--- 1/draft-ietf-shim6-proto-03.txt 2006-03-07 22:13:11.000000000 +0100 +++ 2/draft-ietf-shim6-proto-04.txt 2006-03-07 22:13:12.000000000 +0100 @@ -1,19 +1,19 @@ SHIM6 WG E. Nordmark Internet-Draft Sun Microsystems -Expires: March 5, 2006 M. Bagnulo +Expires: September 5, 2006 M. Bagnulo UC3M - September 2005 + March 4, 2006 Level 3 multihoming shim protocol - draft-ietf-shim6-proto-03.txt + draft-ietf-shim6-proto-04.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that @@ -24,290 +24,315 @@ and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on March 5, 2006. + This Internet-Draft will expire on September 5, 2006. Copyright Notice - Copyright (C) The Internet Society (2005). + Copyright (C) The Internet Society (2006). Abstract - The SHIM6 working group is specifying a layer 3 shim approach and - protocol for providing locator agility below the transport protocols, - so that multihoming can be provided for IPv6 with failover and load - spreading properties, without assuming that a multihomed site will - have a provider independent IPv6 address prefix which is announced in - the global IPv6 routing table. The hosts in a site which has - multiple provider allocated IPv6 address prefixes, will use the shim6 - protocol specified in this document to setup state with peer hosts, - so that the state can later be used to failover to a different - locator pair, should the original one stop working. + The SHIM6 protocol is a layer 3 shim for providing locator agility + below the transport protocols, so that multihoming can be provided + for IPv6 with failover and load sharing properties, without assuming + that a multihomed site will have a provider independent IPv6 address + prefix which is announced in the global IPv6 routing table. The + hosts in a site which has multiple provider allocated IPv6 address + prefixes, will use the shim6 protocol specified in this document to + setup state with peer hosts, so that the state can later be used to + failover to a different locator pair, should the original one stop + working. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Goals . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Non-Goals . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Locators as Upper-layer Identifiers . . . . . . . . . . 6 1.4 IP Multicast . . . . . . . . . . . . . . . . . . . . . . 7 - 1.5 Renumbering Implications . . . . . . . . . . . . . . . . 7 - 1.6 Placement of the shim . . . . . . . . . . . . . . . . . 8 - 1.7 Traffic Engineering . . . . . . . . . . . . . . . . . . 10 + 1.5 Renumbering Implications . . . . . . . . . . . . . . . . 8 + 1.6 Placement of the shim . . . . . . . . . . . . . . . . . 9 + 1.7 Traffic Engineering . . . . . . . . . . . . . . . . . . 11 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 12 2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . 12 - 2.2 Notational Conventions . . . . . . . . . . . . . . . . . 14 + 2.2 Notational Conventions . . . . . . . . . . . . . . . . . 15 3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . 16 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . 17 4.1 Context Tags . . . . . . . . . . . . . . . . . . . . . . 19 4.2 Context Forking . . . . . . . . . . . . . . . . . . . . 19 4.3 API Extensions . . . . . . . . . . . . . . . . . . . . . 20 4.4 Securing shim6 . . . . . . . . . . . . . . . . . . . . . 20 4.5 Overview of Shim Control Messages . . . . . . . . . . . 21 4.6 Extension Header Order . . . . . . . . . . . . . . . . . 22 - 4.7 Locator Validation . . . . . . . . . . . . . . . . . . . 22 5. Message Formats . . . . . . . . . . . . . . . . . . . . . . 24 5.1 Common shim6 Message Format . . . . . . . . . . . . . . 24 5.2 Payload Extension Header Format . . . . . . . . . . . . 24 5.3 Common Shim6 Control header . . . . . . . . . . . . . . 25 5.4 I1 Message Format . . . . . . . . . . . . . . . . . . . 27 5.5 R1 Message Format . . . . . . . . . . . . . . . . . . . 28 5.6 I2 Message Format . . . . . . . . . . . . . . . . . . . 30 5.7 R2 Message Format . . . . . . . . . . . . . . . . . . . 31 5.8 R1bis Message Format . . . . . . . . . . . . . . . . . . 33 5.9 I2bis Message Format . . . . . . . . . . . . . . . . . . 34 5.10 Update Request Message Format . . . . . . . . . . . . . 36 5.11 Update Acknowledgement Message Format . . . . . . . . . 38 5.12 Keepalive Message Format . . . . . . . . . . . . . . . . 39 5.13 Probe Message Format . . . . . . . . . . . . . . . . . . 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 5.14.3 Locator Preferences Option Format . . . . . . . . . 43 5.14.4 CGA Parameter Data Structure Option Format . . . . . 45 5.14.5 CGA Signature Option Format . . . . . . . . . . . . 46 - 5.14.6 ULID Pair Option Format . . . . . . . . . . . . . . 46 - 5.14.7 Forked Instance Identifier Option Format . . . . . . 47 + 5.14.6 ULID Pair Option Format . . . . . . . . . . . . . . 47 + 5.14.7 Forked Instance Identifier Option Format . . . . . . 48 5.14.8 Probe Option Format . . . . . . . . . . . . . . . . 48 5.14.9 Reachability Option Format . . . . . . . . . . . . . 48 5.14.10 Payload Reception Report Option Format . . . . . . 48 6. Conceptual Model of a Host . . . . . . . . . . . . . . . . . 49 6.1 Conceptual Data Structures . . . . . . . . . . . . . . . 49 6.2 Context States . . . . . . . . . . . . . . . . . . . . . 50 7. Establishing ULID-Pair Contexts . . . . . . . . . . . . . . 52 - 7.1 Normal context establishment . . . . . . . . . . . . . . 52 - 7.2 Concurrent context establishment . . . . . . . . . . . . 52 - 7.3 Context recovery . . . . . . . . . . . . . . . . . . . . 54 - 7.4 Context confusion . . . . . . . . . . . . . . . . . . . 56 - 7.5 Sending I1 messages . . . . . . . . . . . . . . . . . . 57 - 7.6 Retransmitting I1 messages . . . . . . . . . . . . . . . 57 - 7.7 Receiving I1 messages . . . . . . . . . . . . . . . . . 58 - 7.7.1 Generating the R1 validator . . . . . . . . . . . . 59 - 7.8 Receiving R1 messages and sending I2 messages . . . . . 59 - 7.9 Retransmitting I2 messages . . . . . . . . . . . . . . . 60 - 7.10 Receiving I2 messages . . . . . . . . . . . . . . . . . 61 - 7.11 Sending R2 messages . . . . . . . . . . . . . . . . . . 62 - 7.12 Match for Context Confusion . . . . . . . . . . . . . . 62 - 7.13 Receiving R2 messages . . . . . . . . . . . . . . . . . 63 - 7.14 Sending R1bis packets . . . . . . . . . . . . . . . . . 64 - 7.14.1 Generating the R1bis validator . . . . . . . . . . . 64 - 7.15 Receiving R1bis messages and sending I2bis messages . . 65 - 7.16 Receiving I2bis messages and sending R2 messages . . . . 66 - 8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 68 - 9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . 69 - 10. Updating the Peer . . . . . . . . . . . . . . . . . . . . 70 - 10.1 Sending Update Request messages . . . . . . . . . . . . 70 - 10.2 Retransmitting Update Request messages . . . . . . . . . 70 - 10.3 Newer Information While Retransmitting . . . . . . . . . 71 - 10.4 Receiving Update Request messages . . . . . . . . . . . 71 - 10.5 Receiving Update Acknowledgement messages . . . . . . . 73 - 11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . 74 - 11.1 Sending ULP Payload after a Switch . . . . . . . . . . . 74 - 12. Receiving Packets . . . . . . . . . . . . . . . . . . . . 76 - 12.1 Receiving Payload Extension Headers . . . . . . . . . . 76 - 12.2 Receiving Shim Control messages . . . . . . . . . . . . 76 - 12.3 Context Lookup . . . . . . . . . . . . . . . . . . . . . 77 - 13. Initial Contact . . . . . . . . . . . . . . . . . . . . . 79 - 14. Protocol constants . . . . . . . . . . . . . . . . . . . . 80 - 15. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 81 - 16. Implications Elsewhere . . . . . . . . . . . . . . . . . . 82 - 17. Security Considerations . . . . . . . . . . . . . . . . . 84 - 18. IANA Considerations . . . . . . . . . . . . . . . . . . . 86 - 19. Possible Protocol Extensions . . . . . . . . . . . . . . . 88 - 20. Change Log . . . . . . . . . . . . . . . . . . . . . . . . 90 - 21. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 93 - A. Simplified State Machine . . . . . . . . . . . . . . . . . . 94 - A.1 Simplified State Machine diagram . . . . . . . . . . . . 99 - B. Context Tag Reuse . . . . . . . . . . . . . . . . . . . . . 100 - B.1 Context Recovery . . . . . . . . . . . . . . . . . . . . 100 - B.2 Context Confusion . . . . . . . . . . . . . . . . . . . 100 - B.3 Three Party Context Confusion . . . . . . . . . . . . . 101 - C. Design Alternatives . . . . . . . . . . . . . . . . . . . . 102 - C.1 Context granularity . . . . . . . . . . . . . . . . . . 102 - C.2 Demultiplexing of data packets in shim6 communications . 102 - C.2.1 Flow-label . . . . . . . . . . . . . . . . . . . . . 103 - C.2.2 Extension Header . . . . . . . . . . . . . . . . . . 105 - C.3 Context Loss Detection . . . . . . . . . . . . . . . . . 106 - C.4 Securing locator sets . . . . . . . . . . . . . . . . . 108 - C.5 ULID-pair context establishment exchange . . . . . . . . 111 - C.6 Updating locator sets . . . . . . . . . . . . . . . . . 112 - C.7 State Cleanup . . . . . . . . . . . . . . . . . . . . . 112 - 22. References . . . . . . . . . . . . . . . . . . . . . . . . 115 - 22.1 Normative References . . . . . . . . . . . . . . . . . . 115 - 22.2 Informative References . . . . . . . . . . . . . . . . . 115 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 117 - Intellectual Property and Copyright Statements . . . . . . . 118 + 7.1 Uniqness of Context Tags . . . . . . . . . . . . . . . . 52 + 7.2 Locator Verification . . . . . . . . . . . . . . . . . . 52 + 7.3 Normal context establishment . . . . . . . . . . . . . . 53 + 7.4 Concurrent context establishment . . . . . . . . . . . . 53 + 7.5 Context recovery . . . . . . . . . . . . . . . . . . . . 55 + 7.6 Context confusion . . . . . . . . . . . . . . . . . . . 57 + 7.7 Sending I1 messages . . . . . . . . . . . . . . . . . . 58 + 7.8 Retransmitting I1 messages . . . . . . . . . . . . . . . 58 + 7.9 Receiving I1 messages . . . . . . . . . . . . . . . . . 59 + 7.9.1 Generating the R1 Validator . . . . . . . . . . . . 60 + 7.10 Receiving R1 messages and sending I2 messages . . . . . 61 + 7.11 Retransmitting I2 messages . . . . . . . . . . . . . . . 62 + 7.12 Receiving I2 messages . . . . . . . . . . . . . . . . . 62 + 7.13 Sending R2 messages . . . . . . . . . . . . . . . . . . 64 + 7.14 Match for Context Confusion . . . . . . . . . . . . . . 64 + 7.15 Receiving R2 messages . . . . . . . . . . . . . . . . . 65 + 7.16 Sending R1bis messages . . . . . . . . . . . . . . . . . 66 + 7.16.1 Generating the R1bis Validator . . . . . . . . . . . 66 + 7.17 Receiving R1bis messages and sending I2bis messages . . 67 + 7.18 Retransmitting I2bis messages . . . . . . . . . . . . . 68 + 7.19 Receiving I2bis messages and sending R2 messages . . . . 68 + 8. Handling ICMP Error Messages . . . . . . . . . . . . . . . . 70 + 9. Teardown of the ULID-Pair Context . . . . . . . . . . . . . 72 + 10. Updating the Peer . . . . . . . . . . . . . . . . . . . . 73 + 10.1 Sending Update Request messages . . . . . . . . . . . . 73 + 10.2 Retransmitting Update Request messages . . . . . . . . . 73 + 10.3 Newer Information While Retransmitting . . . . . . . . . 74 + 10.4 Receiving Update Request messages . . . . . . . . . . . 74 + 10.5 Receiving Update Acknowledgement messages . . . . . . . 76 + 11. Sending ULP Payloads . . . . . . . . . . . . . . . . . . . 77 + 11.1 Sending ULP Payload after a Switch . . . . . . . . . . . 77 + 12. Receiving Packets . . . . . . . . . . . . . . . . . . . . 79 + 12.1 Receiving Payload Extension Headers . . . . . . . . . . 79 + 12.2 Receiving Shim Control messages . . . . . . . . . . . . 79 + 12.3 Context Lookup . . . . . . . . . . . . . . . . . . . . . 80 + 13. Initial Contact . . . . . . . . . . . . . . . . . . . . . 82 + 14. Protocol constants . . . . . . . . . . . . . . . . . . . . 83 + 15. Implications Elsewhere . . . . . . . . . . . . . . . . . . 84 + 16. Security Considerations . . . . . . . . . . . . . . . . . 86 + 17. IANA Considerations . . . . . . . . . . . . . . . . . . . 88 + 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 90 + A. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 91 + B. Possible Protocol Extensions . . . . . . . . . . . . . . . . 92 + C. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 94 + D. Simplified State Machine . . . . . . . . . . . . . . . . . . 97 + D.1 Simplified State Machine diagram . . . . . . . . . . . . 102 + E. Context Tag Reuse . . . . . . . . . . . . . . . . . . . . . 103 + E.1 Context Recovery . . . . . . . . . . . . . . . . . . . . 103 + E.2 Context Confusion . . . . . . . . . . . . . . . . . . . 103 + E.3 Three Party Context Confusion . . . . . . . . . . . . . 104 + F. Design Alternatives . . . . . . . . . . . . . . . . . . . . 105 + F.1 Context granularity . . . . . . . . . . . . . . . . . . 105 + F.2 Demultiplexing of data packets in shim6 communications . 105 + F.2.1 Flow-label . . . . . . . . . . . . . . . . . . . . . 106 + F.2.2 Extension Header . . . . . . . . . . . . . . . . . . 108 + F.3 Context Loss Detection . . . . . . . . . . . . . . . . . 109 + F.4 Securing locator sets . . . . . . . . . . . . . . . . . 111 + F.5 ULID-pair context establishment exchange . . . . . . . . 114 + F.6 Updating locator sets . . . . . . . . . . . . . . . . . 115 + F.7 State Cleanup . . . . . . . . . . . . . . . . . . . . . 115 + 19. References . . . . . . . . . . . . . . . . . . . . . . . . 118 + 19.1 Normative References . . . . . . . . . . . . . . . . . . 118 + 19.2 Informative References . . . . . . . . . . . . . . . . . 118 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 120 + Intellectual Property and Copyright Statements . . . . . . . 121 1. Introduction - The SHIM6 working group, and the MULTI6 WG that preceded it, was - exploring and is now specifying a layer 3 shim approach and protocol - for providing locator agility below the transport protocols, so that - multihoming can be provided for IPv6 with failover and load spreading - properties [16], without assuming that a multihomed site will have a + This document describes a layer 3 shim approach and protocol for + providing locator agility below the transport protocols, so that + multihoming can be provided for IPv6 with failover and load sharing + properties [15], without assuming that a multihomed site will have a provider independent IPv6 address which is announced in the global IPv6 routing table. The hosts in a site which has multiple provider allocated IPv6 address prefixes, will use the shim6 protocol specified in this document to setup state with peer hosts, so that the state can later be used to failover to a different locator pair, 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 specified in HBA [7]. The reachability detection and failure detection, including how a new - working locator pair is discovered after a failure, is specified in - separate documents ([9] and [8]). This document allocates message - types and option types for that sub-protocol, and leaves the - specification of the message and option formats as well as the - protocol behavior to a separate draft. + working locator pair is discovered after a failure, is specified in a + separate documents [8] This document allocates message types and + option types for that sub-protocol, and leaves the specification of + the message and option formats as well as the protocol behavior to + that document. 1.1 Goals The goals for this approach is to: - o Preserve established communications through failures, for example, - TCP connections and application communications using UDP. + o Preserve established communications through certain classes of + 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. - o Address the security threats in [20] through a separate document - [7], and techniques described in this document. + o Address the security threats in [19] through the combination of + 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 so that different sets of communication to a host (e.g., different - connections) might use different locators of the host. This might - enable some forms of traffic engineering, but the details for - traffic engineering, including what requirements can be satisfied, - have not yet been worked out. + connections) might use different locators of the host. Note that + this might cause load to be spread unevenly, thus we use the term + "load spreading" instead of "load balancing". This capability + 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 The assumption is that the problem we are trying to solve is site multihoming, with the ability to have the set of site locator prefixes change over time due to site renumbering. Further, we assume that such changes to the set of locator prefixes can be 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 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 solve the, perhaps related, problem of host mobility. However, it - might turn out that the shim6 protocol can be a useful component, - e.g., for route optimization in the context of host mobility. + might turn out that the shim6 protocol can be a useful component for + future host mobility solutions, e.g., for route optimization. - This proposal also does not try to provide a new network level - identifier namespace separated from the current IP address namespace. - Even though such a concept would be useful to ULPs and applications, - especially if the management burden for such a name space was zero - and there was an efficient yet secure mechanism to map from - identifiers to locators, such a name space isn't necessary (and - furthermore doesn't seem to help) to solve the multihoming problem. + This proposal also does not try to provide a new network level or + transport level identifier namespace separated from the current IP + address namespace. Even though such a concept would be useful to + ULPs and applications, especially if the management burden for such a + name space was negligible and there was an efficient yet secure + mechanism to map from identifiers to locators, such a name space + isn't necessary (and furthermore doesn't seem to help) to solve the + multihoming problem. 1.3 Locators as Upper-layer Identifiers - Central to this approach is to not introduce a new identifier name - space but instead use one of the locators as the upper-layer ID, - while allowing the locators used in the address fields to change over - time in response to failures of using the original locator. + This approach does not introduce a new identifier name space but + instead uses the locator that is selected in the initial contact with + the remote peer as the preserved upper-level identifier. While there + 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 - 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 - 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 with the initial locator pair being the ULID pair. When communication fails the shim can test and select alternate locators. A subsequent section discusses the issues when the selected ULID is not initially working hence there is a need to switch locators up front. Using one of the locators as the ULID has certain benefits for applications which have long-lived session state, or performs callbacks or referrals, because both the FQDN and the 128-bit ULID work as handles for the applications. However, using a single 128- 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. 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 believed that the approach can be extended to handle such a case. For example, the protocol already needs to handle ULIDs that are not initially reachable. Thus the same mechanism can handle ULIDs that are permanently unreachable from outside their site. The issue 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, 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 a performance impact on existing, non-shim6 aware, IPv6 hosts potentially trying to communicate to the (unreachable) ULA. 1.4 IP Multicast IP Multicast requires that the IP source address field contain a topologically correct locator for interface that is used to send the packet, since IP multicast routing uses both the source address and the destination group to determine where to forward the packet. (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 the IP address fields between ULIDs and locators, the fact that all the multicast receivers would need to know the mapping to perform, makes such an approach difficult in practice. Thus it makes sense to 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 field in the RTP headers. Thus the actual IP address fields are not 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. + 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 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 communication between two ULIDs might continue to work after one or both of those ULIDs are no longer reachable as locators, for example 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 another site while it is still being used (with another locator) for existing communication. Worst case we could end up with two separate hosts using the same ULID while both of them are communicating with the same host. @@ -317,21 +342,21 @@ becomes invalid (due to the underlying prefix becoming invalid). If that behavior is desired, it can be accomplished by explicitly discarding the shim state when the ULID becomes invalid. The context 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). However, terminating the communication might be overkill. Even when 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 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 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 was communicating. The protocol as specified in this document does not perform any action when an address becomes invalid. As we gain further understanding of the practical impact of renumbering this might change in a future version of the protocol. @@ -360,21 +385,22 @@ independence. The multihoming shim layer behaves as if it is associated with an extension header, which would be placed after any routing-related headers in the packet (such as any hop-by-hop 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 header, thus none is needed in that case. 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 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 reassembly robust in the case that there is broken multi-path routing which results in using different paths, hence potentially different source locators, for different fragments. Thus, effectively the multihoming shim layer is placed between the IP endpoint sublayer, which handles fragmentation, reassembly, and IPsec, and the IP routing sublayer, which selects which next hop and interface to use for sending out packets. @@ -426,45 +452,62 @@ the data packets. This serves to indicate the correct context to use for decompression when the locator pair in the packet is insufficient to uniquely identify the context. 1.7 Traffic Engineering At the time of this writing it is not clear what requirements for traffic engineering make sense for the shim6 protocol, since the requirements must both result in some useful behavior as well as be implementable using a host-to-host locator agility mechanism like - shim6. What is clear that whatever they are, shim6 will not be able - to provide identical capabilities to traffic engineering using BGP - and Provide Independent IP addresses. + shim6. + + 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 Preferences option, which can be used by hosts to express priority and weight values for each locator. This is intentionally made - identical to the DNS SRV [10] specification of priority and weight, - so that DNS SRV records can be used for initial contact and the shim - for failover, and they can use the same way to describe the - preferences. The format allows adding additional notions of - "metrics" over time. But this is merely a place holder; even in - order to use this there would have to be a mechanism by which the - host can find out what preference values to use, either statically - (e.g., some new DHCPv6 option) or dynamically. + identical to the DNS SRV [9] specification of priority and weight, so + that DNS SRV records can be used for initial contact and the shim for + failover, and they can use the same way to describe the preferences. + The format allows adding additional notions of "metrics" over time. + But the Locator Preference option is merely a place holder when it + comes to providing traffic engineering; in order to use this in a + large site there would have to be a mechanism by which the host can + find out what preference values to use, either statically (e.g., some + new DHCPv6 option) or dynamically. + + Thus traffic engineering is listed as a possible extension in + Appendix B. 2. Terminology This document uses the terms MUST, SHOULD, RECOMMENDED, MAY, SHOULD NOT and MUST NOT defined in RFC 2119 [1]. The terms defined in RFC 2460 [2] are also used. 2.1 Definitions - This document introduces the following terms (taken from [25]): + This document introduces the following terms: upper layer protocol (ULP) A protocol layer immediately above IP. Examples are transport protocols such as TCP and UDP, control protocols such as ICMP, routing protocols such as OSPF, and internet or lower-layer protocols being "tunneled" over (i.e., encapsulated in) IP such as IPX, AppleTalk, or IP itself. @@ -475,25 +518,24 @@ an interface. 128 bits. This document only uses the "address" term in the case where it isn't specific whether it is a locator or an identifier. locator An IP layer topological name for an interface or a set of interfaces. 128 bits. The locators are carried in the IP address fields as the packets traverse the network. - identifier An IP layer name for an IP layer endpoint (stack - name in [27]). The transport endpoint name is a - function of the transport protocol and would - typically include the IP identifier plus a port - number. + identifier An IP layer name for an IP layer endpoint. The + transport endpoint name is a function of the + transport protocol and would typically include + the IP identifier plus a port number. NOTE: This proposal does not specify any new form of IP layer identifier, but still separates the identifying and locating properties of the IP addresses. upper-layer identifier (ULID) An IP address which has been selected for communication with a peer to be used by the upper layer protocol. 128 bits. This is used for pseudo-header checksum computation and connection @@ -520,269 +562,312 @@ direction of the communication, and also identified by the pair of ULID and a Forked Instance Identifier (see below). Context tag Each end of the context allocates a context tag for the context. This is used to uniquely associate both received control packets and payload extension headers as belonging to the context. - Current locator pair Each end of the context has a current locator - pair which is used to send packets to be peer. + Current locator pair + 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 pairs though. Default context At the sending end, the shim uses the ULID pair (passed down from the ULP) to find the context for that pair. Thus, normally, a host can have at most one context for a ULID pair. We call this the "default context". Context forking A mechanism which allows ULPs that are aware of multiple locators to use separate contexts for the same ULID pair, in order to be able use different locator pairs for different communication to the same ULID. Context forking causes more than just the default context to be created for a ULID pair. - Forked Instance Identifier (FII) In order to handle context forking, - a context is identified by a ULID-pair and a - forked context identifier. The default context - has a FII of zero. + Forked Instance Identifier (FII) + In order to handle context forking, a context is + identified by a ULID-pair and a forked context + identifier. The default context has a FII of + zero. Initial contact We use this term to refer to the pre-shim communication when some ULP decides to start communicating with a peer by sending and receiving ULP packets. Typically this would not invoke any operations in the shim, since the shim can defer the context establishment until some 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 A, B, and C are hosts. X is a potentially malicious host. FQDN(A) is the domain name for A. Ls(A) is the locator set for A, which consists of the locators L1(A), L2(A), ... Ln(A). ULID(A) is an upper-layer ID for A. In this proposal, ULID(A) is 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 describe protocol behavior and external variables that an implementation must allow system administrators to change. The specific variable names, how their values change, and how their settings influence protocol behavior are provided to demonstrate protocol behavior. An implementation is not required to have them in the exact form described here, so long as its external behavior is consistent with that described in this document. See Section 6 for a description of the conceptual data structures. 3. Assumptions - The general approach of a level3 shim as well as this specific - proposal makes the following assumptions: + The design intent is to ensure that the shim6 protocol is capable of + 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 - locator pairs will cause the packets to exit - using different ISPs so that all exit ISPs can be tried. Since - there might be only one destination locator, when the peer - supports shim6 but is not multihomed, this implies that the - selection of the exit ISP should be related to the source address - in the packets. + In the case when host A and host B have an active shim6 state, with + host A having only one locator and host B having multiple locators, + it might be that host B is trying to send a packet to host A, and has + detected a failure condition with the current locator pair. As host + B has multiple locators it presumably has multiple ISPs. In this + case there are probably alternate egress paths for host B to be able + 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 - the host tries all locator pairs, that it - has done a good enough job of trying to find a working path to the - peer. Since we want the protocol to provide benefits even if the - peer has a single locator, this seems to imply that the choice of - source locator needs to somehow affect the exit path from the - site. + This leads to the assumption that a host should be able to cause + different egress paths from its site to be used. The most reasonable + approach to accomplish this is to have the host use different source + addresses and have the source address affect the selection of the + site egress. The details of how this can be accomplished is beyond + the scope of this document, but without this capability the ability + of the shim to try different "paths" by trying different locator + pairs will have limited utility. + + The above assumption applies whether or not the ISPs perform ingress + 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 The shim6 protocol operates in several phases over time. The following sequence illustrates the concepts: 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 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. Any shim context establishment can be deferred until later. - o Some heuristic on A or B (or both) determine that it might make - sense to make this communication robust against locator failures. - For instance, this heuristic might be that more than 50 packets - have been sent or received, or a timer expiration while active - packet exchange is in place. This makes the shim initiate the - 4-way context establishment exchange. + o Some heuristic on A or B (or both) determine that it is + appropriate to pay the shim6 overhead to make this host-to-host + communication robust against locator failures. For instance, this + heuristic might be that more than 50 packets have been sent or + received, or a timer expiration while active packet exchange is in + 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 locators for each other. If the context establishment exchange fails, the initiator 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. In particular, there are no shim extension headers added to the ULP packets, since the ULID pair is the same as the locator pair. In addition, there might be some messages exchanged between the shim sub-layers for (un)reachability detection. 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 there is a problem. At this point in time one or both ends of the communication need 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 will rewrite the packets on transmit, and tag the packets with shim6 Payload extension header, which contains the receiver's context tag. The receiver will use the context tag to find the context state which will indicate which addresses to place in the IPv6 header before passing the packet up to the ULP. The result is that from the perspective of the ULP the packet passes unmodified end-to-end, even though the IP routing infrastructure sends the packet to a different locator. o The shim (un)reachability detection will monitor the new locator pair as it monitored the original locator pair, so that subsequent failures can be detected. 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 might have failed or gone down (at layer 2), or an IPv6 address might have become deprecated or invalid. In such cases the host can signal its peer that this address is no longer recommended to try. Thus this triggers something similar to a failure handling in that a new, working locator pair must be found. The protocol also has the ability to express other forms of locator preferences. A change in any preferences can be signaled - to the peer, which might make the peer choose to try a different - locator pair. Thus, this can also be treated similarly to a - failure. + to the peer, which will made the peer record the new preferences. + A change in the preferences might optionally make the peer want to + 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 can garbage collect the state; there is no coordination necessary with the peer host before the state is removed. There is a recovery message defined to be able to signal when there is no context state, which can be used to detect and recover from both premature garbage collection, as well as complete state loss (crash and reboot) of a peer. The exact mechanism to determine when the context state is no longer used is implementation dependent. An implementation might use the existence of ULP state (where known to the implementation) 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 sub-layer) to determine when the state is likely to no longer be used. - NOTE: The ULP packets in shim6 are carried completely unmodified as - long as the ULID pair is used as the locator pair. After a switch to - a different locator pair the packets are "tagged" with a shim6 + NOTE: The ULP packets in shim6 can be carried completely unmodified + as long as the ULID pair is used as the locator pair. After a switch + to a different locator pair the packets are "tagged" with a shim6 extension header, so that the receiver can always determine the context to which they belong. This is accomplished by including an - 8-octet shim payload extension header before the (extension) headers - that are processed by the IP endpoint sublayer and ULPs. + 8-octet shim6 Payload Extension header before the (extension) headers + 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 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 - 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 the message allocated. Thus at a minimum the combination of MUST uniquely identify one + ULID, local ULID, local context tag> have to uniquely identify one context. But since the Payload extension headers are demultiplexed - without looking at the locators in the packet, the receiver MUST - allocate context tags that are unique for all its contexts. 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 [18]. The context tag is a 47- - bit number (the largest which can fit in an 8-octet extension - header). + without looking at the locators in the packet, the receiver will need + to allocate context tags that are unique for all its contexts. The + context tag is a 47-bit number (the largest which can fit in an + 8-octet extension header). The mechanism for detecting a loss of context state at the peer that is currently proposed in this document assumes that the receiver can 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 achieved because after a rehoming event the packets that need 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 It has been asserted that it will be important for future ULPs, in particular, future transport protocols, to be able to control which locator pairs are used for different communication. For instance, host A and host B might communicate using both VoIP traffic and ftp traffic, and those communications might benefit from using different locator pairs. However, the fundamental shim6 mechanism uses a single current locator pair for each context, thus a single context can not accomplish this. For this reason, the shim6 protocol supports the notion of context 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 should be forked into two contexts. In this case the forked-off context will be assigned a non-zero Forked Instance Identifier, while 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 handle forked contexts. 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 - 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 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. 4.3 API Extensions Several API extensions have been discussed for shim6, but their 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 the shim (not create any state, and not use any state created by other traffic). This could be an IPV6_DONTSHIM socket option. Such an option would be useful for protocols, such as DNS, where the application has its own failover mechanism (multiple NS records in the case of DNS) and using the shim could potentially add extra 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 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. o Requiring a Reachability Probe+Reply before a new locator is used as the destination, in order to prevent 3rd party flooding attacks. o The first message does not create any state on the responder. Essentially a 3-way exchange is required before the responder creates any state. This means that a state-based DoS attack (trying to use up all of memory on the responder) at least @@ -796,130 +881,113 @@ establishment, carry the context tag assigned to the particular context. This implies that an attacker needs to discover that context tag before being able to spoof any shim6 control message. Such discovery probably requires to be along the path in order to be sniff the context tag value. The result is that through this technique, the shim6 protocol is protected against off-path attackers. 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 and responder, respectively. Should both ends attempt to set up 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 - 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 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 - 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. The peers' lists of locators are normally exchanged as part of the context establishment exchange. But the set of locators might be - dynamic. For this reason there is a Update message and Update - acknowledgement, and a Locator List option. + dynamic. For this reason there is a Update Request and Update + Acknowledgement messages, and a Locator List option. Even when the list of locators is fixed, a host might determine that some preferences might have changed. For instance, it might determine that there is a locally visible failure that implies that 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 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 - payload packet to the peer. The message type is reserved in this - document, but the message format and processing rules are specified - in [9]. + packet to the peer. The message type is reserved in this document, + but the message format and processing rules are specified in [8]. 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 efficiently find a working pair. This document reserves an Probe 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 ULID-pair context. However, communication might fail during the initial contact (that is, when the application or transport protocol is trying to setup some communication). This is handled using the 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 discovering a working locator pair during initial contact. This is for further study. 4.6 Extension Header Order 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 options header, AH, ESP), but after any routing related headers (hop- by-hop extensions header, routing header, a destinations options header which precedes a routing header). When tunneling is used, whether IP-in-IP tunneling or the special form of tunneling that Mobile IPv6 uses (with Home Address Options and Routing header type 2), there is a choice whether the shim applies inside the tunnel or 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 it makes sense to apply them on the locators which means that the sender would insert the shim6 header after any IP-in-IP encapsulation; this is what occurs naturally when routers apply IP- - in-IP encapsulation. In any case the receiver behavior is well- - 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. + in-IP encapsulation. Thus the packets would have: -4.7 Locator Validation + o Outer IP header - There are two separate aspects of locator validation. One is to - 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]. + o Inner IP header - 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. + o Shim6 extension header (if needed> - 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 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. + o ULP - 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 [20]. + But the shim can also be used to create "shimmed tunnels" i.e., where + an IP-in-IP tunnel uses the shim to be able to switch the tunnel + endpoint addresses between different locators. In such a case the + packets would have: - If the verification method in the Locator List option is not - supported by the host, or if the verification method is not - consistent with what it in the CGA Parameter Data Structure (e.g., - the PDS doesn't contain the multiprefix extension, and the - verification method says to use HBA), then the host MUST ignore the - 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 - Pointer referencing the octet in the Verification method that was - found inconsistent. + o Outer IP header + + o Shim6 extension header (if needed> + + o Inner IP header + + o ULP + + 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 The shim6 messages are all carried using a new IP protocol number [to be assigned by IANA]. The shim6 messages have a common header, defined below, with some fixed fields, followed by type specific fields. The shim6 messages are structured as an IPv6 extension header since the Payload extension header is used to carry the ULP packets after a @@ -946,21 +1014,21 @@ 8-octet units, not including the first 8 octets. P: A single bit to distinguish Payload extension headers from control messages. 5.2 Payload Extension Header Format The payload extension headers is used to carry ULP packets where the receiver must replace the content of the source and/or destination 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. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | 0 |1| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Receiver Context Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ @@ -1217,45 +1285,45 @@ message. Reserved2: 32-bit field. Reserved for future use. Zero on transmit. MUST be ignored on receipt. (Needed to make the options start on a multiple of 8 octet boundary.) The following options are defined for this message: 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 IPv6 header does not match the ULID pair, this option MUST be included. An example of this is when recovering from a lost context. Forked Instance Identifier: When another instance of an existent context with the same ULID pair is being created, a Forked Instance Identifier option is included to distinguish this new instance from the existent one. Locator list: Optionally sent when the initiator immediately wants to tell the responder its list of locators. When it 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 equal preference. CGA Parameter Data Structure: Included when the locator list is included so the receiver can verify the locator list. 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 The R2 message is the fourth message in the context establishment 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 same time and the I1 messages cross in flight. 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 @@ -1292,44 +1360,43 @@ has allocated for the context. Initiator Nonce: 32-bit unsigned integer. Copied from the I2 message. The following options are defined for this message: Locator List: Optionally sent when the responder immediately wants to tell the initiator its list of locators. When it 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 equal preference. CGA Parameter Data Structure: Included when the locator list is included so the receiver can verify the locator list. 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 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 Probe message), and the host does not have any context state for the - locators (in the IPv6 source and destination fields) and the context - tag, then it will generate a R1bis packet. + received context tag, then it will generate a R1bis message. - This packet allows the sender of the packet referring to the non- - existent context to re-establish the context with a reduced packet - exchange. Upon the reception of the R1bis packet, the receiver can - proceed reestablishing the lost context by directly sending an I2bis - message. + This message allows the sender of the packet referring to the non- + existent context to re-establish the context with a reduced context + establishment exchange. Upon the reception of the R1bis message, the + receiver can proceed reestablishing the lost context by directly + sending an I2bis message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 59 | Hdr Ext Len |0| Type = 5 | Reserved1 |0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum |R| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Packet Context Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ @@ -1349,21 +1416,21 @@ Type: 5 Reserved1: 7-bit field. Reserved for future use. Zero on transmit. MUST be ignored on receipt. R: 1-bit field. Reserved for future use. Zero on transmit. MUST be ignored on receipt. Packet Context Tag: 47-bit unsigned integer. The context tag 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 which the initiator will return in the I2bis message. The following options are defined for this message: Responder Validator: Variable length option. Typically a hash generated by the responder, which the responder uses together with the Responder Nonce value to verify that @@ -1429,48 +1496,48 @@ transmit. MUST be ignored on receipt. (Note that 17 bits are not sufficient since the options need start on a multiple of 8 octet boundary.) Packet Context Tag: 47-bit unsigned integer. Copied from the Packet Context Tag contained in the received R1bis. The following options are defined for this message: 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 IPv6 header does not match the ULID pair, this option MUST be included. Forked Instance Identifier: When another instance of an existent context with the same ULID pair is being created, a Forked Instance Identifier option is included to distinguish this new instance from the existent one. Locator list: Optionally sent when the initiator immediately wants to tell the responder its list of locators. When it 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 equal preference. CGA Parameter Data Structure: Included when the locator list is included so the receiver can verify the locator list. 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 - 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 is updated, the message also contains the option(s) necessary for HBA/CGA to secure this. The basic sanity check that prevents off-path attackers from generating bogus updates is the context tag in the message. The update message contains options (the Locator List and the Locator Preferences) that, when included, completely replace the previous locator list and locator preferences, respectively. Thus there is no mechanism to just send deltas to the locator list. @@ -1515,27 +1582,27 @@ The following options are defined for this message: Locator List: The list of the sender's (new) locators. The locators might be unchanged and only the preferences have changed. Locator Preferences: Optionally sent when the locators don't all have 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 I2/I2bis/R2 messages, so the receiver can verify the locator list. 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 This message is sent in response to a Update Request message. It 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 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 verification of a locator until it sees a need to use a locator as the destination. @@ -1574,48 +1641,48 @@ Receiver Context Tag: 47-bit field. The Context Tag the receiver has allocated for the context. Request Nonce: 32-bit unsigned integer. Copied from the Update Request message. No options are currently defined for this message. 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 on a context, it always receives some packets in the reverse direction. When the ULP is sending bidirectional traffic, no extra packets need to be inserted. But for a unidirectional ULP traffic pattern, the shim will send back some Keepalive messages when it is receiving ULP packets. 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 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 directions. The protocol mechanism is that as A is sending probe 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. 5.14 Option Formats 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 - HIP option format, nor is there an intent to use the same name space - for the option type values. But using the same format will hopefully - make it easier to import HIP capabilities into shim6 as extensions to - shim6, should this turn out to be useful. + format [25]. However, there is no intention to track any changes to + the HIP option format, nor is there an intent to use the same name + space for the option type values. But using the same format will + hopefully make it easier to import HIP capabilities into shim6 as + extensions to shim6, should this turn out to be useful. 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 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 padding is added, the Length field MUST NOT include the padding. Any added padding bytes MUST be zeroed by the sender, and their values SHOULD NOT be checked by the receiver. Consequently, the Length field indicates the length of the Contents @@ -1649,21 +1716,21 @@ Length: Length of the Contents, in bytes. Contents: Parameter specific, defined by Type. Padding: Padding, 0-7 bytes, added if needed. +------+---------------------------------+ | Type | Option Name | +------+---------------------------------+ - | 1 | Validator | + | 1 | Responder Validator | | | | | 2 | Locator List | | | | | 3 | Locator Preferences | | | | | 4 | CGA Parameter Data Structure | | | | | 5 | CGA Signature | | | | | 6 | ULID Pair | @@ -1672,35 +1739,35 @@ | | | | 10 | Probe Option | | | | | 11 | Reachability Option | | | | | 12 | Payload Reception Report Option | +------+---------------------------------+ 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 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 - I2 or I2bis message is indeed one that: + the responder can check that the validator it receives back in the I2 + or I2bis message is indeed one that: 1)- it computed, 2)- it computed for the particular context, and 3)- that it isn't a replayed I2/I2bis message. 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 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Validator ~ ~ +-+-+-+-+-+-+-+-+ ~ | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ @@ -1781,21 +1848,21 @@ Table 3 5.14.3 Locator Preferences Option Format The Locator Preferences option can have some flags to indicate 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 "preferences" as a combination of priority and weight the same way that DNS SRV records has such information. The priority would 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. 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 flag 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, and we can add more information by having even larger elements if need be. @@ -1822,22 +1889,22 @@ Case of Element Len = 1 is depicted. Fields: Locator List Generation: 32-bit unsigned integer. Indicates a generation number for the locator list to which the elements should apply. Element Len: 8-bit unsigned integer. The length in octets of each - element. This draft defines the cases when the length - is 1, 2, or 3. + element. This specification defines the cases when + the length is 1, 2, or 3. Element[i]: A field with a number of octets defined by the Element Len field. Provides preferences for the i'th locator in the Locator List option that is in use. Padding: Padding, 0-7 bytes, added if needed. See Section 5.14. When the Element length equals one, then the element consists of only a one octet flags field. The currently defined set of flags are: @@ -1853,27 +1920,33 @@ 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 has the same semantics as the priority in DNS SRV records. 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 octet weight field. The weight has the same semantics as the weight 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 - This option contains the CGA parameter data structure (hereafter - called the PDS). When HBA is used to validate the locators, the PDS - contains the HBA multiprefix extension. When CGA is used to validate - the locators, in addition to the CGA PDS, the signature will need to - be included as a CGA Signature option. + This option contains the CGA Parameter Data Structure (PDS). When + HBA is used to verify the locators, the PDS contains the HBA + multiprefix extension. When CGA is used to verify the locators, in + addition to the PDS option, the host also needs to include the + signature in the form of a CGA Signature option. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 4 |0| Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ CGA Parameter Data Structure ~ ~ +-+-+-+-+-+-+-+-+ ~ | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ @@ -1881,22 +1953,22 @@ Fields: CGA Parameter Data Structure: Variable length content. Content defined in [6] and [7]. Padding: Padding, 0-7 bytes, added if needed. See Section 5.14. 5.14.5 CGA Signature Option Format - When CGA is used for validation of one or more of the locators in the - Locator List option, then the message in question will need to + When CGA is used for verification of one or more of the locators in + the Locator List option, then the message in question will need to contain this option. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 5 |0| Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ CGA Signature ~ ~ +-+-+-+-+-+-+-+-+ ~ | Padding | @@ -1910,24 +1982,24 @@ 1. The 128-bit CGA Message Type tag [CGA] value for SHIM6, 0x4A 30 5662 4858 574B 3655 416F 506A 6D48. (The tag value has been generated randomly by the editor of this specification.). 2. The Locator List Generation value of the correspondent Locator List Option. 3. The subset of locators included in the - correspondent Locator List Option which validation - method is set to CGA. The locators MUST be - included in the order they are listed in the - Locator List Option. + correspondent Locator List Option which + verification method is set to CGA. The locators + MUST be included in the order they are listed in + the Locator List Option. Padding: Padding, 0-7 bytes, added if needed. See Section 5.14. 5.14.6 ULID Pair Option Format 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 for the context differ from the address pair included in the source and destination address fields of the IPv6 packet used to carry the @@ -1971,29 +2043,29 @@ | Forked Instance Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fields: Forked Instance Identifier: 32-bit field containing the identifier of the particular forked instance. 5.14.8 Probe Option Format - This option is defined in [9]. + This option is defined in [8]. 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 - This option is defined in [9]. + This option is defined in [8]. 6. Conceptual Model of a Host This section describes a conceptual model of one possible data structure organization that hosts will maintain for the purposes of shim6. The described organization is provided to facilitate the explanation of how the shim6 protocol should behave. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. @@ -2008,27 +2080,27 @@ o The peer ULID; ULID(peer) o The local ULID; ULID(local) o The Forked Instance Identifier; FII. This is zero for the default context i.e., when there is no forking. 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. - 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). - 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 verify that the ULID is present at that location. o The preferred peer locator - used as destination; Lp(peer) o The set of local locators and the preferences; Ls(local) o The generation number for the most recently sent Locator List option. @@ -2039,24 +2111,24 @@ o The context to expect in received control messages and payload extension headers - allocated by the local host; CT(local) o Timers for retransmission of the messages during context establishment and update messages. o Depending how an implementation determines whether a context is still in use, there might be a need to track the last time a 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 - have been sent and received as specified in [9]. + have been sent and received as specified in [8]. 6.2 Context States The states that are used to describe the shim6 protocol are as follows: +---------------------+---------------------------------------------+ | State | Explanation | +---------------------+---------------------------------------------+ | IDLE | State machine start | @@ -2110,50 +2182,104 @@ ULID-pair contexts are established using a 4-way exchange, which 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 this context tag and its set of locators with the peer. 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 recovering from a context that has been garbage collected or lost at 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 order of I1, R1, I2, R2. + the order of I1, R1, I2, R2 as can be seen in Figure 24. Initiator Responder IDLE IDLE ------------- I1 --------------> I1-SENT <------------ R1 --------------- IDLE ------------- I2 --------------> I2-SENT <------------ R2 --------------- 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 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 having sent a R1 message. 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 - needed to correctly respond to retransmitted I1 messages, which might - be needed if the R2 message has been lost. + I1 from the peer (for the same ULID-pair), with a R2, resulting in + the message exchange shown in Figure 25. Such behavior is needed for + other reasons such as to correctly respond to retransmitted I1 + messages, which occur when the R2 message has been lost. Host A Host B IDLE IDLE -\ I1-SENT---\ ---\ /--- --- I1 ---\ /--- I1-SENT ---\ /--- I1 ---/ ---\ @@ -2163,26 +2289,27 @@ -\ I1-SENT---\ ---\ /--- --- R2 ---\ /--- I1-SENT ---\ /--- R2 ---/ ---\ /--- --> <--- 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 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 - 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 IDLE IDLE -\ ---\ I1-SENT ---\ --- I1 ---\ ---\ ---\ @@ -2195,114 +2322,129 @@ /--- <--- -\ I2-SENT---\ ---\ /--- --- I2---\ /--- I1-SENT ---\ /--- I1 ---/ ---\ /--- --> - <--- I1-SENT + <--- ESTABLISHED -\ I2-SENT---\ ---\ /--- --- R2 ---\ /--- ---\ /--- R2 ---/ ---\ /--- --> <--- 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 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, before we can use it. This need can arise in the following cases: o The communication is working using the ULID pair as the locator pair, but a problem arises, and the end that has retained the context state decides to probe alternate locator pairs. 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 - 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 - UPDATE message). + Update Request message). 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. 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 - 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 Context for CT(peer)=X Discards context for CT(local)=X ESTABLISHED IDLE ---- payload, probe, etc. -----> No context state for CT(local)=X <------------ R1bis ------------ IDLE ------------- I2bis -----------> I2BIS_SENT <------------ R2 --------------- ESTABLISHED ESTABLISHED - Figure 27 + Figure 27: Context loss at receiver 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 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 Context for CT(peer)=X Discards context for ULIDs A1, B1 CT(local)=X ESTABLISHED IDLE Finds <------------ I1 --------------- Tries to setup 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 --------------> 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 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 previous section on recovery. But for the same reasons, when one - host retains context tag X for ULID pair , the other end - might end up allocating that context tag for another ULID pair, e.g., - between the same hosts. In this case we can not use the - recovery mechanisms since there needs to be separate context tags for - the two ULID pairs. + host retains context tag X as CT(peer) for ULID pair , the + other end might end up allocating that context tag as CT(local) for + another ULID pair, e.g., between the same hosts. In this + case we can not use the recovery mechanisms since there needs to be + separate context tags for the two ULID pairs. This type of "confusion" can be observed in two cases (assuming it is A that has retained the state and B has dropped it): o B decides to create a context for ULID pair , and allocates X as its context tag for this, and sends an I1 to A. o A decides to create a context for ULID pair , and starts the exchange by sending I1 to B. When B receives the I2 message, it allocates X as the context tag for this context. @@ -2320,279 +2462,309 @@ 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 would forcibly remove the context state for , so that it can accept the new context for . An implementation MAY re-create a context to replace the one that was removed; in this case for . The normal I1, R1, I2, R2 establishment exchange would then pick unique context tags for that replacement context. This re- creation is OPTIONAL, but might be useful when there is ULP 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 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 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 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 message and set the context state to I1-SENT. The I1 message MUST 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 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 non-zero, the I1 message MUST include a Context Instance Identifier 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 I1 message after I1_TIMEOUT time, then it needs to retransmit the I1 message. The retransmissions should use a retransmission timer with binary exponential backoff to avoid creating congestion issues for 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 nominal value to avoid self-synchronization. If, after I1_RETRIES_MAX retransmissions, there is no response, then 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 sense for the host to remember to not try again to establish a 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 context should the problem have been that the host was not reachable at all when the shim tried to establish the context. 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 - implement shim6. Again,in this case, the host should remember to not - try again to establish a context with that ULID. Such negative + implement shim6. Again, in this case, the host should remember to + not try again to establish a context with that ULID. Such negative caching should retained for at most ICMP_HOLDDOWN_TIME, which should 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 satisfy all of the following validity checks in 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 16 octets. 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 destination fields in the IPv6 header. If there is no FII option in the message, then the FII value is taken to be zero. 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 - unnecessary if there is no ULID-pair option in the I1 message). If - the locators do not fall in the locator sets, then the host MUST - discard the I1 packet and perform no further processing. + unnecessary if there is no ULID-pair option in the I1 message). - If no state is found (i.e., the state is IDLE), or the locators do - fall in the sets, then the host looks at the state of the context: + If the state exists in ESTABLISHED state and the locators do not fall + in the locator sets, then the host replies with a R1 message as + 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 - specified below. + If the state exists in ESTABLISHED state and the locators do fall in + the sets, then the host compares CT(peer) for the context with the CT + contained in the I1 message. - o If the state is ESTABLISHED, it means that the Initiator has lost - the context information for this context and it is trying to - establish a new one. In this case, the host MUST update the - existing context and replace CT(peer) with the Initiator 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 If the context tags match, then this probably means that the R2 + message was lost and this I1 is a retransmission. In this case, + the host replies with a R2 message containing the information + available for the existent context. - o In an other state (I1-SENT, I2-SENT, I2BIS-SENT), we are in the - situation of Concurrent context establishment described above. In - this case, the host sets CT(peer) to the Initiator Context tag of - the I1 packet, and replies with a R2 message. This completes the - I1 processing, with the context state being unchanged. + o If the context tags do not match, then it probably means that the + Initiator has lost the context information for this context and it + is trying to establish a new one for the same ULID-pair. In this + case, the host replies with a R1 message as specified below. This + 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 message, it copies the Initiator Nonce from the I1 message to the R1 - message, generates a Responder Nonce and calculates a validator as - suggested in the following section. No state is created on the host - in this case. + message, generates a Responder Nonce and calculates a Responder + Validator option as suggested in the following section. No state is + created on the host in this case. 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, 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 maintain a single secret (S) and a running counter for the Responder Nonce. - In the case the validator is generated to be included in a R1 packet, - for each I1 message. The responder can increase the counter, use the - counter value as the responder nonce, and use the following - information as input to the one-way function: + In the case the validator is generated to be included in a R1 + message, for each I1 message. The responder can increase the + counter, use the counter value as the responder nonce, and use the + following information as input to the one-way function: o The the secret S o That Responder Nonce o The Initiator Context Tag from the I1 message o The ULIDs from the I1 message o The locators from the I1 message (strictly only needed if they are different from the ULIDs) o The forked instance identifier if such option was included in the 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 satisfy all of the following validity checks in 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 16 octets. Upon the reception of an R1 message, the host extracts the Initiator Nonce and the Locator Pair from the message (the latter from the source and destination fields in the IPv6 header). Next the host looks for an existing context which matches the Initiator Nonce and 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. 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 below. 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 - to a retransmitted I1 packet, so this R1 message MUST be silently + host has already sent an I2 message then this is probably a reply + to a retransmitted I1 message, so this R1 message MUST be silently discarded. - When the host sends an I2 message, then it includes the validator - option that was in the R1 message. The I2 message MUST include the - ULID pair; normally in the IPv6 source and destination fields. If a - ULID-pair option was included in the I1 message then it MUST be - included in the I2 message as well. In addition, if the Forked - Instance Identifier value for this context is non-zero, the I2 + When the host sends an I2 message, then it includes the Responder + Validator option that was in the R1 message. The I2 message MUST + include the ULID pair; normally in the IPv6 source and destination + fields. If a ULID-pair option was included in the I1 message then it + MUST be included in the I2 message as well. In addition, if the + Forked Instance Identifier value for this context is non-zero, the I2 message MUST contain a Forked Instance Identifier Option carrying this value. Besides, the I2 message contains an Initiator Nonce. This is not required to be the same than the one included in the previous I1 message. 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 locator list, then Initiator also signs the key parts of the message and includes a CGA signature option containing the signature. 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 after sending an I2 message it MAY retransmit the I2 message, using - binary exponential backoff and randomized timers. The validator - option might have a limited lifetime, that is, the peer might reject - verifier 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 I2 message I2_RETRIES_MAX times. + 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 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 satisfy all of the following validity checks in addition to those specified in Section 12.2: o The Hdr Ext Len field is at least 2, i.e., the length is at least 24 octets. 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 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 the message, then the FII value is taken to be zero. Next the host verifies that the Responder Nonce is a recent one, and - that the Validator option matches the validator the host would have - computed for the ULID, locators, responder nonce, and FII. + that the Responder Validator option matches the validator the host + would have computed for the ULID, locators, responder nonce, and FII. - If a CGA Parameter Data Structure is included in the message, then - the host MUST verify if the actual PDS contained in the packet + If a CGA Parameter Data Structure (PDS) is included in the message, + then the host MUST verify if the actual PDS contained in the message corresponds to the ULID(peer). - If at least one of the above verification fails, then it silently - discard the packet and it has completed the I2 processing. + If any of the above verifications fails, then the host silently + discard the message and it has completed the I2 processing. - If both verifications are successful, then the host proceeds to look - for a context state for the Initiator. The host looks for a context - with the extracted ULID pair and FII. If none exist then state of - the (non-existing) context is viewed as being IDLE, thus the actions - depend on the state as follows: + If all the above verifications are successful, then the host proceeds + to look for a context state for the Initiator. The host looks for a + context with the extracted ULID pair and FII. If none exist then + state of the (non-existing) context is viewed as being IDLE, thus the + actions depend on the state as follows: 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 - the context, sets its state to ESTABLISHED. It records the peer's - locator set as well as its own locator set in the context. It - SHOULD perform the HBA/CGA verification of the peer's locator set - at this point in time. Then the host sends an R2 message back as - specified below. + allocates a context tag (CT(local)), creates the context state for + the context, and sets its state to ESTABLISHED. It records + CT(peer), and the peer's locator set as well as its own locator + set in the context. It SHOULD perform the HBA/CGA verification of + the peer's locator set at this point in time, as specified in + Section 7.2. Then the host sends an R2 message back as specified + below. - o If the state is ESTABLISHED, CT(peer) matches the Initiator - Context tag, and the IPv6 source address is contained in Ls(peer) - then this I2 message is probably a retransmit, so the host MUST - send a R2 message back as specified below. + o If the state is I1-SENT, then the host verifies if the source + locator is included in Ls(peer) or, it is included in the Locator + List contained in the the I2 message and the HBA/CGA verification + for this specific locator is successful - o If the state is ESTABLISHED, and if at least one of the following - conditions is true: either the CT(peer) is not the same as the - 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. + * If this is not the case, then the message is silently discarded + and the context state remains unchanged. - o In other state (I1-SENT, I2-SENT, or I2BIS-SENT) then we are in - the Concurrent context establishment situation described above. - Then it replies with a R2 message as specified below. The state - of the context 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 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 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 - message with its locators and its context tag, copies the Initiator - Nonce from the I2 message, and includes the necessary options so that - the peer can verify the locators. In particular, the R2 message also - includes the Responder's locator list and the CGA parameter data - structure. If CGA (and not HBA) is used to verify the locator list, - then the Responder also signs the key parts of the message and - includes a CGA signature option containing the signature. + When the host needs to send an R2 message, the host forms the message + using its locators and its context tag, copies the Initiator Nonce + from the triggering message (I2, I2bis, or I1), and includes the + necessary options so that the peer can verify the locators. In + particular, the R2 message includes the Responder's locator list and + the PDS option. If CGA (and not HBA) is used to verify the locator + list, then the Responder also signs the key parts of the message and + includes a CGA Signature option containing the signature. R2 messages are never retransmitted. If the R2 message is lost, then the initiator will retransmit either the I2/I2bis or I1 message. Either retransmission will cause the responder to find the context 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 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 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 updated for an existing context. The host takes CT(peer) for the newly created or updated context, and looks for other contexts which: @@ -2601,279 +2773,371 @@ o Have the same CT(peer). o Where Ls(peer) has at least one locator in common with the newly created or updated context. 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 created or updated context: - o If this is true, then the peer is trying to reuse the context tag - for the creation of a context with different ULID pair or FII, - which is a signal that the Initiator has lost the other context. - In this case, we are in the Context confusion situation, and the - host MUST NOT use the old context to send any packets. It MAY - just discard the old context (after all, the peer has discarded - it), or it MAY attempt to re-establish the old context by sending - a new I1 message and moving its state to I1-SENT. In any case, - once that this situation is detected, the host MUST not keep two - contexts with overlapping Ls(peer) locator sets and the same - context tag in ESTABLISHED state, since this would result in + o If either or both are different, then the peer is reusing the + context tag for the creation of a context with different ULID pair + or FII, which is an indication that the peer has lost the original + context. In this case, we are in the Context confusion situation, + and the host MUST NOT use the old context to send any packets. It + MAY just discard the old context (after all, the peer has + discarded it), or it MAY attempt to re-establish the old context + by sending a new I1 message and moving its state to I1-SENT. In + any case, once that this situation is detected, the host MUST NOT + keep two contexts with overlapping Ls(peer) locator sets and the + same context tag in ESTABLISHED state, since this would result in demultiplexing problems on the peer. - o If this is not true, then the local host must be broken, since it - should have detected the existence of a context for the same ULID - pair and FII earlier. + o If both are the same, then this context is actually the context + that is created or updated, hence there is no confusion. -7.13 Receiving R2 messages +7.15 Receiving R2 messages A host MUST silently discard any received R2 messages that do not satisfy all of the following validity checks in 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 16 octets. Upon the reception of an R2 message, the host extracts the Initiator Nonce and the Locator Pair from the message (the latter from the source and destination fields in the IPv6 header). Next the host looks for an existing context which matches the Initiator Nonce and where the locators are Lp(peer) and Lp(local), respectively. Based on the state: o If no such context is found, i.e., the state is IDLE, then the message is silently dropped. 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 - included in the message, then the host MUST verify if the actual - PDS contained in the packet corresponds to the ULID(peer). If the - verification fails, then the message is silently dropped. If the - verification succeeds, then the host records the information from - the R2 message in the context state. It records the peer's - locator set in the context. It SHOULD perform the HBA/CGA - verification of the peer's locator set at this point in time. + the following actions: If a CGA Parameter Data Structure (PDS) is + included in the message, then the host MUST verify that the actual + PDS contained in the message corresponds to the ULID(peer) as + specified in Section 7.2. If the verification fails, then the + message is silently dropped. If the verification succeeds, then + the host records the information from the R2 message in the + context state; it records the peer's locator set and CT(peer). + 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 possible 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. + 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 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. 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 the context setup messages such as I1, R1, R1bis, I2, I2bis, R2 and future extensions), where the control message refers to a non existent context. 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. Upon reception of any of the packets described above, the host will reply with an R1bis including the following information: o The Responder Nonce is a number picked by the responder which the initiator will return in the I2bis message. 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 - computed as suggested in the next section. + o The Responder Validator option is included, with a validator that + 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 maintain a single secret (S) and a running counter for the Responder Nonce. In the case the validator is generated to be included in a R1bis - packet, for each received payload extension header or control packet, - the responder can increase the counter, use the counter value as the - responder nonce, and use the following information as input to the - one-way function: + message, for each received payload extension header or control + message, the responder can increase the counter, use the counter + value as the responder nonce, and use the following information as + input to the one-way function: o The the secret S 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 - 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 satisfy all of the following validity checks in 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 16 octets. Upon the reception of an R1bis message, the host extracts the Packet Context Tag and the Locator Pair from the message (the latter from the source and destination fields in the IPv6 header). Next the host looks for an existing context where the Packet Context Tag matches CT(peer) and where the locators match Lp(peer) and Lp(local), respectively. 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 - packet is silently discarded. + message is silently discarded. 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 it. For that, the host leaves CT(peer) unchanged in the context - state, transitions to I2BIS-SENT state, and sends a I2bis packet, - including in it the Validator, the Packet Context Tag, and the - Responder Nonce received in the R1bis packet. This I2bis packet - is sent using the locator pair included in the R1bis packet. In - the case that this locator pair differs from the ULID pair defined - for this context, then an ULID option MUST be included in the - I2bis packet. In addition, if the Forked Instance Identifier for - this context is non-zero, then a Forked Instance Identifier option - carrying the instance identifier value for this context MUST be - included in the I2bis message. + state, transitions to I2BIS-SENT state, and sends a I2bis message, + including the computed Responder Validator option, the Packet + Context Tag, and the Responder Nonce received in the R1bis + message. This I2bis message is sent using the locator pair + included in the R1bis message. In the case that this locator pair + differs from the ULID pair defined for this context, then an ULID + option MUST be included in the I2bis message. In addition, if the + Forked Instance Identifier for this context is non-zero, then a + Forked Instance Identifier option carrying the instance identifier + 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 satisfy all of the following validity checks in addition to those specified in Section 12.2: o The Hdr Ext Len field is at least 3, i.e., the length is at least 32 octets. Upon the reception of an I2bis message, the host extracts the ULID 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 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. Next the host verifies that the Responder Nonce is a recent one, and - that the Validator option matches the validator the host would have - computed for the ULID, locators, responder nonce, and FII as part of - sending an R1bis message. + that the Responder Validator option matches the validator the host + would have computed for the ULID, locators, responder nonce, and FII + as part of sending an R1bis message. - If a CGA Parameter Data Structure is included in the message, then - the host MUST verify if the actual PDS contained in the packet + If a CGA Parameter Data Structure (PDS) is included in the message, + then the host MUST verify if the actual PDS contained in the message corresponds to the ULID(peer). - If at least one of the above verification fails, then it silently - discard the packet and it has completed the I2bis processing. + If any of the above verifications fails, then the host silently + discard the message and it has completed the I2bis processing. If both verifications are successful, then the host proceeds to look for a context state for the Initiator. The host looks for a context with the extracted ULID pair and FII. If none exist then state of the (non-existing) context is viewed as being IDLE, thus the actions depend on the state as follows: 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 - the context, sets its state to ESTABLISHED. The host SHOULD NOT - use the Packet Context Tag in the I2bis packet for CT(local); + allocates a context tag (CT(local)), creates the context state for + the context, and sets its state to ESTABLISHED. The host SHOULD + 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 - processes an I2 message. It records the peer's locator set as - well as its own locator set in the context. It SHOULD perform the - HBA/CGA verification of the peer's locator set at this point in - time. Then the host sends an R2 message back as specified in - Section 7.11. + processes an I2 message. It records CT(peer), and the peer's + locator set as well as its own locator set in the context. It + SHOULD perform the HBA/CGA verification of the peer's locator set + at this point in time as specified in Section 7.2. Then the host + sends an R2 message back as specified in Section 7.13. - o If the state is ESTABLISHED, CT(peer) matches the Initiator - Context tag, and the IPv6 source address is contained in Ls(peer) - then this I2bis message is probably a retransmit, so the host MUST - send a R2 message back as specified below. + o If the state is I1-SENT, then the host verifies if the source + locator is included in Ls(peer) or, it is included in the Locator + List contained in the the I2 message and the HBA/CGA verification + for this specific locator is successful - o If the state is ESTABLISHED, and if at least one of the following - conditions is true: either the CT(peer) is not the same as the - 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. + * If this is not the case, then the message is silently + discarded. The the context state remains unchanged. - o In other state (I1-SENT, I2-SENT, or I2BIS-SENT) then we are in - the Concurrent context establishment situation described above. - Then it replies with a R2 message as specified in section - Section 7.11. The state of the context 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 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 The routers in the path as well as the destination might generate various ICMP error messages, such as host unreachable, packet too 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. - When the ULP packets are sent unmodified, 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. But when the shim on the transmitting side - 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 is an implementation issue in the sense that the mechanism is + completely local to the host itself. But the issue of how ICMP + errors are correctly dispatched to the ULP on the host are important, + hence this section specifies the issue. - This mapping is different than when receiving ULP packets from the - peer, because in that case the packets contain CT(local). But the - 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 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. + +--------------+ + | IPv6 Header | + | | + +--------------+ + | ICMPv6 | + | Header | + - - +--------------+ - - + | 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 - header, then this extension header must be removed. The result needs - to be that the ULP receives an ICMP error where the contained "packet - in error" looks as if the shim did not exist. + Figure 29: ICMP error handling without payload extension header + + When the ULP packets are sent without the payload extension header, + 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 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 Each host can unilaterally decide when to tear down a ULID-pair - context. It is RECOMMENDED that hosts not tear down the context when - they know that there is some upper layer protocol that might use the - context. For example, an implementation might know this is there is - an open socket which is connected to the ULID(peer). However, there - might be cases when the knowledge is not readily available to the - shim layer, for instance for UDP applications which not connect their - sockets, or any application which retains some higher level state - across (TCP) connections and UDP packets. + context. It is RECOMMENDED that hosts do not tear down the context + when they know that there is some upper layer protocol that might use + the context. For example, an implementation might know this if there + is an open socket which is connected to the ULID(peer). However, + there might be cases when the knowledge is not readily available to + the shim layer, for instance for UDP applications which do not + connect their sockets, or any application which retains some higher + level state across (TCP) connections and UDP packets. Thus it is RECOMMENDED that implementations minimize premature teardown by observing the amount of traffic that is sent and received 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 or received using the context. Since there is no explicit, coordinated removal of the context state, there are potential issues around context tag reuse. One end might remove the state, and potentially reuse that context tag for some other communication, and the peer might later try to use the old context (which it didn't remove). The protocol has mechanisms to 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 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 - 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.) 10. Updating the Peer The Update Request and Acknowledgement are used both to update 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. 10.1 Sending Update Request messages @@ -2897,23 +3161,23 @@ same nonce for any retransmissions of the Update Request. The nonce is used to match the acknowledgement with the request. 10.2 Retransmitting Update Request messages If the host does not receive an Update Acknowledgement R2 message in response to the Update Request message after UPDATE_TIMEOUT time, then it needs to retransmit the Update Request message. The retransmissions should use a retransmission timer with binary exponential backoff to avoid creating congestion issues for 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 - nominal value to avoid self-synchronization. + network when lots of hosts perform Update Request retransmissions. + Also, the actual timeout value should be randomized between 0.5 and + 1.5 of the nominal value to avoid self-synchronization. Should there be no response, the retransmissions continue forever. The binary exponential backoff stops at MAX_UPDATE_TIMEOUT. But the only way the retransmissions would stop when there is no acknowledgement, is when the shim, through the Probe protocol or some other mechanism, decides to discard the context state due to lack of ULP usage in combination with no responses to the Probes. 10.3 Newer Information While Retransmitting @@ -2952,95 +3216,95 @@ A host MUST silently discard any received Update Request messages that do not satisfy all of the following validity checks in 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 16 octets. Upon the reception of an Update Request message, the host extracts 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 - 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 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 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 host MUST send a R1bis message, and otherwise ignore the Update Request message. - If a CGA Parameter Data Structure is included in the message, then - the host MUST verify if the actual PDS contained in the packet + If a CGA Parameter Data Structure (PDS) is included in the message, + then the host MUST verify if the actual PDS contained in the packet corresponds to the ULID(peer). If this verification fails, the message is silently discarded. Then, depending on the state of the context: o If ESTABLISHED: Proceed to process message. 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 I2BIS-SENT, then send R2 and proceed to process the message. - The validation issues for the locators carried in the Locator Update - message are specified in Section 4.7. If the locator list can not be - validated, this procedure might send an ICMP Parameter Problem error. - In any case, if it can not be validated, there is no further + The verification issues for the locators carried in the Locator + Update message are specified in Section 7.2. If the locator list can + not be verified, this procedure might send an ICMP Parameter Problem + error. In any case, if it can not be verified, there is no further processing of the Update Request. - Once any Locator List option in the Update Request has been - validated, the peer generation number in the context is updated to be - the one in the Locator List option. + Once any Locator List option in the Update Request has been verified, + the peer generation number in the context is updated to be the one in + the Locator List option. 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 context. If they do not match, then the host generates an ICMP parameter problem (type 4, code 0) with the Pointer field referring to the first octet in the Generation number in the Locator Preference option. In addition, if the number of elements in the Locator Preference option does not match the number 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 Locator Preference option. In both cases of failures, no further processing is performed for the Locator Update message. If the generation number matches, the locator preferences are 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 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 result in the host wanting to select a different locator pair for the 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). 10.5 Receiving Update Acknowledgement messages A host MUST silently discard any received Update Acknowledgement messages that do not satisfy all of the following validity checks in 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 16 octets. Upon the reception of an Update Acknowledgement message, the host 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 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 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 case, the sender of the Update Acknowledgement has a stale context 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 Acknowledgement message. Then, depending on the state of the context: @@ -3069,70 +3333,78 @@ 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 ESTABLISHED and I2BIS-SENT states does the host have CT(peer) and Ls(peer) set. 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, whether Lp(peer) == ULID(peer) and Lp(local) == ULID(local). - If this is the case, then packets will be sent unmodified by the - shim. If it is not the case, then the logic in Section 11.1 will - need to be used. + If this is the case, then packets can be sent unmodified by the shim. + If it is not the case, then the logic in Section 11.1 will need to be + used. There will also be some maintenance activity relating to (un)reachability detection, whether packets are sent with the 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 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 the sender needs to transform the packet. Apart from replacing the 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 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 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 checksums, since the ULP checksums are carried end-to-end and the ULP pseudo-header contains the ULIDs which are preserved end-to-end. The sender skips any "routing sub-layer extension headers" that the ULP might have included, thus it skips any hop-by-hop extension header, any routing header, and any destination options header that is followed by a routing header. After any such headers the shim6 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. 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 As in normal IPv6 receive side packet processing the receiver parses 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 zero, then the packet must be passed to the shim6 payload handling for rewriting. Otherwise, the packet is passed to the shim6 control handling. 12.1 Receiving Payload Extension Headers The receiver extracts the context tag from the payload extension header, and uses this to find a ULID-pair context. If no context is found, the receiver SHOULD generate a R1bis message (see - Section 7.14). + Section 7.16). Then, depending on the state of the context: o If ESTABLISHED: Proceed to process message. 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 I2BIS-SENT, then send R2 and proceed to process the message. @@ -3238,31 +3510,31 @@ 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 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 the ULP would pass down the Forked Instance Identifier. 13. Initial Contact 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 - in the shim. + as described in Section 2. At that point in time there is no + activity in the shim. 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 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 protocols to retry with different source and destination addresses, 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 addresses. The implementation of such an approach can potentially result in long timeouts. For instance, a naive implementation at the socket API which uses getaddrinfo() to retrieve all destination addresses and then tries to bind() and connect() to try all source and destination address combinations waiting for TCP to time out for each combination before trying the next one. @@ -3287,50 +3559,48 @@ I1_TIMEOUT = 4 seconds NO_R1_HOLDDOWN_TIME = 1 min ICMP_HOLDDOWN_TIME = 10 min I2_TIMEOUT = 4 seconds I2_RETRIES_MAX = 2 + I2bis_TIMEOUT = 4 seconds + + I2bis_RETRIES_MAX = 2 + VALIDATOR_MIN_LIFETIME = 30 seconds UPDATE_TIMEOUT = 4 seconds The retransmit timers (I1_TIMEOUT, I2_TIMEOUT, UPDATE_TIMEOUT) are subject to binary exponential backoff, as well as randomization 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 performing independent shim operations at the same time. The randomization is applied after the binary exponential backoff. Thus the first retransmission would happen based on a uniformly 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, etc. -15. Open Issues - - The following open issues are known: - - o NONE. - -16. Implications Elsewhere +15. Implications Elsewhere The general shim6 approach, as well as the specifics of this proposed solution, has implications elsewhere. The key implications are: o Applications that perform referrals, or callbacks using IP 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, the applications need to be modified to either use fully qualified domain names as the 'identifiers', or they need to pass all the locators as the 'identifiers' i.e., the 'identifier' from the applications perspective becomes a set of IP addresses instead of a single IP address. o Firewalls that today pass limited traffic, e.g., outbound TCP connections, would presumably block the shim6 protocol. This means that even when shim6 capable hosts are communicating, the I1 @@ -3368,25 +3638,30 @@ different path through the Internet, hence the path MTU might be quite different. Perhaps such a path change would be a good hint to the path MTU mechanism to try a larger MTU? The fact that the shim will add an 8 octet payload extension 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 local to the sending host, thus conveying the change to the ULPs 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. o Requiring a Reachability Probe+Reply before a new locator is used as the destination, in order to prevent 3rd party flooding attacks. o The first message does not create any state on the responder. Essentially a 3-way exchange is required before the responder creates any state. This means that a state-based DoS attack (trying to use up all of memory on the responder) at least @@ -3405,21 +3680,21 @@ technique, the shim6 protocol is protected against off-path attackers. Some of the residual threats in this proposal are: 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 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 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. 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 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 "too much" ingress filtering between the attackers new location and the communicating peers. But this doesn't seem to be that severe, because once the R1bis causes the context to be re- established, a new pair of context tags will be used, which will @@ -3442,30 +3717,33 @@ the 47-bit context tag, the attacker also needs to find a context where, after the receiver's replacement of the locators with the ULIDs, the the ULP checksum is correct. But even this wouldn't be sufficient with ULPs like TCP, since the TCP port numbers and sequence numbers must match an existing connection. Thus, even though the issues for off-path attackers injecting packets are different than today with ingress filtering, it is still very hard for an off-path attacker to guess. If IPsec is applied then the issue goes away completely. -18. IANA Considerations +17. IANA Considerations - IANA needs to allocate a new IP Protocol Number value for this - protocol. + IANA is directed to allocate a new IP Protocol Number value for the + SHIM6 Protocol. - IANA also needs to record a CGA message type for this protocol in the - [CGA] namespace, 0x4A30 5662 4858 574B 3655 416F 506A 6D48. + IANA is directed to record a CGA message type for the SHIM6 Protocol + in the [CGA] namespace registry with the value 0x4A30 5662 4858 574B + 3655 416F 506A 6D48. - This protocol introduces a new shim6 message type name space. The - initial assignment of the types is shown below. + IANA is directed to establish a SHIM6 Parameter Registry with two + components: SHIM6 Type registrations and SHIM6 Options registrations. + + The initial contents of the SHIM6 Type registry are as follows: +------------+-----------------------------------------------------+ | Type Value | Message | +------------+-----------------------------------------------------+ | 0 | RESERVED | | | | | 1 | I1 (first establishment message from the initiator) | | | | | 2 | R1 (first establishment message from the responder) | | | | @@ -3486,30 +3764,28 @@ | 65 | Update Acknowledgement | | | | | 66 | Keepalive | | | | | 67 | Probe Message | | | | | 68-123 | Can be allocated using Standards Action | | | | | 124-127 | For Experimental use | +------------+-----------------------------------------------------+ - - This protocol introduces a new shim6 option type name space. The - initial assignment of the types is shown below. + The initial contents of the SHIM6 Options registry are as follows: +--------------+----------------------------------+ | Type | Option Name | +--------------+----------------------------------+ | 0 | RESERVED | | | | - | 1 | Validator | + | 1 | Responder Validator | | | | | 2 | Locator List | | | | | 3 | Locator Preferences | | | | | 4 | CGA Parameter Data Structure | | | | | 5 | CGA Signature | | | | | 6 | ULID Pair | @@ -3522,55 +3798,84 @@ | | | | 11 | Reachability Option | | | | | 12 | Payload Reception Report Option | | | | | 13-16383 | Allocated using Standards action | | | | | 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 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 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 two communicating endpoints? We can potentially accomplish that 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 the context establishment. The suggestion is to leave this for a future extension to the protocol. o Defining some form of end-to-end "compression" mechanism that removes the need for including the Shim6 Payload extension header when the locator pair is not the ULID pair. - o Specifying a complete solution which carries locator preferences, - both within a site (e.g., DHCP option?), and use the Locator - Preference option to carry those in the shim protocol. This could - mirror the DNS SRV record's notion of priority and weight. + o Supporting the dynamic setting of locator preferences on a site- + wide basis, and use the Locator Preference option in the shim6 + protocol to convey these preferences to remote communicating + 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 - is using, and be able to influence the choice of locators. This - includes providing APIs the ULPs can use to fork a shim context. + is using, and be able to influence the choice of locators + (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 state is removed, so that one can end up with an asymmetric distribution of the context state and still get (most of) the shim benefits. For example, the busy server would go through the context setup but would quickly remove the context state after this (in order to save memory) but the not-so-busy client would 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 because it sees a problem), or a ULP packet in an payload extension header (because it had earlier failed over to an alternative locator pair, but had been silent for a while). This 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 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 doesn't know any alternate locator pairs. @@ -3588,35 +3893,62 @@ requirement to include essentially all of them in the I2 and R2 messages might be constraining. If this is the case we can look into using the CGA Parameter Data Structure for the comparison, instead of the prefix sets, to be able to detect context confusion. This would place some constraint on a (logical) only using e.g., one CGA public key, and would require some carefully 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, 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: o Replaced the Context Error message with the R1bis message. o Removed the Packet In Error option, since it was only used in the Context Error message. o Introduced a I2bis message which is sent in response to an I1bis message, since the responders processing is quite in this case than in the regular R1 case. o Moved the packet formats for the Keepalive and Probe message types - and Event option to [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. o Removed the unused message types. o Added a state machine description as an appendix. o Filled in all the TBDs - except the IANA assignment of the protocol number. o Specified how context recovery and forked contexts work together. @@ -3642,22 +3974,23 @@ This allows extensibility of the protocol with new message types while being able to control when R1bis is generated. o Expanded the context tag from 32 to 47 bits. o Specified that enough locators need to be included in I2 and R2 messages. Specified that the HBA/CGA verification must be performed when the locator set is received. o Specified that ICMP parameter problem errors are sent in certain - error cases, for instance when the validation method is unknown to - the receiver, or there is an unknown message type or option type. + error cases, for instance when the verification method is unknown + to the receiver, or there is an unknown message type or option + type. o Renamed "payload message" to be "payload extension header". o Many editorial clarifications suggested by Geoff Huston. o Modified the dispatching of payload extension header to only compare CT(local) i.e., not compare the source and destination IPv6 address fields. The following changes have been made since draft-ietf-shim6-proto-00: @@ -3693,26 +4026,21 @@ context is forked, that is different ULP messages are sent over different locator pairs, things are a lot easier if there is only one current locator pair used for each context. Thus the forking of the context is now causing a new context to be established for the same ULID; the new context having a new context tag. The original context is referred to as the "default" context for the ULID pair. o Added more background material and textual descriptions. -21. Acknowledgements - - 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 +Appendix D. Simplified State Machine The states are defined in Section 6.2. The intent is that the stylized description below be consistent with the textual description in the specification, but should they conflict, the textual description is normative. The following table describes the possible actions in state IDLE and their respective triggers: +---------------------+---------------------------------------------+ @@ -3855,21 +4183,24 @@ | extension header | sent by peer and lost) | | other control | | | packet | | +---------------------+---------------------------------------------+ The following table describes the possible actions in state ESTABLISHED and their respective triggers: +---------------------+---------------------------------------------+ | 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 | | validator and RESP | ESTABLISHED | | nonce | | | | Otherwise, discard and stay in ESTABLISHED | | | | | Receive I2bis, | If successful, then send R2 and stay in | | verify validator | ESTABLISHED | | and RESP nonce | | | | Otherwise, discard and stay in ESTABLISHED | @@ -3909,26 +4240,26 @@ +---------------------+---------------------------------------------+ | Trigger | Action | +---------------------+---------------------------------------------+ | Wait for | Go to IDLE | | ICMP_HOLDDOWN_TIME | | | | | | 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 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 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 this is that the protocol needs to be robust against a context tag being reused for some other context. This section summarizes the different cases in which a tag can be reused, and how the recovery works. The different cases are exemplified by the following case. Assume @@ -3944,43 +4275,43 @@ . We've called this "Context Recovery" in this document. o The context tag is reassigned to a context for a different ULID pair between the same to hosts, e.g., . We've called this "Context Confusion" in this document. o The context tag is reassigned to a context between B and other host C, for instance for the ULID pair . That is a form 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 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. -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 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 (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 possibility of causing confusion by not using the old context to send 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 recreates a different context for the old ULID pair (), for which B will assign a unique CT(B) as part of the normal context 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 verified, since the new context is established between B and C. Thus when B receives payload extension headers with X as the context tag, it will find the context for , hence rewrite the packets to 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 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 sends a packet with ULIDs and the packet arrives at the ULP @@ -4008,29 +4339,29 @@ 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. The probability of these events is low given the 47 bit context tag size. However, it is important that these recovery mechanisms be tested. Thus during development and testing it is recommended that 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 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 try to work out a bunch of the details, and stimulate discussion. But as has been discussed on the mailing list, there are other choices that make sense. This appendix tries to enumerate some alternatives. -Appendix C.1 Context granularity +Appendix F.1 Context granularity Over the years various suggestions have been made whether the shim 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 shim contexts for separate ULP connections and sessions. A few different options have been discussed: o Each ULP connection maps to its own shim context. o The shim is unaware of the ULP notion of connections and just @@ -4048,21 +4379,21 @@ that want different communication to use different locator pairs, for instance for quality or cost reasons. The protocol has a shim which operates with host-level granularity (strictly speaking, with ULID-pair granularity, to be able to amortize the context establishment over multiple ULP connections. This is combined with the ability for shim-aware ULPs to request context forking so that different ULP traffic can use different 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 may carry locators that differ from the ULIDs presented to the ULPs using the established context. One of main functions of the SHIM6 layer is to perform the mapping between the locators used to forward packets through the network and the ULIDs presented to the ULP. In order to perform that translation for incoming packets, the SHIM6 layer needs to first identify which of the incoming packets need to be translated and then perform the mapping between locators and ULIDs using the associated context. Such operation is called @@ -4087,21 +4418,21 @@ packet to determine the shim context to be used to perform the operation. Two mechanisms for carrying the context tag information have been considered in depth during the shim protocol design. Those carrying 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 appendix we will describe the pros and cons of each approach and 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 field of the IPv6 header. This means that when a shim6 context is established, a Flow Label value is associated with this context (and perhaps a separate flow label for each direction). The simplest approach that does this is to have the triple identify the context at the receiver. @@ -4147,36 +4478,36 @@ negotiation of the Flow Label value to use in the communication is needed before exchanging data packets. This poses problems with non- shim capable hosts, since they would not be able to negotiate an acceptable value for the Flow Label. This limitation can be lifted 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 header that is not currently available, so more creative options would be required, for instance using new Next Header values to indicate that the packet belongs to a shim6 enabled communication and 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 of the shim protocol, which is a preferred function, since it suppresses the delay due to the shim context establishment prior to initiation of the communication and it also allows nodes to define at which stage of the communication they decide, based on their own policies, that a given communication requires to be protected by the shim. In order to cope with the identified limitations, an alternative approach that does not constraints the flow label values used by communications that are using ULIDs equal to the locators (i.e. no shim translation) is to only require that different flow label values are assigned to different shim contexts. In such approach 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 label, and this flow label could be allocated by the receiver as part of the shim context establishment. Since it is allocated during the context establishment, the receiver of the "failed over" packets can 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 performance impact, and respecting that for each locator pair, the flow label value used for a given locator pair doesn't change due to the operation of the multihoming shim. @@ -4197,21 +4528,21 @@ 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 minimum constraints to the Flow Label allocation strategies, limiting the restrictions only to those packets that need to be translated by the shim, but also because Context Loss detection mechanisms greatly benefit from the fact that shim data packets are identified as such, 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 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 carry the context tag in a new Extension Header. These context tags are allocated by the receiving end during the shim6 protocol initial negotiation, implying that each context will have two context tags, one for each direction. Data packets will be demultiplexed using the context tag carried in the Extension Header. This seems a clean approach since it does not overload existing fields. However, it introduces additional overhead in the packet due to the additional header. The additional overhead introduced is 8 octets. However, it @@ -4221,21 +4552,21 @@ ULIDs do not require a context tag, since no rewriting is necessary at the receiver. This approach would reduce the overhead, because the additional header is only required after a failure. On the other hand, this approach would cause changes in the available MTU for some packets, since packets that include the Extension Header will have an MTU 8 octets shorter. However, path changes through the network can 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 issues. -Appendix C.3 Context Loss Detection +Appendix F.3 Context Loss Detection In this appendix we will present different approaches considered to detect context loss and potential context recovery strategies. The scenario being considered is the following: Node A and Node B are communicating using IPA1 and IPB1. Sometime later, a shim context is established between them, with IPA1 and IPB1 as ULIDs and IPA1,...,IPAn and IPB1,...,IPBm as locator set respectively. 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 @@ -4335,25 +4666,25 @@ exchange and at this point time may be critical since we are reestablishing a context that is currently needed (because context 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 a modified R1 message, so that the time required to perform the context establishment exchange can be reduced. Upon the reception of this modified R1 message, the end that still has the context state can finish the context establishment exchange and restore the lost 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 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 new vulnerability in the Internet architecture. It is a non-goal to provide additional protection than the currently available in the single-homed IPv6 Internet. Multiple security mechanisms were considered to protect the shim protocol. In this appendix we will present some of them. The simplest option to protect the shim protocol was to use cookies i.e. a randomly generated bit string that is negotiated during the @@ -4458,21 +4789,21 @@ So, the design decision adopted was that both mechanisms HBA and CGA are supported, so that when only stable address sets are required, the nodes can benefit from the low computational cost offered by HBA while when dynamic locator sets are required, this can be achieved through CGAs with an additional cost. Moreover, because HBAs are defined as a CGA extension, the addresses available in a node can simultaneously be CGAs and HBAs, allowing the usage of the HBA and CGA functionality when needed without requiring a change in the 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 exchange: a 2-way handshake and a 4-way handshake. A key goal for the design of this exchange was that protection against DoS attacks. The attack under consideration was basically a situation where an attacker launches a great amount of ULID-pair establishment request packets, exhausting victim's resources, similar to TCP SYN flooding attacks. @@ -4506,51 +4837,51 @@ 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 detect an ongoing attack and different heuristics need to be considered. 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 protocol thanks to the deferred context establishment capability, a 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 locators: atomic and differential approaches. The atomic approach essentially send the complete locators set each time that a variation in the locator set occurs. The differential approach send the differences between the existing locator set and the new one. The atomic approach imposes additional overhead, since all the locator set has to be exchanged each time while the differential approach requires re-synchronization of both ends through changes i.e. that both ends have the same idea about what the current locator set is. Because of the difficulties imposed by the synchronization 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 about locators, keys and identifiers of a correspondent node: a coordinated approach and an unilateral approach. In the unilateral approach, each node discards the information about the other node without coordination with the other node based on some local timers and heuristics. No packet exchange is required for 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, a No-Context error message may be required to inform about the situation and possibly a recovery mechanism is also needed. 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 the No Context Error message due to a peer having garbage collected 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 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 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 message. @@ -4592,23 +4923,23 @@ coordinated approach using a CLOSE/CLOSE ACK exchange, there is still the possibility of a host rebooting without having the time to perform the CLOSE exchange. So, it is true that the coordinated approach eliminates the possibility of a context confusion situation because premature garbage collection, but it does not prevents the 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 approach, we would still need to deal with context confusion and 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 Levels", BCP 14, RFC 2119, March 1997. [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. @@ -4618,97 +4949,88 @@ [5] Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 2463, December 1998. [6] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005. [7] Bagnulo, M., "Hash Based Addresses (HBA)", draft-ietf-shim6-hba-01 (work in progress), October 2005. - [8] Beijnum, I., "Shim6 Reachability Detection", - draft-ietf-shim6-reach-detect-01 (work in progress), - October 2005. - - [9] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair + [8] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair Exploration Protocol for IPv6 Multihoming", - draft-ietf-shim6-failure-detection-02 (work in progress), - October 2005. + draft-ietf-shim6-failure-detection-03 (work in progress), + 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, 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 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. - [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. - [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), 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, 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. - [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. - [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. - [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. - [20] Nordmark, E., "Threats relating to IPv6 multihoming solutions", - draft-ietf-multi6-multihoming-threats-03 (work in progress), - January 2005. + [19] Nordmark, E. and T. Li, "Threats Relating to IPv6 Multihoming + Solutions", RFC 4218, October 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. - [22] Abley, J., "Shim6 Applicability Statement", + [23] Abley, J., "Shim6 Applicability Statement", draft-ietf-shim6-applicability-00 (work in progress), 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 progress), July 2005. - [24] Bagnulo, M. and J. Arkko, "Functional decomposition of the - multihoming protocol", draft-ietf-shim6-functional-dec-00 (work - 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. + [25] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-05 + (work in progress), March 2006. - [28] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", - draft-ietf-mobike-protocol-07 (work in progress), - December 2005. + [26] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", + draft-ietf-mobike-protocol-08 (work in progress), + February 2006. Authors' Addresses Erik Nordmark Sun Microsystems 17 Network Circle Menlo Park, CA 94025 USA Phone: +1 650 786 2921 @@ -4753,18 +5075,18 @@ This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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 except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society.