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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 5648

MEXT Working Group                                     R. Wakikawa (Ed.)
Internet-Draft                                           Keio University
Intended status: Standards Track                                T. Ernst
Expires: August 27, 2008                                           INRIA
                                                               K. Nagami
                                                           INTEC NetCore
                                                    V. Devarapalli (Ed.)
                                                         Azaire Networks
                                                       February 24, 2008


                Multiple Care-of Addresses Registration
                 draft-ietf-monami6-multiplecoa-06.txt

Status of this Memo

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   This Internet-Draft will expire on August 27, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).









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Abstract

   According to the current Mobile IPv6 specification, a mobile node may
   have several care-of addresses, but only one, called the primary
   care-of address, that can be registered with its home agent and the
   correspondent nodes.  However, for matters of cost, bandwidth, delay,
   etc, it is useful for the mobile node to get Internet access through
   multiple accesses simultaneously, in which case the mobile node would
   be configured with multiple active IPv6 care-of addresses.  This
   document proposes extensions to the Mobile IPv6 protocol to register
   and use multiple care-of addresses.  The extensions proposed in this
   document can be used by Mobile Routers using the NEMO (Network
   Mobility) Basic Support protocol as well.






































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6

   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  7

   4.  Mobile IPv6 Extensions . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Binding Cache Structure and Binding Update List  . . . . .  9
     4.2.  Binding Identifier Mobility Option . . . . . . . . . . . .  9
     4.3.  New Status Values for Binding Acknowledgement  . . . . . . 11

   5.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 13
     5.1.  Management of Care-of Address(es) and Binding
           Identifier(s)  . . . . . . . . . . . . . . . . . . . . . . 13
     5.2.  Return Routability: Sending CoTI and Receiving CoT . . . . 13
     5.3.  Binding Registration . . . . . . . . . . . . . . . . . . . 14
     5.4.  Bulk Registration  . . . . . . . . . . . . . . . . . . . . 14
     5.5.  Binding De-Registration  . . . . . . . . . . . . . . . . . 15
     5.6.  Returning Home . . . . . . . . . . . . . . . . . . . . . . 16
       5.6.1.  Using only Interface attached to the Home Link . . . . 16
       5.6.2.  Using only Interface attached to the Visited Link  . . 16
       5.6.3.  Simultaneous Home and Visited Link Operation . . . . . 17
     5.7.  Receiving Binding Acknowledgement  . . . . . . . . . . . . 19
     5.8.  Receiving Binding Refresh Request  . . . . . . . . . . . . 20
     5.9.  Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 20

   6.  Home Agent and Correspondent Node Operation  . . . . . . . . . 21
     6.1.  Searching Binding Cache with Binding Identifier  . . . . . 21
     6.2.  Receiving CoTI and Sending CoT . . . . . . . . . . . . . . 21
     6.3.  Processing Binding Update  . . . . . . . . . . . . . . . . 22
     6.4.  Sending Binding Refresh Request  . . . . . . . . . . . . . 24
     6.5.  Receiving Packets from Mobile Node . . . . . . . . . . . . 24

   7.  Network Mobility Applicability . . . . . . . . . . . . . . . . 25

   8.  DSMIPv6 Applicability  . . . . . . . . . . . . . . . . . . . . 26
     8.1.  IPv4 Care-of Address Registration  . . . . . . . . . . . . 26
     8.2.  IPv4 HoA Management  . . . . . . . . . . . . . . . . . . . 27

   9.  IPsec and IKEv2 interaction  . . . . . . . . . . . . . . . . . 28
     9.1.  Use of Care-of Address in the IKEv2 exchange . . . . . . . 28
     9.2.  Transport Mode IPsec protected messages  . . . . . . . . . 29
     9.3.  Tunnel Mode IPsec protected messages . . . . . . . . . . . 29
       9.3.1.  Tunneled HoTi and HoT messages . . . . . . . . . . . . 29
       9.3.2.  Tunneled Payload Traffic . . . . . . . . . . . . . . . 30




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   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 31

   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 33

   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34

   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 34
     13.2. Informative References . . . . . . . . . . . . . . . . . . 34

   Appendix A.  Example Configurations  . . . . . . . . . . . . . . . 36

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40
   Intellectual Property and Copyright Statements . . . . . . . . . . 42





































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1.  Introduction

   A mobile node may use various types of network interfaces to obtain
   durable and wide area network connectivity.  This is increasingly
   become true with mobile nodes having multiple interfaces such as
   802.2, 802.11, 802.16, cellular radios, etc..  The motivations for
   and benefits of using multiple points of attachment are discussed in
   [ID-MOTIVATION].  When a mobile node with multiple interfaces uses
   Mobile IPv6 [RFC-3775] for mobility management, it cannot use its
   multiple interfaces to send and receive packets while taking
   advantage of session continuity provided by Mobile IPv6.  This is
   because Mobile IPv6 allows the mobile node to only bind one care-of
   address at a time with its home address.

   This document proposes extensions to Mobile IPv6 to allow a mobile
   node to register multiple care-of addresses for a home address and
   create multiple binding cache entries.  A new Binding Identification
   (BID) number is created for each binding the mobile node wants to
   create and sent in the binding update.  The home agent that receives
   this Binding Update creates separate binding for each BID.  The BID
   information is stored in the corresponding binding cache entry.  The
   BID information can now be used to identify individual bindings.  The
   same extensions can also be used in Binding Updates sent to the
   correspondent nodes.



























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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC-2119].

   Terms used in this draft are defined in [RFC-3775], [RFC-3753] and
   [RFC-4885].  In addition or in replacement of these, the following
   terms are defined or redefined:

   Binding Identification number (BID)

      The BID is an identification number used to distinguish multiple
      bindings registered by the mobile node.  Assignment of distinct
      BIDs allows a mobile node to register multiple binding cache
      entries for a given home address.  The BID MUST be unique for a
      binding to a specific care-of address for a given home address and
      care-of address pair.  Zero and negative values MUST NOT be used.
      Each BID is generated and managed by a mobile node.  The BID is
      stored in the Binding Update List and is sent by the mobile node
      in the Binding Update.  A mobile node MAY change the value of a
      BID at any time according to its administrative policy, for
      instance to protect its privacy.  An implementation must carefully
      assign the BID so as to keep using the same BID for the same
      binding even when the status of the binding is changed.  More
      details can be found in Section 5.1.

   Binding Identifier Mobility Option

      The Binding Identifier mobility option is used to carry the BID
      information.

   Bulk Registration

      A mobile node can register multiple bindings at once by sending a
      single Binding Update.  A mobile node can also replace some or all
      the bindings available at the home agent with the new bindings by
      using the bulk registration.  Bulk registration is supported only
      with the home agent as explained in Section 5.5.  A mobile node
      MUST NOT perform bulk registration with a correspondent node.











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3.  Protocol Overview

   A new extension called the Binding identification number (BID) is
   introduced to distinguish between multiple bindings pertaining to the
   same home address.  If a mobile node configures several IPv6 global
   addresses on one or more of its interfaces, it can register these
   addresses with its home agent as care-of addresses.  If the mobile
   node wants to register multiple bindings, it MUST generate a BID for
   each care-of address and store the BID in the binding update list.  A
   mobile node can manipulate each binding independently by using the
   BIDs.  The mobile node then registers its care-of addresses by
   sending a Binding Update with a Binding Identifier mobility option.
   The BID is included in the Binding Identifier mobility option.  After
   receiving the Binding Update with a Binding Identifier mobility
   option, the home agent MUST copy the BID from the Binding Identifier
   mobility option to the corresponding field in the binding cache
   entry.  If there is an existing binding cache entry for the mobile
   node, and if the BID in the Binding Update does not match the one
   with the existing entry, the home agent MUST create a new binding
   cache entry for the new care-of address and BID.  The mobile node can
   register multiple care-of addresses either independently in
   individual Binding Updates or multiple at once in a single Binding
   Update.

   If the mobile host wishes to register its binding with a
   correspondent node, it must perform return routability operations.
   This includes managing a Care-of Keygen token per care-of address and
   exchanging CoTi and CoT message with the correspondent node for each
   care-of address.  The mobile node MAY use the same BID that it used
   with the home agent for a particular care-of address.  For protocol
   simplicity, bulk registration to correspondent nodes is not supported
   in this document.  This is because the Return Routability mechanism
   introduced in [RFC-3775] cannot be easily extended to verify multiple
   care-of addresses stored in a single Binding Update.

   If the mobile node decides to act as a regular mobile node compliant
   with [RFC-3775], it sends a Binding Update without any Binding
   Identifier mobility options.  The receiver of the Binding Update
   deletes all the bindings registering with a BID and registers only a
   single binding for the mobile node.  Note that the mobile node can
   continue using the BID even if it has only a single binding that is
   active.

   Binding cache lookup is done based on the home address and BID
   information.  This is different from RFC 3775, where only the home
   address is used for binding cache lookup.  The binding cache lookup
   may also involve policy or flow filters in cases where some policy or
   flow filters are used to direct certain packets or flows to a



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   particular care-of address.  The binding cache lookup using policy or
   flow filters is out of scope for this document.  In case the binding
   cache lookup, using the combination of home address and BID, does not
   return a valid binding cache entry, the home agent MAY perform
   another lookup based on only the home address.  This is
   implementation dependent and configurable on the home agent.

   The mobile node may return to the home link through one of its
   interfaces.  There are three options possible for the mobile node
   when its returns home.

   1.  The mobile node uses only the interface with which it attaches to
       the home link.  It de-registers all bindings related to all
       care-of addresses.  The interfaces still attached to the visited
       link(s) are no longer going to be receiving any encapsulated
       traffic from the home agent.

   2.  The mobile node uses only the interfaces still attached to the
       visited link(s).  The interface with which the mobile node
       attaches to the home link is not used.

   3.  The mobile node may simultaneously use both the interface
       attached to the home link and the interfaces still attached to
       the visited link(s).

   Section 5.6 describes the returning home procedures in more detail.

























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4.  Mobile IPv6 Extensions

   This section summarizes the extensions to Mobile IPv6 necessary for
   manage multiple bindings.

4.1.  Binding Cache Structure and Binding Update List

   The BID is required to be stored in the binding cache and binding
   update list structure.

4.2.  Binding Identifier Mobility Option

   The Binding Identifier mobility option is included in the Binding
   Update, Binding Acknowledgement, Binding Refresh Request, and Care-of
   Test Init and Care-of Test message.

                      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 = TBD  |     Length    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       Binding ID (BID)        |     Status    |C|O|H|D|Resrvd |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
       +                                                               +
       :                 IPv4 or IPv6 care-of address (CoA)            :
       +                                                               +
       +---------------------------------------------------------------+

                       Figure 1: BID Mobility Option

   Type

      Type value for Binding Identifier is TBD

   Length

      8-bit unsigned integer.  Length of the option, in octets,
      excluding the Type and Length fields.  MUST be set to 4 when the
      'C' flag is unset.  Otherwise, the Length value MUST be set to
      either 8 or 20 depending on the 'D' (DSMIPv6) flag.

   Binding ID (BID)

      The BID which is assigned to the binding indicated by the care-of
      address in the Binding Update or the BID mobility option.  The BID
      is a 16-bit unsigned integer.  The value of zero is reserved and
      MUST NOT be used.




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   Status

      When the Binding Identifier mobility option is included in a
      Binding Acknowledgement, this field overwrites the status field in
      the Binding Acknowledgement.  If this field is zero, the receiver
      MUST use the registration status stored in the Binding
      Acknowledgement message.  This Status field is also used to carry
      error information related to the care-of address test in the
      Care-of Test message.  The status is 8-bit unsigned integer.  The
      possible status codes are the same as the status codes of Binding
      Acknowledgement.

   Care-of address (C) flag

      When this flag is set, it indicates that a valid care-of address
      is present in the care-of address field in the BID mobility
      option.  This flag MUST be set whenever the mobile node sends
      multiple care-of addresses in a single Binding Update, i.e., bulk
      registration.  It MAY also used as a substitute for alternate
      care-of address option even for Binding Updates that are sent only
      for one care-of address.  This flag is valid only for Binding
      Update sent to the home agent.

   Overwrite (O) flag

      When this flag is set, a mobile node requests the recipient to
      replace all the bindings to binding entries stored in a Binding
      Update.

   Simultaneous Home and Foreign Binding (H) flag

      This flag indicates that the mobile node registers multiple
      bindings to the home agent while is attached to the home link.
      This flag is valid only for a Binding Update sent to the home
      agent.

   DSMIPv6 (D) flag

      This flag indicates that the care-of address is an IPv4 address.
      When this flag is set, the care-of address field MUST contain an
      IPv4 address.

   Reserved

      5 bits Reserved field.  The reserved field MUST be zero.






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   Care-of Address

      This field has the variable length depending on the specified
      flags.  When the 'C' flag is set and the 'D' flag is not, an IPv6
      care-of address for the corresponding BID is stored in this field.
      If both 'C' and 'D' flags are set, an IPv4 Care-of Address is
      carried in this field.  This field MUST NOT be used if a Binding
      Identifier mobility option is included in any other message other
      than a Binding Update or if the 'C' flag is not set.

4.3.  New Status Values for Binding Acknowledgement

   New status values for the status field in a Binding Acknowledgement
   are defined for handling the multiple Care-of Addresses registration:

   MCOA NOTCOMPLETE (TBD < 128)

      In bulk registration, not all the binding identifier mobility
      option are successfully registered.  Some of them are rejected.
      The error status value of the failed mobility option is
      individually stored in the status field of the binding identifier
      mobility option.

   MCOA RETURNHOME WO/NDP (TBD < 128)

      When a mobile node returns home, it MUST NOT use NDP for the home
      address on the home link.  This is explained in more detail in
      Section 5.6

   MCOA MALFORMED (TBD more than 128)

      Registration failed because Binding Identifier mobility option was
      not formatted correctly.

   MCOA BID CONFLICT (TBD more than 128)

      The home agent cannot cache both a regular binding and a BID
      extended binding simultaneously.  It returns this status value
      when the received binding conflicts with the existing binding
      cache entry(ies).

   MCOA PROHIBITED(TBD more than 128)

      It implies the multiple care-of address registration is
      administratively prohibited.






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   MCOA BULK REGISTRATION NOT SUPPORTED (TBD more than 128)

      Bulk binding registration is not supported.
















































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5.  Mobile Node Operation

5.1.  Management of Care-of Address(es) and Binding Identifier(s)

   There are two cases when a mobile node might acquire several care-of
   addresses.  Note that a mixture of the two cases is also possible.

   1.  A mobile node may be using several physical network interfaces
       and acquires a care-of address on each of its interfaces.

   2.  A mobile node uses a single physical network interface, but
       receives advertisements for multiple prefixes on the link the
       interface is attached to.  This will result in the mobile node
       configuring several global addresses on the interface from each
       of the announced prefixes.

   The difference between the above two cases is only in the number of
   physical network interfaces and therefore irrelevant in this
   document.  What is of significance is the fact that the mobile node
   has several addresses it can use as care-of addresses.

   A mobile node assigns a BID to each care-of address when it wants to
   register them simultaneously with its home address.  The BID MUST be
   unique for a given home address and care-of address pair.  The value
   should be an integer between 1 and 65535.  Zero and negative values
   MUST NOT be used as BIDs.  If a mobile node has only one care-of
   address, the assignment of a BID is not needed until it has multiple
   care-of addresses to register with, at which time all of the care-of
   addresses MUST be mapped to BIDs.

5.2.  Return Routability: Sending CoTI and Receiving CoT

   When a mobile node wants to register multiple care-of address with a
   correspondent node, it MUST have the valid Care-of Keygen token per
   care-of address.  The mobile node needs only one Home Keygen token
   for its home address.

   The mobile node MUST include a Binding Identifier mobility option in
   the Care-of Test Init message.  It MUST NOT set any flags in the
   mobility option.  The receiver (i.e. correspondent node) will
   calculate a care-of Keygen token as specified in [RFC-3775] and reply
   with a Care-of Test message, with the Binding Identifier mobility
   option as described in Section 6.2.  When the mobile node receives
   the Care-of Test message, the message is verified as in [RFC-3775].
   If a Binding Identifier mobility option is not present in the CoT
   message in reply to the CoTI message that included a Binding
   Identifier mobility option, the mobile node must assume that the
   correspondent node does not support Multiple Care-of Address



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   registration.  Thus, the mobile node MUST NOT use a Binding
   Identifier mobility option in any future Binding Updates to that
   correspondent node.  The mobile node MAY skip re-sending regular CoTI
   message and keep the received care-of Keygen token for the regular
   Binding Update.

5.3.  Binding Registration

   For the multiple Care-of Addresses registration, the mobile node MUST
   include a Binding Identifier mobility option(s) in the Binding Update
   as shown in Figure 2.  The BID is copied from a corresponding Binding
   Update List entry to the BID field of the Binding Identifier mobility
   option.  When IPsec ESP is used for protecting the Binding Update,
   the care-of address can be carried in the Care-of Address field of
   the Binding Identifier mobility option.  If this is done, the
   alternate care-of address option MUST NOT be included in the Binding
   Update.  For binding registration to a correspondent node, the mobile
   node MUST have both active Home and Care-of Keygen tokens for Kbm
   (see Section 5.2.5 of [RFC-3775]) before sending the Binding Update.
   The care-of Keygen tokens MUST be maintained for each care-of address
   that the mobile node wants to register to the correspondent node.
   The Binding Update to the correspondent node is protected by the
   Binding Authorization Data mobility option that is placed after the
   Binding Identifier mobility option.

               IPv6 header (src=CoA, dst=HA)
                    IPv6 Home Address Option
                    ESP Header  (for home registration)
                    Mobility header
                        -BU
                       Mobility Options
                          - Binding Identifier mobility option
                          - Binding Authorization mobility option
                            (for Route Optimization)

             Figure 2: Binding Update for Binding Registration

5.4.  Bulk Registration

   Bulk registration is an optimization for binding multiple care-of
   addresses to a home address using a single Binding Update.  This is
   very useful if the mobile node, for instance, does not want to send a
   lot of signaling messages through an interface where the bandwidth is
   scarce.

   To use bulk registration, the mobile node includes a Binding
   Identifier Mobility option for each BID and Care-of address pair it
   wants to register in the same Binding Update message.  This is shown



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   in Figure 3.  The rest of the fields and options in the Binding
   Update such as Lifetime, Sequence Number, the flags in the Binding
   Update are common across all care-of addresses.  The alternate
   care-of address option MUST NOT be used.

   In the bulk registration, the Sequence Number field of a Binding
   Update SHOULD be carefully configured.  This is because all the bulk-
   registered bindings use the same Sequence Number specified in the
   Binding Update.  If each binding uses different sequence number, a
   mobile node MUST use the largest sequence number from the Binding
   Update list entries used for the bulk registration.  If the mobile
   node cannot select a sequence number for all the bindings due to
   sequence number out of window, it MUST NOT use the bulk registration
   for the binding whose sequence number is out of window.  A separate
   Binding Update should be sent for the binding.

               IPv6 header (src=CoA, dst=HA)
                    IPv6 Home Address Option
                    ESP Header
                    Mobility header
                        -BU
                       Mobility Options
                          - Binding Identifier mobility options
                            (C flag is set, O flag is optional,
                             BID and CoA are stored)

              Figure 3: Binding Update for Bulk Registration

   If the mobile node wants to replace existing registered bindings on
   the home agent with the bindings in the sent Binding Update, it sets
   the 'O' flag.  Section 6.3 describes this registration procedure in
   detail.

5.5.  Binding De-Registration

   When a mobile node decides to delete all the bindings for its home
   address, it sends a regular de-registration Binding Update with
   lifetime set to zero as defined in [RFC-3775].  The Binding
   Identifier mobility option is not required.

   If a mobile node wants to delete a particular binding(s) from its
   home agent and correspondent nodes, the mobile node sends a Binding
   Update with lifetime set to zero and includes a Binding Identifier
   mobility option(s) with the BID(s) it wants to de-register.  The
   receiver will remove only the care-of address(es) that match(es) the
   specified BID(s).  The care-of addresses field in each mobility
   option SHOULD be omitted by the sender and MUST be ignored by the
   receiver.  This is because the receiver will remove the binding that



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   matches the specified BID.

5.6.  Returning Home

   The mobile node may return to the home link, by attaching to the home
   link through one of its interfaces.  When the mobile node wants to
   return home, it should be configured with information on what
   interface it needs to use.  The mobile node may use only the
   interface with which it is attached to the home link, only the
   interfaces still attached to the visited link or use both interfaces
   attached to the home link and visited link simultaneously.  The
   following describes each option in more detail.

5.6.1.  Using only Interface attached to the Home Link

   The mobile node returns home and de-registers all the bindings as
   shown in Figure 8 and as defined in [RFC-3775].  De-registering all
   the bindings is the same as binding de-registration from foreign link
   described in Section 5.5.  After the de-registration step, all the
   packets routed by the home agent are only forwarded to the interface
   attached to the home link, even if there are other active interfaces
   attached to the visited link.  While the mobile node de-registers all
   the bindings from the home agent, it may continue registering
   bindings for interface attached to visited link to the correspondent
   node as shown in Figure 8.

5.6.2.  Using only Interface attached to the Visited Link

   The mobile node returns home and shuts down the interface attached to
   the home link as shown in Figure 9.  Before shutting down the
   interface, any binding for the care-of address previously associated
   with the interface should be deleted.  To delete the binding cache
   entry, the mobile node SHOULD send a de-registration Binding Update
   with the lifetime set to zero and include the corresponding BID
   information.  If the mobile node does not send a de-registration
   Binding Update, the binding for the care-of address previously
   assigned to the interface remains at the home agent.  This binding is
   deleted only when it expires.  In order to avoid this, the mobile
   node SHOULD send a de-registration binding update for the interface
   attached to the home link.

   This scenario is not the most efficient because all the traffic to
   and from the mobile node is going through the bi-directional tunnel,
   whereas the mobile node is now accessible at one hop on the home link
   from its home agent.






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5.6.3.  Simultaneous Home and Visited Link Operation

   In this case, the mobile node returns home and continues using all
   the interfaces attached to both foreign and home links as shown in
   Figure 10.  The mobile node indicates this by setting the 'H' flag in
   the BID mobility option as defined below.  There are additional
   requirements on the Returning Home procedures for possible ND
   conflicts at the home link described below.

   In [RFC-3775], the home agent intercepts packets meant for the mobile
   node using proxy Neighbor Discovery while the mobile node is away
   from the home link.  When the mobile node returns home, the home
   agent deletes the binding cache and stops proxying for the home
   address so that a mobile node can configure its home address on the
   interface attached to the home link.  In this specification, a mobile
   node may return home, configure the home address on the interface
   attached to the home link, but still use the interfaces attached to
   the foreign links.  In this case, a possible conflict arises when the
   both the home agent and the mobile node try to defend the home
   address.  If the home agent stops proxying for the home address, the
   packets are always routed to the interface attached to the home link
   and are never routed to the interfaces attached to the visited links.
   It is required to avoid the conflict between the home agent and the
   mobile node, while still allowing the simultaneous use of home and
   foreign links.  The following describes the mechanism for achieving
   this.

   In this specification, the home agent MUST intercept all the packets
   meant for the mobile node and decide whether to send the traffic
   directly to the home address on the link or tunnel to the care-of
   address.  The home agent intercepts all the packets even when the
   mobile node is attached to the home link through one of its
   interfaces.  The home agent would make this decision based on the
   type of packets and flows.  How to make this decision is out of scope
   in this document.  The critical part would be to create a neighbor
   cache entry for the mobile node so that the home agent can deliver
   the packets on-link.  The home agent would need to know the Layer-2
   address of the interface with which the mobile node is attached to
   the home link.  In order to create the neighbor cache entry for the
   mobile node, following operations are required.

   The mobile node sends a de-registration Binding Update to the home
   agent from the interface attached to the home link.  In the Binding
   Update, the BID mobility option must include the BID the mobile node
   had previously associated with the interface attached to the home
   link.  The 'H' flag MUST be set in the BID mobility option.  The 'C'
   flag MUST NOT be set and the care-of address field MUST NOT be
   included.  When the 'H' flag is set, the home agent recognizes that



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   the mobile node wants to continue using interfaces attached to both
   home and visited links.  If the 'H' flag is unset, the home agent
   deletes either all the bindings or the binding corresponding to the
   BID included in the Binding Identifier mobility option.

   When the home agent sends the Binding Acknowledgement, it MUST set
   the status value to either 0 [Binding Update Accepted] or to
   [MCOARETURNHOME WO/NDP (TBD)] in the BID mobility option depending on
   home agent configuration at the home link.  The new values are:

   o  Binding Update Accepted (0): NDP is permitted for the home address
      at the home link.  This is regular returning home operation of
      [RFC-3775]

   o  MCOA RETURNHOME WO/NDP (TBD): NDP is prohibited for the home
      address at the home link

   When the home agent is the only router at the home link, it can
   intercept all the packets by normal IP routing without using proxying
   for the home address.  It stops proxy ND for the requested home
   address and responds with the [Binding Update Accepted] status value
   to the mobile node.  The neighbor cache entry for the mobile node is
   created by the regular exchange of Neighbor Solicitation and Neighbor
   Advertisement.  If the home agent is not the only router on the home
   link, it MUST continue defending the home address by proxy neighbor
   discovery in order to intercept the mobile node's traffic.  The home
   agent, then, returns [MCOA RETURNHOME WO/NDP] value in the Status
   field of the BID mobility option.  The home agent also learns the
   mobile node's layer-2 address (i.e., MAC address) during this binding
   de-registration.  It stores the learnt layer-2 address in a neighbor
   cache entry for the mobile node so that it can construct the layer-2
   header for the packets meant for the mobile node and forwards them
   directly to the mobile node's interface attached to the home link.

   According to [RFC-3775], the mobile node MUST NOT assign the home
   address to the interface attached to the home link and MUST NOT
   attempt NDP operations for the home address before the completion of
   binding de-registration.  It MUST NOT send and reply to Neighbor
   Solicitation for the home address.  The home address MUST be
   tentative address at this moment until it receives Binding
   Acknowledgement with success status value.

   When the mobile node receives the Binding Acknowledgement and BID
   mobility option, it assigns home address to the interface attached to
   the home link according to the status field of the BID.  If the value
   is [Binding Update Accepted], the mobile node can start defending the
   home address using regular Neighbor Discovery.




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   If the mobile node receives the [MCOA RETURNHOME WO/NDP], it MUST NOT
   defend its home address on the home link.  When the mobile node sends
   packets from the interface attached to the home link, it MUST learn
   the layer 2 address (i.e., MAC address) of the next hop (i.e. default
   router, it can be home agent) during the binding de- registration and
   construct the packet including layer 2 header with the learnt layer-2
   address of the default router or the home agent.

5.7.  Receiving Binding Acknowledgement

   The verification of a Binding Acknowledgement is the same as Mobile
   IPv6 (section 11.7.3 of [RFC-3775]).  The operation for sending a
   Binding Acknowledgement is described in Section 6.3.

   If a mobile node includes a Binding Identifier mobility option in a
   Binding Update with the 'A' flag set, a Binding Acknowledgement MUST
   carry a Binding Identifier mobility option.  If no such mobility
   option is included in the Binding Acknowledgement in response to a
   Binding Update for multiple care-of address registration, this
   indicates that the originating node of the Binding Acknowledgement
   does not support processing the Binding Identifier mobility option.
   The mobile node MUST then stop multiple care-of address registration
   with that node.

   If a Binding Identifier mobility option is present in the received
   Binding Acknowledgement, the mobile node checks the status field in
   the option.  If the status value in the Binding Identifier mobility
   option is zero, the mobile node uses the value in the Status field of
   the Binding Acknowledgement.  Otherwise, it uses the value in the
   Status field of the Binding Identifier mobility option.

   If the status code is greater than or equal to 128, the mobile node
   starts relevant operations according to the error code.  Otherwise,
   the mobile node assumes that the originator (home agent or
   correspondent node) successfully registered the binding information
   and BID for the mobile node.

   o  If the Status value is [MCOA PROHIBITED], the mobile node MUST
      stop registering multiple bindings to the node that sent the
      Binding Acknowledgement.

   o  If the Status value is [MCOA BULK REGISTRATION NOT SUPPORT], the
      mobile node SHOULD stop using bulk registrations with the node
      that sent the Binding Acknowledgement.

   o  If [MCOA MALFORMED] is specified, it indicates that the binding
      identifier mobility option is formatted wrongly.




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   o  If [MCOA BID CONFLICT] is specified, the binding entry specified
      by the Binding Identifier mobility option is already registered as
      a regular binding.  In such case, the mobile node SHOULD stop
      sending Binding Updates with BID, or SHOULD use the 'O' flag to
      reset all the registered bindings.

5.8.  Receiving Binding Refresh Request

   The verification of a Binding Refresh Request is the same as in
   Mobile IPv6 (section 11.7.4 of [RFC-3775]).  The operation of sending
   a Binding Refresh Request is described in section Section 6.4.

   If a mobile node receives a Binding Refresh Request with a Binding
   Identifier mobility option, it indicates that the node sending the
   Binding Refresh Request message is requesting the mobile node to send
   a new Binding Update for the BID.  The mobile node SHOULD then send a
   Binding Update only for the respective binding.  The mobile node MUST
   include a Binding Identifier mobility option in the Binding Update.

   If no Binding Identifier mobility option is present in a Binding
   Refresh Request, the mobile node sends a Binding Update according to
   its Binding Update List.  On the other hand, if the mobile node does
   not have any Binding Update List entry for the requesting node, the
   mobile node needs to register either a single binding or multiple
   bindings depending on its binding management policy.

5.9.  Bootstrapping

   When a mobile node bootstraps and registers multiple bindings for the
   first time, it MUST set the 'O' flag in the Binding Identifier
   mobility option.  If old bindings still exists at the home agent, the
   mobile node has no knowledge of which bindings still exist at the
   home agent.  This scenario happens when a mobile node reboots and
   looses state regarding the registrations.  If the 'O' flag is set,
   all the bindings are replaced by the new binding(s).  If the mobile
   node receives the Binding Acknowledgement with the status code set to
   135 [Sequence number out of window], it MUST retry sending a Binding
   Update with the last accepted sequence number indicated in the
   Binding Acknowledgement.

   The 'O' flag can also be used in individual Binding Updates sent to
   the correspondent nodes to override any existing binding cache
   entries at the correspondent node.








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6.  Home Agent and Correspondent Node Operation

6.1.  Searching Binding Cache with Binding Identifier

   If either a correspondent node or a home agent has multiple bindings
   for a mobile node in their binding cache database, it can use any of
   the bindings to communicate with the mobile node.  This section
   explains how to retrieve the desired binding for the binding
   management.  This document does not provide any mechnaism to select
   the suitable binding for forwarding data packets.

   A correspondent node SHOULD use both the home address and the BID as
   the search key of the binding cache if it knows the corresponding BID
   (ex. when processing signaling messages).  In the example below, if a
   correspondent node searches the binding with the home address and
   BID2, it gets binding2 for this mobile node.

             binding1 [a:b:c:d::EUI,  care-of address1,  BID1]
             binding2 [a:b:c:d::EUI,  care-of address2,  BID2]
             binding3 [a:b:c:d::EUI,  care-of address3,  BID3]

                   Figure 4: Searching the Binding Cache

   A correspondent node learns the BID when it receives a Binding
   Identifier mobility option.  At that time, the correspondent node
   MUST look up its binding cache database with the home address and the
   BID retrieved from the Binding Update.  If the correspondent node
   does not know the BID, it searches for a binding with only the home
   address.  In such a case, the first matched binding is found.  If the
   correspondent node does not desire to use multiple bindings for a
   mobile node, it can simply ignore the BID.

6.2.  Receiving CoTI and Sending CoT

   When a correspondent node receives a CoTI message which contains a
   Binding Identifier mobility option, it processes it as follows.

   First, the CoTI message is verified as specified in [RFC-3775].  The
   Binding Identifier mobility option is processed as follows:

   o  If a correspondent node does not understand a Binding Identifier
      mobility option, it just ignores and skips processing the option.
      The calculation of a care-of Keygen token will thus be done
      without a BID value.  The correspondent node returns a CoT message
      without a Binding Identifier mobility option.  The mobile node
      knows whether the correspondent supports processing the Binding
      Identifier mobility option, by checking if the option is present
      in the CoT message.



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   o  If either the 'C' or the 'O' flag is set in the Binding Identifier
      mobility option, the correspondent Node SHOULD NOT calculate a
      care-of Keygen token, but MUST include a Binding Identifier
      mobility option with status value set to [MCOA MALFORMED] in the
      Care-of Test message.

   o  Otherwise, the correspondent node MUST include a Binding
      Identifier mobility option with status value set to zero (success)
      in the Care-of Test message.

   o  The Care-of address field of each Binding Identifier mobility
      option, can be omitted, because the mobile node can identify the
      corresponding Binding Update list entry using the BID.

6.3.  Processing Binding Update

   If a Binding Update does not contain a Binding Identifier mobility
   option, its processing is same as in [RFC-3775].  If the receiver
   already has multiple bindings for the home address, it MUST replace
   all the existing bindings by the received binding.  As a result, the
   receiver node MUST have only one binding cache entry for the mobile
   node.  If the Binding Update is for de-registration, the receiver
   MUST delete all existing bindings from its Binding Cache.

   If the Binding Update contains a Binding Identifier mobility
   option(s), it is first validated according to section 9.5.1 of [RFC-
   3775].  Then the receiver processes the Binding Identifier mobility
   option(s) as described in the following steps.

   o  The length value is examined.  The length value MUST be either 4,
      8, or 20 depending on the 'C' and 'D' flags.  If the length is
      incorrect, the receiver MUST reject the Binding Update and returns
      the status value set to [MCOA MALFORMED].

   o  When the 'C' flag is set, the care-of address MUST be present in
      the Binding Identifier mobility option.  If the care-of address is
      not present, the receiver MUST reject the Binding Identifier
      mobility option and returns the status value set to [MCOA
      MALFORMED].  The operation of 'D' flag is described in Section 8

   o  When multiple Binding Identifier mobility options are present in
      the Binding Update, it is treated as bulk registration.  If the
      receiving node is a correspondent node, it MUST reject the Binding
      Update and returns the status value in the binding acknowledgement
      set to [MCOA BULK REGISTRATION NOT SUPPORT]

   o  If the Lifetime field in the Binding Update is set to zero, the
      receiving node deletes the binding entry that corresponds to the



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      BID in the Binding Identifier mobility option.  If the receiving
      node does not have an appropriate binding for the BID, it MUST
      reject the Binding Update and send a Binding Acknowledgement with
      status set to 133 [not home agent for this mobile node].

   o  If the 'O' flag is set in the de-registering Binding Update, it is
      ignored.  If the 'H' flag is set, the home agent stores a home
      address in the Care-of Address field of the binding cache entry.
      The home agent also stops performing proxy ND for the mobile
      node's home address.

   o  If the Lifetime field is not set to zero, the receiving node
      registers a binding with the specified BID as a mobile node's
      binding.  The Care-of address is obtained from the Binding Update
      packet as follows:

      *  If the 'C' flag is set in the Binding Identifier mobility
         option, the care-of address is copied from the care-of address
         field in the Binding Identifier mobility option.

      *  If the 'C' flag is not set in the Binding Identifier mobility
         option, the care-of address is copied from the source address
         field of the IPv6 header.

      *  If the 'C' flag is not set and an alternate care-of address is
         present, the care-of address is copied from the Alternate
         Care-of address mobility option.

   o  Once the care-of address(es) have been retrieved from the Binding
      Update, the receiving nodes creates new binding(s).

      *  If only the 'O' flag is set in the Binding Identifier mobility
         option, the home agent removes all the existing bindings and
         registers the received bindings.

      *  If the receiver has a regular binding which does not have BID
         for the mobile node, it must not process the binding update.
         The receiver should sent a binding acknowledgement with status
         set to [MCOA BID CONFLICT].

      *  If the receiver already has a binding with the same BID but
         different care-of address, it MUST update the binding and
         respond with a Binding Acknowledgement with status set to 0
         [Binding Update accepted].

      *  If the receiver does not have a binding entry for the BID, it
         registers a new binding for the BID and responds with a Binding
         Acknowledgement with status set to 0 [Binding Update accepted].



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   If all the above operations are successfully completed, a Binding
   Acknowledgement containing the Binding Identifier mobility options
   MUST be sent to the mobile node.  Whenever a Binding Acknowledgement
   is sent, all the Binding Identifier mobility options stored in the
   Binding Update MUST be copied to the Binding Acknowledgement except
   the status field.  The Care-of address field in each Binding
   Identifier mobility option, however, can be omitted, because the
   mobile node can match a corresponding binding update list entry using
   the BID.

   When a correspondent node sends a Binding Acknowledgement, the status
   value MUST be always stored in the Status field of the Binding
   Acknowledgement and the Status field of Binding Identifier mobility
   option set to zero.  For the home agent, the status value can be
   stored in the Status field of either a Binding Acknowledgement or a
   Binding Identifier mobility option.  If the status value is specific
   to one of bindings in the bulk registration, the status value MUST be
   stored in the Status field in the corresponding Binding Identifier
   mobility option.  In this case, [MCOA NOTCOMPLETE] MUST be set to the
   Status field of the Binding Acknowledgement so that the receiver can
   examine the Status field of each Binding Identifier mobility option
   for further operations.

6.4.  Sending Binding Refresh Request

   When a node (home agent or correspondent node) sends a Binding
   Refresh Request for a particular binding created with the BID, the
   node SHOULD include the Binding Identifier mobility option in the
   Binding Refresh Request.  If the mobile node had used bulk
   registration, the sender SHOULD include all the Binding Identifier
   mobility options.  If the mobile node had not used bulk registration,
   the sender includes the Binding Identifier mobility options only for
   those bindings that need to be refreshed.

6.5.  Receiving Packets from Mobile Node

   When a node receives packets with a Home Address destination option
   from a mobile node, it MUST check that the care-of address that
   appears in the source address field of the IPv6 header MUST be equal
   to one of the care-of addresses in the binding cache entry.  If no
   binding is found, the packets MUST be silently discarded.  The node
   MUST also send a Binding Error message as specified in [RFC-3775].
   This verification MUST NOT be done for a Binding Update.








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7.  Network Mobility Applicability

   The binding management mechanisms are the same for a mobile host that
   uses Mobile IPv6 and for a mobile router that is using the NEMO Basic
   Support protocol [RFC-3963].  Therefore the extensions described in
   this document can also be used to support a mobile router with
   multiple care-of addresses.












































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8.  DSMIPv6 Applicability

   Dual Stack Mobile IPv6 (DSMIPv6) [ID-DSMIPv6] extends Mobile IPv6 to
   register an IPv4 care-of address instead of the IPv6 care-of address
   when the mobile node is attached to an IPv4-only access network.  It
   also allows the mobile node to acquire an IPv4 home address in
   addition to an IPv6 home address for use with IPv4-only correspondent
   nodes.  This section describes how multiple care-of address
   registration works with IPv4 care-of and home addresses.

8.1.  IPv4 Care-of Address Registration

   The mobile node can use the extensions described in the document to
   register multiple care-of addresses, even if some of the care-of
   addresses are IPv4 address.

   Bulk registration MUST NOT be used for the initial binding from an
   IPv4 care-of address.  This is because, the Binding Update and
   binding acknowledgement exchange is used to detect NAT on the path
   between the mobile node and the home agent.  So the mobile node needs
   to check for a NAT between each IPv4 care-of address and the home
   agent.

   The Binding Update MUST be sent to the IPv4 home agent address by
   using UDP and IPv4 headers as shown in Figure 5.  It is similar to
   [ID-DSMIPv6] except that the IPv4 care-of address option MUST NOT be
   used when the BID mobility option is used.

              IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
                UDP Header
                  IPv6 header (src=V6HoA, dst=HAADDR)
                       ESP Header
                       Mobility header
                           -BU
                          Mobility Options
                            - Binding Identifier (IPv4 CoA)

         Figure 5: Initial Binding Update for IPv4 Care-of Address

   If a NAT is not detected, the mobile node can update the IPv4 care-of
   address by using bulk registration.  The mobile node can register the
   IPv4 care-of address along with other IPv4 and IPv6 care-of
   addresses.  Figure 6 shows the Binding Update format when the mobile
   node sends a Binding Update from one of its IPv6 care-of addresses.
   If the mobile node sends a BU from IPv4 care-of address, it MUST
   follow the format described in Figure 5.  Note that the IPv4 Care-of
   Address must be registered by non bulk Binding registration, whenever
   it is changed.



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              IPv6 header (src=V6CoA, dst=HAADDR)
                    IPv6 Home Address Option
                    ESP Header
                    Mobility header
                        -BU
                       Mobility Options
                          - Binding Identifier (IPv6/v4 CoA)
                          - Binding Identifier (IPv6/v4 CoA)
                          - ...

       Figure 6: Binding Bulk Registration for IPv4 care-of address

   If the home agent rejects the IPv4 care-of address, it MUST store the
   error code value in the Status field of the BID mobility option.

8.2.  IPv4 HoA Management

   When the mobile node wants to configure an IPv4 home address in
   addition to the IPv6 home address, it can request for one using the
   IPv4 Home Address option in the Binding Update.  If the home agent
   accepts the Binding Update, the mobile node can now register multiple
   care-of addresses for the IPv4 home address in addition to the IPv6
   home address.  The same set of care-of addresses will be registered
   for both IPv6 and IPv4 home addresses.  The mobile node cannot bind
   different set of care-of addresses to each home address.

   According to [ID-DSMIPv6], the home agent includes the IPv4 address
   acknowledgement option in the Binding Acknowledgement only if the
   mobile node had requested for an IPv4 home address in the
   corresponding Binding Update.  The IPv4 address acknowledgement
   option MUST be present before any BID option.  The status field of
   the IPv4 address acknowledgement option contains only the error code
   corresponding to the IPv4 home address management.  The error values
   related to the IPv4 care-of address registration MUST be stored in
   the BID mobility option.
















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9.  IPsec and IKEv2 interaction

   Mobile IPv6 [RFC-3775] and the NEMO protocol [RFC-3963] require the
   use of IPsec to protect signaling messages like Binding Updates,
   Binding Acknowledgements and return routability messages.  IPsec may
   also be used protect all tunneled data traffic.  The Mobile IPv6-
   IKEv2 specification [RFC-4877] specifies how IKEv2 can be used to
   setup the required IPsec security associations.  The following
   assumptions were made in [RFC-3775], [RFC-3963] and [RFC-4877] with
   respect to the use of IKEv2 and IPsec.

   o  There is only one primary care-of address per mobile node.

   o  The primary care-of address is stored in the IPsec database for
      tunnel encapsulation and decapsulation.

   o  When the home agent receives a packet from the mobile node, the
      source address is verified against the care-of address in the
      corresponding binding cache entry.  If the packet is a reverse
      tunneled packet from the mobile node, the care-of address check is
      done against the source address on the outer IPv6 header.  The
      reverse tunnel packet could either be a tunneled HoTi message or
      tunneled data traffic to the correspondent node.

   o  The mobile node runs IKEv2 (or IKEv1) with the home agent using
      the care-of address.  The IKE SA is based on the care-of address
      of the mobile node.

   The above assumptions may not be valid when multiple care-of
   addresses are used by the mobile node.  In the following sections,
   the main issues with the use of multiple care-of address with IPsec
   are addressed.

9.1.  Use of Care-of Address in the IKEv2 exchange

   For each home address the mobile node sets up security associations
   with the home agent, the mobile node must pick one care-of address
   and use that as the source address for all IKEv2 messages exchanged
   to create and maintain the IPsec security associations associated
   with the home address.  The resultant IKEv2 security association is
   created based on this care-of address.

   If the mobile node needs to change the care-of address, it just sends
   a Binding Update with the care-of address it wants to use, with the
   corresponding Binding Identifier mobility option, and with the 'K'
   bit set.  This will force the home agent to update the IKEv2 security
   association to use the new care-of address.  If the 'K' bit is not
   supported on the mobile node or the home agent, the mobile node MUST



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   re-establish the IKEv2 security association with the new care-of
   address.  This will also result in new IPsec security associations
   being setup for the home address.

9.2.  Transport Mode IPsec protected messages

   For Mobile IPv6 signaling message protected using IPsec in transport
   mode, the use of a particular care-of address among multiple care-of
   addresses does not matter for IPsec processing.

   For Mobile Prefix Discovery messages, [RFC-3775] requires the home
   agent to verify that the mobile node is using the care-of address
   that is in the binding cache entry that corresponds to the mobile
   node's home address.  If a different address is used as the source
   address, the message is silently dropped by the home agent.  This
   document requires the home agent implementation to process the
   message as long as the source address is one of the care-of addresses
   in the binding cache entry for the mobile node.

9.3.  Tunnel Mode IPsec protected messages

   The use of IPsec in tunnel mode with multiple care-of address
   introduces a few issues that require changes to how the mobile node
   and the home agent send and receive tunneled traffic.  The route
   optimization mechanism described in [RFC-3775] mandates the use of
   IPsec protection in tunnel mode for the HoTi and HoT messages.  The
   mobile node and the home agent may also choose to protect all reverse
   tunneled payload traffic with IPsec in tunnel mode.  The following
   sections address multiple care-of address support for these two types
   of messages.

9.3.1.  Tunneled HoTi and HoT messages

   The mobile node MAY use the same care-of address for all HoTi
   messages sent reverse tunneled through the home agent.  The mobile
   node may use the same care-of address irrespective of which
   correspondent node the HoTi message is being sent.  RFC 3775 requires
   the home agent to verify that the mobile node is using the care-of
   address that is in the binding cache entry, when it receives a
   reverse tunneled HoTi message.  If a different address is used as the
   source address, the message is silently dropped by the home agent.
   This document requires the home agent implementation to decapsulate
   and forward the HoTi message as long as the source address is one of
   the care-of addresses in the binding cache entry for the mobile node.

   When the home agent tunnels a HoT message to the mobile node, the
   care-of address used in the outer IPv6 header is not relevant to the
   HoT message.  So regular IPsec tunnel encapsulation with the care-of



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   address known to the IPsec implementation on the home agent is
   sufficient.

9.3.2.  Tunneled Payload Traffic

   When the mobile sends and receives multiple traffic flows protected
   by IPsec to different care-of addresses, the use of the correct
   care-of address for each flow becomes important.  Support for this
   requires the following two considerations on the home agent.

   o  When the home agent receives a reverse tunneled payload message
      protected by IPsec in tunnel mode, it must check that the care-of
      address is one of the care-of addresses in the binding cache
      entry.  According to RFC 4306, the IPsec implementation on the
      home agent does not check the source address on the outer IPv6
      header.  Therefore the care-of address used in the reverse
      tunneled traffic can be different from the care-of address used as
      the source address in the IKEv2 exchange.  However, the Mobile
      IPv6 stack on the home agent MUST verify that the source address
      is one of the care-of addresses registered by the mobile node
      before decapsulating and forwarding the payload traffic towards
      the correspondent node.

   o  For tunneled IPsec traffic from the home agent to the mobile node,
      The IPsec implementation on the home agent may not be aware of
      which care-of address to use when performing IPsec tunnel
      encapsulation.  The Mobile IP stack on the home agent must specify
      the tunnel end point for the IPsec tunnel.  This may require tight
      integration between the IPsec and Mobile IP implementations on the
      home agent.





















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10.  Security Considerations

   The security considerations for securing the Binding Update and
   binding acknowledgement messages with multiple care-of address are
   very similar to the security considerations for securing the Binding
   Update and binding acknowledgement.  Please see [RFC-3775] for more
   information.  The Binding Update and binding acknowledgement messages
   with multiple care-of addresses MUST be protected using IPsec as show
   in Section 9.  Additional security considerations are described
   below.

   With simultaneous binding support, it is possible for a malicious
   mobile node to successfully bind a number of victims' addresses as
   valid care-of addresses for the mobile node with its home agent.
   Once these addresses have been bound, the malicious mobile node can
   perform a re-direction attack by instructing the home agent (e.g.
   setting filtering rules to direct a large file transfer) to tunnel
   packets to the victims' addresses.  Such risk is highlighted in [ID-
   MIP6ANALYSIS].  These attacks are possible because the care-of
   addresses sent by the mobile node in the Binding Update messages are
   not verified by home agent, i.e., the home agent does not check if
   the mobile node is at the care-of address it is claiming to be.  The
   security model for Mobile IPv6 assumes that there is a trust
   relationship between the mobile node and its home agent.  Any
   malicious attack by the mobile node is traceable by the home agent.
   This acts as a deterrent for the mobile node to launch such attacks.

   Although such risk exists in Mobile IPv6, the risk level is escalated
   when simultaneous multiple care-of address bindings are performed.
   In Mobile IPv6, a mobile node can only have a single care-of address
   binding per home address at a given time.  However, for simultaneous
   multiple care-of address bindings, a mobile node can have more than
   one care-of address binding per home address at a given time.  This
   implies that a mobile node using simultaneous binding support can
   effectively bind more than a single victim's address.  Another
   difference is the degree of risk involved.  In the single care-of
   address binding case, once the re-direction attack is initiated, a
   malicious mobile node would be unable to use its home address for
   communications (such as to receive control packets pertaining to the
   file transfer).  However, in the simultaneous binding support case, a
   malicious mobile node could bind a valid care-of address in addition
   to multiple victims addresses.  This valid care-of address could then
   be used by the malicious mobile node to set up flow filtering rules
   at its home agent, thereby controlling and/or launching new re-
   direction attacks.

   Thus, in view of such risks, it is advisable for a home agent to
   employ some form of care-of address verification mechanism before



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   using the care-of addresses as a valid routing path to a mobile node.
   Solutions related to this are described in [ID-COAVERIFY].

















































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11.  IANA Considerations

   The following Extension Types MUST be assigned by IANA:

   o  Binding Identifier mobility option type: This must be assigned
      from the same space as mobility option in [RFC-3775].

   o  New Successful Status of Binding Acknowledgement: This status code
      must be assigned from the same space as binding acknowledgement
      status codes in [RFC-3775].

      *  MCOA NOTCOMPLETE (TBD)

   o  New Unsuccessful Status of Binding Acknowledgement: These status
      codes must also be assigned from the same space as binding
      acknowledgement status codes in [RFC-3775].

      *  MCOA MALFORMED (TBD)

      *  MCOA BID CONFLICT (TBD)

      *  MCOA PROHIBITED(TBD)

      *  MCOA BULK REGISTRATION NOT SUPPORTED (TBD)



























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12.  Acknowledgements

   The authors would like to thank Masafumi Aramoto, George Tsirtsis,
   Keigo Aso, Julien Charbon, Tero Kauppinen, Benjamin Lim, Susumu
   Koshiba, Martti Kuparinen, Romain Kuntz, Heikki Mahkonen, Hiroki
   Matutani, Koshiro Mitsuya, Nicolas Montavont, Koji Okada, Keisuke
   Uehara, Masafumi Watari in alphabetical order, and the Jun Murai
   Laboratory at the KEIO University.


13.  References


13.1.  Normative References

   [RFC-3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
   in IPv6", RFC 3775, June 2004.

   [RFC-3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
   Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
   January 2005.

   [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC-4877] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
   IKEv2 and the revised IPsec Architecture", RFC 4877, April 2007.

13.2.  Informative References

   [ID-MOTIVATION] Ernst, T., Montavont, N., Wakikawa, R., Ng, C., and
   K. Kuladinithi, "Motivations and Scenarios for Using Multiple
   Interfaces and Global Addresses",
   draft-ietf-monami6-multihoming-motivation-scenario-02 (work in
   progress), July 2007

   [RFC-4980] Ng, C., Paik, Ernst, and C. Bagnulo, "Analysis of
   Multihoming in Network Mobility Support", RFC 4980, October 2007.

   [ID-MIP6ANALYSIS] Montavont, N., Wakikawa, R., Ernst, T., Ng, C., and
   K. Kuladinithi, "Analysis of Multihoming in Mobile IPv6",
   draft-ietf-monami6-mipv6-analysis-04 (work in progress), Novemver
   2007.

   [RFC-3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
   RFC 3753, June 2004.

   [RFC-4885] Ernst, T. and H. Lach, "Network Mobility Support



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   Terminology", RFC 4885, July 2007.

   [ID-DSMIPv6] Soliman, H., "Mobile IPv6 support for dual stack Hosts
   and Routers (DSMIPv6)", draft-ietf-mip6-nemo-v4traversal-06 (work in
   progress), November 2007.

   [ID-COAVERIFY] Lim, B., C. NG and K. Aso, "Verification of Care-of
   Addresses in Multiple Bindings Registration",
   draft-lim-mext-multiple-coa-verify-01 (work in progress), February
   2008.









































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Appendix A.  Example Configurations

   In this section, we describe typical scenarios when a mobile node has
   multiple network interfaces and acquires multiple Care-of Addresses
   bound to a home address.  The home address of the mobile node (MN in
   figures) is a:b:c:d::EUI.  MN has 3 different interfaces and possibly
   acquires care-of addresses 1-3 (CoA1, CoA2, CoA3).  The MN assigns
   BID1, BID2 and BID3 to each care-of address.

                    +----+
                    | CN |
                    +--+-+
                       |
                   +---+------+          +----+
            +------+ Internet |----------+ HA |
            |      +----+---+-+          +--+-+
        CoA2|           |   |               |   Home Link
         +--+--+        |   |         ------+------
         |  MN +========+   |
         +--+--+ CoA1       |
        CoA3|               |
            +---------------+

     Binding Cache Database:
        home agent's binding (Proxy neighbor advertisement is active)
              binding [a:b:c:d::EUI  care-of address1  BID1]
              binding [a:b:c:d::EUI  care-of address2  BID2]
              binding [a:b:c:d::EUI  care-of address3  BID3]
        correspondent node's binding
              binding [a:b:c:d::EUI  care-of address1  BID1]
              binding [a:b:c:d::EUI  care-of address2  BID2]
              binding [a:b:c:d::EUI  care-of address3  BID3]

         Figure 7: Multiple Interfaces Attached to a Foreign Link

   Figure 7 depicts the scenario where all interfaces of the mobile node
   are attached to foreign links.  After binding registrations, the home
   agent (HA) and the correspondent node (CN) have the binding entries
   listed in their binding cache database.  The mobile node can utilize
   all the interfaces.











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                    +----+
                    | CN |
                    +--+-+
                       |
                   +---+------+          +----+
            +------+ Internet |----------+ HA |
            |      +--------+-+          +--+-+
        CoA2|               |               |   Home Link
         +--+--+            |         --+---+------
         |  MN +========+   |           |
         +--+--+        |   |           |
        CoA3|           +---|-----------+
            +---------------+

     Binding Cache Database:
        home agent's binding
              none
        correspondent node's binding
              binding [a:b:c:d::EUI  care-of address2  BID2]
              binding [a:b:c:d::EUI  care-of address3  BID3]



    Figure 8: One of Interface Attached to Home Link and Returning Home

   Figure 8 depicts the scenario where MN returns home with one of its
   interfaces.  After the successful de-registration of the binding to
   HA, HA and CN have the binding entries listed in their binding cache
   database of Figure 8.  After de-registration, the ND state of the
   home address is managed by the MN.  MN can communicate with the HA
   through only the interface attached to the home link.  On the other
   hand, the mobile node can communicate with CN from the other
   interfaces attached to foreign links (i.e. route optimization).  Even
   if MN is attached to the home link, it can still send Binding Updates
   for other active care-of addresses (CoA2 and CoA3) to CNs.  If CN has
   bindings, packets are routed to each Care-of Addresses directly.  Any
   packet arrived at HA are routed to the interface attached to the home
   link.













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                    +----+
                    | CN |
                    +--+-+
                       |
                   +---+------+          +----+
            +------+ Internet |----------+ HA |
            |      +----+-----+          +--+-+
        CoA2|           |                   |   Home Link
         +--+--+        |             --+---+------
         |  MN +========+               |
         +--+--+ CoA1                   |
            |                           |
            +---------------------------+
             (Disable interface)

     Binding Cache Database:
        home agent's binding
              binding [a:b:c:d::EUI  care-of address1  BID1]
              binding [a:b:c:d::EUI  care-of address2  BID2]
        correspondent node's binding
              binding [a:b:c:d::EUI  care-of address1  BID1]
              binding [a:b:c:d::EUI  care-of address2  BID2]

    Figure 9: One of Interface Attached to Home Link and Not Returning
                                   Home

   Figure 9 depicts the scenario where MN disables the interface
   attached to the home link and communicates with the interfaces
   attached to foreign links.  HA continues managing the ND state of the
   home address by Proxy neighbor advertisement.  The HA and the CN have
   the binding entries listed in their binding cache database.  All
   packets routed to the home link are intercepted by the HA and
   tunneled to the other interfaces attached to the foreign link
   according to the binding entries.

















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   Topology-a)
                    +----+
                    | CN |
                    +--+-+
                       |
                   +---+------+          +----+
            +------+ Internet |----------+ HA |
            |      +----+-----+          +--+-+
        CoA2|           |                   |   Home Link
         +--+--+        |             --+---+------
         |  MN +========+               |
         +--+--+ CoA1                   |
       CoA3 |                           |
            +---------------------------+

   Topology-b)
                    +----+
                    | CN |
                    +--+-+
                       |
                   +---+------+    Router    +----+
            +------+ Internet |-------R      | HA |
            |      +----+-----+       |      +--+-+
        CoA2|           |             |         |   Home Link
         +--+--+        |           --+-+-------+------
         |  MN +========+               |
         +--+--+ CoA1                   |
       CoA3 |                           |
            +---------------------------+


     Binding Cache Database:
        home agent's binding
              binding [a:b:c:d::EUI  care-of address1  BID1]
              binding [a:b:c:d::EUI  care-of address2  BID2]
        correspondent node's binding
              binding [a:b:c:d::EUI  care-of address1  BID1]
              binding [a:b:c:d::EUI  care-of address2  BID2]
              binding [a:b:c:d::EUI  care-of address3  BID3]


   Figure 10: Utilize Interfaces Attached to both Home and Foreign Links

   Figure 10 depicts the scenario where interfaces of MN are attached to
   both the home and foreign links.  There are two possible topologies
   whether the HA is single router at the home link or not.  The
   operation of ND is different in two topologies.  The HA and CN have
   the binding entries listed in Figure 10 in their binding cache



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   database regardless of topologies.  The HA also knows that the MN has
   attached to the home link.  All the traffic from the Internet are
   intercepted by the HA and routed to either the interface attached to
   the home link or the interfaces attached to the foreign links.  How
   to make the decision is out of scope in this document.

   There are two different treatments of the ND state of the home
   address.

   o  MN defends the home address by regular ND (topology-a)

   o  HA defends the home address by Proxy ND (topology-b)

   The first case is required that the HA is the single exit router to
   the Internet and is capable of intercepting packets without relying
   on proxy ND.  The MN can manage the ND of the home address on the
   home link.  In the second case, the HA is not only router at the home
   link and cannot intercept all the packets meant for the MN by IP
   routing.  The HA needs to run Proxy ND to intercept all the packets
   at the home link.  Since the MN cannot operate the ND of its home
   address at the home link, HA cannot resolve the layer-2 address of
   the MN at the home link.  The HA MUST learn and record the layer-2
   address (MAC address) of the MN's interface attached to the home link
   to forward packets.  The packets forwarding is achieved without ND
   cache.  The MN is also required to learn and record the layer-2
   address of the HA's interface to send packets from the home link.


Authors' Addresses

   Ryuji Wakikawa (Editor)
   Faculty of Environment and Information Studies, Keio University
   5322 Endo
   Fujisawa, Kanagawa  252-8520
   Japan

   Phone: +81-466-49-1100
   Fax:   +81-466-49-1395
   Email: ryuji@sfc.wide.ad.jp
   URI:   http://www.wakikawa.org/











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   Thierry Ernst
   INRIA
   INRIA Rocquencourt
   Domaine de Voluceau B.P. 105
   Le Chesnay,   78153
   France

   Phone: +33-1-39-63-59-30
   Fax:   +33-1-39-63-54-91
   Email: thierry.ernst@inria.fr
   URI:   http://www.nautilus6.org/~thierry


   Kenichi Nagami
   INTEC NetCore Inc.
   1-3-3, Shin-suna
   Koto-ku, Tokyo  135-0075
   Japan

   Phone: +81-3-5565-5069
   Fax:   +81-3-5565-5094
   Email: nagami@inetcore.com


   Vijay Devarapalli
   Azaire Networks
   3121 Jay Street
   Santa Clara, CA  95054
   USA

   Email: vijay.devarapalli@azairenet.com




















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Full Copyright Statement

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