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Versions: 00 01 02 03 04 05 06 07 RFC 4433

   Mobile IP Working Group                              Milind Kulkarni
   INTERNET-DRAFT                                          Alpesh Patel
   Category: Standards Track                                 Kent Leung
   Date    : 8 January 2004                          Cisco Systems Inc.
   
   
   
                   Mobile IPv4 Dynamic Home Agent Assignment
                   draft-ietf-mip4-dynamic-assignment-00.txt
   
   
   Status of this Memo
   
        This document is an Internet-Draft and is in full conformance
        with 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
   
        Mobile IP (RFC 3344) uses the Home Agent (HA) to anchor
        sessions of a roaming Mobile Node (MN). This draft proposes a
        messaging mechanism for dynamic home agent assignment and HA
        redirection. The goal is to provide a mechanism to assign an
        optimal HA for a Mobile IP session while allowing any suitable
        method for HA selection.
   
   
   
   
   
   
   
   
   
   
   
   
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        Table of Contents
   
     1. Introduction......................................................2
     2. Terminology.......................................................3
     3. Problem Statement.................................................4
     3.1 Scope............................................................5
     3.2 Dynamic Home Agent Discovery in RFC 3344.........................5
     3.3 NAI usage and dynamic HA assignment..............................5
     3.4 Redirected HA address extension..................................5
     4. Messaging mechanism for dynamic HA assignment/redirection.........6
     4.1 Messaging for dynamic HA assignment..............................6
     4.1.1 Example with Message Flow Diagram..............................6
     4.2 Messaging for HA redirection.....................................8
     4.2.1 Example with Message Flow Diagram..............................9
     4.2.2 HA Rejects Registration Request and suggests redirection.......9
     5. Mobility Agent Considerations for dynamic HA assignment..........10
     5.1 Mobile Node Considerations......................................10
     5.1.1 MN using FA CoA...............................................11
     5.1.2 MN using Collocated CoA.......................................11
     5.1.3 Refreshing Assigned HA Address on Mobile Node.................12
     5.2 Foreign Agent Considerations....................................12
     5.3 Home Agent Considerations.......................................12
     5.3.1 Assigned Home Agent Considerations............................13
     6. Requested Home Agent Selection...................................15
     7. Error Values.....................................................16
     8. IANA Considerations..............................................16
     9. Security Considerations..........................................17
     9.1 Message Authentication Codes....................................17
     9.2 Areas of Security Concern in this Protocol......................17
     10. Backward Compatibility Considerations...........................18
     11. Change Log......................................................18
     12. Intellectual Property Rights....................................18
     13. Acknowledgements................................................19
     14. References......................................................19
     Authors' Addresses..................................................20
     Full Copyright Statement............................................20
   
   
   1. Introduction
   
   
        This document adds to the Mobile IP protocol [1], by proposing
        a messaging mechanism for dynamic home agent assignment and
        home agent redirection during initial registration. The goal is
        to assign an optimal HA for a Mobile IP session.  The mobile
        node MUST use Network Access Identifier (NAI) extension for
        home address assignment.
   
        MN requests the network to dynamically assign an HA by setting
        HA field to ALL-ZERO-ONE-ADDR (defined in next section) in
        initial Registration Request. If the request is accepted, the
        HA field in successful Registration Reply contains the HA
   
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        address. The requested HA can suggest an alternate HA and if
        so, the Registration Reply is rejected with a new error code
        (REDIRECT-HA-REQ) and the alternate HA address is specified in
        a new extension (REDIRECTED-HA-ADDRESS).
   
        Alternately, MN can set the HA field to a unicast address. The
        HA receiving the Registration Request can suggest an alternate
        HA and if so, the Registration Reply is rejected with a new
        error code (REDIRECT-HA-REQ) and the alternate HA address is
        specified in a new extension (REDIRECTED-HA-ADDRESS). The HA
        can reject the request if the HA in request does not match any
        of its own addresses.
   
        The messaging mechanism proposed here is generic and can be
        used as a common foundation to facilitate dynamic HA assignment
        using  any  suitable  method.  No  specific  method  is  either
        mandated or suggested. The HA receiving Registration Request
        may suggest an alternate HA (HA redirection) for a number of
        reasons;  including  but  not  limited  to  HA  load-balancing,
        geographical proximity, administrative policy etc.
   
   
   2. Terminology
   
        ALL-ZERO-ONE-ADDR: IP address 0.0.0.0 or 255.255.255.255. An
                          address  of  255.255.255.255  would  indicate
                          assigning HA in home domain. An address of
                          0.0.0.0 would mean MN just needs a dynamic
                          HA, it does not care whether in home or
                          visited domain.
   
        Requested HA:     Destination IP address of Home Agent that the
                          first Registration Request is sent to. Must
                          be a unicast IP address. This address can be
                          obtained as described in section 5.4.
   
        Assigned HA:      If  registration  is  successful,  this  Home
                          Agent  address  field  is  obtained  from
                          successful Registration Reply.
   
        Redirected HA:    If the registration is rejected with error
                          code (REDIRECT-HA-REQ), the HA being referred
                          to  is  specified  in  a  new  extension
                          (REDIRECTED-HA-ADDRESS).
   
        AAA server:       Authentication, Authorization and Accounting
                          Server.
   
        DNS:              Domain Name Service.
   
        DHCP:             Dynamic Host Configuration Protocol.
   
   
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        MN:               Mobile Node as defined in RFC 3344.
   
        HA:               Home Agent as defined in RFC 3344.
   
        FA:               Foreign Agent as defined in RFC 3344.
   
        CoA:              Care of Address.
   
        CCoA:             Collocated Care of Address.
   
        MN HoA:           Mobile Node's Home Address.
   
        NAI:              Network Access Identifier [2].
   
        Src IP:           Source IP address of the packet.
   
        Dest IP:          Destination IP address of the packet.
   
   
   3. Problem Statement
   
        Mobile IPv4 NAI Extension for IPv4 [2] introduced the concept
        of identifying a MN by the NAI and enabling dynamic home
        address  assignment.  When  the  home  address  is  dynamically
        assigned,  it  is  desirable  to  discover  the  Home  Agent
        dynamically or inform the MN about an optimal HA to use for a
        multitude of reasons, such as:
   
        If the distance between the visited network and the home
        network of the mobile node is large, the signaling delay for
        these registrations may be long. In such a case the MN will be
        anchored to its distant home agent, resulting in tunneled
        traffic traveling a long distance between home agent and the
        mobile node. When a Mobile IP session initiates, if the mobile
        node can be assigned an home agent which is close to the mobile
        node it can drastically reduce the latency between the home
        agent and mobile node.
   
        Also, in a large scale Mobile IP deployment, it is cumbersome
        to provision MNs with multiple HA addresses.
   
        It is desirable to achieve some form of load balancing between
        multiple HAs in the network. Dynamic HA assignment and/or HA
        redirection lets the network select the optimal HA from among a
        set of HAs and thus achieve load balancing among a group of
        HAs.
   
        Local administrative policies is yet another reason for dynamic
        HA assignment/HA redirection during the start of a Mobile IP
        session.
   
   
   
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        The problem of discovering a Mobile nodeÆs HA address is
        acknowledged in the MIPv6 working group as part of [8].
   
   3.1 Scope
   
        This specification assumes that the Mobile Node and Assigned
        Home Agent are in the same administrative domain. The scenario
        where the Mobile Node and its anchoring Assigned Home Agent are
        in different administrative domain is beyond the scope of this
        specification.
   
        The draft introduces the terms Requested/Assigned/Redirected HA
        (section 5.4). These terms are merely HA addresses and used for
        depending upon the direction of the registration request or
        reply. The discovery of Requested/Assigned/Redirected HA can be
        done by various means, which are network and/or deployment
        specific    and    hence    this    discovery/assignment    of
        Requested/Assigned/Redirected HA is kept outside the scope of
        this specification.
   
   
   3.2 Dynamic Home Agent Discovery in RFC 3344
   
        Mobile IP RFC 3344 specifies the mechanism for discovering the
        mobile node's home agent using subnet-directed broadcast IP
        address in the home agent field of the Registration Request.
        This mechanism was designed for mobile nodes with a static home
        address and subnet prefix, anchored on fixed home network.  But
        using subnet-directed broadcast as the destination IP address
        of  the  Registration  Request,  it  is  unlikely  that  the
        Registration Request will reach the home subnet because routers
        will drop these packets by default. See CERT Advisory CA-1998-
        01 Smurf IP Denial-of-Service Attacks [3].
   
   
   3.3 NAI usage and dynamic HA assignment
   
        Mobile IPv4 NAI Extension for IPv4 [2] introduced the concept
        of identifying a MN by the NAI and enabling dynamic home
        address assignment. This document mandates that while using
        dynamic HA assignment, MN MUST use NAI and obtain a home
        address.  MN  can  still  suggest  a  static  home  address  in
        Registration Request, but must take the address in Registration
        Reply as the home address for the session. This reference to
        obtaining home address using NAI is as per [2].
   
   
   3.4 Redirected HA address extension
   
        The  Redirected  HA  address  extension,  shown  in  figure  1,
        contains the address of the HA where the MN should attempt the
        next registration. It is a skippable extension and MUST be
   
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        included in Registration Reply when the reply code is REDIRECT-
        HA-REQ.
   
   
     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     |        Redirected-HA-Address
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   
                   Figure 1: The Redirected HA address Extension
   
   
         Type       REDIRECTED-HA-ADDRESS (skippable) [1]
   
         Length     4
   
         HA-Address The address of redirected HA
   
   
   4. Messaging mechanism for dynamic HA assignment/redirection
   
   4.1 Messaging for dynamic HA assignment
   
   
          1. MN sets the Home Agent address field in the Registration
             Request to ALL-ZERO-ONE-ADDR.
          2. The MN (if using collocated CoA) or FA (if using FA CoA)
             sends the Registration Request to the "Requested HA".
          3. "Requested HA" is the home agent, which processes the
             Registration Request in accordance with RFC 3344 and as
             per  the  specification  in  this  document.  It  creates
             mobility binding for successful Registration Request. It
             also sends Registration Reply to the MN.
          4. The MN obtains an "Assigned HA" address from the HA field
             in the successful Registration Reply and uses it for the
             remainder of the session.
          5. Subsequent Registration Request messages for renewal are
             sent to the Assigned HA.
   
   
        Section 5.3.1 describes the Assigned HA in detail. Some ideas
        on how to select the Requested HA are briefly covered in
        section 6.
   
   
   4.1.1 Example with Message Flow Diagram
   
        Detailed explanation of this specification is best described
        with the help of a railroad diagram and description.
   
   
   
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        Figure 2 shows one specific example of a Mobile Node using FA
        Care of Address.
   
        Other scenarios such as mobile node using collocated care of
        address are not described below, but the behavior is similar.
   
           MN            FA          Requested/Assigned HA
           |      1      |                |
           |------------>|       2        |
           |             |--------------->|
           |             |                |
           |             |                |
           |             |       3        |
           |      4      |<---------------|
           |<------------|                |
           |             |                |
           |             |       5        |
           |----------------------------->|
           |             |                |
   
   
               Figure 2: Example of Message flows for the specification
   
   
   
        1. MN sets the Home Agent address field in the Registration
        Request to ALL-ZERO-ONE-ADDR. Since MN is using FA CoA in this
        example, it sends the Registration Request to the FA. The
        Registration Request looks as follows:
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |  MN    |    FA      |         | ALL-ZERO-ONE-ADDR |FA CoA |
        +-----------------------------------------------------------+
   
        2. The FA sends the Registration Request to the Requested HA.
        The Registration Request looks:
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |  FA    |Requested HA|         | ALL-ZERO-ONE-ADDR |FA CoA |
        +-----------------------------------------------------------+
   
        3. HA processes the Registration Request in accordance with RFC
        3344 and the messaging defined in this document and creates
        mobility  binding  for  successful  request.  HA  then  sends
        Registration Reply to the FA, which looks as follows. The
        Assigned  HA  address  corresponds  to  the  HA  receiving  and
        processing the request (and is same as Requested HA, only the
        name is changed for registration reply).
   
   
   
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        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |Assigned|CoA or NATed|         |    Assigned HA    |FA CoA/|
        |   HA   | Src IP     |         |                   |       |
        +-----------------------------------------------------------+
   
        4. The FA relays the Registration Reply to the MN, as follows.
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |  FA    |    MN      |         |    Assigned HA    |FA CoA/|
        +-----------------------------------------------------------+
   
        5. The MN obtains Assigned HA address from the HA field in the
        successful Registration Reply and uses it for the remainder of
        the  session.  MN  sends  subsequent  Re-Registration  or  De-
        Registration Requests for the remaining session directly to the
        Assigned HA.
   
   
   4.2 Messaging for HA redirection
   
   
          1. MN sets the Home Agent address field in the Registration
             Request to ALL-ZERO-ONE-ADDR or unicast address.
          2. The MN (if using collocated CoA) or FA (if using FA CoA)
             sends the Registration Request to the "Requested HA".
          3. When HA receives the Registration Request, if the unicast
             HA address in Request does not match any of its addresses,
             HA can reject the request with Reply code REDIRECT-HA-REQ
             and suggest an alternate HA.
   
             If the HA field is set to ALL-ZERO-ONE-ADDR, HA may reject
             the request with Reply code REDIRECT-HA-REQ and suggest an
             alternate HA.
   
             HA may reject the Request for a number of reasons, which
             are outside the scope of this specification. If the HA
             rejects the Request, the HA field in the Reply is set to
             this HAs address. The HA that is being referred to is
             specified in REDIRECTED-HA-ADDRESS extension. The presence
             of this extension is mandatory when the reply code is set
             to REDIRECT-HA-REQ. HA sends the Reply to the FA/MN
          4. FA sends the Reply to the MN.
          5. If the error code is set to REDIRECT-HA-REQ, MN obtains
             the HA address from REDIRECTED-HA-ADDRESS and sends a
             Registration Request to this HA.
   
   
   
   
   
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   4.2.1 Example with Message Flow Diagram
   
   
        Figure 3 shows one specific example of a Mobile Node using FA
        Care of Address.
   
   
           MN            FA          Requested HA      Redirected HA
           |      1      |                |                     |
           |------------>|       2        |                     |
           |             |--------------->|                     |
           |             |                |                     |
           |             |                |                     |
           |             |       3        |                     |
           |      4      |<---------------|                     |
           |<------------|                |                     |
           |             |                |                     |
           |             |       5        |                     |
           |------------------------------------------------->  |
           |             |                |                     |
   
   
               Figure 3: Example of Message flows for the specification
   
   
   4.2.2 HA Rejects Registration Request and suggests redirection
   
   
        1. MN sets the Home Agent address field in the Registration
        Request to ALL-ZERO-ONE-ADDR or unicast HA address. Since MN is
        using FA CoA in this example, it sends the Registration Request
        to the FA. The Registration Request looks as follows:
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |  MN    |    FA      |         | ALL-ZERO-ONE-ADDR |FA CoA |
        |        |            |         | or unicast addr   |       |
        +-----------------------------------------------------------+
   
        2. The FA sends the Registration Request to the Requested HA.
        Note that the Requested HA could be different from the unicast
        HA address in the Request. The Registration Request looks:
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |  FA    |Requested HA|         | ALL-ZERO-ONE-ADDR |FA CoA |
        |        |            |         | or unicast addr   |       |
        +-----------------------------------------------------------+
   
        3. HA processes the Registration Request in accordance with RFC
        3344 and the messaging defined in this document. If the
   
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        registration   is   successful,   but   local   configuration/
        administrative policy etc. directs HA to refer the MN to
        another HA, HA rejects the Request with error code REDIRECT-HA-
        REQ. HA fills in the address of the directed HA in the
        REDIRECTED-HA-ADDRESS extension. HA then sends Registration
        Reply reject to the FA, which looks as follows:
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |        |CoA or NATed|         |       HA          |FA CoA |
        |   HA   | Src IP     |         |                   |       |
        +-----------------------------------------------------------+
        | REDIRECTED-HA-ADDRESS extension                           |
        +-----------------------------------------------------------+
   
        4. The FA relays the Registration Reply to the MN, as follows.
   
        +-----------------------------------------------------------+
        | Src IP=| Dest IP =  | MN HoA  |    HA Address =   | CoA = |
        |  FA    |    MN      |         |       HA          |FA CoA/|
        +-----------------------------------------------------------+
        | REDIRECTED-HA-ADDRESS extension                           |
        +-----------------------------------------------------------+
   
        5. If MN can authenticate the Reply, MN extracts the HA address
        from REDIRECTED-HA-ADDRESS extension and sends Registration
        Request to this HA.
   
   
   5. Mobility Agent Considerations for dynamic HA assignment
   
        Following sections describe the behavior of each mobility agent
        in detail.
   
   
   5.1 Mobile Node Considerations
   
        The mobile node MUST use NAI extension for home address
        assignment when using the messaging mechanism in this document.
        A mobile node MUST set the Home Agent field in the Registration
        Request to a unicast address or an ALL-ZERO-ONE-ADDR, which is
        either 255.255.255.255 or 0.0.0.0.
   
        The  Registration  Request  MUST  be  protected  by  a  valid
        authenticator as specified in [1] or [5]. Configuring security
        associations is deployment specific and hence outside the scope
        of this specification. The security associations between a MN
        and an individual HA may also be dynamically derived during the
        dynamic HA assignment, based on a shared secret between MN and
        AAA infrastructure.
   
   
   
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        The mobile node must maintain the remaining Mobile IP session
        with the Assigned HA. Following sections describe MN behavior
        in FA CoA mode and collocated CoA mode.
   
   
   5.1.1 MN using FA CoA
   
        When a mobile node initiates Mobile IP session, it MUST set the
        home agent address field in the Registration Request to unicast
        address or ALL-ZERO-ONE-ADDR. The destination IP address of
        Registration Request is the FA. The FA will determine the
        Requested HA and forward the Registration Request to the
        Requested HA. Registration Request processing takes place on
        the Requested HA as per the specification in this draft.
   
        The Registration Request MUST be appropriately authenticated
        for the HA to validate the Request.
   
        If  successful  Registration  Reply  is  received,  MN  obtains
        Assigned HA from the HA field of Reply.
   
        If Registration Reply is received with code REDIRECT-HA-REQ, MN
        MUST authenticate the Reply based on HA address in HA field of
        Reply and attempt Registration with the HA address specified in
        the REDIRECTED-HA-ADDRESS extension.
   
   
   5.1.2 MN using Collocated CoA
   
        Mobile Node in collocated CoA mode MUST set the home agent
        address field in the Registration Request to unicast address or
        ALL-ZERO-ONE-ADDR.  The  destination  IP  address  of  the
        Registration Request is the Requested HA. Some ideas to select
        a Requested HA are briefly covered in section 6.
   
        If successful Reply is received, the MN obtains Assigned HA
        address from successful Registration Reply. The MN MUST cache
        the Assigned HA address for the length of the Mobile IP
        session. The mobile node then MUST use this previously cached
        Assigned HA address as the home agent address in subsequent re-
        registration and de-registration request(s). This will make
        sure that the mobile node will always be anchored to the
        assigned home agent with which it was initially registered.
   
        If Registration Reply is received with code REDIRECT-HA-REQ, MN
        MUST authenticate the Reply based on HA address in HA field of
        Reply and attempt Registration with the HA address specified in
        the REDIRECTED-HA-ADDRESS extension.
   
   
   
   
   
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   5.1.3 Refreshing Assigned HA Address on Mobile Node
   
        When the Mobile IP session terminates, the mobile node MAY
        clear the Assigned HA address cached as the home agent address.
        It MAY request a new HA address for the new Mobile IP session.
        The advantage of this approach is that the mobile node will be
        always  anchored  to  an  optimal  home  agent  from  where  it
        initiated Mobile IP session.
   
   
   5.2 Foreign Agent Considerations
   
        When the mobile node is using foreign agent CoA, it sends the
        Registration Request to the foreign agent. When the FA receives
        a Registration Request with HA address field set to ALL-ZERO-
        ONE-ADDR, it obtains the Requested HA address to forward the
        Registration Request. Some ideas to select a Requested HA are
        briefly covered in section 6.
   
        If  the  FA  cannot  obtain  the  Requested  HA  to  forward  a
        Registration Request from MN, it MUST reject request with error
        code NONZERO-HA-REQD.
   
        Backward compatibility issues related to the mobility agents
        are addressed in section 9.
   
   
   5.3 Home Agent Considerations
   
        Home Agent can process an incoming Registration Request in one
        of the following three ways:
   
        MN or FA sends the Registration Request to the Requested HA.
        The  term  Requested  HA  has  meaning  in  context  of  the
        Registration   Request   message.   When   the   Requested   HA
        successfully  processes  Registration  Request  and  creates  a
        binding and sends a Reply with its address, it becomes the
        Assigned HA. The term Assigned HA is meaningful in context of a
        Registration Reply message.
   
        Home Agent receiving the request with HA field set to ALL-ZERO-
        ONE-ADDR  MAY  reject  the  request  even  if  successfully
        authenticated  for  a  multitude  of  reasons  and  suggest  an
        alternate HA address in Reply. In such a case, the HA puts own
        address in HA field of Reply and sets the Reply code to
        REDIRECT-HA-REQ and adds the REDIRECTED-HA-ADDRESS extension.
   
        Home Agent receiving the request with HA field set to a unicast
        address not matching any of its addresses MUST reject the
        request  even  if  successfully  authenticated.  This  rejected
        message has the code 136 as defined in RFC3344 (3.8.3.2). HA
   
   
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        may reject  the message with code REDIRECT-HA-REQ and suggest
        an alternate HA to use in the REDIRECTED-HA-ADDRESS extension.
   
   
   5.3.1 Assigned Home Agent Considerations
   
        The HA that processes the incoming Registration Request fully
        in accordance with RFC 3344 and this specification becomes the
        Assigned  HA.  The  Registration  Request  terminates  at  the
        Assigned HA.
   
        The  Assigned  HA  creates  mobility  bindings  and  sends
        Registration Reply to the MN by copying its address in the home
        agent field and as the source IP address of the Reply.
   
        There are two IP addresses to consider, destination IP address
        and Home Agent address field in the Registration Request.  When
        destination IP address is unicast, only one HA receives the
        Registration Request.  This HA should unambiguously accept or
        deny the registration, regardless of the value in the Home
        Agent field.  When the Home Agent field is non-unicast, the HA
        should set the value to its own IP address in the Registration
        Reply.
   
        The following table summarizes the behavior of Assigned HA.
   
   
        No. Dest IP Addr  HA field     Processing at Assigned HA
        --  ------------  ------------ -------------------------
        1   Unicast       Unicast    û RFC 3344: Normal HA processing
                          Same as Dest per RFC 3344.
                          IP addr
   
                          Unicast    û RFC   3344:   HA   denies   the
                          Different    registration  with  error  code
                          than Dest IP 136 and sets HA field to its
                          Addr         own IP address in the reply as
                                       per section 3.8.3.2.
   
                                                     OR
   
                                        New    Behavior:    Dest    IP
                                        corresponds to the HA receiving
                                        RRQ,   if   authentication   is
                                        successful, reject RRQ with a
                                        new  error  code  (REDIRECT-HA-
                                        REQ). HA puts its address in HA
                                        address  field  of  Reject.  HA
                                        suggests an alternate HA to use
                                        in   the   new   REDIRECTED-HA-
                                        ADDRESS extension.
   
   
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        2   Unicast       non-unicast  RFC   3344:   HA   denies   the
                                       registration  with  error  code
                                       136 and sets HA field to its
                                       own IP address in the reply as
                                       per section 3.8.3.2.
   
                          ALL-ZERO-    New Behavior: Accept the RRQ as
                          ONE-ADDR     per     this     specification.
                                        Authenticate the RRQ and create
                                        mobility binding if the HA is
                                        acting as Assigned HA. Set HA
                                        field to its own IP address in
                                        the Registration Reply.
   
                                                   OR
   
                                        New    Behavior:    Dest    IP
                                        corresponds to the HA receiving
                                        RRQ,   if   authentication   is
                                        successful, reject RRQ with a
                                        new  error  code  (REDIRECT-HA-
                                        REQ). HA puts its address in HA
                                        address  field  of  Reject.  HA
                                        suggests an alternate HA to use
                                        in   the   new   REDIRECTED-HA-
                                        ADDRESS extension
   
        3   Non-unicast   Unicast      RFC 3344: HA rejects with error
                                        code 136 and sets HA field to
                                        its own IP address in the reply
                                        per section 3.8.2.1.
   
        4   Non-unicast   Non-unicast  RFC 3344: HA rejects with error
                                        code 136 and sets HA field to
                                        its own IP address in the reply
                                        per section 3.8.2.1.
   
   
        Table 1: Registration Request handling at Assigned HA
   
   
        This specification proposes an enhancement to case #1 from RFC
        3344.  As  per  this  specification,  when  a  HA  receives  a
        Registration Request and the HA address (unicast) does not
        match its own address(es), HA can reject the request with the
        error code REDIRECT-HA-REQ and suggest an alternate HA. This
        redirection  can  be  used  for  load-balancing,  geographical
        proximity based on care-of-address or a multitude of reasons.
        HA puts its own address in HA field on Registration Reply
   
   
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        message and put the address of the redirected HA in the
        REDIRECTED-HA-ADDRESS extension.
   
        This  specification  also  proposes  a  subtle  difference  in
        behavior for case #2 above from RFC 3344.  As per the messaging
        proposed here, the mobile node (or the foreign agent) sends the
        Registration Request to the Requested HA address, which is a
        unicast address. Because HA does not receive Registration
        Request that is sent to the subnet-directed broadcast address,
        RFC 3344 section 3.8.2.1 doesn't apply.  Although the Home
        Agent field in the Registration Request is not a unicast
        address, the destination IP address is a unicast address.  This
        avoids the problem associated with subnet-directed broadcast
        destination  IP  address  that  may  result  in  multiple  HAs
        responding.  Thus, there is no need to deny the registration as
        stated in RFC 3344 section 3.8.3.2.
   
        When the destination IP address is a unicast address and Home
        Agent  field  is  ALL-ZERO-ONE-ADDR,  the  HA  accepts/denies
        registration and sets HA field to its own IP address in the
        reply (i.e. registration is not rejected with error code 136).
        HA can reject the request with the error code REDIRECT-HA-REQ
        and suggest an alternate HA. This redirection can be used for
        load-balancing, geographical proximity based on care-of-address
        or a multitude of reasons. HA puts its own address in HA field
        on Registration Reply message and put the address of the
        redirected HA in the REDIRECTED-HA-ADDRESS extension. If HA
        accepts the Request, HA field in Reply is set to this HA
        address.
   
        The Assigned HA performs standard validity checks on the
        Registration Request. If there is any error, the Registration
        Request is rejected with error codes specified in RFC 3344.
   
   
   
   6. Requested Home Agent Selection
   
        The destination IP address of the first Registration Request in
        the Mobile IP session is the Requested HA.  This address MUST
        be a unicast IP address.
   
        Some ideas on how to select the Requested HA are briefly
        covered in this section, however this draft neither suggests
        nor mandates any specific mechanism. There can be more methods
        for selecting the HA to the MN. Here is a high level overview
        of some possibilities:
   
        DHCP:
   
        MN performs DHCP to obtain an IP address on the visited
        network. The Requested HA is learned from the DHCP Mobile IP
   
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        Home  Agent  Option  68  [4].  MN  sends  Registration  Request
        directly to this HA and receives the Assigned HA to be used for
        the remainder of the Mobile IP session.
   
   
        AAA:
   
        MN  performs  challenge/response  [5]  with  the  FA.  The  FA
        retrieves the Requested HA from the AAA server and forwards the
        Registration Request directly to this HA.  The Assigned HA
        sends Registration Reply to the FA, which relays it to the MN.
        MN uses the Assigned HA for the remainder of the Mobile IP
        session.
   
   
        DNS:
   
        In this case hostname of HA is configured on MN or obtained by
        some other means û e.g. using a service location protocol. MN
        performs DNS lookup on the HA hostname.  The DNS infrastructure
        provides resource record with information to identify the
        nearest HA to the MN.  The MN sends Registration Request
        directly to the HA and receives the Assigned HA to be used for
        remainder of the Mobile IP session.
   
        Static configuration:
   
        HA address is statically configured on MN. The MN uses the
        configured address to send the Registration Request.
   
   
   7. Error Values
   
        Each entry in the following table contains the name and value
        for the error code to be returned in a Registration Reply. It
        also includes the section in which the error code is first
        mentioned in this document.
   
        Error Name       Value  Section   Description
        ----------       -----  -------   -----------------------------
        NONZERO-HA-REQD   XX      5.2     Non-zero HA address required
                                          in Registration Request.
        REDIRECT-HA-REQ   YY      5.3.1   Reregister with suggested HA.
   
   
   8. IANA Considerations
   
        The code value NONZERO-HA-REQD defined in Section 7 correspond
        to error values conventionally associated with the rejection by
        the foreign agent (i.e. value in the range 64-127). The code
        value REDIRECT-HA-REQ defined in Section 7 correspond to error
   
   
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        values conventionally associated with the rejection by the home
        agent (i.e. value in the range 128-192).
   
        The extension REDIRECTED-HA-ADDRESS defined in section 3.3
        corresponds to a skippable extension.
   
        IANA should record the values as defined in Section 7 and 3.3.
   
   
   9. Security Considerations
   
        This specification assumes that the Mobile Node and Assigned
        Home  Agent  are  in  the  same  administrative  domain.  This
        specification does not change or degrade the security model
        established in RFC-3344. Most of the time Mobile Nodes will be
        connected to the network via wireless link. Such links are
        vulnerable to passive eavesdropping, replay attacks or many
        other types of attacks. They are considered below.
   
   
   9.1 Message Authentication Codes
   
        The Registration Request and Reply messages are protected by a
        valid authenticator as specified in RFC 3344. Configuring
        security associations is a deployment specific issue and is
        covered by other specifications in Mobile IP WG. There can be
        many  ways  of  configuring  security  associations,  but  this
        specification does not mandate any specific way.
   
        An example is where the security association between a MN and
        an individual HA (Dynamic or Assigned) is dynamically derived
        during the dynamic HA assignment, based on a shared secret
        between MN and AAA infrastructure, as defined in [7]. The
        Registration Request is protected with MN-AAA authentication
        extension and Registration Reply is protected with MHAE. Since
        the security association is shared between MN and AAA, any
        dynamically  assigned  HA  in  the  local  domain  can  proxy
        authenticate the MN using AAA as per [7].
   
        The Assigned Home Agent authenticates Registration Request from
        the mobile node as specified in RFC-3344 and RFC-3012. The MN
        also authenticates the Registration Reply from the Assigned HA,
        thus the existing trust model in RFC 3344 is maintained.
   
   
   9.2 Areas of Security Concern in this Protocol
   
        As per the messaging in this draft, the Assigned Home Agent
        will process the incoming Registration Request as per RFC-3344.
        Hence the Assigned Home Agent will have same security concerns
        as that of the Home Agent in RFC-3344. They are addressed in
        Section 5 ôSecurity Considerationsö of RFC-3344.
   
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   10. Backward Compatibility Considerations
   
   
        Legacy Home Agent:
   
        Legacy home agents may reject the Registration Request with
        error code 136 because the Home Agent field is not a unicast
        address.  However,  some  legacy  HA  implementations  may
        coincidentally process the Registration Request in accordance
        with this draft, when the HA field in RRQ is set to ALL-ZERO-
        ONE-ADDR.
   
        Legacy Foreign Agent:
   
        Legacy foreign agents may forward Registration Request with
        home agent field set to ALL-ZERO-ONE-ADDR by setting the
        destination IP address to ALL-ZERO-ONE-ADDR.  This will result
        packet being dropped or incidentally handled by a next hop HA,
        adjacent to the FA.
   
        Legacy Mobile Node:
   
        MN that does not set HA field to ALL-ZERO-ONE-ADDR will
        continue  to  achieve  its  registrations  through  statically
        configured HA. In collocated mode, the endpoint of the MN's
        tunnel is the Assigned HA.
   
   
   11. Change Log
   
        Version 2 is totally revamped from earlier version. The most
        notable changes are:
   
        Removed references to directed HA/assigned HA. There is no HA
        redirection in the network to incorporate the feedback from
        Pete McCann. The single entity is currently called Assigned HA.
   
        Added a new error code for HA rejection when dst IP is  unicast
        and  HA  address  is  unicast  and  these  two  addresses  are
        different. The HA receiving RRQ rejects the RRQ and puts
        another HA in RRP and its source address in RRP.
   
        Also, when this new error code is used for HA redirection, a
        new HA address is suggested in a new extension
   
   
   12. Intellectual Property Rights
   
        The IETF takes no position regarding the validity or scope of
        any intellectual property or other rights that might be claimed
   
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        to pertain to the implementation or use of the technology
        described in this document or the extent to which any license
        under such rights might or might not be available; neither does
        it represent that it has made any effort to identify any such
        rights.  Information on the IETF's procedures with respect to
        rights in standards-track and standards-related documentation
        can be found in BCP-11.  Copies of claims of rights made
        available for publication and any assurances of licenses to be
        made available, or the result of an attempt made to obtain a
        general license or permission for the use of such proprietary
        rights by implementers or users of this specification can be
        obtained from the IETF Secretariat.
   
        The IETF invites any interested party to bring to its attention
        any  copyrights,  patents  or  patent  applications,  or  other
        proprietary rights, which may cover technology that may be
        required  to  practice  this  standard.    Please  address  the
        information to the IETF Executive Director.
   
   
   13. Acknowledgements
   
        The authors would like to thank Pete McCann for suggestions on
        security considerations and definition of ALL-ZERO-ONE-ADDR.
        Thanks to Kuntal Chowdhury for extensive review and comments on
        this draft. Also thanks to Henrik Levkowetz for detailed
        reviews and suggestions.
   
        The authors would like to thank Mike Andrews, Madhavi Chandra
        and Yoshi Tsuda for their review and suggestions.
   
   
   14. References
   
   [1]  C. Perkins, "IP Mobility Support for IPv4", RFC 3344, August
        2002.
   [2]  P. Calhoun and C. Perkins, "Mobile IP Network Access Identifier
        Extension for IPv4", RFC 2794, March 2000.
   [3]  D. Senie, "Changing the Default for Directed Broadcasts in
        Routers", RFC 2644, August 1999.
   [4]  S. Alexander and R. Droms, "DHCP Options and BOOTP Vendor
        Extensions", RFC 2132, March 1997.
   [5] C. Perkins and P. Calhoun, "Mobile IPv4 Challenge/Response
        Extensions", RFC 3012, November 2000.
   [6] H. Levkowetz and S. Vaarala, "Mobile IP Traversal of Network
        Address Translation (NAT) Devices", RFC 3519, July 803.
   [7] C. Perkins and P. Calhoun, "AAA Registration Keys for Mobile
        IP", draft-ietf-mobileip-aaa-key-13.txt, 22 June 2003.
   [8]  Jari  Arkko,  et.  al.,  ôThoughts  on  bootstrapping  mobility
        securelyö as presented at 57th IETF in Vienna, Austria, 16th
        July, 2003
   
   
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   Authors' Addresses
   
        Milind Kulkarni
        Cisco Systems Inc.
        170 W. Tasman Drive,
        San Jose, CA 95134
        USA
   
        Email: mkulkarn@cisco.com
        Phone:+1 408-527-8382
   
   
        Alpesh Patel
        Cisco Systems Inc.
        170 W. Tasman Drive,
        San Jose, CA 95134
        USA
   
        Email: alpesh@cisco.com
        Phone:+1 408-853-9580
   
   
        Kent Leung
        Cisco Systems Inc.
        170 W. Tasman Drive,
        San Jose, CA 95134
        USA
   
        Email: kleung@cisco.com
        Phone: +1 408-526-5030
   
   Full Copyright Statement
   
        Copyright  (C)  The  Internet  Society  (2002).    All  Rights
        Reserved.
   
        This  document  and  translations  of  it  may  be  copied  and
        furnished to others, and derivative works that comment on or
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        prepared, copied, published and distributed, in whole or in
        part, without restriction of any kind, provided that the above
        copyright notice and this paragraph are included on all such
        copies and derivative works.  However, this document itself may
        not be modified in any way, such as by removing the copyright
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        organizations, except as needed for the purpose of developing
        Internet standards in which case the procedures for copyrights
        defined in the Internet Standards process must be followed, or
        as required to translate it into languages other than English.
   
   
   
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        The limited permissions granted above are perpetual and will
        not be revoked by the Internet Society or its successors or
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   Acknowledgement
   
        Funding for the RFC Editor function is currently provided by
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