draft-ietf-shim6-proto-04.txt   draft-ietf-shim6-proto-05.txt 
SHIM6 WG E. Nordmark SHIM6 WG E. Nordmark
Internet-Draft Sun Microsystems Internet-Draft Sun Microsystems
Expires: September 5, 2006 M. Bagnulo Expires: November 16, 2006 M. Bagnulo
UC3M UC3M
March 4, 2006 May 15, 2006
Level 3 multihoming shim protocol Level 3 multihoming shim protocol
draft-ietf-shim6-proto-04.txt draft-ietf-shim6-proto-05.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 September 5, 2006. This Internet-Draft will expire on November 16, 2006.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
The SHIM6 protocol is a layer 3 shim for providing locator agility The SHIM6 protocol is a layer 3 shim for providing locator agility
below the transport protocols, so that multihoming can be provided below the transport protocols, so that multihoming can be provided
for IPv6 with failover and load sharing properties, without assuming for IPv6 with failover and load sharing properties, without assuming
skipping to change at page 2, line 11 skipping to change at page 2, line 11
prefix which is announced in the global IPv6 routing table. The prefix which is announced in the global IPv6 routing table. The
hosts in a site which has multiple provider allocated IPv6 address hosts in a site which has multiple provider allocated IPv6 address
prefixes, will use the shim6 protocol specified in this document to prefixes, will use the shim6 protocol specified in this document to
setup state with peer hosts, so that the state can later be used to setup state with peer hosts, so that the state can later be used to
failover to a different locator pair, should the original one stop failover to a different locator pair, should the original one stop
working. working.
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 . . . . . . . . . . 6 1.3. Locators as Upper-layer Identifiers . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . 10
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 12 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . 12 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Notational Conventions . . . . . . . . . . . . . . . . . 15 2.2. Notational Conventions . . . . . . . . . . . . . . . . . 15
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . 16 3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 17 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 17
4.1 Context Tags . . . . . . . . . . . . . . . . . . . . . . 19 4.1. Context Tags . . . . . . . . . . . . . . . . . . . . . . 19
4.2 Context Forking . . . . . . . . . . . . . . . . . . . . 19 4.2. Context Forking . . . . . . . . . . . . . . . . . . . . . 19
4.3 API Extensions . . . . . . . . . . . . . . . . . . . . . 20 4.3. API Extensions . . . . . . . . . . . . . . . . . . . . . 20
4.4 Securing shim6 . . . . . . . . . . . . . . . . . . . . . 20 4.4. Securing shim6 . . . . . . . . . . . . . . . . . . . . . 20
4.5 Overview of Shim Control Messages . . . . . . . . . . . 21 4.5. Overview of Shim Control Messages . . . . . . . . . . . . 21
4.6 Extension Header Order . . . . . . . . . . . . . . . . . 22 4.6. Extension Header Order . . . . . . . . . . . . . . . . . 22
5. Message Formats . . . . . . . . . . . . . . . . . . . . . . 24 5. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 24
5.1 Common shim6 Message Format . . . . . . . . . . . . . . 24 5.1. Common shim6 Message Format . . . . . . . . . . . . . . . 24
5.2 Payload Extension Header Format . . . . . . . . . . . . 24 5.2. Payload Extension Header Format . . . . . . . . . . . . . 24
5.3 Common Shim6 Control header . . . . . . . . . . . . . . 25 5.3. Common Shim6 Control header . . . . . . . . . . . . . . . 25
5.4 I1 Message Format . . . . . . . . . . . . . . . . . . . 27 5.4. I1 Message Format . . . . . . . . . . . . . . . . . . . . 27
5.5 R1 Message Format . . . . . . . . . . . . . . . . . . . 28 5.5. R1 Message Format . . . . . . . . . . . . . . . . . . . . 28
5.6 I2 Message Format . . . . . . . . . . . . . . . . . . . 30 5.6. I2 Message Format . . . . . . . . . . . . . . . . . . . . 29
5.7 R2 Message Format . . . . . . . . . . . . . . . . . . . 31 5.7. R2 Message Format . . . . . . . . . . . . . . . . . . . . 31
5.8 R1bis Message Format . . . . . . . . . . . . . . . . . . 33 5.8. R1bis Message Format . . . . . . . . . . . . . . . . . . 33
5.9 I2bis Message Format . . . . . . . . . . . . . . . . . . 34 5.9. I2bis Message Format . . . . . . . . . . . . . . . . . . 34
5.10 Update Request Message Format . . . . . . . . . . . . . 36 5.10. Update Request Message Format . . . . . . . . . . . . . . 36
5.11 Update Acknowledgement Message Format . . . . . . . . . 38 5.11. Update Acknowledgement Message Format . . . . . . . . . . 38
5.12 Keepalive Message Format . . . . . . . . . . . . . . . . 39 5.12. Keepalive Message Format . . . . . . . . . . . . . . . . 39
5.13 Probe Message Format . . . . . . . . . . . . . . . . . . 39 5.13. Probe Message Format . . . . . . . . . . . . . . . . . . 39
5.14 Option Formats . . . . . . . . . . . . . . . . . . . . . 39 5.14. Option Formats . . . . . . . . . . . . . . . . . . . . . 40
5.14.1 Responder Validator Option Format . . . . . . . . . 41 5.14.1. Responder Validator Option Format . . . . . . . . . 42
5.14.2 Locator List Option Format . . . . . . . . . . . . . 42 5.14.2. Locator List Option Format . . . . . . . . . . . . . 42
5.14.3 Locator Preferences Option Format . . . . . . . . . 43 5.14.3. Locator Preferences Option Format . . . . . . . . . 44
5.14.4 CGA Parameter Data Structure Option Format . . . . . 45 5.14.4. CGA Parameter Data Structure Option Format . . . . . 46
5.14.5 CGA Signature Option Format . . . . . . . . . . . . 46 5.14.5. CGA Signature Option Format . . . . . . . . . . . . 46
5.14.6 ULID Pair Option Format . . . . . . . . . . . . . . 47 5.14.6. ULID Pair Option Format . . . . . . . . . . . . . . 47
5.14.7 Forked Instance Identifier Option Format . . . . . . 48 5.14.7. Forked Instance Identifier Option Format . . . . . . 48
5.14.8 Probe Option Format . . . . . . . . . . . . . . . . 48 5.14.8. Probe Option Format . . . . . . . . . . . . . . . . 48
5.14.9 Reachability Option Format . . . . . . . . . . . . . 48 5.14.9. Reachability Option Format . . . . . . . . . . . . . 49
5.14.10 Payload Reception Report Option Format . . . . . . 48 5.14.10. Payload Reception Report Option Format . . . . . . . 49
6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 49 6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 50
6.1 Conceptual Data Structures . . . . . . . . . . . . . . . 49 6.1. Conceptual Data Structures . . . . . . . . . . . . . . . 50
6.2 Context States . . . . . . . . . . . . . . . . . . . . . 50 6.2. Context States . . . . . . . . . . . . . . . . . . . . . 51
7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . 52 7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . . 53
7.1 Uniqness of Context Tags . . . . . . . . . . . . . . . . 52 7.1. Uniqueness of Context Tags . . . . . . . . . . . . . . . 53
7.2 Locator Verification . . . . . . . . . . . . . . . . . . 52 7.2. Locator Verification . . . . . . . . . . . . . . . . . . 53
7.3 Normal context establishment . . . . . . . . . . . . . . 53 7.3. Normal context establishment . . . . . . . . . . . . . . 54
7.4 Concurrent context establishment . . . . . . . . . . . . 53 7.4. Concurrent context establishment . . . . . . . . . . . . 54
7.5 Context recovery . . . . . . . . . . . . . . . . . . . . 55 7.5. Context recovery . . . . . . . . . . . . . . . . . . . . 56
7.6 Context confusion . . . . . . . . . . . . . . . . . . . 57 7.6. Context confusion . . . . . . . . . . . . . . . . . . . . 58
7.7 Sending I1 messages . . . . . . . . . . . . . . . . . . 58 7.7. Sending I1 messages . . . . . . . . . . . . . . . . . . . 59
7.8 Retransmitting I1 messages . . . . . . . . . . . . . . . 58 7.8. Retransmitting I1 messages . . . . . . . . . . . . . . . 59
7.9 Receiving I1 messages . . . . . . . . . . . . . . . . . 59 7.9. Receiving I1 messages . . . . . . . . . . . . . . . . . . 60
7.9.1 Generating the R1 Validator . . . . . . . . . . . . 60 7.10. Sending R1 messages . . . . . . . . . . . . . . . . . . . 61
7.10 Receiving R1 messages and sending I2 messages . . . . . 61 7.10.1. Generating the R1 Validator . . . . . . . . . . . . 61
7.11 Retransmitting I2 messages . . . . . . . . . . . . . . . 62 7.11. Receiving R1 messages and sending I2 messages . . . . . . 62
7.12 Receiving I2 messages . . . . . . . . . . . . . . . . . 62 7.12. Retransmitting I2 messages . . . . . . . . . . . . . . . 63
7.13 Sending R2 messages . . . . . . . . . . . . . . . . . . 64 7.13. Receiving I2 messages . . . . . . . . . . . . . . . . . . 63
7.14 Match for Context Confusion . . . . . . . . . . . . . . 64 7.14. Sending R2 messages . . . . . . . . . . . . . . . . . . . 65
7.15 Receiving R2 messages . . . . . . . . . . . . . . . . . 65 7.15. Match for Context Confusion . . . . . . . . . . . . . . . 65
7.16 Sending R1bis messages . . . . . . . . . . . . . . . . . 66 7.16. Receiving R2 messages . . . . . . . . . . . . . . . . . . 66
7.16.1 Generating the R1bis Validator . . . . . . . . . . . 66 7.17. Sending R1bis messages . . . . . . . . . . . . . . . . . 67
7.17 Receiving R1bis messages and sending I2bis messages . . 67 7.17.1. Generating the R1bis Validator . . . . . . . . . . . 67
7.18 Retransmitting I2bis messages . . . . . . . . . . . . . 68 7.18. Receiving R1bis messages and sending I2bis messages . . . 68
7.19 Receiving I2bis messages and sending R2 messages . . . . 68 7.19. Retransmitting I2bis messages . . . . . . . . . . . . . . 69
8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 70 7.20. Receiving I2bis messages and sending R2 messages . . . . 69
9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . 72 8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 71
10. Updating the Peer . . . . . . . . . . . . . . . . . . . . 73 9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . . 73
10.1 Sending Update Request messages . . . . . . . . . . . . 73 10. Updating the Peer . . . . . . . . . . . . . . . . . . . . . . 74
10.2 Retransmitting Update Request messages . . . . . . . . . 73 10.1. Sending Update Request messages . . . . . . . . . . . . . 74
10.3 Newer Information While Retransmitting . . . . . . . . . 74 10.2. Retransmitting Update Request messages . . . . . . . . . 74
10.4 Receiving Update Request messages . . . . . . . . . . . 74 10.3. Newer Information While Retransmitting . . . . . . . . . 75
10.5 Receiving Update Acknowledgement messages . . . . . . . 76 10.4. Receiving Update Request messages . . . . . . . . . . . . 75
11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . 77 10.5. Receiving Update Acknowledgement messages . . . . . . . . 77
11.1 Sending ULP Payload after a Switch . . . . . . . . . . . 77 11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . . 78
12. Receiving Packets . . . . . . . . . . . . . . . . . . . . 79 11.1. Sending ULP Payload after a Switch . . . . . . . . . . . 78
12.1 Receiving Payload Extension Headers . . . . . . . . . . 79 12. Receiving Packets . . . . . . . . . . . . . . . . . . . . . . 80
12.2 Receiving Shim Control messages . . . . . . . . . . . . 79 12.1. Receiving Payload Extension Headers . . . . . . . . . . . 80
12.3 Context Lookup . . . . . . . . . . . . . . . . . . . . . 80 12.2. Receiving Shim Control messages . . . . . . . . . . . . . 80
13. Initial Contact . . . . . . . . . . . . . . . . . . . . . 82 12.3. Context Lookup . . . . . . . . . . . . . . . . . . . . . 81
14. Protocol constants . . . . . . . . . . . . . . . . . . . . 83 13. Initial Contact . . . . . . . . . . . . . . . . . . . . . . . 83
15. Implications Elsewhere . . . . . . . . . . . . . . . . . . 84 14. Protocol constants . . . . . . . . . . . . . . . . . . . . . 84
16. Security Considerations . . . . . . . . . . . . . . . . . 86 15. Implications Elsewhere . . . . . . . . . . . . . . . . . . . 85
17. IANA Considerations . . . . . . . . . . . . . . . . . . . 88 16. Security Considerations . . . . . . . . . . . . . . . . . . . 87
18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 90 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 89
A. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 91 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 91
B. Possible Protocol Extensions . . . . . . . . . . . . . . . . 92 Appendix A. Possible Protocol Extensions . . . . . . . . . . 92
C. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 94 Appendix B. Simplified State Machine . . . . . . . . . . . . 94
D. Simplified State Machine . . . . . . . . . . . . . . . . . . 97 Appendix B.1. Simplified State Machine diagram . . . . . . . . 100
D.1 Simplified State Machine diagram . . . . . . . . . . . . 102 Appendix C. Context Tag Reuse . . . . . . . . . . . . . . . . 101
E. Context Tag Reuse . . . . . . . . . . . . . . . . . . . . . 103 Appendix C.1. Context Recovery . . . . . . . . . . . . . . . . 101
E.1 Context Recovery . . . . . . . . . . . . . . . . . . . . 103 Appendix C.2. Context Confusion . . . . . . . . . . . . . . . . 101
E.2 Context Confusion . . . . . . . . . . . . . . . . . . . 103 Appendix C.3. Three Party Context Confusion . . . . . . . . . . 102
E.3 Three Party Context Confusion . . . . . . . . . . . . . 104 Appendix D. Design Alternatives . . . . . . . . . . . . . . . 103
F. Design Alternatives . . . . . . . . . . . . . . . . . . . . 105 Appendix D.1. Context granularity . . . . . . . . . . . . . . . 103
F.1 Context granularity . . . . . . . . . . . . . . . . . . 105 Appendix D.2. Demultiplexing of data packets in shim6
F.2 Demultiplexing of data packets in shim6 communications . 105 communications . . . . . . . . . . . . . . . . . 103
F.2.1 Flow-label . . . . . . . . . . . . . . . . . . . . . 106 Appendix D.2.1. Flow-label . . . . . . . . . . . . . . . . . . . 104
F.2.2 Extension Header . . . . . . . . . . . . . . . . . . 108 Appendix D.2.2. Extension Header . . . . . . . . . . . . . . . . 106
F.3 Context Loss Detection . . . . . . . . . . . . . . . . . 109 Appendix D.3. Context Loss Detection . . . . . . . . . . . . . 107
F.4 Securing locator sets . . . . . . . . . . . . . . . . . 111 Appendix D.4. Securing locator sets . . . . . . . . . . . . . . 109
F.5 ULID-pair context establishment exchange . . . . . . . . 114 Appendix D.5. ULID-pair context establishment exchange . . . . 112
F.6 Updating locator sets . . . . . . . . . . . . . . . . . 115 Appendix D.6. Updating locator sets . . . . . . . . . . . . . . 113
F.7 State Cleanup . . . . . . . . . . . . . . . . . . . . . 115 Appendix D.7. State Cleanup . . . . . . . . . . . . . . . . . . 113
19. References . . . . . . . . . . . . . . . . . . . . . . . . 118 Appendix E. Change Log . . . . . . . . . . . . . . . . . . . 116
19.1 Normative References . . . . . . . . . . . . . . . . . . 118 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 120
19.2 Informative References . . . . . . . . . . . . . . . . . 118 19.1. Normative References . . . . . . . . . . . . . . . . . . 120
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 120 19.2. Informative References . . . . . . . . . . . . . . . . . 120
Intellectual Property and Copyright Statements . . . . . . . 121 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 122
Intellectual Property and Copyright Statements . . . . . . . . . 123
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 [15], without assuming that a multihomed site will have a properties [15], 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
specified in this document to setup state with peer hosts, so that specified in this document to setup state with peer hosts, so that
the state can later be used to failover to a different locator pair, the state can later be used to failover to a different locator pair,
should the original one stop working. should the original one stop working.
We assume that redirection attacks are prevented using the mechanism We assume that redirection attacks are prevented using the mechanism
specified in HBA [7]. specified in HBA [7].
The reachability detection and failure detection, including how a new The reachability and failure detection, including how a new working
working locator pair is discovered after a failure, is specified in a locator pair is discovered after a failure, is specified in a
separate documents [8] This document allocates message types and separate documents [8] This document allocates message types and
option types for that sub-protocol, and leaves the specification of option types for that sub-protocol, and leaves the specification of
the message and option formats as well as the protocol behavior to the message and option formats as well as the protocol behavior to
that document. that document.
1.1 Goals 1.1. Goals
The goals for this approach is to: The goals for this approach is to:
o Preserve established communications through certain classes of o Preserve established communications through certain classes of
failures, for example, TCP connections and application failures, for example, TCP connections and application
communications using UDP. communications using UDP.
o Have minimal impact on upper layer protocols in general and on o Have minimal impact on upper layer protocols in general and on
transport protocols in particular. transport protocols in particular.
o Address the security threats in [19] through the combination of o Address the security threats in [19] through the combination of
the HBA/CGA approach specified in a separate document [7], and the HBA/CGA approach specified in a separate document [7], and
techniques described in this document. techniques described in this document.
o Do not require an extra roundtrip up front to setup shim specific o Not require extra roundtrip up front to setup shim specific state.
state. Instead allow the upper layer traffic (e.g., TCP) to flow Instead allow the upper layer traffic (e.g., TCP) to flow as
as normal and defer the setup of the shim state until some number normal and defer the setup of the shim state until some number of
of packets have been exchanged. packets have been exchanged.
o Take advantage of multiple locators/addresses for load spreading o Take advantage of multiple locators/addresses for load spreading
so that different sets of communication to a host (e.g., different so that different sets of communication to a host (e.g., different
connections) might use different locators of the host. Note that connections) might use different locators of the host. Note that
this might cause load to be spread unevenly, thus we use the term this might cause load to be spread unevenly, thus we use the term
"load spreading" instead of "load balancing". This capability "load spreading" instead of "load balancing". This capability
might enable some forms of traffic engineering, but the details might enable some forms of traffic engineering, but the details
for traffic engineering, including what requirements can be for traffic engineering, including what requirements can be
satisfied, are not specified in this document, and form part of a satisfied, are not specified in this document, and form part of a
potential extensions to this protocol. potential extensions to this protocol.
1.2 Non-Goals 1.2. Non-Goals
The assumption is that the problem we are trying to solve is site The assumption is that the problem we are trying to solve is site
multihoming, with the ability to have the set of site locator multihoming, with the ability to have the set of site locator
prefixes change over time due to site renumbering. Further, we prefixes change over time due to site renumbering. Further, we
assume that such changes to the set of locator prefixes can be assume that such changes to the set of locator prefixes can be
relatively slow and managed; slow enough to allow updates to the DNS relatively slow and managed; slow enough to allow updates to the DNS
to propagate. But it is not a goal to try to make communication to propagate. But it is not a goal to try to make communication
survive a renumbering event (which causes all the locators of a host survive a renumbering event (which causes all the locators of a host
to change to a new set of locators). This proposal does not attempt to change to a new set of locators). This proposal does not attempt
to solve the, perhaps related, problem of host mobility. However, it to solve the, perhaps related, problem of host mobility. However, it
skipping to change at page 6, line 32 skipping to change at page 6, line 32
This proposal also does not try to provide a new network level or This proposal also does not try to provide a new network level or
transport level identifier namespace separated from the current IP transport level identifier namespace separated from the current IP
address namespace. Even though such a concept would be useful to address namespace. Even though such a concept would be useful to
ULPs and applications, especially if the management burden for such a ULPs and applications, especially if the management burden for such a
name space was negligible and there was an efficient yet secure name space was negligible and there was an efficient yet secure
mechanism to map from identifiers to locators, such a name space mechanism to map from identifiers to locators, such a name space
isn't necessary (and furthermore doesn't seem to help) to solve the isn't necessary (and furthermore doesn't seem to help) to solve the
multihoming problem. multihoming problem.
1.3 Locators as Upper-layer Identifiers 1.3. Locators as Upper-layer Identifiers
This approach does not introduce a new identifier name space but This approach does not introduce a new identifier name space but
instead uses the locator that is selected in the initial contact with instead uses the locator that is selected in the initial contact with
the remote peer as the preserved upper-level identifier. While there the remote peer as the preserved upper-level identifier. While there
may be subsequent changes in the selected network level locators over may be subsequent changes in the selected network level locators over
time in response to failures in using the original locator, the upper time in response to failures in using the original locator, the upper
level protocol stack elements will continue to use this upper level level protocol stack elements will continue to use this upper level
identifier without change. identifier without change.
This implies that the ULID selection is performed as today's default This implies that the ULID selection is performed as today's default
skipping to change at page 7, line 28 skipping to change at page 7, line 27
For example, the protocol already needs to handle ULIDs that are not For example, the protocol already needs to handle ULIDs that are not
initially reachable. Thus the same mechanism can handle ULIDs that initially reachable. Thus the same mechanism can handle ULIDs that
are permanently unreachable from outside their site. The issue are permanently unreachable from outside their site. The issue
becomes how to make the protocol perform well when the ULID is known becomes how to make the protocol perform well when the ULID is known
a priori to be not reachable (e.g., the ULID is a ULA), for instance, a priori to be not reachable (e.g., the ULID is a ULA), for instance,
avoiding any timeout and retries in this case. In addition one would avoiding any timeout and retries in this case. In addition one would
need to understand how the ULAs would be entered in the DNS to avoid need to understand how the ULAs would be entered in the DNS to avoid
a performance impact on existing, non-shim6 aware, IPv6 hosts a performance impact on existing, non-shim6 aware, IPv6 hosts
potentially trying to communicate to the (unreachable) ULA. potentially trying to communicate to the (unreachable) ULA.
1.4 IP Multicast 1.4. IP Multicast
IP Multicast requires that the IP source address field contain a IP Multicast requires that the IP source address field contain a
topologically correct locator for interface that is used to send the topologically correct locator for interface that is used to send the
packet, since IP multicast routing uses both the source address and packet, since IP multicast routing uses both the source address and
the destination group to determine where to forward the packet. the destination group to determine where to forward the packet.
(This isn't much different than the situation with widely implemented (This isn't much different than the situation with widely implemented
ingress filtering [10] for unicast.) ingress filtering [10] for unicast.)
While in theory it would be possible to apply the shim re-mapping of While in theory it would be possible to apply the shim re-mapping of
the IP address fields between ULIDs and locators, the fact that all the IP address fields between ULIDs and locators, the fact that all
skipping to change at page 8, line 7 skipping to change at page 8, line 5
important to the application. important to the application.
In summary, IP multicast will not need the shim to remap the IP In summary, IP multicast will not need the shim to remap the IP
addresses. addresses.
This doesn't prevent the receiver of multicast to change its This doesn't prevent the receiver of multicast to change its
locators, since the receiver is not explicitly identified; the locators, since the receiver is not explicitly identified; the
destination address is a multicast address and not the unicast destination address is a multicast address and not the unicast
locator of the receiver. locator of the receiver.
1.5 Renumbering Implications 1.5. Renumbering Implications
As stated above, this approach does not try to make communication As stated above, this approach does not try to make communication
survive renumbering in the general case. survive renumbering in the general case.
When a host is renumbered, the effect is that one or more locators When a host is renumbered, the effect is that one or more locators
become invalid, and zero or more locators are added to the host's become invalid, and zero or more locators are added to the host's
network interface. This means that the set of locators that is used network interface. This means that the set of locators that is used
in the shim will change, which the shim can handle as long as not all in the shim will change, which the shim can handle as long as not all
the original locators become invalid at the same time. the original locators become invalid at the same time.
skipping to change at page 8, line 29 skipping to change at page 8, line 27
survive locators becoming invalid can potentially cause some survive locators becoming invalid can potentially cause some
confusion at the upper layers. The fact that a ULID might be used confusion at the upper layers. The fact that a ULID might be used
with a different locator over time open up the possibility that with a different locator over time open up the possibility that
communication between two ULIDs might continue to work after one or communication between two ULIDs might continue to work after one or
both of those ULIDs are no longer reachable as locators, for example both of those ULIDs are no longer reachable as locators, for example
due to a renumbering event. This opens up the possibility that the due to a renumbering event. This opens up the possibility that the
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.
Worst case we could end up with two separate hosts using the same In the worst case we could end up with two separate hosts using the
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 can be avoided if we require that This potential source for confusion can be avoided if we require that
any communication using a ULID must be terminated when the ULID any communication using a ULID must be terminated when the ULID
becomes invalid (due to the underlying prefix becoming invalid). If becomes invalid (due to the underlying prefix becoming invalid). If
that behavior is desired, it can be accomplished by explicitly that behavior is desired, it can be accomplished by explicitly
discarding the shim state when the ULID becomes invalid. The context discarding the shim state when the ULID becomes invalid. The context
recovery mechanism will then make the peer aware that the context is recovery mechanism will then make the peer aware that the context is
gone, and that the ULID is no longer present at the same locator(s). gone, and that the ULID is no longer present at the same locator(s).
However, terminating the communication might be overkill. Even when However, terminating the communication might be overkill. Even when
skipping to change at page 9, line 7 skipping to change at page 9, line 5
the identical address be used by another host, then there still the identical address be used by another host, then there still
wouldn't be a problem until that host attempts to communicate with wouldn't be a problem until that host attempts to communicate with
the same peer host with which the initial user of the IPv6 address the same peer host with which the initial user of the IPv6 address
was communicating. was communicating.
The protocol as specified in this document does not perform any The protocol as specified in this document does not perform any
action when an address becomes invalid. As we gain further action when an address becomes invalid. As we gain further
understanding of the practical impact of renumbering this might understanding of the practical impact of renumbering this might
change in a future version of the protocol. change in a future version of the protocol.
1.6 Placement of the shim 1.6. Placement of the shim
----------------------- -----------------------
| Transport Protocols | | Transport Protocols |
----------------------- -----------------------
------ ------- -------------- ------------- IP endpoint ------ ------- -------------- ------------- IP endpoint
| AH | | ESP | | Frag/reass | | Dest opts | sub-layer | AH | | ESP | | Frag/reass | | Dest opts | sub-layer
------ ------- -------------- ------------- ------ ------- -------------- -------------
--------------------- ---------------------
| shim6 shim layer | | shim6 shim layer |
--------------------- ---------------------
------ IP routing ------ IP routing
| IP | sub-layer | IP | sub-layer
------ ------
Figure 1: Protocol stack Figure 1: Protocol stack
The proposal uses an multihoming shim layer within the IP layer, The proposal uses a multihoming shim layer within the IP layer, i.e.,
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 IPsec can
be made to be unaware of locator changes the same way that transport be made to be unaware of locator changes the same way that transport
protocols can be unaware. Thus the IPsec security associations protocols can be unaware. Thus the IPsec security associations
skipping to change at page 11, line 5 skipping to change at page 10, line 49
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.
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 locators Inherent in a scalable multihoming mechanism that separates locators
from identifiers is that each host ends up with multiple locators. from identifiers is that each host ends up with multiple locators.
This means that at least for initial contact, it is the remote peer This means that at least for initial contact, it is the remote peer
skipping to change at page 11, line 42 skipping to change at page 11, line 38
that DNS SRV records can be used for initial contact and the shim for that DNS SRV records can be used for initial contact and the shim for
failover, and they can use the same way to describe the preferences. failover, and they can use the same way to describe the preferences.
The format allows adding additional notions of "metrics" over time. The format allows adding additional notions of "metrics" over time.
But the Locator Preference option is merely a place holder when it But the Locator Preference option is merely a place holder when it
comes to providing traffic engineering; in order to use this in a 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 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 find out what preference values to use, either statically (e.g., some
new DHCPv6 option) or dynamically. 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 B. Appendix A.
2. Terminology 2. Terminology
This document uses the terms MUST, SHOULD, RECOMMENDED, MAY, SHOULD This document uses the terms MUST, SHOULD, RECOMMENDED, MAY, SHOULD
NOT and MUST NOT defined in RFC 2119 [1]. The terms defined in RFC NOT and MUST NOT defined in RFC 2119 [1]. The terms defined in RFC
2460 [2] are also used. 2460 [2] are also used.
2.1 Definitions 2.1. Definitions
This document introduces the following terms: This document introduces the following terms:
upper layer protocol (ULP) upper layer protocol (ULP)
A protocol layer immediately above IP. Examples A protocol layer immediately above IP. Examples
are transport protocols such as TCP and UDP, are transport protocols such as TCP and UDP,
control protocols such as ICMP, routing protocols control protocols such as ICMP, routing protocols
such as OSPF, and internet or lower-layer such as OSPF, and internet or lower-layer
protocols being "tunneled" over (i.e., protocols being "tunneled" over (i.e.,
encapsulated in) IP such as IPX, AppleTalk, or IP encapsulated in) IP such as IPX, AppleTalk, or IP
skipping to change at page 15, line 5 skipping to change at page 15, line 5
Cryptographically Generated Addresses (CGA) Cryptographically Generated Addresses (CGA)
A form of IPv6 address where the interface ID is A form of IPv6 address where the interface ID is
derived from a cryptographic hash of the public derived from a cryptographic hash of the public
key. See [6]. key. See [6].
CGA Parameter Data Structure (PDS) CGA Parameter Data Structure (PDS)
The information that CGA and HBA exchanges in The information that CGA and HBA exchanges in
order to inform the peer of how the interface ID order to inform the peer of how the interface ID
was computed. See [6]., [7]. was computed. See [6]., [7].
2.2 Notational Conventions 2.2. Notational Conventions
A, B, and C are hosts. X is a potentially malicious host. A, B, and C are hosts. X is a potentially malicious host.
FQDN(A) is the domain name for A. FQDN(A) is the domain name for A.
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). L2(A), ... Ln(A).
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.
skipping to change at page 19, line 18 skipping to change at page 19, line 18
as long as the ULID pair is used as the locator pair. After a switch as long as the ULID pair is used as the locator pair. After a switch
to a different locator pair the packets are "tagged" with a shim6 to a different locator pair the packets are "tagged" with a shim6
extension header, so that the receiver can always determine the extension header, so that the receiver can always determine the
context to which they belong. This is accomplished by including an context to which they belong. This is accomplished by including an
8-octet shim6 Payload Extension header before the (extension) headers 8-octet shim6 Payload Extension header before the (extension) headers
that are processed by the IP endpoint sublayer and ULPs. If that are processed by the IP endpoint sublayer and ULPs. If
subsequently the original ULIDs are selected as the active locator subsequently the original ULIDs are selected as the active locator
pair then the tagging of packets with the shim6 extension header can pair then the tagging of packets with the shim6 extension header can
also be stopped. also be stopped.
4.1 Context Tags 4.1. Context Tags
A context between two hosts is actually a context between two ULIDs. A context between two hosts is actually a context between two ULIDs.
The context is identified by a pair of context tags. Each end gets The context is identified by a pair of context tags. Each end gets
to allocate a context tag, and once the context is established, most to allocate a context tag, and once the context is established, most
shim6 control messages contain the context tag that the receiver of shim6 control messages contain the context tag that the receiver of
the message allocated. Thus at a minimum the combination of <peer the message allocated. Thus at a minimum the combination of <peer
ULID, local ULID, local context tag> have to uniquely identify one ULID, local ULID, local context tag> have to uniquely identify one
context. But since the Payload extension headers are demultiplexed context. But since the Payload extension headers are demultiplexed
without looking at the locators in the packet, the receiver will need without looking at the locators in the packet, the receiver will need
to allocate context tags that are unique for all its contexts. The to allocate context tags that are unique for all its contexts. The
context tag is a 47-bit number (the largest which can fit in an context tag is a 47-bit number (the largest which can fit in an
8-octet extension header). 8-octet extension header).
The mechanism for detecting a loss of context state at the peer that The mechanism for detecting a loss of context state at the peer that
is currently proposed in this document assumes that the receiver can is currently proposed in this document assumes that the receiver can
tell the packets that need locator rewriting, even after it has lost tell the packets that need locator rewriting, even after it has lost
all state (e.g., due to a crash followed by a reboot). This is all state (e.g., due to a crash followed by a reboot). This is
achieved because after a rehoming event the packets that need achieved because after a rehoming event the packets that need
receive-side rewriting, carry the Payload extension header. receive-side rewriting, carry the Payload extension header.
4.2 Context Forking 4.2. Context Forking
It has been asserted that it will be important for future ULPs, in It has been asserted that it will be important for future ULPs, in
particular, future transport protocols, to be able to control which particular, future transport protocols, to be able to control which
locator pairs are used for different communication. For instance, locator pairs are used for different communication. For instance,
host A and host B might communicate using both VoIP traffic and ftp host A and host B might communicate using both VoIP traffic and ftp
traffic, and those communications might benefit from using different traffic, and those communications might benefit from using different
locator pairs. However, the fundamental shim6 mechanism uses a locator pairs. However, the fundamental shim6 mechanism uses a
single current locator pair for each context, thus a single context single current locator pair for each context, thus a single context
can not accomplish this. can not accomplish this.
skipping to change at page 20, line 25 skipping to change at page 20, line 25
No other special considerations are needed in the shim6 protocol to No other special considerations are needed in the shim6 protocol to
handle forked contexts. handle forked contexts.
Note that forking as specified does NOT allow A to be able to tell B Note that forking as specified does NOT allow A to be able to tell B
that certain traffic (a 5-tuple?) should be forked for the reverse that certain traffic (a 5-tuple?) should be forked for the reverse
direction. The shim6 forking mechanism as specified applies only to direction. The shim6 forking mechanism as specified applies only to
the sending of ULP packets. If some ULP wants to fork for both the sending of ULP packets. If some ULP wants to fork for both
directions, it is up to the ULP to set this up, and then instruct the directions, it is up to the ULP to set this up, and then instruct the
shim at each end to transmit using the forked context. shim at each end to transmit using the forked context.
4.3 API Extensions 4.3. API Extensions
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 B Some other API extensions are discussed in Appendix A
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 [7] for verifying the locators to prevent an o The HBA technique [7] 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 before a new locator is used o Requiring a Reachability Probe+Reply before a new locator is used
as the destination, in order to prevent 3rd party flooding as the destination, in order to prevent 3rd party flooding
attacks. attacks.
skipping to change at page 21, line 21 skipping to change at page 21, line 21
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 Such discovery probably requires to be along the path in order to
be sniff the context tag value. The result is that through this be sniff the context tag value. The result is that through this
technique, the shim6 protocol is protected against off-path technique, the shim6 protocol is protected against off-path
attackers. 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 [25].] message. [The names of these messages are borrowed from HIP [25].]
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
skipping to change at page 22, line 24 skipping to change at page 22, line 23
The above probe and keepalive messages assume we have an established The above probe and keepalive messages assume we have an established
ULID-pair context. However, communication might fail during the ULID-pair context. However, communication might fail during the
initial contact (that is, when the application or transport protocol initial contact (that is, when the application or transport protocol
is trying to setup some communication). This is handled using the is trying to setup some communication). This is handled using the
mechanisms in the ULP to try different address pairs as specified in mechanisms in the ULP to try different address pairs as specified in
[12] [13]. In the future versions of the protocol, and with a richer [12] [13]. In the future versions of the protocol, and with a richer
API between the ULP and the shim, the shim might be help optimize API between the ULP and the shim, the shim might be help optimize
discovering a working locator pair during initial contact. This is discovering a working locator pair during initial contact. This is
for further study. for further study.
4.6 Extension Header Order 4.6. Extension Header Order
Since the shim is placed between the IP endpoint sub-layer and the IP Since the shim is placed between the IP endpoint sub-layer and the IP
routing sub-layer in the host, the shim header will be placed before routing sub-layer in the host, the shim header will be placed before
any endpoint extension headers (fragmentation headers, destination any endpoint extension headers (fragmentation headers, destination
options header, AH, ESP), but after any routing related headers (hop- options header, AH, ESP), but after any routing related headers (hop-
by-hop extensions header, routing header, a destinations options by-hop extensions header, routing header, a destinations options
header which precedes a routing header). When tunneling is used, header which precedes a routing header). When tunneling is used,
whether IP-in-IP tunneling or the special form of tunneling that whether IP-in-IP tunneling or the special form of tunneling that
Mobile IPv6 uses (with Home Address Options and Routing header type Mobile IPv6 uses (with Home Address Options and Routing header type
2), there is a choice whether the shim applies inside the tunnel or 2), there is a choice whether the shim applies inside the tunnel or
outside the tunnel, which effects the location of the shim6 header. outside the tunnel, which affects the location of the shim6 header.
In most cases IP-in-IP tunnels are used as a routing technique, thus In most cases IP-in-IP tunnels are used as a routing technique, thus
it makes sense to apply them on the locators which means that the it makes sense to apply them on the locators which means that the
sender would insert the shim6 header after any IP-in-IP sender would insert the shim6 header after any IP-in-IP
encapsulation; this is what occurs naturally when routers apply IP- encapsulation; this is what occurs naturally when routers apply IP-
in-IP encapsulation. Thus the packets would have: in-IP encapsulation. Thus the packets would have:
o Outer IP header o Outer IP header
o Inner IP header o Inner IP header
skipping to change at page 24, line 18 skipping to change at page 24, line 18
be assigned by IANA]. The shim6 messages have a common header, be assigned by IANA]. The shim6 messages have a common header,
defined below, with some fixed fields, followed by type specific defined below, with some fixed fields, followed by type specific
fields. fields.
The shim6 messages are structured as an IPv6 extension header since The shim6 messages are structured as an IPv6 extension header since
the Payload extension header is used to carry the ULP packets after a the Payload extension header is used to carry the ULP packets after a
locator switch. The shim6 control messages use the same extension locator switch. The shim6 control messages use the same extension
header formats so that a single "protocol number" needs to be allowed header formats so that a single "protocol number" needs to be allowed
through firewalls in order for shim6 to function across the firewall. through firewalls in order for shim6 to function across the firewall.
5.1 Common shim6 Message Format 5.1. Common shim6 Message Format
The first 17 bits of the shim6 header is common for the Payload The first 17 bits of the shim6 header is common for the Payload
extension header and the control messages and looks as follows: extension header and the control messages and looks as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len |P| | Next Header | Hdr Ext Len |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields: Fields:
Next Header: The payload which follows this header. Next Header: The payload which follows this header.
Hdr Ext Len: 8-bit unsigned integer. Length of the shim6 header in Hdr Ext Len: 8-bit unsigned integer. Length of the shim6 header in
8-octet units, not including the first 8 octets. 8-octet units, not including the first 8 octets.
P: A single bit to distinguish Payload extension headers P: A single bit to distinguish Payload extension headers
from control messages. from control messages.
5.2 Payload Extension Header Format 5.2. Payload Extension Header Format
The payload extension headers is used to carry ULP packets where the The payload extension headers is used to carry ULP packets where the
receiver must replace the content of the source and/or destination receiver must replace the content of the source and/or destination
fields in the IPv6 header before passing the packet to the ULP. Thus fields in the IPv6 header before passing the packet to the ULP. Thus
this extension header is required when the locators pair that is used this extension header is required when the locators pair that is used
is not the same as the ULID pair. is not the same as the ULID pair.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 25, line 25 skipping to change at page 25, line 18
Next Header: The payload which follows this header. Next Header: The payload which follows this header.
Hdr Ext Len: 0 (since the header is 8 octets). Hdr Ext Len: 0 (since the header is 8 octets).
P: Set to one. A single bit to distinguish this from the P: Set to one. A single bit to distinguish this from the
shim6 control messages. shim6 control messages.
Receiver Context Tag: 47-bit unsigned integer. Allocated by the Receiver Context Tag: 47-bit unsigned integer. Allocated by the
receiver for use to identify the context. receiver for use to identify the context.
5.3 Common Shim6 Control header 5.3. Common Shim6 Control header
The common part of the header has a next header and header extension The common part of the header has a next header and header extension
length field which is consistent with the other IPv6 extension length field which is consistent with the other IPv6 extension
headers, even if the next header value is always "NO NEXT HEADER" for headers, even if the next header value is always "NO NEXT HEADER" for
the control messages; only the payload extension header use the Next the control messages; only the payload extension header use the Next
Header field. Header field.
The shim6 headers must be a multiple of 8 octets, hence the minimum The shim6 headers must be a multiple of 8 octets, hence the minimum
size is 8 octets. size is 8 octets.
skipping to change at page 27, line 31 skipping to change at page 27, line 5
| | | | | |
| 65 | Update Acknowledgement | | 65 | Update Acknowledgement |
| | | | | |
| 66 | Keepalive | | 66 | Keepalive |
| | | | | |
| 67 | Probe Message | | 67 | Probe Message |
+------------+-----------------------------------------------------+ +------------+-----------------------------------------------------+
Table 1 Table 1
5.4 I1 Message Format 5.4. I1 Message Format
The I1 message is the first message in the context establishment The I1 message is the first message in the context establishment
exchange. exchange.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 59 | Hdr Ext Len |0| Type = 1 | Reserved1 |0| | 59 | Hdr Ext Len |0| Type = 1 | Reserved1 |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |R| | | Checksum |R| |
skipping to change at page 28, line 38 skipping to change at page 28, line 15
ULID pair: When the IPv6 source and destination addresses in the ULID pair: When the IPv6 source and destination addresses in the
IPv6 header does not match the ULID pair, this option IPv6 header does not match the ULID pair, this option
MUST be included. An example of this is when MUST be included. An example of this is when
recovering from a lost context. recovering from a lost context.
Forked Instance Identifier: When another instance of an existent Forked Instance Identifier: When another instance of an existent
context with the same ULID pair is being created, a context with the same ULID pair is being created, a
Forked Instance Identifier option is included to Forked Instance Identifier option is included to
distinguish this new instance from the existent one. distinguish this new instance from the existent one.
5.5 R1 Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.5. R1 Message Format
The R1 message is the second message in the context establishment The R1 message is the second message in the context establishment
exchange. The responder sends this in response to an I1 message, exchange. The responder sends this in response to an I1 message,
without creating any state specific to the initiator. without creating any state specific to the initiator.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 59 | Hdr Ext Len |0| Type = 2 | Reserved1 |0| | 59 | Hdr Ext Len |0| Type = 2 | Reserved1 |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 30, line 5 skipping to change at page 29, line 26
The following options are defined for this message: The following options are defined for this message:
Responder Validator: Variable length option. Typically a hash Responder Validator: Variable length option. Typically a hash
generated by the responder, which the responder uses generated by the responder, which the responder uses
together with the Responder Nonce value to verify that together with the Responder Nonce value to verify that
an I2 message is indeed sent in response to a R1 an I2 message is indeed sent in response to a R1
message, and that the parameters in the I2 message are message, and that the parameters in the I2 message are
the same as those in the I1 message. the same as those in the I1 message.
5.6 I2 Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.6. I2 Message Format
The I2 message is the third message in the context establishment The I2 message is the third message in the context establishment
exchange. The initiator sends this in response to a R1 message, exchange. The initiator sends this in response to a R1 message,
after checking the Initiator Nonce, etc. after checking the Initiator Nonce, etc.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 59 | Hdr Ext Len |0| Type = 3 | Reserved1 |0| | 59 | Hdr Ext Len |0| Type = 3 | Reserved1 |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 31, line 42 skipping to change at page 31, line 39
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure: Included when the locator list is
included so the receiver can verify the locator list. included so the receiver can verify the locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for verification. CGA (and not HBA) for verification.
5.7 R2 Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.7. R2 Message Format
The R2 message is the fourth message in the context establishment The R2 message is the fourth message in the context establishment
exchange. The responder sends this in response to an I2 message. exchange. The responder sends this in response to an I2 message.
The R2 message is also used when both hosts send I1 messages at the The R2 message is also used when both hosts send I1 messages at the
same time and the I1 messages cross in flight. same time and the I1 messages cross in flight.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 59 | Hdr Ext Len |0| Type = 4 | Reserved1 |0| | 59 | Hdr Ext Len |0| Type = 4 | Reserved1 |0|
skipping to change at page 33, line 11 skipping to change at page 33, line 11
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure: Included when the locator list is
included so the receiver can verify the locator list. included so the receiver can verify the locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for verification. CGA (and not HBA) for verification.
5.8 R1bis Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.8. R1bis Message Format
Should a host receive a packet with a shim Payload extension header Should a host receive a packet with a shim Payload extension header
or shim6 control message with type code 64-127 (such as an Update or or shim6 control message with type code 64-127 (such as an Update or
Probe message), and the host does not have any context state for the Probe message), and the host does not have any context state for the
received context tag, then it will generate a R1bis message. received context tag, then it will generate a R1bis message.
This message allows the sender of the packet referring to the non- This message allows the sender of the packet referring to the non-
existent context to re-establish the context with a reduced context existent context to re-establish the context with a reduced context
establishment exchange. Upon the reception of the R1bis message, the establishment exchange. Upon the reception of the R1bis message, the
receiver can proceed reestablishing the lost context by directly receiver can proceed reestablishing the lost context by directly
skipping to change at page 34, line 26 skipping to change at page 34, line 29
message. message.
The following options are defined for this message: The following options are defined for this message:
Responder Validator: Variable length option. Typically a hash Responder Validator: Variable length option. Typically a hash
generated by the responder, which the responder uses generated by the responder, which the responder uses
together with the Responder Nonce value to verify that together with the Responder Nonce value to verify that
an I2bis message is indeed sent in response to a R1bis an I2bis message is indeed sent in response to a R1bis
message. message.
5.9 I2bis Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.9. I2bis Message Format
The I2bis message is the third message in the context recovery The I2bis message is the third message in the context recovery
exchange. This is sent in response to a R1bis message, after exchange. This is sent in response to a R1bis message, after
checking that the R1bis message refers to an existing context, etc. checking that the R1bis message refers to an existing context, etc.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 59 | Hdr Ext Len |0| Type = 6 | Reserved1 |0| | 59 | Hdr Ext Len |0| Type = 6 | Reserved1 |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 36, line 44 skipping to change at page 36, line 44
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure: Included when the locator list is
included so the receiver can verify the locator list. included so the receiver can verify the locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for verification. CGA (and not HBA) for verification.
5.10 Update Request Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.10. Update Request Message Format
The Update Request Message is used to update either the list of The Update Request Message is used to update either the list of
locators, the locator preferences, and both. When the list of locators, the locator preferences, and both. When the list of
locators is updated, the message also contains the option(s) locators is updated, the message also contains the option(s)
necessary for HBA/CGA to secure this. The basic sanity check that necessary for HBA/CGA to secure this. The basic sanity check that
prevents off-path attackers from generating bogus updates is the prevents off-path attackers from generating bogus updates is the
context tag in the message. context tag in the message.
The update message contains options (the Locator List and the Locator The update message contains options (the Locator List and the Locator
Preferences) that, when included, completely replace the previous Preferences) that, when included, completely replace the previous
skipping to change at page 38, line 20 skipping to change at page 38, line 20
equal preference. equal preference.
CGA Parameter Data Structure (PDS): Included when the locator list is CGA Parameter Data Structure (PDS): Included when the locator list is
included and the PDS was not included in the included and the PDS was not included in the
I2/I2bis/R2 messages, so the receiver can verify the I2/I2bis/R2 messages, so the receiver can verify the
locator list. locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for verification. CGA (and not HBA) for verification.
5.11 Update Acknowledgement Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.11. Update Acknowledgement Message Format
This message is sent in response to a Update Request message. It This message is sent in response to a Update Request message. It
implies that the Update Request has been received, and that any new implies that the Update Request has been received, and that any new
locators in the Update Request can now be used as the source locators locators in the Update Request can now be used as the source locators
of packets. But it does not imply that the (new) locators have been of packets. But it does not imply that the (new) locators have been
verified to be used as a destination, since the host might defer the verified to be used as a destination, since the host might defer the
verification of a locator until it sees a need to use a locator as verification of a locator until it sees a need to use a locator as
the destination. the destination.
0 1 2 3 0 1 2 3
skipping to change at page 39, line 24 skipping to change at page 39, line 26
transmit. MUST be ignored on receipt. transmit. MUST be ignored on receipt.
Receiver Context Tag: 47-bit field. The Context Tag the receiver has Receiver Context Tag: 47-bit field. The Context Tag the receiver has
allocated for the context. allocated for the context.
Request Nonce: 32-bit unsigned integer. Copied from the Update Request Nonce: 32-bit unsigned integer. Copied from the Update
Request message. Request message.
No options are currently defined for this message. No options are currently defined for this message.
5.12 Keepalive Message Format Future protocol extensions might define additional options for this
message. The C-bit in the option format defines how such a new
option will be handled by an implementation. See Section 5.14.
5.12. Keepalive Message Format
This message format is defined in [8]. This message format is defined in [8].
The message is used to ensure that when a peer is sending ULP packets The message is used to ensure that when a peer is sending ULP packets
on a context, it always receives some packets in the reverse on a context, it always receives some packets in the reverse
direction. When the ULP is sending bidirectional traffic, no extra direction. When the ULP is sending bidirectional traffic, no extra
packets need to be inserted. But for a unidirectional ULP traffic packets need to be inserted. But for a unidirectional ULP traffic
pattern, the shim will send back some Keepalive messages when it is pattern, the shim will send back some Keepalive messages when it is
receiving ULP packets. receiving ULP packets.
5.13 Probe Message Format 5.13. Probe Message Format
This message and its semantics are defined in [8]. This message and its semantics are defined in [8].
The idea behind that mechanism is to be able to handle the case when The idea behind that mechanism is to be able to handle the case when
one locator pair works in from A to B, and another locator pair works one locator pair works in from A to B, and another locator pair works
from B to A, but there is no locator pair which works in both from B to A, but there is no locator pair which works in both
directions. The protocol mechanism is that as A is sending probe directions. The protocol mechanism is that as A is sending probe
messages to B, B will observe which locator pairs it has received messages to B, B will observe which locator pairs it has received
from and report that back in probe messages it is sending to A. from and report that back in probe messages it is sending to A.
5.14 Option Formats 5.14. 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 [25]. However, there is no intention to track any changes to format [25]. 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
skipping to change at page 41, line 31 skipping to change at page 41, line 37
| | | | | |
| 10 | Probe Option | | 10 | Probe Option |
| | | | | |
| 11 | Reachability Option | | 11 | Reachability Option |
| | | | | |
| 12 | Payload Reception Report Option | | 12 | Payload Reception Report Option |
+------+---------------------------------+ +------+---------------------------------+
Table 2 Table 2
5.14.1 Responder Validator Option Format Future protocol extensions might define additional options for the
SHIM6 messages. The C-bit in the option format defines how such a
new option will be handled by an implementation.
The responder can choose exactly what input uses to compute the If a host receives an option that it does not understand (an option
that was defined in some future extension to this protocol) or is not
listed as a valid option for the different message types above, then
the Critical bit in the option determines the outcome.
o If C=0 then the option is silently ignored, and the rest of the
message is processed.
o If C=1 then the host SHOULD send back an ICMP parameter problem
(type 4, code 1), with the Pointer referencing the first octet in
the option Type field. When C=1 the message MUST NOT be
processed.
5.14.1. Responder Validator Option Format
The responder can choose exactly what input is used to compute the
validator, and what one-way function (MD5, SHA1) it uses, as long as validator, and what one-way function (MD5, SHA1) it uses, as long as
the responder can check that the validator it receives back in the I2 the responder can check that the validator it receives back in the I2
or I2bis message is indeed one that: or I2bis message is indeed one that:
1)- it computed, 1)- it computed,
2)- it computed for the particular context, and 2)- it computed for the particular context, and
3)- that it isn't a replayed I2/I2bis message. 3)- that it isn't a replayed I2/I2bis message.
Some suggestions on how to generate the validators are captured in Some suggestions on how to generate the validators are captured in
Section 7.9.1 and Section 7.16.1. Section 7.10.1 and Section 7.17.1.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 |0| Length | | Type = 1 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Validator ~ ~ Validator ~
~ +-+-+-+-+-+-+-+-+ ~ +-+-+-+-+-+-+-+-+
~ | Padding | ~ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields: Fields:
Validator: Variable length content whose interpretation is local Validator: Variable length content whose interpretation is local
to the responder. to the responder.
Padding: Padding, 0-7 bytes, added if needed. See Padding: Padding, 0-7 bytes, added if needed. See
Section 5.14. Section 5.14.
5.14.2 Locator List Option Format 5.14.2. Locator List Option Format
The Locator List Option is used to carry all the locators of the The Locator List Option is used to carry all the locators of the
sender. Note that the order of the locators is important, since the sender. Note that the order of the locators is important, since the
Locator Preferences refers to the locators by using the index in the Locator Preferences refers to the locators by using the index in the
list. list.
Note that we carry all the locators in this option even though some Note that we carry all the locators in this option even though some
of them can be created automatically from the CGA Parameter Data of them can be created automatically from the CGA Parameter Data
Structure. Structure.
skipping to change at page 43, line 43 skipping to change at page 44, line 19
| | | | | |
| 1 | HBA | | 1 | HBA |
| | | | | |
| 2 | CGA | | 2 | CGA |
| | | | | |
| 3-255 | Reserved | | 3-255 | Reserved |
+-------+----------+ +-------+----------+
Table 3 Table 3
5.14.3 Locator Preferences Option Format 5.14.3. Locator Preferences Option Format
The Locator Preferences option can have some flags to indicate The Locator Preferences option can have some flags to indicate
whether or not a locator is known to work. In addition, the sender whether or not a locator is known to work. In addition, the sender
can include a notion of preferences. It might make sense to define can include a notion of preferences. It might make sense to define
"preferences" as a combination of priority and weight the same way "preferences" as a combination of priority and weight the same way
that DNS SRV records has such information. The priority would that DNS SRV records has such information. The priority would
provide a way to rank the locators, and within a given priority, the provide a way to rank the locators, and within a given priority, the
weight would provide a way to do some load sharing. See [9] for how weight would provide a way to do some load sharing. See [9] for how
SRV defines the interaction of priority and weight. SRV defines the interaction of priority and weight.
skipping to change at page 45, line 35 skipping to change at page 46, line 16
1 octet flags field followed by a 1 octet priority field, and a 1 1 octet flags field followed by a 1 octet priority field, and a 1
octet weight field. The weight has the same semantics as the weight octet weight field. The weight has the same semantics as the weight
in DNS SRV records. in DNS SRV records.
This document doesn't specify the format when the Element length is This document doesn't specify the format when the Element length is
more than three, except that any such formats MUST be defined so that more than three, except that any such formats MUST be defined so that
the first three octets are the same as in the above case, that is, a the first three octets are the same as in the above case, that is, a
of a 1 octet flags field followed by a 1 octet priority field, and a of a 1 octet flags field followed by a 1 octet priority field, and a
1 octet weight field. 1 octet weight field.
5.14.4 CGA Parameter Data Structure Option Format 5.14.4. CGA Parameter Data Structure Option Format
This option contains the CGA Parameter Data Structure (PDS). When This option contains the CGA Parameter Data Structure (PDS). When
HBA is used to verify the locators, the PDS contains the HBA HBA is used to verify the locators, the PDS contains the HBA
multiprefix extension. When CGA is used to verify the locators, in multiprefix extension. When CGA is used to verify the locators, in
addition to the PDS option, the host also needs to include the addition to the PDS option, the host also needs to include the
signature in the form of a CGA Signature option. signature in the form of a CGA Signature option.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 46, line 4 skipping to change at page 46, line 33
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 4 |0| Length | | Type = 4 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ CGA Parameter Data Structure ~ ~ CGA Parameter Data Structure ~
~ +-+-+-+-+-+-+-+-+ ~ +-+-+-+-+-+-+-+-+
~ | Padding | ~ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields: Fields:
CGA Parameter Data Structure: Variable length content. Content CGA Parameter Data Structure: Variable length content. Content
defined in [6] and [7]. defined in [6] and [7].
Padding: Padding, 0-7 bytes, added if needed. See Padding: Padding, 0-7 bytes, added if needed. See
Section 5.14. Section 5.14.
5.14.5 CGA Signature Option Format 5.14.5. CGA Signature Option Format
When CGA is used for verification of one or more of the locators in When CGA is used for verification of one or more of the locators in
the Locator List option, then the message in question will need to the Locator List option, then the message in question will need to
contain this option. contain this option.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 5 |0| Length | | Type = 5 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 47, line 8 skipping to change at page 47, line 38
3. The subset of locators included in the 3. The subset of locators included in the
correspondent Locator List Option which correspondent Locator List Option which
verification method is set to CGA. The locators verification method is set to CGA. The locators
MUST be included in the order they are listed in MUST be included in the order they are listed in
the Locator List Option. the Locator List Option.
Padding: Padding, 0-7 bytes, added if needed. See Padding: Padding, 0-7 bytes, added if needed. See
Section 5.14. Section 5.14.
5.14.6 ULID Pair Option Format 5.14.6. ULID Pair Option Format
I1, I2, and I2bis messages MUST contain the ULID pair; normally this I1, I2, and I2bis messages MUST contain the ULID pair; normally this
is in the IPv6 source and destination fields. In case that the ULID is in the IPv6 source and destination fields. In case that the ULID
for the context differ from the address pair included in the source for the context differ from the address pair included in the source
and destination address fields of the IPv6 packet used to carry the and destination address fields of the IPv6 packet used to carry the
I1/I2/I2bis message, the ULID pair option MUST be included in the I1/ I1/I2/I2bis message, the ULID pair option MUST be included in the I1/
I2/I2bis message. I2/I2bis message.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 48, line 5 skipping to change at page 48, line 32
Reserved2: 32-bit field. Reserved for future use. Zero on Reserved2: 32-bit field. Reserved for future use. Zero on
transmit. MUST be ignored on receipt. (Needed to transmit. MUST be ignored on receipt. (Needed to
make the ULIDs start on a multiple of 8 octet make the ULIDs start on a multiple of 8 octet
boundary.) boundary.)
Sender ULID: A 128-bit IPv6 address. Sender ULID: A 128-bit IPv6 address.
Receiver ULID: A 128-bit IPv6 address. Receiver ULID: A 128-bit IPv6 address.
5.14.7 Forked Instance Identifier Option Format 5.14.7. Forked Instance Identifier Option Format
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 7 |0| Length = 4 | | Type = 7 |0| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forked Instance Identifier | | Forked Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields: Fields:
Forked Instance Identifier: 32-bit field containing the identifier of Forked Instance Identifier: 32-bit field containing the identifier of
the particular forked instance. the particular forked instance.
5.14.8 Probe Option Format 5.14.8. Probe Option Format
This option is defined in [8]. This option is defined in [8].
5.14.9 Reachability Option Format 5.14.9. Reachability Option Format
This option is defined in [8]. This option is defined in [8].
5.14.10 Payload Reception Report Option Format 5.14.10. Payload Reception Report Option Format
This option is defined in [8]. This option is defined in [8].
6. Conceptual Model of a Host 6. Conceptual Model of a Host
This section describes a conceptual model of one possible data This section describes a conceptual model of one possible data
structure organization that hosts will maintain for the purposes of structure organization that hosts will maintain for the purposes of
shim6. The described organization is provided to facilitate the shim6. The described organization is provided to facilitate the
explanation of how the shim6 protocol should behave. This document explanation of how the shim6 protocol should behave. This document
does not mandate that implementations adhere to this model as long as does not mandate that implementations adhere to this model as long as
their external behavior is consistent with that described in this their external behavior is consistent with that described in this
document. document.
6.1 Conceptual Data Structures 6.1. Conceptual Data Structures
The key conceptual data structure for the shim6 protocol is the ULID The key conceptual data structure for the shim6 protocol is the ULID
pair context. This is a data structure which contains the following pair context. This is a data structure which contains the following
information: information:
o The state of the context. See Section 6.2. o The state of the context. See Section 6.2.
o The peer ULID; ULID(peer) o The peer ULID; ULID(peer)
o The local ULID; ULID(local) o The local ULID; ULID(local)
skipping to change at page 50, line 19 skipping to change at page 51, line 19
o Depending how an implementation determines whether a context is o Depending how an implementation determines whether a context is
still in use, there might be a need to track the last time a still in use, there might be a need to track the last time a
packet was sent/received using the context. packet was sent/received using the context.
o Reachability state for the locator pairs as specified in [8]. o Reachability state for the locator pairs as specified in [8].
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 [8]. have been sent and received as specified in [8].
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 |
skipping to change at page 50, line 41 skipping to change at page 51, line 41
| 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 payload type unknown (type 4, code 1) | | NO-SUPPORT | ICMP Unrecognized Next Header type |
| | received indicating that shim6 is not | | | (type 4, code 1) received indicating |
| | 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), |
skipping to change at page 52, line 17 skipping to change at page 53, line 17
ULID-pair contexts are established using a 4-way exchange, which ULID-pair contexts are established using a 4-way exchange, which
allows the responder to avoid creating state on the first packet. As allows the responder to avoid creating state on the first packet. As
part of this exchange each end allocates a context tag, and it shares part of this exchange each end allocates a context tag, and it shares
this context tag and its set of locators with the peer. this context tag and its set of locators with the peer.
In some cases the 4-way exchange is not necessary, for instance when In some cases the 4-way exchange is not necessary, for instance when
both ends try to setup the context at the same time, or when both ends try to setup the context at the same time, or when
recovering from a context that has been garbage collected or lost at recovering from a context that has been garbage collected or lost at
one of the hosts. one of the hosts.
7.1 Uniqness of Context Tags 7.1. Uniqueness of Context Tags
As part of establishing a new context, each host has to assign a As part of establishing a new context, each host has to assign a
unique context tag. Since the Payload Extension headers are unique context tag. Since the Payload Extension headers are
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.
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 2^47 context tag values,(e.g. SHOULD randomly cycle through the 2^47 context tag values,(e.g.
following the guidelines described in [17]). following the guidelines described in [17]).
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
which "owns" the ULID is also the one that is claiming the locator which "owns" the ULID is also the one that is claiming the locator
"ownership". The shim6 protocol uses the HBA or CGA techniques for "ownership". The shim6 protocol uses the HBA or CGA techniques for
doing this verification. The other is to verify that the host is doing this verification. The other is to verify that the host is
indeed reachable at the claimed locator. Such verification is needed indeed reachable at the claimed locator. Such verification is needed
skipping to change at page 53, line 22 skipping to change at page 54, line 22
If the verification method in the Locator List option is not If the verification method in the Locator List option is not
supported by the host, or if the verification method is not supported by the host, or if the verification method is not
consistent with the CGA Parameter Data Structure (e.g., the Parameter consistent with the CGA Parameter Data Structure (e.g., the Parameter
Data Structure doesn't contain the multiprefix extension, and the Data Structure doesn't contain the multiprefix extension, and the
verification method says to use HBA), then the host MUST ignore the verification method says to use HBA), then the host MUST ignore the
Locator List and the message in which it is contained, and the host Locator List and the message in which it is contained, and the host
SHOULD generates an ICMP parameter problem (type 4, code 0), with the SHOULD generates an ICMP parameter problem (type 4, code 0), with the
Pointer referencing the octet in the Verification method that was Pointer referencing the octet in the Verification method that was
found inconsistent. found inconsistent.
7.3 Normal context establishment 7.3. Normal context establishment
The normal context establishment consists of a 4 message exchange in The normal context establishment consists of a 4 message exchange in
the order of I1, R1, I2, R2 as can be seen in Figure 24. the order of I1, R1, I2, R2 as can be seen in Figure 24.
Initiator Responder Initiator Responder
IDLE IDLE IDLE IDLE
------------- I1 --------------> ------------- I1 -------------->
I1-SENT I1-SENT
<------------ R1 --------------- <------------ R1 ---------------
IDLE IDLE
------------- I2 --------------> ------------- I2 -------------->
I2-SENT I2-SENT
<------------ R2 --------------- <------------ R2 ---------------
ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED
Figure 24: Normal context establishment Figure 24: Normal context establishment
7.4 Concurrent context establishment 7.4. Concurrent context establishment
When both ends try to initiate a context for the same ULID pair, then When both ends try to initiate a context for the same ULID pair, then
we might end up with crossing I1 messages. Alternatively, since no we might end up with crossing I1 messages. Alternatively, since no
state is created when receiving the I1, a host might send a I1 after state is created when receiving the I1, a host might send a I1 after
having sent a R1 message. having sent a R1 message.
Since a host remembers that it has sent an I1, it can respond to an Since a host remembers that it has sent an I1, it can respond to an
I1 from the peer (for the same ULID-pair), with a R2, resulting in I1 from the peer (for the same ULID-pair), with a R2, resulting in
the message exchange shown in Figure 25. Such behavior is needed for the message exchange shown in Figure 25. Such behavior is needed for
other reasons such as to correctly respond to retransmitted I1 other reasons such as to correctly respond to retransmitted I1
skipping to change at page 55, line 44 skipping to change at page 56, line 44
---\ /--- ---\ /---
--- R2 ---\ /--- --- R2 ---\ /---
---\ ---\
/--- R2 ---/ ---\ /--- R2 ---/ ---\
/--- --> /--- -->
<--- ESTABLISHED <--- ESTABLISHED
ESTABLISHED ESTABLISHED
Figure 26: Crossing I2 and I1 Figure 26: Crossing I2 and I1
7.5 Context recovery 7.5. Context recovery
Due to garbage collection, we can end up with one end having and Due to garbage collection, we can end up with one end having and
using the context state, and the other end not having any state. We using the context state, and the other end not having any state. We
need to be able to recover this state at the end that has lost it, need to be able to recover this state at the end that has lost it,
before we can use it. before we can use it.
This need can arise in the following cases: This need can arise in the following cases:
o The communication is working using the ULID pair as the locator o The communication is working using the ULID pair as the locator
pair, but a problem arises, and the end that has retained the pair, but a problem arises, and the end that has retained the
skipping to change at page 57, line 34 skipping to change at page 58, line 34
with new CT(peer) I2-SENT with new CT(peer) I2-SENT
and Ls(peer). and Ls(peer).
ESTABLISHED ESTABLISHED
------------- R2 --------------> ------------- R2 -------------->
ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED
Figure 28: Context loss at sender Figure 28: Context loss at sender
7.6 Context confusion 7.6. Context confusion
Since each end might garbage collect the context state we can have Since each end might garbage collect the context state we can have
the case when one end has retained the context state and tries to use the case when one end has retained the context state and tries to use
it, while the other end has lost the state. We discussed this in the it, while the other end has lost the state. We discussed this in the
previous section on recovery. But for the same reasons, when one previous section on recovery. But for the same reasons, when one
host retains context tag X as CT(peer) for ULID pair <A1, B1>, the host retains context tag X as CT(peer) for ULID pair <A1, B1>, the
other end might end up allocating that context tag as CT(local) for other end might end up allocating that context tag as CT(local) for
another ULID pair, e.g., <A3, B1> between the same hosts. In this another ULID pair, e.g., <A3, B1> between the same hosts. In this
case we can not use the recovery mechanisms since there needs to be case we can not use the recovery mechanisms since there needs to be
separate context tags for the two ULID pairs. separate context tags for the two ULID pairs.
skipping to change at page 58, line 33 skipping to change at page 59, line 33
re-create a context to replace the one that was removed; in this case re-create a context to replace the one that was removed; in this case
for <A1, B1>. The normal I1, R1, I2, R2 establishment exchange would for <A1, B1>. The normal I1, R1, I2, R2 establishment exchange would
then pick unique context tags for that replacement context. This re- then pick unique context tags for that replacement context. This re-
creation is OPTIONAL, but might be useful when there is ULP creation is OPTIONAL, but might be useful when there is ULP
communication which is using the ULID pair whose context was removed. communication which is using the ULID pair whose context was removed.
Note that an I1 message with a duplicate context tag should not cause Note that an I1 message with a duplicate context tag should not cause
the removal of the old context state; this operation needs to be the removal of the old context state; this operation needs to be
deferred until the reception of the I2 message. deferred until the reception of the I2 message.
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
I1 message after I1_TIMEOUT time, then it needs to retransmit the I1 I1 message after I1_TIMEOUT time, then it needs to retransmit the I1
message. The retransmissions should use a retransmission timer with message. The retransmissions should use a retransmission timer with
binary exponential backoff to avoid creating congestion issues for binary exponential backoff to avoid creating congestion issues for
the network when lots of hosts perform I1 retransmissions. Also, the the network when lots of hosts perform I1 retransmissions. Also, the
actual timeout value should be randomized between 0.5 and 1.5 of the actual timeout value should be randomized between 0.5 and 1.5 of the
nominal value to avoid self-synchronization. nominal value to avoid self-synchronization.
If, after I1_RETRIES_MAX retransmissions, there is no response, then If, after I1_RETRIES_MAX retransmissions, there is no response, then
most likely the peer does not implement the shim6 protocol, or there most likely the peer does not implement the shim6 protocol, or there
could be a firewall that blocks the protocol. In this case it makes could be a firewall that blocks the protocol. In this case it makes
sense for the host to remember to not try again to establish a sense for the host to remember to not try again to establish a
context with that ULID. However, any such negative caching should context with that ULID. However, any such negative caching should
retained for at most NO_R1_HOLDDOWN_TIME, to be able to later setup a retained for at most NO_R1_HOLDDOWN_TIME, to be able to later setup a
context should the problem have been that the host was not reachable context should the problem have been that the host was not reachable
at all when the shim tried to establish the context. at all when the shim tried to establish the context.
If the host receives an ICMP error with "payload type unknown" (type If the host receives an ICMP error with "Unrecognized Next Header"
4, code 1) and the included packet is the I1 message it just sent, type (type 4, code 1) and the included packet is the I1 message it
then this is a more reliable indication that the peer ULID does not just sent, then this is a more reliable indication that the peer ULID
implement shim6. Again, in this case, the host should remember to does not implement shim6. Again, in this case, the host should
not try again to establish a context with that ULID. Such negative remember to not try again to establish a context with that ULID.
caching should retained for at most ICMP_HOLDDOWN_TIME, which should Such negative caching should retained for at most ICMP_HOLDDOWN_TIME,
be significantly longer than the previous case. which should be significantly longer than the previous case.
7.9 Receiving I1 messages 7.9. Receiving I1 messages
A host MUST silently discard any received I1 messages that do not A host MUST silently discard any received I1 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 12.2: specified in Section 12.2:
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 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
skipping to change at page 60, line 27 skipping to change at page 61, line 27
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 are in the situation of Concurrent context establishment described in
in Section 7.4. In this case, the host leaves CT(peer) unchanged, Section 7.4. In this case, the host leaves CT(peer) unchanged, and
and replies with a R2 message. This completes the I1 processing, replies with a R2 message. This completes the I1 processing, with
with the context state being unchanged. the context state being unchanged.
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. 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
message or it is global information that is not associated with the
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 7.13). message (see Section 7.14).
7.9.1 Generating the R1 Validator 7.10.1. Generating the R1 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 for the Responder maintain a single secret (S) and a running counter for the Responder
Nonce. Nonce.
In the case the validator is generated to be included in a R1 In the case the validator is generated to be included in a R1
message, for each I1 message. The responder can increase the message, for each I1 message. The responder can increase the
counter, use the counter value as the responder nonce, and use the counter, use the counter value as the responder nonce, and use the
following information as input to the one-way function: following information as input to the one-way function:
skipping to change at page 61, line 22 skipping to change at page 62, line 27
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 and then the output of the hash function is used as the validator
octet string. octet string.
7.10 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 12.2: specified in Section 12.2:
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
skipping to change at page 62, line 18 skipping to change at page 63, line 23
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 also includes the Initiator's locator list and the CGA The I2 message also includes the Initiator's locator list and the CGA
parameter data structure. If CGA (and not HBA) is used to verify the parameter data structure. If CGA (and not HBA) is used to verify the
locator list, then Initiator also signs the key parts of the message locator list, then Initiator also signs the key parts of the message
and includes a CGA signature option containing the signature. and includes 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.
7.11 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. Thus the initiator VALIDATOR_MIN_LIFETIME to avoid replay attacks. Thus the initiator
SHOULD fall back to retransmitting the I1 message when there is no R2 SHOULD fall back to retransmitting the I1 message when there is no R2
received after retransmitting the I2 message I2_RETRIES_MAX times. received after retransmitting the I2 message I2_RETRIES_MAX times.
7.12 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 12.2: specified in Section 12.2:
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
24 octets. 24 octets.
Upon the reception of an I2 message, the host extracts the ULID pair Upon the reception of an I2 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 verifies that the Responder Nonce is a recent one, and Next the host verifies that the Responder Nonce is a recent one
that the Responder Validator option matches the validator the host (Nonces that are no older than VALIDATOR_MIN_LIFETIME SHOULD be
would have computed for the ULID, locators, responder nonce, and FII. considered recent), and that the Responder Validator option matches
the validator the host would have computed for the ULID, locators,
responder nonce, and FII.
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 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
skipping to change at page 63, line 50 skipping to change at page 65, line 8
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 the I2 message and included in the Locator List contained in the the I2 message and
the HBA/CGA verification for this specific locator is successful the 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 7.13. 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.
7.13 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 7.14. 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
using its locators and its context tag, copies the Initiator Nonce using its locators and its context tag, copies the Initiator Nonce
from the triggering message (I2, I2bis, or I1), and includes the from the triggering message (I2, I2bis, or I1), and includes the
necessary options so that the peer can verify the locators. In necessary options so that the peer can verify the locators. In
particular, the R2 message includes the Responder's locator list and particular, the R2 message includes the Responder's locator list and
the PDS option. If CGA (and not HBA) is used to verify the locator the PDS option. If CGA (and not HBA) is used to verify the locator
list, then the Responder also signs the key parts of the message and list, then the Responder also signs the key parts of the message and
includes a CGA Signature option containing the signature. includes a CGA Signature option containing the signature.
R2 messages are never retransmitted. If the R2 message is lost, then R2 messages are never retransmitted. If the R2 message is lost, then
the initiator will retransmit either the I2/I2bis or I1 message. the initiator will retransmit either the I2/I2bis or I1 message.
Either retransmission will cause the responder to find the context Either retransmission will cause the responder to find the context
state and respond with an R2 message. state and respond with an R2 message.
7.14 Match for Context Confusion 7.15. Match for Context Confusion
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:
skipping to change at page 65, line 18 skipping to change at page 66, line 23
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.
7.15 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 12.2: specified in Section 12.2:
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
skipping to change at page 65, line 47 skipping to change at page 67, line 4
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 7.14. Section 7.15.
7.16 Sending R1bis messages 7.17. Sending R1bis messages
Upon the receipt of a shim6 payload extension header where there is Upon the receipt of a shim6 payload extension header where there is
no current SHIM6 context at the receiver, the receiver is to respond no current SHIM6 context at the receiver, the receiver is to respond
with an R1bis message in order to enable a fast re-establishment of with an R1bis message in order to enable a fast re-establishment of
the lost SHIM6 context. the lost SHIM6 context.
Also a host is to respond with a R1bis upon receipt of any control Also a host is to respond with a R1bis upon receipt of any control
messages that has a message type in the range 64-127 (i.e., excluding messages that has a message type in the range 64-127 (i.e., excluding
the context setup messages such as I1, R1, R1bis, I2, I2bis, R2 and the context setup messages such as I1, R1, R1bis, I2, I2bis, R2 and
future extensions), where the control message refers to a non future extensions), where the control message refers to a non
skipping to change at page 66, line 40 skipping to change at page 67, line 45
o The Responder Nonce is a number picked by the responder which the o The Responder Nonce is a number picked by the responder which the
initiator will return in the I2bis message. initiator will return in the I2bis message.
o Packet Context Tag is the context tag contained in the received o Packet Context Tag is the context tag contained in the received
packet that triggered the generation of the R1bis message. packet that triggered the generation of the R1bis message.
o The Responder Validator option is included, with a validator that o The Responder Validator option is included, with a validator that
is computed as suggested in the next section. is computed as suggested in the next section.
7.16.1 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 for the Responder maintain a single secret (S) and a running counter for the Responder
Nonce. Nonce.
In the case the validator is generated to be included in a R1bis In the case the validator is generated to be included in a R1bis
message, for each received payload extension header or control message, for each received payload extension header or control
message, the responder can increase the counter, use the counter message, the responder can increase the counter, use the counter
value as the responder nonce, and use the following information as value as the responder nonce, and use the following information as
input to the one-way function: input to the one-way function:
skipping to change at page 67, line 16 skipping to change at page 68, line 19
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 and then the output of the hash function is used as the validator
octet string. octet string.
7.17 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 12.2: specified in Section 12.2:
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
skipping to change at page 68, line 5 skipping to change at page 69, line 7
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. value for this context MUST be included in the I2bis message.
7.18 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. Thus the initiator VALIDATOR_MIN_LIFETIME to avoid replay attacks. Thus the initiator
SHOULD fall back to retransmitting the I1 message when there is no R2 SHOULD fall back to retransmitting the I1 message when there is no R2
received after retransmitting the I2bis message I2bis_RETRIES_MAX received after retransmitting the I2bis message I2bis_RETRIES_MAX
times. times.
7.19 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 12.2: specified in Section 12.2:
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
32 octets. 32 octets.
Upon the reception of an I2bis message, the host extracts the ULID Upon the reception of an I2bis message, the host extracts the ULID
pair and the Forked Instance identifier from the message. If there pair and the Forked Instance identifier from the message. If there
is no ULID-pair option, then the ULID pair is taken from the source is no 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 and destination fields in the IPv6 header. If there is no FII option
in the message, then the FII value is taken to be zero. in the message, then the FII value is taken to be zero.
Next the host verifies that the Responder Nonce is a recent one, and Next the host verifies that the Responder Nonce is a recent one
that the Responder Validator option matches the validator the host (Nonces that are no older than VALIDATOR_MIN_LIFETIME SHOULD be
would have computed for the ULID, locators, responder nonce, and FII considered recent), and that the Responder Validator option matches
as part of sending an R1bis message. the validator the host would have computed for the ULID, locators,
responder nonce, and FII as part of sending an R1bis 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 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
skipping to change at page 69, line 10 skipping to change at page 70, line 14
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 7.13. 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 the I2 message and the HBA/CGA verification List contained in the the I2 message and the HBA/CGA verification
for this specific locator is successful for 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
skipping to change at page 69, line 39 skipping to change at page 70, line 43
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 the I2 message and included in the Locator List contained in the the I2 message and
the HBA/CGA verification for this specific locator is successful the HBA/CGA verification for 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 in Section 7.13. 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.
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 host unreachable, packet too
big, and payload type unknown. It is critical that these packets big, and Unrecognized Next Header type. It is critical that these
make it back up to the ULPs so that they can take appropriate action. packets make it back up to the ULPs so that they can take appropriate
action.
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.
+--------------+ +--------------+
| IPv6 Header | | IPv6 Header |
| | | |
+--------------+ +--------------+
skipping to change at page 72, line 33 skipping to change at page 73, line 33
Since there is no explicit, coordinated removal of the context state, Since there is no explicit, coordinated removal of the context state,
there are potential issues around context tag reuse. One end might there are potential issues around context tag reuse. One end might
remove the state, and potentially reuse that context tag for some remove the state, and potentially reuse that context tag for some
other communication, and the peer might later try to use the old other communication, and the peer might later try to use the old
context (which it didn't remove). The protocol has mechanisms to context (which it didn't remove). The protocol has mechanisms to
recover from this, which work whether the state removal was total and recover from this, which work whether the state removal was total and
accidental (e.g., crash and reboot of the host), or just a garbage accidental (e.g., crash and reboot of the host), or just a garbage
collection of shim state that didn't seem to be used. However, the collection of shim state that didn't seem to be used. However, the
host should try to minimize the reuse of context tags by trying to host should try to minimize the reuse of context tags by trying to
randomly cycle through the 2^47 context tag values. (See Appendix E randomly cycle through the 2^47 context tag values. (See Appendix C
for a summary how the recovery works in the different cases.) for a summary how the recovery works in the different cases.)
10. Updating the Peer 10. Updating the Peer
The Update Request and Acknowledgement are used both to update the The Update Request and Acknowledgement are used both to update the
list of locators (only possible when CGA is used to verify the list of locators (only possible when CGA is used to verify the
locator(s)), as well as updating the preferences associated with each locator(s)), as well as updating the preferences associated with each
locator. locator.
10.1 Sending Update Request messages 10.1. Sending Update Request messages
When a host has a change in the locator set, then it can communicate When a host has a change in the locator set, then it can communicate
this to the peer by sending an Update Request. When a host has a this to the peer by sending an Update Request. When a host has a
change in the preferences for its locator set, it can also change in the preferences for its locator set, it can also
communicate this to the peer. The Update Request message can include communicate this to the peer. The Update Request message can include
just a Locator List option, to convey the new set of locators (which just a Locator List option, to convey the new set of locators (which
requires a CGA signature option as well), just a Locator Preferences requires a CGA signature option as well), just a Locator Preferences
option, or both a new Locator List and new Locator Preferences. option, or both a new Locator List and new Locator Preferences.
Should the host send a new Locator List, the host picks a new random Should the host send a new Locator List, the host picks a new random
local generation number, records this in the context, and puts it in local generation number, records this in the context, and puts it in
the Locator List option. Any Locator Preference option, whether send the Locator List option. Any Locator Preference option, whether send
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.
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
network when lots of hosts perform Update Request retransmissions. network when lots of hosts perform Update Request retransmissions.
Also, the actual timeout value should be randomized between 0.5 and Also, the actual timeout value should be randomized between 0.5 and
1.5 of the nominal value to avoid self-synchronization. 1.5 of the nominal value to avoid self-synchronization.
Should there be no response, the retransmissions continue forever. Should there be no response, the retransmissions continue forever.
The binary exponential backoff stops at MAX_UPDATE_TIMEOUT. But the The binary exponential backoff stops at MAX_UPDATE_TIMEOUT. But the
only way the retransmissions would stop when there is no only way the retransmissions would stop when there is no
acknowledgement, is when the shim, through the Probe protocol or some acknowledgement, is when the shim, through the Probe protocol or some
other mechanism, decides to discard the context state due to lack of other mechanism, decides to discard the context state due to lack of
ULP usage in combination with no responses to the Probes. ULP usage in combination with no responses to the Probes.
10.3 Newer Information While Retransmitting 10.3. Newer Information While Retransmitting
There can be at most one outstanding Update Request message at any There can be at most one outstanding Update Request message at any
time. Thus until e.g. an update with a new Locator List has been time. Thus until e.g. an update with a new Locator List has been
acknowledged, any even newer Locator List or new Locator Preferences acknowledged, any even newer Locator List or new Locator Preferences
can not just be sent. However, when there is newer information and can not just be sent. However, when there is newer information and
the older information has not yet been acknowledged, the host can the older information has not yet been acknowledged, the host can
instead of waiting for an acknowledgement, abandon the previous instead of waiting for an acknowledgement, abandon the previous
update and construct a new Update Request (with a new Request Nonce) update and construct a new Update Request (with a new Request Nonce)
which includes the new information as well as the information that which includes the new information as well as the information that
hadn't yet been acknowledged. hadn't yet been acknowledged.
skipping to change at page 74, line 37 skipping to change at page 75, line 37
o Form a Locator Preference option which uses the new generation o Form a Locator Preference option which uses the new generation
number and has the BROKEN flag for the first locator. number and has the BROKEN flag for the first locator.
o Send the Update Request and start a retransmission timer. o Send the Update Request and start a retransmission timer.
Any Update Acknowledgement which doesn't match the current request Any Update Acknowledgement which doesn't match the current request
nonce, for instance an acknowledgement for the abandoned Update nonce, for instance an acknowledgement for the abandoned Update
Request, will be silently ignored. Request, will be silently ignored.
10.4 Receiving Update Request messages 10.4. Receiving Update Request messages
A host MUST silently discard any received Update Request messages A host MUST silently discard any received Update Request messages
that do not satisfy all of the following validity checks in addition that do not satisfy all of the following validity checks in addition
to those specified in Section 12.2: to those specified in Section 12.2:
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 Update Request message, the host extracts Upon the reception of an Update Request message, the host extracts
the Context Tag from the message. It then looks for a context which the Context Tag from the message. It then looks for a context which
has a CT(local) that matches the context tag. If no such context is has a CT(local) that matches the context tag. If no such context is
found, it sends a R1bis message as specified in Section 7.16. found, it sends a R1bis message 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 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,
skipping to change at page 76, line 13 skipping to change at page 77, line 13
new locator list or locator preferences have been recorded, the host new locator list or locator preferences have been recorded, the host
sends an Update Acknowledgement message, copying the nonce from the sends an Update Acknowledgement message, copying the nonce from the
request, and using the CT(peer) in as the Receiver Context Tag. request, and using the CT(peer) in as the Receiver Context Tag.
Any new locators, or more likely new locator preferences, might Any new locators, or more likely new locator preferences, might
result in the host wanting to select a different locator pair for the result in the host wanting to select a different locator pair for the
context. For instance, if the Locator Preferences lists the current context. For instance, if the Locator Preferences lists the current
Lp(peer) as BROKEN. The host uses the Probe message in [8] to verify Lp(peer) as BROKEN. The host uses the Probe message in [8] to verify
that the new locator is reachable before changing Lp(peer). that the new locator is reachable before changing Lp(peer).
10.5 Receiving Update Acknowledgement messages 10.5. Receiving Update Acknowledgement messages
A host MUST silently discard any received Update Acknowledgement A host MUST silently discard any received Update Acknowledgement
messages that do not satisfy all of the following validity checks in messages that do not satisfy all of the following validity checks in
addition to those specified in Section 12.2: addition to those specified in Section 12.2:
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 Update Acknowledgement message, the host Upon the reception of an Update Acknowledgement message, the host
extracts the Context Tag and the Request Nonce from the message. It extracts the Context Tag and the Request Nonce from the message. It
then looks for a context which has a CT(local) that matches the then looks for a context which has a CT(local) that matches the
context tag. If no such context is found, it sends a R1bis message context tag. If no such context is found, it sends a R1bis message
as specified in Section 7.16. 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:
skipping to change at page 77, line 32 skipping to change at page 78, line 32
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.
There will also be some maintenance activity relating to There will also be some maintenance activity relating to
(un)reachability detection, whether packets are sent with the (un)reachability detection, whether packets are sent with the
original locators or not. The details of this is out of scope for original locators or not. The details of this is out of scope for
this document and is specified in [8]. this document and is specified in [8].
11.1 Sending ULP Payload after a Switch 11.1. Sending ULP Payload after a Switch
When sending packets, if there is a ULID-pair context for the ULID When sending packets, if there is a ULID-pair context for the ULID
pair, and the ULID pair is no longer used as the locator pair, then pair, and the ULID pair is no longer used as the locator pair, then
the sender needs to transform the packet. Apart from replacing the the sender needs to transform the packet. Apart from replacing the
IPv6 source and destination fields with a locator pair, an 8-octet IPv6 source and destination fields with a locator pair, an 8-octet
header is added so that the receiver can find the context and inverse header is added so that the receiver can find the context and inverse
the transformation. the transformation.
If there has been a failure causing a switch, and later the context If there has been a failure causing a switch, and later the context
switches back to sending things using the ULID pair as the locator switches back to sending things using the ULID pair as the locator
skipping to change at page 79, line 14 skipping to change at page 80, line 14
12. Receiving Packets 12. Receiving Packets
As in normal IPv6 receive side packet processing the receiver parses As in normal IPv6 receive side packet processing the receiver parses
the (extension) headers in order. Should it find a shim6 extension the (extension) headers in order. Should it find a shim6 extension
header it will look at the "P" field in that header. If this bit is header it will look at the "P" field in that header. If this bit is
zero, then the packet must be passed to the shim6 payload handling zero, then the packet must be passed to the shim6 payload handling
for rewriting. Otherwise, the packet is passed to the shim6 control for rewriting. Otherwise, the packet is passed to the shim6 control
handling. handling.
12.1 Receiving Payload Extension Headers 12.1. 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 7.16). 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 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.
skipping to change at page 79, line 47 skipping to change at page 80, line 47
header value (which might be some function associated with the IP header value (which might be some function associated with the IP
endpoint sublayer, or a ULP). endpoint sublayer, or a ULP).
If the host is using some heuristic for determining when to perform a If the host is using some heuristic for determining when to perform a
deferred context establishment, then the host might need to do some deferred context establishment, then the host might need to do some
accounting (count the number of packets sent and received) for accounting (count the number of packets sent and received) for
packets that does not have a shim6 extension header and for which packets that does not have a shim6 extension header and for which
there is no context. But the need for this depends on what there is no context. But the need for this depends on what
heuristics the implementation has chosen. heuristics the implementation has chosen.
12.2 Receiving Shim Control messages 12.2. Receiving Shim Control messages
A shim control message has the checksum field verified. The Shim A shim control message has the checksum field verified. The Shim
header length field is also verified against the length of the IPv6 header length field is also verified against the length of the IPv6
packet to make sure that the shim message doesn't claim to end past packet to make sure that the shim message doesn't claim to end past
the end of the IPv6 packet. Finally, it checks that the neither the the end of the IPv6 packet. Finally, it checks that the neither the
IPv6 destination field nor the IPv6 source field is a multicast IPv6 destination field nor the IPv6 source field is a multicast
address. If any of those checks fail, the packet is silently address. If any of those checks fail, the packet is silently
dropped. dropped.
The message is then dispatched based on the shim message type. Each The message is then dispatched based on the shim message type. Each
skipping to change at page 80, line 21 skipping to change at page 81, line 21
unknown to the receiver, then an ICMPv6 Parameter Problem error is unknown to the receiver, then an ICMPv6 Parameter Problem error is
generated and sent back. The pointer field in the Parameter Problem generated and sent back. The pointer field in the Parameter Problem
is set to point at the first octet of the shim message type. The is set to point at the first octet of the shim message type. The
error is rate limited just like other ICMP errors [5]. error is rate limited just like other ICMP errors [5].
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 an ICMPv6 Parameter Problem, with the Pointer then the host MUST send an ICMPv6 Parameter Problem, with the Pointer
field referencing the first octet of the Option Type. field referencing the first octet of the Option Type.
12.3 Context Lookup 12.3. 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
skipping to change at page 83, line 9 skipping to change at page 84, line 9
providing an easy to use connect-by-name() API for TCP and other providing an easy to use connect-by-name() API for TCP and other
connection-oriented transports is easy; providing a similar connection-oriented transports is easy; providing a similar
capability at the API for UDP is hard due to the protocol itself not capability at the API for UDP is hard due to the protocol itself not
providing any "success" feedback. But even the UDP issue is one of providing any "success" feedback. But even the UDP issue is one of
APIs and implementation. APIs and implementation.
14. Protocol constants 14. Protocol constants
The protocol uses the following constants: The protocol uses the following constants:
I1_RETRIES_MAX I1_RETRIES_MAX = 4
I1_TIMEOUT = 4 seconds I1_TIMEOUT = 4 seconds
NO_R1_HOLDDOWN_TIME = 1 min NO_R1_HOLDDOWN_TIME = 1 min
ICMP_HOLDDOWN_TIME = 10 min ICMP_HOLDDOWN_TIME = 10 min
I2_TIMEOUT = 4 seconds I2_TIMEOUT = 4 seconds
I2_RETRIES_MAX = 2 I2_RETRIES_MAX = 2
skipping to change at page 87, line 10 skipping to change at page 88, line 10
"too much" ingress filtering between the attackers new location "too much" ingress filtering between the attackers new location
and the communicating peers. But this doesn't seem to be that and the communicating peers. But this doesn't seem to be that
severe, because once the R1bis causes the context to be re- severe, because once the R1bis causes the context to be re-
established, a new pair of context tags will be used, which will established, a new pair of context tags will be used, which will
not be known to the attacker. If this is still a concern, we not be known to the attacker. If this is still a concern, we
could require a 2-way handshake "did you really loose the state?" could require a 2-way handshake "did you really loose the state?"
in response to the error message. in response to the error message.
o It might be possible for an attacker to try random 47-bit context o It might be possible for an attacker to try random 47-bit context
tags and see if they can cause disruption for communication tags and see if they can cause disruption for communication
between two hosts. If a 47-bit tag, which is the largest that between two hosts. In particular, in the case of payload packets,
fits in an 8-octet extension header, isn't sufficient, one could the effects of such attack would be similar of those of an
use an even larger tag in the shim6 control messages, and use the attacker sending packets with spoofed source address. In the case
low-order 47 bits in the payload extension header. of control packets, it is not enough to find the correct context
tag, but additional information is required (e.g. nonces, proper
source addresses) (see previous bullet for the case of R1bis). If
a 47-bit tag, which is the largest that fits in an 8-octet
extension header, isn't sufficient, one could use an even larger
tag in the shim6 control messages, and use the low-order 47 bits
in the payload extension header.
o When the payload extension header is used, an attacker that can o When the payload extension header is used, an attacker that can
guess the 47-bit random context tag, can inject packets into the guess the 47-bit random context tag, can inject packets into the
context with any source locator. Thus if there is ingress context with any source locator. Thus if there is ingress
filtering between the attacker, this could potentially allow to filtering between the attacker, this could potentially allow to
bypass the ingress filtering. However, in addition to guessing bypass the ingress filtering. However, in addition to guessing
the 47-bit context tag, the attacker also needs to find a context the 47-bit context tag, the attacker also needs to find a context
where, after the receiver's replacement of the locators with the where, after the receiver's replacement of the locators with the
ULIDs, the the ULP checksum is correct. But even this wouldn't be ULIDs, the the ULP checksum is correct. But even this wouldn't be
sufficient with ULPs like TCP, since the TCP port numbers and sufficient with ULPs like TCP, since the TCP port numbers and
sequence numbers must match an existing connection. Thus, even sequence numbers must match an existing connection. Thus, even
though the issues for off-path attackers injecting packets are though the issues for off-path attackers injecting packets are
different than today with ingress filtering, it is still very hard different than today with ingress filtering, it is still very hard
for an off-path attacker to guess. If IPsec is applied then the for an off-path attacker to guess. If IPsec is applied then the
issue goes away completely. issue goes away completely.
o The validator included in the R1 and R1bis packets are generated
as a hash of several input parameters. However, most of the
inputs are actually determined by the sender, and only the secret
value S is unknown to the sender. However, the resulting
protection is deemed to be enough since it would be easier for the
attacker to just obtain a new validator sending a I1 packet than
performing all the computations required to determine the secret
S. However, it is recommended that the host changes the secret S
periodically.
17. IANA Considerations 17. IANA Considerations
IANA is directed to allocate a new IP Protocol Number value for the IANA is directed to allocate a new IP Protocol Number value for the
SHIM6 Protocol. SHIM6 Protocol.
IANA is directed to record a CGA message type for the SHIM6 Protocol IANA is directed to record a CGA message type for the SHIM6 Protocol
in the [CGA] namespace registry with the value 0x4A30 5662 4858 574B in the [CGA] namespace registry with the value 0x4A30 5662 4858 574B
3655 416F 506A 6D48. 3655 416F 506A 6D48.
IANA is directed to establish a SHIM6 Parameter Registry with two IANA is directed to establish a SHIM6 Parameter Registry with two
skipping to change at page 89, line 6 skipping to change at page 90, line 6
| 66 | Keepalive | | 66 | Keepalive |
| | | | | |
| 67 | Probe Message | | 67 | Probe Message |
| | | | | |
| 68-123 | Can be allocated using Standards Action | | 68-123 | Can be allocated using Standards Action |
| | | | | |
| 124-127 | For Experimental use | | 124-127 | For Experimental use |
+------------+-----------------------------------------------------+ +------------+-----------------------------------------------------+
The initial contents of the SHIM6 Options registry are as follows: The initial contents of the SHIM6 Options registry are as follows:
+--------------+----------------------------------+ +-------------+----------------------------------+
| Type | Option Name | | Type | Option Name |
+--------------+----------------------------------+ +-------------+----------------------------------+
| 0 | RESERVED | | 0 | RESERVED |
| | | | | |
| 1 | Responder Validator | | 1 | Responder Validator |
| | | | | |
| 2 | Locator List | | 2 | Locator List |
| | | | | |
| 3 | Locator Preferences | | 3 | Locator Preferences |
| | | | | |
| 4 | CGA Parameter Data Structure | | 4 | CGA Parameter Data Structure |
| | | | | |
skipping to change at page 89, line 36 skipping to change at page 90, line 36
| | | | | |
| 10 | Probe Option | | 10 | Probe Option |
| | | | | |
| 11 | Reachability Option | | 11 | Reachability Option |
| | | | | |
| 12 | Payload Reception Report Option | | 12 | Payload Reception Report Option |
| | | | | |
| 13-16383 | Allocated using Standards action | | 13-16383 | Allocated using Standards action |
| | | | | |
| 16384-32767 | For Experimental use | | 16384-32767 | For Experimental use |
+--------------+----------------------------------+ +-------------+----------------------------------+
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 Geoff
Houston and Shinta Sugimoto on earlier versions of this draft. Huston, Shinta Sugimoto and Pekka Savola on earlier versions of this
draft.
Appendix A. Open Issues
The following known open issues in this protocol specification are:
o NONE.
Appendix B. 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 singly-homed, and cope with a site's ISPs that do ingress
skipping to change at page 94, line 5 skipping to change at page 94, 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 [21]. initial draft on this topic [21].
Appendix C. Change Log Appendix B. Simplified State Machine
The following changes have been made since draft-ietf-shim6-proto-03:
o Editorial clarifications based on comments from Geoff, Shinta,
Jari.
o Added "no IPv6 NATs as an explicit assumption.
o Moving some things out of the Introduction and Overview sections
to remove all SHOULDs and MUSTs from there.
o Added requirement that any Locator Preference options which use an
element length greater than 3 octets have the already defined
first 3 octets of flags, priority and weight.
o Fixed security hole where a single message (I1) could cause
CT(peer) to be updated. Now a three-way handshake is required
before CT(peer) is updated for an existing context.
The following changes have been made since draft-ietf-shim6-proto-02:
o Replaced the Context Error message with the R1bis message.
o Removed the Packet In Error option, since it was only used in the
Context Error message.
o Introduced a I2bis message which is sent in response to an I1bis
message, since the responders processing is quite in this case
than in the regular R1 case.
o Moved the packet formats for the Keepalive and Probe message types
and Event option to [8]. Only the message type values and option
type value are specified for those in this document.
o Removed the unused message types.
o Added a state machine description as an appendix.
o Filled in all the TBDs - except the IANA assignment of the
protocol number.
o Specified how context recovery and forked contexts work together.
This required the introduction of a Forked Instance option to be
able to tell which of possibly forked instances is being
recovered.
o Renamed the "host-pair context" to be "ULID-pair context".
o Picked some initial retransmit timers for I1 and I2; 4 seconds.
o Added timer values as protocol constants. The retransmit timers
use binary exponential backoff and randomization (between .5 and
1.5 of the nominal value).
o Require that the R1/R1bis verifiers be usable for some minimum
time so that the initiator knows for how long time it can safely
retransmit I2 before it needs to go back to sending I1 again.
Picked 30 seconds.
o Split the message type codes into 0-63, which will not generate
R1bis messages, and 64-127 which will generate R1bis messages.
This allows extensibility of the protocol with new message types
while being able to control when R1bis is generated.
o Expanded the context tag from 32 to 47 bits.
o Specified that enough locators need to be included in I2 and R2
messages. Specified that the HBA/CGA verification must be
performed when the locator set is received.
o Specified that ICMP parameter problem errors are sent in certain
error cases, for instance when the verification method is unknown
to the receiver, or there is an unknown message type or option
type.
o Renamed "payload message" to be "payload extension header".
o Many editorial clarifications suggested by Geoff Huston.
o Modified the dispatching of payload extension header to only
compare CT(local) i.e., not compare the source and destination
IPv6 address fields.
The following changes have been made since draft-ietf-shim6-proto-00:
o Removed the use of the flow label and the overloading of the IP
protocol numbers. Instead, when the locator pair is not the ULID
pair, the ULP payloads will be carried with an 8 octet extension
header. The belief is that it is possible to remove these extra
bytes by defining future shim6 extensions that exchange more
information between the hosts, without having to overload the flow
label or the IP protocol numbers.
o Grew the context tag from 20 bits to 32 bits, with the possibility
to grow it to 47 bits. This implies changes to the message
formats.
o Almost by accident, the new shim6 message format is very close to
the HIP message format.
o Adopted the HIP format for the options, since this makes it easier
to describe variable length options. The original, ND-style,
option format requires internal padding in the options to make
them 8 octet length in total, while the HIP format handles that
using the option length field.
o Removed some of the control messages, and renamed the other ones.
o Added a "generation" number to the Locator List option, so that
the peers can ensure that the preferences refer to the right
"version" of the Locator List.
o In order for FBD and exploration to work when there the use of the
context is forked, that is different ULP messages are sent over
different locator pairs, things are a lot easier if there is only
one current locator pair used for each context. Thus the forking
of the context is now causing a new context to be established for
the same ULID; the new context having a new context tag. The
original context is referred to as the "default" context for the
ULID pair.
o Added more background material and textual descriptions.
Appendix D. 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:
+---------------------+---------------------------------------------+ +---------------------+---------------------------------------------+
skipping to change at page 102, line 28 skipping to change at page 100, line 5
+---------------------+---------------------------------------------+ +---------------------+---------------------------------------------+
| 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 D.1 Simplified State Machine diagram Appendix B.1. Simplified State Machine diagram
For the time being, a pdf version of the state machine diagram can be Timeout/Null +------------+
found at: http://www.it.uc3m.es/marcelo/state_machine.pdf I1/R1 +------------------| NO SUPPORT |
Payload or Control/R1bis | +------------+
+---------+ | ^
| | | ICMP Error/Null|
| V V |
+-----------------+ Timeout/Null +----------+ |
| |<---------------| E-FAILED | |
+-| IDLE | +----------+ |
I2 or I2bis/R2 | | | ^ |
| +-----------------+ (Tiemout#>MAX)/Null| |
| ^ | | |
| | +------+ | |
I2 or I2bis/R2 | | Heuristic/I1| I1/R2 | |
Payload/Null | | | Control/Null | |
I1/R1 or R2 | +--+ | Payload/Null | |
R1 or R2/Null | |Heuristic/Null | (Tiemout#<MAX)/I1 | |
+----------+ | | | +--------+ | |
| V V | | | V | |
+-------------------+ R2/Null | +----------------+
| | I2 or I2bis/R2 +------->| |
| ESTABLISHED |<----------------------------| I1-SENT |
| | | |
+-------------------+ +----------------+
| ^ ^ | ^ ^
| | |R2/Null +-------------+ | |
| | +----------+ |R1/I2 | |
| | | V | |
| | +------------------+ | |
| | | |-------------+ |
| | | I2-SENT | (Timeout#>Max)/I1 |
| | | | |
| | +------------------+ |
| | | ^ |
| | +--------------+ |
| | I1 or I2bis or I2 or Payload/R2 |
| | (Timeout#<Max)/I2 |
| | R1 or R1bis/Null |
| +-------+ (Timeout#>Max)/I1 |
| R2/Null| +------------------------------------------+
| V |
| +-------------------+
| | |<-+ (Timeout#<Max)/I2bis
+-------->| I2bis-SENT | | I1 or I2 or I2bis/R2
R1bis/I2bis | |--+ R1 or R1bis/Null
+-------------------+ Payload/R2
Appendix E. Context Tag Reuse Appendix C. Context Tag Reuse
The shim6 protocol doesn't have a mechanism for coordinated state The shim6 protocol doesn't have a mechanism for coordinated state
removal between the peers, because such state removal doesn't seem to removal between the peers, because such state removal doesn't seem to
help given that a host can crash and reboot at any time. A result of help given that a host can crash and reboot at any time. A result of
this is that the protocol needs to be robust against a context tag this is that the protocol needs to be robust against a context tag
being reused for some other context. This section summarizes the being reused for some other context. This section summarizes the
different cases in which a tag can be reused, and how the recovery different cases in which a tag can be reused, and how the recovery
works. works.
The different cases are exemplified by the following case. Assume The different cases are exemplified by the following case. Assume
skipping to change at page 103, line 35 skipping to change at page 101, line 35
<A1, B2>. We've called this "Context Recovery" in this document. <A1, B2>. We've called this "Context Recovery" in this document.
o The context tag is reassigned to a context for a different ULID o The context tag is reassigned to a context for a different ULID
pair between the same to hosts, e.g., <A3, B3>. We've called this pair between the same to hosts, e.g., <A3, B3>. We've called this
"Context Confusion" in this document. "Context Confusion" in this document.
o The context tag is reassigned to a context between B and other o The context tag is reassigned to a context between B and other
host C, for instance for the ULID pair <C3, B2>. That is a form host C, for instance for the ULID pair <C3, B2>. That is a form
of three party context confusion. of three party context confusion.
Appendix E.1 Context Recovery Appendix C.1. Context Recovery
This case is relatively simple, and is discussed in Section 7.5. The This case is relatively simple, and is discussed in Section 7.5. The
observation is that since the ULID pair is the same, when either A or observation is that since the ULID pair is the same, when either A or
B tries to establish the new context, A can keep the old context B tries to establish the new context, A can keep the old context
while B re-creates the context with the same context tag CT(B) = X. while B re-creates the context with the same context tag CT(B) = X.
Appendix E.2 Context Confusion Appendix C.2. Context Confusion
This cases is a bit more complex, and is discussed in Section 7.6. This cases is a bit more complex, and is discussed in Section 7.6.
When the new context is created, whether A or B initiates it, host A When the new context is created, whether A or B initiates it, host A
can detect when it receives B's locator set (in the I2, or R2 can detect when it receives B's locator set (in the I2, or R2
message), that it ends up with two contexts to the same peer host message), that it ends up with two contexts to the same peer host
(overlapping Ls(peer) locator sets) that have the same context tag (overlapping Ls(peer) locator sets) that have the same context tag
CT(peer) = X. At this point in time host A can clear up any CT(peer) = X. At this point in time host A can clear up any
possibility of causing confusion by not using the old context to send possibility of causing confusion by not using the old context to send
any more packets. It either just discards the old context (it might any more packets. It either just discards the old context (it might
not be used by any ULP traffic, since B had discarded it), or it not be used by any ULP traffic, since B had discarded it), or it
recreates a different context for the old ULID pair (<A1, B2>), for recreates a different context for the old ULID pair (<A1, B2>), for
which B will assign a unique CT(B) as part of the normal context which B will assign a unique CT(B) as part of the normal context
establishment mechanism. establishment mechanism.
Appendix E.3 Three Party Context Confusion Appendix C.3. Three Party Context Confusion
The third case does not have a place where the old state on A can be The third case does not have a place where the old state on A can be
verified, since the new context is established between B and C. Thus verified, since the new context is established between B and C. Thus
when B receives payload extension headers with X as the context tag, when B receives payload extension headers with X as the context tag,
it will find the context for <C3, B2>, hence rewrite the packets to it will find the context for <C3, B2>, hence rewrite the packets to
have C3 in the source address field and B2 in the destination address have C3 in the source address field and B2 in the destination address
field before passing them up to the ULP. This rewriting is correct field before passing them up to the ULP. This rewriting is correct
when the packets are in fact sent by host C, but if host A ever when the packets are in fact sent by host C, but if host A ever
happens to send a packet using the old context, then the ULP on A happens to send a packet using the old context, then the ULP on A
sends a packet with ULIDs <A1, B2> and the packet arrives at the ULP sends a packet with ULIDs <A1, B2> and the packet arrives at the ULP
skipping to change at page 105, line 5 skipping to change at page 103, line 5
In summary, there are cases where a context tag might be reused while In summary, there are cases where a context tag might be reused while
some peer retains the state, but the protocol can recover from it. some peer retains the state, but the protocol can recover from it.
The probability of these events is low given the 47 bit context tag The probability of these events is low given the 47 bit context tag
size. However, it is important that these recovery mechanisms be size. However, it is important that these recovery mechanisms be
tested. Thus during development and testing it is recommended that tested. Thus during development and testing it is recommended that
implementations not use the full 47 bit space, but instead keep e.g. implementations not use the full 47 bit space, but instead keep e.g.
the top 40 bits as zero, only leaving the host with 128 unique the top 40 bits as zero, only leaving the host with 128 unique
context tags. This will help test the recovery mechanisms. context tags. This will help test the recovery mechanisms.
Appendix F. Design Alternatives Appendix D. Design Alternatives
This document has picked a certain set of design choices in order to This document has picked a certain set of design choices in order to
try to work out a bunch of the details, and stimulate discussion. try to work out a bunch of the details, and stimulate discussion.
But as has been discussed on the mailing list, there are other But as has been discussed on the mailing list, there are other
choices that make sense. This appendix tries to enumerate some choices that make sense. This appendix tries to enumerate some
alternatives. alternatives.
Appendix F.1 Context granularity Appendix D.1. Context granularity
Over the years various suggestions have been made whether the shim Over the years various suggestions have been made whether the shim
should, even if it operates at the IP layer, be aware of ULP should, even if it operates at the IP layer, be aware of ULP
connections and sessions, and as a result be able to make separate connections and sessions, and as a result be able to make separate
shim contexts for separate ULP connections and sessions. A few shim contexts for separate ULP connections and sessions. A few
different options have been discussed: different options have been discussed:
o Each ULP connection maps to its own shim context. o Each ULP connection maps to its own shim context.
o The shim is unaware of the ULP notion of connections and just o The shim is unaware of the ULP notion of connections and just
skipping to change at page 105, line 45 skipping to change at page 103, line 45
that want different communication to use different locator pairs, for that want different communication to use different locator pairs, for
instance for quality or cost reasons. instance for quality or cost reasons.
The protocol has a shim which operates with host-level granularity The protocol has a shim which operates with host-level granularity
(strictly speaking, with ULID-pair granularity, to be able to (strictly speaking, with ULID-pair granularity, to be able to
amortize the context establishment over multiple ULP connections. amortize the context establishment over multiple ULP connections.
This is combined with the ability for shim-aware ULPs to request This is combined with the ability for shim-aware ULPs to request
context forking so that different ULP traffic can use different context forking so that different ULP traffic can use different
locator pairs. locator pairs.
Appendix F.2 Demultiplexing of data packets in shim6 communications Appendix D.2. Demultiplexing of data packets in shim6 communications
Once a ULID-pair context is established between two hosts, packets Once a ULID-pair context is established between two hosts, packets
may carry locators that differ from the ULIDs presented to the ULPs may carry locators that differ from the ULIDs presented to the ULPs
using the established context. One of main functions of the SHIM6 using the established context. One of main functions of the SHIM6
layer is to perform the mapping between the locators used to forward layer is to perform the mapping between the locators used to forward
packets through the network and the ULIDs presented to the ULP. In packets through the network and the ULIDs presented to the ULP. In
order to perform that translation for incoming packets, the SHIM6 order to perform that translation for incoming packets, the SHIM6
layer needs to first identify which of the incoming packets need to layer needs to first identify which of the incoming packets need to
be translated and then perform the mapping between locators and ULIDs be translated and then perform the mapping between locators and ULIDs
using the associated context. Such operation is called using the associated context. Such operation is called
skipping to change at page 106, line 35 skipping to change at page 104, line 35
packet to determine the shim context to be used to perform the packet to determine the shim context to be used to perform the
operation. operation.
Two mechanisms for carrying the context tag information have been Two mechanisms for carrying the context tag information have been
considered in depth during the shim protocol design. Those carrying considered in depth during the shim protocol design. Those carrying
the context tag in the flow label field of the IPv6 header and the the context tag in the flow label field of the IPv6 header and the
usage of a new extension header to carry the context tag. In this usage of a new extension header to carry the context tag. In this
appendix we will describe the pros and cons of each approach and appendix we will describe the pros and cons of each approach and
justify the selected option. justify the selected option.
Appendix F.2.1 Flow-label Appendix D.2.1. Flow-label
A possible approach is to carry the context tag in the Flow Label A possible approach is to carry the context tag in the Flow Label
field of the IPv6 header. This means that when a shim6 context is field of the IPv6 header. This means that when a shim6 context is
established, a Flow Label value is associated with this context (and established, a Flow Label value is associated with this context (and
perhaps a separate flow label for each direction). perhaps a separate flow label for each direction).
The simplest approach that does this is to have the triple <Flow The simplest approach that does this is to have the triple <Flow
Label, Source Locator, Destination Locator> identify the context at Label, Source Locator, Destination Locator> identify the context at
the receiver. the receiver.
skipping to change at page 108, line 49 skipping to change at page 106, line 49
would be the preferred approach if the context tag is to be carried would be the preferred approach if the context tag is to be carried
in the Flow Label field. This is not only because it imposes the in the Flow Label field. This is not only because it imposes the
minimum constraints to the Flow Label allocation strategies, limiting minimum constraints to the Flow Label allocation strategies, limiting
the restrictions only to those packets that need to be translated by the restrictions only to those packets that need to be translated by
the shim, but also because Context Loss detection mechanisms greatly the shim, but also because Context Loss detection mechanisms greatly
benefit from the fact that shim data packets are identified as such, benefit from the fact that shim data packets are identified as such,
allowing the receiving end to identify if a shim context associated allowing the receiving end to identify if a shim context associated
to a received packet is suppose to exist, as it will be discussed in to a received packet is suppose to exist, as it will be discussed in
the Context Loss detection appendix below. the Context Loss detection appendix below.
Appendix F.2.2 Extension Header Appendix D.2.2. Extension Header
Another approach, which is the one selected for this protocol, is to Another approach, which is the one selected for this protocol, is to
carry the context tag in a new Extension Header. These context tags carry the context tag in a new Extension Header. These context tags
are allocated by the receiving end during the shim6 protocol initial are allocated by the receiving end during the shim6 protocol initial
negotiation, implying that each context will have two context tags, negotiation, implying that each context will have two context tags,
one for each direction. Data packets will be demultiplexed using the one for each direction. Data packets will be demultiplexed using the
context tag carried in the Extension Header. This seems a clean context tag carried in the Extension Header. This seems a clean
approach since it does not overload existing fields. However, it approach since it does not overload existing fields. However, it
introduces additional overhead in the packet due to the additional introduces additional overhead in the packet due to the additional
header. The additional overhead introduced is 8 octets. However, it header. The additional overhead introduced is 8 octets. However, it
skipping to change at page 109, line 25 skipping to change at page 107, line 25
ULIDs do not require a context tag, since no rewriting is necessary ULIDs do not require a context tag, since no rewriting is necessary
at the receiver. This approach would reduce the overhead, because at the receiver. This approach would reduce the overhead, because
the additional header is only required after a failure. On the other the additional header is only required after a failure. On the other
hand, this approach would cause changes in the available MTU for some hand, this approach would cause changes in the available MTU for some
packets, since packets that include the Extension Header will have an packets, since packets that include the Extension Header will have an
MTU 8 octets shorter. However, path changes through the network can MTU 8 octets shorter. However, path changes through the network can
result in different MTU in any case, thus having a locator change, result in different MTU in any case, thus having a locator change,
which implies a path change, affect the MTU doesn't introduce any new which implies a path change, affect the MTU doesn't introduce any new
issues. issues.
Appendix F.3 Context Loss Detection Appendix D.3. Context Loss Detection
In this appendix we will present different approaches considered to In this appendix we will present different approaches considered to
detect context loss and potential context recovery strategies. The detect context loss and potential context recovery strategies. The
scenario being considered is the following: Node A and Node B are scenario being considered is the following: Node A and Node B are
communicating using IPA1 and IPB1. Sometime later, a shim context is communicating using IPA1 and IPB1. Sometime later, a shim context is
established between them, with IPA1 and IPB1 as ULIDs and established between them, with IPA1 and IPB1 as ULIDs and
IPA1,...,IPAn and IPB1,...,IPBm as locator set respectively. IPA1,...,IPAn and IPB1,...,IPBm as locator set respectively.
It may happen, that later on, one of the hosts, e.g. Host A looses It may happen, that later on, one of the hosts, e.g. Host A looses
the shim context. The reason for this can be that Host A has a more the shim context. The reason for this can be that Host A has a more
skipping to change at page 111, line 43 skipping to change at page 109, line 43
exchange and at this point time may be critical since we are exchange and at this point time may be critical since we are
reestablishing a context that is currently needed (because context reestablishing a context that is currently needed (because context
loss detection may occur after a failure). So, another option, which loss detection may occur after a failure). So, another option, which
is the one used in this protocol, is to replace the error message by is the one used in this protocol, is to replace the error message by
a modified R1 message, so that the time required to perform the a modified R1 message, so that the time required to perform the
context establishment exchange can be reduced. Upon the reception of context establishment exchange can be reduced. Upon the reception of
this modified R1 message, the end that still has the context state this modified R1 message, the end that still has the context state
can finish the context establishment exchange and restore the lost can finish the context establishment exchange and restore the lost
context. context.
Appendix F.4 Securing locator sets Appendix D.4. Securing locator sets
The adoption of a protocol like SHIM that allows the binding of a The adoption of a protocol like SHIM that allows the binding of a
given ULID with a set of locators opens the doors for different types given ULID with a set of locators opens the doors for different types
of redirection attacks as described in [19]. The goal in terms of of redirection attacks as described in [19]. The goal in terms of
security for the design of the shim protocol is not to introduce any security for the design of the shim protocol is not to introduce any
new vulnerability in the Internet architecture. It is a non-goal to new vulnerability in the Internet architecture. It is a non-goal to
provide additional protection than the currently available in the provide additional protection than the currently available in the
single-homed IPv6 Internet. single-homed IPv6 Internet.
Multiple security mechanisms were considered to protect the shim Multiple security mechanisms were considered to protect the shim
skipping to change at page 114, line 21 skipping to change at page 112, line 21
So, the design decision adopted was that both mechanisms HBA and CGA So, the design decision adopted was that both mechanisms HBA and CGA
are supported, so that when only stable address sets are required, are supported, so that when only stable address sets are required,
the nodes can benefit from the low computational cost offered by HBA the nodes can benefit from the low computational cost offered by HBA
while when dynamic locator sets are required, this can be achieved while when dynamic locator sets are required, this can be achieved
through CGAs with an additional cost. Moreover, because HBAs are through CGAs with an additional cost. Moreover, because HBAs are
defined as a CGA extension, the addresses available in a node can defined as a CGA extension, the addresses available in a node can
simultaneously be CGAs and HBAs, allowing the usage of the HBA and simultaneously be CGAs and HBAs, allowing the usage of the HBA and
CGA functionality when needed without requiring a change in the CGA functionality when needed without requiring a change in the
addresses used. addresses used.
Appendix F.5 ULID-pair context establishment exchange Appendix D.5. ULID-pair context establishment exchange
Two options were considered for the ULID-pair context establishment Two options were considered for the ULID-pair context establishment
exchange: a 2-way handshake and a 4-way handshake. exchange: a 2-way handshake and a 4-way handshake.
A key goal for the design of this exchange was that protection A key goal for the design of this exchange was that protection
against DoS attacks. The attack under consideration was basically a against DoS attacks. The attack under consideration was basically a
situation where an attacker launches a great amount of ULID-pair situation where an attacker launches a great amount of ULID-pair
establishment request packets, exhausting victim's resources, similar establishment request packets, exhausting victim's resources, similar
to TCP SYN flooding attacks. to TCP SYN flooding attacks.
skipping to change at page 115, line 21 skipping to change at page 113, line 21
should be noted, that because this is 2-way exchange, it is not should be noted, that because this is 2-way exchange, it is not
possible to use the number of half open sessions (as in TCP) to possible to use the number of half open sessions (as in TCP) to
detect an ongoing attack and different heuristics need to be detect an ongoing attack and different heuristics need to be
considered. considered.
The design decision taken was that considering the current impact of The design decision taken was that considering the current impact of
DoS attacks and the low impact of the 4-way exchange in the shim DoS attacks and the low impact of the 4-way exchange in the shim
protocol thanks to the deferred context establishment capability, a protocol thanks to the deferred context establishment capability, a
4-way exchange would be adopted for the base protocol. 4-way exchange would be adopted for the base protocol.
Appendix F.6 Updating locator sets Appendix D.6. Updating locator sets
There are two possible approaches to the addition and removal of There are two possible approaches to the addition and removal of
locators: atomic and differential approaches. The atomic approach locators: atomic and differential approaches. The atomic approach
essentially send the complete locators set each time that a variation essentially send the complete locators set each time that a variation
in the locator set occurs. The differential approach send the in the locator set occurs. The differential approach send the
differences between the existing locator set and the new one. The differences between the existing locator set and the new one. The
atomic approach imposes additional overhead, since all the locator atomic approach imposes additional overhead, since all the locator
set has to be exchanged each time while the differential approach set has to be exchanged each time while the differential approach
requires re-synchronization of both ends through changes i.e. that requires re-synchronization of both ends through changes i.e. that
both ends have the same idea about what the current locator set is. both ends have the same idea about what the current locator set is.
Because of the difficulties imposed by the synchronization Because of the difficulties imposed by the synchronization
requirement, the atomic approach was selected. requirement, the atomic approach was selected.
Appendix F.7 State Cleanup Appendix D.7. State Cleanup
There are essentially two approaches for discarding an existing state There are essentially two approaches for discarding an existing state
about locators, keys and identifiers of a correspondent node: a about locators, keys and identifiers of a correspondent node: a
coordinated approach and an unilateral approach. coordinated approach and an unilateral approach.
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,
skipping to change at page 118, line 5 skipping to change at page 116, line 5
coordinated approach using a CLOSE/CLOSE ACK exchange, there is still coordinated approach using a CLOSE/CLOSE ACK exchange, there is still
the possibility of a host rebooting without having the time to the possibility of a host rebooting without having the time to
perform the CLOSE exchange. So, it is true that the coordinated perform the CLOSE exchange. So, it is true that the coordinated
approach eliminates the possibility of a context confusion situation approach eliminates the possibility of a context confusion situation
because premature garbage collection, but it does not prevents the because premature garbage collection, but it does not prevents 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
[RFC Editor: please remove this section]
The following changes have been made since draft-ietf-shim6-proto-04:
o Defined I1_RETRIES_MAX as 4.
o Added text in section 7.9 clarifying the no per context state is
stored at the receiver in order to reply an I1 message.
o Added text in section 5 and in section 5.14 in particular, on
defining additional options (including critical and non critical
options).
o Added text in the security considerations about threats related to
secret S for generating the validators and recommendation to
change S periodically.
o Added text in the security considerations about the effects of
attacks based on guessing the context tag being similar to
spoofing source addresses in the case of payload packets.
o Added clarification on what a recent nonce is in I2 and I2bis.
o Removed (empty) open issues section.
o Editorial corrections.
The following changes have been made since draft-ietf-shim6-proto-03:
o Editorial clarifications based on comments from Geoff, Shinta,
Jari.
o Added "no IPv6 NATs as an explicit assumption.
o Moving some things out of the Introduction and Overview sections
to remove all SHOULDs and MUSTs from there.
o Added requirement that any Locator Preference options which use an
element length greater than 3 octets have the already defined
first 3 octets of flags, priority and weight.
o Fixed security hole where a single message (I1) could cause
CT(peer) to be updated. Now a three-way handshake is required
before CT(peer) is updated for an existing context.
The following changes have been made since draft-ietf-shim6-proto-02:
o Replaced the Context Error message with the R1bis message.
o Removed the Packet In Error option, since it was only used in the
Context Error message.
o Introduced a I2bis message which is sent in response to an I1bis
message, since the responders processing is quite in this case
than in the regular R1 case.
o Moved the packet formats for the Keepalive and Probe message types
and Event option to [8]. Only the message type values and option
type value are specified for those in this document.
o Removed the unused message types.
o Added a state machine description as an appendix.
o Filled in all the TBDs - except the IANA assignment of the
protocol number.
o Specified how context recovery and forked contexts work together.
This required the introduction of a Forked Instance option to be
able to tell which of possibly forked instances is being
recovered.
o Renamed the "host-pair context" to be "ULID-pair context".
o Picked some initial retransmit timers for I1 and I2; 4 seconds.
o Added timer values as protocol constants. The retransmit timers
use binary exponential backoff and randomization (between .5 and
1.5 of the nominal value).
o Require that the R1/R1bis verifiers be usable for some minimum
time so that the initiator knows for how long time it can safely
retransmit I2 before it needs to go back to sending I1 again.
Picked 30 seconds.
o Split the message type codes into 0-63, which will not generate
R1bis messages, and 64-127 which will generate R1bis messages.
This allows extensibility of the protocol with new message types
while being able to control when R1bis is generated.
o Expanded the context tag from 32 to 47 bits.
o Specified that enough locators need to be included in I2 and R2
messages. Specified that the HBA/CGA verification must be
performed when the locator set is received.
o Specified that ICMP parameter problem errors are sent in certain
error cases, for instance when the verification method is unknown
to the receiver, or there is an unknown message type or option
type.
o Renamed "payload message" to be "payload extension header".
o Many editorial clarifications suggested by Geoff Huston.
o Modified the dispatching of payload extension header to only
compare CT(local) i.e., not compare the source and destination
IPv6 address fields.
The following changes have been made since draft-ietf-shim6-proto-00:
o Removed the use of the flow label and the overloading of the IP
protocol numbers. Instead, when the locator pair is not the ULID
pair, the ULP payloads will be carried with an 8 octet extension
header. The belief is that it is possible to remove these extra
bytes by defining future shim6 extensions that exchange more
information between the hosts, without having to overload the flow
label or the IP protocol numbers.
o Grew the context tag from 20 bits to 32 bits, with the possibility
to grow it to 47 bits. This implies changes to the message
formats.
o Almost by accident, the new shim6 message format is very close to
the HIP message format.
o Adopted the HIP format for the options, since this makes it easier
to describe variable length options. The original, ND-style,
option format requires internal padding in the options to make
them 8 octet length in total, while the HIP format handles that
using the option length field.
o Removed some of the control messages, and renamed the other ones.
o Added a "generation" number to the Locator List option, so that
the peers can ensure that the preferences refer to the right
"version" of the Locator List.
o In order for FBD and exploration to work when there the use of the
context is forked, that is different ULP messages are sent over
different locator pairs, things are a lot easier if there is only
one current locator pair used for each context. Thus the forking
of the context is now causing a new context to be established for
the same ULID; the new context having a new context tag. The
original context is referred to as the "default" context for the
ULID pair.
o Added more background material and textual descriptions.
19. References 19. References
19.1 Normative References 19.1. Normative References
[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] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery [3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998. for IP Version 6 (IPv6)", RFC 2461, December 1998.
skipping to change at page 118, line 36 skipping to change at page 120, line 36
RFC 3972, March 2005. RFC 3972, March 2005.
[7] Bagnulo, M., "Hash Based Addresses (HBA)", [7] Bagnulo, M., "Hash Based Addresses (HBA)",
draft-ietf-shim6-hba-01 (work in progress), October 2005. draft-ietf-shim6-hba-01 (work in progress), October 2005.
[8] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair [8] 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-03 (work in progress), draft-ietf-shim6-failure-detection-03 (work in progress),
December 2005. December 2005.
19.2 Informative References 19.2. Informative References
[9] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [9] 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.
[10] Ferguson, P. and D. Senie, "Network Ingress Filtering: [10] 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.
[11] Narten, T. and R. Draves, "Privacy Extensions for Stateless [11] Narten, T. and R. Draves, "Privacy Extensions for Stateless
 End of changes. 133 change blocks. 
397 lines changed or deleted 540 lines changed or added

This html diff was produced by rfcdiff 1.31. The latest version is available from http://www.levkowetz.com/ietf/tools/rfcdiff/