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

Monami6 Working Group                               R. Wakikawa (Editor)
Internet-Draft                                           Keio University
Intended status: Standards Track                                T. Ernst
Expires: July 31, 2008                                             INRIA
                                                               K. Nagami
                                                           INTEC NetCore
                                                          V. Devarapalli
                                                         Azaire Networks
                                                        January 28, 2008


                Multiple Care-of Addresses Registration
                 draft-ietf-monami6-multiplecoa-05.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on July 31, 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, termed the primary
   care-of address, 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 access media simultaneously, in which case multiple active
   IPv6 care-of addresses would be assigned to the mobile node.  We thus
   propose Mobile IPv6 extensions designed to register multiple care-of
   addresses bound to a single Home Address instead of the sole primary
   care-of address.  For doing so, a new identification number must be
   carried in each binding for the receiver to distinguish between the
   bindings corresponding to the same Home Address.  Those extensions
   are targeted to NEMO (Network Mobility) Basic Support as well as to
   Mobile IPv6.



































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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.  Message Format Changes . . . . . . . . . . . . . . . . . .  9
       4.2.1.  Binding Identifier Mobility Option . . . . . . . . . .  9
     4.3.  New Status Values for Binding Acknowledgment . . . . . . . 11

   5.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 13
     5.1.  Management of Care-of Addresses and Binding Identifier . . 13
     5.2.  Return Routability: Sending CoTI and Receiving CoT . . . . 13
     5.3.  Binding Registration . . . . . . . . . . . . . . . . . . . 14
     5.4.  Binding Bulk Registration  . . . . . . . . . . . . . . . . 15
     5.5.  Binding De-Registration  . . . . . . . . . . . . . . . . . 16
     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 Acknowledgment . . . . . . . . . . . . . 19
     5.8.  Receiving Binding Refresh Request  . . . . . . . . . . . . 20
     5.9.  Sending Packets to Home Agent  . . . . . . . . . . . . . . 20
     5.10. Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 21

   6.  Home Agent and Correspondent Node Operation  . . . . . . . . . 22
     6.1.  Searching Binding Cache with Binding Identifier  . . . . . 22
     6.2.  Receiving CoTI and Sending CoT . . . . . . . . . . . . . . 22
     6.3.  Processing Binding Update  . . . . . . . . . . . . . . . . 23
     6.4.  Sending Binding Refresh Request  . . . . . . . . . . . . . 25
     6.5.  Receiving Packets from Mobile Node . . . . . . . . . . . . 26

   7.  Network Mobility Applicability . . . . . . . . . . . . . . . . 27

   8.  DSMIPv6 Applicability  . . . . . . . . . . . . . . . . . . . . 28
     8.1.  IPv4 Care-of Address Registration  . . . . . . . . . . . . 28
     8.2.  IPv4 HoA Management  . . . . . . . . . . . . . . . . . . . 29

   9.  IPsec and IKEv2 interaction  . . . . . . . . . . . . . . . . . 30
     9.1.  Use of Care-of Address in the IKEv2 exchange . . . . . . . 30
     9.2.  Transport Mode IPsec protected messages  . . . . . . . . . 31
     9.3.  Tunnel Mode IPsec protected messages . . . . . . . . . . . 31
       9.3.1.  Tunneled HoTi and HoT messages . . . . . . . . . . . . 31
       9.3.2.  Tunneled Payload Traffic . . . . . . . . . . . . . . . 32



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   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 33

   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 34

   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 35

   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 35
     13.2. Informative References . . . . . . . . . . . . . . . . . . 36

   Appendix A.  Example Configurations  . . . . . . . . . . . . . . . 37

   Appendix B.  Changes From Previous Versions  . . . . . . . . . . . 42

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42
   Intellectual Property and Copyright Statements . . . . . . . . . . 44



































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1.  Introduction

   A mobile node may use various types of network interfaces to obtain
   durable and wide area network connectivity.  The assumed scenarios
   and motivations for multiple points of attachment, and benefits for
   doing it are discussed at large in [ID-MOTIVATION].

   IPv6 [RFC-2460] conceptually allows a node to have several addresses
   on a given interface.  Consequently, Mobile IPv6 [RFC-3775] has
   mechanisms to manage multiple ``Home Addresses'' based on home
   agent's managed prefixes such as mobile prefix solicitation and
   mobile prefix advertisement.  But assigning a single Home Address to
   a node is more advantageous than assigning multiple Home Addresses
   because applications do not need to be aware of the multiplicity of
   Home Addresses.  If multiple home addresses are available,
   applications must reset the connection information when the mobile
   node changes its active network interface (i.e. change the Home
   Address).

   According to the Mobile IPv6 specification, a mobile node is not
   allowed to register multiple care-of addresses bound to a single Home
   Address.  Since NEMO Basic Support [RFC-3963] is based on Mobile
   IPv6, the same issues apply to a mobile node acting as a mobile
   router.  Multihoming issues pertaining to mobile nodes operating
   Mobile IPv6 and mobile routers operating NEMO Basic Support are
   respectively discussed [ID-MIP6ANALYSIS] and [RFC-4980] in Monami6
   and NEMO Working Group.

   In this document, we thus propose a new identification number called
   Binding Identification (BID) number for each binding cache entry to
   accommodate multiple bindings registration.  The mobile node notifies
   the BID to both its Home Agent and correspondent nodes by means of a
   Binding Update.  Correspondent nodes and the home agent record the
   BID into their binding cache.  The Home Address thus identifies a
   mobile node itself whereas the BID identifies each binding registered
   by a mobile node.  By using the BID, multiple bindings can then be
   distinguished.














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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
      BID 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.  The zero value and a negative value MUST
      NOT be used.  Each BID is generated and managed by a mobile node.
      After being generated by the 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.

   Bulk Registration

      A mobile node can register multiple bindings at once by sending a
      single binding update.  The mobile node does not necessarily put
      all the available care-of addresses in the binding update, but
      several care-of addresses.  A mobile node can also replace all the
      bindings available at the home agent with the new bindings by
      using the bulk registration.  The bulk registration is supported
      only for home registration and de-registration as explained in
      Section 5.5.  A mobile node MUST NOT perform bulk registration
      with correspondent nodes.








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3.  Protocol Overview

   A new identification number (BID) is introduced to distinguish
   multiple bindings pertaining to the same Home Address.  Once a mobile
   node gets several IPv6 global addresses on one or more of its
   interfaces, it can register these addresses with its home agent.  If
   the mobile node wants to register multiple bindings, it MUST generate
   a BID for each care-of address and record the BID into the binding
   update list.  A mobile node can manipulate each binding independently
   by using a BID.  The mobile node then registers its care-of addresses
   by sending a Binding Update with a Binding Identifier mobility
   option.  The BID MUST be included in the Binding Identifier mobility
   option.  After receiving such Binding Update and 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.  Even if there is already an entry for the mobile node's
   home address, the home agent MUST register a new binding entry for
   the BID stored in the Binding Identifier mobility option.  The mobile
   node registers 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.
   The mobile host MUST manage a Care-of Keygen Token per care-of
   address.  The mobile host exchanges CoTI and CoT for the
   corresponding care-of addresses if necessary.  When the mobile host
   registers several care-of addresses to a correspondent node, it uses
   the same BID as the one generated for the home registration's
   bindings.  The binding registration step is the same as for the home
   registration except for calculating authenticator.  For protocol
   simplicity, the bulk registration is not supported for correspondent
   nodes in this document.  Return Routability 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 just 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 BID even if only a single binding is active at some
   time.

   When a home agent and a correspondent node check the binding cache
   database for the mobile node, they search a corresponding binding
   entry with the pair of Home Address and BID of the desired binding.
   If necessary, a mobile node can use policy and filter information to



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   look up the best binding per sessions, flow, packets, but this is out
   of scope in this document.  If there is no desired binding, it
   searches the binding cache database with the Home Address as
   specified in Mobile IPv6.  The first matched binding entry may be
   found, although this is implementation dependent.

   The mobile node may return to the home link through one 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 which are still attached to
       the visited link are not used.

   2.  The mobile node uses only the interfaces still attached to the
       visited link.  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 links.

   Section 5.6 describes the returning home procedures in more detail.



























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4.  Mobile IPv6 Extensions

   This section summarizes the changes to Mobile IPv6 necessary to
   manage multiple bindings bound to a same Home Address.

4.1.  Binding Cache Structure and Binding Update List

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

4.2.  Message Format Changes

4.2.1.  Binding Identifier Mobility Option

   The Binding Identifier mobility option is included in the Binding
   Update, Binding Acknowledgment, 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)







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      The BID which is assigned to the binding carried in the Binding
      Update with this mobility option.  BID is 16-bit unsigned integer.
      A value of zero is reserved.

   Status

      When the Binding Identifier mobility option is included in a
      Binding Acknowledgment, this field overwrites the status field
      correspondent to each binding in the Binding Acknowledgment.  If
      this field is zero, the receiver MUST use the registration status
      stored in the Binding Acknowledgment message.  This Status field
      can be used to carry error information for a Care-of Test message.
      The status is 8-bit unsigned integer.  The possible status codes
      are the same as the status codes of Binding Acknowledgment.

   Care-of address (C) flag

      When this flag is set, a mobile node can store a Care-of Address
      corresponding to the BID in the Binding Identifier mobility
      option.  This flag MUST be used whenever a mobile node sends
      multiple care-of addresses in a single Binding Update, i.e. bulk
      registration.  It MUST be also used for the independent binding
      registration as a substitute for an alternate care-of address
      option.  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 a home agent to
      replace all the bindings to binding entries stored in a Binding
      Update.  This flag is valid only for binding update sent to the
      home agent.

   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 field MUST be set to
      IPv4 care-of address.  If this flag is set, the Care-of Address
      field MUST be used.






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   Reserved

      5 bits Reserved field.  Reserved field MUST be set with all 0.

   Care-of Address

      This field has the variable length depending on the specified
      flags.  When C flag is set and D flag is unset, an IPv6 Care-of
      Address matched to the BID is stored in this field.  If both C and
      D flags are set, an IPv4 Care-of Address is stored.  This field
      MUST NOT be used if a Binding Identifier mobility option is
      included in any other messages than a Binding Update message.  The
      receiver SHOULD ignore this field if the mobility option is not
      presented in Binding Update message.

4.3.  New Status Values for Binding Acknowledgment

   New status values for the status field in a Binding Acknowledgment
   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.  The detail can be found in Section 5.6

   MCOA MALFORMED (TBD more than 128)

      Registration failed because Binding Identifier mobility option is
      not formed 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).







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   MCOA PROHIBITED(TBD more than 128)

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

   MCOA BULK REGISTRATION NOT SUPPORTED (TBD more than 128)

      The bulk binding registration is not supported.











































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5.  Mobile Node Operation

5.1.  Management of Care-of Addresses and Binding Identifier

   There are two cases when a mobile node has several Care-of Addresses.
   Note that a mixture of the two cases are possible.

   1.  A mobile node uses 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
       multiple prefixes are announced on the link the interface is
       attached to.  Several global addresses are configured on this
       interface for each of the announced prefixes.

   The difference between the above two cases is only a number of
   physical network interfaces and therefore does not matter in this
   document.  The Identification number is used to identify a binding.
   To implement this, a mobile node MAY assign an identification number
   for each care-of addresses.  How to assign an identification number
   is implementation specific, but the following rules MUST be followed.

   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 binding to a specific care-of address for a given home
   address and care-of address pair.  The value should be generated from
   a value comprised between 1 to 65535.  Zero and negative values MUST
   NOT be used as a BID.  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.

5.2.  Return Routability: Sending CoTI and Receiving CoT

   When a mobile node wants to register bindings to a Correspondent
   Node, it MUST have the valid care-of Keygen token per care-of
   address, while the HoTI and HoT can be exchanged only once for a Home
   Address.

   If the Mobile Node manages bindings with BID, it MUST include a
   Binding Identifier mobility option in a Care-of Test Init message.
   It MUST NOT set the 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 a Care-of Test message and the
   Binding Identifier mobility option as described in Section 6.2.  When
   the mobile node receives the Care-of Test message, the Care-of Test
   message is verified as same as in [RFC-3775].  If a Binding
   Identifier mobility option is not presented in CoT in reply to the
   CoTI containing the Binding Identifier mobility option, the



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   correspondent node does not support the Multiple Care-of Address
   registration.  Thus, the mobile node MUST NOT use a Binding
   Identifier mobility option in the future Binding Update.  The Mobile
   Node MAY skip re-sending regular CoTI message and keep the received
   care-of Keygen token for the regular Binding Update, because the
   correspondent node just ignores and skip the Binding Identifier
   mobility option and calculates the care-of Keygen token as [RFC-3775]
   specified.

5.3.  Binding Registration

   When a mobile node sends a Binding Update, it MUST decide whether it
   registers multiple care-of addresses or not.  However, how this
   decision is taken is out-of scope in this document.  If a mobile node
   decides not to register multiple care-of addresses, it completely
   follows the RFC3775 specification.

   For the multiple Care-of Addresses registration, the mobile node MUST
   include a Binding Identifier mobility option(s) in the Mobility
   Option field of a 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 ESP is used
   for binding update, the care-of address MUST be stored in the Care-of
   Address field by setting C flag as a substitute for the alternate
   care-of address option.  The alternate care-of address option MUST be
   omitted.  Additionally 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]).  The care-of Keygen
   tokens MUST be maintained for each care-of address that the mobile
   node wants to register to the correspondent node, as described in
   Section 5.2.  After computing an Authenticator value for the Binding
   Authorization mobility option, it sends a Binding Update which
   contains a Binding Identifier mobility option.  The Binding Update is
   protected by a Binding Authorization Data mobility option 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




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5.4.  Binding Bulk Registration

   The bulk registration is an optimization for registering multiple
   care-of addresses only to a home agent by using a single Binding
   Update.  If a mobile node, for instance, does not want to send a lot
   of control messages through an interface which bandwidth is scarce,
   it can use this bulk registration and send a Binding Update
   containing multiple or all the valid care-of addresses.

   A mobile node sets the C flag in a Binding Identifier mobility option
   and includes the particular care-of address in the Binding Identifier
   mobility option.  The mobile node stores multiple sets of a Binding
   Identifier mobility option in a Binding Update as shown in Figure 3.
   In the bulk registration, all the other binding information such as
   Lifetime, Sequence Number, binding Flags are shared among the bulked
   Care-of Addresses.  The alternate care-of address option MUST be
   omitted when ESP is used to protect a binding update.

   In the bulk registration, the Sequence Number field of a Binding
   Update SHOULD be carefully configured.  This is because all the bulk-
   registered bindings uses 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 used for the bulk registration.  If it 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 which
   sequence number is out of window and uses a separate Binding Update
   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 Binding 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 can
   set O flag.  Section 6.3 describes this registration procedure in
   detail.






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5.5.  Binding De-Registration

   When a mobile node decides to delete all the bindings for its home
   address at a visiting network, it simply sends a regular de-
   registration Binding Update which lifetime is set to zero.  A 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 (e.g. from foreign link), the
   mobile node simply sets zero lifetime for the sending binding update.
   The Binding Update MUST contain an appropriate Binding Identifier
   mobility option(s).  The receiver will remove only the care-of
   address(es) that matches to the specified BID.  For the bulk de-
   registration, the care-of addresses field of each mobility option
   SHOULD be omitted, because the receiver will remove all the care-of
   addresses matching 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 the interfaces on the mobile node.  When the
   mobile node wants to return home, it should be configured with 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 9.  How to de-register all the bindings is the same
   as binding de-registration from foreign link described in
   Section 5.5.  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 9.  These bindings at
   correspondent node MUST be created before a mobile node returns home.

5.6.2.  Using only Interface attached to the Visited Link

   The mobile node returns home and shutdown the interface attached to
   the home link as shown in Figure 10.  The binding of the home
   attached interface MUST be deleted by sending a de-registration
   binding update from one of active interface attached to the foreign
   links.  This scenario is not the most efficient because all the



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   traffic from and to the mobile node is going through the bi-
   directional tunnel, whereas the mobile node is now accessible at one
   hop from its home agent.

5.6.3.  Simultaneous Home and Visited Link Operation

   The mobile node returns home and continues using all the interfaces
   attached to both foreign and home links as shown in Figure 11.  The
   mobile node indicates this by setting the 'H' flag in the BID
   mobility option.  There are additional requirements on the Returning
   Home procedures for possible ND conflicts at the home link described
   below.

   In [RFC3775], the home agent intercepts packets meant for the mobile
   node using proxy NDP while the mobile node is away from the home
   link.  When the mobile node returns home, the home agent deletes the
   binding cache and stop the proxy NDP 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 while it keeps several interfaces attached to the foreign links
   and continues using them.  Therefore, even though both the mobile
   node and the home agent need to intercept packets, the ND states of
   the home address can conflict between the home agent and the mobile
   node.  For instance, if the proxy ND for the Home Address is stopped
   by the home agent, packets are always routed to the interface
   attached to the home link and are never routed to the interface
   attached to the foreign link.  It is required to avoid this ND
   conflicts in the case of the simultaneous home and foreign
   attachment.

   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 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 delicate 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 be stored for the BID assigned
   to the interface.  The H flag MUST be set in the BID mobility option.
   When the H flag is appears, the home agent learns and remembers that
   the mobile node wants to continue using interfaces attached to both



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   foreign and home links.  If H flag is unset, the home agent deletes
   either all the bindings or the binding corresponding to the BID.

   When the home agent sends the Binding Acknowledgment, it MUST store
   one of two status values such as [Binding Update Accepted (0)] [MCOA
   RETURNHOME 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
      [RFC3775]

   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 IP routing without proxy NDP.  It stops
   proxy ND for the requested home address and replies the [Binding
   Update Accepted] value to the mobile node.  The neighbor cache entry
   for the mobile node is created by the regular NDP operation (i.e.
   NS/NA exchange).  On the other hand, if the home agent is not the
   only router, it MUST continue defending the home address by proxy NDP
   to capture all 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 keeps the learned layer-2 address as the 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 [RFC3775], 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
   Acknowledgment with success status value.

   When the mobile node receives the binding acknowledgment and BID
   mobility option, it assigns home address at 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 NDP.  The home agent can create neighbor cache
   entry for the mobile node by NS and NA exchange as normal IPv6
   operation.

   If the home agent receives the [MCOA RETURNHOME WO/NDP], it MUST NOT



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   defends its home address at the home link by NDP.  When the mobile
   node sends packets from the interface attached to the home link, it
   MUST learn the layer2 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 learned home agent's layer-2 address.

5.7.  Receiving Binding Acknowledgment

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

   If a mobile node includes a Binding Identifier mobility option in a
   Binding Update with A flag set, a Binding Acknowledgment MUST carry a
   Binding Identifier mobility option in the Mobility Options field.  If
   no such mobility option is included in the Binding Acknowledgment
   replied to the Binding Update for the multiple care-of address
   registration, this indicates that the originator node of this Binding
   Acknowledgment might not recognize the Binding Identifier mobility
   option.  The mobile node SHOULD stop registering multiple care-of
   addresses by using a Binding Identifier mobility option.

   If a Binding Identifier mobility option is present in the received
   Binding Acknowledgment, the mobile node checks the registration
   status for the Care-of address(es).  The status value MUST be
   retrieved as follows.  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 Acknowledgment.  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 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
      give up registering multiple bindings to the peer sending the
      Binding Acknowledgment.  It MUST return to the regular Mobile IPv6
      [RFC-3775] for the peer node.

   o  If the Status value is [MCOA BULK REGISTRATION NOT SUPPORT], the
      mobile node SHOULD stop using bulk registration to the peer
      sending the Binding Acknowledgment.

   o  If [MCOA MALFORMED] is specified, it indicates that the binding
      identifier mobility option is formatted wrongly.  For example, if
      the C flag is set, all mobility options MUST have C flag.  It is



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      same for O flag.  How to handle other error status codes is
      specified in [RFC-3775].

   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 O flag for the
      peer 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, this Binding Refresh Request requests a
   new binding indicated by the BID.  The mobile node SHOULD update only
   the respective binding.  The mobile node MUST put a Binding
   Identifier mobility option into the Binding Update sent to refresh
   the entry.

   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.  Sending Packets to Home Agent

   When a multihomed mobile node sends packets to its home agent, there
   are conceptually two ways to construct packets.

   1.  Using Home Address Option. (required additional 24 bytes)

   2.  Using IPv6-IPv6 tunnel. (required additional 40 bytes)

   Beside the additional size of packets, no difference is observed
   between these two.  The routing path is always the same and no
   redundant path such as dog-leg route occurs.  However, in this
   document, the mobile node is capable of using multiple care-of
   addresses for outgoing packets.  This is problem in home agent side
   because they must verify the Care-of address for all the packets
   received from the mobile node (i.e. ingress filtering).  When it uses
   the Home Address option, the home agent MAY check the care-of address
   in the packet with the registering binding entries.  This causes
   additional overhead to the home agent.  Therefore, the mobile node



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   SHOULD use the bi-directional tunnel even if it registers a
   binding(s) to the home agent.

5.10.  Bootstrapping

   When a mobile node bootstraps and registers multiple bindings at the
   first time, it SHOULD set O flag in the Binding Identifier mobility
   option.  If old bindings still exists at the Home Agent, the mobile
   node has no way to know which bindings are still remained at the home
   agent.  This scenario happens when a mobile node reboots without
   correct de-registration.  If O flag is used, all the bindings are
   replaced to the new binding(s).  Thus, the garbage bindings are
   surely replaced by new bindings registered with the first Binding
   Update.  If the mobile node receives the Binding Acknowledgment 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
   which is notified by the Binding Acknowledgment.

   For Correspondent nodes, the mobile node cannot use the O flag
   because of no bulk registration support.  Thus, if necessary, it MUST
   sends a regular binding first to overwrite the remaining bindings at
   the correspondent node.  Then, it can re-register the set of bindings
   by using Multiple Care-of Address Registration.




























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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.  How to select the
   most suitable binding from the binding cache database is out of scope
   in this document.

   Whenever a correspondent node searches a binding cache for a home
   address, it SHOULD uses both the Home Address and the BID as the
   search key if it knows the corresponding BID.  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 basically learns the BID when it receives a
   Binding Identifier mobility option.  At the 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 a
   Home Address as performed in Mobile IPv6.  In such case, the first
   matched binding is found.  But which binding entry is returned for
   the normal search depends on implementations.  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 MUST process it with following
   steps.

   First of all, the CoTI message is verified according to [RFC-3775].
   The Binding Identifier mobility option MUST be, then, processed as
   follows:

   o  If a correspondent node does not understand a Binding Identifier
      mobility option, it just ignores and skip this 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 can thus know



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      whether the correspondent can process the Binding Identifier
      mobility option or not, by checking if such option is present in
      the CoT message.

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

   o  Otherwise, the correspondent node MUST include a Binding
      Identifier mobility option which status value MUST be set to zero
      in the returning a CoT message.

   o  All the Binding Identifier mobility options SHOULD be copied from
      the received one except for the Status Field for CoT.  The Care-of
      address field of each Binding Identifier mobility option, however,
      can be omitted, because the mobile node can match a corresponding
      binding update list by using 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].  But 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 a binding for the mobile node.  If the
   Binding Update is for de-registration, the receiver MUST delete all
   existing bindings from its Binding Cache.

   If a Binding Update contains a Binding Identifier mobility option(s),
   it is validated according to section 9.5.1 of [RFC-3775] and the
   following step.

   o  If the home registration flag is set in the Binding Update, the
      home agent MUST carefully operate Duplicate Address Detection
      (DAD) for the received Home Address.  If the home agent has
      already had a binding(s) for the Mobile Node, it MUST avoid
      running DAD check when it receives the Binding Update.

   The receiver node MUST process the Binding Identifier mobility
   option(s) in the following steps.  When a correspondent node sends a
   Binding Acknowledgment, the status value MUST be always stored in the
   Status field of the Binding Acknowledgment and keep the Status field
   of Binding Identifier mobility option to zero.

   For the Home Agent, the status value can be stored in the Status
   field of either a Binding Acknowledgment or a Binding Identifier



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   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 Acknowledgment so that the receiver can examine the
   Status field of each Binding Identifier mobility option for further
   operations.

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

   o  When C flag is specified, the care-of address MUST be given in the
      Binding Identifier mobility option.  Otherwise, 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 presented,
      the receiver MUST support the bulk registration.  Only a home
      agent can accept the bulk registration.  Otherwise, it MUST reject
      the Binding Update and returns the status value set to [MCOA BULK
      REGISTRATION NOT SUPPORT] in the Binding Acknowledgment.

   o  If the Lifetime field of the Binding Update is zero, the receiver
      node deletes the binding entry which BID is same as BID sent by
      the Binding Identifier mobility option.  If the receiver node does
      not have appropriate binding which BID is matched with the Binding
      Update, it MUST reject this de-registration Binding Update for the
      binding cache.  If the receiver is a Home Agent, it SHOULD also
      return the status value set to [not Home Agent for this mobile
      node, 133].

   o  If O flag is set in the de-registering Binding Update, the
      receiver can ignore this flag for de-registration.  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 no
      longer performs proxy NDP for this mobile node until this entry is
      deleted.

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

      *  If C flag is set in the Binding Identifier mobility option, the
         care-of address must be taken from the care-of address field in



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         each Binding Identifier mobility option.

      *  If C flag is not set in the Binding Identifier mobility option,
         the care-of address must be taken from the Source Address field
         of the IPv6 header.

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

   o  Once the care-of address(es) has been retrieved from the Binding
      Update, it starts registering binding(s).

      *  Only if O flag is set in the mobility option, the home agent
         first 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 de-registers the regular binding and
         registers a new binding including BID according to the Binding
         Update.  In this case, the receiver MUST return [MCOA BID
         CONFLICT].

      *  If the receiver node has already registered the binding which
         BID is matched with requesting BID, then it MUST update the
         binding with the Binding Update and returns [0 Binding Update
         accepted].

      *  If the receiver does not have a binding entry which BID is
         matched with the requesting BID, it registers a new binding for
         the BID and returns [0 Binding Update accepted].

   If all the above operations are successfully finished, the Binding
   Acknowledgment containing the Binding Identifier mobility options
   MUST be replied to the mobile node if A flag is set in the Binding
   Acknowledgment.  Whenever a Binding Acknowledgment is returned, all
   the Binding Identifier mobility options stored in the Binding Update
   MUST be copied to the Binding Acknowledgment.  The Care-of address
   field of each Binding Identifier mobility option, however, can be
   omitted, because the mobile node can match a corresponding binding
   update list by using BID.

6.4.  Sending Binding Refresh Request

   When a node sends a Binding Refresh Request for a particular binding
   registering with BID, the node SHOULD contain a Binding Identifier
   mobility option in the Binding Refresh Request.




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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 appeared
   in the Source Address field 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 and MUST send a Binding Error
   message according to RFC3775.  This verification MUST NOT be done for
   a Binding Update.










































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7.  Network Mobility Applicability

   Support of multihomed mobile routers is advocated in the NEMO working
   group (see R12 "The solution MUST function for multihomed MR and
   multihomed mobile networks" in [RFC-4886].  Issues regarding mobile
   routers with multiple interfaces and other multihoming configurations
   are documented in [RFC-4980].

   Since the binding management mechanisms are the same for a mobile
   host operating Mobile IPv6 and for a mobile router operating NEMO
   Basic Support (RFC 3963), our extensions can also be used to deal
   with multiple care-of addresses registration sent from a multihomed
   mobile router.  Figure 5 shows an example format of a Binding Update
   used by a mobile router.

               IPv6 header (src=CoA, dst=HA)
                    IPv6 Home Address Option
                    ESP Header
                    Mobility header
                        -BU
                       Mobility Options
                          - Binding Identifier
                          - Mobile Network Prefix

                       Figure 5: NEMO Binding Update


























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8.  DSMIPv6 Applicability

   Dual Stack Mobile IPv6 (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

   In DSMIPv6, the binding update and acknowledgment exchange is used to
   detect NAT.  Thus, when a mobile node registers its IPv4 care-of
   address bound to IPv6 home address, it MUST first attempt to send a
   Binding Update with Binding Identifier mobility option independently.
   The bulk registration MUST NOT be used for the first binding update
   of the IPv4 care-of address.  The Binding Update MUST be sent to the
   IPv4 home agent address by using UDP and IPv4 headers as shown in
   Figure 6.  It is similar to [DSMIP] except for using BID mobility
   option instead of IPv4 care-of address option.

              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 6: Initial Binding Update for IPv4 Care-of Address

   When the home agent detects NAT for the received binding update, it
   MUST send the NAT detection option in the Binding Acknowledgment.
   Whenever the NAT detection option is found, the mobile node MUST NOT
   use the bulk registration for the IPv4 care-of address.  Otherwise,
   it can send the IPv4 care-of address with other care-of addresses in
   the bulk registration mode.  How to handle NAT is same as [DSMIP].

   If 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 with other care-of addresses.  Figure 7 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 follows the Figure 6 and store
   more BID mobility options in the mobility options field.  Note that
   IPv4 Care-of Address must be registered by non bulk Binding



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   registration, whenever it is changed.  NAT detection MUST be carried
   out for every new IPv4 addresses.

              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 7: Binding Bulk Registration for IPv4 care-of address

   If the IPv4 care-of address is successfully registered, the mobile
   node sets up a relevant tunnel to the home agent according to
   [DSMIP].

   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.  The
   home agent MUST send the binding acknowledgment and all the received
   BID mobility options to the mobile node.  In this case, the IPv4
   address acknowledgment option MUST NOT be included in the Binding
   Acknowledgment.  All the error codes for IPv4 care-of address
   registration MUST be stored in the Status field of the BID mobility
   option.  The IPv4 address acknowledgment option is used only when a
   mobile node requests IPv4 home address management.

8.2.  IPv4 HoA Management

   When the mobile node obtains an IPv4 home address, it MUST store the
   IPv4 Home Address option in the Binding Update.  If the home agent
   accepts the binding update, the mobile node can also 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 binding different set of care-of addresses to each home
   address.

   The home agent MUST returns a binding acknowledgment and IPv4 address
   acknowledgment option to the mobile node only when a mobile node
   requests IPv4 home address mobility management.  In this case, this
   option MUST be presented before any BID options.  The status field of
   the IPv4 address acknowledgment option contains only the error code
   regarding IPv4 home address management.  The error value of 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 Acknowledgments and return routability messages.  IPsec may
   also be used protect all reverse 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 the MIP6-IKEv2
   specification 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 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

   As shown in Section 9, the Multiple Care-of Addresses Registration
   requires IPsec protection for all the signaling between a mobile node
   and its home agent.

   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] and is possible because the care-of addresses specified
   by the mobile node in the binding update messages are not verified by
   home agent (since Mobile IPv6 assumes an existing trust relationship
   between the mobile node and its home agent).

   Although such risk exists in Mobile IPv6, the risk level is escalated
   when simultaneous multiple care-of address bindings are performed.
   One fundamental difference is the degree of risk involved is much
   greater in the simultaneous binding support case.  For a single
   care-of address binding, 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 fundamental difference is the form 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 risk, it is advisable for a home agent to
   employ some form of care-of address verification mechanism before
   using the care-of addresses as a valid routing path to a mobile node.
   Some solutions to advert such problems are described in Appendix.








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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 [RFC3775].

   o  New Successful Status of Binding Acknowledgment:This status code
      must be assigned from the same space as binding acknowledgement
      status codes in [RFC3775].

      *  MCOA NOTCOMPLETE (TBD)

   o  New Unsuccessful Status of Binding Acknowledgment: These status
      codes must also be assigned from the same space as binding
      acknowledgement status codes in [RFC3775].

      *  MCOA MALFORMED (TBD)

      *  MCOA BID CONFLICT (TBD)

      *  MCOA PROHIBITED(TBD)

      *  MCOA BULK REGISTRATION NOT SUPPORTED (TBD)



























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12.  Acknowledgments

   The authors would like to thank Masafumi Aramoto (Sharp Corporation),
   George Tsirtsis (Qualcomm), Keigo Aso (Panasonic), Julien Charbon,
   Tero Kauppinen (Ericsson), Benjamin Lim (Panasonic), Susumu Koshiba,
   Martti Kuparinen (Ericsson), Romain Kuntz (Keio-U), Heikki Mahkonen
   (Ericsson), Hiroki Matutani (Tokyo-U), Koshiro Mitsuya (Keio-U),
   Nicolas Montavont, Koji Okada (Keio-U), Keisuke Uehara (Keio-U),
   Masafumi Watari (KDDI R&D) in alphabetical order, the Jun Murai Lab.
   at KEIO University.


13.  References


13.1.  Normative References

   [RFC-2460] Deering, S. and R. Hinden, "Internet Protocol Version 6
   (IPv6)", IETF RFC 2460, December 1998.

   [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.

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

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

   [RFC-4885] Ernst, T. and H. Lach, "Network Mobility Support
   Terminology", RFC 4885, July 2007.

   [RFC-4886] Ernst, T., "Network Mobility Support Goals and
   Requirements", RFC 4886, July 2007.

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





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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.

   [RFC-3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
   RFC 3972, March 2005.

   [RFC-4866] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
   Optimization for Mobile IPv6", RFC 4866, May 2007.

   [RFC-792] Postel, J., "Internet Control Message Protocol", STD 5, RFC
   792, September 1981.
































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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 8: Multiple Interfaces Attached to a Foreign Link

   Figure 8 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 9: One of Interface Attached to Home Link and Returning Home

   Figure 9 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 9.  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 10: One of Interface Attached to Home Link and Not Returning
                                   Home

   Figure 10 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 11: Utilize Interfaces Attached to both Home and Foreign Links

   Figure 11 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 11 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
   addrss 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.

























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Appendix B.  Changes From Previous Versions

   Changes from draft-ietf-monami6-multiplecoa-04.txt

   o  Binding Unique Identifier is renamed to Bidning Identifier

   o  New Status Code [MCOA NOTCOMPLETE], the home agent uses this
      status code in the Binding Acknowledgement when not all the
      bindings are accepted in the bulk registration.

   o  [MCOA FLAG CONFLICTS] are now merged with [MCOA MALFORMED]

   o  Add care-of address verification issue in the Security
      Consideration, the text is proposed by Benjamin Lim.

   o  Support DSMIPv6

   o  Support simultaneous foreign and home location.  (Section 5.5)

   o  Editorial updates, thanks George Tsirtsis for detailed comments!


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/


   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




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   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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