in I2-SENT |
	skipping to change at page 105, line 4 ¶		skipping to change at page 109, line 4 ¶
	| | to I1-SENT |		| | to I1-SENT |
	| | |		| | |
	| R1bis | N/A (Dispatcher doesn't deliver since |		| R1bis | N/A (Dispatcher doesn't deliver since |
	| | CT(peer) is not set) |		| | CT(peer) is not set) |
	| | |		| | |
	| Receive payload or | Accept and send I2 (probably R2 was sent |		| Receive payload or | Accept and send I2 (probably R2 was sent |
	| extension header | by peer and lost) |		| extension header | by peer and lost) |
	| other control | |		| other control | |
	| packet | |		| packet | |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	The following table describes the possible actions in state I2BIS-		The following table describes the possible actions in STATE I2BIS-
	SENT and their respective triggers:		SENT and their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Receive R2, verify | If successful move to ESTABLISHED |		| Receive R2, verify | If successful move to ESTABLISHED |
	| INIT nonce | |		| INIT nonce | |
	| | If fail, stay in I2BIS-SENT |		| | If fail, stay in I2BIS-SENT |
	| | |		| | |
	| Receive I1 | Send R2 and stay in I2BIS-SENT |		| Receive I1 | Send R2 and stay in I2BIS-SENT |
	skipping to change at page 106, line 4 ¶		skipping to change at page 110, line 4 ¶
	| | go to I1-SENT |		| | go to I1-SENT |
	| | |		| | |
	| R1bis | N/A (Dispatcher doesn't deliver since |		| R1bis | N/A (Dispatcher doesn't deliver since |
	| | CT(peer) is not set) |		| | CT(peer) is not set) |
	| | |		| | |
	| Receive payload or | Accept and send I2bis (probably R2 was |		| Receive payload or | Accept and send I2bis (probably R2 was |
	| extension header | sent by peer and lost) |		| extension header | sent by peer and lost) |
	| other control | |		| other control | |
	| packet | |		| packet | |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	The following table describes the possible actions in state		The following table describes the possible actions in STATE
	ESTABLISHED and their respective triggers:		ESTABLISHED and their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Receive I1, compare | If no match, send R1 and stay in ESTABLISHED|		| Receive I1, compare | If no match, send R1 and stay in ESTABLISHED|
	| CT(peer) with | |		| CT(peer) with | |
	| received CT | If match, send R2 and stay in ESTABLISHED |		| received CT | If match, send R2 and stay in ESTABLISHED |
	| | |		| | |
	| | |		| | |
	skipping to change at page 107, line 4 ¶		skipping to change at page 111, line 4 ¶
	| extension header | |		| extension header | |
	| other control | |		| other control | |
	| packet | |		| packet | |
	| | |		| | |
	| Implementation | Discard state and go to IDLE |		| Implementation | Discard state and go to IDLE |
	| specific heuristic | |		| specific heuristic | |
	| (E.g., No open ULP | |		| (E.g., No open ULP | |
	| sockets and idle | |		| sockets and idle | |
	| for some time ) | |		| for some time ) | |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	The following table describes the possible actions in state E-FAILED		The following table describes the possible actions in STATE E-FAILED
	and their respective triggers:		and their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Wait for | Go to IDLE |		| Wait for | Go to IDLE |
	| NO_R1_HOLDDOWN_TIME | |		| NO_R1_HOLDDOWN_TIME | |
	| | |		| | |
	| Any packet | Process as in IDLE |		| Any packet | Process as in IDLE |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	The following table describes the possible actions in state NO-		The following table describes the possible actions in STATE NO-
	SUPPORT and their respective triggers:		SUPPORT and their respective triggers:
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Trigger | Action |		| Trigger | Action |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	| Wait for | Go to IDLE |		| Wait for | Go to IDLE |
	| ICMP_HOLDDOWN_TIME | |		| ICMP_HOLDDOWN_TIME | |
	| | |		| | |
	| Any packet | Process as in IDLE |		| Any packet | Process as in IDLE |
	+---------------------+---------------------------------------------+		+---------------------+---------------------------------------------+
	Appendix B.1. Simplified State Machine diagram		Appendix B.1. Simplified STATE Machine diagram
	Timeout/Null +------------+		Timeout/Null +------------+
	I1/R1 +------------------| NO SUPPORT |		I1/R1 +------------------| NO SUPPORT |
	Payload or Control/R1bis | +------------+		Payload or Control/R1bis | +------------+
	+---------+ | ^		+---------+ | ^
	| | | ICMP Error/Null|		| | | ICMP Error/Null|
	| V V |		| V V |
	+-----------------+ Timeout/Null +----------+ |		+-----------------+ Timeout/Null +----------+ |
	| |<---------------| E-FAILED | |		| |<---------------| E-FAILED | |
	+-| IDLE | +----------+ |		+-| IDLE | +----------+ |
	I2 or I2bis/R2 | | | ^ |		I2 or I2bis/R2 | | | ^ |
	skipping to change at page 119, line 16 ¶		skipping to change at page 123, line 16 ¶
	securely bind an address that is being used as ULID with a locator		securely bind an address that is being used as ULID with a locator
	set that can be used to exchange packets. The mechanism provided by		set that can be used to exchange packets. The mechanism provided by
	IPsec to securely bind the address used with the cryptographic keys		IPsec to securely bind the address used with the cryptographic keys
	is the usage of digital certificates. This implies that an IPsec		is the usage of digital certificates. This implies that an IPsec
	based solution would require that the generation of digital		based solution would require that the generation of digital
	certificates that bind the key and the ULID by a common third trusted		certificates that bind the key and the ULID by a common third trusted
	party for both parties involved in the communication. Considering		party for both parties involved in the communication. Considering
	that the scope of application of the shim protocol is global, this		that the scope of application of the shim protocol is global, this
	would imply a global public key infrastructure. The major issues		would imply a global public key infrastructure. The major issues
	with this approach are the deployment difficulties associated with a		with this approach are the deployment difficulties associated with a
	global PKI.		global PKI. The other possibility would be to use some form of
			opportunistic IPSec, like BTNS [22]. However, this would still
			present some issues, in particular, this approach requires a leap-of-
			faith in order to bind a given address to the public ky that is being
			used, which would actually prevent from providing the most critical
			security feature that a Shim6 security solution needs to achieve,
			i.e. proving identifier ownership. On top of that, using IPsec would
			require to turn on per-packet AH/ESP just for multihoming to occur.
	Finally two different technologies were selected to protect the shim		Finally two different technologies were selected to protect the shim
	protocol: HBA [4] and CGA [2]. These two approaches provide a		protocol: HBA [4] and CGA [2]. These two approaches provide a
	similar level of protection but they provide different functionality		similar level of protection but they provide different functionality
	with a different computational cost.		with a different computational cost.
	The HBA mechanism relies on the capability of generating all the		The HBA mechanism relies on the capability of generating all the
	addresses of a multihomed host as an unalterable set of intrinsically		addresses of a multihomed host as an unalterable set of intrinsically
	bound IPv6 addresses, known as an HBA set. In this approach,		bound IPv6 addresses, known as an HBA set. In this approach,
	addresses incorporate a cryptographic one-way hash of the prefix-set		addresses incorporate a cryptographic one-way hash of the prefix-set
	skipping to change at page 121, line 51 ¶		skipping to change at page 126, line 10 ¶
	In the unilateral approach, each node discards the information about		In the unilateral approach, each node discards the information about
	the other node without coordination with the other node based on some		the other node without coordination with the other node based on some
	local timers and heuristics. No packet exchange is required for		local timers and heuristics. No packet exchange is required for
	this. In this case, it would be possible that one of the nodes has		this. In this case, it would be possible that one of the nodes has
	discarded the state while the other node still hasn't. In this case,		discarded the state while the other node still hasn't. In this case,
	a No-Context error message may be required to inform about the		a No-Context error message may be required to inform about the
	situation and possibly a recovery mechanism is also needed.		situation and possibly a recovery mechanism is also needed.
	A coordinated approach would use an explicit CLOSE mechanism, akin to		A coordinated approach would use an explicit CLOSE mechanism, akin to
	the one specified in HIP [19]. If an explicit CLOSE handshake and		the one specified in HIP [20]. If an explicit CLOSE handshake and
	associated timer is used, then there would no longer be a need for		associated timer is used, then there would no longer be a need for
	the No Context Error message due to a peer having garbage collected		the No Context Error message due to a peer having garbage collected
	its end of the context. However, there is still potentially a need		its end of the context. However, there is still potentially a need
	to have a No Context Error message in the case of a complete state		to have a No Context Error message in the case of a complete state
	loss of the peer (also known as a crash followed by a reboot). Only		loss of the peer (also known as a crash followed by a reboot). Only
	if we assume that the reboot takes at least the CLOSE timer, or that		if we assume that the reboot takes at least the CLOSE timer, or that
	it is ok to not provide complete service until CLOSE timer minutes		it is ok to not provide complete service until CLOSE timer minutes
	after the crash, can we completely do away with the No Context Error		after the crash, can we completely do away with the No Context Error
	message.		message.
	skipping to change at page 124, line 9 ¶		skipping to change at page 128, line 9 ¶
	because premature garbage collection, but it does not prevent the		because premature garbage collection, but it does not prevent the
	same situations due to a crash and reboot of one of the involved		same situations due to a crash and reboot of one of the involved
	hosts. The result is that even if we went for a coordinated		hosts. The result is that even if we went for a coordinated
	approach, we would still need to deal with context confusion and		approach, we would still need to deal with context confusion and
	provide the means to detect and recover from this situations.		provide the means to detect and recover from this situations.
	Appendix E. Change Log		Appendix E. Change Log
	[RFC Editor: please remove this section]		[RFC Editor: please remove this section]
			The following changes have been made since draft-ietf-shim6-proto-09:
			o Explicitly added a reference to the applicability document
			o Added text on why oportunistic IPSec was not used for securing
			locator sets
			o Reowrded the Validator generation text to make it clearer
			o Reworded security considerations to explicitly address RFC 4218
			threats
			o Added OandM section
			o Added text on TE considerations
			o Added requirement to properly support RFC4884 icmp messages
			o added th usage of Packetization Layer Path MTU Discovery
			o reworded the placement of shim6 w.r.t. ipsec
			o added text on the IPsec considerations
	The following changes have been made since draft-ietf-shim6-proto-08:		The following changes have been made since draft-ietf-shim6-proto-08:
	o Clarified that the validator option must be included in R1 and I2		o Clarified that the validator option must be included in R1 and I2
	messages		messages
	o changed preferred peer/local locator to current peer/local locator		o changed preferred peer/local locator to current peer/local locator
	to align it with faliure detection draft		to align it with faliure detection draft
	o Reworded sections describing the generation and reception of		o Reworded sections describing the generation and reception of
	I2,I2bis, R2 and Update message to clarify that the CGA PDS may be		I2,I2bis, R2 and Update message to clarify that the CGA PDS may be
	skipping to change at page 130, line 19 ¶		skipping to change at page 135, line 19 ¶
	[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement		[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
	Levels", BCP 14, RFC 2119, March 1997.		Levels", BCP 14, RFC 2119, March 1997.
	[2] Aura, T., "Cryptographically Generated Addresses (CGA)",		[2] Aura, T., "Cryptographically Generated Addresses (CGA)",
	RFC 3972, March 2005.		RFC 3972, March 2005.
	[3] Kent, S. and K. Seo, "Security Architecture for the Internet		[3] Kent, S. and K. Seo, "Security Architecture for the Internet
	Protocol", RFC 4301, December 2005.		Protocol", RFC 4301, December 2005.
	[4] Bagnulo, M., "Hash Based Addresses (HBA)",		[4] Bagnulo, M., "Hash Based Addresses (HBA)",
	draft-ietf-shim6-hba-03 (work in progress), May 2007.		draft-ietf-shim6-hba-05 (work in progress), December 2007.
	[5] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair		[5] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair
	Exploration Protocol for IPv6 Multihoming",		Exploration Protocol for IPv6 Multihoming",
	draft-ietf-shim6-failure-detection-09 (work in progress),		draft-ietf-shim6-failure-detection-11 (work in progress),
	July 2007.		February 2008.
	19.2. Informative References		19.2. Informative References
	[6] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for		[6] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
	specifying the location of services (DNS SRV)", RFC 2782,		specifying the location of services (DNS SRV)", RFC 2782,
	February 2000.		February 2000.
	[7] Ferguson, P. and D. Senie, "Network Ingress Filtering:		[7] Ferguson, P. and D. Senie, "Network Ingress Filtering:
	Defeating Denial of Service Attacks which employ IP Source		Defeating Denial of Service Attacks which employ IP Source
	Address Spoofing", BCP 38, RFC 2827, May 2000.		Address Spoofing", BCP 38, RFC 2827, May 2000.
	skipping to change at page 131, line 24 ¶		skipping to change at page 136, line 24 ¶
	[16] Huitema, C., "Ingress filtering compatibility for IPv6		[16] Huitema, C., "Ingress filtering compatibility for IPv6
	multihomed sites", draft-huitema-shim6-ingress-filtering-00		multihomed sites", draft-huitema-shim6-ingress-filtering-00
	(work in progress), September 2005.		(work in progress), September 2005.
	[17] Bagnulo, M. and E. Nordmark, "SHIM - MIPv6 Interaction",		[17] Bagnulo, M. and E. Nordmark, "SHIM - MIPv6 Interaction",
	draft-bagnulo-shim6-mip-00 (work in progress), July 2005.		draft-bagnulo-shim6-mip-00 (work in progress), July 2005.
	[18] Nordmark, E., "Shim6 Application Referral Issues",		[18] Nordmark, E., "Shim6 Application Referral Issues",
	draft-ietf-shim6-app-refer-00 (work in progress), July 2005.		draft-ietf-shim6-app-refer-00 (work in progress), July 2005.
	[19] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,		[19] Bagnulo, M. and J. Abley, "Applicability Statement for the
			Level 3 Multihoming Shim Protocol (Shim6)",
			draft-ietf-shim6-applicability-03 (work in progress),
			July 2007.
			[20] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
	"Host Identity Protocol", draft-ietf-hip-base-10 (work in		"Host Identity Protocol", draft-ietf-hip-base-10 (work in
	progress), October 2007.		progress), October 2007.
	[20] Schuetz, S., "TCP Response to Lower-Layer Connectivity-Change		[21] Schuetz, S., Koutsianas, N., Eggert, L., Eddy, W., Swami, Y.,
	Indications", draft-schuetz-tcpm-tcp-rlci-01 (work in		and K. Le, "TCP Response to Lower-Layer Connectivity-Change
	progress), March 2007.		Indications", draft-schuetz-tcpm-tcp-rlci-02 (work in
			progress), November 2007.
			[22] Williams, N. and M. Richardson, "Better-Than-Nothing-Security:
			An Unauthenticated Mode of IPsec", draft-ietf-btns-core-06
			(work in progress), January 2008.
			[23] Komu, M., Bagnulo, M., Slavov, K., and S. Sugimoto, "Socket
			Application Program Interface (API) for Multihoming Shim",
			draft-ietf-shim6-multihome-shim-api-04 (work in progress),
			February 2008.
			[24] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
			Discovery", RFC 4821, March 2007.
			[25] Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "Extended
			ICMP to Support Multi-Part Messages", RFC 4884, April 2007.
	Authors' Addresses		Authors' Addresses
	Erik Nordmark		Erik Nordmark
	Sun Microsystems		Sun Microsystems
	17 Network Circle		17 Network Circle
	Menlo Park, CA 94025		Menlo Park, CA 94025
	USA		USA
	Phone: +1 650 786 2921		Phone: +1 650 786 2921
	skipping to change at page 133, line 7 ¶		skipping to change at page 138, line 7 ¶
	Av. Universidad 30		Av. Universidad 30
	Leganes, Madrid 28911		Leganes, Madrid 28911
	SPAIN		SPAIN
	Phone: +34 91 6248814		Phone: +34 91 6248814
	Email: marcelo@it.uc3m.es		Email: marcelo@it.uc3m.es
	URI: http://www.it.uc3m.es		URI: http://www.it.uc3m.es
	Full Copyright Statement		Full Copyright Statement
	Copyright (C) The IETF Trust (2007).		Copyright (C) The IETF Trust (2008).
	This document is subject to the rights, licenses and restrictions		This document is subject to the rights, licenses and restrictions
	contained in BCP 78, and except as set forth therein, the authors		contained in BCP 78, and except as set forth therein, the authors
	retain all their rights.		retain all their rights.
	This document and the information contained herein are provided on an		This document and the information contained herein are provided on an
	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS		"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND		OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
	THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS		THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
	OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF		OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
End of changes. 128 change blocks.
	308 lines changed or deleted		567 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/