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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
Internet-Draft                                           Keio University
Intended status: Standards Track                                T. Ernst
Expires: January 10, 2008                                          INRIA
                                                               K. Nagami
                                                           INTEC NetCore
                                                          V. Devarapalli
                                                         Azaire Networks
                                                            July 9, 2007


                Multiple Care-of Addresses Registration
                 draft-ietf-monami6-multiplecoa-03.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on January 10, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).









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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
     3.1.  Multiple Care-of Addresses Registration  . . . . . . . . .  7
     3.2.  Multiple Bindings Management . . . . . . . . . . . . . . .  7
     3.3.  Returning Home . . . . . . . . . . . . . . . . . . . . . .  8

   4.  Mobile IPv6 Extensions . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Binding Cache Structure and Binding Update List  . . . . . 10
     4.2.  Message Format Changes . . . . . . . . . . . . . . . . . . 10
       4.2.1.  Binding Unique Identifier sub-option . . . . . . . . . 10
       4.2.2.  Binding Acknowledgment . . . . . . . . . . . . . . . . 12

   5.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 14
     5.1.  Management of Care-of Addresses and Binding Unique
           Identifier . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.2.  Return Routability: Sending CoTI and Receiving CoT . . . . 14
     5.3.  Binding Registration . . . . . . . . . . . . . . . . . . . 15
     5.4.  Binding Bulk Registration  . . . . . . . . . . . . . . . . 16
     5.5.  Binding De-Registration  . . . . . . . . . . . . . . . . . 16
     5.6.  Returning Home . . . . . . . . . . . . . . . . . . . . . . 17
     5.7.  Using Alternate care-of address  . . . . . . . . . . . . . 18
     5.8.  Receiving Binding Acknowledgment . . . . . . . . . . . . . 19
     5.9.  Receiving Binding Refresh Request  . . . . . . . . . . . . 20
     5.10. Sending Packets to Home Agent  . . . . . . . . . . . . . . 20
     5.11. Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 21

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

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

   8.  IPsec and IKEv2 interaction  . . . . . . . . . . . . . . . . . 28
     8.1.  Use of Care-of Address in the IKEv2 exchange . . . . . . . 28
     8.2.  Transport Mode IPsec protected messages  . . . . . . . . . 29
     8.3.  Tunnel Mode IPsec protected messages . . . . . . . . . . . 29
       8.3.1.  Tunneled HoTi and HoT messages . . . . . . . . . . . . 29
       8.3.2.  Tunneled Payload Traffic . . . . . . . . . . . . . . . 30

   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 31



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   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 32

   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 33

   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 33
     12.2. Informative References . . . . . . . . . . . . . . . . . . 34

   Appendix A.  Example Configurations  . . . . . . . . . . . . . . . 34

   Appendix B.  Changes From Previous Versions  . . . . . . . . . . . 38

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
   Intellectual Property and Copyright Statements . . . . . . . . . . 40





































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1.  Introduction

   A mobile node should use various type of network interfaces to obtain
   durable and wide area network connectivity.  Assumed scenarios and
   motivations for multiple points of attachment, and benefits for doing
   it are discussed at large in [10].

   IPv6 [1] conceptually allows a node to have several addresses on a
   given interface.  Consequently, Mobile IPv6 [2] 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 [3] is based on Mobile IPv6, the
   same issues applies to a mobile node acting as mobile router.
   Multihoming issues pertaining to mobile nodes operating Mobile IPv6
   and mobile routers operating NEMO Basic Support are respectively
   discussed [4] and [11] in Monami6 and NEMO Working Group.

   In this document, we thus propose a new identification number called
   Binding Unique Identification (BID) number for each binding cache
   entry to accommodate multiple bindings registration.  The BID is
   assigned to either the interfaces or care-of addresses bound to a
   single home address of a mobile node.  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

   Terms used in this draft are defined in [2], [5] and [6].  In
   addition or in replacement of these, the following terms are defined
   or redefined:

   Binding Unique 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 is generated to
      register multiple bindings in the binding cache for a given
      address in a way it cannot be duplicated with another BID.  The
      zero value and a negative value MUST NOT be used.  After being
      generated by the mobile node, the BID is stored in the Binding
      Update List and is sent by the mobile node by means of a sub-
      option of a 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.

      The BID is conceptually assigned to a binding.  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 Unique Identifier sub-option

      The Binding Unique Identifier sub-option is used to carry the BID.

   Bulk Registration

      A mobile node can register multiple bindings 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 which can be stored in a Binding Update.  The
      bulk registration is supported only for home registration and
      deregistration as explained in Section 5.5.  Note that a mobile
      node should not try to perform bulk registration with
      correspondent nodes.

   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 [7].







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3.  Protocol Overview

   We propose a new identification number (BID) to distinguish multiple
   bindings pertaining to the same Home Address.  The procedures for the
   mobile node to register multiple bindings are described in the
   paragraphs below.

3.1.  Multiple Care-of Addresses Registration

   Once a mobile node gets several IPv6 global addresses on interfaces,
   it can register these addresses with its home agent (home
   registration).  If the mobile node wants to register multiple
   bindings to its home agent, it MUST generate a BID for each care-of
   address and record it into the binding update list.  The mobile node
   then registers its care-of addresses by sending a Binding Update with
   a Binding Unique Identifier sub-option.  The BID MUST be put in the
   Binding Unique Identifier sub-option.  After receiving the Binding
   Update, the home agent verifies the request and records the binding
   in its binding cache.  If the newly defined sub-option is present in
   the Binding Update, the home agent MUST copy the BID from the Binding
   Update to the corresponding field in the binding entry.  Even if
   there is already an entry for the mobile node, the home agent MUST
   register a new binding entry for the BID stored in the Binding Unique
   Identifier sub-option.  The mobile node registers multiple care-of
   addresses either independently (in individual BUs) or multiple at
   once (in a single BU).

   If the mobile node wishes to register its binding with a
   correspondent node, it must operate return routability operations.
   The mobile node MUST manage a Care-of Keygen Token per care-of
   address.  If it is necessary (ex.  Care-of Keygen token is expired),
   the mobile node exchanges CoTI and CoT for the releative care-of
   addresses.  When the mobile node 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 by using Binding Unique Identifier sub-option as well
   as the other sub-options specified in RFC 3775.  For simplicity, the
   bulk registration is not supported for correspondent nodes in this
   document.

3.2.  Multiple Bindings Management

   The BID is used as a search key for a corresponding entry in the
   binding cache in addition to the Home Address.  When a home agent and
   a correspondent node check the binding cache database for the mobile
   node, it searches a corresponding binding entry with the Home Address
   and BID of the desired binding.  If necessary, a mobile node can use



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   policy and filter information to look up the best binding per
   sessions, flow, packets, but this is out of scope in this document
   and is currently discussed in Monami6 WG.

   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.

   When one of the care-of addresses has changed, the mobile node sends
   a Binding Update with the new care-of address and the corresponding
   BID.  The receiver of the Binding Update updates the binding which
   BID matches the BID contained in the received Binding Unique
   Identifier sub-option.  The mobile node can manage each binding
   independently owing to BID.

   If the mobile node decides to act as a regular mobile node compliant
   with [2] , it just sends a Binding Update without a Binding Unique
   Identifier sub-option (i.e. normal Binding Update).  The receiver of
   the Binding Update registers only a single binding for the mobile
   node and, if necessary, deletes all the bindings registering with a
   BID.  Note that the mobile node can continue to use BID even if only
   a single binding is active at some time.

3.3.  Returning Home

   When the mobile node returns home, there are two situations, since
   the home agent defends the mobile node's Home Address by using the
   proxy neighbor advertisement.  It is impossible to utilize all the
   interfaces when one interface is attached to the home link and the
   others are attached to foreign links.  If the proxy Neighbor
   Advertisement for the Home Address is stopped, packets are always
   routed to the interface attached to the home link.  If proxy is not
   stopped, packets are never routed to the interface attached to the
   home link.  The decision whether a mobile node returns home or not is
   up to implementers.

   The first situation is when a mobile node wants to return home with
   interface attached to the home link.  In this case, the mobile node
   MUST de-register all the bindings by sending a Binding Update with
   lifetime set to zero.  The mobile node MAY NOT put any Binding Unique
   Identifier sub-option in this packet.  Then, the receiver deletes all
   the bindings from its binding cache database.  A home agent MUST stop
   proxy neighbor advertisement for the home address of the mobile node.

   The second situation is when a mobile node does not want to return
   home, though one of its interfaces is attached to its home link.  The
   mobile node disables the interface attached to the home link and



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   keeps using the rest of interfaces attached to foreign links.  In
   this case, the mobile node sends a de-registration Binding Update for
   the interface attached to the home link with the Binding Unique
   Identifier sub-option.  The receiver of the de-registration Binding
   Update deletes only the relative binding entry from the binding cache
   database.  The home agent does not stop proxying neighbor
   advertisement as long as there are still bindings for the other
   interfaces.  It is important to understand that this scenario is not
   the most efficient because all the 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 HA.

   In the above two cases, a mobile node cannot use interfaces attached
   to both home and foreign links simultaneously.  This restriction is
   related to the Proxy NDP operation on a Home Agent.  The Home Agent
   needs to defend a mobile node's home address by the proxy NDP for
   packet interception, while the mobile node defends its home address
   by regular NDP to send and receive packets at the interface attached
   to the home link.  Two nodes, Home Agent and Mobile Node, compete ND
   state.  This will causes address duplication problem at the end.
   This document recommends not to use the Proxy NDP for this scenario.
   When one of the Mobile Node's interface is attached to the home link
   and the other is attached to the foreign link and it decides to
   utilize both interfaces, it notifies the Home Agent using the H flag
   which means the Mobile Node is attached to the home link.  If the
   proxy NDP is disabled, the main problem can be solved.  In the
   Multiple Care-of Address Registration case, the elimination of Proxy
   NDP enable that Mobile Node and Home Agent maintain multiple
   bindings, one of the Mobile Node's interface is attached to the home
   link and the other is attached to the foreign link.





















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4.  Mobile IPv6 Extensions

   In this section are described 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 following additional items are required in the binding cache and
   binding update list structure.

   BID

      The value MUST be zero if the Binding Unique identifier does not
      appear in a Binding Update.

4.2.  Message Format Changes

4.2.1.  Binding Unique Identifier sub-option

   The Binding Unique Identifier sub-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 Unique ID (BID)   |     Status    |C|O|H|Reserved |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
       +                                                               +
       +                    care-of address (CoA)                      +
       +                                                               +
       +---------------------------------------------------------------+


                         Figure 1: BID Sub-Option

   Type

      Type value for Binding Unique Identifier will be assigned later.

   Length







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      Length value MUST be 4 when C flag is unset.  On the other hand if
      C flag is set, Length value MUST be set to 20.

   Binding Unique ID (BID)

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

   Status

      When the Binding Unique Identifier sub-option is included in a
      Binding Acknowledgment, this field indicates the status
      correspondent to each binding.  The mobile node knows the
      registration status of each binding.  The status is 8-bit unsigned
      integer.  The possible status codes are listed below.  If the
      status field is below 128, it indicates that the binding
      registration was successful.

      MCOA ACCEPTING BID (0)

         The registration of the correspond binding is successfully
         operated.

      MCOA REASON UNSPECIFIED (128)

         Registration failed because of unknown errors

      MCOA INCOMPLIANT (129)

         Registration failed because Binding Unique Identifier sub-
         option is not compliant.

      MCOA BID CONFLICT (130)

         It indicates that a regular binding (ie without the BID set) is
         already registered for the home address, and is conflicting
         with a received Binding Update which BID was set.

   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 Unique Identifier sub-
      option.  This flag must be used whenever a mobile node sends
      multiple bindings in a single Binding Update, i.e. bulk
      registration.





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   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 for Home Registration and
      Deregistration.

   Home Binding (H) flag

      This flag indicates that the mobile node is attached to the home
      link.  This flag is valid for Home Registration, Deregistration
      and bulk registration.

   Reserved

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

   Care-of Address

      Only when C flag is set, only a single Care-of Address matched to
      the BID is stored.  This field is valid only if a Binding Unique
      Identifier sub-option is stored in Binding Update message.
      Otherwise, this field can be omitted.  The receiver SHOULD ignore
      this field if the sub-option is presented in other than Binding
      Update.

4.2.2.  Binding Acknowledgment

   The message format of Binding Acknowledgment does not change, but
   operations listed below are added in this draft.

   If a Binding Unique Identifier sub-option is included in a Binding
   Update with the A flag set, a receiver MUST reply a Binding
   Acknowledgment.  The receiver node MUST include the same Binding
   Unique Identifier sub-option(s) in the Binding Acknowledgment.  The
   receiver MUST specify relative status in the Status field of the
   Binding Acknowledgment.

   There are two status fields: the Status field of a Binding
   Acknowledgment and the Status field of a Binding Unique Identifier
   sub-option.  In this specification, the Status field of a Binding
   Acknowledgment indicates the registration status of a "Binding
   Update".  The status value in the Binding Acknowledgment is for all
   Binding Unique Identifier sub-options stored in the Binding
   Acknowledgment.  For example, if the status value is 134 in the
   status field of the Binding Acknowledgment, all the care-of addresses
   stored in the Binding Unique Identifier sub-options are rejected
   because the duplicate address detection has failed on the home agent.



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   The status field of the Binding Unique Identifier sub-option only
   informs the receiver about the binding relative to the sub-option.
   Whether each Care-of address has been successfully registered
   successfully or not is given in the Status field of each Binding
   Unique Identifier sub-option.

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

   MCOA PROHIBITED(TBD)

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

   MCOA BULK REGISTRATION NOT SUPPORTED (TBD)

      The bulk binding registration is not supported.

   MCOA FLAG CONFLICTS (TBD)

      The flags of the sub-options presented in a Binding Update
      conflicts.





























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5.  Mobile Node Operation

5.1.  Management of Care-of Addresses and Binding Unique Identifier

   There are two cases when a mobile node has several Care-of Addresses:

   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 up to implementers.

   A mobile node assigns a BID to each care-of address when it wants to
   register them simultaneously with its Home Address .  The value
   should be generated from a value comprised between 1 to 65535.  Zero
   and negative values MUST NOT be taken 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 send a CoTI 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 Unique
   Identifier sub-option in a Care-of Test Init message.  It MUST NOT
   set the C and O flag in the sub-option.

   The receiver (i.e. correspondent node) will calculate a care-of
   keygen token as specified in [2] and reply a Care-of Test message
   which contains a Binding Unique Identifier sub-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 [2] and the
   Binding Unique Identifier sub-option in the Care-of Test MUST be
   processed as follows:

   o  If a Binding Unique Identifier sub-option is not presented in CoT
      in reply to the CoTI containing the Binding Unique Identifier sub-
      option, a correspondent node does not support the Multiple Care-of



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      Address registration.  Thus, the mobile node MUST NOT use a
      Binding Unique Identifier sub-option in the Binding Update.  It
      MUST send a regular Binding Update (i.e. no BID) to the
      correspondent node [2].  The Mobile Node MAY skip resending
      regular CoTI message and use the received care-of keygen token for
      the regular Binding Update, because the correspondent node just
      ignores and skip the Binding Unique Identifier sub-option and
      calculates the care-of keygen token as [2] specified.

   o  If the status field of a Binding Unique Identifier sub-option is
      set to [MCOA INCOMPLIANT], the received care-of keygen token MUST
      NOT be used for sending a Binding Update.  It MUST re-send a
      Care-of Test Init message again with a corrected Binding Unique
      Identifier sub-option which C flag MUST be unset.

   o  If the status field is set to less than 128, it sends a Binding
      Update through Return Routability procedure.

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, this decision
   is out-of scope in this document.  If a mobile node decides not to
   register multiple care-of addresses, it completely follows the
   standard RFC 3775 specification.

   If a mobile node needs to register multiple Care-of Addresses, it
   MUST use BID to identify a care-of address.  The mobile node includes
   a Binding Unique Identifier sub-option in the Mobility Option field
   of a Binding Update.  The BID is copied from a corresponding Binding
   Update List entry to the BID field of the Binding Unique Identifier
   sub-option.  If the mobile node wants to replace existing registered
   bindings on the home agent to the binding entry(s) in the Binding
   Update, it can set O flag.

   If a mobile node registers bindings to a correspondent node, it MUST
   have both active home and care-of keygen tokens for Kbm (see Section
   5.2.5 of [2].  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, it sends a Binding Update which contains a
   Binding Unique Identifier sub-option.  The Binding Update is
   protected by a Binding Authorization Data sub-option placed after the
   Binding Unique Identifier sub-option.  The Mobile Node MUST NOT set
   the C flag in the Binding Unique Identifier sub-option.






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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 from a
   specific interface which has wider bandwidth.

   In this case, a mobile node sets the C flag in a Binding Unique
   Identifier sub-option and stores the particular care-of address in
   the Binding Unique Identifier sub-option.  When the C flag is set,
   the length field of the suboption MUST be set to 20.  The mobile node
   can store multiple sets of a Binding Unique Identifier sub-option in
   a Binding Update.  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.  In the bulk registration, all the
   other binding information such as Lifetime, Sequence Number, binding
   Flags are shared among the bulked Care-of Addresses.  Whether a
   mobile node registers multiple Care-of Addresses separately or in
   bulk is up to implementations.

   In the bulk registration, the Sequence Number field of a Binding
   Update SHOULD be carefully configured.  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.

   When multiple Binding Unique Identifier sub-options are presented,
   the flag field of all the sub-options MUST have the same value.  For
   example, if C flag is set, the same flag MUST be set to all the sub-
   options.

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.  A
   Binding Unique Identifier sub-option is not required.  See
   Section 6.3 for details.

   If a mobile node wants to delete a particular binding from its home
   agent and correspondent nodes (e.g. from foreign link), the mobile
   node simply sets zero lifetime or uses the home address as the source



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   address in a Binding Update.  The Binding Update MUST contain a
   relative Binding Unique Identifier Sub-option (C flag MUST NOT be
   set).  The receiver will remove only the care-of address that matches
   the specified BID.

   On the other hand, when a mobile node decides to return home (ie only
   uses its interface attached to the home link), it MUST de-register
   all the registered bindings.  To do so, the mobile node stores
   multiple Binding Unique Identifier sub-options in a Binding Update
   which lifetime is set to zero or which source address is set to the
   Home Address.  C flag MUST be specified in all the Binding Unique
   Identifier sub-options.  The care-of addresses field of each sub-
   option MAY be omitted, because the receiver will remove all the
   care-of addresses which matches the specified BID.

   O flag is always ignored if a Binding Update is for binding de-
   registration

5.6.  Returning Home

   When a mobile node returns home, it MUST de-register all bindings
   with the home agent.

   Although the mobile node SHOULD delete the bindings with
   Correspondent Nodes as well, the node MAY still keep the binding of
   the other interface active attached to foreign links only at the
   Correspondent Nodes.  In such case, the mobile node still receives
   packets at the other interface attached to a foreign link thanks to
   route optimization.  The mobile node also receives packets at the
   interface attached to the home link when correspondent nodes does not
   use route optimization.

   Note that when the mobile node does not want to return home even if
   one of interfaces is attached to the home link, the mobile node MUST
   disable the interface.  Otherwise, address duplication will be
   observed because the home agent still defend the Home Address by the
   proxy neighbor advertisement and the mobile node also enables the
   same Home Address on the home link.  After disabling the interface
   attached to the home link, the mobile node MUST delete the binding
   for the interface by sending a de-registration binding update.  The
   de-registration binding update must be sent from one of active
   interfaces attached to foreign links.  As a result, the mobile node
   no longer receives packets at the interface attached to the home
   link.  All packets are routed to other interfaces attached to a
   foreign link.

   Alternatively, the Mobile Node may choose to activate both the
   interfaces attached to the home link and the foreign link, and



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   communicates with all of the interfaces.  The Mobile Node notifies
   the Home Agent using the H flag which means the Mobile Node is
   attached to the home link.  The Mobile Node may notify the care-of
   address of the interface(s) attached to the foreign link(s) in the
   same message using bulk registration.  The Home Agent then no longer
   uses Proxy Neighbor Advertisement to intercept packets and the Mobile
   Node can utilize both of interfaces attached to the home link and the
   foreign link simultaneously.  The Home Agent can intercept packets by
   IP routing, but not by proxy Neighbor Discovery.

   When the Mobile Node returns home, it de-registers a binding for the
   interface.  While the bindings for the interfaces attached to the
   foreign link are still active.  Intercepting packets, the Home Agent
   can decide whether it tunnels to the foreign interface or routes to
   the home interface of the Mobile Node.  To do so, the Home Agent must
   know that the Mobile Node is back to the home link.  However, if the
   binding is deleted according to [2], there is no way for the Home
   Agent to know that the Mobile Node is at the home, too.  The Home
   Agent SHOULD invalidate the binding for the interface attached to the
   home link and MAY NOT delete it.  It can alternatively mark that the
   Mobile Node is at the home link, too.  As an example, the Home Agent
   inserts the Home Address of the Mobile Node in the Care-of Address
   field of the Mobile Node.  The binding is named "Home Binding" in
   this doc.  The Home Agent MAY manage this home binding as same as the
   other binding entry in terms of lifetime validation, etc.  The Mobile
   Node MAY send multiple binding de- registration to keep this home
   binding active.  Alternatively, the Home Agent can use infinity
   lifetime for the lifetime of the home binding.  When the Mobile Node
   leaves the Home Link, it can update the home binding to the normal
   binding.  Before that, the Home Agent believes the Mobile Node is at
   the home and may route packets for the Mobile Node to the Home Link.

5.7.  Using Alternate care-of address

   A mobile node can use an alternate care-of address in a following
   situation.  One care-of address becomes invalid (e.g because the link
   where it is attached to is no longer available) and MUST be deleted.
   In such case, the mobile node can not send a Binding Update from the
   care-of address because the interface's link is lost.  The mobile
   node needs to de-register the remote binding of the care-of address
   through one of its active care-of addresses.

   In this case, the mobile node include both Alternate Care-of Address
   sub-option and Binding Unique Identifier sub-option in a Binding
   Update.  An Alternate care-of address sub-option can be presented
   only once in a Binding Update after a Binding Unique Identifier sub-
   option.  The care-of address stored in an Alternate Care-of address
   sub-option is replaced the address in the source address field as



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   same as [2] specified.

   If C flag is set in a Binding Unique Identifier sub-option, an
   Alternate Care-of Address sub-option SHOULD NOT be used.  A receiver
   uses the care-of addresses and BID stored in each Binding Unique
   Identifier sub-option to modify corresponding binding cache entries.
   Any address can be specified in the Source address field of the IPv6
   header of the Binding Update even without an Alternate Care-of
   Address sub-option.

5.8.  Receiving Binding Acknowledgment

   The verification of a Binding Acknowledgment is the same as in 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 Unique Identifier sub-option in a
   Binding Update with A flag set, a Binding Acknowledgment MUST have a
   Binding Unique Identifier sub-option in the Mobility Options field.
   If no such sub-option appears in the Binding Acknowledgment replied
   to the Binding Update for the multiple care-of address registration,
   this means that the originator node of this Binding Acknowledgment
   might not recognize the Binding Unique Identifier sub-option.  The
   mobile node SHOULD stop registering multiple care-of addresses by
   using a Binding Unique Identifier sub-option.  If the originator is
   the home agent, the mobile node MAY try to discover a new home agent
   supporting the multiple care-of address registration or give up with
   the multiple care-of address registration.

   If a Binding Unique Identifier sub-option is present in the received
   Binding Acknowledgment, the mobile node checks the Status field of
   the Binding Acknowledgment.  If the status code indicates successful
   registration (less than 128), the originator successfully registered
   the binding information and BID for the mobile node.

   If the status code of the Binding Acknowledgment is greater than or
   equal to 128, the mobile node proceeds with relevant operations
   according to the status code of the Binding Acknowledgment.  The
   status value of the stored Binding Unique Identifier sub-option may
   be used to decide further operation.

   o  If the Status value of the Binding Acknowledgment 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 [2] 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



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      sending the Binding Acknowledgment.

   o  If [MCOA FLAG CONFLICTS] is specified in the Binding
      Acknowledgment, it indicates that the different flag values are
      used in Binding Unique Identifier sub-options in a Binding Update.
      If the C flag is set, all sub-options MUST have C flag.  It is
      same for O flag.  How to handle other error status codes is
      specified in [2].

   The mobile node also learn detailed registration status from the
   Status field of each Binding Unique Identifier sub-option.  If the
   value is greater than or equal to 128, the mobile node proceeds with
   relevant operations according to the status value.

   o  If [MCOA BID CONFLICT] is specified, the binding entry specified
      by the Binding Unique Identifier sub-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 sending the Binding Acknowledgment.

5.9.  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
   Unique Identifier sub-option, this Binding Refresh Request requests a
   binding indicated by the BID.  The mobile node SHOULD update only the
   respective binding.  The mobile node MUST put a Binding Unique
   Identifier sub-option into the Binding Update sent to refresh the
   entry.

   If no Binding Unique Identifier sub-option is present in a Binding
   Refresh Request, the mobile node sends a Binding Update according to
   its Binding Update List for the requesting node.  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.

5.10.  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)




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   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 or triangular 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.  Therefore, the mobile
   node SHOULD use the bi-directional tunnel even if it registers a
   binding(s) to the home agent.  When it uses the Home Address option,
   the home agent MAY reject the packets because the Care-of address in
   the packet and the first found Care-of Address in the binding Cache
   of the home agent are different.  The mobile node then receive
   Binding Error for the packet drop.

5.11.  Bootstrapping

   When a mobile node bootstraps and registers multiple bindings at the
   first time, it SHOULD set O flag in the Binding Unique Identifier
   sub-option. when old bindings still exists at the Home Agent and
   Correspondent Nodes, the mobile node has no way to verify which
   bindings are left as a garbage in those nodes.  This scenario happens
   when a mobile node reboots without correct deregistration.  If O flag
   is used, all the bindings are replaced to the new binding(s).  Thus,
   the garbage bindings are surely removed by the first Binding Update.
   XXX SEQ























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6.  Home Agent and Correspondent Node Operation

6.1.  Searching Binding Cache with Binding Unique 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 2: Searching the Binding Cache

   A correspondent node basically learns the BID when it receives a
   Binding Unique Identifier sub-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 Care-of Test Init message which
   contains a Binding Unique Identifier sub-option, it MUST process it
   with following steps.

   First of all, the Care-of Test Init message is verified according to
   [2].  The Binding Unique Identifier sub-option MUST be processed as
   follows:





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   o  If a correspondent node does not understand a Binding Unique
      Identifier sub-option, it will ignore and skip this option.  The
      calculation of a care-of keygen token will thus be done without a
      BID value.  After regular processing of HoTI message according to
      [2], it will return a Care-of Test message without use of a
      Binding Unique Identifier sub-option.  The mobile node can thus
      know whether its correspondent can process or not the Binding
      Unique Identifier sub-option by checking if such option is present
      in the Care-of Test message.

   o  If C flag is set in the sub-option, the Correspondent Node SHOULD
      NOT calculate a care-of keygen token and MUST include a Binding
      Unique Identifier sub-option which status value set to [MCOA
      INCOMPLIANT] in the returned Care-of Test message.  All the fields
      of the Care-of Test message MUST be set to zero.  All the Binding
      Unique Identifier sub-options SHOULD be copied from the received
      one except for the Status Field and the Care-of Address field.

   o  If O flag is set in the sub-option, the Correspondent Node can
      ignore this flag and can process it as described in the next
      bullet.

   o  Otherwise, the correspondent node MUST include a Binding Unique
      Identifier sub-option which status value MUST be set to [MCOA
      ACCEPTING BID] in the returning a Care-of Test message.  The
      Binding Unique Identifier sub-option SHOULD be copied from the
      received one except for the Status Field and the Care-of address
      Field.

6.3.  Processing Binding Update

   If a Binding Update does not contain a Binding Unique Identifier sub-
   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 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.

   On the other hand, if a Binding Update contains a Binding Unique
   Identifier sub-option(s), the Binding Update is also validated
   according to section 9.5.1 of [2] and the following step.

   o  If the home flag is set in the Binding Update, the home agent MUST
      carefully operate 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 when it receives the Binding Update.




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   If a Binding Unique Identifier sub-option(s) is present, the receiver
   node MUST process the sub-option.

   o  The length value is examined.  The length value MUST be either 4
      or 20 depending on C flag.  If the length is incorrect, the
      receiver MUST rejects the Binding Update and returns all the
      received Binding Unique Identifier sub-option which status value
      is set to [MCOA INCOMPLIANT].  The status field of the Binding
      Acknowledgment MUST be set to [REASON UNSPECIFIED, 128].

   o  When C flag is set, the receiver MUST support the bulk
      registration.  Otherwise, it MUST reject the Binding Update and
      returns all the received Binding Unique Identifier sub-option
      which status value is set to [MCOA REASON UNSPECIFIED].  The
      status field of the Binding Acknowledgment MUST be set to [MCOA
      BULK REGISTRATION NOT SUPPORTED].

   o  When either C or O flag is set, the flags field of all the Binding
      Unique Identifier sub-option stored in the same Binding Update
      MUST be equal.  Otherwise, the receiver MUST reject the Binding
      Update and returns all the received Binding Unique Identifier sub-
      option which status value is set to [MCOA REASON UNSPECIFIED].
      The status field of the Binding Acknowledgment MUST be set to
      [MCOA FLAG CONFLICTS].

   o  When C flag is specified, the care-of address MUST be given in the
      Binding Unique Identifier sub-option.  Otherwise, the receiver
      MUST reject the Binding Update and returns all the received
      Binding Unique Identifier sub-option which status value is set to
      [MCOA INCOMPLIANT].  The status field of the Binding
      Acknowledgment MUST be set to [REASON UNSPECIFIED, 128].

   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 Unique Identifier sub-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.  If the receiver is a Home Agent, it SHOULD also return a
      Binding Acknowledgment to the mobile node, in which the Status
      field is set to [not Home Agent for this mobile node, 133].  If O
      flag is set in the deregistering Binding Update, the receiver can
      ignore this flag for deregistration.  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



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      Care-of address is picked from the Binding Update packet as
      follows:

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

      *  If C flag is not set in the Binding Unique Identifier sub-
         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 sub-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 sub-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 specify [MCOA BID
         CONFLICT] to the Binding Unique Identifier sub-option which is
         replied to the Mobile Node.  The Status field of the replying
         Binding Acknowledgment MUST be set to [Binding Update ACCEPTED,
         0].

      *  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.

      *  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.

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



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6.4.  Sending Binding Refresh Request

   When either a correspondent node or home agent notices that a
   registered binding will be expired soon, it MAY send a Binding
   Refresh Request.  If the registered binding has BID, the
   correspondent node SHOULD contain a Binding Unique Identifier sub-
   option in the Binding Refresh Request.  Then, the Correspondent Node
   can receive a Binding Update with a Binding Unique Identifier sub-
   option and can update only the particular binding.  If the registered
   binding does not have BID, then the correspondent node sends a
   Binding Refresh Request without the sub-option.

6.5.  Receiving Packets from Mobile Node

   When a correspondent 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 [8].

   Issues regarding mobile routers with multiple interfaces and other
   multihoming configurations are documented in [11].

   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.





































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8.  IPsec and IKEv2 interaction

   Mobile IPv6 [2] and the NEMO protocol [3] 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 [9] 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.

8.1.  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 Unique Identifier sub-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.

8.2.  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.

8.3.  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.

8.3.1.  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.

8.3.2.  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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9.  Security Considerations

   As shown in Section 8, the Multiple Care-of Addresses Registration
   requires IPsec protected all the signalings between a mobile node and
   its home agent.














































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10.  IANA Considerations

   The following Extension Types MUST be assigned by IANA:

   1.  Binding Unique Identifier sub-option type

   2.  New Status of Binding Acknowledgement












































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11.  Acknowledgments

   The authors would like to thank Masafumi Aramoto (Sharp Corporation),
   Keigo Aso (Panasonic), Julien Charbon, Tero Kauppinen (Ericsson),
   Benjamin Koh (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.


12.  References

12.1.  Normative References

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

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

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

   [4]   Montavont, N., Wakikawa, R., Ernst, T., Ng, C., and K.
         Kuladinithi, "Analysis of Multihoming in Mobile IPv6",
         draft-ietf-monami6-mipv6-analysis-02 (work in progress),
         February 2007.

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

   [6]   Ernst, T. and H. Lach, "Network Mobility Support Terminology",
         draft-ietf-nemo-terminology-06 (work in progress),
         November 2006.

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

   [8]   Ernst, T., "Network Mobility Support Goals and Requirements",
         draft-ietf-nemo-requirements-06 (work in progress),
         November 2006.

   [9]   Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
         IKEv2 and the revised IPsec Architecture",
         draft-ietf-mip6-ikev2-ipsec-08 (work in progress),
         December 2006.



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12.2.  Informative References

   [10]  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-01 (work in
         progress), October 2006.

   [11]  Ng, C., Paik, Ernst, and C. Bagnulo, "Analysis of Multihoming
         in Network Mobility Support",
         draft-ietf-nemo-multihoming-issues-06 (work in progress),
         June 2006.


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]




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         Figure 3: Multiple Interfaces Attached to a Foreign Link

   Figure 3 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.


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

     Binding Cache Database:
        home agent's binding (Proxy neighbor advertisement is inactive)
              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 4: One of Interface Attached to Home Link and Returning Home

   Figure 4 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 4.  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 when MN is
   attached to the home link, it can still send Binding Updates for
   other active care-of addresses (CoA2 and CoA3).  If CN has bindings,
   packets are routed to each Care-of Addresses directly.  Any packet
   arrived at HA are routed to the primary interface.







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

     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]
        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 5: One of Interface Attached to Home Link and Not Returning
                                   Home

   Figure 5 depicts the scenario where MN disables the interface
   attached to the home link and communicates with the interfaces
   attached to foreign links.  The HA and the CN have the binding
   entries listed in their binding cache database.  MN disable the
   interface attached to the home link, because the HA still defends the
   home address of the MN by proxy neighbor advertisements.  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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                    +----+
                    | CN |
                    +--+-+
                       |
                   +---+------+          +----+
            +------+ Internet |----------+ HA |
            |      +----------+          +--+-+
        CoA2|                               |   Home Link
         +--+--+                 --+----+---+------
         |  MN +===================+    |
         +--+--+                        |
            |                           |
            +---------------------------+

     Binding Cache Database:
        home agent's binding (Proxy neighbor advertisement is inactive)
              none
        correspondent node's binding
              binding [a:b:c:d::EUI  care-of address2  BID2]


   Figure 6: Several Interfaces Attached to Home Link and Returning Home

   Figure 6 depicts the scenario where multiple interfaces of MN are
   attached to the home link.  The HA and CN have the binding entries
   listed in Figure 6 in their binding cache database.  The MN can not
   use the interface attached to a foreign link unless a CN has a
   binding for the interface.  All packets which arrive at the HA are
   routed to one of the MN's interfaces attached to the home link.






















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Appendix B.  Changes From Previous Versions

   Changes from draft-ietf-monami6-multiplecoa-02.txt

   o  Add Security Considerations

   o  Add IANA Considerations

   o  Add H flag for BID option and Modify Returning Home.


Authors' Addresses

   Ryuji Wakikawa
   Keio University
   Department of Environmental Information, 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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