Individual Submission                                          G. Huston
Internet-Draft                                                   Telstra
Expires: October 31, 2004                                    May 2, 2004

           Architectural Approaches to Multi-Homing for IPv6

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   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://

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on October 31, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.


   This memo provides an analysis of the aspects of multi-homing support
   for the IPv6 protocol suite. The purpose of this analysis is to
   provide a taxonomy for classification of various proposed approaches
   to multi-homing. It is also an objective of this exercise to identify
   common aspects of this domain of study, and also to provide a
   framework that can allow exploration of some of the further
   implications of various architectural extensions that are intended to
   support multi-homing.

Huston                  Expires October 31, 2004                [Page 1]

Internet-Draft            Multi6 Architectures                  May 2004

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.    The Multi-Homing Space . . . . . . . . . . . . . . . . . . .  3
   3.    Requirements and Considerations  . . . . . . . . . . . . . .  5
   4.    Approaches to Multi-Homing . . . . . . . . . . . . . . . . .  6
   4.1   Multi-Homing: Routing  . . . . . . . . . . . . . . . . . . .  6
   4.2   Multi-homing: Identity Considerations  . . . . . . . . . . .  7
   4.3   Multi-homing: Identity Protocol Element  . . . . . . . . . .  9
   4.4   Multi-homing: Modified Protocol Element  . . . . . . . . . . 11
   4.5   Modified Site-Exit and Host Behaviors  . . . . . . . . . . . 11
   4.6   Approaches to Endpoint Identity  . . . . . . . . . . . . . . 13
   4.7   Endpoint Identity Structure  . . . . . . . . . . . . . . . . 13
   5.    Common Issues for Multi-Homing Approaches  . . . . . . . . . 15
   5.1   Triggering Locator Switches  . . . . . . . . . . . . . . . . 15
   5.2   Session Startup and Maintenance  . . . . . . . . . . . . . . 17
   6.    Security Considerations  . . . . . . . . . . . . . . . . . . 17
   7.    Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
         Normative References . . . . . . . . . . . . . . . . . . . . 18
         Author's Address . . . . . . . . . . . . . . . . . . . . . . 18
   A.    Notes on Various approaches  . . . . . . . . . . . . . . . . 18
   A.1   Host Identity Protocol (HIP) . . . . . . . . . . . . . . . . 18
   A.2   Multihoming without IP Identifiers (NOID)  . . . . . . . . . 19
   A.3   Common Endpoint Locator Pools (CELP) . . . . . . . . . . . . 20
   A.4   Weak Identifier Multihoming Protocol (WIMP)  . . . . . . . . 21
   A.5   Host-Centric IPv6 Multihoming  . . . . . . . . . . . . . . . 22
   A.6   Summaries of Selected ID/LOC Separation Documents  . . . . . 23
   A.6.1 New or Updated Documents Since IETF58  . . . . . . . . . . . 24
   A.6.2 Older Documents that Remain Active/Interesting . . . . . . . 26
   A.6.3 Related Multi-Homing drafts, Status unknown  . . . . . . . . 27
         Intellectual Property and Copyright Statements . . . . . . . 30

Huston                  Expires October 31, 2004                [Page 2]

Internet-Draft            Multi6 Architectures                  May 2004

1. Introduction

   The objective of this exercise is to allow various technical
   proposals relating to the support of multi-homing environment in IPv6
   to be placed within an architectural taxonomy. This is intended to
   allow these proposals to be classified and compared in a structured
   fashion. It is also an objective of this exercise to identify common
   aspects across all proposals within this domain of study, and also to
   provide a framework that can allow exploration of some of the further
   implications of various architectural extensions that are intended to
   support multi-homing. The scope of this study is limited to the IPv6
   protocol suite architecture, although reference is made to IPv4
   approaches as required.

2. The Multi-Homing Space

   The simplest formulation of the multi-homing environment is indicated
   in Figure 1.

Huston                  Expires October 31, 2004                [Page 3]

Internet-Draft            Multi6 Architectures                  May 2004

                           | host |
                           |  R   |
                    + - - - - - - - - - - - +
                    | Internet Connectivity |
                    + - - - - - - - - - - - +
                         /            \
                   +---------+    +---------+
                   | ISP A   |    |  ISP B  |
                   +---------+    +---------+
                       | Path a        | Path b
         + - - - - - - - - - - - - - - - - - - - - +
         | multi-      |               |           |
           homed   +------+         +------+
         | site    | site |         | site |       |
                   | exit |         | exit |
         |         |router|         |router|       |
                   |  A   |         |  B   |
         |         +------+         +------+       |
                      |                |
         |         local site connectivity         |
         |           +-----------+                 |
         |           |   host    |                 |
         + - - - - - - - - - - - - - - - - - - - - +

   The Multi-Homed Domain

                                Figure 1

   The environment of multi-homing is one that is intended to provide
   sufficient support to local hosts so as to allow local hosts to
   exchange IP packets with remote hosts, such that this exchange of
   packets is to be seamlessly supported across dynamic changes in
   connectivity. This implies that if a local multi-homed-aware host
   establishes an application session with the remote host using "Path
   a", and this path fails, the application session should be mapped
   across to "Path b" without requiring any application-visible
   re-establishment of the session. In other words, the application
   session should not be required to be explicitly aware of underlying
   path changes at the level of packet forwarding paths chosen by the

Huston                  Expires October 31, 2004                [Page 4]

Internet-Draft            Multi6 Architectures                  May 2004

   This simple multi-homing scenario also includes "site-exit' routers,
   where the local site interfaces to the upstream Internet transit
   providers. The nature of the interactions between the external
   routing system and the site-exit routers, and interactions between
   the site-exit routers and the local multi-homed host, and the
   interactions between local connectivity forwarding and the local host
   and site exit routers are not defined a priori in this scenario, as
   they form part of the framework of interaction between the various
   multi-homing components.

   The major characteristic of this scenario is that the address space
   used by, and advertised as reachable by, ISP A is distinct from the
   address space used by ISP B.

   This simple scenario is intended to illustrate the basic multi-homing
   environment. Variations of this scenario include additional external
   providers of transit connectivity to the local site, complex site
   requirements and constraints, where the site may not interface
   uniformly to all external transit providers, sequential rather than
   simultaneous external transit reachability, communication with remote
   multi-homed hosts, multi-way communications, use of host addresses in
   a referential context (third party referrals) and the imposition of
   policy constraints on path selection. However, the basic scenario is
   sufficient to illustrate the major architectural aspects of support
   for multi-homing, so this scenario will be used as the reference
   model for this analysis.

3. Requirements and Considerations

   RFC 3582 [RFC3582] documents some requirements that a multi-homing
   approach should attempt to address. These requirements include:
   o  redundancy
   o  load sharing
   o  traffic engineering
   o  policy constraints
   o  simplicity of approach
   o  transport-layer survivability
   o  DNS compatibility
   o  packet filtering capability
   o  scaleability
   o  legacy compatibility
   The reader is referred to [RFC3582] for a complete description of
   each of these requirements.

   In addition, work in progress
   [draft-lear-multi6-things-to-think-about] documents further
   considerations for IPv6 multi-homing. Again, the reader is referred
   to this document for the detailed enumeration of these

Huston                  Expires October 31, 2004                [Page 5]

Internet-Draft            Multi6 Architectures                  May 2004

   considerations. The general topic areas considered in this study
   o  interaction with routing systems,
   o  aspects of a split between end-point-identifier and forwarding
   o  changes to packets on the wire, and
   o  the interaction between names, endpoints and the DNS.

   In considering various approaches, further consideration also
   o  the role of helpers and agents in the approach,
   o  modifications to host behaviors,
   o  the required trust model to support the interactions, and
   o  the nature of potential vulnerabilities in the approach.

4. Approaches to Multi-Homing

   There appear to be four generic forms of architectural approaches to
   this problem, namely:
   o  Routing
      Use the IPv4 multi-homing approach
   o  New Protocol Element
      Insertion of a new element in the protocol stack that manages a
      persistent identity for the session
   o  Modify a Protocol Element
      Modify the Transport or IP protocol stack element in the host in
      order to support dynamic forwarding locator change
   o  Modified Site-Exit Router / Local Host interaction
      Modify the site-exit router and local forwarding system to allow
      various behaviors including source-based forwarding, site-exit
      hand-offs, and address rewriting by site-exit routers

   These approaches will be described in detail in the following

4.1 Multi-Homing: Routing

   The approach used in IPv4 for multi-homing support is to preserve the
   semantics of the IPv4 address as both an endpoint identifier and a
   forwarding locator. For this to work in a multi-homing context it is
   necessary for the transit ISPs to announce the local site's address
   prefix as a distinct routing entry in the inter-domain routing
   system. This approach could be used in an IPv6 context, and, as with
   IPv4, no modifications to the IPv6 architecture are required to
   support this approach.

   The local site's address prefix may be a more specific address prefix
   drawn from the address space advertised by one of the transit

Huston                  Expires October 31, 2004                [Page 6]

Internet-Draft            Multi6 Architectures                  May 2004

   providers, or from some third party provider not current directly
   connected to the local site. Alternatively the address space may be a
   distinct address block obtained by direct assignment from a Regional
   Internet Registry as Provider Independent space. Each host within the
   local site is uniquely addressed from the site's address prefix.

   All transit providers for the site accept a prefix advertisement from
   the multi-homed site, and advertise this prefix globally in the
   inter-domain routing table. When connectivity between the local site
   and an individual transit provider is lost, normal operation of the
   routing protocol will ensure that the routing advertisement
   corresponding to this particular path will be withdrawn from the
   routing system, and those remote domain domains who had selected this
   path as the best available will select another candidate path as the
   best path. Upon restoration of the path, the path is re-advertised in
   the inter-domain routing system. Remote domains will undertake a
   further selection of the best path based on this re-advertised
   reachability information. Neither the local or the remote host need
   to have multiple addresses, nor undertake any form of address
   selection. The path chosen for forward and reverse direction path
   flows is a decision made by the routing system.

   This approach generally meets all the criteria for multi-homing
   approaches with one noteable exception: scaleability. Each site that
   multi-homes in this fashion adds a further entry in the global
   inter-domain routing table. Within the constraints of current routing
   and forwarding technologies it is not clearly evident that this
   approach can scale to encompass a population of multi-homed sites of
   the order of 10**7 such sites. The implication here is that this
   would add a similar number of unique prefixes into the inter-domain
   routing environment, which in turn would add to the storage and
   computational load imposed on inter-domain routing routing elements
   within the network. This scale of additional load is not supportable
   within the current capabilities of the IPv4 global Internet, nor is
   it clear at present that the routing capabilities of the entire
   network could be expanded to manage this load in a cost-effective
   fashion, within the bounds of the current inter-domain routing
   protocol architecture.

4.2 Multi-homing: Identity Considerations

   The intent of multi-homing in the IPv6 domain is to achieve a
   comparable functional outcome for multi-homed sites without an
   associated additional load being imposed on the routing system. The
   overall intent of IPv6 is to provide a scaleable protocol framework
   to support the deployment of communications services for an extended
   period of time, and this implies that the scaling properties of the
   deployment environment remain tractable within projections of size of

Huston                  Expires October 31, 2004                [Page 7]

Internet-Draft            Multi6 Architectures                  May 2004

   deployment and underlying technology capabilities. Within the
   inter-domain routing space, the basic approach used in IPv4 and IPv6
   is to attempt to align address deployment with network topology, so
   that address aggregation can be used to create a structured hierarchy
   of the routing space.

   Within this constraint of topological-based address deployment and
   provider aggregatable addressing architectures, the local site that
   is connected to multiple providers is delegated addresses from each
   of these providers' address blocks. In the example network in Figure
   1, the local multi-homed host will concievably be addressed in two
   ways: one using transit provider A's address prefix and the other
   using transit provider B's address prefix.

   If remote host R is to initiate a communication with the local
   multi-homed host, it would normally query the DNS for an address for
   the local host. In this context the DNS would return 2 addresses (One
   using the A prefix and the other using the B prefix). The remote host
   would select one of these addresses and send a packet to this
   destination address. This would direct the pact to the local host
   along a path through A or B, depending on the selected address. If
   the path between the local site and the transit provider fails, then
   the address prefix announced by the transit provider to the
   inter-domain routing system will continue to be the provider's
   address prefix. The remote host will not see any change in routing,
   yet packets sent to the local host will now fail to be delivered. The
   question posed by the multi-homing problem is: "If the remote host is
   aware of multi-homing, how could it switch over to using the
   equivalent address for teh local multi-homed host hat transits the
   other provider?"

   If the local multi-homed host wishes to initiate a session with
   remote host R, it needs to send a packet to R with a valid source and
   destination address. While the destination address is that of R, what
   source address should the local host use? There are two implications
   for this choice. Firstly the remote host will, by default use this
   source address as the destination address in its response, and hence
   this choice of source address will direct the reverse path from R to
   the local host. Secondly, the ISPs A and B may be using reverse
   unicast address filtering on source addresses of packets passed to
   the ISP, as a means of prevention of source address spoofing. This
   implies that if the multi-homed address selects a source address from
   address prefix A, and the local routing to R selects a best path via
   ISP B, then ISP B's ingress filters will discard the packet.

   Within this addressing structure there is no form of routing-based
   repair of certain network failues. If the link between the local site
   and ISP A fails, there is no change in the route advertisements made

Huston                  Expires October 31, 2004                [Page 8]

Internet-Draft            Multi6 Architectures                  May 2004

   by ISP A to its external routing peers. Even though the multi-homed
   sitines to be reachable via ISP B, packets directed to the site using
   ISP A's prefix will be discarded by ISP A as the destination is
   unreachable. The implication here is that if the local host wishes to
   maintain a session across such events it needs to communicate to
   remote host R that it is possible to switch to using a destination
   address for the multi-homed host that is based on ISP B' address

   In an aggregated routing environment multiple transit paths to a host
   imply multiple address prefixes for the host, where each possible
   transit path is identified by an address for the host. The
   implication of this constraint on multi-homing is that paths being
   passed to the local multi-homed site via transit provider ISP A must
   use a forwarding-level destination IP address drawn from ISP A's
   advertised address prefix set that maps to the multi-homed host.
   Equally, packets being passed via the transit of ISP B must use a
   destination address drawn from ISP B's address prefix set. The
   further implication here is that path selection (ISP A vs ISP B
   transit for incoming packets) is an outcome of the process of
   selecting an address for the destination host.

   The architectural consideration here is that in the conventional IP
   protocol architecture the assumption is made that the transport-layer
   endpoint identity is the same identity used by the internet-layer
   forwarding layer, namely the IP address.

   If multiple forwarding paths are to be supported for a single
   transport session, and path selection is to be decoupled from the
   functions of transport session initiation and maintenance, then the
   corollary of this requirement in architectural terms appears to be
   that some changes are required in the protocol architecture to
   decouple the concepts of identification of the endpoint and
   identification of the location and associated path selection for the
   endpoint. This change in the protocol architecture would permit a
   transport session to use an invariant endpoint identity value to
   initiate and maintain a session, while allowing the forwarding layer
   to dynamically change paths and associated endpoint locator
   identities without impacting on the operation of the session, nor
   would such a decoupled concept of identities and locators add any
   incremental load to the inter-domain routing system.

   Some generic approaches to this form of separation of endpoint
   identity and locator value are described in the following sections.

4.3 Multi-homing: Identity Protocol Element

   One approach to this objective is to add a new element into the model

Huston                  Expires October 31, 2004                [Page 9]

Internet-Draft            Multi6 Architectures                  May 2004

   of the protocol stack.

   The presentation to the upper level protocol stack element (ULP)
   would use endpoint identifiers to uniquely identify both the local
   stack and the remote stack. This will provide the ULP with stable
   identifiers for the duration of the ULP session.

   The presentation to the lower level protocol stack element (LLP)
   would be of the form of a locator. This implies that the protocol
   stack element would need to maintain a mapping of endpoint identifier
   values to locator values. In a multi-homing context one of the
   essential characteristics of this mapping is that it needs to be
   dynamic, in that environmental triggers should be able to trigger a
   change in mappings, which in turn would correspond to a change in the
   paths (forward and/or reverse) used by the endpoints to traverse the
   network. In this way the ULP session is defined by a peering of
   endpoint identifiers that remain constant throughout the lifetime of
   the ULP session, while the locators may change to maintain end-to-end
   reachability for the session.

   The operation of the new protocol stack element (termed here the
   "endpoint identity protocol stack element", or "EIP") is to establish
   a synchronized state with its remote counterpart. This would allow
   the stack elements to exchange a set of locators that may be used
   within the context of the session. A change in the local binding
   between the current endpoint identity value and a locator will cause
   a change in the source locator value used in the forwarding level
   packet header. The actions of the remote EIP upon receipt of this
   packet with the new locator is to firstly recognize this locator as
   part of an existing session, and, upon some trigger condition, to
   change its session view of the mapping of the remote endpoint
   identity to the corresponding locator, and use this locator as the
   destination locator in subsequent packets passed to the LLP.

   From the perspective of the IP protocol architecture there are two
   possible locations to insert the EIP into the protocol stack.

   One possible location is at the upper level of the transport
   protocol. Here the application program interface (API) of the
   application level protocols would interface to the EIP element, and
   use endpoint identifiers to refer to the remote entity. The EIP would
   pass locators to the API of the transport layer.

   The second approach is to insert the EIP between the transport and
   internet protocol stack elements, so that the transport layer would
   function using endpoint identifiers, and maintain a transport session
   using these endpoint identifiers. The IP or internetwork layer would
   function using locators, and the mapping from endpoint identifier to

Huston                  Expires October 31, 2004               [Page 10]

Internet-Draft            Multi6 Architectures                  May 2004

   locator is undertaken within the EIP stack element.

4.4 Multi-homing: Modified Protocol Element

   As an alternative to insertion of a new protocol stack element into
   the protocol architecture, an alternative approach is to modify an
   existing protocol stack element to include the functionality
   performed by the EIP element. This modification could be undertaken
   within the transport protocol stack element, or within the
   internetworking stack element. The functional outcome from these
   modifications would be to create a mechanism to support the use of
   multiple locators within the context of a single endpoint-to-endpoint

   Within the transport layer, this functionality can be achieved, for
   example, by the binding of a set of locators to a single session, and
   then communicating this locator set to the remote transport entity.
   This would allow the local transport entity to switch the mapping to
   a different locator for either the local endpoint or the remote
   endpoint while maintaining the integrity of the ULP session.

   Within the IP level this functionality could be supported by a form
   of dynamic rewriting of the packet header as it is processed by the
   protocol element. Incoming packets with the source and destination
   locators in the packet header are mapped to packets with the
   equivalent endpoint identifiers in both fields, and the reverse
   mapping is performed to outgoing packets passed from the transport
   layer. Mechanisms that support direct rewriting of the packet header
   are potential candidates in this approach, as are various forms of
   packet header transformations of encapsulation, where the original
   endpoint identifier packet header is preserved in the packet and an
   outer level locator packet header is wrapped around the packet as it
   is passed through the internetworking protocol stack element.

   In all these scenarios, there are common issues of what state is
   kept, by which part of the protocol stack, how state is maintained
   with additions, removals of locator bindings, and does only one piece
   of code have to be aware of the endpoint / locator split or do
   multiple protocol elements have to be modified? For example, if the
   functionality is added at the internetworking (IP) layer, there is no
   context of an active transport session, so that removal of identity /
   locator state information for terminated sessions needs to be
   triggered by some additional mechanism from the transport layer to
   the internetworking layer.

4.5 Modified Site-Exit and Host Behaviors

   The above approaches all assume that the hosts are explicitly aware

Huston                  Expires October 31, 2004               [Page 11]

Internet-Draft            Multi6 Architectures                  May 2004

   of the multi-homed environment and use modified protocol behavior to
   support multi-homing functionality. A further approach to this
   objective is to split this functionality across a number of network
   elements and potentially perform packet header rewriting from a
   persistent endpoint identity value to a locator value at a remote

   One possible approach proposes the use of site-exit routers to
   perform some form of packet header manipulation as packets are passed
   out from the local multi-homed site to a particular transit provider.
   The local site routing system will select the best path to a
   destination host based on the remote hosts's locator value. The local
   host will write its endpoint identity as the source address of the
   packet. When the packet reaches a site-exit router, the site-exit
   router will rewrite the source field of the packet to a corresponding
   locator that selects a reverse path through the same transit ISP when
   the locator is used as a destination locator by the remote host. In
   order to preserve session integrity there is a need for a
   corresponding reverse transformation to be undertaken on incoming
   packets, where the destination locator has to be mapped back to the
   host's endpoint identifier. There are a number of considerations
   whether this is best performed at the site exit router on packet
   ingress to the site, or by the local host.

   Packet header rewriting by remote network elements has a large number
   of associated considerations, and documentation relating to the
   considerations of the use of Network Address Translators ([NAT
   Considerations] contains much of this material.

   An alternative for packet header rewriting on site exit is for the
   host to undertake the endpoint-to-locator mapping, using one of the
   approaches outlined above. The consideration here is that there is
   some significant deployment of unicast reverse path filtering in
   Internet environments as a counter-measure to source address
   spoofing. Using the example in Figure 1, if a host selects a locator
   drawn from the ISP B address prefix, and local routing directs that
   packet to site-exit router A, then if the packet is passed to ISP A,
   the this would be discarded by such filters. Various approaches have
   been proposed to modify the behavior of the site forwarding
   environment all with the end effect that packets using a source
   locator drawn from the ISP B address prefix are passed to site-exit
   router B. These approaches include forms of source address routing
   and site-exit router hand-over mechanisms, as well as augmentation of
   the routing information between site-exit routers and local
   multi-homed hosts, so that the choice of locator by the local host
   for the remote host is consistent with the current local routing
   state for the local site to reach the remote host.

Huston                  Expires October 31, 2004               [Page 12]

Internet-Draft            Multi6 Architectures                  May 2004

4.6 Approaches to Endpoint Identity

   Both of the above mechanisms assume some form of exchange of
   information that allows both parties to the communication to be aware
   of the remote endpoint identity and the associated mapping to
   locators. There are a number of choices in terms of the way in which
   this information exchange can be implemented.

   The first such possible approach is termed here a 'conventional'
   approach, where the mode of operation is in terms of encapsulating
   the protocol data unit (PDU) passed from the ULP with additional data
   elements that specifically refer to the function of the endpoint
   identity protocol stack element. The compound data element is passed
   to the LLP as its PDU. The corresponding actions on receipt of a PDU
   from a LLP is to extract the fields of the data unit that correspond
   to the EIP function, and pass the reminder of the PSU to the ULP. The
   EIP operates in an "in-band" mode, communicating with its remote peer
   entity through additional information wrapped around the ULP PDU.

   Another approach is to allow the EIP to communicate using a separate
   communications channel, where the EIP generates dedicated messages
   that are directed to its peer EIP, and passes these PDUs to the LLP
   independently of the PDUs that are passed top the EIP from the ULP.
   This allows the EIP to exchange information and synchronize state
   with the remote EIP semi-independently of the ULP protocol exchange.
   As a part of the EIP function is to transform the ULP PDU to include
   locator information there is an associated requirement to ensure that
   the EIP peering state remains synchronized to the exchange of ULP
   PDUs, so that the remote EIP can correctly recognize the locator to
   endpoint mapping for each active session.

   Another potential approach here is to allow the endpoint to locator
   mappings to be held at a third party point. This model is already
   used for supporting the name to IP address mappings performed by the
   Domain Name system, where the mapping is obtained by reference to a
   third party, namely a DNS resolver. A similar form of third party
   mapping between endpoints and a locator set could be supported
   through the use of the DNS, or a similar third party referential
   mechanism. Rather than have each party exchange endpoint to locator
   mappings, this approach would see this mapping being obtained as a
   result of a lookup for a DNS Endpoint to Locator set map contained as
   DNS Resource Records, for example.

4.7 Endpoint Identity Structure

   The previous section has used the term "endpoint identity" without
   examining what form this identity may take. There are a number of
   salient considerations regarding the structure and form of this

Huston                  Expires October 31, 2004               [Page 13]

Internet-Draft            Multi6 Architectures                  May 2004

   identity that should be enumerated within an architectural overview
   of this space.

   One possible form of an identity is the use of identity tokens lifted
   from the underlying protocol's "address space". In other words an
   endpoint identity is a special case instance of an IPv6 protocol
   address. There are a number of advantages in using this form of
   endpoint identity, observing that the suite of IP protocols and
   associated applications already manipulate IP addresses. The
   essential difference in a domain that distinguishes between endpoint
   identity and locator is that the endpoint identity parts of the
   protocol would operate on those addresses that assume the role of
   endpoint identities, and the EIP mapping function would undertake a
   mapping from an endpoint "address" to a set of potential locator
   "addresses", and also undertake a reverse mapping from a locator
   "address" to the distinguished endpoint identifier "address". The
   address space is hierarchically structured, permitting a suitably
   efficient mapping to be performed in both directions, and the
   underlying semantics of addresses in the context of public networking
   includes the necessary considerations of global uniqueness of
   endpoint identity token values.

   It is possible to take this approach further and allow the endpoint
   identifier to also be a valid locator. This would impliy the
   existence of a 'distinguished' or 'home' locator, and other locators
   could be dynamically mapped to this initial locator peering as
   required. The drawback of this approach is that the endpoint
   identifier is now based on one of the transit provider's address
   prefix, and a change of transit provider would necessarily require a
   change of endpoint identifier values within the multi-homed site. An
   alternative approach for address-formatted identifiers is to use
   address values which are not part of the global unicast locator
   space, allowing applications and protocol elements to distinguish
   between endpoint identity values and locators based on address prefix
   value. It is also possible to allow the endpoint identity and locator
   space to overlap, and distinguish between the two identity realms by
   the context of usage rather than by a prefix comparison.

   It is also feasible to use the fully qualified domain name (FQDN) as
   an endpoint identity, undertaking a similar mapping as described
   above, using the FQDN as the lookup "key". The implication here is
   that there is no default 'address' that is to be associated with the
   endpoint identifier.

   The syntactic properties of these two different identity realms have
   obvious considerations in terms of the manner in which these
   identities may be used within PDUs.

Huston                  Expires October 31, 2004               [Page 14]

Internet-Draft            Multi6 Architectures                  May 2004

   It is also an option to consider a new structured identity space
   which is not generated through the reuse of IPv6 address values nor
   drawn from the FQDN. Given that the address space would need to be
   structured in such a fashion that permits it to be used as a lookup
   key to obtain the corresponding locator set, the obvious question in
   such an option is what additional or altered characteristics would be
   used in such an endpoint identity space that would distinguish it
   from either of the above approaches?

   Instead of structured tokens that double as lookup keys to obtain
   mappings from endpoint identities to locator sets, the alternative is
   to use an unstructured token space, where individual token values are
   drawn opportunistically for use within a multi-homed session context.
   Here the semantics of the endpoint identity are subtly changed. The
   endpoint identity is not a persistent alias or reference to the
   identity of the endpoint, but a means to allow an EIP to confirm that
   two locators are part of the same mapped locator set for an endpoint.
   In this context the unstructured opportunistic endpoint identifier
   values are used in determining locator equivalence rather than in
   some form of lookup function.

5. Common Issues for Multi-Homing Approaches

   The above overview encompasses a very wide range of potential
   approaches to multi-homing, and each particular approach necessarily
   has an associated set of considerations regarding its applicability.

   There are, however, a set of considerations that appear to be common
   across all approaches, and they are examined in further detail in
   this section.

5.1 Triggering Locator Switches

   Ultimately, regardless of the method of generation, a packet
   generated from a local multi-homed host to a remote host must have a
   source locator in the IP packet that is passed into the transit
   network. In a multi-homed situation the local multi-homed host has a
   number of self-referential locators that are equivalent aliases in
   almost every respect. The difference between locators is the
   inference that at the remote end the choice of locator may determine
   the path used to send a packet back to the local multi-homed host.
   The issue here is how does the local host make a selection of the
   "best" source locator to use? Obviously the parameters of this
   selection include the objective to select a locator that represents a
   currently viable path from the remote host to the local multi-homed
   host. Local routing information for the multi-homed host does not
   include this reverse path information. Equally, the local host does
   not necessarily know of any additional policy constraints that apply

Huston                  Expires October 31, 2004               [Page 15]

Internet-Draft            Multi6 Architectures                  May 2004

   to the remote host that may result in a remote host's preference to
   use one locator over another for the local host. Considerations of
   unicast reverse path forwarding filters also indicate that the
   selection of a source locator should result in the packet being
   passed to a site-exit router that is connected to the associated ISP
   transit provider, and that the site-exit router passes the packet to
   the associated ISP.

   If the local multi-homed host is communicating with a remote
   multi-homed host, the local host may have some discretion in the
   choice of a destination locator. The considerations relating to the
   selection of a destination locator include considerations of local
   routing state (to ensure that the chosen destination locator reflects
   a viable path to the remote endpoint), policy constraints that may
   determine a "best" path to the remote endpoint. In such situations it
   may also be the case that the source address selection should also be
   considered in relation to the destination locator selection.

   Another common issue is the consideration of the point when a locator
   is not considered to be viable, and the consequences to the transport
   session state.
   o  Transport Layer Triggers

      A change in state for a currently used path to another path could
      be triggered by indications of packet loss along the current path,
      or by transport session timeouts, assuming an internal signalling
      mechanism between the transport stack element and the locator pool
      management stack element.
   o  Routing Triggers

      Alternatively, in the absense of local transport triggers, the
      site exit router could communicate failure of the outbound
      forwarding path in the case where the remote host is multi-homed
      with an associated locator set. Conventional routing would be
      incapable of detecting a failure in the inbound forwarding path,
      so there are some limitations in the approach of using routing
      triggers to change locator bindings.
   o  Heartbeat Triggers

      An alternative to these approaches is the use of a session
      heartbeat protocol, where failure of the heartbeat would cause the
      session to seek a new locator binding that would re-establish the

   The sensitivity of the locator-switch trigger is a consideration
   here. A very fine-grained sensitivity of the locator switch trigger
   may generate false triggers arising from short-term transient path
   congestion, while coarse-grained triggers may impose an undue

Huston                  Expires October 31, 2004               [Page 16]

Internet-Draft            Multi6 Architectures                  May 2004

   performance penalty on the session due to an extended time to detect
   a path failure.

5.2 Session Startup and Maintenance

   The next issue if that of the difference between the initial session
   startup mode of operation and the maintenance of the session state.

   In a split endpoint identifier / locator environment there needs to
   be at least one initial locator associated with an endpoint
   identifier in order to establish an initial connection between the
   two hosts. This locator could be loaded into the DNS in a
   conventional fashion, or, if the endpoint identifier is a
   distinguished address value, the initial communication could be
   established using the endpoint identifier in the role of a locator
   (i.e. using this as a conventional address).

   The initial actions in establishing a session would be simular. If
   the session is based on specification of a FQDN, the FQDN is first
   mapped to an endpoint identity value, and this endpoint identity
   value could then be mapped to a locator set. The locators in this set
   are then candidate locators for use in establishing an initial
   synchronized state between the two hosts. Once the state is
   established it is then possible to update the initial locator set
   with the current set of useable locators. This update could be part
   of the initial synchronization actions, or deferred until required.

   This leads to the concept of the use of a 'distinguished' locator
   that acts as the endpoint identifier, and a pool of alternative
   locators that are associated with this 'home' locator. This
   association may be statically defined, using referential pointers in
   a third party referral structure (such as the DNS), or dynmically
   added to the session through the actions of the endpoint identity
   protocol stack element, or both.

6. Security Considerations

   There are a significant number of security considerations that result
   from the action of distinguishing within the protocol suite endpoint
   identity and locator identity.

   It is not proposed to enumerate these considerations in detail within
   this draft, but to provide a distinct document that describes the
   security considerations of this domain. Subsequent revisions of this
   draft will refer the reader to this yet-to-be-drafted document.

Huston                  Expires October 31, 2004               [Page 17]

Internet-Draft            Multi6 Architectures                  May 2004

7. Acknowledgements

   The author acknowledges the exensive contribution of Margaret
   Wasserman in preparing the original draft of the summary of current
   approaches to multi-homing.

Normative References

Author's Address

   Geoff Huston

Appendix A. Notes on Various approaches

   These notes were orginally drafted by Margaret Wasserman. The notes
   on various approaches are non-exclusive, i.e. solutions not reviewed
   or mentioned here are not ruled out of discussion. Also the review
   comments are not comprehensive, and the selection reflects the time
   constraints of the contributors to this section than any qualititive
   judgement on any of the approaches. The author is desirous, in future
   revisions of this draft, in augmenting this selection of reviewed

A.1 Host Identity Protocol (HIP)

   HIP is an ID/Locator separation mechanism intended to solve a much
   wider problem space than site multi-homing. HIP uses cryptographic
   identifiers termed Host Identity Tags (HITs) at the application
   layer, which are mapped to locators (IP Addresses) by a HIP protocol
   stack layer that interfaces between the transport layer and IP
   internetwork layer.

   The essential characteristic of HIP is it use of opportunistic
   identity generation, as it uses a cyptographic host identifier as the
   basis of the persistent identity. The transport session cab be agile
   across locators, or even across IP protocol versions, as the HIT is
   used to determine session integrity. allowing the hosts to determine
   what packets legitimately form part of the session.

   HIP is proposed as a new protocol element, located at layer 3.5 (i.e.
   above the internetwork IP layer and below the transport layer). The
   presentation to the transport layer uses 128 bit hash values (the
   HIT) in place of IP addresses, while the presentation to the internet
   layer uses conventional IP addresses.

   Being opportunistic and unstructured, the HIT space is not an

Huston                  Expires October 31, 2004               [Page 18]

Internet-Draft            Multi6 Architectures                  May 2004

   efficient search space, nor can a HIT be used as a unique search key.
   HITs are part of an an equivalence function, to allow each host to
   determine that an incoming packet is part of an established session.
   HITs cannot be used as an identity value in a conventional referral
   sense (HostA wants to tell HostB to talk to HostC). While an
   application could pass a HIT to a third-party (and legacy
   applications would unknowingly do so), the third party would have no
   way to map that HIT to a locator (an IP address) as HIP does not
   include any global HIT->Locator mapping mechanism.

   o  New Protocol Stack Element
   o  Layer 3.5 (Above IP, below Transport
   o  Unstructured, opportunistic identity values (non-referential)
   o  DNS rendezvous
   o  No Locator exchange protocol

   Current IETF Documents:
   o  draft-moskowitz-hip-arch
   o  draft-moskowitz-hip
   o  draft-nikander-hip-mm
   o  draft-nikander-esp-beet-mode

A.2 Multihoming without IP Identifiers (NOID)

   NOID proposes an approach for endpoint identifier and locator
   separation where the endpoint identifier space is drawn from the
   locator space. Instead of creating a new namespace for endpoint
   identifiers, the endpoint identifier may be chosen from the set of
   locators that can be used to reach a given endpoint. Until an event
   occurs that modifies the list of usable locators, the initial
   endpoint identifier value can serve as a locator.

   NOID uses next-header values in the IPv6 header to indicate whether a
   given packet should be processed by the NOID layer. At a conceptual
   level, NOID adds a layer to the middle of IP above most IP
   processing, but below IPSec, fragmentation and reassembly functions.

   NOID makes use of the global DNS as a mapping system between IDs and
   Locators. A node who wishes to communicate with another node can use
   the FQDN to get a list of possible locators (IP Addresses). That node
   will then choose one of the locators to use as an Application-level
   ID (AID).

   NOID offers some support for application referrals. If Host A passes
   an AID to Host B that is supposed to point to Host C, Host B should
   be able to do a reverse DNS lookup to map the AID to an FQDN and then
   use the FQDN to get the complete set of locators. However, for this

Huston                  Expires October 31, 2004               [Page 19]

Internet-Draft            Multi6 Architectures                  May 2004

   to be effective, nodes would need to have both forward and reverse
   DNS entries. There might also be a need to dynamically update the DNS
   as a node becomes reachable or unreachable at certain locators.

   o  New Protocol Stack Element
   o  Layer 3 (Inserted in the upper part of IP, below IPSEC and
      fragementation / reassembly
   o  Identity values based on locator set
   o  DNS rendezvous
   o  Identity peering protocol

   Current IETF Documents:
   o  draft-nordmark-multi6-noid
   o  draft-templin-isnoid

A.3 Common Endpoint Locator Pools (CELP)

   CELP explores the concept of sharing information about locator
   reachability between transport-layer "multi-addressing" mechanisms
   (such as SCTP and DCCP) and Internet-layer multiaddressing
   mechanisms, referred to in the draft as "wedge-layer approaches"
   (such as NOID). (This concept was originally discussed on the MULTI6
   mailing list under the name 'SLAP'.)

   The motivation behind CELP is that muliple multiaddressing mechanisms
   may be used (by different applications or for different connections)
   on a single endpoint, and that it would beneficial for those
   mechanisms to share information about the reachability of the IP
   addresses in a given locator pool. If a transport-layer mechansim,
   such as SCTP, could share its knowledge regarding the reachability of
   a certain locator, it might be possible to minimize or elimate
   Internet-layer control packets that are used to maintain that
   information at the Internet layer. In some ways, this is similar to
   IPv6 Neighbor Discovery's use of upper layer advice regarding
   neighbor reachability to avoid sending unncecessary ND packets.

   This document offers a definition of the term "endpoint" that refers
   to a locator pool that may have a smaller scope than an entire IP
   node (i.e. a given locator pool may only contain a subset of the
   locators available on an IP node).

   The CELP document is more of a consideration of approach than an
   actual proposal for a solution. It doesn't specify in detail how it
   would work with any particular transport-layer or Internet-layer
   multiaddressing mechanisms. However, it is an approach that could be
   applied to many combinations of solutions.

Huston                  Expires October 31, 2004               [Page 20]

Internet-Draft            Multi6 Architectures                  May 2004

   o  Considerations relating to sharing locator reachability
      information across session instances.

   Current IETF Documents:
   o  draft-crocker-celp

A.4 Weak Identifier Multihoming Protocol (WIMP)

   WIMP is an endpoint identifier / locator separation protocol that is
   heavily focused on mitigating the threats outlined in work in
   progress on security threats in multi-homing scenarios
   [draft-nordmark-multi6-threats-00.txt]. The WIMP approach uses
   divided secrets and hash chaining to ensure that new locators are
   supplied by the same node that supplied the original locator.

   WIMP uses a separate name space for 128-bit non-routable IDs that are
   never used in packets on the network. These IDs are locally generated
   for both local and remote nodes by hashing a nonce (for the
   initiator's endpoint identity) or the FQDN (for the responder's
   endpoint identity). (The approach assumes a requirement that all
   responders will have a FQDN.)

   The WIMP protocol introduces a WIMP layer that maps between IDs and
   locators based on internal state. The WIMP layer is conceptually
   located within the network layer, above most IP processing and below
   IPsec, fragmentation/reassembly and destination options, similar to

   Communication between two end-points requires establishment of a WIMP
   session. Once the session is established, it can be used for multiple
   simultaneous or sequential connections to the same end-point. During
   WIMP session establishment, WIMP introduces a separate header into
   the data packets, between the IP and TCP/UDP headers that contains
   information about the WIMP session. The WIMP session establishment
   packets can optionally be piggy-backed on data packets. WIMP does not
   introduce a separate header into all IPv6 packets. Instead, once a
   WIMP session is established, the IPv6 FlowID is used to hold an
   identifier for the WIMP host-pair context associated with a given

   WIMP is intended to provide a solution to some of the security
   concerns, particularly regarding connection hijacking, that have been
   raised for some other endpoint identity / locator separation

   Reviewers of WIMP have raised some questions of this approach,
   particularly concerning the use of an optional header while operating

Huston                  Expires October 31, 2004               [Page 21]

Internet-Draft            Multi6 Architectures                  May 2004

   below IP fragmentation. The piggy-backing mechanism requires that the
   packets not be fragmented, but it doesn't explain how upper layers
   will become aware of the MTU limitations on those packets and/or how
   this mechanism would interact with Path MTU discovery. Like HIP, WIMP
   makes no provision to handle application-level referrals and does not
   contain a mechanism for global endpoint identifier to locator
   mapping. It has also been pointed out that it is interesting to
   consider whether the WIMP approach to security, hash chaining, could
   be applied to other endpoint identity / locator separations
   mechanisms, such as NOID.

   o  New Protocol Stack Element
   o  Layer 3 (Inserted in the upper part of IP, below IPSEC and
      fragementation / reassembly
   o  Identity values based on hash of FQDN
   o  Identity peering protocol

   Current IETF Documents:
   o  draft-ylitalo-multi6-wimp

A.5 Host-Centric IPv6 Multihoming

   Host-Centric Multihoming is, in some ways, the simplest way to
   address the IPv6 site multihoming problem. The concept is that every
   host in the multihomed site is configured with multiple prefixes that
   correspond to different service providers. Each host configures
   addresses within those prefixes and selects among those addresses
   when connecting to a remote host. This configuration is automated
   using Router Renumbering and IPv6 Address Autoconfiguration. However,
   this simple solution Layer 3 (inserted in the upper part of IP, below
   IPSEC and fragementation / reassembly has several practical
   limitations and drawbacks, and this draft attempt to address them.

   In particular, the Host-Centric Multihoming proposal attempts to
   address the "site exit issue". Hosts cannot control the exit path
   that their packets will take from the local site, so hosts with
   multiple addresses may use a source IP address from one ISP on
   packets that end-up being routed through a different ISP. In many
   cases, the ISPs will run ingress filtering and will discard those

   One solution to the site exit problem is to changes the ISP ingress
   filters to accept all of the source address prefixes that are used
   within the site. Other approaches are to perform source-based routing
   within the site, to deploy a single site-exit router or to structure
   the network so that all exit routers are connected to a single DMZ
   network that employs source-based routing. A virtual DMZ can be

Huston                  Expires October 31, 2004               [Page 22]

Internet-Draft            Multi6 Architectures                  May 2004

   constructed by configuring a mesh of tunnels between all exit
   routers, tunneling packets to the correct exit router based on source
   address. Each of these solutions has operational drawbacks and/or
   introduces inefficiencies.

   This proposal suggests another solution to the site exit problem
   called "source address discovery". Based on Path MTU discovery, this
   mechanism involves adding extra information to the ICMP Destination
   Unreachable message that the packet was discarded due to an ingress
   filter. This extra information indicates what address prefix should
   be used to pass the ingress filter. Rather than adding a field to the
   ICMP message, this extra information is communicated via the source
   address that the route Layer 3 (Inserted in the upper part of IP,
   below IPSEC and fragementation / reassembly).

   It also proposes a "superior" alternative called "exit router
   discovery", which allows hosts to specify which exit router will be
   used for each packet. Instead of sending ICMP error messages when
   ingress filtering causes packets to be discarded, the exit router
   will send the equivalent of a redirect message and future packets
   with the same source/destination address pair will be tunneled to the
   indicated exit router. This mechanism involves tunneling to a
   site-exit anycast address that is derived from the sites' prefixes.
   The draft primary focuses on the specification of this "superior"
   approach, largely ignoring some pertinent questions such as: Will
   residential and enterprise-level IPv6 routers reall support anycast

   One important thing to note about the host-centric multihoming
   solution is that it doesn't appear to provide any ability for
   transport connections to survive a change in the topology that causes
   a host to become unreachable at an address that is currently used as
   a connection end-point. It also does not offer any support for legacy
   applications that do application-level referrals, requiring that a
   full set of locators be exchanged as part of the referral.

A.6 Summaries of Selected ID/LOC Separation Documents

   This section summarizes a set of selected ID/Loc separation
   documents. The selection includes documents that appear to be active,
   and this section provides a very short summary of each one. The first
   sub-section lists documents that are new or updated since IETF 58 and
   the second sub-section lists older documents that remain active. The
   documents in each sub-section are listed alphabetically by draft

Huston                  Expires October 31, 2004               [Page 23]

Internet-Draft            Multi6 Architectures                  May 2004

A.6.1 New or Updated Documents Since IETF58

   o  TLC-FM: Transport Layer Common Framework for Multihoming
         This draft proposes a transport-layer mechanism for ID /Locator
         mapping. There is a conceptual layer within the transport layer
         that provides support for common multihoming functions. It is
         compatible with the use of Mobile IPv6 (MIP6) to provide
         mobility support.
         In TLC-FM, like SCTP, the ID consists of a collection of
         locators that may be used to reach a given host. It employs
         transport-level clues (such as TCP retransmissions) to decide
         when to switch locators. For UDP connections, ICMP error
         messages or application-level hints are necessary.
         This mechanism is not well enough specified to fully evaluate
         it, but it doesn't appear to offer any support for
         application-level referrals.

   o  Multi-Homing Tunnel Broker (MHTB)
         This document defines an enhancement to RFC 3178, IPv6
         Multihoming Support at Site Exit Routers, to reduce the
         administrative overhead of maintaining a configured tunnel for
         each multihoming association. However, this draft does not
         address another major drawback of the RFC 3178 approach, that
         it does not protect against the complete failure of one or more
         connected ISPs.

   o  Framework for Common Endpoint Locator Pools (CELP)
         Dave Crocker and Avri Doria's CELP draft, reviewed in the
         previous section.

   o  Multi-Homing: the SCTP Solution
         One confusing question about the direction of this work is why
         SCTP is being discussed as a "solution" to site multihoming,
         when a clear requirement for a site multihoming solutions is
         the ability to support existing TCP-based and UDP-based
         applications. This document isn't really a proposal, though --
         it consists of answers to the questions posted in Eliot Lear's
         "Things MULTI6 Developers Should Think About" draft, and does
         not discuss how SCTP does (or doesn't) address the requirements
         outlined in the Multi6 requirements RFC.
         An interesting thing about this proposal is that it claims that
         SCTP is not an ID/Loc separation mechanism, however in some
         academic sense it actually is. The ID is the group of available
         IP addresses, and the locator is whichever address is currently

Huston                  Expires October 31, 2004               [Page 24]

Internet-Draft            Multi6 Architectures                  May 2004

         being used for communication. SCTP also experiences the same
         complexities as other proposals (AKA NOID, CELP) that use a
         pool of locators as the ID -- How do you choose which locator
         to use? And how do you detect when a member of the pool becomes
         invalid for use as a locator? So, while it isn't actually a
         solution for site multihoming, SCTP may provide some useful
         experiences and mechanisms that may apply to a class of
         possible solutions.

   o  Host Identity Protocol (HIP) Rendezvous Mechanisms
         This is an overview draft that discusses the concept of HIP
         rendezvous mechanisms to improve the applicability of HIP for
         mobility and multihoming. This is a survey document that
         outlines the problem and discusses different type of solutions
         to the problem.

   o  Host-Centric IPv6 Multihoming
         Draft by Christian Huitema and others, described above.

   o  Things MULTI6 Developers Should Think About
         Eliot Lear's efforts to collect a set of practical questions
         that should be considered for all MULTI6 protocols.

   o  Host Identity Protocol (HIP)
         This is the base protocol specification for HIP. Along with the
         HIP architecture, these documents form the basis of the HIP

   o  Consideration on HIP Based IPv6 Multi-Homing
         Pekka Nikander's document that submits HIP as a solution for
         the MULTI6 problem space.

   o  8+8 Addressing for IPv6 End to End Multihoming

   o  Threats Relating to Transport Layer Protocols Handling Multiple

   o  Multihoming Using IPv6 Addressing Derived from AS Numbers
         This draft provides a mechanism for organizations that have
         been assigned a 16-bit AS number to use that number to

Huston                  Expires October 31, 2004               [Page 25]

Internet-Draft            Multi6 Architectures                  May 2004

         auto-generate a globally routable, provider-independent address

   o  Problem Statement: HIP Operation over Network Address Translators
         Summarizes the problems with running HIP and IPsec-based data
         transmission across NATs.

   o  Operational Approach to Achieve IPv6 Multihomed Network
         This document proposes to support site multihoming in IPv6 by
         assigning additional /32 prefixes and AS numbers to "groups" of
         providers who will provide multihomed /48 prefixes to their
         mutual customers.
         It is currently unclear to the reviewer how/if this proposal
         would work and/or scale since it seems to involve two different
         providers advertising the same /32 and the same AS number into
         the default free zone. It requires some type of peering "to
         share prefix assignments" between ISPs, and the diagram shows
         some type of connection between the ISPs, but I don't know what
         the details of that connection are.
         It also has the potential to more quickly exhaust the AS number
         space and to result in a substantially larger number of routes
         in default free routers, since the number of "groups" could
         scale exponentially with the number of providers.

   o  Crypto Based Host Identifiers (CBHI)
         This draft defines a crytographic mechanism for generating host
         identifiers. It is intended for use with other protocols that
         require host identifiers, such as ODT (see below).

   o  On Demand Tunneling for Multihoming (ODT)
         This draft discusses an automatic tunnelling-based solution for

   o  Weak Identifier Multihoming Protocol (WIMP)
         WIMP proposal, described above.

A.6.2 Older Documents that Remain Active/Interesting

   o  RFC 3582: Goals for IPv6 Site-Multihoming Architectures

   o  Choices for Multiaddressing

Huston                  Expires October 31, 2004               [Page 26]

Internet-Draft            Multi6 Architectures                  May 2004

   o  What's In a Name: Thoughts from the NSRG

   o  A Roadmap for Multihoming in IPv6

   o  Host Identity Protocol (HIP) Architecture

   o  End-Host Mobility and Multi-Homing with Host Identity Protocol

   o  Threats Relating to IPv6 Multihoming Solutions

   o  Multihoming without IP Identifiers (NOID)
         Erik Nordmark's NOID specification, described above.

A.6.3 Related Multi-Homing drafts, Status unknown

   This is a list of ID/Loc separation and/or MULTI6 documents, listed
   alphabetically by draft name.
   o  Extension Header for Site-Multi-homing Support

   o  Application of the MIPv6 Protocol to the Multi-Homing Problem

   o  Multiple Address Service for Transport (MAST): An Extended

   o  NAROS : Host-Centric IPv6 Multihoming with Traffic Engineering

   o  Application and Use of the IPv6 Provider Independent Global
      Unicast Format

   o  Simple Dual Homing Experiment

   o  Host-Centric IPv6 Multihoming

Huston                  Expires October 31, 2004               [Page 27]

Internet-Draft            Multi6 Architectures                  May 2004

   o  IPv4 Multihoming
         This documents how multi-homing is supported at present in the
         IPv4 protocol domain.

   o  Multihoming in IPv6 by Multiple Announcement of Longer Prefixes

   o  Multihoming using 64-bit Crypto-based IDs

   o  Strong Identity Multihoming using 128-bit Identifiers (SIM/

   o  IPv6 Address Assignment and Route Selection for End-to-End

   o  Hierarchical IPv6 Subnet ID Autoconfiguration for Multi-Address
      Model Multi-Link Multihoming Site

   o  Hierarchical IPv6 Subnet ID Autoconfiguration for Multi-Address
      Model Multi-Link Multihoming Site

   o  The Architecture of End to End Multihoming

   o  8+8 Addressing for IPv6 End to End Multihoming

   o  Threats Relating to Transport Layer Protocols Handling Multiple

   o  Multihomed ISPs and Policy Control

   o  GAPI: A Geographically Aggregatable Provider Independent Address
      Space to Support Multihoming in IPv6

   o  Multi Homing Translation Protocol (MHTP

Huston                  Expires October 31, 2004               [Page 28]

Internet-Draft            Multi6 Architectures                  May 2004

   o  Multihoming Using IPv6 Addressing Derived from AS Numbers

   o  IPv6 Site Multihoming: Now What?

   o  Operation of NOID Multihoming Protocol on ISATAP Nodes

   o  LIN6: A Solution to Multihoming and Mobility in IPv6

   o  Operational Approach to achieve IPv6 multihomed network

   o  Two Prefixes in One Address

   o  Crypto Based Host Identifiers

   o  Provider-Internal Aggregation based on Geography to Support
      Multihoming in IPv6

   o  On Demand Tunneling For Multihoming

Huston                  Expires October 31, 2004               [Page 29]

Internet-Draft            Multi6 Architectures                  May 2004

Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive

Full Copyright Statement

   Copyright (C) The Internet Society (2004). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an

Huston                  Expires October 31, 2004               [Page 30]

Internet-Draft            Multi6 Architectures                  May 2004



   Funding for the RFC Editor function is currently provided by the
   Internet Society.

Huston                  Expires October 31, 2004               [Page 31]