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Network Working Group                                        B. Sarikaya
Internet-Draft                                                    F. Xia
Intended status: BCP                                          Huawei USA
Expires: August 20, 2010                               February 16, 2010


  DHCPv6 Prefix Delegation as IPv6 Migration Tool in Cellular Networks
            <draft-sarikaya-v6ops-prefix-delegation-00.txt>

Abstract

   According to IPv6 operation in cellular networks, one prefix can only
   be assigned to one interface of a mobile node by an access router and
   different mobile nodes can't share a prefix.  Managing Per-MN
   interface prefixes is likely to increase the processing load at the
   access router.  Based on the idea that DHCPv6 servers can manage
   prefixes as well as addresses, we propose a new technique in which
   the access router offloads delegation and release tasks of the
   prefixes to an DHCPv6 server.  The access router first requests a
   prefix for an incoming mobile node to the DHCPv6 server.  The access
   router next advertises the prefix information to the mobile node with
   a Router Advertisement message.  When the mobile node hands off, the
   prefix is returned to the DHCPv6 server.  We also describe how less
   than /64 prefixes can be allocated.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 20, 2010.




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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Prefix Delegation Using DHCPv6 . . . . . . . . . . . . . . . .  4
     3.1.  Prefix Request Procedure for Stateless Address
           Configuration  . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Prefix Request Procedure for Stateful Address
           Configuration  . . . . . . . . . . . . . . . . . . . . . .  6
     3.3.  Prefix Release Procedure . . . . . . . . . . . . . . . . .  7
     3.4.  Renumbering  . . . . . . . . . . . . . . . . . . . . . . .  7
       3.4.1.  Renumbering Through Renew Message  . . . . . . . . . .  7
       3.4.2.  Server Initiated Reconfiguration . . . . . . . . . . .  8
     3.5.  Miscellaneous Considerations . . . . . . . . . . . . . . .  8
       3.5.1.  Allocating Prefixes With Length Less Than /64  . . . .  8
       3.5.2.  Allocating More Than One Prefix  . . . . . . . . . . .  8
       3.5.3.  Triggers for an AR to Initiate Prefix Request
               Procedure  . . . . . . . . . . . . . . . . . . . . . .  9
       3.5.4.  How to Generate IAID . . . . . . . . . . . . . . . . .  9
       3.5.5.  Policy to Delegate Prefixes  . . . . . . . . . . . . .  9
   4.  Prefix Delegation Using RADIUS and Diameter  . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  Protocol Variables . . . . . . . . . . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13






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1.  Introduction

   Figure 1 illustrates the key elements of a typical cellular access
   network.  In a Long Term Evolution (LTE) network, access router is
   the serving gateway or the packet data network (PDN) gateway
   [23.401].

      Customer |  Access Provider  | Wireless Core
      Premise  |                   | (Backend Network)
                                                          +------+
                                            +-------------|DHCP  |
    +-----+            +-----+     +------+ | +--------+  |Server|
    | UE  |---(LTE)----| BS  |-----+Access+---+ Edge   |  +------+
    +-----+            +-----+     |Router|   | Router +==>ISP Network
                                   +--+---+   +--------+
    +-----+            +-----+        |            |  +------+
    | UE  |---(LTE)----| BS  |--------+            +--|AAA   |
    +-----+            +-----+                        |Server|
                                                      +------+

        Figure 1: Key elements of a typical cellular access network

   User equipment (UE) attach to a base station (BS) through LTE air
   interface.  A BS manages connectivity of UEs and extend connections
   to an Access Router (AR).  The Access router is the first IP hop
   router of UEs.

   As to IPv6 addressing, there are two models, shared prefix and Per-MN
   interface prefix.  In the shared prefix model, an IPv6 prefix is
   shared by multiple MNs.  While in the Per-MN interface prefix model,
   a prefix is only assigned to one interface of the MN.  Different MNs
   can't share a prefix, and an interface can have multiple prefixes.

   [RFC4968] briefly compares the two models.  Per-MN interface prefix
   model has some advantages, such as, no complicated duplicate address
   detection (DAD), fit naturally to the point-to-point links and so on.
   In Per-MN interface prefix model, prefix management is an issue.

   When an MN attaches an AR, the AR requests one or more prefixes for
   the MN.  When the MN detaches the AR, the prefixes should be
   released.  When the MN becomes idle, the AR should hold the prefixes
   allocated.  When an operator wants to renumber its network, prefixes
   with different lifetime are advertised to the MN.

   DHCPv6 is a preferable way to manage the prefixes.  At the same time,
   AAA protocols, RADIUS and Diameter, can be used in prefix delegation.





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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 BCP 14 [RFC2119].

   This document uses the terminology defined in [RFC3315], [RFC3633]
   and [23.401].


3.  Prefix Delegation Using DHCPv6

   Access router refers to the cellular network entity that has DHCP
   Client.  According to [23.401] DHCP Client is located in PDN Gateway.
   So AR is the PDN Gateway in LTE architecture.

3.1.  Prefix Request Procedure for Stateless Address Configuration


































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       +-------+               +-------+             +-----------+
       |  MN   |               |  AR   |             |DHCP Server|
       +-------+               +-------+             +-----------+
           |                       |                       |
           |  1 N/W Entry & Auth   |                       |
           |<--------------------->|                       |
           |                       |2 Relay-forward/Solicit|
           |                       |---------------------> |
           |                       |                       |
           |                       |3 Relay-reply/Advertise|
           |                       |<--------------------- |
           |                       |                       |
           |                       |4 Relay-forward/Request|
           |                       |---------------------> |
           |                       |                       |
           |                       |5 Relay-reply/Reply    |
           |                       |<--------------------- |
           |6 Initial Service Flow |                       |
           |       Established     |                       |
           |<--------------------->|                       |
           |                       |                       |
           | 7 Router Advertisement|                       |
           |<----------------------|                       |
           |                       |                       |
           |   8 MLD Join          |                       |
           |---------------------->|                       |
           |                       |                       |
           | 9 DAD Procedure       |                       |
           |<--------------------->|                       |
           |                       |                       |

                         Figure 2: Prefix request

   There are two function modules in the AR, DHCP Client and DHCP Relay.
   DHCP messages should be relayed if the AR and a DHCP server are not
   connected directly, otherwise DHCP relay function in the AR is not
   necessary.  Figure 2 illustrates the scenario that the AR and the
   DHCP Server aren't connected directly:

   1.  An MN performs initial network entry and authentication
       procedures.
   2.  On successful completion of Step 1, the AR initiates DHCP Solicit
       procedure to request prefixes for the MN.  The AR 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.  The AR creates an IA_PD and
       assigns it an IAID.  The AR MUST include the IA_PD option in the
       Solicit message.



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   3.  The DHCP server sends an Advertise message to the AR in the same
       way as described in section 17.2.2, "Creation and transmission of
       Advertise messages" of RFC 3315.
   4.  The AR 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.  The AR 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.  AR stores the prefix information it received in the Reply
       message.
   6.  A virtual link is created for exchanging control traffic between
       MN and AR and becomes active.
   7.  The AR advertises prefixes to MN with router advertizement (RA)
       once the virtual link is active.
   8.  The MN constructs a solicited node multicast address for the
       corresponding Link Local Address and sends MLD Join request for
       the solicited node multicast address.
   9.  The MN starts verifying address uniqueness by sending a DAD NS on
       the virtual link.  AR can check the address uniqueness within the
       virtual link scope.

   4-way exchange between AR as requesting router (RR) and DHCP server
   as delegating router (DR) in Figure 2 MAY be reduced into a two
   message exchange using the Rapid Commit option [RFC3315].  AR
   includes a Rapid Commit option in the Solicit message.  DR then sends
   a Reply message containing one or more prefixes.

3.2.  Prefix Request Procedure for Stateful Address Configuration

   After the initial network entry and authentication, an initial
   service flow is established for the MN.  DHCP Relay follows the
   procedure shown in Figure 2 to get the new prefix for this interface
   of MN.

   DHCPv6 client at the MN sends DHCP Request to DHCP Relay function at
   AR.  AR MUST make sure that DHCP server assigns MN address from this
   prefix.  AR as DHCP Relay forwards DHCP Request message in DHCP Relay
   Option and adds Option 82 to the message [RFC3046].  Option 82 MUST
   contain MN' prefix.  DHCP server MUST process Option 82 and MUST
   assign an address to MN using the prefix in Option 82.  DHCP server
   replies with Relay reply message.  DHCP Relay sends DHCP Reply
   message to MN containing its address.

   MN configures its interface with the address assigned by DHCP server
   in DHCP Reply message.





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3.3.  Prefix Release Procedure

       +-------+               +-------+             +-----------+
       |  MN   |               |  AR   |             |DHCP Server|
       +-------+               +-------+             +-----------+
           |                       |                       |
           |  1 De-registration    |                       |
           |  Handover, or others  |                       |
           |<--------------------->|                       |
           |                       |2 Relay-forward/Release|
           |                       |---------------------->|
           |                       |                       |
           |                       |3 Relay-reply/Reply    |
           |                       |<--------------------- |
           |                       |                       |
           |                       |                       |

                         Figure 3: Prefix Release

   Prefixes can be released in two ways, prefix aging or DHCP release
   procedure.  In the former way, a prefix SHOULD not be used by an MN
   when the prefix ages, and the DHCP Server can delegate it to another
   MN.  A prefix lifetime is delivered from the DHCPv6 server to the MN
   through DHCP IA_PD Prefix option [RFC3633] and RA Prefix Information
   option [RFC4861].  Figure 3 illustrates how the AR releases prefixes
   to an DHCP Server which isn't connected directly:

   1.  An MN detachment signaling, such as switch-off or handover,
       triggers prefix release procedure.
   2.  The AR initiates a Release message to give back the prefixes to
       the DHCP server.
   3.  The server responds with a Reply message, and then the prefixes
       can be reused by other MNs.

3.4.  Renumbering

3.4.1.  Renumbering Through Renew Message

   To extend the valid and preferred lifetimes for the prefixes
   associated with an MN, the AR sends a Renew message to the DHCP
   server.  The server determines new lifetimes for the prefixes and
   returns the prefix to AR in a Reply message.  The DHCP server MAY add
   new prefixes to the MN for renumbering in its Reply message.  For a
   more detailed description of these message, refer to [RFC3633] and of
   renumbering, refer to [RFC4192].






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3.4.2.  Server Initiated Reconfiguration

   DHCP server initiates a configuration message exchange with the AR by
   sending a Reconfigure message.  The reconfigure message triggers the
   AR to send Renew message as described in Section 3.4.1.

3.5.  Miscellaneous Considerations

3.5.1.  Allocating Prefixes With Length Less Than /64

   According to [RFC3314] one /64 prefix needs to be assigned to each
   mobile node.  In some cases prefixes with length less than /64 need
   to be assigned to MNs.  The protocol described in Section 3.1 can be
   easily tailored for the purpose of allocating prefixes with length
   less than /64.

   In Step 1, MN sends its identity during attach procedure, e.g.
   International Mobile Subscriber Identity (IMSI) or certain type of
   IMSI such as Provisional Connectivity ID (PCID) [23.812].

   In Step 2, Requesting Router MAY consider the type of MN identity
   when sending DHCP Solicit message.  For MNs that need to be assigned
   prefixes longer than /64, Requesting Router SHOULD include IA_PD
   Prefix Option into the created IA_PD.  Requesting Router MUST set
   prefix-length field to a value less than 64, e.g. 60.  More than one
   IA_PD Prefix option may be included in the Solicit message.

   In Step 5, Delegating Router sends a reply message containing the
   prefix(es) requested.

   There are many applications where prefixes with length less than /64
   is needed.  In Machine to Machine applications the host may act as
   machine to machine communication gateway, which has to assign IPv6
   addresses to the sensors, switches, or other devices within the
   control area of the gateway.  Each of these devices may require a
   different /64 prefix.  Another application is the Mobile Router.
   Mobile Router gets Mobile Network Prefix(es) and advertizes these
   prefixes in the mobile network [RFC3963]

3.5.2.  Allocating More Than One Prefix

   DHCPv6 PD described in Section 3.1 can be easily tailored to assign
   more than one prefix to MNs.  Requesting Router SHOULD include more
   than one IA_PD Prefix options into the created IA_PD.  This will
   result in Delegating Router assigning more than one prefix.  The
   prefix length depends on the value assigned in prefix-length field of
   IA_PD Prefix option.




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   Machine to machine gateways [23.812] and Proxy Mobile IPv6 hosts
   [RFC5213] typically need more than one prefix assigned.  Machine to
   machine gateways may need prefixes with length less than /64.

3.5.3.  Triggers for an AR to Initiate Prefix Request Procedure

   There are some other triggers for an AR to initiate prefix request
   procedure besides network entry and authentication, such as, when an
   AR receives handover initiate (HI) message in FMIPv6 [RFC4068], or
   other handover signaling.  After getting an incoming MN' necessary
   information (such as MAC address), the AR SHOULD initiate prefix
   request procedure as soon as possible.

3.5.4.  How to Generate IAID

   IAID is 4 bytes in length and should be unique in an AR scope.
   Prefix table SHOULD be maintained.  Prefix table contains IAID, MAC
   address and the prefix(es) assigned to MN.  In LTE networks,
   International Mobile Subscriber Identity (IMNI) corrsponds to the MAC
   address.  MAC address of the interface SHOULD be stored in the prefix
   table and this field is used as the key for searching the table.

   IAID SHOULD be set to Start_IAID, an integer of 4 octets.  The
   following IAID generation algorithm is used:

   1.  Set this IAID value in IA_PD Prefix Option.  Request prefix for
       this MN as in Section 3.1 or Section 3.2.
   2.  Store IAID, MAC address and the prefix(es) received in the next
       entry of the prefix table.
   3.  Increment IAID.

   Prefix table entry for an MN that handsover to another AR MUST be
   removed.  IAID value is released to be reused.

3.5.5.  Policy to Delegate Prefixes

   AR should broadcast the prefix(es) dynamically upstream as the route
   information of all the MNs connected to this AR.  In point-to-point
   links, this causes high routing protocol traffic (IGMP, OSPF, etc.)
   due to Per-MN interface prefixes.  To solve the problem, route
   aggregation SHOULD be used.  For example, each AR can be assigned a
   /48 or /32 prefix (aggregate prefix, aka service provider common
   prefix) while each interface of MN can be assigned a /64 prefix.  The
   /64 prefix is an extension of /48 one, for example, an AR's /48
   prefix is 3FFE:FFFF:0::/48, an interface of MN is assigned 3FFE:FFFF:
   0:2::/64 prefix.  The AR only broadcasts it's /48 or /32 prefix
   information to Internet.




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   This policy can be enforced as follows: DHCP Relay MUST set the IPv6
   Prefix field in IA_PD Prefix option in IA_PD option in the Relay
   Forward message to the aggregate prefix (/48, /32, or /16 prefix
   assigned to the AR).


4.  Prefix Delegation Using RADIUS and Diameter

   In the bootstrapping procedure, an AR as RADIUS client sends Access-
   Request message with an MN' information to RADIUS server.  If the MN
   passes the authentication, the RADIUS server MAY send Access-Accept
   message with prefix information to the AR using Framed-IPv6-Prefix
   attribute.  There is no prefix delegation involved in this process.
   Using such a process AR can handle initial prefix assignments to MNs
   but managing lifetime of the prefixes is totally left to the AR.
   Also AR can not use Framed-IPv6-Prefix attribute based assignment for
   MNs that handover but no full authentication is executed.

   [RFC4818] defines a RADIUS attribute Delegated-IPv6-Prefix that
   carries an IPv6 prefix to be delegated.  This attribute is usable
   within either RADIUS or Diameter.  [RFC4818] recommends the
   delegating router to use AAA server to receive the prefixes to be
   delegated using Delegated-IPv6-Prefix attribute/AVP.

   DHCP server as the delegating router in Figure 2 MAY send an Access-
   Request packet containing Delegated-IPv6-Prefix attribute to the
   RADIUS server to request prefixes.  In the Access-Request message,
   the delegating router MAY provide a hint by the AR that it would
   prefer a prefix, for example, a /48 prefix.  The RADIUS server MAY
   delegate a /64 prefix which is an extension of the /48 prefix in an
   Access-Accept message containing Delegated-IPv6-Prefix attribute.
   The attribute can appear multiple times when RADIUS server assigns
   multiple prefixes.

   When Diameter is used, DHCP server as the delegating router in
   Figure 2 sends AA-Request message.  AA-Request message MAY contain
   Delegated-IPv6-Prefix AVP.  Diameter server replies with AA-Answer
   message.  AA-Answer message MAY contain Delegated-IPv6-Prefix AVP.
   The AVP can appear multiple times when Diameter server assigns
   multiple prefixes to MN.  The Delegated-IPv6-Prefix AVP MAY appear in
   an AA-Request packet as a hint by the AR to the Diameter server that
   it would prefer a prefix, for example, a /48 prefix.  Diameter server
   MAY delegate in an AA-Answer message with a /64 prefix which is an
   extension of the /48 prefix.

   AR MUST advertize the prefix(es) to MN in RtrAdv message.

   Prefix release and site renumbering are open issues for RADIUS/



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   Diameter protocols to manage prefixes.


5.  Security Considerations

   This draft introduces no additional messages.  Comparing to
   [RFC3633], [RFC2865] and [RFC3588] there is no additional threats to
   be introduced.  DHCPv6, RADIUS and Diameter security procedures
   apply.


6.  Protocol Variables

   Start_IAID 4 octet integer value.

   It can be initialized to ZERO.


7.  IANA Considerations

   None.


8.  Acknowledgements

   TBD.


9.  References

9.1.  Normative References

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

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC2866]  Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.

   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, January 2001.

   [RFC3314]  Wasserman, M., "Recommendations for IPv6 in Third
              Generation Partnership Project (3GPP) Standards",
              RFC 3314, September 2002.




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   [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.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

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

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

   [RFC4068]  Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068,
              July 2005.

   [RFC4818]  Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix
              Attribute", RFC 4818, April 2007.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

9.2.  Informative References

   [23.401]   "3GPP TS 23.401 V9.3.0, General Packet Radio Service
              (GPRS) enhancements for Evolved Universal Terrestrial
              Radio Access Network  (E-UTRAN) access (Release 9).",
              2009.

   [23.812]   "3GPP TR 23.812 V9.0.0, Feasibility Study on the Security
              Aspects of Remote Provisioning and Change of Subscription
              for M2M Equipment; (Release 9).", 2009.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.

   [RFC4968]  Madanapalli, S., "Analysis of IPv6 Link Models for 802.16
              Based Networks", RFC 4968, August 2007.



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Authors' Addresses

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

   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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