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Versions: (draft-droms-nemo-dhcpv6-pd) 00 01 02 03

IPv6 Group                                                      R. Droms
Internet-Draft                                                P. Thubert
Intended status: Informational                                     Cisco
Expires: June 8, 2008                                   December 6, 2007


                   DHCPv6 Prefix Delegation for NEMO
                      draft-ietf-nemo-dhcpv6-pd-03

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   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on June 8, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   One aspect of network mobility support is the assignment of a prefix
   or prefixes to a Mobile Router (MR) for use on the links in the
   Mobile Network.  DHCPv6 prefix delegation can be used for this
   configuration task.







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1.  Introduction

   One aspect of network mobility support is the assignment of a prefix
   or prefixes to a Mobile Router for use on the links in the Mobile
   Network.  DHCPv6 prefix delegation [RFC3633] (DHCPv6PD) can be used
   for this configuration task.


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 [RFC2119].

   The following terms used in this document are defined in the IPv6
   Addressing Architecture document [RFC3513]:
      link-local unicast address
      link-local scope multicast address

   The following terms used in this document are defined in the mobile
   IPv6 specification [RFC3775]:
      home agent (HA)
      home link

   The following terms used in this document are defined in the Mobile
   Network terminology document [I-D.ietf-nemo-terminology]:
      Mobile Router (MR)
      Mobile Network
      mobile host (MH)

   The following terms used in this document are defined in the DHCPv6
   [RFC3315] and DHCPv6 prefix delegation [RFC3633] specifications:
      delegating router (DR)
      requesting router (RR)
      DHCPv6 relay agent


3.  Application of DHCPv6 prefix delegation to mobile networks for
    delegation of home prefixes

   The NEMO Basic protocol [RFC3963] extends the mobile IPv6 protocol
   [RFC3775] to enable network mobility.  In this extension, a MR uses
   the mobile IPv6 protocol to establish a maintain a session with its
   HA, and uses bidirectional tunneling between the MR and HA to provide
   a path through which hosts attached to links in the Mobile Network
   can maintain connectivity with nodes not in the Mobile Network.

   The requirements for NEMO [I-D.ietf-nemo-requirements] include the



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   ability of the MR to receive delegated prefixes that can then be
   assigned to links in the Mobile Network.  DHCPv6PD can be used to
   meet this requirement for prefix delegation.

   To use DHCPv6PD for Mobile Networks, the HA assumes the role of
   either the DR or a DHCPv6 relay agent and the MR assumes the role of
   the RR.  Throughout the remainder of this document, the HA will be
   assumed to be acting as a DHCPv6PD DR or relay agent and the MR will
   be assumed to be acting as a RR.

   If the HA is acts as relay agent, some other device acts as the DR.
   For example, the server providing DHCPv6 service in the home network
   might also provide NEMO DHCPv6PD service.  Or, a home network with
   several HAs might configure one of those HAs as a DHCPv6PD server
   while the other HAs act as relay agents.

   The HA and MR exchange DHCPv6PD protocol messages through the tunnel
   connecting them.  The tunnel acts as the link labeled "DSL to
   subscriber premises" in figure 1 of the DHCPv6PD specification.

   The DHCPv6PD server is provisioned with prefixes to be assigned using
   any of the prefix assignment mechanisms described in the DHCPv6PD
   specifications.  Other updates to the HA data structures required as
   a side effect of prefix delegation are specified by the particular
   network mobility protocol.  For example, in the case of Basic Network
   Mobility Support [RFC3963], the HA would add an entry in its binding
   cache registering the delegated prefix to the MR to which the prefix
   was delegated.

3.1.  When the MR uses DHCPv6

   The MR initiates a DHCPv6 message exchange for prefix delegation
   whenever it establishes an MRHA tunnel to its HA.  If the MR does not
   have any active delegated prefixes (with unexpired leases), the MR
   initiates a DHCPv6 message exchange with a DHCPv6 Solicit message as
   described in section 17 of RFC 3315 and section 12 of RFC 3633.  If
   the MR has one or more active delegated prefixes, the MR initiates a
   DHCPv6 message exchange with a DHCPv6 Confirm message as described in
   section 18.1.2 of RFC 3315 and section 12 of RFC 3633.

3.2.  Use of MRHA tunnel for DHCPv6 messages

   The DHCPv6 specification requires the use of link-local unicast and
   link-local scope multicast addresses in DHCPv6 messages (except in
   certain cases as defined in section 22.12 of the DHCPv6
   specification).  Section 10.4.2 of the mobile IPv6 specification
   describes forwarding of intercepted packets, and the third paragraph
   of that section begins:



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      However, packets addressed to the mobile node's link-local address
      MUST NOT be tunneled to the mobile node.

   The DHCPv6 messages exchanged between the HA and the MR originate
   only with the HA and the MR, and therefore are not "intercepted
   packets" and may be sent between the HA and the MR through the
   tunnel.

   Even though the MRHA tunnel is a point to point connection, the MR
   SHOULD use multicast DHCPv6 messages as described in RFC 3315 over
   that tunnel.

3.3.  Exchanging DHCPv6 messages when MR is at home

   When the MR is on its home link, the HA uses the home link to
   exchange DHCPv6PD messages with the MR.  It is the responsibility of
   the implementation to determine when the MR is on its home link and
   to avoid use of any existing tunnel.

3.4.  Minimizing DHCPv6PD messages

   DHCPv6PD in a Mobile Network can be combined with the Rapid Commit
   option [RFC3315] to provide DHCPv6 prefix delegation with a two
   message exchange between the mobile node and the DHCPv6 PD server.

3.5.  DHCPv6PD and DHAAD

   The MR acting as RR needs a direct link to the DR (or relay)
   function.  When the MR is away from Home, that link is the MRHA
   tunnel.  If a MR needs to obtain a prefix by means of DHCPv6PD, it
   has to locate a HA that is capable of serving either as a DHCPv6PD
   relay agent or server.  Since the use of DHCPv6PD is optional and
   comes as an addition to existing protocols [RFC 3775] and [RFC 3963],
   it can not be expected that all HAs are DHCPv6PD capable.

   This specification extends Dynamic Home Agent Address Discovery and
   the Home Agent Information Option in order to enable the detection by
   a MR of all HAs that are DHCPv6PD capable.  A new 'D' bit is
   introduced to let Home Agents advertise that they are willing to
   participate to DHCP.  Note that there is no need for the MR acting as
   RR to know whether a HA is actually a DR or simply acting as a relay.

3.5.1.  Modified Dynamic Home Agent Address Discovery Request

   A new flag (D) (Support for DHCPv6PD) is introduced in the DHAAD
   Request message, defined in [RFC3775] and [RFC 3963].  The Mobile
   Router sets this flag to indicate that it wants to discover Home
   Agents participating to DHCPv6 Prefix Delegation.



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   A the MR which sets the 'D' flag MUST also set the 'R' flag, to
   declare that it is a Mobile Router and asks for a HA that supports
   Mobile Routers, as defined in [RFC 3963].


      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Code      |            Checksum           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Identifier           |R|D|        Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        DHCPv6PD Support Flag (D)

           A one-bit flag that when set indicates that the Mobile Router
           wants to discover Home Agents participating to DHCPv6 Prefix
           Delegation.


   For a description of the other fields in the message, see [RFC3775]
   and [RFC 3963].

3.5.2.  Modified Dynamic Home Agent Address Discovery Reply

   A new flag (D) (Support for DHCPv6PD) is introduced in the DHAAD
   Reply message, defined in [RFC3775] and [RFC 3963].  If a Home Agent
   receives a Dynamic Home Agent Discovery request message with the
   DHCPv6PD Support Flag set, it MUST reply with a list of Home Agents
   participating to DHCPv6PD.

   The DHCPv6PD Support Flag MUST be set if there is at least one Home
   Agent participating to DHCPv6PD.  In that case, the reply will list
   only those HAs that participate to DHCPv6PD, whether they act as
   servers (DRs) or relays.

   A HA that supports DHCPv6PD MUST support Mobile Routers as well, so
   if the 'D' bit is set, then the 'R' bit should be set as well.  So
   there is no need in an implementation to support the case where some
   HAs would support Mobile Routers while others would be participating
   to DHCPv6 Prefix Delegation but none could do both.

   If none of the Home Agents support DHCPv6PD, the Home Agent MAY reply
   with a list of Home Agents that only support NEMO basic Mobile
   Routers or Mobile IPv6 Mobile Nodes.  In this case, the DHCPv6PD
   Support Flag MUST be set to 0.

   The modified message format is as follows.



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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |            Checksum           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Identifier          |R|D|         Reserved          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      DHCPv6PD Support Flag (D)

         A one-bit flag that when set indicates that the Home Agents
         listed in this message participate to DHCPv6 Prefix Delegation.

   For a description of the other fields in the message, see [RFC3775]
   and [RFC 3963].

3.5.3.  Modified Home Agent Information Option

   A new flag (D) (Support for DHCPv6PD) is introduced in the Home Agent
   Information Option defined in [RFC3775] and [RFC 3963].

   If a Home Agent participates to DHCPv6PD, it SHOULD set the flag.  If
   the HA sets the 'D' flag, then it MUST also set the 'R' flag,
   Indicating that it supports Mobile Routers, as defined in [RFC 3963].


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |    Length     |R|D|       Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Home Agent Preference     |      Home Agent Lifetime      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           DHCPv6PD Support Flag (D)

            A one-bit flag that when set indicates that the Home Agents
            participates to DHCPv6 Prefix Delegation.

   For a description of the other fields in the message, see [RFC3775]
   and [RFC 3963].





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3.6.  Location of DHCPv6PD Delegating Router function

   Support of DHCPv6PD for a Mobile Network is optional.

   The use of a DHCPv6 relay agent is not defined for DHCPv6PD in the
   DHCPv6PD specification [RFC3633].  If the DHCPv6PD DR function is
   implemented in the HA for the MR, no relay agent function is
   required.

   It may be desirable to use a single DR to manage RRs in a network
   with multiple HAs.  In this scenario, the HAs will act as DHCP relay
   agents, forwarding messages between the RRs and the DR.

   Use of the DHCPv6 relay agent function with DHCPv6PD requires that
   there be some mechanism through which routing information for the
   delegated prefixes can be added to the appropriate routing
   infrastructure.  If the HA is acting as a DHCPv6 relay agent, the HA
   SHOULD add a route to the delegated prefix and advertise that route
   after receiving a binding update for the prefix from the RR
   [RFC3963].

   In particular, if the MR uses NEMO explicit mode, then it must add
   the delegated prefix to prefix list in the Binding Update messages.
   If the binding cache is cleared before the prefix valid lifetime, the
   MR might bind that prefix again using explicit mode, till the
   lifetime expires.

   In implicit mode, the HA must save the delegated prefix with the
   binding cache entry of the Mobile Router.  When the BCE is cleared,
   the HA loses the information about the delegated prefix.  Because the
   MR will use DHCPv6 when it reestablishes its tunnel to the HA (see
   Section 3.1), the HA will be able to add the delegated prefix back to
   the BCE.

   At the time this draft was written, one way in which a DR can
   explicitly notify a relay agent about delegated prefixes, is to use
   the "DHCP Relay Agent Assignment Notification Option"
   [I-D.ietf-dhc-dhcpv6-agentopt-delegate].

   Another alternative, if the RR is part of the same administrative
   domain as the home network to which it is attached through the HA,
   and the RR can be trusted, the RR can use a routing protocol like
   OSPF to advertise any delegated prefixes.

   NEMO explicit mode is recommended to take advantage of the function
   already defined for NEMO.





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3.7.  Other DHCPv6 functions

   The DHCPv6 messages exchanged between the MR and the HA may also be
   used for other DHCPv6 functions in addition to DHCPv6PD.  For
   example, the HA may assign global addresses to the MR and may pass
   other configuration information such as a list of available DNS
   recursive resolvers to the MR using the same DHCPv6 messages as used
   for DHCPV6PD.

   The HA may act as a DHCPv6 relay agent for MHs while it acts as a DR
   for MRs.


4.  Changes in this draft

4.1.  Revision -01

   Removed section 3.2, "Delegating Access Prefixes".

   Modified sections 3 and 3.6 (was section 3.1.3), "Location of
   DHCPv6PD Delegating Router function," to allow for DHCPv6PD through a
   relay agent and to allow for a single DR on a home network to perform
   PD for RRs through more than one HA.

   Added section 3.1 describing when the MR should use DHCPv6 PD.

   Added section 3.4 describing use of Rapid Commit to minimize DHCPv6PD
   messages and

   Added section 3.5 recommending that DHCPv6PD and DHAAD be kept
   independent and describing flags indicating availability of PD
   service from HA.

   Added section 3.7 describing the use of DHCPv6 for other
   configuration in parallel with PD.


5.  Security Considerations

   This document describes the use of DHCPv6 for prefix delegation in
   Mobile Networks.  It does not introduce any additional security
   considerations beyond those described in the "Security
   Considerations" section of the DHCPv6 base specification [RFC3315]
   and the "Security Considerations" of the DHCPv6 Prefix Delegation
   specification [RFC3633].

   Following the DHCPv6 Prefix Delegation specification, HAs and MRs
   SHOULD use DHCPv6 authentication as described in section



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   "Authentication of DHCP messages" of the DHCPv6 specification
   [RFC3315], to guard against attacks mounted through prefix
   delegation.


6.  IANA Considerations

   This document describes the use of DHCPv6 for prefix delegation in
   Mobile Networks.  It does not introduce any additional IANA
   considerations.


7.  Normative References

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

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

   [RFC3513]  Hinden, R. and S. Deering, "Internet Protocol Version 6
              (IPv6) Addressing Architecture", RFC 3513, April 2003.

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

   [I-D.ietf-nemo-terminology]
              Ernst, T. and H. Lach, "Network Mobility Support
              Terminology", draft-ietf-nemo-terminology-06 (work in
              progress), November 2006.

   [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.

   [I-D.ietf-nemo-requirements]
              Ernst, T., "Network Mobility Support Goals and
              Requirements", draft-ietf-nemo-requirements-06 (work in
              progress), November 2006.

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

   [I-D.ietf-dhc-dhcpv6-agentopt-delegate]
              Droms, R., "DHCPv6 Relay Agent Assignment Notification
              (RAAN) Option", draft-ietf-dhc-dhcpv6-agentopt-delegate-02



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              (work in progress), November 2006.


Authors' Addresses

   Ralph Droms
   Cisco
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Phone: +1 978.936.1674
   Email: rdroms@cisco.com


   Pascal Thubert
   Cisco
   Village d'Entreprises Green Side
   400, Avenue Roumanille
   Biot - Sophia Antipolis  06410
   FRANCE

   Email: pthubert@cisco.com




























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