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Versions: 00 01 02 03 RFC 3963

NEMO Working Group                                     Vijay Devarapalli
INTERNET DRAFT                                                     Nokia
Category:  Standards Track                                Ryuji Wakikawa
Expires June 2004                                        Keio University
                                                      Alexandru Petrescu
                                                                Motorola
                                                          Pascal Thubert
                                                           Cisco Systems
                                                           December 2003

             Network Mobility (NEMO) Basic Support Protocol
                  draft-ietf-nemo-basic-support-02.txt


Status of This Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at
   any time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at:
        http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at:
        http://www.ietf.org/shadow.html.


Abstract

   This document describes the NEMO Basic Support protocol that enables
   mobile networks to attach to different points in the Internet.  The
   protocol is an extension of Mobile IPv6 and allows for session
   continuity for every node in the mobile network as the network moves.
   It also allows every node in the mobile network to be reachable while
   moving around.  The Mobile Router, which connects the network to the
   Internet, runs the NEMO Basic Support protocol with its Home Agent.
   The protocol is designed in such a way that network mobility is
   transparent to the nodes inside the mobile network.









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                                 Contents


Status of This Memo                                                    1

Abstract                                                               1

 1. Introduction                                                       4

 2. Terminology                                                        5

 3. Overview of the NEMO Protocol                                      6

 4. Message Formats                                                    9
     4.1. Binding Update  . . . . . . . . . . . . . . . . . . . . .    9
     4.2. Binding Acknowledgement . . . . . . . . . . . . . . . . .    9
     4.3. Mobile Network Prefix Option  . . . . . . . . . . . . . .   10

 5. Mobile Router Operation                                           12
     5.1. Data Structures . . . . . . . . . . . . . . . . . . . . .   12
     5.2. Sending Binding Updates . . . . . . . . . . . . . . . . .   13
     5.3. Receiving Binding Acknowledgements  . . . . . . . . . . .   13
     5.4. Error Processing  . . . . . . . . . . . . . . . . . . . .   14
     5.5. Establishment of Bi-directional Tunnel  . . . . . . . . .   15
     5.6. Neighbor Discovery for Mobile Router  . . . . . . . . . .   16
     5.7. Multicast Groups for Mobile Router  . . . . . . . . . . .   16
     5.8. Returning Home  . . . . . . . . . . . . . . . . . . . . .   16

 6. Home Agent Operation                                              18
     6.1. Data Structures . . . . . . . . . . . . . . . . . . . . .   18
           6.1.1. Binding Cache . . . . . . . . . . . . . . . . . .   18
           6.1.2. Prefix Table  . . . . . . . . . . . . . . . . . .   18
     6.2. Mobile Network Prefix Registration  . . . . . . . . . . .   19
     6.3. Advertising Mobile Network Reachability . . . . . . . . .   20
     6.4. Establishment of Bi-directional Tunnel  . . . . . . . . .   20
     6.5. Forwarding Packets  . . . . . . . . . . . . . . . . . . .   21
     6.6. Sending Binding Acknowledgements  . . . . . . . . . . . .   21
     6.7. Mobile Network Prefix De-Registration . . . . . . . . . .   22

 7. Modifications to Dynamic Home Agent Discovery                     23
     7.1. Modified Dynamic Home Agent Discovery Request . . . . . .   23
     7.2. Modified Dynamic Home Agent Discovery Reply . . . . . . .   23
     7.3. Modified Home Agent Information Option  . . . . . . . . .   24

 8. Support for Dynamic Routing Protocols                             25

 9. Security Considerations                                           27



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10. IANA Considerations                                               28

11. Contributors                                                      28

12. Acknowledgements                                                  28

 A. Examples of NEMO Basic Support Operation                          31

 B. Changes from Previous Version                                     34











































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1. Introduction

   This document describes protocol extensions to Mobile IPv6 (MIPv6)
   [1] to enable support for network mobility.  The extensions are
   backward compatible with Mobile IPv6.  In particular, a NEMO
   compliant Home Agent can operate as a Mobile IPv6 Home Agent as well.

   The NEMO Basic Support works in such a way that session continuity is
   ensured for all the nodes in the mobile network even as the Mobile
   Router changes its point of attachment to the Internet.  It also
   provides connectivity and reachability for all nodes in the mobile
   network as the network moves.  The solution supports both mobile
   nodes and hosts that do not support mobility in the mobile network.

   Within the context of this document, the definition of a Mobile
   Router extends that of a Mobile IPv6 [1] Mobile Node, by adding
   the capability of routing between its point of attachment (Care-of
   Address) and a subnet which moves with the Mobile Router.

   The solution described in this document requires setting up a
   bi-directional tunnel between the Mobile Router and its Home Agent.
   This tunnel is set up when the Mobile Router sends a successful
   Binding Update to its Home Agent, informing the Home Agent of its
   current point of attachment.

   All traffic between the nodes in the mobile network and Correspondent
   Nodes passes through the Home Agent.  This document does not describe
   route optimization of this traffic.

   The terminology document [9] describes Nested Mobility as a scenario
   where a Mobile Router allows another Mobile Router to attach to its
   mobile network.  There could be arbitrary levels of nested mobility.
   The operation of each Mobile Router remains the same whether the
   Mobile Router attaches to another Mobile Router or to a fixed Access
   Router on the Internet.  The solution described here does not place
   any restriction on the number of levels for nested mobility.  But it
   should be noted that this might introduce significant overhead on the
   data packets as each level of nesting introduces another IPv6 header
   encapsulation.













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2. Terminology

   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 [2].

   Network Mobility related terminology is defined in [8] [9].  This
   document in addition defines the following terms.

      Mobile Network Prefix

              An IPv6 prefix that is delegated to a Mobile
              Router and advertised in the mobile network.  There could
              be more than one Mobile Network Prefix being advertised in
              a mobile network.

      Prefix Table

              It is a list of Mobile Network Prefixes indexed by
              the Home Address of a Mobile Router.  The prefix table is
              managed by the Home Agent and is used by the Home Agent
              to determine which Mobile Network Prefixes belong to a
              particular Mobile Router.





























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3. Overview of the NEMO Protocol

   A Mobile Network is a network segment or subnet which can move and
   attach to arbitrary points in the Internet.  A mobile network can
   only be accessed via specific gateways called Mobile Routers that
   manage its movement.  Mobile networks have atleast one Mobile Router
   serving them.  A Mobile Router does not distribute the mobile network
   routes to the infrastructure at its point of attachment (i.e.  in the
   visited network).  Instead, it maintains a bidirectional tunnel to a
   Home Agent that advertises an aggregation of mobile networks to the
   infrasructure.  The Mobile Router is also the default gateway for the
   mobile network.

   A mobile network can also consist of multiple and nested subnets.  A
   router with no support for mobility may be permanently attached to
   a mobile network for local distribution.  Also, Mobile Routers may
   be attached to mobile networks owned by different Mobile Routers and
   form a graph.  In particular, with Basic NEMO Support, each Mobile
   Router is attached to another mobile network by a single interface,
   and if loops are avoided, the graph is a tree.

   A Mobile Router has an unique Home Address through which it is
   reachable when it is registered with its Home Agent.  The Home
   Address is configured from a prefix that is aggregated and advertised
   by its Home Agent.  The prefix could either be the prefix advertised
   on the home link or the prefix delegated to the Mobile Router.
   The Mobile Router can have more than one Home Address if there
   are multiple prefixes in the home link.  The Mobile Router also
   advertises one or more prefixes in the mobile network attached to it.
   The actual mechanism for assigning these prefixes to a given Mobile
   Router is outside the scope of this specification.

   When the Mobile Router moves away from the home link and attaches to
   a new access router, it acquires a Care-of Address from the visited
   link.  The Mobile Router can at any time act either as a Mobile Host
   or a Mobile Router.  In either case, as soon as the Mobile Router
   acquires a Care-of Address, it immediately sends a Binding Update to
   its Home Agent as described in [1].  When the Home Agent receives
   this Binding Update it creates a binding cache entry binding the
   Mobile Router's Home Address to its Care-of address at the current
   point of attachment.

   If the Mobile Router wishes to act as a Mobile Router and provide
   connectivity to nodes in the mobile network, it indicates this to the
   Home Agent by setting a flag (R) in the Binding Update.  It MAY also
   include information about the Mobile Network Prefix in the Binding
   Update using one of the modes described in Section 5.2, so that the
   Home Agent can forward packets meant for nodes in the mobile network
   to the Mobile Router.  A new Mobility Header Option is described in



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   this document to carry prefix information.  This option is described
   in Section 4.3.  If the mobile network has more than one IPv6 prefix
   and wants the Home Agent to setup forwarding for all these prefixes,
   it includes multiple prefix information options in a single Binding
   Update.  The Home Agent sets up forwarding for each of these prefixes
   to the Mobile Router's Care-of Address.  In some scenarios the Home
   Agent already knows which prefixes belong to a Mobile Router.  In
   these scenarios, the Mobile Router does not include any prefix
   information in the Binding Update.  The Home Agent sets up forwarding
   for all prefixes owned by the Mobile Router, when it receives a
   Binding Update from the mobile router with the router flag (R) set.

   The Home Agent acknowledges the Binding Update by sending a Binding
   Acknowledgement to the Mobile Router.  A positive acknowledgement
   means that the Home Agent has set up forwarding for the mobile
   network.  Once the binding process completes, a bi-directional tunnel
   is established between the Home Agent and the Mobile Router.  The
   tunnel end points are Mobile Router's Care-of Address and the Home
   Agent's address.  If a packet with a source address belonging to
   the Mobile Network Prefix is received from the mobile network, the
   Mobile Router reverse-tunnels the packet to the Home Agent through
   this tunnel.  This reverse-tunneling is done by using IP-in-IP
   encapsulation [3].  The Home Agent decapsulates this packet and
   forwards it to the Correspondent Node.  For traffic originated by
   itself, the Mobile Router can use either reverse tunneling or route
   optimization as specified in [1].

   When a data packet is sent by a Correspondent Node to a node in the
   mobile network, it gets routed to the Home Agent which currently
   has the binding for the Mobile Router.  It is expected that the
   Mobile Router's network prefix would be aggregated at the Home Agent,
   which advertises the resulting aggregation.  Alternatively, the Home
   Agent may receive the data packets destined to the mobile network
   by advertising routes to the Mobile Network Prefix.  The actual
   mechanism by which these routes are advertised is outside the scope
   of this document.  When the Home Agent receives a data packet meant
   for a node in the mobile network, it tunnels the packet to Mobile
   Router's current Care-of address.  The Mobile Router decapsulates
   the packet and forwards it onto the interface where the mobile
   network is connected.  The Mobile Router before decapsulating the
   tunneled packet, has to check if the Source address on the outer IPv6
   header is the Home Agent's address.  It also has to make sure the
   destination address on the inner IPv6 header belongs to one of its
   Mobile Network Prefixes before forwarding the packet to the mobile
   network.

   The mobile network could consist of nodes that do not support
   mobility and nodes that support mobility.  A node in the mobile
   network can also be a fixed or a mobile router.  The protocol



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   described here ensures complete transparency of network mobility to
   the nodes in the mobile network.  Mobile Nodes that attach to the
   mobile network treat it as a normal IPv6 access network and run the
   Mobile IPv6 protocol.

   It is also possible for the Mobile Router and the Home Agent to run
   a routing protocol through the bi-directional tunnel.  In that case,
   the Mobile Router need not include prefix information in the Binding
   Update.  Instead the Home Agent uses the routing protocol updates to
   setup forwarding for the mobile network.  When running the routing
   protocol it is required that the bi-directional tunnel be treated as
   a tunnel interface.  The tunnel interface is included as the list of
   interfaces on which routing protocol is active.  The Mobile Router
   should be configured not to run the routing protocol on its egress
   interface when it is away from the home link.

   Finally, the Home Agent may be configured with static routes to the
   Mobile Network Prefix via the Mobile Router's Home Address.  In that
   case, the routes are set independently of the binding flows and the
   returning Home of a Mobile Router.  The benefit is that such movement
   does not induce any additional signalling in the form of routing
   updates in the Home Network.  The drawback of that model is that the
   routes are present even if the related Mobile Routers that are not
   reachable (at Home or bound) at a given point of time.




























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4. Message Formats

4.1. Binding Update

   A new flag (R) is included in the Binding Update to indicate to the
   Home Agent if the Binding Update is coming from a Mobile Router
   and not from a mobile node.  The rest of the Binding Update format
   remains the same as defined in [1].


        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 #           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |A|H|L|K|R|      Reserved       |           Lifetime            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility options                       .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Mobile Router Flag (R)

         The Mobile Router Flag is set to indicate to the Home Agent
         that the Binding Update is from a Mobile Router.  If the flag
         is set to 0, the Home Agent assumes that the Mobile Router is
         just behaving as a Mobile Node, and MUST NOT forward packets
         destined for the mobile network to the Mobile Router.

      Mobility Options

         Variable length field which can include zero or more mobility
         options.  This document defines a new mobility option in
         addition to what is defined in [1].

      For a description of the other fields in the message, see [1].


4.2. Binding Acknowledgement

   A new flag (R) is included in the Binding Acknowledgement to indicate
   that the Home Agent which processed the corresponding Binding Update
   supports Mobile Routers.  The flag is set only if the corresponding
   Binding Update had the Mobile Router flag (R) set to 1.  The rest of




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   the Binding Acknowledgement format remains the same as defined in
   [1].


        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
                                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       |   Status      |K|R|  Reserved |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Sequence #            |           Lifetime            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                        Mobility options                       .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Mobile Router Flag (R)

         The Mobile Router Flag is set to indicate that the Home Agent
         which processed the Binding Update supports Mobile Routers.  It
         is set to 1 only if the corresponding Binding Update had the
         Mobile Router flag set to 1.

      For a description of the other fields in the message, see [1].

   This document also introduces the following new Binding
   Acknowledgement status values.

      140     Mobile Router Operation not permitted

      141     Invalid Prefix

      142     Not Authorized for Prefix

      143     Forwarding Setup failed

   Status values less than 128 indicate that the Binding Update was
   processed successfully by the receiving nodes.  Values greater than
   128 indicate that the Binding Update was rejected by the Home Agent.


4.3. Mobile Network Prefix Option

   The Mobile Network Prefix Option is included in the Binding Update
   to indicate to the Home Agent the prefix information for the mobile
   network.  There could be multiple Mobile Network Prefix Options



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   if the Mobile Router has more than one IPv6 prefix in the mobile
   network and wants the Home Agent to forward packets for each of these
   prefixes to the Mobile Router's current location.

   The Mobile Network Prefix Option has an alignment requirement of
   8n+4.  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     |   Length      |   Reserved    | Prefix Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                   Mobile Network Prefix                       +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Type

         TBA

      Length

         8 bit unsigned integer indicating the length in octets of the
         option excluding the type and length fields.  Set to 18.

      Reserved

         This field is unused for now.  The value MUST be initialized to
         zero by the sender, and MUST be ignored by the receiver.

      Prefix Length

         8 bit unsigned integer indicating the prefix length of the IPv6
         prefix contained in the option.

      Mobile Network Prefix

         A 16 byte field contains the Mobile Network Prefix.







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5. Mobile Router Operation

   Mobile Router operation is derived largely from the combined
   behaviors of a Host, of a Router [6], and of a Mobile Node [1].

   A Mobile Node can act in two different ways:  (1) as a Mobile Host
   (in which case the Mobile IPv6 Home Agent doesn't maintain any prefix
   information related to the Mobile Host's Home Address, but does
   maintain a binding cache entry related to the Mobile Host's Home
   Address) and (2) as a Mobile Router (in which case, in addition to
   maintaining the binding cache entry corresponding to the Mobile
   Router Home Address, the Mobile IPv6 Home Agent also maintains
   forwarding information related to prefixes assigned to the mobile
   network).  The distinction between the the two modes is represented
   by the value of the Mobile Router flag (R).

   A Mobile Router MUST implement all requirements for IPv6 Mobile
   Nodes, Section 8.5 in [1].  However if a Mobile Router is not
   expected to initiate sessions of its own and behaves purely as a
   router serving the mobile network most of the time, then the Route
   Optimization functionality MAY be implemented.


5.1. Data Structures

   Like a Mobile Host, a Mobile Router also maintains a Binding Update
   List, described in Section 11.1 of Mobile IPv6 specification[1].  The
   Binding Update list is a conceptual data structure which records
   information that is sent in the Binding Updates.  There is one entry
   per each destination that the Mobile Router is currently sending
   Binding Updates to.

   This document introduces a new Prefix Information field in the
   Binding Update list structure.  This field is used to store any
   prefix information that the Mobile Router includes in the Binding
   Update.  If the Mobile Router sets the Mobile Router flag (R) in the
   Binding Update, but does not include any prefix information in it
   this field is set to null.  The Mobile Router does not include prefix
   information in the Binding Update in the implicit mode or when it
   runs a dynamic routing protocol with its Home Agent.

   Similar to a Mobile Host, a Mobile Router stores the information
   regarding status of flags of the Binding Update, in the corresponding
   Binding Update List entry.  This document introduces a new mobile
   router flag (R) for this entry.  The status of this flag is stored in
   the Binding Update list whenever a Binding Update is sent.

   A Mobile Router also maintains a Home Agent list populated according
   to the same procedure as a Mobile Host.



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5.2. Sending Binding Updates

   A Mobile Router sends Binding Updates to its Home Agent as described
   in [1].  It uses one of the following modes to instruct the Home
   Agent to determine the prefixes that belong to the Mobile Router.  In
   all the modes, the Mobile Router sets the Mobile Router flag (R).

      Implicit:

         In this mode, the Mobile Router does not include either a
         Mobile Network Prefix Option or a Mobile Network Prefix Length
         Option in the Binding Update (but it does include the Home
         Address Option in the Destination Options header, as all Mobile
         Hosts do).  The Home Agent can use any mechanism (not defined
         in this document) to determine the Mobile Network Prefix(es)
         owned by the Mobile Router and setup forwarding for the mobile
         network.  One example would be manual configuration at the
         Home Agent mapping the Mobile Router's Home Address to the
         information required for setting up forwarding for the mobile
         network.

      Explicit:

         In this mode, the Mobile Router includes one or more Mobile
         Network Prefix Options in the Binding Update.  These options
         contain information about the Mobile Network Prefix(es)
         configured on the mobile network.

   A Mobile Router MUST implement atleast one mode and MAY implement
   both modes.  If the Mobile Router flag is set, Home Registration flag
   (H) MUST be set.


5.3. Receiving Binding Acknowledgements

   The Mobile Router receives Binding Acknowledgements from the Home
   Agent, corresponding to the Binding Updates it sent.  If the Binding
   Acknowledgement status is set to '0' (Binding Update accepted) and
   the Mobile Router flag (R) is set to 1, the Mobile Router assumes
   that the Home Agent has successfully processed the Binding Update
   and has set up forwarding for the mobile network.  The Mobile Router
   can then start using the bi-directional tunnel for reverse tunneling
   traffic from the mobile network.  If the Mobile Router flag (R) is
   not set, then the Mobile Router concludes that its current Home
   Agent does not support Mobile Routers and performs Dynamic Home
   Agent Discovery again to discover Home Agents which support Mobile
   Routers.  Additional the Mobile Router MUST also de-register with the
   Home Agent which did not support Mobile Routers before attempting
   registration with another Home Agent.



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5.4. Error Processing

   If the Binding Acknowledgement status is set to a value between 128
   and 140, the Mobile Router takes necessary actions as described in
   the Mobile IPv6 specification [1].

   If the Mobile Router sent a Binding Update to the Home Agent in
   implicit mode (i.e.  the prefix field in the Binding Update list
   entry is null) then the Mobile Router interprets only the error
   status '140' (Mobile Router Operation not permitted) and '143'
   (Forwarding Setup failed).  For this Binding Update, the Mobile
   Router MUST discard Binding Acknowledgements with codes '141' and
   '142'.

   For the same Binding Update, if the status is '140', then the Mobile
   Router should send a similar Binding Update (implicit mode) to
   another Home Agent on the same home link.  If no Home Agent replies
   positively then the Mobile Router MUST refrain from sending any
   Binding Update with the Mobile Router flag set to any Home Agent on
   the home link, and log the information.

   For the same Binding Update, if the status is '143', then the Mobile
   Router should send a similar Binding Update (implicit mode) to
   another Home Agent on the same home link.  If no Home Agent replies
   positively then Mobile Router SHOULD refrain from sending this
   Binding Update to any Home Agent on the home link, and MAY send
   Binding Updates in another mode (e.g.  explicitly include a prefix)
   to a Home Agent on the same home link.

   If the Mobile Router sent a Binding Update to Home Agent in explict
   mode then the Mobile Router interprets only the error status
   '141' (Invalid Prefix) and '142' (Not Authorized for Prefix).
   For this Binding Update, the Mobile Router MUST discard Binding
   Acknowledgements with codes '140' and '143'.

   For the same Binding Update, if the status is set to '141', then the
   Mobile Router should send a similar Binding Update to another Home
   Agent on the same home link.  If no Home Agent replies positively
   then Mobile Router SHOULD refrain from sending this Binding Updates
   to any Home Agent on the home link.  At this point, Mobile Router MAY
   try to obtain and own a prefix by the same means that it initially
   got assigned the current Mobile Network Prefix.  Alternatively,
   Mobile Router MAY send Binding Updates in another mode (e.g.
   implicit mode) to a Home Agent on the same home link.

   For the same Binding Update, if the status is set to '142', then the
   Mobile Router should send a similar Binding Update to another Home
   Agent on the same home link.  If no Home Agent replies positively
   then Mobile Router SHOULD refrain from sending this Binding Updates



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   to any Home Agent on the home link.  Additionally, the Home Agent
   MUST stop advertising the respective prefix(es) in the mobile network
   with associated Router Advertisements, and modify its own forwarding
   information accordingly.  Following this, the Mobile Router MAY send
   Binding Updates in another mode (e.g.  implicit) to a Home Agent on
   the same home link.

   If at the end of this Error Processing procedure the Mobile Router
   has tried every available modes of sending Binding Updates and still
   has not received a positive Binding Acknowledgement (status value
   between 0 and 127) for this Home Address from any Home Agent on its
   home link, then the Mobile Router MUST stop sending Binding Updates
   with the Mobile Router flag set for this Home Address and log the
   information.

   In all the above cases, the Mobile Router MUST conclude that the Home
   Agent did not create a binding cache entry for the Mobile Router's
   Home Address.


5.5. Establishment of Bi-directional Tunnel

   When a successful Binding Acknowledgement is received, the Mobile
   Router sets up its endpoint of the bi-directional tunnel.

   The bi-directional tunnel between Mobile Router and Home Agent allows
   packets to flow in both directions between these entities, while the
   Mobile Router is connected to a Visited Link.  The bi-directional
   tunnel involves two virtual links [3]:  one virtual link has the
   address of the tunnel entry point as the Care-of Address of the
   Mobile Router and the tunnel exit point as the address of the
   Home Agent; the other virtual link has as tunnel entry point the
   Home Agent address and as tunnel exit point the Care-of Address
   of the Mobile Router.  Both addresses are unicast addresses.  All
   IPv6 traffic to and from the mobile network is sent through this
   bi-directional tunnel.

   A Mobile Router MAY limit the number of mobile routers that attach to
   its mobile network (the number of levels in the nested aggregation)
   by means of setting the Tunnel Encapsulation Limit field of the
   Tunnel Encapsulation option.

   A Mobile Router uses the Tunnel Hop Limit that is normally assigned
   to routers (not to hosts).  Please refer to [3] for more details.








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5.6. Neighbor Discovery for Mobile Router

   When the Mobile Router is at home, it MAY be configured to send
   Router Advertisements and reply to Router Solicitations on the
   interface attached to the home link.  The value of the Router
   Lifetime field MUST be set to zero to prevent other nodes from
   configuring the Mobile Router as the default router.

   A Mobile Router SHOULD NOT send unsolicited Router Advertisements
   and SHOULD NOT reply to Router Solicitations on any egress interface
   when that interface is attached to a visited link.  However, the
   Mobile Router SHOULD reply with Neighbor Advertisements to Neighbor
   Solicitations received on the egress interface, for topologically
   correct addresses.

   A router typically ignores router advertisements sent by other
   routers on a link.  However, a Mobile Router MUST NOT ignore Router
   Advertisements received on the egress interface.  The received Router
   Advertisements MAY be used for address configuration, default router
   selection or movement detection.


5.7. Multicast Groups for Mobile Router

   When at home, the Mobile Router joins the multicast group All Routers
   Address with scopes '1' interface-local (on the home-advertising
   interface) and '2' link-local on any of its egress interfaces.  When
   in a visited network, the Mobile Router MUST NOT join the above
   multicast groups on the corresponding interface.


5.8. Returning Home

   When the Mobile Router realizes it has returned to its home link
   through movement detection mechanisms, it MUST de-register with
   its Home Agent.  The Mobile Router MUST implement and follow the
   returning home procedures defined for a mobile node in [1].  In
   addition, the Mobile Router MAY start behaving as a router on its
   egress interface.  In particular,

    -  The Mobile Router MAY send router advertisements on its egress
       interfaces.  But the router lifetime SHOULD be set to 0, so that
       hosts on the home link do not pick the Mobile Router as the
       default router.

    -  The Mobile Router MAY join the All Routers multicast group on the
       home link.





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    -  The Mobile Router MAY send routing protocol messages on its
       egress interface if it is configured to run a dynamic routing
       protocol.

















































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6. Home Agent Operation

   In order for a Mobile Router to operate correctly, the Home Agent
   MUST satisfy all the requirements listed in Section 8.4 of [1].  The
   Home Agent MUST implement both modes described in Section 5.2 of this
   document.


6.1. Data Structures

6.1.1. Binding Cache

   The Home Agent maintains Binding Cache Entries for each Mobile Router
   that is currently registered with the Home Agent.  The Binding Cache
   is a conceptual data structure described in detail in [1].

   The Home Agent might need to store the Mobile Network Prefixes
   associated with a Mobile Router in the corresponding Binding Cache
   Entry.  This is required if the Binding Update (that created the
   Binding Cache Entry) contained explicit prefix information.  This
   information can be used later to cleanup routes installed in explicit
   mode, when the Binding Cache Entry is removed, and to maintain the
   routing table, for instance should the routes be manually removed.

   The Home Agent also stores the status of the Mobile Router Flag (R)
   in the Binding Cache entry.


6.1.2. Prefix Table

   The Home Agent SHOULD be able to prevent a Mobile Router from
   claiming Mobile Network Prefixes that belong to another Mobile
   Router.  The Home Agent can prevent such attacks if it maintains a
   Prefix Table and verifies the Prefix Information provided by the
   Mobile Router against the entries in the Prefix Table.  The Prefix
   Table SHOULD be used by the Home Agent when it processes a Binding
   Update in explicit mode.  It is not required when a dynamic routing
   protocol is run between the Mobile Router and the Home Agent.

   Each entry in the Prefix Table conceptually contains the following
   fields:

    -  The Home Address of the Mobile Router.  This field is used as the
       key for searching the pre-configured prefix table.

    -  The Mobile Network Prefix of the Mobile Router associated with
       the Home Address.





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6.2. Mobile Network Prefix Registration

   The Home Agent processes the Binding Update as described in Section
   10.3.1 of the Mobile IPv6 specification [1].  This section describes
   the processing of the Binding Update if the Mobile Router (R) flag is
   set.  The Home Agent performs the following check in addition.

    -  The Home Registration (H) flag MUST be set.  If not, the
       Home Agent MUST reject the Binding Update and send a Binding
       Acknowledgement with status set to 140.  Note:  The basic support
       does not allow sending Binding Update for a Mobile Network Prefix
       to correspondent nodes (for route optimization).

    -  Mobile IPv6 specification [1] requires that the Home Address in
       the Binding Update should be configured from a prefix advertised
       on the home link.  Otherwise the Binding Update is rejected
       with status value 132 [1].  This specification relaxes this
       requirement so that the Home Agent rejects the Binding Update
       only if Home Address does not belong to the prefix that the Home
       Agent is configured to serve.

   If the Home Agent does not reject the Binding Update as described
   above, then it retrieves the Mobile Network Prefix information as
   described below.

    -  If a Mobile Network Prefix Option is present in the Binding
       Update, the prefix information for the Mobile Network Prefix is
       retrieved from the Mobile Network Prefix field and the Prefix
       Length field of the option.  If the Binding Update contains more
       than one option, the Home Agent MUST set up forwarding for all of
       the Mobile Network Prefixes.  If the Home Agent fails to setup
       forwarding to all the prefixes listed in the Binding Update, then
       it MUST NOT forward traffic to any of the prefixes, reject the
       Binding Update and send a Binding Acknowledgement with status set
       to 141 (Invalid Prefix).

       If the Home Agent verifies the prefix information with the Prefix
       Table and the check fails, the Home Agent MUST discard the
       Binding Update and send a Binding Acknowldegement with status set
       to 142 (Not Authorized for Prefix).

    -  If there are is no option in the Binding Update carying
       prefix information, the Home Agent uses manual pre-configured
       information to determine the prefixes assigned to the Mobile
       Router and for setting up forwarding for the mobile network.  If
       there is no information that the Home Agent can use, it MUST
       reject the Binding Update and send a Binding Acknowledgement with
       status set to 143 (Forwarding Setup failed).




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   If the Lifetime specified in the Binding Update is zero or the
   specified Care-of address matches the Home Address in the Binding
   Update, then this is a request to delete the cached binding for
   the home address and specified Mobile Network Prefixes.  The
   Binding Update is processed according to the procedure described in
   Section 6.7.

   If all checks are passed, the Home Agent creates a binding cache
   entry for Mobile Router's Home Address, or updates the binding cache
   entry if it already exists.  Otherwise, the Home Agent MUST NOT
   register the binding of the Mobile Router's Home Address.

   The Home Agent defends the Mobile Router's Home Address through Proxy
   Neighbor Discovery by multicasting onto the home link a Neighbor
   Advertisement message on behalf of the mobile router.  All fields in
   the Proxy Neighbor Advertisement message should be set in the same
   way they would be set by the Mobile Router itself if sending this
   Neighbor Advertisement while at home, as described in [7], with the
   exception that the Router (R) bit in the Advertisement MUST be set if
   the Mobile Router (R) flag has been set in the Binding Update.

   The Home Agent also creates a bi-directional tunnel to the mobile
   router for the requested Mobile Network Prefix, or update an existing
   bi-directional tunnel as described in Section 6.4.


6.3. Advertising Mobile Network Reachability

   In order to be able to receive packets meant for the mobile network,
   the Home Agent advertises reachability to the mobile network.  If the
   Home Link is configured with a prefix that is an aggregation and if
   the Mobile Network Prefix is aggregated under that prefix, then the
   routing updates advertising reachability to the mobile network are
   sent only on the Home Link.  If the Home Agent is the only default
   router on the Home Link, routes to the Mobile Network Prefix get
   aggregated naturally under the Home Agent and the Home Agent does not
   have to do anything special.

   If the Home Agent receives routing updates through a dynamic routing
   protocol from the Mobile Router, those routes are propagated by
   the routing protocol running on the Home Agent on the relevant
   interfaces.


6.4. Establishment of Bi-directional Tunnel

   The implementation of the bi-directional tunnels and the mechanism
   of attaching them to the IP stack are outside the scope of this




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   specification.  However, all implementations MUST be capable of the
   following operations.

    -  The Home Agent can tunnel packets meant for the mobile network
       prefix to the Mobile Router's current location, the Care-of
       Address of the Mobile Router.

    -  The Home Agent can accept packets tunneled by the Mobile Router
       with source address of the outer IPv6 header set to the Care-of
       Address of the Mobile Router.


6.5. Forwarding Packets

   When the Home Agent receives a data packet destined for the mobile
   network, it MUST forward the packet to the Mobile Router through the
   bi-directional tunnel.  The Home Agent either uses only the routing
   table, only the Binding Cache or a combination of routing table
   and Binding Cache to route packets to the mobile network.  This is
   implementation specific.  Two examples are shown below.

    1. The Home Agent maintains a route to the Mobile Network Prefix
       with the next hop set to the Mobile Router's Home Address.  When
       the Home Agent tries to forward the packet to the next hop, it
       finds a binding cache entry for the home address.  Then the Home
       Agent extracts the Mobile Router's Care-of address and tunnels
       the packet to the Care-of address.

    2. The Home Agent maintains a route to the Mobile Network Prefix
       with the outgoing interface set to the bi-directional tunnel
       interface between the Home Agent and the Mobile Router.  For
       this purpose, the Home Agent MUST treat this tunnel as a tunnel
       interface.  When the packets are forwarded through the tunnel
       interface, they get encapsulated automatically with the source
       address and destination address in the outer IPv6 header set to
       the Home Agent's address and the Mobile Router's Care-of address,
       respectively.


6.6. Sending Binding Acknowledgements

   A Home Agent serving a Mobile Router sends Binding Acknowledgements
   according to the same rules it uses for sending Binding
   Acknowledgements to Mobile Hosts [1], with the following
   enhancements.

   The Home Agent sets the status code in the Binding Acknowledgement
   to '0' (Binding Update accepted) in order to indicate to the Mobile
   Router that it successfully processed the Binding Update.  It also



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   sets the Mobile Router flag (R) to indicate to the Mobile Router that
   it has setup forwarding for the mobile network.

   If the Home Agent is configured not to support mobile routers, it
   sets the status code in the Binding Acknowledgement to '140' (Mobile
   Router Operation not permitted).

   If one or more prefixes received in the Binding Update are invalid
   and the Home Agent cannot setup forwarding for the prefixes, the Home
   Agent sets the status code in the Binding Acknowledgement to '141'
   (Invalid Prefix) in order to indicate this to the Mobile Router.

   If the Mobile Router is not authorized to use this Home Address to
   forward packets for one or more prefixes that are present in the
   Binding Update, the Home Agent sets the status code in the Binding
   Acknowledgement to '142' (Not Authorized for Prefix) in order to
   indicate this.

   The Home Agent sets the status code to 143 (Forwarding Setup
   failed) if it is unable to determine the information needed to setup
   forwarding for the mobile network.  This is used in the Implicit mode
   where the Mobile Router does not include any prefix information in
   the Binding Update.


6.7. Mobile Network Prefix De-Registration

   The Mobile Router de-registers with the Home Agent by sending a
   Binding Update with the lifetime set to zero.  When the Home Agent
   successfully processes the de-registration BU, it deletes the Binding
   Cache Entry for the Mobile Router's Home Address and stops proxying
   the Home Address.  This is described in detail in the Mobile IPv6
   specification [1].

   In addition, the Home Agent also removes the bi-directional tunnel
   and stops forwarding packets to the mobile network.  The Home Agent
   should keep all necessary information to clean up whichever routes it
   installed, whether they come from implicit or explicit source.














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7. Modifications to Dynamic Home Agent Discovery

   This document extends the Dynamic Home Agent Discovery mechanism
   defined in [1], so that Mobile Routers attempt registration only with
   Home Agents that support Mobile Routers.


7.1. Modified Dynamic Home Agent Discovery Request

   A new flag (R) (Support for Mobile Routers) is introduced in the
   Dynamic Home Agent Discovery Reguest message defined in [1].  The
   Mobile Router sets this flag to indicate that it wants to discover
   Home Agents that support Mobile Routers.

        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      |     Code      |            Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Identifier           |R|          Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Mobile Router Support Flag (R)

         A 1 bit flag which when set indicates that the Mobile Router
         wants to discover Home Agents that support Mobile Routers.

      For a description of the other fields in the message, see [1].


7.2. Modified Dynamic Home Agent Discovery Reply

   A new flag (R) (Support for Mobile Routers) is introduced in the
   Dynamic Home Agent Discovery Reply message defined in [1].  If a Home
   Agent receives a Dynamic Home Agent Discovery request message with
   the Mobile Router Support flag set, it MUST reply with a list of Home
   Agents that support Mobile Routers.  The Mobile Router Support flag
   MUST be set if there is atleast one Home Agent that supports Mobile
   Routers.  If none of the Home Agents support Mobile Routers, the Home
   Agent MAY reply with a list of Home Agents that support just Mobile
   IPv6 Mobile Nodes.  In this case, the Mobile Router Support flag MUST
   be set to 0.










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   The modified 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |            Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Identifier          |R|           Reserved          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       .                                                               .
       .                      Home Agent Addresses                     .
       .                                                               .
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Mobile Router Support Flag (R)

         A 1 bit flag which when set indicates that the Home Agents
         listed in this message support Mobile Routers.

      For a description of the other fields in the message, see [1].


7.3. Modified Home Agent Information Option

   A new flag (R) (Support for Mobile Routers) is introduced in the Home
   Agent Information Option defined in [1].  If a Home Agent supports
   Mobile Routers, it SHOULD set the flag.

        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     |R|         Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Home Agent Preference     |      Home Agent Lifetime      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Mobile Router Support Flag (R)

         A 1 bit flag which when set indicates that the Home Agent
         supports Mobile Routers.

      For a description of the other fields in the message, see [1].






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8. Support for Dynamic Routing Protocols

   In the solution described so far, forwarding to the mobile network
   at the Home Agent is set up when the Home Agent receives a Binding
   Update from the Mobile Router.  An alternative to this is for the
   Home Agent and the Mobile Router to run an intra-domain routing
   protocol like RIPng [11] and OSPF [12] through the bi-directional
   tunnel.  The Mobile Router can continue running the same routing
   protocol that it was running when it was attached to the home link.

   This feature is very useful when the mobile network is large with
   multiple subnets containing different IPv6 prefixes.  Routing changes
   in the mobile network are propagated to the Home Agent quickly.
   Routing changes in the home link are also propogated to the Mobile
   Router very quickly.

   When the Mobile Router is attached to the home link, it runs a
   routing protocol by sending routing updates through its egress
   interface.  When the mobile router moves and attaches to a visited
   network, it MUST stop sending routing updates on the interface with
   which it attaches to the visited link.  This is very important so
   that IPv6 prefixes specific to the mobile network do not leak into
   the visited network.  The Mobile Router then starts sending routing
   protocol messages through the bi-directional tunnel towards the Home
   Agent.  Most routing protocols use link local addresses as source
   addresses for the routing information messages.  The Mobile Router is
   allowed to use link local addresses for the inner IPv6 header of an
   encapsulated packet.  But these messages after decapsulation MUST NOT
   be forwarded to another link by either the Mobile Router or the Home
   Agent.

   When the Home Agent receives the encapsulated routing protocol
   message, it processes the inner packets and updates its routing table
   accordingly.  The next hop information in these routing entries is
   filled with the Mobile Router's link local address with the outgoing
   interface set to the bi-directional tunnel.

   Similary, the Home Agent also sends routing updates through the
   bi-directional tunnel to the Mobile Router.  The Mobile Router
   processes these routing protocol messages and updates its routing
   table.  For all routes advertised by the Home Agent, the Mobile
   Router sets the outgoing interface to the bi-directional tunnel to
   the Home Agent.

   When the Mobile Router and the Home Agent exchange routes through
   a dynamic routing protocol, the Mobile Router should be careful in
   including the same Mobile Network Prefixes in the Binding Update to
   the Home Agent and in the routing protocol updates.  The Home Agent
   depending on its configuration might not add routes based on the



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   prefix information in the Binding Updates at all, and might use only
   the routing protocol updates.  Moreover, including the same prefix
   information in both the Binding Update and the routing protocol
   update is redundant.

   Since the routing protocol messages from the Home Agent to the Mobile
   Router could potentially contain information about the internal
   routing structure of the home network, these messages require
   authentications and confidentiality protection.  Confidentialy
   protection using IPsec ESP [4] MUST be supported and SHOULD be
   used.  For protecting routing protocol messages using ESP, the
   bi-directional tunnel between the Mobile Router and the Home
   Agent should be treated as the outgoing interface, with link local
   addresses as source and destination addresses for the messages.
   IPsec ESP with a non-null encryption algorithm should be used
   in transport mode for protecting the routing protocol messages.
   Examples of SPD entries for protecting OSPFv3 messages are described
   in [13].


































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9. Security Considerations

   All signaling messages between the Mobile Router and the Home Agent
   MUST be authenticated by IPsec [5].  The use of IPsec to protect
   Mobile IPv6 signaling messages is described in detail in the HA-MN
   IPsec specification [2].  The signaling messages described in this
   document just extend Mobile IPv6 messages and do not require any
   changes to what is described in the HA-MN IPsec specification.

   The Mobile Router has to perform ingress filtering on packets
   received from the mobile network to ensure that nodes in the Mobile
   Network do not use the bi-directional tunnel to launch IP spoofing
   attacks.  In particular the Mobile Router SHOULD check that the IP
   source address in the packets received from the nodes in the Mobile
   Network belongs to the Mobile Network Prefix and is not the same as
   one of the addresses used by the Mobile Router.  In case the Mobile
   Router receives a IP-in-IP tunneled packet from a node in the Mobile
   Network and the Mobile Router has to forward the decapsulated packet,
   it SHOULD perform the above mentioned checks on the source address of
   the inner packet.

   The Home Agent has to verify that packets received through the
   bi-directional tunnel belong to the mobile network.  This check is
   necessary in order to prevent nodes from using the Home Agent to
   launch attacks that would have otherwise been prevented by ingress
   filtering.  The source address of the outer IPv6 header MUST be set
   to the Mobile Router's current Care-of address.  The source address
   of the inner IPv6 header MUST be a topologically correct address with
   respect to the IPv6 prefixes used in the mobile network.

   When the Mobile Router is running a dynamic routing protocol as
   described in Section 8, it injects routing update messages into the
   Home Link.  The Home Agent MUST verify that the Mobile Router is
   allowed to send routing updates before processing the messages and
   propagating the routing information.

   Please refer to the Mobile IPv6 specification [1] for security
   considerations when the Mobile Router operates as a Mobile Host.














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Internet Draft             NEMO Basic Support              December 2003


10. IANA Considerations

   This document defines a new Mobility Header Option, the Mobile
   Network Prefix Option.  This option is described in Section 4.3.  The
   type value for this option needs to be assigned from the same space
   used by the mobility options defined in [1].

   This document also defines the following new Binding Acknowledgement
   status values.  These status values are defined in Section 4.2
   and need to be assigned from the same space used for Binding
   Acknowledgement status values in [1].

    -  Mobile Router Operation not permitted

    -  Invalid Prefix

    -  Not Authorized for Prefix

    -  Forwarding Setup failed


11. Contributors

   We would like to acknowledge Ludovic Bellier, Claude Castelluccia,
   Thierry Ernst, Miguel Catalina-Gallego, Christophe Janneteau, T.J.
   Kniveton, Hong-Yon Lach, Jari T. Malinen, Koshiro Mitsuya, Alexis
   Olivereau, Charles E. Perkins and Keisuke Uehara, for their work on
   earlier proposals for Network Mobility.  This document inherits a lot
   of ideas from these proposals.


12. Acknowledgements

   We thank all members of the NEMO Working Group, and of the preceding
   MONET BoF for fruitful discussions on the mailing list and at IETF
   meetings.

   Kent Leung, Marco Molteni and Patrick Wetterwald for their work on
   Network Mobility for IPv4 and IPv6.

   Tim Leinmueller for many insightful remarks and for Section 7.

   Jari Arkko, James Kempf and Chan-Wah Ng for their thorough review and
   comments.








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References

   [1]  D. Johnson, C. Perkins and J. Arkko. Mobility Support in IPv6.
        Internet Draft, IETF. draft-ietf-mobileip-ipv6-24.txt (work in
        progress). June 2003.

   [2]  J. Arkko, V. Devarapalli and F. Dupont. Using IPsec to Protect
        Mobile IPv6 Signaling between Mobile Nodes and Home Agents.
        Internet Draft, IETF. draft-ietf-mobileip-mipv6-ha-ipsec-06.txt
        (work in progress). June 2003.

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

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

   [5]  S. Kent and R. Atkinson. Security Architecture for the Internet
        Protocol. RFC 2401, IETF. November 1998.

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

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


References

   [8]  J. Manner and M. Kojo. Mobility Related Terminology. Internet
        Draft, IETF. draft-ietf-seamoby-mobility-terminology-05.txt
        (work in progress). November 2003.

   [9]  T. Ernst and H.-Y. Lach. Network Mobility Support Terminology.
        Internet Draft, IETF. draft-ietf-nemo-terminology-00.txt (work
        in progress). May 2003.

   [10] T. Ernst. Network Mobility Support Goals and Requirements.
        Internet Draft, IETF. draft-ietf-nemo-requirements-01.txt (work
        in progress). May 2003.

   [11] G. Malkin and R. Minnear. RIPng for IPv6. RFC 2080, IETF.
        January 1997.

   [12] R. Coltun, D. Ferguson and J. Moy. OSPF for IPv6. RFC 2470,
        IETF. December 1999.






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Internet Draft             NEMO Basic Support              December 2003


   [13] M. Gupta and N. Melam. Authentication/Confidentiality for
        OSPFv3. Internet Draft, IETF. draft-ietf-ospf-ospfv3-auth-04.txt
        (work in progress). December 2003.

   [14] T. Ernst. Network Mobility Support in IPv6. PhD Thesis,
        University Joseph Fourier, Grenoble, France. October 2001.

   [15] T. Ernst, K, Mitsuya and K. Uehara. Network Mobility from the
        InternetCAR perspective. Journal of Interconnection Networks
        (JOIN), Vol. 4, No. 3. September 2003.










































Devarapalli, et al.                                            [Page 30]


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A. Examples of NEMO Basic Support Operation

   This section tries to illustrate the NEMO protocol using a Mobile
   Router and a Mobile Node belonging to different administrative
   domains.  The Mobile Router's mobile network consists of a Local
   Fixed Node (LFN) and a Local Fixed Router (LFR) [9].  The LFR has
   an access link to which other Mobile Nodes or Mobile Routers could
   attach to.

   Figure 1 depicts the scenario where both the Mobile Router and the
   Mobile Node are at home.


                     +----+       +-------+
                     | MN |       | HA_MN |
                     +--+-+  1::  +---+---+
                       2+-------------+3
                                      |
                                      |
        +-------+2 2:: +-------------------+ 3:: 2+-------+
        | CN_MN |------|     Internet      |------| CN_MR |
        +-------+      +-------------------+      +-------+
                             4::      |
                                      |
                       2+-------------+3
                     +--+-+       +---+---+
                     | MR |       | HA_MR |
                     +--+-+       +-------+
                    5:: |1
                ----------
                2|      |3
            +--+-+   +--+-+
            | LFN|   | LFR|
            +--+-+   +--+-+
                    6:: |1
                ----------


            Figure 1: Mobile Router and Mobile Node at home.













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   The Mobile Router then moves away from the home link and attaches to
   a visited link.  This is shown in Figure 2.  The Mobile Router sends
   a Binding Update to HA_MR when it attaches to a visited link and
   configures a Care-of Addres.  HA_MR creates a binding cache entry for
   the Mobile Router's Home Address and also sets up forwarding for the
   prefixes on the mobile network.


                     +----+       +-------+
                     | MN |       | HA_MN |
                     +--+-+  1::  +---+---+
                       2+-------------+3
                                      |
                                      |
        +-------+2 2:: +-------------------+ 3:: 2+-------+
        | CN_MN |------|     Internet      |------| CN_MR |
        +-------+      ++------------------+      +-------+
                        | 7::     4:: |           4::2->7::2
                        |             |
                       2+             +3
                     +--+-+       +---+---+
                     | MR |       | HA_MR | 4::2->7::2
                     +--+-+       +-------+ 5::/prefixlen -> forward
                    5:: |1                                   to MR
                ----------                  6::/prefixlen -> forward
                2|      |3                                   to MR
            +--+-+   +--+-+
            | LFN|   | LFR|
            +--+-+   +--+-+
                    6:: |1
                ----------



               Figure 2: Mobile Router on a Visited Link.

















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   Figure 3 shows the Mobile Node moving away from its home link and
   attaching to the Mobile Router.  The Mobile Node configures a Care-of
   Address from the prefix advertised on the mobile network and sends a
   Binding Update to its Home Agent (HA_MN) and its Correspondent Node
   (CN_MN). Both HA_MN and CN_MN create binding cache entries for the
   Mobile Node's Home Address.


                                  +-------+
                                  | HA_MN | 1::2->6::2
                             1::  +---+---+
                             ---------|3
                                      |
                                      |
        +-------+2 2:: +-------------------+ 3:: 2+-------+
        | CN_MN |------|     Internet      |------| CN_MR |
        +-------+      ++------------------+      +-------+
       1::2->6::2       | 7::     4:: |           4::2->7::2
                        |             |
                       2+             +3
                     +--+-+       +---+---+
                     | MR |       | HA_MR | 4::2->7::2
                     +--+-+       +-------+ 5::/prefixlen -> forward
                    5:: |1                                   to MR
                ----------                  6::/prefixlen -> forward
                2|      |3                                   to MR
            +--+-+   +--+-+
            | LFN|   | LFR|
            +--+-+   +--+-+
                    6:: |1
                --------+-
                        |2
                     +--+-+
                     | MN |
                     +----+


                Figure 3: Mobile Node attached to Mobile
                        Router on a Visited Link













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B. Changes from Previous Version

   The following changes have been made to this document from version 01

    -  Dynamic Home Agent Discovery was modified to return only Home
       Agents that support Mobile Routers.  A new section was added to
       the specification.  (Issue 16).

    -  A new flag (R) was introduced in the Binding Acknowledgement for
       the Home Agent to indicate to the Mobile Router that it processed
       the Mobile Router flag (R) in the corresponding Binding Update.
       (Issue 16).

    -  Relaxed a Mobile IPv6 requirement which said the Home Agent MUST
       drop a Binding Update if the home address is not configured from
       the home prefix.  NEMO Home Agent drops the Binding Update only
       if the Home Address does not belong to the prefix that the Home
       Agent is currently configured to serve.  (Issue 19)

    -  Explicit Prefix Length mode is removed.  (Issue 20).

    -  Text related to Mobile Router performing ingress filtering was
       added to the Security Considerations section to prevent some
       threats due to tunneling.  (Issue 23).

    -  Added a new section on Mobile Router returning home.  (Issue 25).

    -  Clarified that the Prefix Table is not required when a dynamic
       routing protocol is being run between the Mobile Router and the
       Home Agent.  (Issue 26).

    -  Clarified the use of Prefix Table.  (Issue 25).

    -  Clarified Mobile Router sending router advertisements on its
       egress interface when at home.  (Issue 21 and 26).

    -  Clarified implementation requirements with respect to the Mobile
       IPv6 specification.  (Issue 27).

    -  Modified/added network mobility terms so that the NEMO
       terminology document becomes an informative reference.  (Issue
       28).

    -  Provided more information for creating SPD entries for protecting
       routing protocol messages.  (Issue 29).







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Authors Addresses


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

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

        Alexandru Petrescu
        Motorola Labs
        Parc les Algorithmes Saint Aubin
        Gif-sur-Yvette 91193
        France
        Email:  Alexandru.Petrescu@motorola.com

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






















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