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Network Working Group                                        B. Sarikaya
Internet-Draft                                                    F. Xia
Expires: September 11, 2008                                   Huawei USA
                                                          March 10, 2008


             Relay Based DHCPv6 Prefix Delegation for NEMO
               draft-sarikaya-mext-relay-dhcpv6pd-00.txt

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Abstract

   This document defines DHCP Relay Agent based prefix delegation
   support for a mobile network.  Mobile Router uses DHCPv6 prefix
   delegation to dynamically request its Mobile Network Prefixes from
   DHCP Server.  DHCP Relay Agent located in MR enables MR to run the
   prefix delegation application with the same DHCP Server even after MR
   moves to a different local network.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Nemo Prefix Delegation Architecture . . . . . . . . . . . . . . 3
     3.1.  Message Encapsulation . . . . . . . . . . . . . . . . . . . 4
   4.  Nemo Prefix Delegation Protocol . . . . . . . . . . . . . . . . 5
   5.  Nemo Prefix Delegation Using AAA  . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     9.2.  Informative references  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9

























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1.  Introduction

   Nemo Basic Support Protocol requires that IPv6 prefixes called Home
   Network Prefix(es) delegated to a Mobile Router and advertized in the
   Mobile Network [RFC3963].  However the protocol does not provide any
   means of provisioning MNPs dynamically.

   Prefix delegation is widely discussed in IETF 16NG, MEXT, and NETLMM
   Working Groups.  Corresponding solutions are also introduced.  NEMO
   deals with synchronization of Mobile Network prefixes between a
   Mobile Router and a Home Agent, while the method is agnostic to the
   way that a Home Agent gets prefixes from back end servers.

   [RFC3633] defines Prefix Delegation options and procedures to provide
   a mechanism for automated delegation of IPv6 prefixes using the
   Dynamic Host Configuration Protocol (DHCP).  A mechanism to manage
   prefixes dynamically by an AAA server can also be defined.

   [I-D.ietf-nemo-prefix-delegation] defines prefix request option for
   the binding update and prefix confirm for the binding acknowledgment
   messages of the Nemo Basic Support Protocol.  Using these messages MR
   can request a prefix from HA with BU and HA can give prefixes to MR
   with BA.  However, how HA gets prefixes is not defined.


2.  Terminology

   This document uses the terminology defined in [RFC3315], [RFC3633]
   and [RFC4885].


3.  Nemo Prefix Delegation Architecture

   We assume that the prefixes are managed by an authority that owns the
   Home Network and subnets it into MNPs that it assigns to the MRs.  An
   MNP can be preassigned to the associated MR (e.g. manually or
   automatically with a provisioning system).

   For dynamic prefix management there are two architectures.  In HA-
   based architecture, HA is the requesting router and the DHCP Server
   is the delegating router.  HA needs to be collocated with a DHCP
   Client to solicit/request prefixes from the DHCP Server.  HA is
   configured with the address of the delegating router which is a
   backend DHCP Server.  MR needs to request dynamically the prefixes
   from HA using BU/BA exchange defined in
   [I-D.ietf-nemo-prefix-delegation].

   In MR-based architecture, MR is the requesting router and the



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   delegating router is a DHCP Server located in the home network.  In
   this document, we elaborate on the signaling required for this
   architecture.

   [I-D.ietf-nemo-dhcpv6-pd] uses the MR-based architecture but it does
   not incorporate a DHCP Relay at the MR.  [I-D.ietf-nemo-dhcpv6-pd]
   assumes a DHCP Client at the MR which requires an onlink DHCP Relay
   or Server [I-D.dupont-mext-dhcrelay].  However when MR moves it is
   not possible to satisfy this requirement.

   Figure 1 shows the MR-based architecture.


    +-----+   HA-MR    +-----+        +--------+    --------------
    | MR  |-- tunnel --| HA  |--------+ Edge   |   /              \
    +-----+            +-----+        | Router +-- |  Backend     |
    |Relay|            |Relay|        +--------+   \             /
    +-----+            +-----+                      -------------
    |DHCP  |<---                                          |
    |Client|   |                                        +------+
    +------+    -----DHCP Prefix Delegation------------>|DHCP  |
                                                        |Server|
                                                        +------+


                      Figure 1: MR-based Architecture

   MR is co-located with DHCP Relay Agent.  In order to run DHCP Prefix
   Delegation we also need a local DHCP Client at the MR.  DHCP Client
   will initiate or respond to DHCP messages required for the MR to be
   the requesting router.

   DHCP Relay co-located with MR will relay the client's messages back
   and forth.  DHCP Relay co-located at HA will be configured with the
   backend DHCP Server's address.  The backend DHCP Server will be the
   delegating router.

3.1.  Message Encapsulation

   DHCP Relay co-located at the MR encapsulates DHCP Client's messages
   in the form of DHCPv6 datagrams.  These datagrams need to be sent
   over HA-MR tunnel when MR is not on the home link.  This requires
   that each such message is piggybacked in a Binding Update message
   sent from MR to HA.

   IPv6 extension headers for each message sent by the DHCP Relay co-
   located at MR MUST contain the mobility header as described in
   Section 6.1 of [RFC3775].  MH type MUST be set to 5 for Binding



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   Update.  The payload MUST contain the DHCP message being sent.

   DHCP Relay co-located at the HA encapsulates DHCP Prefix Delegation
   messages to be sent in the form of DHCPv6 datagrams.  These datagrams
   need to be sent over HA-MR tunnel to the MR.  This requires that each
   such message is piggybacked in a Binding Acknowledgement message sent
   from HA to MR.

   IPv6 extension header for each message sent by the DHCP Relay co-
   located at HA towards MR MUST contain the mobility header as
   described in Section 6.1 of [RFC3775].  MH type MUST be set to 6 for
   Binding Acknowledgement.  The payload MUST contain the DHCP message
   being sent.


4.  Nemo Prefix Delegation Protocol

   Figure 2 shows the process that a Mobile Router as the requesting
   router requests prefixes from a DHCP Server as the delegating router
   using DHCPv6 [RFC3315] and DHCPv6 Prefix delegation [RFC3633].


            MR       HA       DHCP Server
            |                       |
         -->|                       |1. Trigger to DHCP Client
            |2 Relay-forward/Solicit|2. DHCP Relay-Forward/Solicit
            |---------------------> |
            |3 Relay-reply/Advertise|3. DHCP Relay-reply/ Advertise
            |<--------------------- |
            |4 Relay-forward/Request|4. DHCP Relay-Forward/Request (MNP)
            |---------------------> |
            |5 Relay-reply/Reply    |5. DHCP Relay-reply/Reply (MNP)
            |<--------------------- |


                    Figure 2: Prefix Delegation in NEMO

   1.  DHCP Client co-located with MR needs to be triggered to start
       requesting prefixes using DHCPv6 Prefix Delegation.  The initial
       trigger should be when MR boots up.  The subsequent triggers are
       timeout based.  Each prefix received has a lifetime.  When the
       lifetime of a prefix expires, a trigger SHOULD be received at the
       DHCP Client.
   2.  DHCP Client at the MR initiates DHCP Solicit procedure to request
       prefixes for the MN.  HA creates and transmits a Solicit message
       as described in sections 17.1.1, "Creation of Solicit Messages"
       and 17.1.2, "Transmission of Solicit Messages" of RFC 3315.  MR
       creates an IA_PD and assigns it an IAID.  MR MUST include the



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       IA_PD option in the Solicit message.
   3.  The DHCP server sends an Advertise message to MR in the same way
       as described in section 17.2.2, "Creation and transmission of
       Advertise messages" of RFC 3315.
   4.  MR uses the same message exchanges as described in section 18,
       "DHCP Client-Initiated Configuration Exchange" of RFC 3315 to
       obtain or update prefixes from a DHCP server.  MR and the DHCP
       server use the IA_PD Prefix option to exchange information about
       prefixes in much the same way as IA Address options are used for
       assigned addresses.
   5.  MR stores the prefix information it received in the Reply
       message.

   HA SHOULD add the route to the delegated prefix(es) and advertise the
   prefix(es) upstream.  HA SHOULD use route aggregation, i.e. advertise
   the /48 prefix that is the extension of the delegated /64 prefixes.

   In Explicit Mode of NEMO Basic Protocol, MR includes the delegated
   prefix(es) to the prefix list in Prefix Information Option of Binding
   Update message.  This message triggers HA to add a route for the
   prefixes included.


5.  Nemo Prefix Delegation Using AAA

   Diameter prefix delegation application is currently to be defined.
   Once such an application is defined, Nemo prefix delegation using
   this Diameter application will be included in this section.


6.  Security Considerations

   This document does not by itself introduce any security issues.


7.  IANA Considerations

   None.


8.  Acknowledgements

   TBD.


9.  References





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9.1.  Normative References

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

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [I-D.ietf-nemo-prefix-delegation]
              Kniveton, T. and P. Thubert, "Mobile Network Prefix
              Delegation", draft-ietf-nemo-prefix-delegation-02 (work in
              progress), August 2007.

   [I-D.dupont-mext-dhcrelay]
              Dupont, F. and W. Haddad, "DHCPv6 Relay Agents and NEMO",
              draft-dupont-mext-dhcrelay-00 (work in progress),
              February 2008.

   [I-D.ietf-nemo-dhcpv6-pd]
              Droms, R. and P. Thubert, "DHCPv6 Prefix Delegation for
              NEMO", draft-ietf-nemo-dhcpv6-pd-03 (work in progress),
              December 2007.

9.2.  Informative references

   [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.

   [RFC4885]  Ernst, T. and H-Y. Lach, "Network Mobility Support
              Terminology", RFC 4885, July 2007.









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Authors' Addresses

   Behcet Sarikaya
   Huawei USA
   1700 Alma Dr. Suite 500
   Plano, TX  75075

   Phone: +1 972-509-5599
   Email: sarikaya@ieee.org


   Frank Xia
   Huawei USA
   1700 Alma Dr. Suite 500
   Plano, TX  75075

   Phone: +1 972-509-5599
   Email: xiayangsong@huawei.com

































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