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