draft-ietf-shim6-proto-03.txt   draft-ietf-shim6-proto-04.txt 
SHIM6 WG E. Nordmark SHIM6 WG E. Nordmark
Internet-Draft Sun Microsystems Internet-Draft Sun Microsystems
Expires: March 5, 2006 M. Bagnulo Expires: September 5, 2006 M. Bagnulo
UC3M UC3M
September 2005 March 4, 2006
Level 3 multihoming shim protocol Level 3 multihoming shim protocol
draft-ietf-shim6-proto-03.txt draft-ietf-shim6-proto-04.txt
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Copyright Notice Copyright Notice
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Abstract Abstract
The SHIM6 working group is specifying a layer 3 shim approach and The SHIM6 protocol is a layer 3 shim for providing locator agility
protocol for providing locator agility below the transport protocols, below the transport protocols, so that multihoming can be provided
so that multihoming can be provided for IPv6 with failover and load for IPv6 with failover and load sharing properties, without assuming
spreading properties, without assuming that a multihomed site will that a multihomed site will have a provider independent IPv6 address
have a provider independent IPv6 address prefix which is announced in prefix which is announced in the global IPv6 routing table. The
the global IPv6 routing table. The hosts in a site which has hosts in a site which has multiple provider allocated IPv6 address
multiple provider allocated IPv6 address prefixes, will use the shim6 prefixes, will use the shim6 protocol specified in this document to
protocol specified in this document to setup state with peer hosts, setup state with peer hosts, so that the state can later be used to
so that the state can later be used to failover to a different failover to a different locator pair, should the original one stop
locator pair, should the original one stop working. working.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Goals . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Goals . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Non-Goals . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Non-Goals . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Locators as Upper-layer Identifiers . . . . . . . . . . 6 1.3 Locators as Upper-layer Identifiers . . . . . . . . . . 6
1.4 IP Multicast . . . . . . . . . . . . . . . . . . . . . . 7 1.4 IP Multicast . . . . . . . . . . . . . . . . . . . . . . 7
1.5 Renumbering Implications . . . . . . . . . . . . . . . . 7 1.5 Renumbering Implications . . . . . . . . . . . . . . . . 8
1.6 Placement of the shim . . . . . . . . . . . . . . . . . 8 1.6 Placement of the shim . . . . . . . . . . . . . . . . . 9
1.7 Traffic Engineering . . . . . . . . . . . . . . . . . . 10 1.7 Traffic Engineering . . . . . . . . . . . . . . . . . . 11
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 12 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . 12 2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Notational Conventions . . . . . . . . . . . . . . . . . 14 2.2 Notational Conventions . . . . . . . . . . . . . . . . . 15
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . 16 3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 17 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 17
4.1 Context Tags . . . . . . . . . . . . . . . . . . . . . . 19 4.1 Context Tags . . . . . . . . . . . . . . . . . . . . . . 19
4.2 Context Forking . . . . . . . . . . . . . . . . . . . . 19 4.2 Context Forking . . . . . . . . . . . . . . . . . . . . 19
4.3 API Extensions . . . . . . . . . . . . . . . . . . . . . 20 4.3 API Extensions . . . . . . . . . . . . . . . . . . . . . 20
4.4 Securing shim6 . . . . . . . . . . . . . . . . . . . . . 20 4.4 Securing shim6 . . . . . . . . . . . . . . . . . . . . . 20
4.5 Overview of Shim Control Messages . . . . . . . . . . . 21 4.5 Overview of Shim Control Messages . . . . . . . . . . . 21
4.6 Extension Header Order . . . . . . . . . . . . . . . . . 22 4.6 Extension Header Order . . . . . . . . . . . . . . . . . 22
4.7 Locator Validation . . . . . . . . . . . . . . . . . . . 22
5. Message Formats . . . . . . . . . . . . . . . . . . . . . . 24 5. Message Formats . . . . . . . . . . . . . . . . . . . . . . 24
5.1 Common shim6 Message Format . . . . . . . . . . . . . . 24 5.1 Common shim6 Message Format . . . . . . . . . . . . . . 24
5.2 Payload Extension Header Format . . . . . . . . . . . . 24 5.2 Payload Extension Header Format . . . . . . . . . . . . 24
5.3 Common Shim6 Control header . . . . . . . . . . . . . . 25 5.3 Common Shim6 Control header . . . . . . . . . . . . . . 25
5.4 I1 Message Format . . . . . . . . . . . . . . . . . . . 27 5.4 I1 Message Format . . . . . . . . . . . . . . . . . . . 27
5.5 R1 Message Format . . . . . . . . . . . . . . . . . . . 28 5.5 R1 Message Format . . . . . . . . . . . . . . . . . . . 28
5.6 I2 Message Format . . . . . . . . . . . . . . . . . . . 30 5.6 I2 Message Format . . . . . . . . . . . . . . . . . . . 30
5.7 R2 Message Format . . . . . . . . . . . . . . . . . . . 31 5.7 R2 Message Format . . . . . . . . . . . . . . . . . . . 31
5.8 R1bis Message Format . . . . . . . . . . . . . . . . . . 33 5.8 R1bis Message Format . . . . . . . . . . . . . . . . . . 33
5.9 I2bis Message Format . . . . . . . . . . . . . . . . . . 34 5.9 I2bis Message Format . . . . . . . . . . . . . . . . . . 34
5.10 Update Request Message Format . . . . . . . . . . . . . 36 5.10 Update Request Message Format . . . . . . . . . . . . . 36
5.11 Update Acknowledgement Message Format . . . . . . . . . 38 5.11 Update Acknowledgement Message Format . . . . . . . . . 38
5.12 Keepalive Message Format . . . . . . . . . . . . . . . . 39 5.12 Keepalive Message Format . . . . . . . . . . . . . . . . 39
5.13 Probe Message Format . . . . . . . . . . . . . . . . . . 39 5.13 Probe Message Format . . . . . . . . . . . . . . . . . . 39
5.14 Option Formats . . . . . . . . . . . . . . . . . . . . . 39 5.14 Option Formats . . . . . . . . . . . . . . . . . . . . . 39
5.14.1 Validator Option Format . . . . . . . . . . . . . . 41 5.14.1 Responder Validator Option Format . . . . . . . . . 41
5.14.2 Locator List Option Format . . . . . . . . . . . . . 42 5.14.2 Locator List Option Format . . . . . . . . . . . . . 42
5.14.3 Locator Preferences Option Format . . . . . . . . . 43 5.14.3 Locator Preferences Option Format . . . . . . . . . 43
5.14.4 CGA Parameter Data Structure Option Format . . . . . 45 5.14.4 CGA Parameter Data Structure Option Format . . . . . 45
5.14.5 CGA Signature Option Format . . . . . . . . . . . . 46 5.14.5 CGA Signature Option Format . . . . . . . . . . . . 46
5.14.6 ULID Pair Option Format . . . . . . . . . . . . . . 46 5.14.6 ULID Pair Option Format . . . . . . . . . . . . . . 47
5.14.7 Forked Instance Identifier Option Format . . . . . . 47 5.14.7 Forked Instance Identifier Option Format . . . . . . 48
5.14.8 Probe Option Format . . . . . . . . . . . . . . . . 48 5.14.8 Probe Option Format . . . . . . . . . . . . . . . . 48
5.14.9 Reachability Option Format . . . . . . . . . . . . . 48 5.14.9 Reachability Option Format . . . . . . . . . . . . . 48
5.14.10 Payload Reception Report Option Format . . . . . . 48 5.14.10 Payload Reception Report Option Format . . . . . . 48
6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 49 6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 49
6.1 Conceptual Data Structures . . . . . . . . . . . . . . . 49 6.1 Conceptual Data Structures . . . . . . . . . . . . . . . 49
6.2 Context States . . . . . . . . . . . . . . . . . . . . . 50 6.2 Context States . . . . . . . . . . . . . . . . . . . . . 50
7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . 52 7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . 52
7.1 Normal context establishment . . . . . . . . . . . . . . 52 7.1 Uniqness of Context Tags . . . . . . . . . . . . . . . . 52
7.2 Concurrent context establishment . . . . . . . . . . . . 52 7.2 Locator Verification . . . . . . . . . . . . . . . . . . 52
7.3 Context recovery . . . . . . . . . . . . . . . . . . . . 54 7.3 Normal context establishment . . . . . . . . . . . . . . 53
7.4 Context confusion . . . . . . . . . . . . . . . . . . . 56 7.4 Concurrent context establishment . . . . . . . . . . . . 53
7.5 Sending I1 messages . . . . . . . . . . . . . . . . . . 57 7.5 Context recovery . . . . . . . . . . . . . . . . . . . . 55
7.6 Retransmitting I1 messages . . . . . . . . . . . . . . . 57 7.6 Context confusion . . . . . . . . . . . . . . . . . . . 57
7.7 Receiving I1 messages . . . . . . . . . . . . . . . . . 58 7.7 Sending I1 messages . . . . . . . . . . . . . . . . . . 58
7.7.1 Generating the R1 validator . . . . . . . . . . . . 59 7.8 Retransmitting I1 messages . . . . . . . . . . . . . . . 58
7.8 Receiving R1 messages and sending I2 messages . . . . . 59 7.9 Receiving I1 messages . . . . . . . . . . . . . . . . . 59
7.9 Retransmitting I2 messages . . . . . . . . . . . . . . . 60 7.9.1 Generating the R1 Validator . . . . . . . . . . . . 60
7.10 Receiving I2 messages . . . . . . . . . . . . . . . . . 61 7.10 Receiving R1 messages and sending I2 messages . . . . . 61
7.11 Sending R2 messages . . . . . . . . . . . . . . . . . . 62 7.11 Retransmitting I2 messages . . . . . . . . . . . . . . . 62
7.12 Match for Context Confusion . . . . . . . . . . . . . . 62 7.12 Receiving I2 messages . . . . . . . . . . . . . . . . . 62
7.13 Receiving R2 messages . . . . . . . . . . . . . . . . . 63 7.13 Sending R2 messages . . . . . . . . . . . . . . . . . . 64
7.14 Sending R1bis packets . . . . . . . . . . . . . . . . . 64 7.14 Match for Context Confusion . . . . . . . . . . . . . . 64
7.14.1 Generating the R1bis validator . . . . . . . . . . . 64 7.15 Receiving R2 messages . . . . . . . . . . . . . . . . . 65
7.15 Receiving R1bis messages and sending I2bis messages . . 65 7.16 Sending R1bis messages . . . . . . . . . . . . . . . . . 66
7.16 Receiving I2bis messages and sending R2 messages . . . . 66 7.16.1 Generating the R1bis Validator . . . . . . . . . . . 66
8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 68 7.17 Receiving R1bis messages and sending I2bis messages . . 67
9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . 69 7.18 Retransmitting I2bis messages . . . . . . . . . . . . . 68
10. Updating the Peer . . . . . . . . . . . . . . . . . . . . 70 7.19 Receiving I2bis messages and sending R2 messages . . . . 68
10.1 Sending Update Request messages . . . . . . . . . . . . 70 8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 70
10.2 Retransmitting Update Request messages . . . . . . . . . 70 9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . 72
10.3 Newer Information While Retransmitting . . . . . . . . . 71 10. Updating the Peer . . . . . . . . . . . . . . . . . . . . 73
10.4 Receiving Update Request messages . . . . . . . . . . . 71 10.1 Sending Update Request messages . . . . . . . . . . . . 73
10.5 Receiving Update Acknowledgement messages . . . . . . . 73 10.2 Retransmitting Update Request messages . . . . . . . . . 73
11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . 74 10.3 Newer Information While Retransmitting . . . . . . . . . 74
11.1 Sending ULP Payload after a Switch . . . . . . . . . . . 74 10.4 Receiving Update Request messages . . . . . . . . . . . 74
12. Receiving Packets . . . . . . . . . . . . . . . . . . . . 76 10.5 Receiving Update Acknowledgement messages . . . . . . . 76
12.1 Receiving Payload Extension Headers . . . . . . . . . . 76 11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . 77
12.2 Receiving Shim Control messages . . . . . . . . . . . . 76 11.1 Sending ULP Payload after a Switch . . . . . . . . . . . 77
12.3 Context Lookup . . . . . . . . . . . . . . . . . . . . . 77 12. Receiving Packets . . . . . . . . . . . . . . . . . . . . 79
13. Initial Contact . . . . . . . . . . . . . . . . . . . . . 79 12.1 Receiving Payload Extension Headers . . . . . . . . . . 79
14. Protocol constants . . . . . . . . . . . . . . . . . . . . 80 12.2 Receiving Shim Control messages . . . . . . . . . . . . 79
15. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 81 12.3 Context Lookup . . . . . . . . . . . . . . . . . . . . . 80
16. Implications Elsewhere . . . . . . . . . . . . . . . . . . 82 13. Initial Contact . . . . . . . . . . . . . . . . . . . . . 82
17. Security Considerations . . . . . . . . . . . . . . . . . 84 14. Protocol constants . . . . . . . . . . . . . . . . . . . . 83
18. IANA Considerations . . . . . . . . . . . . . . . . . . . 86 15. Implications Elsewhere . . . . . . . . . . . . . . . . . . 84
19. Possible Protocol Extensions . . . . . . . . . . . . . . . 88 16. Security Considerations . . . . . . . . . . . . . . . . . 86
20. Change Log . . . . . . . . . . . . . . . . . . . . . . . . 90 17. IANA Considerations . . . . . . . . . . . . . . . . . . . 88
21. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 93 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 90
A. Simplified State Machine . . . . . . . . . . . . . . . . . . 94 A. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 91
A.1 Simplified State Machine diagram . . . . . . . . . . . . 99 B. Possible Protocol Extensions . . . . . . . . . . . . . . . . 92
B. Context Tag Reuse . . . . . . . . . . . . . . . . . . . . . 100 C. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 94
B.1 Context Recovery . . . . . . . . . . . . . . . . . . . . 100 D. Simplified State Machine . . . . . . . . . . . . . . . . . . 97
B.2 Context Confusion . . . . . . . . . . . . . . . . . . . 100 D.1 Simplified State Machine diagram . . . . . . . . . . . . 102
B.3 Three Party Context Confusion . . . . . . . . . . . . . 101 E. Context Tag Reuse . . . . . . . . . . . . . . . . . . . . . 103
C. Design Alternatives . . . . . . . . . . . . . . . . . . . . 102 E.1 Context Recovery . . . . . . . . . . . . . . . . . . . . 103
C.1 Context granularity . . . . . . . . . . . . . . . . . . 102 E.2 Context Confusion . . . . . . . . . . . . . . . . . . . 103
C.2 Demultiplexing of data packets in shim6 communications . 102 E.3 Three Party Context Confusion . . . . . . . . . . . . . 104
C.2.1 Flow-label . . . . . . . . . . . . . . . . . . . . . 103 F. Design Alternatives . . . . . . . . . . . . . . . . . . . . 105
C.2.2 Extension Header . . . . . . . . . . . . . . . . . . 105 F.1 Context granularity . . . . . . . . . . . . . . . . . . 105
C.3 Context Loss Detection . . . . . . . . . . . . . . . . . 106 F.2 Demultiplexing of data packets in shim6 communications . 105
C.4 Securing locator sets . . . . . . . . . . . . . . . . . 108 F.2.1 Flow-label . . . . . . . . . . . . . . . . . . . . . 106
C.5 ULID-pair context establishment exchange . . . . . . . . 111 F.2.2 Extension Header . . . . . . . . . . . . . . . . . . 108
C.6 Updating locator sets . . . . . . . . . . . . . . . . . 112 F.3 Context Loss Detection . . . . . . . . . . . . . . . . . 109
C.7 State Cleanup . . . . . . . . . . . . . . . . . . . . . 112 F.4 Securing locator sets . . . . . . . . . . . . . . . . . 111
22. References . . . . . . . . . . . . . . . . . . . . . . . . 115 F.5 ULID-pair context establishment exchange . . . . . . . . 114
22.1 Normative References . . . . . . . . . . . . . . . . . . 115 F.6 Updating locator sets . . . . . . . . . . . . . . . . . 115
22.2 Informative References . . . . . . . . . . . . . . . . . 115 F.7 State Cleanup . . . . . . . . . . . . . . . . . . . . . 115
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 117 19. References . . . . . . . . . . . . . . . . . . . . . . . . 118
Intellectual Property and Copyright Statements . . . . . . . 118 19.1 Normative References . . . . . . . . . . . . . . . . . . 118
19.2 Informative References . . . . . . . . . . . . . . . . . 118
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 120
Intellectual Property and Copyright Statements . . . . . . . 121
1. Introduction 1. Introduction
The SHIM6 working group, and the MULTI6 WG that preceded it, was This document describes a layer 3 shim approach and protocol for
exploring and is now specifying a layer 3 shim approach and protocol providing locator agility below the transport protocols, so that
for 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 spreading properties [15], without assuming that a multihomed site will have a
properties [16], without assuming that a multihomed site will have a
provider independent IPv6 address which is announced in the global provider independent IPv6 address which is announced in the global
IPv6 routing table. The hosts in a site which has multiple provider IPv6 routing table. The hosts in a site which has multiple provider
allocated IPv6 address prefixes, will use the shim6 protocol allocated IPv6 address prefixes, will use the shim6 protocol
specified in this document to setup state with peer hosts, so that specified in this document to setup state with peer hosts, so that
the state can later be used to failover to a different locator pair, the state can later be used to failover to a different locator pair,
should the original one stop working. should the original one stop working.
This document takes the outlines contained in [25] and [24] and
expands to an actual protocol specification.
We assume that redirection attacks are prevented using the mechanism We assume that redirection attacks are prevented using the mechanism
specified in HBA [7]. specified in HBA [7].
The reachability detection and failure detection, including how a new The reachability detection and failure detection, including how a new
working locator pair is discovered after a failure, is specified in working locator pair is discovered after a failure, is specified in a
separate documents ([9] and [8]). This document allocates message separate documents [8] This document allocates message types and
types and option types for that sub-protocol, and leaves the option types for that sub-protocol, and leaves the specification of
specification of the message and option formats as well as the the message and option formats as well as the protocol behavior to
protocol behavior to a separate draft. that document.
1.1 Goals 1.1 Goals
The goals for this approach is to: The goals for this approach is to:
o Preserve established communications through failures, for example, o Preserve established communications through certain classes of
TCP connections and application communications using UDP. failures, for example, TCP connections and application
communications using UDP.
o Have no impact on upper layer protocols in general and on o Have minimal impact on upper layer protocols in general and on
transport protocols in particular. transport protocols in particular.
o Address the security threats in [20] through a separate document o Address the security threats in [19] through the combination of
[7], and techniques described in this document. the HBA/CGA approach specified in a separate document [7], and
techniques described in this document.
o No extra roundtrip for setup; deferred setup. o Do not require an extra roundtrip up front to setup shim specific
state. Instead allow the upper layer traffic (e.g., TCP) to flow
as normal and defer the setup of the shim state until some number
of packets have been exchanged.
o Take advantage of multiple locators/addresses for load spreading o Take advantage of multiple locators/addresses for load spreading
so that different sets of communication to a host (e.g., different so that different sets of communication to a host (e.g., different
connections) might use different locators of the host. This might connections) might use different locators of the host. Note that
enable some forms of traffic engineering, but the details for this might cause load to be spread unevenly, thus we use the term
traffic engineering, including what requirements can be satisfied, "load spreading" instead of "load balancing". This capability
have not yet been worked out. might enable some forms of traffic engineering, but the details
for traffic engineering, including what requirements can be
satisfied, are not specified in this document, and form part of a
potential extensions to this protocol.
1.2 Non-Goals 1.2 Non-Goals
The assumption is that the problem we are trying to solve is site The assumption is that the problem we are trying to solve is site
multihoming, with the ability to have the set of site locator multihoming, with the ability to have the set of site locator
prefixes change over time due to site renumbering. Further, we prefixes change over time due to site renumbering. Further, we
assume that such changes to the set of locator prefixes can be assume that such changes to the set of locator prefixes can be
relatively slow and managed; slow enough to allow updates to the DNS relatively slow and managed; slow enough to allow updates to the DNS
to propagate. But it is not a goal to try to make communication to propagate. But it is not a goal to try to make communication
survive a renumbering event (which causes all the locators of a host survive a renumbering event (which causes all the locators of a host
to change to a new set of locators). This proposal does not attempt to change to a new set of locators). This proposal does not attempt
to solve the, perhaps related, problem of host mobility. However, it to solve the, perhaps related, problem of host mobility. However, it
might turn out that the shim6 protocol can be a useful component, might turn out that the shim6 protocol can be a useful component for
e.g., for route optimization in the context of host mobility. future host mobility solutions, e.g., for route optimization.
This proposal also does not try to provide a new network level This proposal also does not try to provide a new network level or
identifier namespace separated from the current IP address namespace. transport level identifier namespace separated from the current IP
Even though such a concept would be useful to ULPs and applications, address namespace. Even though such a concept would be useful to
especially if the management burden for such a name space was zero ULPs and applications, especially if the management burden for such a
and there was an efficient yet secure mechanism to map from name space was negligible and there was an efficient yet secure
identifiers to locators, such a name space isn't necessary (and mechanism to map from identifiers to locators, such a name space
furthermore doesn't seem to help) to solve the multihoming problem. isn't necessary (and furthermore doesn't seem to help) to solve the
multihoming problem.
1.3 Locators as Upper-layer Identifiers 1.3 Locators as Upper-layer Identifiers
Central to this approach is to not introduce a new identifier name This approach does not introduce a new identifier name space but
space but instead use one of the locators as the upper-layer ID, instead uses the locator that is selected in the initial contact with
while allowing the locators used in the address fields to change over the remote peer as the preserved upper-level identifier. While there
time in response to failures of using the original locator. may be subsequent changes in the selected network level locators over
time in response to failures in using the original locator, the upper
level protocol stack elements will continue to use this upper level
identifier without change.
This implies that the ULID selection is performed as today's default This implies that the ULID selection is performed as today's default
address selection as specified in RFC 3484 [13]. Some extensions are address selection as specified in RFC 3484 [12]. Some extensions are
needed to RFC 3484 to try different source addresses, whether or not needed to RFC 3484 to try different source addresses, whether or not
the shim6 protocol is used, as outlined in [14]. Underneath, and the shim6 protocol is used, as outlined in [13]. Underneath, and
transparently, the multihoming shim selects working locator pairs transparently, the multihoming shim selects working locator pairs
with the initial locator pair being the ULID pair. When with the initial locator pair being the ULID pair. When
communication fails the shim can test and select alternate locators. communication fails the shim can test and select alternate locators.
A subsequent section discusses the issues when the selected ULID is A subsequent section discusses the issues when the selected ULID is
not initially working hence there is a need to switch locators up not initially working hence there is a need to switch locators up
front. front.
Using one of the locators as the ULID has certain benefits for Using one of the locators as the ULID has certain benefits for
applications which have long-lived session state, or performs applications which have long-lived session state, or performs
callbacks or referrals, because both the FQDN and the 128-bit ULID callbacks or referrals, because both the FQDN and the 128-bit ULID
work as handles for the applications. However, using a single 128- work as handles for the applications. However, using a single 128-
bit ULID doesn't provide seamless communication when that locator is bit ULID doesn't provide seamless communication when that locator is
unreachable. See [21] for further discussion of the application unreachable. See [22] for further discussion of the application
implications. implications.
There has been some discussion of using non-routable locators, such There has been some discussion of using non-routable locators, such
as unique-local addresses [19], as ULIDs in a multihoming solution. as unique-local addresses [18], as ULIDs in a multihoming solution.
While this document doesn't specify all aspects of this, it is While this document doesn't specify all aspects of this, it is
believed that the approach can be extended to handle such a case. believed that the approach can be extended to handle such a case.
For example, the protocol already needs to handle ULIDs that are not For example, the protocol already needs to handle ULIDs that are not
initially reachable. Thus the same mechanism can handle ULIDs that initially reachable. Thus the same mechanism can handle ULIDs that
are permanently unreachable from outside their site. The issue are permanently unreachable from outside their site. The issue
becomes how to make the protocol perform well when the ULID is known becomes how to make the protocol perform well when the ULID is known
a priori to be not reachable (e.g., the ULID is a ULA), for instance, a priori to be not reachable (e.g., the ULID is a ULA), for instance,
avoiding any timeout and retries in this case. In addition one would avoiding any timeout and retries in this case. In addition one would
need to understand how the ULAs would be entered in the DNS to avoid need to understand how the ULAs would be entered in the DNS to avoid
a performance impact on existing, non-shim6 aware, IPv6 hosts a performance impact on existing, non-shim6 aware, IPv6 hosts
potentially trying to communicate to the (unreachable) ULA. potentially trying to communicate to the (unreachable) ULA.
1.4 IP Multicast 1.4 IP Multicast
IP Multicast requires that the IP source address field contain a IP Multicast requires that the IP source address field contain a
topologically correct locator for interface that is used to send the topologically correct locator for interface that is used to send the
packet, since IP multicast routing uses both the source address and packet, since IP multicast routing uses both the source address and
the destination group to determine where to forward the packet. the destination group to determine where to forward the packet.
(This isn't much different than the situation with widely implemented (This isn't much different than the situation with widely implemented
ingress filtering [11] for unicast.) ingress filtering [10] for unicast.)
While in theory it would be possible to apply the shim re-mapping of While in theory it would be possible to apply the shim re-mapping of
the IP address fields between ULIDs and locators, the fact that all the IP address fields between ULIDs and locators, the fact that all
the multicast receivers would need to know the mapping to perform, the multicast receivers would need to know the mapping to perform,
makes such an approach difficult in practice. Thus it makes sense to makes such an approach difficult in practice. Thus it makes sense to
have multicast ULPs operate directly on locators and not use the have multicast ULPs operate directly on locators and not use the
shim. This is quite a natural fit for protocols which use RTP [15], shim. This is quite a natural fit for protocols which use RTP [14],
since RTP already has an explicit identifier in the form of the SSRC since RTP already has an explicit identifier in the form of the SSRC
field in the RTP headers. Thus the actual IP address fields are not field in the RTP headers. Thus the actual IP address fields are not
important to the application. important to the application.
In summary, IP multicast will not use the shim to remap the IP In summary, IP multicast will not need the shim to remap the IP
addresses. addresses.
This doesn't prevent the receiver of multicast to change its
locators, since the receiver is not explicitly identified; the
destination address is a multicast address and not the unicast
locator of the receiver.
1.5 Renumbering Implications 1.5 Renumbering Implications
As stated above, this approach does not try to make communication As stated above, this approach does not try to make communication
survive renumbering. However, the fact that a ULID might be used survive renumbering in the general case.
When a host is renumbered, the effect is that one or more locators
become invalid, and zero or more locators are added to the host's
network interface. This means that the set of locators that is used
in the shim will change, which the shim can handle as long as not all
the original locators become invalid at the same time.
But IP addresses are also used as ULID, and making the communication
survive locators becoming invalid can potentially cause some
confusion at the upper layers. The fact that a ULID might be used
with a different locator over time open up the possibility that with a different locator over time open up the possibility that
communication between two ULIDs might continue to work after one or communication between two ULIDs might continue to work after one or
both of those ULIDs are no longer reachable as locators, for example both of those ULIDs are no longer reachable as locators, for example
due to a renumbering event. This opens up the possibility that the due to a renumbering event. This opens up the possibility that the
ULID (or at least the prefix on which it is based) is reassigned to ULID (or at least the prefix on which it is based) is reassigned to
another site while it is still being used (with another locator) for another site while it is still being used (with another locator) for
existing communication. existing communication.
Worst case we could end up with two separate hosts using the same Worst case we could end up with two separate hosts using the same
ULID while both of them are communicating with the same host. ULID while both of them are communicating with the same host.
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becomes invalid (due to the underlying prefix becoming invalid). If becomes invalid (due to the underlying prefix becoming invalid). If
that behavior is desired, it can be accomplished by explicitly that behavior is desired, it can be accomplished by explicitly
discarding the shim state when the ULID becomes invalid. The context discarding the shim state when the ULID becomes invalid. The context
recovery mechanism will then make the peer aware that the context is recovery mechanism will then make the peer aware that the context is
gone, and that the ULID is no longer present at the same locator(s). gone, and that the ULID is no longer present at the same locator(s).
However, terminating the communication might be overkill. Even when However, terminating the communication might be overkill. Even when
an IPv6 prefix is retired and reassigned to some other site, there is an IPv6 prefix is retired and reassigned to some other site, there is
a very small probability that another host in that site picks the a very small probability that another host in that site picks the
same 128 bit address (whether using DHCPv6, stateless address same 128 bit address (whether using DHCPv6, stateless address
autoconfiguration, or picking a random interface ID [12]). Should autoconfiguration, or picking a random interface ID [11]). Should
the identical address be used by another host, then there still the identical address be used by another host, then there still
wouldn't be a problem until that host attempts to communicate with wouldn't be a problem until that host attempts to communicate with
the same peer host with which the initial user of the IPv6 address the same peer host with which the initial user of the IPv6 address
was communicating. was communicating.
The protocol as specified in this document does not perform any The protocol as specified in this document does not perform any
action when an address becomes invalid. As we gain further action when an address becomes invalid. As we gain further
understanding of the practical impact of renumbering this might understanding of the practical impact of renumbering this might
change in a future version of the protocol. change in a future version of the protocol.
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independence. The multihoming shim layer behaves as if it is independence. The multihoming shim layer behaves as if it is
associated with an extension header, which would be placed after any associated with an extension header, which would be placed after any
routing-related headers in the packet (such as any hop-by-hop routing-related headers in the packet (such as any hop-by-hop
options, or routing header). However, when the locator pair is the options, or routing header). However, when the locator pair is the
ULID pair there is no data that needs to be carried in an extension ULID pair there is no data that needs to be carried in an extension
header, thus none is needed in that case. header, thus none is needed in that case.
Layering AH and ESP above the multihoming shim means that IPsec can Layering AH and ESP above the multihoming shim means that IPsec can
be made to be unaware of locator changes the same way that transport be made to be unaware of locator changes the same way that transport
protocols can be unaware. Thus the IPsec security associations protocols can be unaware. Thus the IPsec security associations
remain stable even though the locators are changing. remain stable even though the locators are changing. This means that
the IP addresses specified in the selectors should be the ULIDs.
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.
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the data packets. This serves to indicate the correct context to use the data packets. This serves to indicate the correct context to use
for decompression when the locator pair in the packet is insufficient for decompression when the locator pair in the packet is insufficient
to uniquely identify the context. to uniquely identify the context.
1.7 Traffic Engineering 1.7 Traffic Engineering
At the time of this writing it is not clear what requirements for At the time of this writing it is not clear what requirements for
traffic engineering make sense for the shim6 protocol, since the traffic engineering make sense for the shim6 protocol, since the
requirements must both result in some useful behavior as well as be requirements must both result in some useful behavior as well as be
implementable using a host-to-host locator agility mechanism like implementable using a host-to-host locator agility mechanism like
shim6. What is clear that whatever they are, shim6 will not be able shim6.
to provide identical capabilities to traffic engineering using BGP
and Provide Independent IP addresses. Inherent in a scalable multihoming mechanism that separates locators
from identifiers is that each host ends up with multiple locators.
This means that at least for initial contact, it is the remote peer
that needs to select which peer locator to try first. In the case of
shim6 this is performed by applying RFC 3484 address selection.
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
peer performs no destination address selection.
Thus in "single prefix multihoming" the site, and in many cases its
upstream ISPs, can use BGP to exert some control of the ingress used
to reach the site. This capability can't easily be recreated in
"multiple prefix multihoming" such as shim6.
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 is intentionally made
identical to the DNS SRV [10] specification of priority and weight, identical to the DNS SRV [9] specification of priority and weight, so
so that DNS SRV records can be used for initial contact and the shim that DNS SRV records can be used for initial contact and the shim for
for failover, and they can use the same way to describe the failover, and they can use the same way to describe the preferences.
preferences. The format allows adding additional notions of The format allows adding additional notions of "metrics" over time.
"metrics" over time. But this is merely a place holder; even in But the Locator Preference option is merely a place holder when it
order to use this there would have to be a mechanism by which the comes to providing traffic engineering; in order to use this in a
host can find out what preference values to use, either statically large site there would have to be a mechanism by which the host can
(e.g., some new DHCPv6 option) or dynamically. 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
Appendix B.
2. Terminology 2. Terminology
This document uses the terms MUST, SHOULD, RECOMMENDED, MAY, SHOULD This document uses the terms MUST, SHOULD, RECOMMENDED, MAY, SHOULD
NOT and MUST NOT defined in RFC 2119 [1]. The terms defined in RFC NOT and MUST NOT defined in RFC 2119 [1]. The terms defined in RFC
2460 [2] are also used. 2460 [2] are also used.
2.1 Definitions 2.1 Definitions
This document introduces the following terms (taken from [25]): This document introduces the following terms:
upper layer protocol (ULP) upper layer protocol (ULP)
A protocol layer immediately above IP. Examples A protocol layer immediately above IP. Examples
are transport protocols such as TCP and UDP, are transport protocols such as TCP and UDP,
control protocols such as ICMP, routing protocols control protocols such as ICMP, routing protocols
such as OSPF, and internet or lower-layer such as OSPF, and internet or lower-layer
protocols being "tunneled" over (i.e., protocols being "tunneled" over (i.e.,
encapsulated in) IP such as IPX, AppleTalk, or IP encapsulated in) IP such as IPX, AppleTalk, or IP
itself. itself.
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an interface. 128 bits. This document only uses an interface. 128 bits. This document only uses
the "address" term in the case where it isn't the "address" term in the case where it isn't
specific whether it is a locator or an specific whether it is a locator or an
identifier. identifier.
locator An IP layer topological name for an interface or locator An IP layer topological name for an interface or
a set of interfaces. 128 bits. The locators are a set of interfaces. 128 bits. The locators are
carried in the IP address fields as the packets carried in the IP address fields as the packets
traverse the network. traverse the network.
identifier An IP layer name for an IP layer endpoint (stack identifier An IP layer name for an IP layer endpoint. The
name in [27]). The transport endpoint name is a transport endpoint name is a function of the
function of the transport protocol and would transport protocol and would typically include
typically include the IP identifier plus a port the IP identifier plus a port number.
number.
NOTE: This proposal does not specify any new form NOTE: This proposal does not specify any new form
of IP layer identifier, but still separates the of IP layer identifier, but still separates the
identifying and locating properties of the IP identifying and locating properties of the IP
addresses. addresses.
upper-layer identifier (ULID) upper-layer identifier (ULID)
An IP address which has been selected for An IP address which has been selected for
communication with a peer to be used by the upper communication with a peer to be used by the upper
layer protocol. 128 bits. This is used for layer protocol. 128 bits. This is used for
pseudo-header checksum computation and connection pseudo-header checksum computation and connection
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direction of the communication, and also direction of the communication, and also
identified by the pair of ULID and a Forked identified by the pair of ULID and a Forked
Instance Identifier (see below). Instance Identifier (see below).
Context tag Each end of the context allocates a context tag Context tag Each end of the context allocates a context tag
for the context. This is used to uniquely for the context. This is used to uniquely
associate both received control packets and associate both received control packets and
payload extension headers as belonging to the payload extension headers as belonging to the
context. context.
Current locator pair Each end of the context has a current locator Current locator pair
pair which is used to send packets to be peer. Each end of the context has a current locator
pair which is used to send packets to the peer.
The two ends might use different current locator The two ends might use different current locator
pairs though. pairs though.
Default context At the sending end, the shim uses the ULID pair Default context At the sending end, the shim uses the ULID pair
(passed down from the ULP) to find the context (passed down from the ULP) to find the context
for that pair. Thus, normally, a host can have for that pair. Thus, normally, a host can have
at most one context for a ULID pair. We call at most one context for a ULID pair. We call
this the "default context". this the "default context".
Context forking A mechanism which allows ULPs that are aware of Context forking A mechanism which allows ULPs that are aware of
multiple locators to use separate contexts for multiple locators to use separate contexts for
the same ULID pair, in order to be able use the same ULID pair, in order to be able use
different locator pairs for different different locator pairs for different
communication to the same ULID. Context forking communication to the same ULID. Context forking
causes more than just the default context to be causes more than just the default context to be
created for a ULID pair. created for a ULID pair.
Forked Instance Identifier (FII) In order to handle context forking, Forked Instance Identifier (FII)
a context is identified by a ULID-pair and a In order to handle context forking, a context is
forked context identifier. The default context identified by a ULID-pair and a forked context
has a FII of zero. identifier. The default context has a FII of
zero.
Initial contact We use this term to refer to the pre-shim Initial contact We use this term to refer to the pre-shim
communication when some ULP decides to start communication when some ULP decides to start
communicating with a peer by sending and communicating with a peer by sending and
receiving ULP packets. Typically this would not receiving ULP packets. Typically this would not
invoke any operations in the shim, since the shim invoke any operations in the shim, since the shim
can defer the context establishment until some can defer the context establishment until some
arbitrary later point in time. arbitrary later point in time.
Hash Based Addresses (HBA)
A form of IPv6 address where the interface ID is
derived from a cryptographic hash of all the
prefixes assigned to the host. See [7].
Cryptographically Generated Addresses (CGA)
A form of IPv6 address where the interface ID is
derived from a cryptographic hash of the public
key. See [6].
CGA Parameter Data Structure (PDS)
The information that CGA and HBA exchanges in
order to inform the peer of how the interface ID
was computed. See [6]., [7].
2.2 Notational Conventions 2.2 Notational Conventions
A, B, and C are hosts. X is a potentially malicious host. A, B, and C are hosts. X is a potentially malicious host.
FQDN(A) is the domain name for A. FQDN(A) is the domain name for A.
Ls(A) is the locator set for A, which consists of the locators L1(A), Ls(A) is the locator set for A, which consists of the locators L1(A),
L2(A), ... Ln(A). L2(A), ... Ln(A).
ULID(A) is an upper-layer ID for A. In this proposal, ULID(A) is ULID(A) is an upper-layer ID for A. In this proposal, ULID(A) is
always one member of A's locator set. always one member of A's locator set.
CT(x) is a Context Tag. CT(X) is a context tag assigned by X.
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.
3. Assumptions 3. Assumptions
The general approach of a level3 shim as well as this specific The design intent is to ensure that the shim6 protocol is capable of
proposal makes the following assumptions: handling path failures independently of the number of IP addresses
(locators) available to the two communicating hosts, and
independently of which host detects the failure condition.
o When there is ingress filtering in the ISPs, that the use of all In the case when host A and host B have an active shim6 state, with
<source, destination> locator pairs will cause the packets to exit host A having only one locator and host B having multiple locators,
using different ISPs so that all exit ISPs can be tried. Since it might be that host B is trying to send a packet to host A, and has
there might be only one destination locator, when the peer detected a failure condition with the current locator pair. As host
supports shim6 but is not multihomed, this implies that the B has multiple locators it presumably has multiple ISPs. In this
selection of the exit ISP should be related to the source address case there are probably alternate egress paths for host B to be able
in the packets. to try to reach A, but B can not vary the destination address (host A
locator) to select such alternate paths, since A has only one
locator.
o Even without ingress filtering, there is the assumption that if This leads to the assumption that a host should be able to cause
the host tries all <source, destination> locator pairs, that it different egress paths from its site to be used. The most reasonable
has done a good enough job of trying to find a working path to the approach to accomplish this is to have the host use different source
peer. Since we want the protocol to provide benefits even if the addresses and have the source address affect the selection of the
peer has a single locator, this seems to imply that the choice of site egress. The details of how this can be accomplished is beyond
source locator needs to somehow affect the exit path from the the scope of this document, but without this capability the ability
site. 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
filtering.
In addition, when the site's ISPs perform ingress filtering based on
packet source addresses, shim6 assumes that packets sent with
different source and destination combinations have a reasonable
chance of making it through the relevant ISP's ingress filters. This
can be accomplished in several ways (all outside the scope of this
document), such as having the ISPs relax there ingress filters, or
selecting the egress such that it matches the IP source address
prefix.
Further discussion of this issue is captured in [20].
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
IPv6 addresses and that those addresses will also make sense to their
peer.
4. Protocol Overview 4. Protocol Overview
The shim6 protocol operates in several phases over time. The The shim6 protocol operates in several phases over time. The
following sequence illustrates the concepts: following sequence illustrates the concepts:
o An application on host A decides to contact B using some upper- o An application on host A decides to contact B using some upper-
layer protocol. This results in the ULP on A sending packets to layer protocol. This results in the ULP on A sending packets to
B. We call this the initial contact. Assuming the IP addresses B. We call this the initial contact. Assuming the IP addresses
selected by Default Address Selection [13] and its extensions [14] selected by Default Address Selection [12] and its extensions [13]
work, then there is no action by the shim at this point in time. work, then there is no action by the shim at this point in time.
Any shim context establishment can be deferred until later. Any shim context establishment can be deferred until later.
o Some heuristic on A or B (or both) determine that it might make o Some heuristic on A or B (or both) determine that it is
sense to make this communication robust against locator failures. appropriate to pay the shim6 overhead to make this host-to-host
For instance, this heuristic might be that more than 50 packets communication robust against locator failures. For instance, this
have been sent or received, or a timer expiration while active heuristic might be that more than 50 packets have been sent or
packet exchange is in place. This makes the shim initiate the received, or a timer expiration while active packet exchange is in
4-way context establishment exchange. place. This makes the shim initiate the 4-way context
establishment exchange.
As a result of this exchange, both A and B will know a list of As a result of this exchange, both A and B will know a list of
locators for each other. locators for each other.
If the context establishment exchange fails, the initiator will If the context establishment exchange fails, the initiator will
then know that the other end does not support shim6, and will then know that the other end does not support shim6, and will
revert to standard unicast behavior for the session. continue with standard unicast behavior for the session.
o Communication continues without any change for the ULP packets. o Communication continues without any change for the ULP packets.
In particular, there are no shim extension headers added to the In particular, there are no shim extension headers added to the
ULP packets, since the ULID pair is the same as the locator pair. ULP packets, since the ULID pair is the same as the locator pair.
In addition, there might be some messages exchanged between the In addition, there might be some messages exchanged between the
shim sub-layers for (un)reachability detection. shim sub-layers for (un)reachability detection.
o At some point in time something fails. Depending on the approach o At some point in time something fails. Depending on the approach
to reachability detection, there might be some advise from the to reachability detection, there might be some advice from the
ULP, or the shim (un)reachability detection might discover that ULP, or the shim (un)reachability detection might discover that
there is a problem. there is a problem.
At this point in time one or both ends of the communication need At this point in time one or both ends of the communication need
to probe the different alternate locator pairs until a working to probe the different alternate locator pairs until a working
pair is found, and rehome to using that pair. pair is found, and switch to using that locator pair.
o Once a working alternative locator pair has been found, the shim o Once a working alternative locator pair has been found, the shim
will rewrite the packets on transmit, and tag the packets with will rewrite the packets on transmit, and tag the packets with
shim6 Payload extension header, which contains the receiver's shim6 Payload extension header, which contains the receiver's
context tag. The receiver will use the context tag to find the context tag. The receiver will use the context tag to find the
context state which will indicate which addresses to place in the context state which will indicate which addresses to place in the
IPv6 header before passing the packet up to the ULP. The result IPv6 header before passing the packet up to the ULP. The result
is that from the perspective of the ULP the packet passes is that from the perspective of the ULP the packet passes
unmodified end-to-end, even though the IP routing infrastructure unmodified end-to-end, even though the IP routing infrastructure
sends the packet to a different locator. sends the packet to a different locator.
o The shim (un)reachability detection will monitor the new locator o The shim (un)reachability detection will monitor the new locator
pair as it monitored the original locator pair, so that subsequent pair as it monitored the original locator pair, so that subsequent
failures can be detected. failures can be detected.
o In addition to failures detected based on end-to-end observations, o In addition to failures detected based on end-to-end observations,
one endpoint might be know for certain that one or more of its one endpoint might know for certain that one or more of its
locators is not working. For instance, the network interface locators is not working. For instance, the network interface
might have failed or gone down (at layer 2), or an IPv6 address might have failed or gone down (at layer 2), or an IPv6 address
might have become deprecated or invalid. In such cases the host might have become deprecated or invalid. In such cases the host
can signal its peer that this address is no longer recommended to can signal its peer that this address is no longer recommended to
try. Thus this triggers something similar to a failure handling try. Thus this triggers something similar to a failure handling
in that a new, working locator pair must be found. in that a new, working locator pair must be found.
The protocol also has the ability to express other forms of The protocol also has the ability to express other forms of
locator preferences. A change in any preferences can be signaled locator preferences. A change in any preferences can be signaled
to the peer, which might make the peer choose to try a different to the peer, which will made the peer record the new preferences.
locator pair. Thus, this can also be treated similarly to a A change in the preferences might optionally make the peer want to
failure. use a different locator pair. If it makes this decision, it
follows the same locator switching procedure as after a failure
(by verifying that its peer is indeed present at the alternate
locator, etc).
o When the shim thinks that the context state is no longer used, it o When the shim thinks that the context state is no longer used, it
can garbage collect the state; there is no coordination necessary can garbage collect the state; there is no coordination necessary
with the peer host before the state is removed. There is a with the peer host before the state is removed. There is a
recovery message defined to be able to signal when there is no recovery message defined to be able to signal when there is no
context state, which can be used to detect and recover from both context state, which can be used to detect and recover from both
premature garbage collection, as well as complete state loss premature garbage collection, as well as complete state loss
(crash and reboot) of a peer. (crash and reboot) of a peer.
The exact mechanism to determine when the context state is no The exact mechanism to determine when the context state is no
longer used is implementation dependent. An implementation might longer used is implementation dependent. An implementation might
use the existence of ULP state (where known to the implementation) use the existence of ULP state (where known to the implementation)
as an indication that the state is still used, combined with a as an indication that the state is still used, combined with a
timer (to handle ULP state that might not be known to the shim timer (to handle ULP state that might not be known to the shim
sub-layer) to determine when the state is likely to no longer be sub-layer) to determine when the state is likely to no longer be
used. used.
NOTE: The ULP packets in shim6 are carried completely unmodified as NOTE: The ULP packets in shim6 can be carried completely unmodified
long as the ULID pair is used as the locator pair. After a switch to as long as the ULID pair is used as the locator pair. After a switch
a different locator pair the packets are "tagged" with a shim6 to a different locator pair the packets are "tagged" with a shim6
extension header, so that the receiver can always determine the extension header, so that the receiver can always determine the
context to which they belong. This is accomplished by including an context to which they belong. This is accomplished by including an
8-octet shim payload extension header before the (extension) headers 8-octet shim6 Payload Extension header before the (extension) headers
that are processed by the IP endpoint sublayer and ULPs. that are processed by the IP endpoint sublayer and ULPs. If
subsequently the original ULIDs are selected as the active locator
pair then the tagging of packets with the shim6 extension header can
also be stopped.
4.1 Context Tags 4.1 Context Tags
A context between two hosts is actually a context between two ULIDs. A context between two hosts is actually a context between two ULIDs.
The context is identified by a pair of context tags. Each end gets The context is identified by a pair of context tags. Each end gets
to allocate a context tag, and once the context is established, the to allocate a context tag, and once the context is established, most
shim6 control messages contain the context tag that the receiver of shim6 control messages contain the context tag that the receiver of
the message allocated. Thus at a minimum the combination of <peer the message allocated. Thus at a minimum the combination of <peer
ULID, local ULID, local context tag> MUST uniquely identify one ULID, local ULID, local context tag> have to uniquely identify one
context. But since the Payload extension headers are demultiplexed context. But since the Payload extension headers are demultiplexed
without looking at the locators in the packet, the receiver MUST without looking at the locators in the packet, the receiver will need
allocate context tags that are unique for all its contexts. In to allocate context tags that are unique for all its contexts. The
addition, in order to minimize the reuse of context tags, the host context tag is a 47-bit number (the largest which can fit in an
SHOULD randomly cycle through the 2^47 context tag values,(e.g. 8-octet extension header).
following the guidelines described in [18]. The context tag is a 47-
bit number (the largest which can fit in an 8-octet extension
header).
The mechanism for detecting a loss of context state at the peer that The mechanism for detecting a loss of context state at the peer that
is currently proposed in this document assumes that the receiver can is currently proposed in this document assumes that the receiver can
tell the packets that need locator rewriting, even after it has lost tell the packets that need locator rewriting, even after it has lost
all state (e.g., due to a crash followed by a reboot). This is all state (e.g., due to a crash followed by a reboot). This is
achieved because after a rehoming event the packets that need achieved because after a rehoming event the packets that need
receive-side rewriting, carry the Payload extension header. receive-side rewriting, carry the Payload extension header.
Even though we do not overload the flow label field to carry the
context tag, any protocol (such as RSVP or NSIS) which signals
information about flows from the host stack to devices in the path,
need to be made aware of the locator agility introduced by a layer 3
shim, so that the signaling can be performed for the locator pairs
that are currently being used.
4.2 Context Forking 4.2 Context Forking
It has been asserted that it will be important for future ULPs, in It has been asserted that it will be important for future ULPs, in
particular, future transport protocols, to be able to control which particular, future transport protocols, to be able to control which
locator pairs are used for different communication. For instance, locator pairs are used for different communication. For instance,
host A and host B might communicate using both VoIP traffic and ftp host A and host B might communicate using both VoIP traffic and ftp
traffic, and those communications might benefit from using different traffic, and those communications might benefit from using different
locator pairs. However, the fundamental shim6 mechanism uses a locator pairs. However, the fundamental shim6 mechanism uses a
single current locator pair for each context, thus a single context single current locator pair for each context, thus a single context
can not accomplish this. can not accomplish this.
For this reason, the shim6 protocol supports the notion of context For this reason, the shim6 protocol supports the notion of context
forking. This is a mechanism by which a ULP can specify (using some forking. This is a mechanism by which a ULP can specify (using some
API not yet defined) that a context for e.g., the ULID pair <A1, B2> API not yet defined) that a context for e.g., the ULID pair <A1, B2>
should be forked into two contexts. In this case the forked-off should be forked into two contexts. In this case the forked-off
context will be assigned a non-zero Forked Instance Identifier, while context will be assigned a non-zero Forked Instance Identifier, while
the default context has FII zero. the default context has FII zero.
The Forked Instance Identifier is a 32-bit identifier which has no
semantics in the protocol other then being part of the tuple which
identifies the context. The hosts can allocate FIIs e.g., as
sequential numbers for any given ULID pair.
No other special considerations are needed in the shim6 protocol to No other special considerations are needed in the shim6 protocol to
handle forked contexts. handle forked contexts.
Note that forking as specified does NOT allow A to be able to tell B Note that forking as specified does NOT allow A to be able to tell B
that certain traffic (a 5-tuple?) should be forked for the reverse that certain traffic (a 5-tuple?) should be forked for the reverse
direction. The shim forking mechanism as specified applies only to direction. The shim6 forking mechanism as specified applies only to
the sending of ULP packets. If some ULP wants to fork for both the sending of ULP packets. If some ULP wants to fork for both
directions, it is up to the ULP to set this up, and then instruct the directions, it is up to the ULP to set this up, and then instruct the
shim at each end to transmit using the forked context. shim at each end to transmit using the forked context.
4.3 API Extensions 4.3 API Extensions
Several API extensions have been discussed for shim6, but their Several API extensions have been discussed for shim6, but their
actual specification is out of scope for this document. The simplest actual specification is out of scope for this document. The simplest
one would be to add a socket option to be able to have traffic bypass one would be to add a socket option to be able to have traffic bypass
the shim (not create any state, and not use any state created by the shim (not create any state, and not use any state created by
other traffic). This could be an IPV6_DONTSHIM socket option. Such other traffic). This could be an IPV6_DONTSHIM socket option. Such
an option would be useful for protocols, such as DNS, where the an option would be useful for protocols, such as DNS, where the
application has its own failover mechanism (multiple NS records in application has its own failover mechanism (multiple NS records in
the case of DNS) and using the shim could potentially add extra the case of DNS) and using the shim could potentially add extra
latency with no added benefits. latency with no added benefits.
Some other API extensions are discussed in Section 19 Some other API extensions are discussed in Appendix B
4.4 Securing shim6 4.4 Securing shim6
The mechanisms are secured using a combination of techniques: The mechanisms are secured using a combination of techniques:
o The HBA technique [7] for validating the locators to prevent an o The HBA technique [7] for verifying the locators to prevent an
attacker from redirecting the packet stream to somewhere else. attacker from redirecting the packet stream to somewhere else.
o Requiring a Reachability Probe+Reply before a new locator is used o Requiring a Reachability Probe+Reply before a new locator is used
as the destination, in order to prevent 3rd party flooding as the destination, in order to prevent 3rd party flooding
attacks. attacks.
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
skipping to change at page 21, line 20 skipping to change at page 21, line 23
establishment, carry the context tag assigned to the particular establishment, carry the context tag assigned to the particular
context. This implies that an attacker needs to discover that context. This implies that an attacker needs to discover that
context tag before being able to spoof any shim6 control message. context tag before being able to spoof any shim6 control message.
Such discovery probably requires to be along the path in order to Such discovery probably requires to be along the path in order to
be sniff the context tag value. The result is that through this be sniff the context tag value. The result is that through this
technique, the shim6 protocol is protected against off-path technique, the shim6 protocol is protected against off-path
attackers. attackers.
4.5 Overview of Shim Control Messages 4.5 Overview of Shim Control Messages
The shim 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 [26].] message. [The names of these messages are borrowed from HIP [25].]
R1bis and I2bis messages are defined, which are used to recover a R1bis and I2bis messages are defined, which are used to recover a
context after it has been lost. A R1bis message is sent when a shim6 context after it has been lost. A R1bis message is sent when a shim6
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 shim 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
dynamic. For this reason there is a Update message and Update dynamic. For this reason there is a Update Request and Update
acknowledgement, and a Locator List option. Acknowledgement messages, and a Locator List option.
Even when the list of locators is fixed, a host might determine that Even when the list of locators is fixed, a host might determine that
some preferences might have changed. For instance, it might some preferences might have changed. For instance, it might
determine that there is a locally visible failure that implies that determine that there is a locally visible failure that implies that
some locator(s) are no longer usable. This uses a Locator some locator(s) are no longer usable. This uses a Locator
Preferences option in the Update message. Preferences option in the Update Request message.
The mechanism for (un)reachability detection is called Force The mechanism for (un)reachability detection is called Forced
Bidirectional Communication (FBD). The FBD approach uses a Keepalive Bidirectional Communication (FBD). The FBD approach uses a Keepalive
message, which is sent when a host has received packets from the message, which is sent when a host has received packets from the
peer, but the ULP has not given the host an opportunity to send any peer, but the ULP has not given the host an opportunity to send any
payload packet to the peer. The message type is reserved in this packet to the peer. The message type is reserved in this document,
document, but the message format and processing rules are specified but the message format and processing rules are specified in [8].
in [9].
In addition, when the context is established and there is a failure In addition, when the context is established and there is a failure
there needs to be a way to probe the set of locator pairs to there needs to be a way to probe the set of locator pairs to
efficiently find a working pair. This document reserves an Probe efficiently find a working pair. This document reserves an Probe
message type, with the packet format and processing rules specified message type, with the packet format and processing rules specified
in [9]. in [8].
The above probe and keepalive messages assume we have an established The above probe and keepalive messages assume we have an established
ULID-pair context. However, communication might fail during the ULID-pair context. However, communication might fail during the
initial contact (that is, when the application or transport protocol initial contact (that is, when the application or transport protocol
is trying to setup some communication). This is handled using the is trying to setup some communication). This is handled using the
mechanisms in the ULP to try different address pairs as specified in mechanisms in the ULP to try different address pairs as specified in
[13] [14]. In the future versions of the protocol, and with a richer [12] [13]. In the future versions of the protocol, and with a richer
API between the ULP and the shim, the shim might be help optimize API between the ULP and the shim, the shim might be help optimize
discovering a working locator pair during initial contact. This is discovering a working locator pair during initial contact. This is
for further study. for further study.
4.6 Extension Header Order 4.6 Extension Header Order
Since the shim is placed between the IP endpoint sub-layer and the IP Since the shim is placed between the IP endpoint sub-layer and the IP
routing sub-layer in the host, the shim header MUST be placed before routing sub-layer in the host, the shim header will be placed before
any endpoint extension headers (fragmentation headers, destination any endpoint extension headers (fragmentation headers, destination
options header, AH, ESP), but after any routing related headers (hop- options header, AH, ESP), but after any routing related headers (hop-
by-hop extensions header, routing header, a destinations options by-hop extensions header, routing header, a destinations options
header which precedes a routing header). When tunneling is used, header which precedes a routing header). When tunneling is used,
whether IP-in-IP tunneling or the special form of tunneling that whether IP-in-IP tunneling or the special form of tunneling that
Mobile IPv6 uses (with Home Address Options and Routing header type Mobile IPv6 uses (with Home Address Options and Routing header type
2), there is a choice whether the shim applies inside the tunnel or 2), there is a choice whether the shim applies inside the tunnel or
outside the tunnel, which effects the location of the shim6 header. outside the tunnel, which effects the location of the shim6 header.
In most cases IP-in-IP tunnels are used as a routing technique, thus In most cases IP-in-IP tunnels are used as a routing technique, thus
it makes sense to apply them on the locators which means that the it makes sense to apply them on the locators which means that the
sender would insert the shim6 header after any IP-in-IP sender would insert the shim6 header after any IP-in-IP
encapsulation; this is what occurs naturally when routers apply IP- encapsulation; this is what occurs naturally when routers apply IP-
in-IP encapsulation. In any case the receiver behavior is well- in-IP encapsulation. Thus the packets would have:
defined; a receiver processes the extension headers in order. The
precise interaction between Mobile IPv6 and shim6 is for further
study, but it might make sense to have Mobile IPv6 operate on
locators as well, meaning that the shim would be layered on top of
the MIPv6 mechanism.
4.7 Locator Validation o Outer IP header
There are two separate aspects of locator validation. One is to o Inner IP header
verify that the locator is tied to the ULID, i.e., that the host
which "owns" the ULID also "owns" the locator. The shim6 protocol
uses the HBA and CGA techniques for doing this validation. The other
is to verify that the host is indeed reachable at the claimed
locator. Such verification is needed both to make sure communication
can proceed, but also to prevent 3rd party flooding attacks [20].
These different verifications happen at different times, since the o Shim6 extension header (if needed>
first might need to be performed before packets can be received by
the peer with the source locator in question, but the latter
verification is only needed before packets are sent to the locator.
Before a host can use a locator (different than the ULID) as the o ULP
source locator, it must know that the peer will accept packets with
that source locator as being part of this context. Thus the HBA and
CGA verification SHOULD be performed by the host before the host
acknowledges the new locator, by sending an Update Acknowledgement
message, or an R2 message.
Before a host can use a locator (different than the ULID) as the But the shim can also be used to create "shimmed tunnels" i.e., where
destination locator it MUST perform the HBA/CGA verification if this an IP-in-IP tunnel uses the shim to be able to switch the tunnel
was not performed before upon the reception of the locator set. In endpoint addresses between different locators. In such a case the
addition, it MUST verify that the ULID is indeed present at that packets would have:
locator. This verification is performed by doing a return-
routability test as part of the Probe sub-protocol [20].
If the verification method in the Locator List option is not o Outer IP header
supported by the host, or if the verification method is not
consistent with what it in the CGA Parameter Data Structure (e.g., o Shim6 extension header (if needed>
the PDS doesn't contain the multiprefix extension, and the
verification method says to use HBA), then the host MUST ignore the o Inner IP header
Locator List and the packet in which it is contained, and the host
SHOULD generates an ICMP parameter problem (type 4, code 0), with the o ULP
Pointer referencing the octet in the Verification method that was
found inconsistent. In any case, the receiver behavior is well-defined; a receiver
processes the extension headers in order. However, the precise
interaction between Mobile IPv6 and shim6 is for further study, but
it might make sense to have Mobile IPv6 operate on locators as well,
meaning that the shim would be layered on top of the MIPv6 mechanism.
5. Message Formats 5. Message Formats
The shim6 messages are all carried using a new IP protocol number [to The shim6 messages are all carried using a new IP protocol number [to
be assigned by IANA]. The shim6 messages have a common header, be assigned by IANA]. The shim6 messages have a common header,
defined below, with some fixed fields, followed by type specific defined below, with some fixed fields, followed by type specific
fields. fields.
The shim6 messages are structured as an IPv6 extension header since The shim6 messages are structured as an IPv6 extension header since
the Payload extension header is used to carry the ULP packets after a the Payload extension header is used to carry the ULP packets after a
skipping to change at page 24, line 44 skipping to change at page 24, line 44
8-octet units, not including the first 8 octets. 8-octet units, not including the first 8 octets.
P: A single bit to distinguish Payload extension headers P: A single bit to distinguish Payload extension headers
from control messages. from control messages.
5.2 Payload Extension Header Format 5.2 Payload Extension Header Format
The payload extension headers is used to carry ULP packets where the The payload extension headers is used to carry ULP packets where the
receiver must replace the content of the source and/or destination receiver must replace the content of the source and/or destination
fields in the IPv6 header before passing the packet to the ULP. Thus fields in the IPv6 header before passing the packet to the ULP. Thus
this extension header is included when the locators pair that is used this extension header is required when the locators pair that is used
is not the same as the ULID pair. is not the same as the ULID pair.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | 0 |1| | | Next Header | 0 |1| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Receiver Context Tag | | Receiver Context Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 31, line 16 skipping to change at page 31, line 16
message. message.
Reserved2: 32-bit field. Reserved for future use. Zero on Reserved2: 32-bit field. Reserved for future use. Zero on
transmit. MUST be ignored on receipt. (Needed to transmit. MUST be ignored on receipt. (Needed to
make the options start on a multiple of 8 octet make the options start on a multiple of 8 octet
boundary.) boundary.)
The following options are defined for this message: The following options are defined for this message:
Responder Validator: Variable length option. Just a copy of the Responder Validator: Variable length option. Just a copy of the
Validator option in the R1 message. Responder Validator option in the R1 message.
ULID pair: When the IPv6 source and destination addresses in the ULID pair: When the IPv6 source and destination addresses in the
IPv6 header does not match the ULID pair, this option IPv6 header does not match the ULID pair, this option
MUST be included. An example of this is when MUST be included. An example of this is when
recovering from a lost context. recovering from a lost context.
Forked Instance Identifier: When another instance of an existent Forked Instance Identifier: When another instance of an existent
context with the same ULID pair is being created, a context with the same ULID pair is being created, a
Forked Instance Identifier option is included to Forked Instance Identifier option is included to
distinguish this new instance from the existent one. distinguish this new instance from the existent one.
Locator list: Optionally sent when the initiator immediately wants Locator list: Optionally sent when the initiator immediately wants
to tell the responder its list of locators. When it to tell the responder its list of locators. When it
is sent, the necessary HBA/CGA information for is sent, the necessary HBA/CGA information for
validating the locator list MUST also be included. verifying the locator list MUST also be included.
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure: Included when the locator list is
included so the receiver can verify the locator list. included so the receiver can verify the locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for validation. CGA (and not HBA) for verification.
5.7 R2 Message Format 5.7 R2 Message Format
The R2 message is the fourth message in the context establishment The R2 message is the fourth message in the context establishment
exchange. The responder sends this in response to an I2 message. exchange. The responder sends this in response to an I2 message.
The R2 message is also used when both hosts send I1 messages at the The R2 message is also used when both hosts send I1 messages at the
same time and the I1 messages cross in flight. same time and the I1 messages cross in flight.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 32, line 47 skipping to change at page 32, line 47
has allocated for the context. has allocated for the context.
Initiator Nonce: 32-bit unsigned integer. Copied from the I2 Initiator Nonce: 32-bit unsigned integer. Copied from the I2
message. message.
The following options are defined for this message: The following options are defined for this message:
Locator List: Optionally sent when the responder immediately wants Locator List: Optionally sent when the responder immediately wants
to tell the initiator its list of locators. When it to tell the initiator its list of locators. When it
is sent, the necessary HBA/CGA information for is sent, the necessary HBA/CGA information for
validating the locator list MUST also be included. verifying the locator list MUST also be included.
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure: Included when the locator list is
included so the receiver can verify the locator list. included so the receiver can verify the locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for validation. CGA (and not HBA) for verification.
5.8 R1bis Message Format 5.8 R1bis Message Format
Should a host receive a packet with a shim Payload extension header Should a host receive a packet with a shim Payload extension header
or shim6 control message with type code 64-127 (such as an Update or or shim6 control message with type code 64-127 (such as an Update or
Probe message), and the host does not have any context state for the Probe message), and the host does not have any context state for the
locators (in the IPv6 source and destination fields) and the context received context tag, then it will generate a R1bis message.
tag, then it will generate a R1bis packet.
This packet allows the sender of the packet referring to the non- This message allows the sender of the packet referring to the non-
existent context to re-establish the context with a reduced packet existent context to re-establish the context with a reduced context
exchange. Upon the reception of the R1bis packet, the receiver can establishment exchange. Upon the reception of the R1bis message, the
proceed reestablishing the lost context by directly sending an I2bis receiver can proceed reestablishing the lost context by directly
message. sending an I2bis message.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 59 | Hdr Ext Len |0| Type = 5 | Reserved1 |0| | 59 | Hdr Ext Len |0| Type = 5 | Reserved1 |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |R| | | Checksum |R| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Packet Context Tag | | Packet Context Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 34, line 12 skipping to change at page 34, line 12
Type: 5 Type: 5
Reserved1: 7-bit field. Reserved for future use. Zero on Reserved1: 7-bit field. Reserved for future use. Zero on
transmit. MUST be ignored on receipt. transmit. MUST be ignored on receipt.
R: 1-bit field. Reserved for future use. Zero on R: 1-bit field. Reserved for future use. Zero on
transmit. MUST be ignored on receipt. transmit. MUST be ignored on receipt.
Packet Context Tag: 47-bit unsigned integer. The context tag Packet Context Tag: 47-bit unsigned integer. The context tag
contained in the received packet that triggered the contained in the received packet that triggered the
generation of the R1bis packet. generation of the R1bis message.
Responder Nonce: 32-bit unsigned integer. A number picked by the Responder Nonce: 32-bit unsigned integer. A number picked by the
responder which the initiator will return in the I2bis responder which the initiator will return in the I2bis
message. message.
The following options are defined for this message: The following options are defined for this message:
Responder Validator: Variable length option. Typically a hash Responder Validator: Variable length option. Typically a hash
generated by the responder, which the responder uses generated by the responder, which the responder uses
together with the Responder Nonce value to verify that together with the Responder Nonce value to verify that
skipping to change at page 36, line 19 skipping to change at page 36, line 19
transmit. MUST be ignored on receipt. (Note that 17 transmit. MUST be ignored on receipt. (Note that 17
bits are not sufficient since the options need start bits are not sufficient since the options need start
on a multiple of 8 octet boundary.) on a multiple of 8 octet boundary.)
Packet Context Tag: 47-bit unsigned integer. Copied from the Packet Packet Context Tag: 47-bit unsigned integer. Copied from the Packet
Context Tag contained in the received R1bis. Context Tag contained in the received R1bis.
The following options are defined for this message: The following options are defined for this message:
Responder Validator: Variable length option. Just a copy of the Responder Validator: Variable length option. Just a copy of the
Validator option in the R1bis message. Responder Validator option in the R1bis message.
ULID pair: When the IPv6 source and destination addresses in the ULID pair: When the IPv6 source and destination addresses in the
IPv6 header does not match the ULID pair, this option IPv6 header does not match the ULID pair, this option
MUST be included. MUST be included.
Forked Instance Identifier: When another instance of an existent Forked Instance Identifier: When another instance of an existent
context with the same ULID pair is being created, a context with the same ULID pair is being created, a
Forked Instance Identifier option is included to Forked Instance Identifier option is included to
distinguish this new instance from the existent one. distinguish this new instance from the existent one.
Locator list: Optionally sent when the initiator immediately wants Locator list: Optionally sent when the initiator immediately wants
to tell the responder its list of locators. When it to tell the responder its list of locators. When it
is sent, the necessary HBA/CGA information for is sent, the necessary HBA/CGA information for
validating the locator list MUST also be included. verifying the locator list MUST also be included.
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure: Included when the locator list is
included so the receiver can verify the locator list. included so the receiver can verify the locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for validation. CGA (and not HBA) for verification.
5.10 Update Request Message Format 5.10 Update Request Message Format
The Update Request Message is used to update either the list or The Update Request Message is used to update either the list of
locators, the locator preferences, and both. When the list of locators, the locator preferences, and both. When the list of
locators is updated, the message also contains the option(s) locators is updated, the message also contains the option(s)
necessary for HBA/CGA to secure this. The basic sanity check that necessary for HBA/CGA to secure this. The basic sanity check that
prevents off-path attackers from generating bogus updates is the prevents off-path attackers from generating bogus updates is the
context tag in the message. context tag in the message.
The update message contains options (the Locator List and the Locator The update message contains options (the Locator List and the Locator
Preferences) that, when included, completely replace the previous Preferences) that, when included, completely replace the previous
locator list and locator preferences, respectively. Thus there is no locator list and locator preferences, respectively. Thus there is no
mechanism to just send deltas to the locator list. mechanism to just send deltas to the locator list.
skipping to change at page 38, line 12 skipping to change at page 38, line 12
The following options are defined for this message: The following options are defined for this message:
Locator List: The list of the sender's (new) locators. The locators Locator List: The list of the sender's (new) locators. The locators
might be unchanged and only the preferences have might be unchanged and only the preferences have
changed. changed.
Locator Preferences: Optionally sent when the locators don't all have Locator Preferences: Optionally sent when the locators don't all have
equal preference. equal preference.
CGA Parameter Data Structure: Included when the locator list is CGA Parameter Data Structure (PDS): Included when the locator list is
included and the PDS was not included in the included and the PDS was not included in the
I2/I2bis/R2 messages, so the receiver can verify the I2/I2bis/R2 messages, so the receiver can verify the
locator list. locator list.
CGA Signature: Included when the some of the locators in the list use CGA Signature: Included when the some of the locators in the list use
CGA (and not HBA) for validation. CGA (and not HBA) for verification.
5.11 Update Acknowledgement Message Format 5.11 Update Acknowledgement Message Format
This message is sent in response to a Update Request message. It This message is sent in response to a Update Request message. It
implies that the Update Request has been received, and that any new implies that the Update Request has been received, and that any new
locators in the Update Request can now be used as the source locators locators in the Update Request can now be used as the source locators
of packets. But it does not imply that the (new) locators have been of packets. But it does not imply that the (new) locators have been
verified to be used as a destination, since the host might defer the verified to be used as a destination, since the host might defer the
verification of a locator until it sees a need to use a locator as verification of a locator until it sees a need to use a locator as
the destination. the destination.
skipping to change at page 39, line 26 skipping to change at page 39, line 26
Receiver Context Tag: 47-bit field. The Context Tag the receiver has Receiver Context Tag: 47-bit field. The Context Tag the receiver has
allocated for the context. allocated for the context.
Request Nonce: 32-bit unsigned integer. Copied from the Update Request Nonce: 32-bit unsigned integer. Copied from the Update
Request message. Request message.
No options are currently defined for this message. No options are currently defined for this message.
5.12 Keepalive Message Format 5.12 Keepalive Message Format
This message format is defined in [9]. This message format is defined in [8].
The message is used to ensure that when a peer is sending ULP packets The message is used to ensure that when a peer is sending ULP packets
on a context, it always receives some packets in the reverse on a context, it always receives some packets in the reverse
direction. When the ULP is sending bidirectional traffic, no extra direction. When the ULP is sending bidirectional traffic, no extra
packets need to be inserted. But for a unidirectional ULP traffic packets need to be inserted. But for a unidirectional ULP traffic
pattern, the shim will send back some Keepalive messages when it is pattern, the shim will send back some Keepalive messages when it is
receiving ULP packets. receiving ULP packets.
5.13 Probe Message Format 5.13 Probe Message Format
This message and its semantics are defined in [9]. This message and its semantics are defined in [8].
The idea behind that mechanism is to be able to handle the case when The idea behind that mechanism is to be able to handle the case when
one locator pair works in from A to B, and another locator pair works one locator pair works in from A to B, and another locator pair works
from B to A, but there is no locator pair which works in both from B to A, but there is no locator pair which works in both
directions. The protocol mechanism is that as A is sending probe directions. The protocol mechanism is that as A is sending probe
messages to B, B will observe which locator pairs it has received messages to B, B will observe which locator pairs it has received
from and report that back in probe messages it is sending to A. from and report that back in probe messages it is sending to A.
5.14 Option Formats 5.14 Option Formats
The format of the options is a snapshot of the current HIP option The format of the options is a snapshot of the current HIP option
format [26]. However, there is no intend to track any changes to the format [25]. However, there is no intention to track any changes to
HIP option format, nor is there an intent to use the same name space the HIP option format, nor is there an intent to use the same name
for the option type values. But using the same format will hopefully space for the option type values. But using the same format will
make it easier to import HIP capabilities into shim6 as extensions to hopefully make it easier to import HIP capabilities into shim6 as
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
added padding bytes MUST be zeroed by the sender, and their values added padding bytes MUST be zeroed by the sender, and their values
SHOULD NOT be checked by the receiver. SHOULD NOT be checked by the receiver.
Consequently, the Length field indicates the length of the Contents Consequently, the Length field indicates the length of the Contents
skipping to change at page 41, line 8 skipping to change at page 41, line 8
Length: Length of the Contents, in bytes. Length: Length of the Contents, in bytes.
Contents: Parameter specific, defined by Type. Contents: Parameter specific, defined by Type.
Padding: Padding, 0-7 bytes, added if needed. Padding: Padding, 0-7 bytes, added if needed.
+------+---------------------------------+ +------+---------------------------------+
| Type | Option Name | | Type | Option Name |
+------+---------------------------------+ +------+---------------------------------+
| 1 | Validator | | 1 | Responder Validator |
| | | | | |
| 2 | Locator List | | 2 | Locator List |
| | | | | |
| 3 | Locator Preferences | | 3 | Locator Preferences |
| | | | | |
| 4 | CGA Parameter Data Structure | | 4 | CGA Parameter Data Structure |
| | | | | |
| 5 | CGA Signature | | 5 | CGA Signature |
| | | | | |
| 6 | ULID Pair | | 6 | ULID Pair |
skipping to change at page 41, line 31 skipping to change at page 41, line 31
| | | | | |
| 10 | Probe Option | | 10 | Probe Option |
| | | | | |
| 11 | Reachability Option | | 11 | Reachability Option |
| | | | | |
| 12 | Payload Reception Report Option | | 12 | Payload Reception Report Option |
+------+---------------------------------+ +------+---------------------------------+
Table 2 Table 2
5.14.1 Validator Option Format 5.14.1 Responder Validator Option Format
The responder can choose exactly what input uses to compute the The responder can choose exactly what input uses to compute the
validator, and what one-way function (MD5, SHA1) it uses, as long as validator, and what one-way function (MD5, SHA1) it uses, as long as
the responder can verify that the validator it receives back in the the responder can check that the validator it receives back in the I2
I2 or I2bis message is indeed one that: or I2bis message is indeed one that:
1)- it computed, 1)- it computed,
2)- it computed for the particular context, and 2)- it computed for the particular context, and
3)- that it isn't a replayed I2/I2bis message. 3)- that it isn't a replayed I2/I2bis message.
Some suggestions on how to generate the validators are captured in Some suggestions on how to generate the validators are captured in
Section 7.7.1 and Section 7.14.1. Section 7.9.1 and Section 7.16.1.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 |0| Length | | Type = 1 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Validator ~ ~ Validator ~
~ +-+-+-+-+-+-+-+-+ ~ +-+-+-+-+-+-+-+-+
~ | Padding | ~ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 43, line 51 skipping to change at page 43, line 51
Table 3 Table 3
5.14.3 Locator Preferences Option Format 5.14.3 Locator Preferences Option Format
The Locator Preferences option can have some flags to indicate The Locator Preferences option can have some flags to indicate
whether or not a locator is known to work. In addition, the sender whether or not a locator is known to work. In addition, the sender
can include a notion of preferences. It might make sense to define can include a notion of preferences. It might make sense to define
"preferences" as a combination of priority and weight the same way "preferences" as a combination of priority and weight the same way
that DNS SRV records has such information. The priority would that DNS SRV records has such information. The priority would
provide a way to rank the locators, and within a given priority, the provide a way to rank the locators, and within a given priority, the
weight would provide a way to do some load sharing. See [10] for how weight would provide a way to do some load sharing. See [9] for how
SRV defines the interaction of priority and weight. SRV defines the interaction of priority and weight.
The minimum notion of preferences we need is to be able to indicate The minimum notion of preferences we need is to be able to indicate
that a locator is "dead". We can handle this using a single octet that a locator is "dead". We can handle this using a single octet
flag for each locator. flag for each locator.
We can extend that by carrying a larger "element" for each locator. We can extend that by carrying a larger "element" for each locator.
This document presently also defines 2-octet and 3-octet elements, This document presently also defines 2-octet and 3-octet elements,
and we can add more information by having even larger elements if and we can add more information by having even larger elements if
need be. need be.
skipping to change at page 44, line 44 skipping to change at page 44, line 44
Case of Element Len = 1 is depicted. Case of Element Len = 1 is depicted.
Fields: Fields:
Locator List Generation: 32-bit unsigned integer. Indicates a Locator List Generation: 32-bit unsigned integer. Indicates a
generation number for the locator list to which the generation number for the locator list to which the
elements should apply. elements should apply.
Element Len: 8-bit unsigned integer. The length in octets of each Element Len: 8-bit unsigned integer. The length in octets of each
element. This draft defines the cases when the length element. This specification defines the cases when
is 1, 2, or 3. the length is 1, 2, or 3.
Element[i]: A field with a number of octets defined by the Element Element[i]: A field with a number of octets defined by the Element
Len field. Provides preferences for the i'th locator Len field. Provides preferences for the i'th locator
in the Locator List option that is in use. in the Locator List option that is in use.
Padding: Padding, 0-7 bytes, added if needed. See Padding: Padding, 0-7 bytes, added if needed. See
Section 5.14. Section 5.14.
When the Element length equals one, then the element consists of only When the Element length equals one, then the element consists of only
a one octet flags field. The currently defined set of flags are: a one octet flags field. The currently defined set of flags are:
skipping to change at page 45, line 29 skipping to change at page 45, line 29
When the Element length equals two, then the element consists of a 1 When the Element length equals two, then the element consists of a 1
octet flags field followed by a 1 octet priority field. The priority octet flags field followed by a 1 octet priority field. The priority
has the same semantics as the priority in DNS SRV records. has the same semantics as the priority in DNS SRV records.
When the Element length equals three, then the element consists of a When the Element length equals three, then the element consists of a
1 octet flags field followed by a 1 octet priority field, and a 1 1 octet flags field followed by a 1 octet priority field, and a 1
octet weight field. The weight has the same semantics as the weight octet weight field. The weight has the same semantics as the weight
in DNS SRV records. in DNS SRV records.
This document doesn't specify the format when the Element length is
more than three, except that any such formats MUST be defined so that
the first three octets are the same as in the above case, that is, a
of a 1 octet flags field followed by a 1 octet priority field, and a
1 octet weight field.
5.14.4 CGA Parameter Data Structure Option Format 5.14.4 CGA Parameter Data Structure Option Format
This option contains the CGA parameter data structure (hereafter This option contains the CGA Parameter Data Structure (PDS). When
called the PDS). When HBA is used to validate the locators, the PDS HBA is used to verify the locators, the PDS contains the HBA
contains the HBA multiprefix extension. When CGA is used to validate multiprefix extension. When CGA is used to verify the locators, in
the locators, in addition to the CGA PDS, the signature will need to addition to the PDS option, the host also needs to include the
be included as a CGA Signature option. signature in the form of a CGA Signature option.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 4 |0| Length | | Type = 4 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ CGA Parameter Data Structure ~ ~ CGA Parameter Data Structure ~
~ +-+-+-+-+-+-+-+-+ ~ +-+-+-+-+-+-+-+-+
~ | Padding | ~ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 46, line 10 skipping to change at page 46, line 14
Fields: Fields:
CGA Parameter Data Structure: Variable length content. Content CGA Parameter Data Structure: Variable length content. Content
defined in [6] and [7]. defined in [6] and [7].
Padding: Padding, 0-7 bytes, added if needed. See Padding: Padding, 0-7 bytes, added if needed. See
Section 5.14. Section 5.14.
5.14.5 CGA Signature Option Format 5.14.5 CGA Signature Option Format
When CGA is used for validation of one or more of the locators in the When CGA is used for verification of one or more of the locators in
Locator List option, then the message in question will need to the Locator List option, then the message in question will need to
contain this option. contain this option.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 5 |0| Length | | Type = 5 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ CGA Signature ~ ~ CGA Signature ~
~ +-+-+-+-+-+-+-+-+ ~ +-+-+-+-+-+-+-+-+
~ | Padding | ~ | Padding |
skipping to change at page 46, line 39 skipping to change at page 46, line 43
1. The 128-bit CGA Message Type tag [CGA] value for 1. The 128-bit CGA Message Type tag [CGA] value for
SHIM6, 0x4A 30 5662 4858 574B 3655 416F 506A 6D48. SHIM6, 0x4A 30 5662 4858 574B 3655 416F 506A 6D48.
(The tag value has been generated randomly by the (The tag value has been generated randomly by the
editor of this specification.). editor of this specification.).
2. The Locator List Generation value of the 2. The Locator List Generation value of the
correspondent Locator List Option. correspondent Locator List Option.
3. The subset of locators included in the 3. The subset of locators included in the
correspondent Locator List Option which validation correspondent Locator List Option which
method is set to CGA. The locators MUST be verification method is set to CGA. The locators
included in the order they are listed in the MUST be included in the order they are listed in
Locator List Option. the Locator List Option.
Padding: Padding, 0-7 bytes, added if needed. See Padding: Padding, 0-7 bytes, added if needed. See
Section 5.14. Section 5.14.
5.14.6 ULID Pair Option Format 5.14.6 ULID Pair Option Format
I1, I2, and I2bis messages MUST contain the ULID pair; normally this I1, I2, and I2bis messages MUST contain the ULID pair; normally this
is in the IPv6 source and destination fields. In case that the ULID is in the IPv6 source and destination fields. In case that the ULID
for the context differ from the address pair included in the source for the context differ from the address pair included in the source
and destination address fields of the IPv6 packet used to carry the and destination address fields of the IPv6 packet used to carry the
skipping to change at page 48, line 10 skipping to change at page 48, line 22
| Forked Instance Identifier | | Forked Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields: Fields:
Forked Instance Identifier: 32-bit field containing the identifier of Forked Instance Identifier: 32-bit field containing the identifier of
the particular forked instance. the particular forked instance.
5.14.8 Probe Option Format 5.14.8 Probe Option Format
This option is defined in [9]. This option is defined in [8].
5.14.9 Reachability Option Format 5.14.9 Reachability Option Format
This option is defined in [9]. This option is defined in [8].
5.14.10 Payload Reception Report Option Format 5.14.10 Payload Reception Report Option Format
This option is defined in [9]. This option is defined in [8].
6. Conceptual Model of a Host 6. Conceptual Model of a Host
This section describes a conceptual model of one possible data This section describes a conceptual model of one possible data
structure organization that hosts will maintain for the purposes of structure organization that hosts will maintain for the purposes of
shim6. The described organization is provided to facilitate the shim6. The described organization is provided to facilitate the
explanation of how the shim6 protocol should behave. This document explanation of how the shim6 protocol should behave. This document
does not mandate that implementations adhere to this model as long as does not mandate that implementations adhere to this model as long as
their external behavior is consistent with that described in this their external behavior is consistent with that described in this
document. document.
skipping to change at page 49, line 32 skipping to change at page 49, line 32
o The peer ULID; ULID(peer) o The peer ULID; ULID(peer)
o The local ULID; ULID(local) o The local ULID; ULID(local)
o The Forked Instance Identifier; FII. This is zero for the default o The Forked Instance Identifier; FII. This is zero for the default
context i.e., when there is no forking. context i.e., when there is no forking.
o The list of peer locators, with their preferences; Ls(peer) o The list of peer locators, with their preferences; Ls(peer)
o The generation number for the most recently received, validated o The generation number for the most recently received, verified
peer locator list. peer locator list.
o For each peer locator, the validation method to use (from the o For each peer locator, the verification method to use (from the
Locator List option). Locator List option).
o For each peer locator, a bit whether it has been validated using o For each peer locator, a bit whether it has been verified using
HBA or CGA, and a bit whether the locator has been probed to HBA or CGA, and a bit whether the locator has been probed to
verify that the ULID is present at that location. verify that the ULID is present at that location.
o The preferred peer locator - used as destination; Lp(peer) o The preferred peer locator - used as destination; Lp(peer)
o The set of local locators and the preferences; Ls(local) o The set of local locators and the preferences; Ls(local)
o The generation number for the most recently sent Locator List o The generation number for the most recently sent Locator List
option. option.
skipping to change at page 50, line 14 skipping to change at page 50, line 14
o The context to expect in received control messages and payload o The context to expect in received control messages and payload
extension headers - allocated by the local host; CT(local) extension headers - allocated by the local host; CT(local)
o Timers for retransmission of the messages during context o Timers for retransmission of the messages during context
establishment and update messages. establishment and update messages.
o Depending how an implementation determines whether a context is o Depending how an implementation determines whether a context is
still in use, there might be a need to track the last time a still in use, there might be a need to track the last time a
packet was sent/received using the context. packet was sent/received using the context.
o Reachability state for the locator pairs as specified in [9]. o Reachability state for the locator pairs as specified in [8].
o During pair exploration, information about the probe messages that o During pair exploration, information about the probe messages that
have been sent and received as specified in [9]. have been sent and received as specified in [8].
6.2 Context States 6.2 Context States
The states that are used to describe the shim6 protocol are as The states that are used to describe the shim6 protocol are as
follows: follows:
+---------------------+---------------------------------------------+ +---------------------+---------------------------------------------+
| State | Explanation | | State | Explanation |
+---------------------+---------------------------------------------+ +---------------------+---------------------------------------------+
| IDLE | State machine start | | IDLE | State machine start |
skipping to change at page 52, line 17 skipping to change at page 52, line 17
ULID-pair contexts are established using a 4-way exchange, which ULID-pair contexts are established using a 4-way exchange, which
allows the responder to avoid creating state on the first packet. As allows the responder to avoid creating state on the first packet. As
part of this exchange each end allocates a context tag, and it shares part of this exchange each end allocates a context tag, and it shares
this context tag and its set of locators with the peer. this context tag and its set of locators with the peer.
In some cases the 4-way exchange is not necessary, for instance when In some cases the 4-way exchange is not necessary, for instance when
both ends try to setup the context at the same time, or when both ends try to setup the context at the same time, or when
recovering from a context that has been garbage collected or lost at recovering from a context that has been garbage collected or lost at
one of the hosts. one of the hosts.
7.1 Normal context establishment 7.1 Uniqness of Context Tags
As part of establishing a new context, each host has to assign a
unique context tag. Since the Payload Extension headers are
demultiplexed based solely on the context tag value (without using
the locators), the context tag MUST be unique for each context.
In addition, in order to minimize the reuse of context tags, the host
SHOULD randomly cycle through the 2^47 context tag values,(e.g.
following the guidelines described in [17]).
7.2 Locator Verification
The peer's locators might need to be verified during context
establishment as well as when handling locator updates in Section 10.
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
which "owns" the ULID is also the one that is claiming the locator
"ownership". The shim6 protocol uses the HBA or CGA techniques for
doing this verification. The other is to verify that the host is
indeed reachable at the claimed locator. Such verification is needed
both to make sure communication can proceed, but also to prevent 3rd
party flooding attacks [19]. These different verifications happen at
different times, since the first might need to be performed before
packets can be received by the peer with the source locator in
question, but the latter verification is only needed before packets
are sent to the locator.
Before a host can use a locator (different than the ULID) as the
source locator, it must know that the peer will accept packets with
that source locator as being part of this context. Thus the HBA/CGA
verification SHOULD be performed by the host before the host
acknowledges the new locator, by sending an Update Acknowledgement
message, or an R2 message.
Before a host can use a locator (different than the ULID) as the
destination locator it MUST perform the HBA/CGA verification if this
was not performed before upon the reception of the locator set. In
addition, it MUST verify that the ULID is indeed present at that
locator. This verification is performed by doing a return-
routability test as part of the Probe sub-protocol [8].
If the verification method in the Locator List option is not
supported by the host, or if the verification method is not
consistent with the CGA Parameter Data Structure (e.g., the Parameter
Data Structure doesn't contain the multiprefix extension, and the
verification method says to use HBA), then the host MUST ignore the
Locator List and the message in which it is contained, and the host
SHOULD generates an ICMP parameter problem (type 4, code 0), with the
Pointer referencing the octet in the Verification method that was
found inconsistent.
7.3 Normal context establishment
The normal context establishment consists of a 4 message exchange in The normal context establishment consists of a 4 message exchange in
the order of I1, R1, I2, R2. the order of I1, R1, I2, R2 as can be seen in Figure 24.
Initiator Responder Initiator Responder
IDLE IDLE IDLE IDLE
------------- I1 --------------> ------------- I1 -------------->
I1-SENT I1-SENT
<------------ R1 --------------- <------------ R1 ---------------
IDLE IDLE
------------- I2 --------------> ------------- I2 -------------->
I2-SENT I2-SENT
<------------ R2 --------------- <------------ R2 ---------------
ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED
Figure 24 Figure 24: Normal context establishment
7.2 Concurrent context establishment 7.4 Concurrent context establishment
When both ends try to initiate a context for the same ULID pair, then When both ends try to initiate a context for the same ULID pair, then
we might end up with crossing I1 messages. Alternatively, since no we might end up with crossing I1 messages. Alternatively, since no
state is created when receiving the I1, a host might send a I1 after state is created when receiving the I1, a host might send a I1 after
having sent a R1 message. having sent a R1 message.
Since a host remembers that it has sent an I1, it can respond to an Since a host remembers that it has sent an I1, it can respond to an
I1 from the peer (for the same ULID), with a R2. Such behavior is I1 from the peer (for the same ULID-pair), with a R2, resulting in
needed to correctly respond to retransmitted I1 messages, which might the message exchange shown in Figure 25. Such behavior is needed for
be needed if the R2 message has been lost. other reasons such as to correctly respond to retransmitted I1
messages, which occur when the R2 message has been lost.
Host A Host B Host A Host B
IDLE IDLE IDLE IDLE
-\ -\
I1-SENT---\ I1-SENT---\
---\ /--- ---\ /---
--- I1 ---\ /--- I1-SENT --- I1 ---\ /--- I1-SENT
---\ ---\
/--- I1 ---/ ---\ /--- I1 ---/ ---\
skipping to change at page 53, line 27 skipping to change at page 54, line 28
-\ -\
I1-SENT---\ I1-SENT---\
---\ /--- ---\ /---
--- R2 ---\ /--- I1-SENT --- R2 ---\ /--- I1-SENT
---\ ---\
/--- R2 ---/ ---\ /--- R2 ---/ ---\
/--- --> /--- -->
<--- ESTABLISHED <--- ESTABLISHED
ESTABLISHED ESTABLISHED
Figure 25 Figure 25: Crossing I1 messages
If a host has received an I1 and sent an R1, it has no state to If a host has received an I1 and sent an R1, it has no state to
remember this. Thus if the ULP on the host sends down packets, this remember this. Thus if the ULP on the host sends down packets, this
might trigger the host to send an I1 message itself. Thus while one might trigger the host to send an I1 message itself. Thus while one
end is sending an I1 the other is sending an I2. end is sending an I1 the other is sending an I2 as can be seen in
Figure 26.
Host A Host B Host A Host B
IDLE IDLE IDLE IDLE
-\ -\
---\ ---\
I1-SENT ---\ I1-SENT ---\
--- I1 ---\ --- I1 ---\
---\ ---\
---\ ---\
skipping to change at page 54, line 30 skipping to change at page 55, line 30
/--- /---
<--- <---
-\ -\
I2-SENT---\ I2-SENT---\
---\ /--- ---\ /---
--- I2---\ /--- I1-SENT --- I2---\ /--- I1-SENT
---\ ---\
/--- I1 ---/ ---\ /--- I1 ---/ ---\
/--- --> /--- -->
<--- I1-SENT <--- ESTABLISHED
-\ -\
I2-SENT---\ I2-SENT---\
---\ /--- ---\ /---
--- R2 ---\ /--- --- R2 ---\ /---
---\ ---\
/--- R2 ---/ ---\ /--- R2 ---/ ---\
/--- --> /--- -->
<--- ESTABLISHED <--- ESTABLISHED
ESTABLISHED ESTABLISHED
Figure 26 Figure 26: Crossing I2 and I1
7.3 Context recovery 7.5 Context recovery
Due to garbage collection, we can end up with one end having and Due to garbage collection, we can end up with one end having and
using the context state, and the other end not having any state. We using the context state, and the other end not having any state. We
need to be able to recover this state at the end that has lost it, need to be able to recover this state at the end that has lost it,
before we can use it. before we can use it.
This need can arise in the following cases: This need can arise in the following cases:
o The communication is working using the ULID pair as the locator o The communication is working using the ULID pair as the locator
pair, but a problem arises, and the end that has retained the pair, but a problem arises, and the end that has retained the
context state decides to probe alternate locator pairs. context state decides to probe alternate locator pairs.
o The communication is working using a locator pair that is not the o The communication is working using a locator pair that is not the
ULID pair, hence the ULP packets sent from a peer that has ULID pair, hence the ULP packets sent from a peer that has
retained the context state use the shim payload extension header. retained the context state use the shim6 Payload extension header.
o The host that retained the state sends a control message (e.g. an o The host that retained the state sends a control message (e.g. an
UPDATE message). Update Request message).
In all the cases the result is that the peer without state receives a In all the cases the result is that the peer without state receives a
shim message for which it has to context for the context tag. shim message for which it has to context for the context tag.
In all of those cases we can recover the context by having the node In all of those cases we can recover the context by having the node
which doesn't have a context state, send back an R1bis message, and which doesn't have a context state, send back an R1bis message, and
have then complete the recovery with a I2bis and R2 message. have then complete the recovery with a I2bis and R2 message as can be
seen in Figure 27.
Host A Host B Host A Host B
Context for Context for
CT(peer)=X Discards context for CT(peer)=X Discards context for
CT(local)=X CT(local)=X
ESTABLISHED IDLE ESTABLISHED IDLE
---- payload, probe, etc. -----> No context state ---- payload, probe, etc. -----> No context state
for CT(local)=X for CT(local)=X
<------------ R1bis ------------ <------------ R1bis ------------
IDLE IDLE
------------- I2bis -----------> ------------- I2bis ----------->
I2BIS_SENT I2BIS_SENT
<------------ R2 --------------- <------------ R2 ---------------
ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED
Figure 27 Figure 27: Context loss at receiver
If one end has garbage collected or lost the context state, it might If one end has garbage collected or lost the context state, it might
try to create a new context state (for the same ULID pair), by try to create a new context state (for the same ULID pair), by
sending an I1 message. The peer (that still has the context state) sending an I1 message. The peer (that still has the context state)
can simply reply with an R2 message in this case. will reply with an R1 message and the full 4-way exchange will be
performed again in this case as can be seen in Figure 28.
Host A Host B Host A Host B
Context for Context for
CT(peer)=X Discards context for CT(peer)=X Discards context for
ULIDs A1, B1 CT(local)=X ULIDs A1, B1 CT(local)=X
ESTABLISHED IDLE ESTABLISHED IDLE
Finds <------------ I1 --------------- Tries to setup Finds <------------ I1 --------------- Tries to setup
existing for ULIDs A1, B1 existing for ULIDs A1, B1
context I1-SENT context,
but CT(peer) I1-SENT
doesn't match
------------- R1 --------------->
Left old context
in ESTABLISHED
<------------ I2 ---------------
Recreate context
with new CT(peer) I2-SENT
and Ls(peer).
ESTABLISHED
------------- R2 --------------> ------------- R2 -------------->
ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED
Figure 28 Figure 28: Context loss at sender
7.4 Context confusion 7.6 Context confusion
Since each end might garbage collect the context state we can have Since each end might garbage collect the context state we can have
the case when one end has retained the context state and tries to use the case when one end has retained the context state and tries to use
it, while the other end has lost the state. We discussed this in the it, while the other end has lost the state. We discussed this in the
previous section on recovery. But for the same reasons, when one previous section on recovery. But for the same reasons, when one
host retains context tag X for ULID pair <A1, B1>, the other end host retains context tag X as CT(peer) for ULID pair <A1, B1>, the
might end up allocating that context tag for another ULID pair, e.g., other end might end up allocating that context tag as CT(local) for
<A3, B1> between the same hosts. In this case we can not use the another ULID pair, e.g., <A3, B1> between the same hosts. In this
recovery mechanisms since there needs to be separate context tags for case we can not use the recovery mechanisms since there needs to be
the two ULID pairs. separate context tags for the two ULID pairs.
This type of "confusion" can be observed in two cases (assuming it is This type of "confusion" can be observed in two cases (assuming it is
A that has retained the state and B has dropped it): A that has retained the state and B has dropped it):
o B decides to create a context for ULID pair <A3, B1>, and o B decides to create a context for ULID pair <A3, B1>, and
allocates X as its context tag for this, and sends an I1 to A. allocates X as its context tag for this, and sends an I1 to A.
o A decides to create a context for ULID pair <A3, B1>, and starts o A decides to create a context for ULID pair <A3, B1>, and starts
the exchange by sending I1 to B. When B receives the I2 message, the exchange by sending I1 to B. When B receives the I2 message,
it allocates X as the context tag for this context. it allocates X as the context tag for this context.
skipping to change at page 57, line 15 skipping to change at page 58, line 29
The requirement is that the old context which used the context tag The requirement is that the old context which used the context tag
MUST be removed; it can no longer be used to send packets. Thus A MUST be removed; it can no longer be used to send packets. Thus A
would forcibly remove the context state for <A1, B1, X>, so that it would forcibly remove the context state for <A1, B1, X>, so that it
can accept the new context for <A3, B1, X>. An implementation MAY can accept the new context for <A3, B1, X>. An implementation MAY
re-create a context to replace the one that was removed; in this case re-create a context to replace the one that was removed; in this case
for <A1, B1>. The normal I1, R1, I2, R2 establishment exchange would for <A1, B1>. The normal I1, R1, I2, R2 establishment exchange would
then pick unique context tags for that replacement context. This re- then pick unique context tags for that replacement context. This re-
creation is OPTIONAL, but might be useful when there is ULP creation is OPTIONAL, but might be useful when there is ULP
communication which is using the ULID pair whose context was removed. communication which is using the ULID pair whose context was removed.
7.5 Sending I1 messages Note that an I1 message with a duplicate context tag should not cause
the removal of the old context state; this operation needs to be
deferred until the reception of the I2 message.
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.
7.6 Retransmitting I1 messages 7.8 Retransmitting I1 messages
If the host does not receive an I2 or R2 message in response to the If the host does not receive an I2 or R2 message in response to the
I1 message after I1_TIMEOUT time, then it needs to retransmit the I1 I1 message after I1_TIMEOUT time, then it needs to retransmit the I1
message. The retransmissions should use a retransmission timer with message. The retransmissions should use a retransmission timer with
binary exponential backoff to avoid creating congestion issues for binary exponential backoff to avoid creating congestion issues for
the network when lots of hosts perform I1 retransmissions. Also, the the network when lots of hosts perform I1 retransmissions. Also, the
actual timeout value should be randomized between 0.5 and 1.5 of the actual timeout value should be randomized between 0.5 and 1.5 of the
nominal value to avoid self-synchronization. nominal value to avoid self-synchronization.
If, after I1_RETRIES_MAX retransmissions, there is no response, then If, after I1_RETRIES_MAX retransmissions, there is no response, then
most likely the peer does not implement the shim6 protocol, or there most likely the peer does not implement the shim6 protocol, or there
could be a firewall that blocks the protocol. In this case it makes could be a firewall that blocks the protocol. In this case it makes
sense for the host to remember to not try again to establish a sense for the host to remember to not try again to establish a
context with that ULID. However, any such negative caching should context with that ULID. However, any such negative caching should
retained for at most NO_R1_HOLDDOWN_TIME, to be able to later setup a retained for at most NO_R1_HOLDDOWN_TIME, to be able to later setup a
context should the problem have been that the host was not reachable context should the problem have been that the host was not reachable
at all when the shim tried to establish the context. at all when the shim tried to establish the context.
If the host receives an ICMP error with "payload type unknown" (type If the host receives an ICMP error with "payload type unknown" (type
4, code 1) and the included packet is the I1 packet it just sent, 4, code 1) and the included packet is the I1 message it just sent,
then this is a more reliable indication that the peer ULID does not then this is a more reliable indication that the peer ULID does not
implement shim6. Again,in this case, the host should remember to not implement shim6. Again, in this case, the host should remember to
try again to establish a context with that ULID. Such negative not try again to establish a context with that ULID. Such negative
caching should retained for at most ICMP_HOLDDOWN_TIME, which should caching should retained for at most ICMP_HOLDDOWN_TIME, which should
be significantly longer than the previous case. be significantly longer than the previous case.
7.7 Receiving I1 messages 7.9 Receiving I1 messages
A host MUST silently discard any received I1 messages that do not A host MUST silently discard any received I1 messages that do not
satisfy all of the following validity checks in addition to those satisfy all of the following validity checks in addition to those
specified in Section 12.2: specified in Section 12.2:
o The Hdr Ext Len field is at least 1, i.e., the length is at least o The Hdr Ext Len field is at least 1, i.e., the length is at least
16 octets. 16 octets.
Upon the reception of an I1 message, the host extracts the ULID pair Upon the reception of an I1 message, the host extracts the ULID pair
and the Forked Instance identifier from the message. If there is no and the Forked Instance Identifier from the message. If there is no
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. If such a context exists, the host verifies that pair and the FII.
If no state is found (i.e., the state is IDLE), then the host replies
with a R1 message as specified below.
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). If unnecessary if there is no ULID-pair option in the I1 message).
the locators do not fall in the locator sets, then the host MUST
discard the I1 packet and perform no further processing.
If no state is found (i.e., the state is IDLE), or the locators do If the state exists in ESTABLISHED state and the locators do not fall
fall in the sets, then the host looks at the state of the context: in the locator sets, then the host replies with a R1 message as
specified below. This completes the I1 processing, with the context
state being unchanged.
o If the state is IDLE, then the host will form an R1 packet as If the state exists in ESTABLISHED state and the locators do fall in
specified below. the sets, then the host compares CT(peer) for the context with the CT
contained in the I1 message.
o If the state is ESTABLISHED, it means that the Initiator has lost o If the context tags match, then this probably means that the R2
the context information for this context and it is trying to message was lost and this I1 is a retransmission. In this case,
establish a new one. In this case, the host MUST update the the host replies with a R2 message containing the information
existing context and replace CT(peer) with the Initiator Context available for the existent context.
Tag included in the I1 message and then reply with an R2 message,
including the associated state information. In this case the host
MUST look for any other (old) context with a matching CT(peer) as
specified in Section 7.12. This completes the I1 processing, with
the context state being unchanged.
o In an other state (I1-SENT, I2-SENT, I2BIS-SENT), we are in the o If the context tags do not match, then it probably means that the
situation of Concurrent context establishment described above. In Initiator has lost the context information for this context and it
this case, the host sets CT(peer) to the Initiator Context tag of is trying to establish a new one for the same ULID-pair. In this
the I1 packet, and replies with a R2 message. This completes the case, the host replies with a R1 message as specified below. This
I1 processing, with the context state being unchanged. completes the I1 processing, with the context state being
unchanged.
If the state exists in other state (I1-SENT, I2-SENT, I2BIS-SENT), we
are in the situation of Concurrent context establishment described
in Section 7.4. In this case, the host leaves CT(peer) unchanged,
and replies with a R2 message. This completes the I1 processing,
with the context state being unchanged.
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 validator as message, generates a Responder Nonce and calculates a Responder
suggested in the following section. No state is created on the host Validator option as suggested in the following section. No state is
in this case. created on the host in this case.
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 7.11). message (see Section 7.13).
7.7.1 Generating the R1 validator 7.9.1 Generating the R1 Validator
One way for the responder to properly generate validators is to One way for the responder to properly generate validators is to
maintain a single secret (S) and a running counter for the Responder maintain a single secret (S) and a running counter for the Responder
Nonce. Nonce.
In the case the validator is generated to be included in a R1 packet, In the case the validator is generated to be included in a R1
for each I1 message. The responder can increase the counter, use the message, for each I1 message. The responder can increase the
counter value as the responder nonce, and use the following counter, use the counter value as the responder nonce, and use the
information as input to the one-way function: following information as input to the one-way function:
o The the secret S o The 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 as validator string. and then the output of the hash function is used as the validator
octet string.
7.8 Receiving R1 messages and sending I2 messages 7.10 Receiving R1 messages and sending I2 messages
A host MUST silently discard any received R1 messages that do not A host MUST silently discard any received R1 messages that do not
satisfy all of the following validity checks in addition to those satisfy all of the following validity checks in addition to those
specified in Section 12.2: specified in Section 12.2:
o The Hdr Ext Len field is at least 1, i.e., the length is at least o The Hdr Ext Len field is at least 1, i.e., the length is at least
16 octets. 16 octets.
Upon the reception of an R1 message, the host extracts the Initiator Upon the reception of an R1 message, the host extracts the Initiator
Nonce and the Locator Pair from the message (the latter from the Nonce and the Locator Pair from the message (the latter from the
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 not found, then the R1 packet 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 packet then this is probably a reply host has already sent an I2 message then this is probably a reply
to a retransmitted I1 packet, 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 validator When the host sends an I2 message, then it includes the Responder
option that was in the R1 message. The I2 message MUST include the Validator option that was in the R1 message. The I2 message MUST
ULID pair; normally in the IPv6 source and destination fields. If a include the ULID pair; normally in the IPv6 source and destination
ULID-pair option was included in the I1 message then it MUST be fields. If a ULID-pair option was included in the I1 message then it
included in the I2 message as well. In addition, if the Forked MUST be included in the I2 message as well. In addition, if the
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 also includes the Initiator's locator list and the CGA The I2 message also includes the Initiator's locator list and the CGA
parameter data structure. If CGA (and not HBA) is used to verify the parameter data structure. If CGA (and not HBA) is used to verify the
locator list, then Initiator also signs the key parts of the message locator list, then Initiator also signs the key parts of the message
and includes a CGA signature option containing the signature. and includes a CGA signature option containing the signature.
When the I2 message has been sent, the state is set to I2-SENT. When the I2 message has been sent, the state is set to I2-SENT.
7.9 Retransmitting I2 messages 7.11 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 validator binary exponential backoff and randomized timers. The Responder
option might have a limited lifetime, that is, the peer might reject Validator option might have a limited lifetime, that is, the peer
verifier options that are older than VALIDATOR_MIN_LIFETIME to avoid might reject Responder Validator options that are older than
replay attacks. Thus the initiator SHOULD fall back to VALIDATOR_MIN_LIFETIME to avoid replay attacks. Thus the initiator
retransmitting the I1 message when there is no R2 received after SHOULD fall back to retransmitting the I1 message when there is no R2
retransmitting the I2 message I2_RETRIES_MAX times. received after retransmitting the I2 message I2_RETRIES_MAX times.
7.10 Receiving I2 messages 7.12 Receiving I2 messages
A host MUST silently discard any received I2 messages that do not A host MUST silently discard any received I2 messages that do not
satisfy all of the following validity checks in addition to those satisfy all of the following validity checks in addition to those
specified in Section 12.2: specified in Section 12.2:
o The Hdr Ext Len field is at least 2, i.e., the length is at least o The Hdr Ext Len field is at least 2, i.e., the length is at least
24 octets. 24 octets.
Upon the reception of an I2 message, the host extracts the ULID pair Upon the reception of an I2 message, the host extracts the ULID pair
and the Forked Instance identifier from the message. If there is no and the Forked Instance identifier from the message. If there is no
ULID-pair option, then the ULID pair is taken from the source and ULID-pair option, then the ULID pair is taken from the source and
destination fields in the IPv6 header. If there is no FII option in destination fields in the IPv6 header. If there is no FII option in
the message, then the FII value is taken to be zero. the message, then the FII value is taken to be zero.
Next the host verifies that the Responder Nonce is a recent one, and Next the host verifies that the Responder Nonce is a recent one, and
that the Validator option matches the validator the host would have that the Responder Validator option matches the validator the host
computed for the ULID, locators, responder nonce, and FII. would have computed for the ULID, locators, responder nonce, and FII.
If a CGA Parameter Data Structure is included in the message, then If a CGA Parameter Data Structure (PDS) is included in the message,
the host MUST verify if the actual PDS contained in the packet then the host MUST verify if the actual PDS contained in the message
corresponds to the ULID(peer). corresponds to the ULID(peer).
If at least one of the above verification fails, then it silently If any of the above verifications fails, then the host silently
discard the packet and it has completed the I2 processing. discard the message and it has completed the I2 processing.
If both verifications are successful, then the host proceeds to look If all the above verifications are successful, then the host proceeds
for a context state for the Initiator. The host looks for a context to look for a context state for the Initiator. The host looks for a
with the extracted ULID pair and FII. If none exist then state of context with the extracted ULID pair and FII. If none exist then
the (non-existing) context is viewed as being IDLE, thus the actions state of the (non-existing) context is viewed as being IDLE, thus the
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, sets its state to ESTABLISHED. It records the peer's the context, and sets its state to ESTABLISHED. It records
locator set as well as its own locator set in the context. It CT(peer), and the peer's locator set as well as its own locator
SHOULD perform the HBA/CGA verification of the peer's locator set set in the context. It SHOULD perform the HBA/CGA verification of
at this point in time. Then the host sends an R2 message back as the peer's locator set at this point in time, as specified in
specified below. Section 7.2. Then the host sends an R2 message back as specified
below.
o If the state is ESTABLISHED, CT(peer) matches the Initiator o If the state is I1-SENT, then the host verifies if the source
Context tag, and the IPv6 source address is contained in Ls(peer) locator is included in Ls(peer) or, it is included in the Locator
then this I2 message is probably a retransmit, so the host MUST List contained in the the I2 message and the HBA/CGA verification
send a R2 message back as specified below. for this specific locator is successful
o If the state is ESTABLISHED, and if at least one of the following * If this is not the case, then the message is silently discarded
conditions is true: either the CT(peer) is not the same as the and the context state remains unchanged.
Initiator Context tag, or the IPv6 source address is not contained
in Ls(peer) then silently discard the packet. Then the host has
completed the I2 processing.
o In other state (I1-SENT, I2-SENT, or I2BIS-SENT) then we are in * If this is the case, then the host updates the context
the Concurrent context establishment situation described above. information (CT(peer), Ls(peer)) with the data contained in the
Then it replies with a R2 message as specified below. The state I2 message and the host MUST send a R2 message back as
of the context remains unchanged. specified below. Note that before updating Ls(peer)
information, the host SHOULD perform the HBA/CGA validation of
the peer's locator set at this point in time as specified in
Section 7.2. The host moves to ESTABLISHED state.
7.11 Sending R2 messages 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
included in the Locator List contained in the 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 discarded
and the context state remains unchanged.
* If this is the case, then the host updates the context
information (CT(peer), Ls(peer)) with the data contained in the
I2 message and the host MUST send a R2 message back as
specified in Section 7.13. Note that before updating Ls(peer)
information, the host SHOULD perform the HBA/CGA validation of
the peer's locator set at this point in time as specified in
Section 7.2. The context state remains unchanged.
7.13 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 7.12. using the same CT(peer) for the same peer host. See Section 7.14.
In any case that the host sends an R2 message, the host forms the R2 When the host needs to send an R2 message, the host forms the message
message with its locators and its context tag, copies the Initiator using its locators and its context tag, copies the Initiator Nonce
Nonce from the I2 message, and includes the necessary options so that from the triggering message (I2, I2bis, or I1), and includes the
the peer can verify the locators. In particular, the R2 message also necessary options so that the peer can verify the locators. In
includes the Responder's locator list and the CGA parameter data particular, the R2 message includes the Responder's locator list and
structure. If CGA (and not HBA) is used to verify the locator list, the PDS option. If CGA (and not HBA) is used to verify the locator
then the Responder also signs the key parts of the message and list, then the Responder also signs the key parts of the message and
includes a CGA signature option containing the signature. includes a CGA Signature option containing the signature.
R2 messages are never retransmitted. If the R2 message is lost, then R2 messages are never retransmitted. If the R2 message is lost, then
the initiator will retransmit either the I2/I2bis or I1 message. the initiator will retransmit either the I2/I2bis or I1 message.
Either retransmission will cause the responder to find the context Either retransmission will cause the responder to find the context
state and respond with an R2 message. state and respond with an R2 message.
7.12 Match for Context Confusion 7.14 Match for Context Confusion
When the host receives an I2, I2bis, or R2 it MUST look for a When the host receives an I2, I2bis, or R2 it MUST look for a
possible context confusion i.e. where it would end up with multiple possible context confusion i.e. where it would end up with multiple
contexts using the same CT(peer) for the same peer host. This can contexts using the same CT(peer) for the same peer host. This can
happen when it has received the above messages since they create a happen when it has received the above messages since they create a
new context with a new CT(peer). Same issue applies when CT(peer) is new context with a new CT(peer). Same issue applies when CT(peer) is
updated for an existing context. updated for an existing context.
The host takes CT(peer) for the newly created or updated context, and The host takes CT(peer) for the newly created or updated context, and
looks for other contexts which: looks for other contexts which:
skipping to change at page 63, line 9 skipping to change at page 64, line 49
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 this is true, then the peer is trying to reuse the context tag o If either or both are different, then the peer is reusing the
for the creation of a context with different ULID pair or FII, context tag for the creation of a context with different ULID pair
which is a signal that the Initiator has lost the other context. or FII, which is an indication that the peer has lost the original
In this case, we are in the Context confusion situation, and the context. In this case, we are in the Context confusion situation,
host MUST NOT use the old context to send any packets. It MAY and the host MUST NOT use the old context to send any packets. It
just discard the old context (after all, the peer has discarded MAY just discard the old context (after all, the peer has
it), or it MAY attempt to re-establish the old context by sending discarded it), or it MAY attempt to re-establish the old context
a new I1 message and moving its state to I1-SENT. In any case, by sending a new I1 message and moving its state to I1-SENT. In
once that this situation is detected, the host MUST not keep two any case, once that this situation is detected, the host MUST NOT
contexts with overlapping Ls(peer) locator sets and the same keep two contexts with overlapping Ls(peer) locator sets and the
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 this is not true, then the local host must be broken, since it o If both are the same, then this context is actually the context
should have detected the existence of a context for the same ULID that is created or updated, hence there is no confusion.
pair and FII earlier.
7.13 Receiving R2 messages 7.15 Receiving R2 messages
A host MUST silently discard any received R2 messages that do not A host MUST silently discard any received R2 messages that do not
satisfy all of the following validity checks in addition to those satisfy all of the following validity checks in addition to those
specified in Section 12.2: specified in Section 12.2:
o The Hdr Ext Len field is at least 1, i.e., the length is at least o The Hdr Ext Len field is at least 1, i.e., the length is at least
16 octets. 16 octets.
Upon the reception of an R2 message, the host extracts the Initiator Upon the reception of an R2 message, the host extracts the Initiator
Nonce and the Locator Pair from the message (the latter from the Nonce and the Locator Pair from the message (the latter from the
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 is the following actions: If a CGA Parameter Data Structure (PDS) is
included in the message, then the host MUST verify if the actual included in the message, then the host MUST verify that the actual
PDS contained in the packet corresponds to the ULID(peer). If the PDS contained in the message corresponds to the ULID(peer) as
verification fails, then the message is silently dropped. If the specified in Section 7.2. If the verification fails, then the
verification succeeds, then the host records the information from message is silently dropped. If the verification succeeds, then
the R2 message in the context state. It records the peer's the host records the information from the R2 message in the
locator set in the context. It SHOULD perform the HBA/CGA context state; it records the peer's locator set and CT(peer).
verification of the peer's locator set at this point in time. 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.
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
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 7.12. Section 7.14.
7.14 Sending R1bis packets 7.16 Sending R1bis messages
Upon the receipt of a shim6 payload extension header where there is Upon the receipt of a shim6 payload extension header where there is
no current SHIM6 context at the receiver, the receiver is to respond no current SHIM6 context at the receiver, the receiver is to respond
with an R1bis packet in order to enable a fast re-establishment of with an R1bis message in order to enable a fast re-establishment of
the lost SHIM6 context. the lost SHIM6 context.
Also a host is to respond with a R1bis upon receipt of any control Also a host is to respond with a R1bis upon receipt of any control
messages that has a message type in the range 64-127 (i.e., excluding messages that has a message type in the range 64-127 (i.e., excluding
the context setup messages such as I1, R1, R1bis, I2, I2bis, R2 and the context setup messages such as I1, R1, R1bis, I2, I2bis, R2 and
future extensions), where the control message refers to a non future extensions), where the control message refers to a non
existent context. existent context.
We assume that all the incoming packets that trigger the generation We assume that all the incoming packets that trigger the generation
of an R1bis packet contain a locator pair (in the address fields of of an R1bis message contain a locator pair (in the address fields of
the IPv6 header) and a Context Tag. the IPv6 header) and a Context Tag.
Upon reception of any of the packets described above, the host will Upon reception of any of the packets described above, the host will
reply with an R1bis including the following information: reply with an R1bis including the following information:
o The Responder Nonce is a number picked by the responder which the o The Responder Nonce is a number picked by the responder which the
initiator will return in the I2bis message. initiator will return in the I2bis message.
o Packet Context Tag is the context tag contained in the received o Packet Context Tag is the context tag contained in the received
packet that triggered the generation of the R1bis packet. packet that triggered the generation of the R1bis message.
o The Validator option is included, with a validator that is o The Responder Validator option is included, with a validator that
computed as suggested in the next section. is computed as suggested in the next section.
7.14.1 Generating the R1bis validator 7.16.1 Generating the R1bis Validator
One way for the responder to properly generate validators is to One way for the responder to properly generate validators is to
maintain a single secret (S) and a running counter for the Responder maintain a single secret (S) and a running counter for the Responder
Nonce. Nonce.
In the case the validator is generated to be included in a R1bis In the case the validator is generated to be included in a R1bis
packet, for each received payload extension header or control packet, message, for each received payload extension header or control
the responder can increase the counter, use the counter value as the message, the responder can increase the counter, use the counter
responder nonce, and use the following information as input to the value as the responder nonce, and use the following information as
one-way function: input to the one-way function:
o The the secret S o The the secret S
o That Responder Nonce o That Responder Nonce
o The 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 use the output of the hash function as validator string. and then the output of the hash function is used as the validator
octet string.
7.15 Receiving R1bis messages and sending I2bis messages 7.17 Receiving R1bis messages and sending I2bis messages
A host MUST silently discard any received R1bis messages that do not A host MUST silently discard any received R1bis messages that do not
satisfy all of the following validity checks in addition to those satisfy all of the following validity checks in addition to those
specified in Section 12.2: specified in Section 12.2:
o The Hdr Ext Len field is at least 1, i.e., the length is at least o The Hdr Ext Len field is at least 1, i.e., the length is at least
16 octets. 16 octets.
Upon the reception of an R1bis message, the host extracts the Packet Upon the reception of an R1bis message, the host extracts the Packet
Context Tag and the Locator Pair from the message (the latter from Context Tag and the Locator Pair from the message (the latter from
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 packet 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
packet 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 packet, state, transitions to I2BIS-SENT state, and sends a I2bis message,
including in it the Validator, the Packet Context Tag, and the including the computed Responder Validator option, the Packet
Responder Nonce received in the R1bis packet. This I2bis packet Context Tag, and the Responder Nonce received in the R1bis
is sent using the locator pair included in the R1bis packet. In message. This I2bis message is sent using the locator pair
the case that this locator pair differs from the ULID pair defined included in the R1bis message. In the case that this locator pair
for this context, then an ULID option MUST be included in the differs from the ULID pair defined for this context, then an ULID
I2bis packet. In addition, if the Forked Instance Identifier for option MUST be included in the I2bis message. In addition, if the
this context is non-zero, then a Forked Instance Identifier option Forked Instance Identifier for this context is non-zero, then a
carrying the instance identifier value for this context MUST be Forked Instance Identifier option carrying the instance identifier
included in the I2bis message. value for this context MUST be included in the I2bis message.
7.16 Receiving I2bis messages and sending R2 messages 7.18 Retransmitting I2bis messages
If the initiator does not receive an R2 message after I2bis_TIMEOUT
time after sending an I2bis message it MAY retransmit the I2bis
message, using binary exponential backoff and randomized timers. The
Responder Validator option might have a limited lifetime, that is,
the peer might reject Responder Validator options that are older than
VALIDATOR_MIN_LIFETIME to avoid replay attacks. Thus the initiator
SHOULD fall back to retransmitting the I1 message when there is no R2
received after retransmitting the I2bis message I2bis_RETRIES_MAX
times.
7.19 Receiving I2bis messages and sending R2 messages
A host MUST silently discard any received I2bis messages that do not A host MUST silently discard any received I2bis messages that do not
satisfy all of the following validity checks in addition to those satisfy all of the following validity checks in addition to those
specified in Section 12.2: specified in Section 12.2:
o The Hdr Ext Len field is at least 3, i.e., the length is at least o The Hdr Ext Len field is at least 3, i.e., the length is at least
32 octets. 32 octets.
Upon the reception of an I2bis message, the host extracts the ULID Upon the reception of an I2bis message, the host extracts the ULID
pair and the Forked Instance identifier from the message. If there pair and the Forked Instance identifier from the message. If there
is no ULID-pair option, then the ULID pair is taken from the source is no ULID-pair option, then the ULID pair is taken from the source
and destination fields in the IPv6 header. If there is no FII option and destination fields in the IPv6 header. If there is no FII option
in the message, then the FII value is taken to be zero. in the message, then the FII value is taken to be zero.
Next the host verifies that the Responder Nonce is a recent one, and Next the host verifies that the Responder Nonce is a recent one, and
that the Validator option matches the validator the host would have that the Responder Validator option matches the validator the host
computed for the ULID, locators, responder nonce, and FII as part of would have computed for the ULID, locators, responder nonce, and FII
sending an R1bis message. as part of sending an R1bis message.
If a CGA Parameter Data Structure is included in the message, then If a CGA Parameter Data Structure (PDS) is included in the message,
the host MUST verify if the actual PDS contained in the packet then the host MUST verify if the actual PDS contained in the message
corresponds to the ULID(peer). corresponds to the ULID(peer).
If at least one of the above verification fails, then it silently If any of the above verifications fails, then the host silently
discard the packet 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, sets its state to ESTABLISHED. The host SHOULD NOT the context, and sets its state to ESTABLISHED. The host SHOULD
use the Packet Context Tag in the I2bis packet 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 the peer's locator set as processes an I2 message. It records CT(peer), and the peer's
well as its own locator set in the context. It SHOULD perform the locator set as well as its own locator set in the context. It
HBA/CGA verification of the peer's locator set at this point in SHOULD perform the HBA/CGA verification of the peer's locator set
time. Then the host sends an R2 message back as specified in at this point in time as specified in Section 7.2. Then the host
Section 7.11. sends an R2 message back as specified in Section 7.13.
o If the state is ESTABLISHED, CT(peer) matches the Initiator o If the state is I1-SENT, then the host verifies if the source
Context tag, and the IPv6 source address is contained in Ls(peer) locator is included in Ls(peer) or, it is included in the Locator
then this I2bis message is probably a retransmit, so the host MUST List contained in the the I2 message and the HBA/CGA verification
send a R2 message back as specified below. for this specific locator is successful
o If the state is ESTABLISHED, and if at least one of the following * If this is not the case, then the message is silently
conditions is true: either the CT(peer) is not the same as the discarded. The the context state remains unchanged.
Initiator Context tag, or the IPv6 source address is not contained
in Ls(peer) then silently discard the packet. Then the host has
completed the I2bis processing.
o In other state (I1-SENT, I2-SENT, or I2BIS-SENT) then we are in * If this is the case, then the host updates the context
the Concurrent context establishment situation described above. information (CT(peer), Ls(peer)) with the data contained in the
Then it replies with a R2 message as specified in section I2 message and the host MUST send a R2 message back as
Section 7.11. The state of the context remains unchanged. specified below. Note that before updating Ls(peer)
information, the host SHOULD perform the HBA/CGA validation of
the peer's locator set at this point in time as specified in
Section 7.2. The host moves to ESTABLISHED state.
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
included in the Locator List contained in the 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
discarded. The the context state remains unchanged.
* If this is the case, then the host updates the context
information (CT(peer), Ls(peer)) with the data contained in the
I2 message and the host MUST send a R2 message back as
specified in Section 7.13. Note that before updating Ls(peer)
information, the host SHOULD perform the HBA/CGA validation of
the peer's locator set at this point 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 host unreachable, packet too
big, and payload type unknown. It is critical that these packets big, and payload type unknown. It is critical that these packets
make it back up to the ULPs so that they can take appropriate action. make it back up to the ULPs so that they can take appropriate action.
When the ULP packets are sent unmodified, that is, while the initial This is an implementation issue in the sense that the mechanism is
locators=ULIDs are working, this introduces no new concerns; an completely local to the host itself. But the issue of how ICMP
implementation's existing mechanism for delivering these errors to errors are correctly dispatched to the ULP on the host are important,
the ULP will work. But when the shim on the transmitting side hence this section specifies the issue.
replaces the ULIDs in the IP address fields with 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 implementation will have to
apply the reverse mapping to the "packet in error" before passing the
ICMP error up to the ULP.
This mapping is different than when receiving ULP packets from the +--------------+
peer, because in that case the packets contain CT(local). But the | IPv6 Header |
ICMP errors have a "packet in error" with CT(peer) since they were | |
intended to be received by the peer. In any case, since the <Source +--------------+
Locator, Destination Locator, CT(peer)> has to be unique when | ICMPv6 |
received by the peer, the local host should also only be able to find | Header |
one context that matches this tuple. - - +--------------+ - -
| IPv6 Header |
| src, dst as | Can be dispatched
IPv6 | sent by ULP | unmodified to ULP
| on host | ICMP error handler
Packet +--------------+
| ULP |
in | Header |
+--------------+
Error | |
~ Data ~
| |
- - +--------------+ - -
If the ULP packet had been encapsulated in a shim6 payload extension Figure 29: ICMP error handling without payload extension header
header, then this extension header must be removed. The result needs
to be that the ULP receives an ICMP error where the contained "packet When the ULP packets are sent without the payload extension header,
in error" looks as if the shim did not exist. that is, while the initial locators=ULIDs are working, this
introduces no new concerns; an implementation's existing mechanism
for delivering these errors to the ULP will work. See Figure 29.
But when the shim on the transmitting side inserts the payload
extension header and replaces the ULIDs in the IP address fields with
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
implementation will have to apply the reverse mapping to the "packet
in error" before passing the ICMP error up to the ULP. See
Figure 30.
+--------------+
| IPv6 Header |
| |
+--------------+
| ICMPv6 |
| Header |
- - +--------------+ - -
| IPv6 Header |
| src, dst as | Needs to be
IPv6 | modified by | transformed to
| shim on host | have ULIDs
+--------------+ in src, dst fields,
Packet | SHIM6 ext. | and SHIM6 ext.
| Header | header removed
in +--------------+ before it can be
| Transport | dispatched to the ULP
Error | Header | ICMP error handler.
+--------------+
| |
~ Data ~
| |
- - +--------------+ - -
Figure 30: ICMP error handling with payload extension header
Note that this mapping is different than when receiving packets from
the peer with a payload extension headers, because in that case the
packets contain CT(local). But the ICMP errors have a "packet in
error" with an payload extension header containing CT(peer). This is
because they were intended to be received by the peer. In any case,
since the <Source Locator, Destination Locator, CT(peer)> has to be
unique when received by the peer, the local host should also only be
able to find one context that matches this tuple.
If the ICMP error is a Packet Too Big, the reported MTU must be
adjusted to be 8 octets less, since the shim will add 8 octets when
sending packets.
After the "packet in error" has had the original ULIDs inserted, then
this payload extension header can be removed. The result is a
"packet in error" that is passed to the ULP which looks as if the
shim did not exist.
9. Teardown of the ULID-Pair Context 9. Teardown of the ULID-Pair Context
Each host can unilaterally decide when to tear down a ULID-pair Each host can unilaterally decide when to tear down a ULID-pair
context. It is RECOMMENDED that hosts not tear down the context when context. It is RECOMMENDED that hosts do not tear down the context
they know that there is some upper layer protocol that might use the when they know that there is some upper layer protocol that might use
context. For example, an implementation might know this is there is the context. For example, an implementation might know this if there
an open socket which is connected to the ULID(peer). However, there is an open socket which is connected to the ULID(peer). However,
might be cases when the knowledge is not readily available to the there might be cases when the knowledge is not readily available to
shim layer, for instance for UDP applications which not connect their the shim layer, for instance for UDP applications which do not
sockets, or any application which retains some higher level state connect their sockets, or any application which retains some higher
across (TCP) connections and UDP packets. level state across (TCP) connections and UDP packets.
Thus it is RECOMMENDED that implementations minimize premature Thus it is RECOMMENDED that implementations minimize premature
teardown by observing the amount of traffic that is sent and received teardown by observing the amount of traffic that is sent and received
using the context, and only after it appears quiescent, tear down the using the context, and only after it appears quiescent, tear down the
state. A reasonable approach would be to not tear down a context state. A reasonable approach would be not to tear down a context
until at least 5 minutes have passed since the last message was sent until at least 5 minutes have passed since the last message was sent
or received using the context. or received using the context.
Since there is no explicit, coordinated removal of the context state, Since there is no explicit, coordinated removal of the context state,
there are potential issues around context tag reuse. One end might there are potential issues around context tag reuse. One end might
remove the state, and potentially reuse that context tag for some remove the state, and potentially reuse that context tag for some
other communication, and the peer might later try to use the old other communication, and the peer might later try to use the old
context (which it didn't remove). The protocol has mechanisms to context (which it didn't remove). The protocol has mechanisms to
recover from this, which work whether the state removal was total and recover from this, which work whether the state removal was total and
accidental (e.g., crash and reboot of the host), or just a garbage accidental (e.g., crash and reboot of the host), or just a garbage
collection of shim state that didn't seem to be used. However, the collection of shim state that didn't seem to be used. However, the
host should try to minimize the reuse of context tags by trying to host should try to minimize the reuse of context tags by trying to
randomly cycle through the 2^47 context tag values. (See Appendix B randomly cycle through the 2^47 context tag values. (See Appendix E
for a summary how the recovery works in the different cases.) for a summary how the recovery works in the different cases.)
10. Updating the Peer 10. Updating the Peer
The Update Request and Acknowledgement are used both to update the The Update Request and Acknowledgement are used both to update the
list of locators (only possible when CGA is used to verify the list of locators (only possible when CGA is used to verify the
locator(s)), as well as updating the preferences associated with each locator(s)), as well as updating the preferences associated with each
locator. locator.
10.1 Sending Update Request messages 10.1 Sending Update Request messages
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same nonce for any retransmissions of the Update Request. The nonce same nonce for any retransmissions of the Update Request. The nonce
is used to match the acknowledgement with the request. is used to match the acknowledgement with the request.
10.2 Retransmitting Update Request messages 10.2 Retransmitting Update Request messages
If the host does not receive an Update Acknowledgement R2 message in If the host does not receive an Update Acknowledgement R2 message in
response to the Update Request message after UPDATE_TIMEOUT time, response to the Update Request message after UPDATE_TIMEOUT time,
then it needs to retransmit the Update Request message. The then it needs to retransmit the Update Request message. The
retransmissions should use a retransmission timer with binary retransmissions should use a retransmission timer with binary
exponential backoff to avoid creating congestion issues for the exponential backoff to avoid creating congestion issues for the
network when lots of hosts perform I1 retransmissions. Also, the network when lots of hosts perform Update Request retransmissions.
actual timeout value should be randomized between 0.5 and 1.5 of the Also, the actual timeout value should be randomized between 0.5 and
nominal value to avoid self-synchronization. 1.5 of the nominal value to avoid self-synchronization.
Should there be no response, the retransmissions continue forever. Should there be no response, the retransmissions continue forever.
The binary exponential backoff stops at MAX_UPDATE_TIMEOUT. But the The binary exponential backoff stops at MAX_UPDATE_TIMEOUT. But the
only way the retransmissions would stop when there is no only way the retransmissions would stop when there is no
acknowledgement, is when the shim, through the Probe protocol or some acknowledgement, is when the shim, through the Probe protocol or some
other mechanism, decides to discard the context state due to lack of other mechanism, decides to discard the context state due to lack of
ULP usage in combination with no responses to the Probes. ULP usage in combination with no responses to the Probes.
10.3 Newer Information While Retransmitting 10.3 Newer Information While Retransmitting
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A host MUST silently discard any received Update Request messages A host MUST silently discard any received Update Request messages
that do not satisfy all of the following validity checks in addition that do not satisfy all of the following validity checks in addition
to those specified in Section 12.2: to those specified in Section 12.2:
o The Hdr Ext Len field is at least 1, i.e., the length is at least o The Hdr Ext Len field is at least 1, i.e., the length is at least
16 octets. 16 octets.
Upon the reception of an Update Request message, the host extracts Upon the reception of an Update Request message, the host extracts
the Context Tag from the message. It then looks for a context which the Context Tag from the message. It then looks for a context which
has a CT(local) that matches the context tag. If no such context is has a CT(local) that matches the context tag. If no such context is
found, it sends a R1bis message as specified in Section 7.14. found, it sends a R1bis message as specified in Section 7.16.
Since context tags can be reused, the host MUST verify that the IPv6 Since context tags can be reused, the host MUST verify that the IPv6
source address field is part of Ls(peer) and that the IPv6 source address field is part of Ls(peer) and that the IPv6
destination address field is part of Ls(local). If this is not the destination address field is part of Ls(local). If this is not the
case, the sender of the Update Request has a stale context which case, the sender of the Update Request has a stale context which
happens to match the CT(local) for this context. In this case the happens to match the CT(local) for this context. In this case the
host MUST send a R1bis message, and otherwise ignore the Update host MUST send a R1bis message, and otherwise ignore the Update
Request message. Request message.
If a CGA Parameter Data Structure is included in the message, then If a CGA Parameter Data Structure (PDS) is included in the message,
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 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.
The validation issues for the locators carried in the Locator Update The verification issues for the locators carried in the Locator
message are specified in Section 4.7. If the locator list can not be Update message are specified in Section 7.2. If the locator list can
validated, this procedure might send an ICMP Parameter Problem error. not be verified, this procedure might send an ICMP Parameter Problem
In any case, if it can not be validated, there is no further error. In any case, if it can not be verified, there is no further
processing of the Update Request. processing of the Update Request.
Once any Locator List option in the Update Request has been Once any Locator List option in the Update Request has been verified,
validated, the peer generation number in the context is updated to be the peer generation number in the context is updated to be the one in
the one in the Locator List option. the Locator List option.
If the Update message contains a Locator Preference option, then the If the Update message contains a Locator Preference option, then the
Generation number in the preference option is compared with the peer Generation number in the preference option is compared with the peer
generation number in the context. If they do not match, then the generation number in the context. If they do not match, then the
host generates an ICMP parameter problem (type 4, code 0) with the host generates an ICMP parameter problem (type 4, code 0) with the
Pointer field referring to the first octet in the Generation number Pointer field referring to the first octet in the Generation number
in the Locator Preference option. In addition, if the number of in the Locator Preference option. In addition, if the number of
elements in the Locator Preference option does not match the number elements in the Locator Preference option does not match the number
of locators in Ls(peer), then an ICMP parameter problem is sent with of locators in Ls(peer), then an ICMP parameter problem is sent with
the Pointer referring to the first octet of the Length field in the the Pointer referring to the first octet of the Length field in the
Locator Preference option. In both cases of failures, no further Locator Preference option. In both cases of failures, no further
processing is performed for the Locator Update message. processing is performed for the Locator Update message.
If the generation number matches, the locator preferences are If the generation number matches, the locator preferences are
recorded in the context. recorded in the context.
Once the Locator List option (if present) has been validated and any Once the Locator List option (if present) has been verified and any
new locator list or locator preferences have been recorded, the host new locator list or locator preferences have been recorded, the host
sends an Update Acknowledgement message, copying the nonce from the sends an Update Acknowledgement message, copying the nonce from the
request, and using the CT(peer) in as the Receiver Context tag. request, and using the CT(peer) in as the Receiver Context Tag.
Any new locators, or more likely new locator preferences, might Any new locators, or more likely new locator preferences, might
result in the host wanting to select a different locator pair for the result in the host wanting to select a different locator pair for the
context. For instance, if the Locator Preferences lists the current context. For instance, if the Locator Preferences lists the current
Lp(peer) as BROKEN. The host uses the Probe message in [9] to verify Lp(peer) as BROKEN. The host uses the Probe message in [8] to verify
that the new locator is reachable before changing Lp(peer). that the new locator is reachable before changing Lp(peer).
10.5 Receiving Update Acknowledgement messages 10.5 Receiving Update Acknowledgement messages
A host MUST silently discard any received Update Acknowledgement A host MUST silently discard any received Update Acknowledgement
messages that do not satisfy all of the following validity checks in messages that do not satisfy all of the following validity checks in
addition to those specified in Section 12.2: addition to those specified in Section 12.2:
o The Hdr Ext Len field is at least 1, i.e., the length is at least o The Hdr Ext Len field is at least 1, i.e., the length is at least
16 octets. 16 octets.
Upon the reception of an Update Acknowledgement message, the host Upon the reception of an Update Acknowledgement message, the host
extracts the Context Tag and the Request Nonce from the message. It extracts the Context Tag and the Request Nonce from the message. It
then looks for a context which has a CT(local) that matches the then looks for a context which has a CT(local) that matches the
context tag. If no such context is found, it sends a R1bis message context tag. If no such context is found, it sends a R1bis message
as specified in Section 7.14. as specified in Section 7.16.
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:
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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 will be sent unmodified by the If this is the case, then packets can be sent unmodified by the shim.
shim. If it is not the case, then the logic in Section 11.1 will If it is not the case, then the logic in Section 11.1 will need to be
need to be used. used.
There will also be some maintenance activity relating to There will also be some maintenance activity relating to
(un)reachability detection, whether packets are sent with the (un)reachability detection, whether packets are sent with the
original locators or not. The details of this is out of scope for original locators or not. The details of this is out of scope for
this document and will be covered is follow-ons to [8]. this document and is specified in [8].
11.1 Sending ULP Payload after a Switch 11.1 Sending ULP Payload after a Switch
When sending packets, if there is a ULID-pair context for the ULID When sending packets, if there is a ULID-pair context for the ULID
pair, and the ULID pair is no longer used as the locator pair, then pair, and the ULID pair is no longer used as the locator pair, then
the sender needs to transform the packet. Apart from replacing the the sender needs to transform the packet. Apart from replacing the
IPv6 source and destination fields with a locator pair, an 8-octet IPv6 source and destination fields with a locator pair, an 8-octet
header is added so that the receiver can find the context and inverse header is added so that the receiver can find the context and inverse
the transformation. the transformation.
If there has been a failure causing a switch, and later the context
switches back to sending things using the ULID pair as the locator
pair, then there is no longer a need to do any packet transformation
by the sender, hence there is no need to include the 8-octet
extension header.
First, the IP address fields are replaced. The IPv6 source address First, the IP address fields are replaced. The IPv6 source address
field is set to Lp(local) and the destination address field is set to field is set to Lp(local) and the destination address field is set to
Lp(peer). NOTE that this MUST NOT cause any recalculation of the ULP Lp(peer). NOTE that this MUST NOT cause any recalculation of the ULP
checksums, since the ULP checksums are carried end-to-end and the ULP checksums, since the ULP checksums are carried end-to-end and the ULP
pseudo-header contains the ULIDs which are preserved end-to-end. pseudo-header contains the ULIDs which are preserved end-to-end.
The sender skips any "routing sub-layer extension headers" that the The sender skips any "routing sub-layer extension headers" that the
ULP might have included, thus it skips any hop-by-hop extension ULP might have included, thus it skips any hop-by-hop extension
header, any routing header, and any destination options header that header, any routing header, and any destination options header that
is followed by a routing header. After any such headers the shim6 is followed by a routing header. After any such headers the shim6
extension header will be added. This might be before a Fragment extension header will be added. This might be before a Fragment
header, a Destination Options header, an ESP or AH header, or a ULP header, a Destination Options header, an ESP or AH header, or a ULP
header. header.
The inserted shim6 Payload extension header includes the peer's The inserted shim6 Payload extension header includes the peer's
context tag. context tag. It takes on the next header value from the preceding
extension header, since that extension header will have a next header
value of SHIM6.
12. Receiving Packets 12. Receiving Packets
As in normal IPv6 receive side packet processing the receiver parses As in normal IPv6 receive side packet processing the receiver parses
the (extension) headers in order. Should it find a shim6 extension the (extension) headers in order. Should it find a shim6 extension
header it will look at the "P" field in that header. If this bit is header it will look at the "P" field in that header. If this bit is
zero, then the packet must be passed to the shim6 payload handling zero, then the packet must be passed to the shim6 payload handling
for rewriting. Otherwise, the packet is passed to the shim6 control for rewriting. Otherwise, the packet is passed to the shim6 control
handling. handling.
12.1 Receiving Payload Extension Headers 12.1 Receiving Payload Extension Headers
The receiver extracts the context tag from the payload extension The receiver extracts the context tag from the payload extension
header, and uses this to find a ULID-pair context. If no context is header, and uses this to find a ULID-pair context. If no context is
found, the receiver SHOULD generate a R1bis message (see found, the receiver SHOULD generate a R1bis message (see
Section 7.14). Section 7.16).
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.
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In addition, the shim on the sending side needs to be able to find In addition, the shim on the sending side needs to be able to find
the context state when a ULP packet is passed down from the ULP. In the context state when a ULP packet is passed down from the ULP. In
that case the lookup key is the pair of ULIDs and FII=0. If we have that case the lookup key is the pair of ULIDs and FII=0. If we have
a ULP API that allows the ULP to do context forking, then presumably a ULP API that allows the ULP to do context forking, then presumably
the ULP would pass down the Forked Instance Identifier. the ULP would pass down the Forked Instance Identifier.
13. Initial Contact 13. Initial Contact
The initial contact is some non-shim communication between two ULIDs, The initial contact is some non-shim communication between two ULIDs,
as defined in Section 2. At that point in time there is no activity as described in Section 2. At that point in time there is no
in the shim. activity in the shim.
Whether the shim ends up being used or not (e.g., the peer might not Whether the shim ends up being used or not (e.g., the peer might not
support shim6) it is highly desirable that the initial contact can be support shim6) it is highly desirable that the initial contact can be
established even if there is a failure for one or more IP addresses. established even if there is a failure for one or more IP addresses.
The approach taken is to rely on the applications and the transport The approach taken is to rely on the applications and the transport
protocols to retry with different source and destination addresses, protocols to retry with different source and destination addresses,
consistent with what is already specified in Default Address consistent with what is already specified in Default Address
Selection [13], and some fixes to that specification [14] to make it Selection [12], and some fixes to that specification [13] to make it
try different source addresses and not only different destination try different source addresses and not only different destination
addresses. addresses.
The implementation of such an approach can potentially result in long The implementation of such an approach can potentially result in long
timeouts. For instance, a naive implementation at the socket API timeouts. For instance, a naive implementation at the socket API
which uses getaddrinfo() to retrieve all destination addresses and which uses getaddrinfo() to retrieve all destination addresses and
then tries to bind() and connect() to try all source and destination then tries to bind() and connect() to try all source and destination
address combinations waiting for TCP to time out for each combination address combinations waiting for TCP to time out for each combination
before trying the next one. before trying the next one.
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I1_TIMEOUT = 4 seconds I1_TIMEOUT = 4 seconds
NO_R1_HOLDDOWN_TIME = 1 min NO_R1_HOLDDOWN_TIME = 1 min
ICMP_HOLDDOWN_TIME = 10 min ICMP_HOLDDOWN_TIME = 10 min
I2_TIMEOUT = 4 seconds I2_TIMEOUT = 4 seconds
I2_RETRIES_MAX = 2 I2_RETRIES_MAX = 2
I2bis_TIMEOUT = 4 seconds
I2bis_RETRIES_MAX = 2
VALIDATOR_MIN_LIFETIME = 30 seconds VALIDATOR_MIN_LIFETIME = 30 seconds
UPDATE_TIMEOUT = 4 seconds UPDATE_TIMEOUT = 4 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,
etc. etc.
15. Open Issues 15. Implications Elsewhere
The following open issues are known:
o NONE.
16. Implications Elsewhere
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. The key implications are: solution, has implications elsewhere. The key implications are:
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 [21]. But in order for such applications to be as described in [22]. 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
locators as the 'identifiers' i.e., the 'identifier' from the locators as the 'identifiers' i.e., the 'identifier' from the
applications perspective becomes a set of IP addresses instead of applications perspective becomes a set of IP addresses instead of
a single IP address. a single IP address.
o Firewalls that today pass limited traffic, e.g., outbound TCP o Firewalls that today pass limited traffic, e.g., outbound TCP
connections, would presumably block the shim6 protocol. This connections, would presumably block the shim6 protocol. This
means that even when shim6 capable hosts are communicating, the I1 means that even when shim6 capable hosts are communicating, the I1
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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. Perhaps such a path change would be a good hint
to the path MTU mechanism to try a larger MTU? to the path MTU mechanism to try a larger MTU?
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.
17. Security Considerations o The precise interaction between Mobile IPv6 and shim6 is for
further study, but it might make sense to have Mobile IPv6 operate
on locators, meaning that the shim would be layered on top of the
MIPv6 mechanism.
This document satisfies the concerns specified in [20] as follows: 16. Security Considerations
o The HBA technique [7] for validating the locators to prevent an This document satisfies the concerns specified in [19] as follows:
o The HBA technique [7] for verifying the locators to prevent an
attacker from redirecting the packet stream to somewhere else. attacker from redirecting the packet stream to somewhere else.
o Requiring a Reachability Probe+Reply before a new locator is used o Requiring a Reachability Probe+Reply before a new locator is used
as the destination, in order to prevent 3rd party flooding as the destination, in order to prevent 3rd party flooding
attacks. attacks.
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
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technique, the shim6 protocol is protected against off-path technique, the shim6 protocol is protected against off-path
attackers. attackers.
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.
o An attacker which is present on the path so that it can find out o An attacker which is present on the path so that it can find out
the context tags, can generate a R1bis message after it has moved the context tags, can generate a R1bis message after it has moved
off the path. For this packet to be effective it needs to have a off the path. For this packet to be effective it needs to have a
source locator which belongs to the context, thus there can not be source locator which belongs to the context, thus there can not be
"too much" ingress filtering between the attackers new location "too much" ingress filtering between the attackers new location
and the communicating peers. But this doesn't seem to be that and the communicating peers. But this doesn't seem to be that
severe, because once the R1bis causes the context to be re- severe, because once the R1bis causes the context to be re-
established, a new pair of context tags will be used, which will established, a new pair of context tags will be used, which will
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the 47-bit context tag, the attacker also needs to find a context the 47-bit context tag, the attacker also needs to find a context
where, after the receiver's replacement of the locators with the where, after the receiver's replacement of the locators with the
ULIDs, the the ULP checksum is correct. But even this wouldn't be ULIDs, the the ULP checksum is correct. But even this wouldn't be
sufficient with ULPs like TCP, since the TCP port numbers and sufficient with ULPs like TCP, since the TCP port numbers and
sequence numbers must match an existing connection. Thus, even sequence numbers must match an existing connection. Thus, even
though the issues for off-path attackers injecting packets are though the issues for off-path attackers injecting packets are
different than today with ingress filtering, it is still very hard different than today with ingress filtering, it is still very hard
for an off-path attacker to guess. If IPsec is applied then the for an off-path attacker to guess. If IPsec is applied then the
issue goes away completely. issue goes away completely.
18. IANA Considerations 17. IANA Considerations
IANA needs to allocate a new IP Protocol Number value for this IANA is directed to allocate a new IP Protocol Number value for the
protocol. SHIM6 Protocol.
IANA also needs to record a CGA message type for this protocol in the IANA is directed to record a CGA message type for the SHIM6 Protocol
[CGA] namespace, 0x4A30 5662 4858 574B 3655 416F 506A 6D48. in the [CGA] namespace registry with the value 0x4A30 5662 4858 574B
3655 416F 506A 6D48.
This protocol introduces a new shim6 message type name space. The IANA is directed to establish a SHIM6 Parameter Registry with two
initial assignment of the types is shown below. components: SHIM6 Type registrations and SHIM6 Options registrations.
The initial contents of the SHIM6 Type registry are as follows:
+------------+-----------------------------------------------------+ +------------+-----------------------------------------------------+
| Type Value | Message | | Type Value | Message |
+------------+-----------------------------------------------------+ +------------+-----------------------------------------------------+
| 0 | RESERVED | | 0 | RESERVED |
| | | | | |
| 1 | I1 (first establishment message from the initiator) | | 1 | I1 (first establishment message from the initiator) |
| | | | | |
| 2 | R1 (first establishment message from the responder) | | 2 | R1 (first establishment message from the responder) |
| | | | | |
skipping to change at page 86, line 49 skipping to change at page 89, line 4
| 65 | Update Acknowledgement | | 65 | Update Acknowledgement |
| | | | | |
| 66 | Keepalive | | 66 | Keepalive |
| | | | | |
| 67 | Probe Message | | 67 | Probe Message |
| | | | | |
| 68-123 | Can be allocated using Standards Action | | 68-123 | Can be allocated using Standards Action |
| | | | | |
| 124-127 | For Experimental use | | 124-127 | For Experimental use |
+------------+-----------------------------------------------------+ +------------+-----------------------------------------------------+
The initial contents of the SHIM6 Options registry are as follows:
This protocol introduces a new shim6 option type name space. The
initial assignment of the types is shown below.
+--------------+----------------------------------+ +--------------+----------------------------------+
| Type | Option Name | | Type | Option Name |
+--------------+----------------------------------+ +--------------+----------------------------------+
| 0 | RESERVED | | 0 | RESERVED |
| | | | | |
| 1 | Validator | | 1 | Responder Validator |
| | | | | |
| 2 | Locator List | | 2 | Locator List |
| | | | | |
| 3 | Locator Preferences | | 3 | Locator Preferences |
| | | | | |
| 4 | CGA Parameter Data Structure | | 4 | CGA Parameter Data Structure |
| | | | | |
| 5 | CGA Signature | | 5 | CGA Signature |
| | | | | |
| 6 | ULID Pair | | 6 | ULID Pair |
skipping to change at page 88, line 5 skipping to change at page 90, line 5
| | | | | |
| 11 | Reachability Option | | 11 | Reachability Option |
| | | | | |
| 12 | Payload Reception Report Option | | 12 | Payload Reception Report Option |
| | | | | |
| 13-16383 | Allocated using Standards action | | 13-16383 | Allocated using Standards action |
| | | | | |
| 16384-32767 | For Experimental use | | 16384-32767 | For Experimental use |
+--------------+----------------------------------+ +--------------+----------------------------------+
19. Possible Protocol Extensions 18. Acknowledgements
Over the years many people active in the multi6 and shim6 WGs have
contributed ideas a suggestions that are reflected in this
specification. Special thanks to the careful comments from Geoff
Houston and Shinta Sugimoto on earlier versions of this draft.
Appendix A. Open Issues
The following known open issues in this protocol specification are:
o NONE.
Appendix B. Possible Protocol Extensions
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
shim6 protocol to be able to recover from a wide range of
failures, for instance when one of the communicating hosts is
singly-homed, and cope with a site's ISPs that do ingress
filtering based on the source IPv6 address, there is a need for
the host to be able to influence the egress selection from its
site. Further discussion of this issue is captured in [20].
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.
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 Specifying a complete solution which carries locator preferences, o Supporting the dynamic setting of locator preferences on a site-
both within a site (e.g., DHCP option?), and use the Locator wide basis, and use the Locator Preference option in the shim6
Preference option to carry those in the shim protocol. This could protocol to convey these preferences to remote communicating
mirror the DNS SRV record's notion of priority and weight. hosts. This could mirror the DNS SRV record's notion of priority
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. This is using, and be able to influence the choice of locators
includes providing APIs the ULPs can use to fork a shim context. (controlling preferences as well as triggering a locator pair
switch). This includes providing APIs the ULPs can use to fork a
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
context setup but would quickly remove the context state after context setup but would quickly remove the context state after
this (in order to save memory) but the not-so-busy client would this (in order to save memory) but the not-so-busy client would
retain the context state. The context recovery mechanism retain the context state. The context recovery mechanism
presented in Section 7.3 would then be recreate the state should presented in Section 7.5 would then be recreate the state should
the client send either a shim control message (e.g., probe message the client send either a shim control message (e.g., probe message
because it sees a problem), or a ULP packet in an payload because it sees a problem), or a ULP packet in an payload
extension header (because it had earlier failed over to an extension header (because it had earlier failed over to an
alternative locator pair, but had been silent for a while). This alternative locator pair, but had been silent for a while). This
seems to provide the benefits of the shim as long as the client seems to provide the benefits of the shim as long as the client
can detect the failure. If the client doesn't send anything, and can detect the failure. If the client doesn't send anything, and
it is the server that tries to send, then it will not be able to it is the server that tries to send, then it will not be able to
recover because the shim on the server has no context state, hence recover because the shim on the server has no context state, hence
doesn't know any alternate locator pairs. doesn't know any alternate locator pairs.
skipping to change at page 90, line 5 skipping to change at page 93, line 38
requirement to include essentially all of them in the I2 and R2 requirement to include essentially all of them in the I2 and R2
messages might be constraining. If this is the case we can look messages might be constraining. If this is the case we can look
into using the CGA Parameter Data Structure for the comparison, into using the CGA Parameter Data Structure for the comparison,
instead of the prefix sets, to be able to detect context instead of the prefix sets, to be able to detect context
confusion. This would place some constraint on a (logical) only confusion. This would place some constraint on a (logical) only
using e.g., one CGA public key, and would require some carefully using e.g., one CGA public key, and would require some carefully
crafted rules on how two PDSs are compared for "being the same crafted rules on how two PDSs are compared for "being the same
host". But if we don't expect more than a handful locators per host". But if we don't expect more than a handful locators per
host, then we don't need this added complexity. host, then we don't need this added complexity.
20. Change Log o ULP specified timers for the reachability detection mechanism
(which can be useful particularly when there are forked contexts).
o Pre-verify some "backup" locator pair, so that the failover time
can be shorter.
o Study how shim6 and Mobile IPv6 might interact. There existing an
initial draft on this topic [21].
Appendix C. Change Log
The following changes have been made since draft-ietf-shim6-proto-03:
o Editorial clarifications based on comments from Geoff, Shinta,
Jari.
o Added "no IPv6 NATs as an explicit assumption.
o Moving some things out of the Introduction and Overview sections
to remove all SHOULDs and MUSTs from there.
o Added requirement that any Locator Preference options which use an
element length greater than 3 octets have the already defined
first 3 octets of flags, priority and weight.
o Fixed security hole where a single message (I1) could cause
CT(peer) to be updated. Now a three-way handshake is required
before CT(peer) is updated for an existing context.
The following changes have been made since draft-ietf-shim6-proto-02: The following changes have been made since draft-ietf-shim6-proto-02:
o Replaced the Context Error message with the R1bis message. o Replaced the Context Error message with the R1bis message.
o Removed the Packet In Error option, since it was only used in the o Removed the Packet In Error option, since it was only used in the
Context Error message. Context Error message.
o Introduced a I2bis message which is sent in response to an I1bis o Introduced a I2bis message which is sent in response to an I1bis
message, since the responders processing is quite in this case message, since the responders processing is quite in this case
than in the regular R1 case. than in the regular R1 case.
o Moved the packet formats for the Keepalive and Probe message types o Moved the packet formats for the Keepalive and Probe message types
and Event option to [9]. Only the message type values and option and Event option to [8]. Only the message type values and option
type value are specified for those in this document. type value are specified for those in this document.
o Removed the unused message types. o Removed the unused message types.
o Added a state machine description as an appendix. o Added a state machine description as an appendix.
o Filled in all the TBDs - except the IANA assignment of the o Filled in all the TBDs - except the IANA assignment of the
protocol number. protocol number.
o Specified how context recovery and forked contexts work together. o Specified how context recovery and forked contexts work together.
skipping to change at page 91, line 12 skipping to change at page 95, line 30
This allows extensibility of the protocol with new message types This allows extensibility of the protocol with new message types
while being able to control when R1bis is generated. while being able to control when R1bis is generated.
o Expanded the context tag from 32 to 47 bits. o Expanded the context tag from 32 to 47 bits.
o Specified that enough locators need to be included in I2 and R2 o Specified that enough locators need to be included in I2 and R2
messages. Specified that the HBA/CGA verification must be messages. Specified that the HBA/CGA verification must be
performed when the locator set is received. performed when the locator set is received.
o Specified that ICMP parameter problem errors are sent in certain o Specified that ICMP parameter problem errors are sent in certain
error cases, for instance when the validation method is unknown to error cases, for instance when the verification method is unknown
the receiver, or there is an unknown message type or option type. to the receiver, or there is an unknown message type or option
type.
o Renamed "payload message" to be "payload extension header". o Renamed "payload message" to be "payload extension header".
o Many editorial clarifications suggested by Geoff Huston. o Many editorial clarifications suggested by Geoff Huston.
o Modified the dispatching of payload extension header to only o Modified the dispatching of payload extension header to only
compare CT(local) i.e., not compare the source and destination compare CT(local) i.e., not compare the source and destination
IPv6 address fields. IPv6 address fields.
The following changes have been made since draft-ietf-shim6-proto-00: The following changes have been made since draft-ietf-shim6-proto-00:
skipping to change at page 93, line 5 skipping to change at page 97, line 5
context is forked, that is different ULP messages are sent over context is forked, that is different ULP messages are sent over
different locator pairs, things are a lot easier if there is only different locator pairs, things are a lot easier if there is only
one current locator pair used for each context. Thus the forking one current locator pair used for each context. Thus the forking
of the context is now causing a new context to be established for of the context is now causing a new context to be established for
the same ULID; the new context having a new context tag. The the same ULID; the new context having a new context tag. The
original context is referred to as the "default" context for the original context is referred to as the "default" context for the
ULID pair. ULID pair.
o Added more background material and textual descriptions. o Added more background material and textual descriptions.
21. Acknowledgements Appendix D. Simplified State Machine
Over the years many people active in the multi6 and shim6 WGs have
contributed ideas a suggestions that are reflected in this draft.
Appendix A. Simplified State Machine
The states are defined in Section 6.2. The intent is that the The states are defined in Section 6.2. The intent is that the
stylized description below be consistent with the textual description stylized description below be consistent with the textual description
in the specification, but should they conflict, the textual in the specification, but should they conflict, the textual
description is normative. description is normative.
The following table describes the possible actions in state IDLE and The following table describes the possible actions in state IDLE and
their respective triggers: their respective triggers:
+---------------------+---------------------------------------------+ +---------------------+---------------------------------------------+
skipping to change at page 98, line 10 skipping to change at page 101, line 10
| 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 | Send R2 and stay in ESTABLISHED | | Receive I1, compare | If no match, send R1 and stay in ESTABLISHED|
| CT(peer) with | |
| received CT | If match, send R2 and stay in ESTABLISHED |
| | |
| | | | | |
| Receive I2, verify | If successful, then send R2 and stay in | | Receive I2, verify | If successful, then send R2 and stay in |
| validator and RESP | ESTABLISHED | | validator and RESP | ESTABLISHED |
| nonce | | | nonce | |
| | Otherwise, discard and stay in ESTABLISHED | | | Otherwise, discard and stay in ESTABLISHED |
| | | | | |
| Receive I2bis, | If successful, then send R2 and stay in | | Receive I2bis, | If successful, then send R2 and stay in |
| verify validator | ESTABLISHED | | verify validator | ESTABLISHED |
| and RESP nonce | | | and RESP nonce | |
| | Otherwise, discard and stay in ESTABLISHED | | | Otherwise, discard and stay in ESTABLISHED |
skipping to change at page 99, line 16 skipping to change at page 102, line 28
+---------------------+---------------------------------------------+ +---------------------+---------------------------------------------+
| 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 A.1 Simplified State Machine diagram Appendix D.1 Simplified State Machine diagram
For the time being, a pdf version of the state machine diagram can be For the time being, a pdf version of the state machine diagram can be
found at: http://www.it.uc3m.es/marcelo/state_machine.pdf found at: http://www.it.uc3m.es/marcelo/state_machine.pdf
Appendix B. Context Tag Reuse Appendix E. Context Tag Reuse
The shim6 protocol doesn't have a mechanism for coordinated state The shim6 protocol doesn't have a mechanism for coordinated state
removal between the peers, because such state removal doesn't seem to removal between the peers, because such state removal doesn't seem to
help given that a host can crash and reboot at any time. A result of help given that a host can crash and reboot at any time. A result of
this is that the protocol needs to be robust against a context tag this is that the protocol needs to be robust against a context tag
being reused for some other context. This section summarizes the being reused for some other context. This section summarizes the
different cases in which a tag can be reused, and how the recovery different cases in which a tag can be reused, and how the recovery
works. works.
The different cases are exemplified by the following case. Assume The different cases are exemplified by the following case. Assume
skipping to change at page 100, line 35 skipping to change at page 103, line 35
<A1, B2>. We've called this "Context Recovery" in this document. <A1, B2>. We've called this "Context Recovery" in this document.
o The context tag is reassigned to a context for a different ULID o The context tag is reassigned to a context for a different ULID
pair between the same to hosts, e.g., <A3, B3>. We've called this pair between the same to hosts, e.g., <A3, B3>. We've called this
"Context Confusion" in this document. "Context Confusion" in this document.
o The context tag is reassigned to a context between B and other o The context tag is reassigned to a context between B and other
host C, for instance for the ULID pair <C3, B2>. That is a form host C, for instance for the ULID pair <C3, B2>. That is a form
of three party context confusion. of three party context confusion.
Appendix B.1 Context Recovery Appendix E.1 Context Recovery
This case is relatively simple, and is discussed in Section 7.3. The This case is relatively simple, and is discussed in Section 7.5. The
observation is that since the ULID pair is the same, when either A or observation is that since the ULID pair is the same, when either A or
B tries to establish the new context, A can keep the old context B tries to establish the new context, A can keep the old context
while B re-creates the context with the same context tag CT(B) = X. while B re-creates the context with the same context tag CT(B) = X.
Appendix B.2 Context Confusion Appendix E.2 Context Confusion
This cases is a bit more complex, and is discussed in Section 7.4. This cases is a bit more complex, and is discussed in Section 7.6.
When the new context is created, whether A or B initiates it, host A When the new context is created, whether A or B initiates it, host A
can detect when it receives B's locator set (in the I2, or R2 can detect when it receives B's locator set (in the I2, or R2
message), that it ends up with two contexts to the same peer host message), that it ends up with two contexts to the same peer host
(overlapping Ls(peer) locator sets) that have the same context tag (overlapping Ls(peer) locator sets) that have the same context tag
CT(peer) = X. At this point in time host A can clear up any CT(peer) = X. At this point in time host A can clear up any
possibility of causing confusion by not using the old context to send possibility of causing confusion by not using the old context to send
any more packets. It either just discards the old context (it might any more packets. It either just discards the old context (it might
not be used by any ULP traffic, since B had discarded it), or it not be used by any ULP traffic, since B had discarded it), or it
recreates a different context for the old ULID pair (<A1, B2>), for recreates a different context for the old ULID pair (<A1, B2>), for
which B will assign a unique CT(B) as part of the normal context which B will assign a unique CT(B) as part of the normal context
establishment mechanism. establishment mechanism.
Appendix B.3 Three Party Context Confusion Appendix E.3 Three Party Context Confusion
The third case does not have a place where the old state on A can be The third case does not have a place where the old state on A can be
verified, since the new context is established between B and C. Thus verified, since the new context is established between B and C. Thus
when B receives payload extension headers with X as the context tag, when B receives payload extension headers with X as the context tag,
it will find the context for <C3, B2>, hence rewrite the packets to it will find the context for <C3, B2>, hence rewrite the packets to
have C3 in the source address field and B2 in the destination address have C3 in the source address field and B2 in the destination address
field before passing them up to the ULP. This rewriting is correct field before passing them up to the ULP. This rewriting is correct
when the packets are in fact sent by host C, but if host A ever when the packets are in fact sent by host C, but if host A ever
happens to send a packet using the old context, then the ULP on A happens to send a packet using the old context, then the ULP on A
sends a packet with ULIDs <A1, B2> and the packet arrives at the ULP sends a packet with ULIDs <A1, B2> and the packet arrives at the ULP
skipping to change at page 102, line 5 skipping to change at page 105, line 5
In summary, there are cases where a context tag might be reused while In summary, there are cases where a context tag might be reused while
some peer retains the state, but the protocol can recover from it. some peer retains the state, but the protocol can recover from it.
The probability of these events is low given the 47 bit context tag The probability of these events is low given the 47 bit context tag
size. However, it is important that these recovery mechanisms be size. However, it is important that these recovery mechanisms be
tested. Thus during development and testing it is recommended that tested. Thus during development and testing it is recommended that
implementations not use the full 47 bit space, but instead keep e.g. implementations not use the full 47 bit space, but instead keep e.g.
the top 40 bits as zero, only leaving the host with 128 unique the top 40 bits as zero, only leaving the host with 128 unique
context tags. This will help test the recovery mechanisms. context tags. This will help test the recovery mechanisms.
Appendix C. Design Alternatives Appendix F. Design Alternatives
This document has picked a certain set of design choices in order to This document has picked a certain set of design choices in order to
try to work out a bunch of the details, and stimulate discussion. try to work out a bunch of the details, and stimulate discussion.
But as has been discussed on the mailing list, there are other But as has been discussed on the mailing list, there are other
choices that make sense. This appendix tries to enumerate some choices that make sense. This appendix tries to enumerate some
alternatives. alternatives.
Appendix C.1 Context granularity Appendix F.1 Context granularity
Over the years various suggestions have been made whether the shim Over the years various suggestions have been made whether the shim
should, even if it operates at the IP layer, be aware of ULP should, even if it operates at the IP layer, be aware of ULP
connections and sessions, and as a result be able to make separate connections and sessions, and as a result be able to make separate
shim contexts for separate ULP connections and sessions. A few shim contexts for separate ULP connections and sessions. A few
different options have been discussed: different options have been discussed:
o Each ULP connection maps to its own shim context. o Each ULP connection maps to its own shim context.
o The shim is unaware of the ULP notion of connections and just o The shim is unaware of the ULP notion of connections and just
skipping to change at page 102, line 45 skipping to change at page 105, line 45
that want different communication to use different locator pairs, for that want different communication to use different locator pairs, for
instance for quality or cost reasons. instance for quality or cost reasons.
The protocol has a shim which operates with host-level granularity The protocol has a shim which operates with host-level granularity
(strictly speaking, with ULID-pair granularity, to be able to (strictly speaking, with ULID-pair granularity, to be able to
amortize the context establishment over multiple ULP connections. amortize the context establishment over multiple ULP connections.
This is combined with the ability for shim-aware ULPs to request This is combined with the ability for shim-aware ULPs to request
context forking so that different ULP traffic can use different context forking so that different ULP traffic can use different
locator pairs. locator pairs.
Appendix C.2 Demultiplexing of data packets in shim6 communications Appendix F.2 Demultiplexing of data packets in shim6 communications
Once a ULID-pair context is established between two hosts, packets Once a ULID-pair context is established between two hosts, packets
may carry locators that differ from the ULIDs presented to the ULPs may carry locators that differ from the ULIDs presented to the ULPs
using the established context. One of main functions of the SHIM6 using the established context. One of main functions of the SHIM6
layer is to perform the mapping between the locators used to forward layer is to perform the mapping between the locators used to forward
packets through the network and the ULIDs presented to the ULP. In packets through the network and the ULIDs presented to the ULP. In
order to perform that translation for incoming packets, the SHIM6 order to perform that translation for incoming packets, the SHIM6
layer needs to first identify which of the incoming packets need to layer needs to first identify which of the incoming packets need to
be translated and then perform the mapping between locators and ULIDs be translated and then perform the mapping between locators and ULIDs
using the associated context. Such operation is called using the associated context. Such operation is called
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packet to determine the shim context to be used to perform the packet to determine the shim context to be used to perform the
operation. operation.
Two mechanisms for carrying the context tag information have been Two mechanisms for carrying the context tag information have been
considered in depth during the shim protocol design. Those carrying considered in depth during the shim protocol design. Those carrying
the context tag in the flow label field of the IPv6 header and the the context tag in the flow label field of the IPv6 header and the
usage of a new extension header to carry the context tag. In this usage of a new extension header to carry the context tag. In this
appendix we will describe the pros and cons of each approach and appendix we will describe the pros and cons of each approach and
justify the selected option. justify the selected option.
Appendix C.2.1 Flow-label Appendix F.2.1 Flow-label
A possible approach is to carry the context tag in the Flow Label A possible approach is to carry the context tag in the Flow Label
field of the IPv6 header. This means that when a shim6 context is field of the IPv6 header. This means that when a shim6 context is
established, a Flow Label value is associated with this context (and established, a Flow Label value is associated with this context (and
perhaps a separate flow label for each direction). perhaps a separate flow label for each direction).
The simplest approach that does this is to have the triple <Flow The simplest approach that does this is to have the triple <Flow
Label, Source Locator, Destination Locator> identify the context at Label, Source Locator, Destination Locator> identify the context at
the receiver. the receiver.
skipping to change at page 104, line 47 skipping to change at page 107, line 47
negotiation of the Flow Label value to use in the communication is negotiation of the Flow Label value to use in the communication is
needed before exchanging data packets. This poses problems with non- needed before exchanging data packets. This poses problems with non-
shim capable hosts, since they would not be able to negotiate an shim capable hosts, since they would not be able to negotiate an
acceptable value for the Flow Label. This limitation can be lifted acceptable value for the Flow Label. This limitation can be lifted
by marking the packets that belong to shim sessions from those that by marking the packets that belong to shim sessions from those that
do not. These marking would require at least a bit in the IPv6 do not. These marking would require at least a bit in the IPv6
header that is not currently available, so more creative options header that is not currently available, so more creative options
would be required, for instance using new Next Header values to would be required, for instance using new Next Header values to
indicate that the packet belongs to a shim6 enabled communication and indicate that the packet belongs to a shim6 enabled communication and
that the Flow Label carries context information as proposed in the that the Flow Label carries context information as proposed in the
now expire NOID draft. . However, even if this is done, this now expired NOID draft. . However, even if this is done, this
approach is incompatible with the deferred establishment capability approach is incompatible with the deferred establishment capability
of the shim protocol, which is a preferred function, since it of the shim protocol, which is a preferred function, since it
suppresses the delay due to the shim context establishment prior to suppresses the delay due to the shim context establishment prior to
initiation of the communication and it also allows nodes to define at initiation of the communication and it also allows nodes to define at
which stage of the communication they decide, based on their own which stage of the communication they decide, based on their own
policies, that a given communication requires to be protected by the policies, that a given communication requires to be protected by the
shim. shim.
In order to cope with the identified limitations, an alternative In order to cope with the identified limitations, an alternative
approach that does not constraints the flow label values used by approach that does not constraints the flow label values used by
communications that are using ULIDs equal to the locators (i.e. no communications that are using ULIDs equal to the locators (i.e. no
shim translation) is to only require that different flow label values shim translation) is to only require that different flow label values
are assigned to different shim contexts. In such approach are assigned to different shim contexts. In such approach
communications start with unmodified flow label usage (could be zero, communications start with unmodified flow label usage (could be zero,
or as suggested in [17]). The packets sent after a failure when a or as suggested in [16]). The packets sent after a failure when a
different locator pair is used would use a completely different flow different locator pair is used would use a completely different flow
label, and this flow label could be allocated by the receiver as part label, and this flow label could be allocated by the receiver as part
of the shim context establishment. Since it is allocated during the of the shim context establishment. Since it is allocated during the
context establishment, the receiver of the "failed over" packets can context establishment, the receiver of the "failed over" packets can
pick a flow label of its choosing (that is unique in the sense that pick a flow label of its choosing (that is unique in the sense that
no other context is using it as a context tag), without any no other context is using it as a context tag), without any
performance impact, and respecting that for each locator pair, the performance impact, and respecting that for each locator pair, the
flow label value used for a given locator pair doesn't change due to flow label value used for a given locator pair doesn't change due to
the operation of the multihoming shim. the operation of the multihoming shim.
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would be the preferred approach if the context tag is to be carried would be the preferred approach if the context tag is to be carried
in the Flow Label field. This is not only because it imposes the in the Flow Label field. This is not only because it imposes the
minimum constraints to the Flow Label allocation strategies, limiting minimum constraints to the Flow Label allocation strategies, limiting
the restrictions only to those packets that need to be translated by the restrictions only to those packets that need to be translated by
the shim, but also because Context Loss detection mechanisms greatly the shim, but also because Context Loss detection mechanisms greatly
benefit from the fact that shim data packets are identified as such, benefit from the fact that shim data packets are identified as such,
allowing the receiving end to identify if a shim context associated allowing the receiving end to identify if a shim context associated
to a received packet is suppose to exist, as it will be discussed in to a received packet is suppose to exist, as it will be discussed in
the Context Loss detection appendix below. the Context Loss detection appendix below.
Appendix C.2.2 Extension Header Appendix F.2.2 Extension Header
Another approach, which is the one selected for this protocol, is to Another approach, which is the one selected for this protocol, is to
carry the context tag in a new Extension Header. These context tags carry the context tag in a new Extension Header. These context tags
are allocated by the receiving end during the shim6 protocol initial are allocated by the receiving end during the shim6 protocol initial
negotiation, implying that each context will have two context tags, negotiation, implying that each context will have two context tags,
one for each direction. Data packets will be demultiplexed using the one for each direction. Data packets will be demultiplexed using the
context tag carried in the Extension Header. This seems a clean context tag carried in the Extension Header. This seems a clean
approach since it does not overload existing fields. However, it approach since it does not overload existing fields. However, it
introduces additional overhead in the packet due to the additional introduces additional overhead in the packet due to the additional
header. The additional overhead introduced is 8 octets. However, it header. The additional overhead introduced is 8 octets. However, it
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ULIDs do not require a context tag, since no rewriting is necessary ULIDs do not require a context tag, since no rewriting is necessary
at the receiver. This approach would reduce the overhead, because at the receiver. This approach would reduce the overhead, because
the additional header is only required after a failure. On the other the additional header is only required after a failure. On the other
hand, this approach would cause changes in the available MTU for some hand, this approach would cause changes in the available MTU for some
packets, since packets that include the Extension Header will have an packets, since packets that include the Extension Header will have an
MTU 8 octets shorter. However, path changes through the network can MTU 8 octets shorter. However, path changes through the network can
result in different MTU in any case, thus having a locator change, result in different MTU in any case, thus having a locator change,
which implies a path change, affect the MTU doesn't introduce any new which implies a path change, affect the MTU doesn't introduce any new
issues. issues.
Appendix C.3 Context Loss Detection Appendix F.3 Context Loss Detection
In this appendix we will present different approaches considered to In this appendix we will present different approaches considered to
detect context loss and potential context recovery strategies. The detect context loss and potential context recovery strategies. The
scenario being considered is the following: Node A and Node B are scenario being considered is the following: Node A and Node B are
communicating using IPA1 and IPB1. Sometime later, a shim context is communicating using IPA1 and IPB1. Sometime later, a shim context is
established between them, with IPA1 and IPB1 as ULIDs and established between them, with IPA1 and IPB1 as ULIDs and
IPA1,...,IPAn and IPB1,...,IPBm as locator set respectively. IPA1,...,IPAn and IPB1,...,IPBm as locator set respectively.
It may happen, that later on, one of the hosts, e.g. Host A looses It may happen, that later on, one of the hosts, e.g. Host A looses
the shim context. The reason for this can be that Host A has a more the shim context. The reason for this can be that Host A has a more
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exchange and at this point time may be critical since we are exchange and at this point time may be critical since we are
reestablishing a context that is currently needed (because context reestablishing a context that is currently needed (because context
loss detection may occur after a failure). So, another option, which loss detection may occur after a failure). So, another option, which
is the one used in this protocol, is to replace the error message by is the one used in this protocol, is to replace the error message by
a modified R1 message, so that the time required to perform the a modified R1 message, so that the time required to perform the
context establishment exchange can be reduced. Upon the reception of context establishment exchange can be reduced. Upon the reception of
this modified R1 message, the end that still has the context state this modified R1 message, the end that still has the context state
can finish the context establishment exchange and restore the lost can finish the context establishment exchange and restore the lost
context. context.
Appendix C.4 Securing locator sets Appendix F.4 Securing locator sets
The adoption of a protocol like SHIM that allows the binding of a The adoption of a protocol like SHIM that allows the binding of a
given ULID with a set of locators opens the doors for different types given ULID with a set of locators opens the doors for different types
of redirection attacks as described in [20]. The goal in terms of of redirection attacks as described in [19]. The goal in terms of
security for the design of the shim protocol is not to introduce any security for the design of the shim protocol is not to introduce any
new vulnerability in the Internet architecture. It is a non-goal to new vulnerability in the Internet architecture. It is a non-goal to
provide additional protection than the currently available in the provide additional protection than the currently available in the
single-homed IPv6 Internet. single-homed IPv6 Internet.
Multiple security mechanisms were considered to protect the shim Multiple security mechanisms were considered to protect the shim
protocol. In this appendix we will present some of them. protocol. In this appendix we will present some of them.
The simplest option to protect the shim protocol was to use cookies The simplest option to protect the shim protocol was to use cookies
i.e. a randomly generated bit string that is negotiated during the i.e. a randomly generated bit string that is negotiated during the
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So, the design decision adopted was that both mechanisms HBA and CGA So, the design decision adopted was that both mechanisms HBA and CGA
are supported, so that when only stable address sets are required, are supported, so that when only stable address sets are required,
the nodes can benefit from the low computational cost offered by HBA the nodes can benefit from the low computational cost offered by HBA
while when dynamic locator sets are required, this can be achieved while when dynamic locator sets are required, this can be achieved
through CGAs with an additional cost. Moreover, because HBAs are through CGAs with an additional cost. Moreover, because HBAs are
defined as a CGA extension, the addresses available in a node can defined as a CGA extension, the addresses available in a node can
simultaneously be CGAs and HBAs, allowing the usage of the HBA and simultaneously be CGAs and HBAs, allowing the usage of the HBA and
CGA functionality when needed without requiring a change in the CGA functionality when needed without requiring a change in the
addresses used. addresses used.
Appendix C.5 ULID-pair context establishment exchange Appendix F.5 ULID-pair context establishment exchange
Two options were considered for the ULID-pair context establishment Two options were considered for the ULID-pair context establishment
exchange: a 2-way handshake and a 4-way handshake. exchange: a 2-way handshake and a 4-way handshake.
A key goal for the design of this exchange was that protection A key goal for the design of this exchange was that protection
against DoS attacks. The attack under consideration was basically a against DoS attacks. The attack under consideration was basically a
situation where an attacker launches a great amount of ULID-pair situation where an attacker launches a great amount of ULID-pair
establishment request packets, exhausting victim's resources, similar establishment request packets, exhausting victim's resources, similar
to TCP SYN flooding attacks. to TCP SYN flooding attacks.
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should be noted, that because this is 2-way exchange, it is not should be noted, that because this is 2-way exchange, it is not
possible to use the number of half open sessions (as in TCP) to possible to use the number of half open sessions (as in TCP) to
detect an ongoing attack and different heuristics need to be detect an ongoing attack and different heuristics need to be
considered. considered.
The design decision taken was that considering the current impact of The design decision taken was that considering the current impact of
DoS attacks and the low impact of the 4-way exchange in the shim DoS attacks and the low impact of the 4-way exchange in the shim
protocol thanks to the deferred context establishment capability, a protocol thanks to the deferred context establishment capability, a
4-way exchange would be adopted for the base protocol. 4-way exchange would be adopted for the base protocol.
Appendix C.6 Updating locator sets Appendix F.6 Updating locator sets
There are two possible approaches to the addition and removal of There are two possible approaches to the addition and removal of
locators: atomic and differential approaches. The atomic approach locators: atomic and differential approaches. The atomic approach
essentially send the complete locators set each time that a variation essentially send the complete locators set each time that a variation
in the locator set occurs. The differential approach send the in the locator set occurs. The differential approach send the
differences between the existing locator set and the new one. The differences between the existing locator set and the new one. The
atomic approach imposes additional overhead, since all the locator atomic approach imposes additional overhead, since all the locator
set has to be exchanged each time while the differential approach set has to be exchanged each time while the differential approach
requires re-synchronization of both ends through changes i.e. that requires re-synchronization of both ends through changes i.e. that
both ends have the same idea about what the current locator set is. both ends have the same idea about what the current locator set is.
Because of the difficulties imposed by the synchronization Because of the difficulties imposed by the synchronization
requirement, the atomic approach was selected. requirement, the atomic approach was selected.
Appendix C.7 State Cleanup Appendix F.7 State Cleanup
There are essentially two approaches for discarding an existing state There are essentially two approaches for discarding an existing state
about locators, keys and identifiers of a correspondent node: a about locators, keys and identifiers of a correspondent node: a
coordinated approach and an unilateral approach. coordinated approach and an unilateral approach.
In the unilateral approach, each node discards the information about In the unilateral approach, each node discards the information about
the other node without coordination with the other node based on some the other node without coordination with the other node based on some
local timers and heuristics. No packet exchange is required for local timers and heuristics. No packet exchange is required for
this. In this case, it would be possible that one of the nodes has this. In this case, it would be possible that one of the nodes has
discarded the state while the other node still hasn't. In this case, discarded the state while the other node still hasn't. In this case,
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 [26]. If an explicit CLOSE handshake and the one specified in HIP [25]. 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.
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coordinated approach using a CLOSE/CLOSE ACK exchange, there is still coordinated approach using a CLOSE/CLOSE ACK exchange, there is still
the possibility of a host rebooting without having the time to the possibility of a host rebooting without having the time to
perform the CLOSE exchange. So, it is true that the coordinated perform the CLOSE exchange. So, it is true that the coordinated
approach eliminates the possibility of a context confusion situation approach eliminates the possibility of a context confusion situation
because premature garbage collection, but it does not prevents the because premature garbage collection, but it does not prevents the
same situations due to a crash and reboot of one of the involved same situations due to a crash and reboot of one of the involved
hosts. The result is that even if we went for a coordinated hosts. The result is that even if we went for a coordinated
approach, we would still need to deal with context confusion and approach, we would still need to deal with context confusion and
provide the means to detect and recover from this situations. provide the means to detect and recover from this situations.
22. References 19. References
22.1 Normative References 19.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery [3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998. for IP Version 6 (IPv6)", RFC 2461, December 1998.
skipping to change at page 115, line 31 skipping to change at page 118, line 31
[5] Conta, A. and S. Deering, "Internet Control Message Protocol [5] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6) (ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998. Specification", RFC 2463, December 1998.
[6] Aura, T., "Cryptographically Generated Addresses (CGA)", [6] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005. RFC 3972, March 2005.
[7] Bagnulo, M., "Hash Based Addresses (HBA)", [7] Bagnulo, M., "Hash Based Addresses (HBA)",
draft-ietf-shim6-hba-01 (work in progress), October 2005. draft-ietf-shim6-hba-01 (work in progress), October 2005.
[8] Beijnum, I., "Shim6 Reachability Detection", [8] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair
draft-ietf-shim6-reach-detect-01 (work in progress),
October 2005.
[9] 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-02 (work in progress), draft-ietf-shim6-failure-detection-03 (work in progress),
October 2005. December 2005.
22.2 Informative References 19.2 Informative References
[10] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [9] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[11] Ferguson, P. and D. Senie, "Network Ingress Filtering: [10] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000. Address Spoofing", BCP 38, RFC 2827, May 2000.
[12] Narten, T. and R. Draves, "Privacy Extensions for Stateless [11] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001. Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[13] Draves, R., "Default Address Selection for Internet Protocol [12] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003. version 6 (IPv6)", RFC 3484, February 2003.
[14] Bagnulo, M., "Updating RFC 3484 for multihoming support", [13] Bagnulo, M., "Updating RFC 3484 for multihoming support",
draft-bagnulo-ipv6-rfc3484-update-00 (work in progress), draft-bagnulo-ipv6-rfc3484-update-00 (work in progress),
December 2005. December 2005.
[15] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, [14] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64, "RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003. RFC 3550, July 2003.
[16] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site- [15] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
Multihoming Architectures", RFC 3582, August 2003. Multihoming Architectures", RFC 3582, August 2003.
[17] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering, "IPv6 [16] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering, "IPv6
Flow Label Specification", RFC 3697, March 2004. Flow Label Specification", RFC 3697, March 2004.
[18] Eastlake, D., Schiller, J., and S. Crocker, "Randomness [17] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005. Requirements for Security", BCP 106, RFC 4086, June 2005.
[19] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast [18] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005. Addresses", RFC 4193, October 2005.
[20] Nordmark, E., "Threats relating to IPv6 multihoming solutions", [19] Nordmark, E. and T. Li, "Threats Relating to IPv6 Multihoming
draft-ietf-multi6-multihoming-threats-03 (work in progress), Solutions", RFC 4218, October 2005.
January 2005.
[21] Nordmark, E., "Shim6 Application Referral Issues", [20] Huitema, C., "Ingress filtering compatibility for IPv6
multihomed sites", draft-huitema-shim6-ingress-filtering-00
(work in progress), September 2005.
[21] Bagnulo, M. and E. Nordmark, "SHIM - MIPv6 Interaction",
draft-bagnulo-shim6-mip-00 (work in progress), July 2005.
[22] 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.
[22] Abley, J., "Shim6 Applicability Statement", [23] Abley, J., "Shim6 Applicability Statement",
draft-ietf-shim6-applicability-00 (work in progress), draft-ietf-shim6-applicability-00 (work in progress),
July 2005. July 2005.
[23] Huston, G., "Architectural Commentary on Site Multi-homing [24] Huston, G., "Architectural Commentary on Site Multi-homing
using a Level 3 Shim", draft-ietf-shim6-arch-00 (work in using a Level 3 Shim", draft-ietf-shim6-arch-00 (work in
progress), July 2005. progress), July 2005.
[24] Bagnulo, M. and J. Arkko, "Functional decomposition of the [25] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-05
multihoming protocol", draft-ietf-shim6-functional-dec-00 (work (work in progress), March 2006.
in progress), July 2005.
[25] Nordmark, E. and M. Bagnulo, "Multihoming L3 Shim Approach",
draft-ietf-shim6-l3shim-00 (work in progress), July 2005.
[26] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-04
(work in progress), October 2005.
[27] Lear, E. and R. Droms, "What's In A Name:Thoughts from the
NSRG", draft-irtf-nsrg-report-10 (work in progress),
September 2003.
[28] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", [26] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
draft-ietf-mobike-protocol-07 (work in progress), draft-ietf-mobike-protocol-08 (work in progress),
December 2005. February 2006.
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 118, line 41 skipping to change at page 121, line 41
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 AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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