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Versions: 00 01

MIP6/NEMO Working Group                                   Ryuji Wakikawa
INTERNET DRAFT                                      Keio University/WIDE
Category:  Individual                                     Pascal Thubert
03 Mar 2006                                                Cisco Systems
                                                       Vijay Devarapalli
                                                                   Nokia

                Inter Home Agents Protocol Specification
                draft-wakikawa-mip6-nemo-haha-spec-01.txt


   Status of This Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 30, 2006.


   Copyright Notice

   Copyright (C) The Internet Society (2006).


   Abstract

   This document provides the protocol specification of the inter Home
   Agent protocol designed for both Mobile IPv6 and the NEMO Basic
   Support protocol.  This document describes Home Agent configurations,
   message formats and Mobile Host, Mobile Router, and Home Agent
   operations.


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                                  Contents


Status of This Memo                                                    1

Copyright Notice                                                       1

Abstract                                                               1

 1. Introduction                                                       3

 2. Terminology                                                        4

 3. Variety of Home Agent Configuration                                5
     3.1. With Home Link  . . . . . . . . . . . . . . . . . . . . .    6
     3.2. Without Home Link . . . . . . . . . . . . . . . . . . . .    8

 4. Message Formats                                                    9
     4.1. New Mobility Header Messages  . . . . . . . . . . . . . .    9
           4.1.1. Home Agent HELLO Message  . . . . . . . . . . . .    9
           4.1.2. Binding Information Request Message . . . . . . .   10
           4.1.3. Binding Information Update Message  . . . . . . .   12
           4.1.4. Binding Information Acknowledgment Message  . . .   13
           4.1.5. Home Agent Switch Request Message . . . . . . . .   14
     4.2. New Mobility Options  . . . . . . . . . . . . . . . . . .   15
           4.2.1. IP Address Option . . . . . . . . . . . . . . . .   15
           4.2.2. Mobile Network Prefix Option  . . . . . . . . . .   15
           4.2.3. Binding Cache Entry Information Option  . . . . .   16

 5. Home Agent Operation                                              17
     5.1. Requesting Binding Cache  . . . . . . . . . . . . . . . .   17
     5.2. Notifying Binding Cache . . . . . . . . . . . . . . . . .   17
     5.3. Trigger Home Agent Switching  . . . . . . . . . . . . . .   18
     5.4. Exchanging Home Agent Hello . . . . . . . . . . . . . . .   18

 6. Mobile Node Operation                                             19
     6.1. Receiving Home Agent Switch Request . . . . . . . . . . .   19

Addresses                                                             21


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   1. Introduction

   This document specifies the inter Home Agents protocol (HAHA
   protocol).  The concept of HAHA protocol is described in [2].  The
   five new mobility header messages and the two new mobility header
   sub-option are defined to exchange binding information of mobile node
   and mobile router among home agents.  Home Agent operations on this
   HAHA protocol are summarized in [3].

   We assume that several Home Agents serve the same home network
   together at the same time.  These home agents can be located either
   at the same home link or at the different link.  Each home agent MUST
   be able to communicate with the other Home Agent.  It is recommended
   to utilize IPsec ESP encryption for all traffic between Home
   Agents.  Each Home Agent can be pre-known all the other Home Agent
   operationally or can be discovered dynamically.  In either case,
   as like BGP operation, network administrator should be carefully
   authorized each Home Agent to join a HAHA network.

   The Binding Information Request, the Binding Information Update,
   and the Binding Information Acknowledgment are used by Home Agents
   to synchronize binding information of all mobile nodes and routers
   served by the Home Agents.  When a binding cache is created at a Home
   Agent, the binding cache can be notified to all the Home Agents by
   Binding Information Update.  After receiving the Binding Information
   Update, Binding Information Acknowledgment is returned to confirm
   binding cache recipient.  If a Home Agent needs to solicit certain
   binding cache, it sends Binding Information Request to the HAHA
   network.

   The Home Agent Switch Request is sent by a Home Agent to a Mobile
   Host or Router.  To change the primary Home Agent, this message
   triggers Dynamic Home Agent Address Discovery at the Mobile Host or
   Router.  The sender Home Agent can includes one of Home Agent address
   as a desired Home Agent to switch over.

   The Home Agent HELLO is periodically pulsed among Home Agents.  It
   uses live confirmation like HELLO of other routing protocols.  This
   HELLO has the same field of Home Agent information option of Router
   Advertisement in order to manage Home Agent list.  A Home Agent
   manages the list of other Home Agents by receiving the HELLOs.


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   2. Terminology

   This document uses terms defined in [6], [5], [11], and [13].

   Note:  In this document,three terms are used to express mobile
   entities as defined at  [13].  A Mobile Host is an end host capable
   of Mobile IPv6.  A Mobile Router is a router of a mobile network
   supporting the Basic NEMO protocol.  A Mobile Node is an entity
   moving on the Internet.  A Mobile Node implies either a Mobile Host,
   Mobile Router, or both.

   The keywords ``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.

      Primary Home Agent

              A Home Agent who receives Binding Updates from a Mobile
              Node.  The Mobile Node is always associated with a primary
              Home Agent to register its binding.

      Binding Cache Copy (BCC)

              A copy of Binding.  BCC has all the fields of Binding
              defined in [5] and an additional field for an address of
              the Home Agent that is registered by Mobile Node.  BCC can
              be stored in Binding Cache Database with small extensions,
              but BCC MUST be marked as BCC in Binding Cache Database.

      HA address

              is already defined in Mobile IPv6 [5] like ``the IP
              address of a home agent on its home link.''

      HAHA address

              is an externally assigned local global address which the
              Home Agent has associated with one of its own network
              interfaces other than the interface attached to its home
              link.


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   3. Variety of Home Agent Configuration

   This section shows possible Home Agents configurations for HAHA
   protocol.  Those configurations are applicable to both Mobile IPv6
   and the NEMO Basic Support protocol.

   The home network assignment is described in the home network model
   document [11].  Aggregated Home Network, Extended Home Network, and
   Virtual Home Network are introduced.

   HAHA protocol allows to distribute Home Agents anywhere on
   the Internet.  This section describes distributed Home Agent
   configuration for all the home networks.  We classify the Home Agent
   configuration into two cases depending on a physical home link
   availability or not in this document.


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   3.1. With Home Link

   When multiple Home Agents are configured locally with a single home
   link, there are two possible configurations like below.


                  Internet
                    |
                 Home Link
             ==+====+====+======
               +    +    +
              HA1  HA2  HA3 ...  (HA has only a HA address)


               Figure 1: Home Agents with only HA address


                 Internet
                    |
             --+----+----+------
               +    +    +
              HA1  HA2  HA3  ... (HA has both a HA address
               +    +    +       and a HAHA address)
             ==+====+====+======
                Home Link


       Figure 2: Home Agents with both HA address and HAHA address


   When Home Agents are locally distributed, like Figure 1 and Figure 2,
   every Home Agents operate the same operation.  In both cases, a
   Mobile Node sends a binding update to a HA address and setup a
   bi-directional tunnel between the Mobile Node's care-of address and
   the HA address of each Home Agent.  After the creation of a Binding
   Cache, the Home Agent starts HAHA protocol to synchronize the Binding
   Cache among all the Home Agents by sending Binding Information
   Update to all the HA addresses.  To activate all the Home Agents
   with Binding Synchronization, Home Agents MUST consider who will be
   responsible for Proxy Neighbor Discover of the Mobile Node (Proxy
   NDP negotiation).  Only for Figure 2, each Home Agent can advertise
   a route of the aggregated home network to the Internet to intercept
   packets without Proxy NDP.

   As the alternate configuration, multiple Home Agents can be globally
   distributed on the Internet like Figure 3 and Figure 4.  The
   Home Link is physically separated and configured at the different
   networks.  Since the same route of the aggregated home network


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   are advertised from separated home links, each Home Link must be
   connected somehow at the L2 technology such as L2TP. Otherwise,
   for example in below figures, packets to HA1 may be routed to the
   Home Link2 according to the Internet routing and there is no way to
   re-routed to the Home Link1.


                    +- - - + Internet +- - -+
                    |                       |
              Home Link1  L2-connectivity  Home Link2
             ==+====+====+== = = = = ==+====+====+==
               +    +    +             +    +    +
              HA1  HA2  HA3           HA4  HA5  HA6


               Figure 3: Home Agents with only HA address


                    +- - - + Internet +- - -+
                    |                       |
                    |                       |
             --+----+----+--         --+----+----+--
               +    +    +             +    +    +
              HA1  HA2  HA3           HA4  HA5  HA6
               +    +    +             +    +    +
             ==+====+====+== = = = = ==+====+====+==
              Home Link1  L2-connectivity  Home Link2


       Figure 4: Home Agents with both HA address and HAHA address


   In both Figure 3 and Figure 4, operations are same as the case
   of Figure 1 and Figure 2.  However, in the case of Figure 4, the
   Home Agent may use HAHA address on behalf of HA address in all
   the operations.  In such case, any messages of HAHA protocol are
   transmitted over the Internet, but not on the separated home link.

   A possible issue for the globally distributed Home Agents with home
   link is the redundant re-routing.  Even if packets meant for a Mobile
   Node are arrived to the closest Home Link according to the Internet
   routing, packets may be forwarded to the far Home Link through L2
   connection between Home Links.  This is because only single Home
   Agent takes responsibility for intercepting and forwarding packets
   to the Mobile Node even if all the Home Agents have the same binding
   cache for the Mobile Node.  As we noted before for Figure 2, Proxy
   NDP operation can be eliminated from Figure 4 by all the Home Agents


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   advertising the aggregated home network route to the Internet in
   Figure 4.  In this case, all Home Agents can defend packets for the
   Mobile Node and the redundant re-routing is never happened.


   3.2. Without Home Link

   In Mobile IPv6, an aggregated home network is used and configured
   virtually.  Home Agent configure its Home Link without physical
   link.  In the NEMO basic support, an either aggregated or extended
   home network can be applied.  An extended home network conceptually
   eliminates the home link.


                    +- - - + Internet +- - - -+
                    |            +            |
                    |            |            |
                    +            +            +
                   HA1          HA2          HA3
                    +            +            +
                   VHL1         VHL2         VHL3
            Virtual Home Link(VHL) is not physically existed.


                 Figure 5: Home Agent without Home Link


   For both an aggregated and an extended home network, each Home Agent
   MUST have a HAHA address.  Home Agent may have a HA address when a
   home network is an aggregated home network.  Each Home Agent MUST
   advertise a route of the aggregated home network to the Internet to
   intercept packets without Proxy NDP. With this route advertisement,
   Home Agent can be placed anywhere on the Internet.  There is no
   classification such as local or global Home Agent distribution since
   there is no different between local or global distribution.

   A Mobile Node sends a binding update to a HAHA address and setup
   a bi-directional tunnel between the Mobile Node's care-of address
   and the HAHA address.  After creation of a Binding Cache, the Home
   Agent starts HAHA protocol to synchronize the Binding Cache among all
   the Home Agents by sending Binding Information Update to the HAHA
   address of each Home Agent.  All of Home Agents can intercept and
   forward packets meant for a Mobile Node according to synchronized
   binding cache information.  Since the home link is virtual, proxy NDP
   operation is totally eliminated from Mobile IPv6 and the NEMO Basic
   Support.


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   4. Message Formats

   4.1. New Mobility Header Messages

   The Mobility Header format is defined in section 6 of [5].  This
   document defines five new mobility messages.


   4.1.1. Home Agent HELLO Message

   The Home Agent HELLO message is pulsed to other Home Agents in order
   to inform activeness of the sender home agent.  The format of the
   Home Agent HELLO message is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |          Sequence             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Home Agent Preference    |      Home Agent Lifetime      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      HELLO Interval           |    Reserved   |  Prefix length|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                                                               |
       |                      Home Agent Address                       |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility Options                       .
       .                                                               .
       .                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Sequence

         16-bit unsigned integer.  The Sequence number of the HELLO
         message can be used to verify whether this HELLO message is the
         latest one or not.  This value does not need to be recorded in
         Home Agent List.

      Home Agent Preference

         16-bit unsigned integer.  The preference for the home agent
         sending this hello.  This preference is same as the home agent
         preference value of home agent information option defined in
         Mobile IPv6.


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      Home Agent Lifetime

         16-bit unsigned integer.  The lifetime for the home agent
         sending this HELLO. This lifetime is same as the home agent
         Lifetime value of home agent information option defined in
         Mobile IPv6.

      HELLO Interval

         16-bit unsigned integer.  The interval for the home agent
         sending this HELLO.

      Reserved

         8-bit unsigned integer.  It must be initialized to zero by the
         sender and must be ignored by the receiver.

      Prefix Length

         8-bit unsigned integer.  The prefix length of the home prefix
         that HA is serving.  The home prefix is retrieved from the
         Prefix Length field and following Home Agent Address field.

      Home Agent Address

         A 16 byte field contains an IPv6 global address of the home
         agent sending this hello.

   This message MUST include the Mobile Network Prefix Option defined in
   section 4.2.2 that is served by the Home Agent if available.

   Home Agent HELLO message MUST be authenticated and encrypted by IPsec
   ESP.


   4.1.2. Binding Information Request Message

   The Binding Information Request Message is used to request Binding
   Cache Information corresponding to a particular Mobile Node.  It is
   sent only between Home Agents.  This message is often used during


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   bootstrap of a Home Agent.  The format of the Binding Information
   Request message is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |          Identifier           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility Options                       .
       .                                                               .
       .                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Identifier

         The 16-bit identifier to aid in matching Home Agent Information
         Update message.  The identifier should never be set to 0.  It
         should always be more than 1.

      Mobility Options

         MUST contain either IPv6 Address Option (Sub-type:  Home
         Address) or Mobile Network Prefix Option.

         If a Home Agents wants the Binding Cache Information for a
         particular Mobile Node, it includes an IPv6 Address Option
         (Sub-type:  Home Address).  If a Home Agent wants to know the
         forwarding state setting up for a particular Mobile Network
         Prefix, it includes a Mobile Network Prefix Option.

   Binding Information Request message MUST be authenticated and
   encrypted by IPsec ESP.


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   4.1.3. Binding Information Update Message

   The Binding Information Update message is used by the Home Agents
   to exchange Binding Cache Information.  The message format is as
   follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |          Identifier           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility Options                       .
       .                                                               .
       .                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Identifier

         The 16-bit identifier to aid in matching Home Agent Information
         Request and Home Agent Information Acknowledge message.  The
         identifier should never be set to 0.  It should always be
         more than 1.  The identifier should be set random number for
         unsolicited Binding Information Update messages.  Otherwise,
         the identifier should be set to the identifier in a Binding
         Information Request message if this is a solicited Binding
         Information Update message.

      Mobility Options

         MUST contain Binding Cache Entry Information option and MAY
         contain Mobile Network Prefix option followed by Binding Cache
         Entry Information option if necessary.

   This message MUST be authenticated and encrypted by IPsec ESP.


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   4.1.4. Binding Information Acknowledgment Message

   The Binding Information Acknowledgment message is used by the Home
   Agents to confirm recipient of a Binding Information Update message.
   The message format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |          Identifier           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Status              |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Identifier

         The 16-bit identifier should be copied from the identifier
         field of the received Home Agent Information Update message.

      Status

         16-bit Status value.  Values of Status field greater than or
         equal to 128 indicate that the Binding Information Update was
         rejected by the receiving node.  The following Status values
         are currently defined:

            0       Binding is successfully synchronized

      Reserved

         16-bit field reserved for future use.  The value SHOULD be
         initialized to zero by the sender, and MUST be ignored by the
         receiver.

   Binding Information Acknowledgment message MUST be authenticated and
   encrypted by IPsec ESP.


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   4.1.5. Home Agent Switch Request Message

   This message is sent by a Home Agent to a Mobile Node to trigger
   Dynamic Home Agent Discovery.  The message format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |           Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility Options                       .
       .                                                               .
       .                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Reserved

         16-bit field reserved for future use.  The value SHOULD be
         initialized to zero by the sender, and MUST be ignored by the
         receiver.

      Mobility Options

         MAY contain an IPv6 Address option (Sub-type:  Home Agent
         Address) to specify a desired Home Agent.  If the IPv6 Address
         Option is present, a receiver (i.e.  Mobile Node) switches
         to the specified Home Agent immediately as its primary Home
         Agent.  If the IPv6 Address option is not present, the receiver
         re-selects a Primary Home Agent by itself.  The Mobile Node MAY
         start Dynamic Home Agent Address Discovery.

   Home Agent Switch Request message MUST be authenticated and encrypted
   by the use of IPsec ESP mode.


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   4.2. New Mobility Options

   4.2.1. IP Address Option

   This option is already defined at FMIP specification [4] like the
   below figure.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Type     |   Length      |   Sub Type    | Prefix Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Reserved                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                         IPv6 Address                          +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   HAHA protocol introduces new Sub-Type value for Home Agent address
   and Home Address.

      Sub-Type

            4       Home Agent Address

            5       Home Address


   4.2.2. Mobile Network Prefix Option

   This option is already defined in the NEMO basic support [10].  This
   option is included in the Binding Information Request message only if
   a Home Agent is requesting information regarding a particular Mobile
   Network Prefix.


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   4.2.3. Binding Cache Entry Information Option

   The Binding Cache Entry Information option has an alignment
   requirement of 8n+2.  Its format is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |   Type = 0xa  | Option Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                        Home Address                           |
       +                                                               +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                        Care-of Address                        +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Flags                |       Sequence Number         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Lifetime             |   # of MNPs   |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       .                                                               .
       .                                                               .
       .                Mobile Network Prefixe Option                  .
       .                                                               .
       .                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Binding Cache Entry Information option is valid in the Binding
   Information Update.

   The fields of Home Address, Care-of Address, Flags, Sequence Number,
   and Lifetime are copied from the registered binding of a particular
   Mobile Node or Mobile Router.  8-bit Reserved field MUST be set to
   zero.

   The field ``Number of MNPs'' tells the receiving Home Agent which
   Mobile Network Prefixes are owned by a Mobile Router.  The prefixes
   are stored in Mobile Network Prefix Option followed by the Binding


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   Cache Entry Information option.  The Home Agent who receives this
   option can setup forwarding for each Mobile Network Prefix.  For
   Mobile IPv6, the ``Number of MNPs'' field is set to 0.


   5. Home Agent Operation

   This section gives HAHA protocol operations on Home Agent.
   HAHA protocol operations consists of two functions:  Binding
   Synchronization and Home Agent Switching.


   5.1. Requesting Binding Cache

   When a Home Agent wants a binding for a particular Mobile Node, it
   can solicit Binding Information Update message.  The Home Agent sends
   a Binding Information Request message to Home Agents.  The Home
   Agent MUST set a random value to the Identifier field in the Binding
   Information Request message and MUST include either a Home Address
   mobility option or a Mobile Network Prefix mobility option.


   5.2. Notifying Binding Cache

   The primary Home Agent can send Binding Information Update messages
   either when it is solicited by Binding Information Request message or
   when it creates/updates binding for a particular Mobile Node.

   When the primary Home Agent receives a Binding Information Request
   message, it MUST verifies the Source address field of the IPv6
   header.  If the source address is not among the known Home Agents,
   the message MUST be silently discarded.

   If a Home Agent who receives a Binding Information Request message
   is not the primary Home Agent for the requested Mobile Node, it
   MUST ignore the message.  Otherwise, it SHOULD reply to the Binding
   Information Request message.

   The binding information of the requested Mobile Node are stored in
   the Binding Information Update message.  The primary Home Agent
   MUST copy the binding information of the requested Mobile Node to
   each fields of a Binding Cache Entry Information option.  If the
   Binding Information Update message is sent in response to the Binding
   Information Request message, the primary Home Agent MUST copy the
   Identifier field of the Request message to the same filed in the
   Update message.  Otherwise, it MUST set zero to the Identifier field.

   When a Home Agent receives a Binding Information Update message, it
   MUST verify the Source address field of the IPv6 header.  If the


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   source address is not among the known Home Agents, the message MUST
   be silently discarded.  If the Binding Information Update message
   is sent from the primary Home Agent, the Home Agent SHOULD record
   the binding information and the primary Home Agent address into its
   Binding Cache.  After registering the binding, the Home Agent MUST
   return a Binding Information Acknowledgment message to the sender
   Home Agent of the Binding Information Update message.

   If the sender Home Agent of the Binding Information Update message
   does not receive a Binding Information Acknowledgment message, it
   MUST retry to send a Binding Information Update message.

   Both a Binding Information Update message, a Binding Information
   Request message and a Binding Information Acknowledgment message MUST
   be authenticated and encrypted by IPsec ESP. If a message does not
   have IPsec ESP header, the message MUST be ignored.


   5.3. Trigger Home Agent Switching

   A Mobile Node can change its primary Home Agent when it is requested
   by a Home Agent.  When a Mobile Node receives a Home Agent Switch
   Request, it checks the Home Address field in the request.  If the
   address in the Home Address field is global scope address and is
   already recorded in the Home Agent list of the Mobile Node, the
   Mobile Node MUST immediately switch to the requested Home Agent by
   the Home Agent Switch Request.

   On the other hand, if the requested address in the Home Agent Switch
   Request message is either unknown or empty, the Mobile Node MUST send
   a Dynamic Home Agent Discovery Request message to the Mobile IPv6
   Home-Agents anycast address.  After receiving a Dynamic Home Agent
   Discovery Reply, the Mobile Node selects the most appropriate home
   agent and changes its primary Home Agent to the selected Home Agent.

   The primary Home Agent switching is completed when the Mobile Node
   registers its binding to the new Home Agent.


   5.4. Exchanging Home Agent Hello

   Mobile IPv6 uses Router Advertisement messages to manage Home Agent
   lists on each Home Agents.  When Home Agents are placed at different
   links, Router Solicitation and Advertisement messages can not
   be used due to link-local limitation.  Therefore, a new Mobility
   Header message is defined to notify similar information of Router
   Advertisement among Home Agents over the home link.


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   A Home Agent MUST know other Home Agents which configured in
   different links beforehand.  This is manually configured on each
   Home Agent.  This mechanism MUST be used only between Home Agents on
   different links serving the same home prefix.  It SHOULD not be used
   between Home Agents on the same link.

   A Home Agent MUST periodically send a Home Agent HELLO message.  The
   Home Agent SHOULD also send a Home Agent HELLO message when its local
   information such as preference, lifetime, and registration status,
   etc.  changes.

   A Home Agent HELLO message MUST be constructed with same information
   of a Router Advertisement message described in section 7 of [5] and
   MUST be sent by a unicast to the destination (other Home Agents).

   The receiver of a Home Agent HELLO message MUST verify the Source
   address field of the IPv6 header.  If a Home Agent HELLO message
   is received from unknown Home Agent, the message MUST be silently
   dropped.  If the source address is not in the list of known Home
   Agents, the message MUST be silently dropped.  Otherwise, the
   receiver processes the Home Agent HELLO message to update its Home
   Agent list.  The Sequence field should be checked to ensure the
   freshness of the received HELLO message.

   Any Home Agent HELLO message satisfying all of these tests MUST be
   processed to update its Home Agent list.  The receiver Home Agent
   copy each field of the Home Agent HELLO message to its local Home
   Agent List.  If the Lifetime field is set to zero, the receiver MUST
   delete the sender Home Agent from the Home Agent List.

   When a new Home Agent boots up, it SHOULD wait particular time to
   listen Home Agent HELLO messages of all configured Home Agents.


   6. Mobile Node Operation

   6.1. Receiving Home Agent Switch Request

   A Mobile Node can change its primary Home Agent when it is requested
   by a Home Agent.  When a Mobile Node receives a Home Agent Switch
   Request, it checks the Home Address field in the request.  If the
   address in the Home Address field is global scope address and is
   already recorded in the Home Agent list of the Mobile Node, the
   Mobile Node MUST immediately switch to the requested Home Agent by
   the Home Agent Switch Request.

   On the other hand, if the requested address in the Home Agent Switch
   Request message is either unknown or empty, the Mobile Node MUST send
   a Dynamic Home Agent Discovery Request message to the Mobile IPv6


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   Home-Agents anycast address.  After receiving a Dynamic Home Agent
   Discovery Reply, the Mobile Node selects the most appropriate home
   agent and changes its primary Home Agent to the selected Home Agent.

   The primary Home Agent switching is completed when the Mobile Node
   registers its binding to the new Home Agent.


   References

   [1] J. Faizan, H. El-Rewini, M. Khalil, Problem Statement:  Home
       Agent Reliability (work in progress). Internet Draft, IETF.
       draft-jfaizan-mipv6-ha-reliability-01.txt Februry 2004.

   [2] R. Wakikawa, V. Devarapalli, P. Thubert, Inter Home
       Agents Protocol (HAHA) (expired). Internet Draft, IETF.
       draft-wakikawa-mip6-nemo-haha-01.txt Februry 2004.

   [3] P. Thubert, R. Wakikawa, V. Devarapalli, Global HA to
       HA protocol (work in progress). Internet Draft, IETF.
       draft-thubert-nemo-global-haha-01, October 2005.

   [4] R. Koodli. Fast Handovers for Mobile IPv6 (Experimental).
       RFC4068, IETF. July 2005.

   [5] D. Johnson, C. Perkins and J. Arkko. Mobility Support in IPv6
       (Standards Track). RFC3775, IETF. June 2004.

   [6] T. Ernst and H. Lach. Network Mobility Support Terminology (work
       in progress). Internet Draft, IETF. draft-ietf-nemo-terminology-*
 *04.txt
       October 2005.

   [7] J. Arkko, V. Devarapalli and F. Dupont. Using IPsec to Protect
       Mobile IPv6 Signaling between Mobile Nodes and Home Agents.
       RFC3776. IETF. June 2004.

   [8] S. Kent and R. Atkinson. IP Encapsulating Security Payload (ESP).
       RFC 2402, IETF. November 1998.

   [9] A. Conta and S. Deering. Generic Packet Tunneling in IPv6
       Specification. RFC 2473, IETF. December 1998.

   [10] V. Devarapalli and R. Wakikawa and A. Petrescu and P. Thubert.
       Nemo Basic Support Protocol (Standards Track), RFC3963, IETF.
       January 2005.

   [11] P. Thubert and R. Wakikawa and V. Devarapalli. NEMO Home
       Network models (work in progress). Internet Draft, IETF.
       draft-ietf-nemo-home-network-models-06.txt Februry, 2006


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   [12] T. Narten and E. Nordmark and W. Simpson. Neighbor Discovery for
       IP Version 6 (IPv6). RFC 2461, IETF. December 1998.

   [13] J. Manner and M. Kojo. Mobility Related Terminology.
       (Informational) RFC3753, June 2004.


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   Change Log from Previous Version

   Changes from draft-wakikawa-mip6-nemo-haha-protocol-00.txt.

    -  Updating References

    -  Correcting Typos

    -  Updating IPv6 address option


   Authors Addresses


        Ryuji Wakikawa
        Keio University and WIDE
        5322 Endo Fujisawa Kanagawa
        252-8520
        Japan
        Email:  ryuji@sfc.wide.ad.jp

        Pascal Thubert
        Cisco Systems Technology Center
        Village d'Entreprises Green Side
        400, Avenue Roumanille
        Biot - Sophia Antipolis 06410
        France
        Email:  pthubert@cisco.com

        Vijay Devarapalli
        Nokia Research Center
        313 Fairchild Drive
        Mountain View, CA 94043
        USA
        Email:  vijay.devarapalli@nokia.com


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