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Versions: 00

DHC WG                                                         I. Farrer
Internet-Draft                                       Deutsche Telekom AG
Intended status: Standards Track                                  Q. Sun
Expires: August 16, 2014                                          Y. Cui
                                                     Tsinghua University
                                                       February 12, 2014


                DHCPv4 over DHCPv6 Source Address Option
                   draft-fsc-dhc-dhcp4o6-saddr-opt-00

Abstract

   DHCPv4 over DHCPv6 [I-D.ietf-dhc-dhcpv4-over-dhcpv6] describes one
   possible mechanism for dynamically configuring IPv4 over an IPv6 only
   network.  For DHCPv4 over DHCPv6 to function with some softwire
   mechanisms, the operator must obtain information about the DHCP 4o6
   client's allocated IPv4 address and PSID, as well as the /128 IPv6
   prefix that the client will use as the source of IPv4-in-IPv6 tunnel.
   This memo defines a DHCPv6 option to convey this IPv6 prefix between
   the DHCP 4o6 client and server.  It is designed to work in
   conjunction with the DHCPv4 IPv4 address allocation process message
   flow.

Requirements Language

   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 RFC 2119 [RFC2119].

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on August 16, 2014.





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Copyright Notice

   Copyright (c) 2014 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicabiliity  . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
   4.  DHCPv4 over DHCPv6 Source Address Option  . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   DHCPv4 over DHCPv6 [I-D.ietf-dhc-dhcpv4-over-dhcpv6] describes a
   mechanism for dynamically configuring IPv4 over an IPv6 only network
   by transporting the complete set of DHCPv4 messages within a specific
   pair of DHCPv6 messages.  The IPv4 configuration provisioned to the
   DHCP 4o6 clients is then generally used for configuring IPv4 over
   IPv6 services.  IPv4 addresses can be dynamically leased to DHCP 4o6
   clients in the same manner as IPv4 addresses are leased to DHCPv4
   clients in IPv4 networks.  The main advantages to this approach is a
   greater efficiency in the use of limited IPv4 address resources over
   IPv6 networks.

   Currently defined IPv4 over IPv6 transition technologies are, by
   design, quite prescriptive in the location of the tunnel endpoint
   within the home network.  The tunnel endpoint must usually be
   configured on either the home gateway device, or sourced from a very
   specific IPv6 tunnel prefix allocated to the home network (and in
   some cases, both).  This is necessary to enable the end-to-end



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   provisioning chain between the IPv4-over-IPv6 client in the home
   network, the border router (the egress point from the IPv4 over IPv6
   domain to the IPv4-only domain) and the provisioning systems
   responsible for configuring the functional elements.

   The dynamic leasing of IPv4 addresses to clients alters this end-to-
   end provisioning chain.  It can no longer be assumed that a Softwire
   Initiator sourcing from a specific IPv6 prefix have to use a certain
   IPv6 address as the source for encapsulating its IPv4 packets.
   Therefore, a mechanism is necessary to inform the service provider of
   the binding between the allocated IPv4 address (learnt through
   DHCPv4) and the IPv6 address that the IPv4 over IPv6 client will use
   for accessing IPv4-over-IPv6 services.  The service provider can then
   use this binding information to provision other functional elements
   it their network such as the border router accordingly.

   A second benefit of such a mechanism is that it allows much more
   flexibility in the location of the IPv4 over IPv6 tunnel endpoint as
   this will be dynamically signalled back to the service provider.  The
   DHCP 4o6 client and tunnel client could be run on end devices
   attached to any valid IPv6 prefix allocated to an end-user, located
   anywhere within an arbitrary home network topology.

   As The DHCP 4o6 server manages the leasing of IPv4 addresses to the
   DHCP 4o6 clients, which runs on the Softwire Initiators, it holds the
   most accurate IPv4 lease information available across the IPv6
   network between the server and the client.  It follows that the DHCP
   4o6 server should also hold information about the /128 IPv6 prefixes
   that active clients are using, so that the server contains a single,
   comprehensive and up to date dynamic IPv4/IPv6 binding table.

   This memo describes a DHCPv6 option so that the server can indicate
   to the client a preferred IPv6 prefix to use (if necessary) and for
   the client to signal back the /128 IPv6 prefix that they will bind
   the allocated IPv4 configuration to.  The DHCP 4o6 server then stores
   this information alongside the IPv4 lease information.

   Current mechanisms suitable for extending to incorporate DHCPv4 over
   DHCPv6 with dynamic IPv4 address leasing include
   [I-D.ietf-softwire-map] and [I-D.ietf-softwire-lw4over6].  For these
   mechanisms to function, the operator needs the information about the
   DHCP 4o6 client's allocated IPv4 address, PSID and also the /128 IPv6
   prefix that the client will use to source the IPv4-in-IPv6 tunnel
   endpoint.







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2.  Applicabiliity

   Although DHCPv4 over DHCPv6 is used as the configuration protocol
   throughout this document, the DHCPv6 option and provisioning process
   which is described here may also be used with other DHCP based IPv4
   over IPv6 configuration mechanisms, such as DHCPv4 over IPv6
   [I-D.ietf-dhc-dhcpv4-over-ipv6].

3.  Solution Overview

   The DHCPv6 option (OPTION_DHCPV4OV6_SADDR) described by this memo is
   intended to be used alongside the normal DHCPv4 IPv4 address
   allocation message flow as described in [RFC2131], in the context of
   DHCPv4 over DHCPv6 [I-D.ietf-dhc-dhcpv4-over-dhcpv6] .  It is a two-
   way communication process, allowing the service provider to
   (optionally) indicate to the client a preferred prefix alongside the
   DHCPOFFER message, which can be used for binding the received IPv4
   configuration and sourcing tunnel traffic.  When the client has
   selected the IPv6 prefix to bind the IPv4 configuration to, it passes
   this back to the DHCP 4o6 server along with the DHCPREQUEST message.
   This may be necessary if there are multiple IPv6 prefixes in use in
   the customer network, or if the specific IPv4 over IPv6 transition
   mechanism requires the use of a particular prefix for any reason.

   The following diagram shows the client/server message flow and how
   the different fields of OPTION_DHCPV4OV6_SADDR are used.  In each
   step, the relevant DHCPv4 message is given above the arrow and the
   relevant paramaters used in OPTION_DHCPV4OV6_SADDR's fields below the
   arrow.






















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             DHCP 4o6                                     DHCP 4o6
              Client                                       Server
                |                DHCPDISCOVER                 |
         Step 1 |-------------------------------------------->|
                |    OPTION_DHCPV4OV6_SADDR (blank fields)    |
                |                                             |
                |                  DHCPOFFER                  |
         Step 2 |<--------------------------------------------|
                |  OPTION_DHCPV4OV6_SADDR (cipv6-prefix-hint  |
                |  with service provider's preferred prefix)  |
                |                                             |
                |                 DHCPREQUEST                 |
         Step 3 |-------------------------------------------->|
                |  OPTION_DHCPV4OV6_SADDR (cipv6-bound-prefix |
                |   with client's bound /128 IPv6 prefix)     |
                |                                             |
                |                   DHCPACK                   |
         Step 4 |<--------------------------------------------|
                |  OPTION_DHCPV4OV6_SADDR (cipv6-bound-prefix |
                |   with client's bound /128 IPv6 prefix)     |
                |                                             |


                      IPv6/IPv4 Binding Message Flow

   The OPTION_DHCPV4OV6_SADDR (defined below) option is included by the
   DHCP 4o6 client within DHCPv4-query messages.  The DHCP 4o6 server
   MAY reply with this option within DHCPv4-response messages.

   The DHCP 4o6 Server and Client MAY implement the
   OPTION_DHCPV4OV6_SADDR option.  If used, this option MUST be present
   within all future DHCPv4 over DHCPv6 transactions.

   The option comprises of two prefixes (with associated prefix length
   fields):

   cipv6-prefix-hint  Used by the server to indicate a preferred prefix
                      that the client should use to bind IPv4
                      configuration to.  If this field contains a
                      prefix, the client MUST perform a longest prefix
                      match between cipv6-prefix-hint and all prefixes
                      configured on the device.  The selected prefix
                      MUST then be used to bind the received IPv4
                      configuration to.  If this field is left blank,
                      then the client can select any valid IPv6 prefix.
   cipv6-bound-prefix Used by the client to inform the DHCP 4o6 Server
                      of the IPv6 prefix that it has bound the IPv4




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                      configuration to.  This MUST be a /128 prefix
                      configured on the client.

4.  DHCPv4 over DHCPv6 Source Address Option

   The format of DHCPv4 over DHCPv6 Source address option is defined as
   follows:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    OPTION_DHCPV4OV6_SADDR     |         option-length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | cipv6-hintlen |                                               |
       +-+-+-+-+-+-+-+-+          cipv6-prefix-hint                    .
       .                          (variable length)                    .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |cipv6-boundlen |                                               |
       +-+-+-+-+-+-+-+-+          cipv6-bound-prefix                   .
       .                          (variable length)                    .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   o  option-code: OPTION_DHCPV4OV6_SADDR (TBA)
   o  option-length: 2 + length of cipv6-prefix-hint + length of cipv6
      -bound-prefix, specified in bytes.
   o  cipv6-hintlen: 8-bit field expressing the bit mask length of the
      IPv6 prefix specified in cipv6-prefix-hint.
   o  cipv6-prefix-hint: The IPv6 prefix that the server uses to
      indicate the preferred prefix that the client should use to bind
      IPv4 configuration to.
   o  cipv6-boundlen: 8-bit field expressing the bit mask length of the
      IPv6 prefix specified in cipv6-bound-prefix.  Default: 128.
   o  cipv6-bound-prefix: The IPv6 prefix that the client is using to
      bind the allocated IPv4 configuration to.

5.  Security Considerations

   TBD

6.  IANA Considerations

   IANA is requested to allocate the DHCPv6 option code:
   OPTION_DHCPV4OV6_SADDR.







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7.  Acknowledgements

8.  References

8.1.  Normative References

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

8.2.  Informative References

   [I-D.ietf-dhc-dhcpv4-over-dhcpv6]
              Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
              Farrer, "DHCPv4 over DHCPv6 Transport", draft-ietf-dhc-
              dhcpv4-over-dhcpv6-04 (work in progress), January 2014.

   [I-D.ietf-dhc-dhcpv4-over-ipv6]
              Cui, Y., Wu, P., Wu, J., Lemon, T., and Q. Sun, "DHCPv4
              over IPv6 Transport", draft-ietf-dhc-dhcpv4-over-ipv6-08
              (work in progress), October 2013.

   [I-D.ietf-softwire-lw4over6]
              Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
              I. Farrer, "Lightweight 4over6: An Extension to the DS-
              Lite Architecture", draft-ietf-softwire-lw4over6-06 (work
              in progress), February 2014.

   [I-D.ietf-softwire-map-dhcp]
              Mrugalski, T., Troan, O., Dec, W., Bao, C.,
              leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options
              for configuration of Softwire Address and Port Mapped
              Clients", draft-ietf-softwire-map-dhcp-06 (work in
              progress), November 2013.

   [I-D.ietf-softwire-map]
              Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, "Mapping of Address and Port
              with Encapsulation (MAP)", draft-ietf-softwire-map-10
              (work in progress), January 2014.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
              2131, March 1997.

   [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.





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   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927, May
              2005.

   [RFC4361]  Lemon, T. and B. Sommerfeld, "Node-specific Client
              Identifiers for Dynamic Host Configuration Protocol
              Version Four (DHCPv4)", RFC 4361, February 2006.

   [RFC6148]  Kurapati, P., Desetti, R., and B. Joshi, "DHCPv4 Lease
              Query by Relay Agent Remote ID", RFC 6148, February 2011.

   [RFC6346]  Bush, R., "The Address plus Port (A+P) Approach to the
              IPv4 Address Shortage", RFC 6346, August 2011.

Authors' Addresses

   Ian Farrer
   Deutsche Telekom AG
   CTO-ATI, Landgrabenweg 151
   Bonn, NRW  53227
   Germany

   Email: ian.farrer@telekom.de


   Qi Sun
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6278-5822
   Email: sunqi@csnet1.cs.tsinghua.edu.cn


   Yong Cui
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6260-3059
   Email: yong@csnet1.cs.tsinghua.edu.cn










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