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Versions: (draft-laganier-netlmm-mn-ar-if) 00 01 02 03

Network Working Group                                        J. Laganier
Internet-Draft                                          DoCoMo Euro-Labs
Intended status: Informational                              S. Narayanan
Expires: August 16, 2008                                      iTCD/CSUMB
                                                               P. McCann
                                                                Motorola
                                                       February 13, 2008


  Interface between a Proxy MIPv6 Mobility Access Gateway and a Mobile
                                  Node
                     draft-ietf-netlmm-mn-ar-if-03

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
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   This Internet-Draft will expire on August 16, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).










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Abstract

   This document describes an interface between mobile nodes (MNs) and a
   mobility access gateway (MAG) of a network-based localized mobility
   management (NETLMM) domain.  The interface has two functions which
   are invoked when a MN attaches and detaches from a MAG.  The
   attachment function lets the MAG authenticate the MN identifier, does
   address(es) and default router configuration for the MN, and informs
   the MAG about the multicast listener state of the MN.  During the
   attachment function the NETLMM protocol is triggered between the MAG
   and Localized Mobility Anchor (LMA) to register the MN in the local
   domain.  The detachment function lets the MAG detect that the MN has
   left so that it can deregister the MN at the LMA using the NETLMM
   protocol.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Operating Environment  . . . . . . . . . . . . . . . . . . . .  7
   4.  Interactions of NETLMM Architecture with Subnet and Link
       Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  NETLMM Subnet Model  . . . . . . . . . . . . . . . . . . . 10
     4.2.  NETLMM Link Model  . . . . . . . . . . . . . . . . . . . . 11
   5.  Address Collision Considerations . . . . . . . . . . . . . . . 12
   6.  MN_ATTACH Function . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  MAG_GET_MN_ID Sub-function . . . . . . . . . . . . . . . . 13
     6.2.  MAG_GET_HI Sub-function  . . . . . . . . . . . . . . . . . 15
     6.3.  MN_GET_ADDR_PARMS Sub-function . . . . . . . . . . . . . . 15
     6.4.  MN_GET_DEFAULT_ROUTER Sub-function . . . . . . . . . . . . 16
     6.5.  MAG_GET_MN_MCAST_GROUPS Sub-function . . . . . . . . . . . 16
   7.  MN_DETACH Function . . . . . . . . . . . . . . . . . . . . . . 17
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     11.1. Normative references . . . . . . . . . . . . . . . . . . . 21
     11.2. Informative references . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Version history . . . . . . . . . . . . . . . . . . . 23
     A.1.  -02 to -04 . . . . . . . . . . . . . . . . . . . . . . . . 23
     A.2.  -01 to -02 . . . . . . . . . . . . . . . . . . . . . . . . 23
     A.3.  -00 to -01 . . . . . . . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
   Intellectual Property and Copyright Statements . . . . . . . . . . 25






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1.  Introduction

   It is suggested in [RFC4830] that it would be desirable to have a
   localized mobility management protocol in which the host is not
   involved.  The requirements for such a protocol have been analyzed in
   [RFC4831].  Accordingly, a protocol for network-based localized
   mobility management (NETLMM) of IPv6 nodes is specified by the NETLMM
   working group [I-D.ietf-netlmm-proxymip6].  Because the NETLMM
   protocol is network based, the mobile node (MN) is not required to
   implement a new mechanism in its IP stack, nor to change its IP
   address when it attaches to a new mobility access gateway (MAG).

   Because the IPv6 MN will use a vanilla IPv6 stack, the interface
   between an MN and its MAG has to be preserved.  This means that
   standard IPv6 should work seamlessly with the network-based localized
   mobility support.  More specifically, we require the proposed
   solution to be compatible with the mechanisms specified in:

   o  Neighbor Discovery for IP version 6 [RFC2461]

   o  IPv6 Stateless Address Autoconfiguration [RFC2462]

   o  Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315]

   o  Privacy Extensions for Stateless Address Autoconfiguration in IPv6
      [RFC3041]

   o  Detecting Network Attachment in IPv6 Networks (DNAv6)
      [I-D.ietf-dna-protocol]

   o  SEcure Neighbor Discovery (SEND) [RFC3971]

   o  Cryptographically Generated Addresses (CGAs) [RFC3972]

   This document describes an interface between mobile nodes (MNs) and a
   mobility access gateway (MAG) of a network-based localized mobility
   management (NETLMM) domain.  The interface has two functions which
   are invoked when a MN attaches and detaches from a MAG.  The
   attachment function lets the MAG authenticate the MN identifier, does
   address(es) and default router configuration for the MN, and informs
   the MAG about the multicast listener state of the MN.  During the
   attachment function the NETLMM protocol is triggered between the MAG
   and Localized Mobility Anchor (LMA) to register the MN in the local
   domain.  The detachment function lets the MAG detect that the MN has
   left so that it can deregister the MN at the LMA using the NETLMM
   protocol.

   In the absence of link-layer specific mechanisms implementing these



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   functions, this document describes which IP protocols should be used
   to provide the necessary interface between the MN and the MAG.

















































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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The following terms are defined within the scope of this document:

   Mobile Node (MN)
      an IPv6 node moving in the NETLMM domain.

   Mobility Access Gateway (MAG)
      a default router that connects the MN to the NETLMM domain.

   Localized Mobility Anchor (LMA)
      a router located in the NETLMM domain that handles packet
      exchanges with nodes in the domain.

   Network-based Localized Mobility Management Domain (NETLMM domain)
      an administrative domain spanning links served by a set of LMAs
      (and their associated MAGs and MNs) that provision addresses from
      the same IP subnet prefix(es).

   Network-based Localized Mobility Management Protocol (NLMP)
      The NETLMM Protocol used in the backhaul of the NETLMM domain
      between MAGs and LMA.

   The following abbreviations are used throughout this document:

   NETLMM: Network-based Localized Mobility Management

   ND: Neighbor Discovery.

   NS: Neighbor Solicitation.

   NA: Neighbor Advertizement.

   RS: Router Solicitation.

   RA: Router Advertisement.

   NDP: Neighbor Discovery Protocol.

   SLAAC: StateLess Address AutoConfiguration

   DHCP: Dynamic Host Configuration Protocol

   SEND: SEcure Neighbor Discovery.



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   DNA: Detecting Network Attachment.

   CGA: Cryptographically Generated Address.

   MNID: An authenticated MN identifier (e.g.  NAI, a SEND public key
   used by the MN for generating its CGAs,an IMSI or TMSI, etc.).













































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3.  Operating Environment

   The MN-MAG NETLMM interface is used between an MN and a MAG of a
   NETLMM domain.  It allows the MAG and/or MN to detect network
   attachment and detachment, causing the MAG to use the NETLMM protocol
   to update routing at the LMA so that the MN stays reachable when it
   roams across the NETLMM domain.

         /---------------------------\
        /          Internet           \
        \                             /
         \-------+---------+---------/
                 |         |
         /--------+---------+--------\  ----
        /                             \    ^
       /          +-----+              \   |
       |          | LMA |-+            |   N
       |          +-----+ |-+          |   E
       |            +-----+ |          |   T
       |              +-----+          |   L
       |        Backhaul Network       |   M
       |    +------+       +------+    |   M
       |- - | MAG1 | ..... | MAG2 | - -|
       |    +------+       +------+    |   d
       |       / \  Access   / \       |   o
       |      /   \ Network /   \      |   m
       |     /     \       /     \     |   a
       |     +----+                    |   i
       |     | MN | ------->           |   n
       \     +----+ MAG change         /   |
        \                             /    v
         \---------------------------/  ----

                    Figure 1: Reference Network Diagram

   The deployment scenario is shown in Figure 1 above: several MAGs are
   attached to an IP routing domain connected to the outside Internet
   via an LMA.  The MNs, MAGs, LMAs, and in-between routing fabric
   constitute the NETLMM domain.  Packets arriving at the LMA and
   destined to a MN are tunneled to the appropriate MAG.  Packets from
   the MN are received by the MAG and tunneled to the LMA and then
   decapsulated and sent on to the Internet.

   In the absence of a link-layer specific mechanisms to implement the
   MN-MAG interface, it is required to have a common interface defined
   at the IP layer.  Because no NETLMM specific software support is
   assumed to be present on MNs, this interface has to rely only on
   standards track IPv6 protocols such as ND, DHCP, SEND, and DNA.



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   Interactions of these components with NETLMM are represented in
   Figure 2 below (note that hints received by DNA from other layers are
   omitted for clarity):


                  MN|MAG
                Interface
                    |

                    |     +------------+      +----------+
                          |            |      |          |
                    |     | +--------+ | NLMP | +------+ |
                          | | NETLMM |<-------->|NETLMM| |
                    |     | +--------+ |      | +------+ |
                          |   ^     ^  |      |    ^     |
   +----------+     |     |   |     |  |      |    |     |
   |          |           |   v     |  |      |    |     |
   | +------+ |     |     | +-----+ |  |      |    |     |
   | |  DNA | |  NDP/DHCP | | DNA | |  |      |    |     |
   | | SEND |<------|------>|SEND | |  |      |    |     |
   | |  ND  | |           | | ND  | |  |      |    |     |
   | | DHCP | |     |     | |DHCP | |  |      |    |     |
   | +------+ |           | +-----+ |  |      |    |     |
   |    ^     |     |     |   ^     |  |      |    |     |
   |    |     |           |   |     |  |      |    |     |
   |    v     |     |     |   v     |  |      |    v     |
   | +------+ |           | +----+  |  |      | +------+ |
   | |      | |     |     | |    |<-+  |      | |      | |
   | |      | |   IPv6    | |    |     | IPv6 | |      | |
   | | IPv6 |<------|------>|IPv6|<------------>| IPv6 | |
   | +------+ |           | +----+     |      | +------+ |
   |          |     |     |            |      |          |
   |    MN    |           |    MAG     |      |   LMA    |
   +----------+     |     +------------+      +----------+

                    |

                  Figure 2: NETLMM Component Interactions

   An overview of the interactions between the MN-MAG interface and the
   NETLMM protocol is shown in Figure 3.










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                 MN|MAG
               Interface
    MN             |             MAG                LMA
    |              |              |                  |
    |   /          |          \   |   /          \   |
    |  /|          |          |\  |  /|          |\  |
    | / +---------------------+ \ | / +----------+ \ |
    |/         MN_ATTACH         \|/     NETLMM     \|
    |\          function         /|\    protocol    /|
    | \ +---------------------+ / | \ +----------+ / |
    |  \|          |          |/  |  \|          |/  |
    |   \          |          /   |   \          /   |
    |              |              |                  |
    |   /          |          \   |   /          \   |
    |  /|          |          |\  |  /|          |\  |
    | / +---------------------+ \ | / +----------+ \ |
    |/        data packet        \|/  data packet   \|
    |\          traffic          /|\    traffic     /|
    | \ +---------------------+ / | \ +----------+ / |
    |  \|          |          |/  |  \|          |/  |
    |   \          |          /   |   \          /   |
    |              |              |                  |
    |   /          |          \   |   /          \   |
    |  /|          |          |\  |  /|          |\  |
    | / +---------------------+ \ | / +----------+ \ |
    |/         MN_DETACH         \|/     NETLMM     \|
    |\          function         /|\    protocol    /|
    | \ +---------------------+ / | \ +----------+ / |
    |  \|          |          |/  |  \|          |/  |
    |   \          |          /   |   \          /   |
    |              |              |                  |

             Figure 3: NETLMM MN-MAG Interface Usage Overview


















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4.  Interactions of NETLMM Architecture with Subnet and Link Models

   Within the Internet addressing model, the terms link and subnet have
   a tight relationship.  Their generally admitted definitions are
   [I-D.thaler-intarea-multilink-subnet-issues]:

      Link: a topological area of an IP network delimited by routers.

      Subnet: a topological area of an IP network that uses the same
      unsubdivided address prefix.

   There has recently been protocol proposals achieving multi-link
   subnets, i.e. the ability for a subnet to span multiple links.
   However, the consensus in the IETF has been, and remains, that one
   subnet spans only one link
   [I-D.thaler-intarea-multilink-subnet-issues].

   A straightforward approach to the design of NETLMM would have been to
   lay a single subnet on the entire NETLMM domain.  That would ensure
   that the MN does not see layer 3 movements since the subnet would
   never change.  However, such an approach would constitute a multi-
   link subnet, and is thus not deemed acceptable.

   The following subsection will discuss what kind of subnet and link
   models have been chosen for the NETLMM architecture.

4.1.  NETLMM Subnet Model

   Thus, the NETLMM addressing model is subject to the following two
   constraints:

   o  The subnet of a MN does not change when the MN changes its
      attachment point in the domain.

   o  The subnet of a MN does not span more than one link.

   Because of the first constraint, the subnet of a MN must be valid
   wherever in the domain the MN attaches to.  However, because of the
   second constraint, the subnet cannot be valid at more than one such
   attachment point.  Thus, the subnet of the MN has to follow the
   movements of the MN.  This addressing model is denoted "per-MN subnet
   model", and satisfies constraints of both the Internet and NETLMM
   architectures:

      A unique prefix MUST be assigned by the NETLMM fabric to each of
      the MNs in the domain.  The MAG MUST NOT configure a global
      unicast address based on this prefix.




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4.2.  NETLMM Link Model

   The choice of the per-MN addressing model is however conflicting with
   the use of a shared link layer (e.g.  Ethernet, 802.11) as a last hop
   of the NETLMM domain.

   In the per-MN subnet model, two MNs always have different subnets.
   Hence, even though they might be attached to the same shared link
   layer, they will never communicate directly with global addresses.
   That happens since on-link determination will always conclude that
   they are attached to different link because it is based on subnet
   comparisons.

   They will however be able to communicate directly with link-local
   addresses.  This is not problematic since link-local addresses are
   confined to one link and therefore it does not introduce multi-link
   subnet issues.

   There is however one problem that arises due to the use of Solicited-
   Node and All-Nodes multicast IPv6 addresses [RFC4291] as a
   destination address for sending unsolicited Neighbor Advertisement
   (NA) messages [RFC2461].  When one MN sends such message, it can be
   received by other MNs on the same link which will, as a result,
   create a neighbor cache entry for the sender of the NA.  If the NA
   contained as a target address one of the MN's global unicast address,
   the receiver is then in a position to communicate directly with this
   global unicast address, even though it does not share a common subnet
   prefix (they are per-MN subnet prefixes).  This is not a problem as
   long as these two MNs remain attached on the same link.  But if later
   on one of the MN moves onto a different link, they will no longer be
   able to communicate directly and this will result in a communication
   failure, although they were using global addresses whose reachability
   should be maintained.  This is not acceptable.

      Thus, the interface described in this document MUST only be used
      in deployments where the link between the MN and the MAG is point-
      to-point.  The interface MUST NOT be used in deployments where the
      link between the MN and the MAG is shared and/or multi-access.
      Future specifications MAY define interfaces for use with shared
      and/or multi-access links.











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5.  Address Collision Considerations

   As per the DNAv6 protocol [I-D.ietf-dna-protocol], the MN will not
   execute Duplicate Address Detection (DAD)[RFC2462] after a handoff
   within the same domain.  This is because the MN will always receive
   the same subnet prefix in the RA and conclude that it did not change
   link.  Hence there seems to be no need for executing DAD again.
   However, in NETLMM the link did changed.  Because the link is point-
   to-point the only new entity on the link is the MAG, and it is
   possible that a collision occurs between link local addresses of the
   MN and the MAG (Note that no collisions are possible with global
   unicast address(es) since the subnet prefix has been uniquely
   assigned to the MN).

   One solution to this issue would be that in a given domain, each MAG
   also defends link-local addresses of other MAGs in the domain.  This
   would ensure that when the MN first attaches to the NETLMM domain and
   executes DAD it is able to pro-actively detect collisions that may
   happen with any MAG of the domain.  Such a solution has however two
   drawbacks:

   o  Each MAG needs to know link-local addresses of all other MAGs in
      the domain.

   o  If SEND is used, each MAG also need to know private keys of all
      other MAGs since SEND requires a Neighbor Advertisement (NA)
      message defending an address to be signed with the SEND public key
      generating the CGA link-local address.

   A much simpler solution is:

      All MAGs in a NETLMM domain MUST configure the same link-local
      address.

   When SEND is used, that means that all MAGs share a single SEND
   public-private key pair, and hence a single link-local CGA.

   Since all MAGs in a domain have the same link local address, if the
   MN executes DAD at his first attachment and concludes that there is
   no collision with the link-local address of the first MAG, a
   collision with any other MAG in the domain is impossible.










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6.  MN_ATTACH Function

   The MN_ATTACH function is invoked by the MN whenever it attaches to a
   new MAG, and consists of the following sub-functions:

   o  MAG_GET_MN_ID: It provides the MAG with the identifier of the MN
      (MNID).  This identifier MUST be securely bound to the MN, and the
      corresponding binding MUST be verifiable by the MAG.  This
      triggers the MAG to authenticate the MN as the owner of this MNID.
      If authentication fails the MN_ATTACH function terminates with
      failure status, otherwise it continues.

   o  MAG_GET_HI: It provides the MAG with information to put in the
      Access Technology Type, Mobile Node Interface Identifier, and
      Handoff Indication fields.

   o  MN_GET_ADDR_PARMS: It provides the MN with IPv6 addressing
      configuration parameters, i.e.  IPv6 subnet prefix(es) or global
      address(es).  The MAG will then register the MN IPv6 subnet
      prefix(es) or address(es) with the LMA using the NETLMM protocol.

   o  MN_GET_DEFAULT_ROUTER: It provides the MN with the link local IPv6
      address of its default router (e.g. the MAG).

   o  MAG_GET_MN_MCAST_GROUPS: It provides the MAG with the multicast
      group(s) that the MN previously joined (while attached to a
      previous MAG).  This triggers the MAG to subscribe to the
      multicast tree(s) corresponding to the group(s) joined by the MN.

   The MN_ATTACH function will typically be implemented by multiple
   protocols, some of them possibly non-IP protocols.  The following
   subsections will describe in more details the MAG_GET_MN_ID,
   MAG_GET_HI, MN_GET_ADDR_PARMS, MN_GET_DEFAULT_ROUTER, and
   MAG_GET_MN_MCAST_GROUPS subfunctions, in particular what they
   achieve, and how.

6.1.  MAG_GET_MN_ID Sub-function

   The MAG_GET_MN_ID function provides the MAG with the identifier of
   the MN (MNID).  This identifier MUST be securely bound to the MN, and
   the corresponding binding MUST be verifiable by the MAG [RFC4832].
   This triggers the MAG to authenticate the MN as the owner of this
   MNID.  If authentication fails the MN_ATTACH function terminates with
   failure status, otherwise it continues.

   When the MN_ATTACH function includes a network access authentication
   protocol, such as EAP [RFC3748], the Network Access Identifier (NAI)
   authenticated by the network access authentication protocol is a



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   valid MN ID if it satisfies above constraints (freshness of
   authentication, verifiable by the MAG).

   When the mix of protocols implementing the MN_ATTACH does not include
   a network access authentication protocol, or the network access
   authentication protocol does not provide a suitable MN identifier, or
   does not guarantee fresh authentication of the MN, an alternative
   authentication method based on the DNAv6 protocol
   [I-D.ietf-dna-protocol] and the SEND protocol [RFC3971] MUST be used
   to authenticate the MN, as described below:

   MN      MAG      LMA
    |------>|        |      REQ1. RS(Nonce_MN,PK_MN,Signature_MN)
    |<------|        |      REQ2. NS(Nonce_MAG,PK_MAG,Signature_MAG)
    |------>|        |      REP2. NA(Nonce_MAG,PK_MN,Signature_MN)
    |<------|        |      REP1. RA(Nonce_MN,PK_MAG,Signature_MAG)

              Figure 4: DNAv6/SEND based MNID authentication

   o  In step REQ1, after attachment occurs, and upon the occurrence of
      a Layer 2 link-up event notification, the MN initiates self-
      authentication to the MAG by sending an RS from its link local
      address to the link-scope all-routers multicast address, as per
      Section 5.2.5 of the DNAv6 protocol [I-D.ietf-dna-protocol].
      Since this RS is not sent from the unspecified address, it
      contains the MN SEND public key (PK_MN) in a CGA option, as per
      Section 5.1.1 of the SEND protocol [RFC3971].  This public key is
      used as an MN ID by the MAG.

   o  In step REQ2, after the MAG received from the MN an RS containing
      the MN ID (PK_MN) and the MN link local address, the MAG MUST
      solicit the link-local address of the MN by sending an NS to the
      link-local address of the MN.  This NS contains a fresh nonce
      (Nonce_MN) as per Section 5.3.3. of the SEND protocol [RFC3971].

   o  In step REP2, after the MN received from the MAG a NS containing a
      fresh nonce, it replies to the MAG with an NA containing the same
      fresh nonce as per Section 5.3.3 of the SEND protocol [RFC3971].
      This NA is signed with the MN public key (i.e. the MN ID) as per
      Section 5.2.1 of the SEND protocol [RFC3971].  The MAG will verify
      1) that the Nonce is fresh as per Section 5.3.4.1 of the SEND
      protocol [RFC3971], and 2) that the signature is valid for this
      public key as per Section 5.2.2 of the SEND protocol [RFC3971].
      If these verifications succeed, the MAG has successfully
      authenticated the MN as the owner of the MN ID.

   o  In step REP1, the MAG concludes the DNAv6 protocol
      [I-D.ietf-dna-protocol] by sending to the MN an RA.  This step is



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      not part of the authentication of the MN and is shown here for
      completeness only.  Note that a NETLMM exchange between the MAG
      and LMA MUST occur between REP2 and REP1 so that the MAG can
      obtain the proper Home Network Prefix to advertise toward the MN
      in REP1 (the Router Advertisement).

6.2.  MAG_GET_HI Sub-function

   During the MAG_GET_HI function the MAG MUST be given an indication of
   the link technology in use and MUST populate the Access Technology
   Type (ATT) appropriately.  Usually the MAG will also obtain a link-
   layer address through link establishment or from the Router
   Solicitation message in step REQ1.  For example, the IPv6CP
   Interface-Identifier option [RFC5072] may be negotiated during PPP
   establishment.  The MAG SHOULD place the link-layer address in the
   Mobile Node Interface Identifier (MNIID) option of the Proxy BU.  The
   MAG MUST set the Handoff Indicator option to an appropriate value
   depending on the information it has from link establishment or
   context transfer signaling.  If the MAG knows that there was a
   previous session for this MN using a different ATT and MNIID, then it
   SHOULD set the HI field to 1 (Attachment over a new interface).  If
   the MAG knows that there was a previous session using a different ATT
   but the same MNIID, the MAG SHOULD set the HI field to 2 (Handoff
   between two different interfaces of the mobile node).  If the MAG
   knows that there was a previous session using the same ATT and the
   same MNIID, the MAG SHOULD set the HI field to 3 (Handoff between
   mobile access gateways for the same interface).  If the MAG has no
   information about previous sessions the MAG SHOULD set the HI field
   to 4 (Handoff state unknown).  On subsequent Proxy BUs (sent to
   refresh the lifetime) the MAG SHOULD always set the HI field to 5
   (Handoff state not changed (Re-registration)).

6.3.  MN_GET_ADDR_PARMS Sub-function

   The MN_GET_ADDR_PARMS function allows the MN to configure IP
   addresses.  This can be achieved via different means, including:

   o  Stateless Address Autoconfiguration (SLAAC) [RFC2462]: Allows the
      MN to configure both link local and global unicast address(es).

   o  Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315]:
      Allows the MN to configure global unicast address(es).  Typically
      not used to configure link local unicast address(es).

   o  IP Version 6 over PPP [RFC5072]: Allows the MN to configure link
      local unicast address(es).

   Whenever the MN attaches to a new MAG which is in the same domain as



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   its old MAG, the MN_GET_ADDR_PARMS at the new MAG MUST must not
   change the address(es) that were configured by the MN at the old MAG.

6.4.  MN_GET_DEFAULT_ROUTER Sub-function

   The MN_GET_DEFAULT_ROUTER function provides the MN with its default
   router.  This can be achieved via different means, including:

   o  Router Discovery as specified by the Neighbor Discovery Protocol
      [RFC2461].

   o  IP Version 6 over PPP (PPPv6) [RFC5072].

   Note that Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
   [RFC3315] does not provide a default router.  Instead, Router
   Discovery has to be used.

6.5.  MAG_GET_MN_MCAST_GROUPS Sub-function

   The MAG acts as a multicast router for the MN.  The
   MAG_GET_MN_MCAST_GROUPS provides the MAG with the Multicast Address
   Listening state of the newly attached MN (this state might have been
   established while attached to a previous MAG).  This triggers the MAG
   to subscribe to the multicast tree(s) corresponding to the source(s)
   the MN is listening to.

   In many system architectures, this can be achieved by having, upon
   movement of the MN, the old MAG doing context transfer to the new MAG
   of the Multicast Address Listening state learned via MLDv2 [RFC3810]
   messages.

   When the deployment does not offer such context transfer, upon each
   new MN attachment the MAG MUST send a MLDv2 [RFC3810] General Query
   to the link-scope all-nodes multicast address as per Section 5.1.15
   and 7.1 of the MLDv2 protocol [RFC3810].  A newly attached MN will
   then report its Multicast Address Listening state as per Section 6.2
   of the MLDv2 protocol [RFC3810], thus allowing the MAG to register to
   the appropriate multicast tree(s).













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7.  MN_DETACH Function

   When an MN detaches from a MAG, the MAG has to deregister this MN
   with the LMA.

   When the underlying link layer provides a reliable indication of an
   MN having detached from the MAG, the MAG MUST deregister the MN with
   the LMA upon reception of such indication.

   When the underlying link layer provides no reliable indication of an
   MN having detached from the MAG, it is necessary to allow the MAG to
   detect an MN which silently detaches, or crashes, so that it can
   deregister the MN as a consequence.  When such a link layer is used,
   the MAG MUST periodically execute Neighbor Unreachability Detection
   as per Section 7.3 of the Neighbor Discovery Protocol [RFC2461] with
   each of the attached MNs, even though it has no traffic to deliver to
   the MN.

   When an MN detaches from a MAG, the MAG MUST conclude that multicast
   address listening for the MN terminates for all the sources it was
   listening to.






























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8.  Security Considerations

   The security threats to the MN-AR protocol include:

   o  Eavesdropping on the MN-AR exchange, where an attacker may learn
      information such as the MNID that might be confidential.

   o  Malicious redirection of packets to a location other than that of
      the MN, where traffic can be observed more easily by an attacker.

   o  Causing denial-of-service by de-registering the MN prematurely.

   When the link layer incorporates strong authentication with a secure
   binding to the MN's link address, these threats are mitigated.  A
   protocol such as EAP can be used in a mode where the NAI is obscured,
   obviating threat 1.  EAP can also generate keys that get securely
   bound to native link encryption and authentication mechanisms.  As
   long as all MAGs in a domain faithfully authenticate each MN then
   threats 2 and 3 are also mitigated.

   In the absence of strong layer-2 security, the default protocol based
   on DNAv6 and SEND has somewhat weaker security properties.  The MN_PK
   will be visible to anyone that can eavesdrop on the link.  The
   protocol is vulnerable to a man-in-the-middle attack where the
   messages are relayed by an attacker to an MN that believes it is
   attached to a legitimate MAG.  This could allow an attacker to
   redirect traffic.  Finally, if the layer-2 protocol is left
   vulnerable to spoofing an attacker may be able to generate a link-
   down event which would cause the MAG to deregister the MN.






















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9.  IANA Considerations

   There are no IANA considerations.
















































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10.  Acknowledgments

   As usual in the IETF, this document is the result of a collaboration
   between many people.  The authors would like to thanks (in
   alphabetical order) James Kempf, Alexandru Petrescu, Fred Templin and
   Christian Vogt for discussion and/or comments that helped with first
   versions of this document.

   Ian Chakeres contributed the reference network diagram.

   Julien Laganier is partly funded by Ambient Networks, a research
   project supported by the European Commission under its Sixth
   Framework Program.  The views and conclusions contained herein are
   those of the authors and should not be interpreted as necessarily
   representing the official policies or endorsements, either expressed
   or implied, of the Ambient Networks project or the European
   Commission.


































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11.  References

11.1.  Normative references

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,
              December 1998.

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 2462, December 1998.

   [RFC3041]  Narten, T. and R. Draves, "Privacy Extensions for
              Stateless Address Autoconfiguration in IPv6", RFC 3041,
              January 2001.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)",
              RFC 3748, June 2004.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [I-D.ietf-dna-protocol]
              Kempf, J., "Detecting Network Attachment in IPv6 Networks
              (DNAv6)", draft-ietf-dna-protocol-06 (work in progress),
              June 2007.

   [I-D.ietf-netlmm-proxymip6]
              Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6",
              draft-ietf-netlmm-proxymip6-10 (work in progress),
              February 2008.



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11.2.  Informative references

   [RFC5072]  S.Varada, Haskins, D., and E. Allen, "IP Version 6 over
              PPP", RFC 5072, September 2007.

   [RFC4830]  Kempf, J., "Problem Statement for Network-Based Localized
              Mobility Management (NETLMM)", RFC 4830, April 2007.

   [RFC4831]  Kempf, J., "Goals for Network-Based Localized Mobility
              Management (NETLMM)", RFC 4831, April 2007.

   [RFC4832]  Vogt, C. and J. Kempf, "Security Threats to Network-Based
              Localized Mobility Management (NETLMM)", RFC 4832,
              April 2007.

   [I-D.thaler-intarea-multilink-subnet-issues]
              Thaler, D., "Issues With Protocols Proposing Multilink
              Subnets", draft-thaler-intarea-multilink-subnet-issues-00
              (work in progress), March 2006.
































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Appendix A.  Version history

A.1.  -02 to -04

   o  -03 was a tombstone

   o  Pete McCann added as editor

   o  Various editorial fixes

   o  Modified description of REP1 to indicate that Proxy BU/BA must
      complete before

   o  Added description of how to set ATT, MNIID, and HI

A.2.  -01 to -02

   o  revamped document structure to make it agnostic to attachment
      method (e.g. authentication, address-configuration, etc.).

   o  specified per-MN subnet prefix, and point-to-point link model.

   o  specified support for multicast.

   o  various editorial changes.

A.3.  -00 to -01

   o  added DHCP access method including DHCP prefix delegation.

   o  added new network reference diagram.

   o  added definitions for NETLMM domain and NLMP.

   o  updated NA proxying method for colliding CGAs.

   o  added text on sending IP multicast messages to a Layer-2 unicast
      address.

   o  added new Section 4.5 text on MNID/IP address binding.

   o  added new Section 5. on multilink subnet issues.

   o  various editorial changes.







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Authors' Addresses

   Julien Laganier
   DoCoMo Communications Laboratories Europe GmbH
   Landsberger Strasse 312
   Munich  D-80687
   Germany

   Phone: +49 89 56824 231
   Email: julien.ietf@laposte.net
   URI:   http://www.docomolab-euro.com/


   Sathya Narayanan
   School of Information Technology and Communications Design
   California State University, Monterey Bay
   3110, Inter-Garrison Road, Building 18, Room 150
   Seaside, CA  93955
   USA

   Phone: +1 831 582 3621
   Email: sathya@njit.edu


   Pete McCann
   Motorola
   MD 2240
   1301 E. Algonquin Rd
   Schaumburg, IL  60196
   USA

   Phone: +1 847 576 3440
   Email: pete.mccann@motorola.com


















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Full Copyright Statement

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   This document is subject to the rights, licenses and restrictions
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Acknowledgment

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