Network Working Group                                             Y. Cui
Internet-Draft                                                     P. Wu
Intended status: Standards Track                                   J. Wu
Expires: June 2, September 13, 2012                          Tsinghua University
                                                                T. Lemon
                                                           Nominum, Inc.
                                                       November 30, 2011
                                                          March 12, 2012

                       DHCPv4 over IPv6 Transport



   In IPv6 networks, there are demands arising for remains a need to provide IPv4 address allocation under
   IPv6 environment, especially in IPv6 transition scenarios. service for
   some residual devices.  This document describes the a mechanism for
   allocating IPv4 addresses to survive DHCPv4 over IPv6 network. such devices using DHCPv4 messages are transported in IPv6 packets when traversing the with an IPv6 network.  DHCPv4 protocol behavior of the
   transport.  It is done by extending DHCP client and server is
   extended to support this IPv6 transport.  For the relay case, behavior,
   and by adding a new
   suboption of the Relay Agent Information Option is defined option to carry the remote IPv6
   address of the clients. client.

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
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   This Internet-Draft will expire on June 2, September 13, 2012.

Copyright Notice

   Copyright (c) 2011 2012 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
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   ( in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Protocol Summary  . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Client Relay Agent IPv6 Address Sub-option  . . . . . . . . . . 6
   6.  Client Relay Agent Behavior . . . . . . . . . . . . . . . . . . 6
   7.  IPv6-Transport Server Behavior  . . . . . . . . . . . . . . . . 7
   8.  IPv6-Transport Relay Agent Behavior . . . . . . . . . . . . . . 7
   9.  Security Consideration  . . . . . . . . . . . . . . . . . . . . 8
   10. IANA consideration  . . . . . . . . . . . . . . . . . . . . . . 8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     11.1.  Normative References . . . . . . . . . . . . . . . . . . . 8
     11.2.  Informative References . . . . . . . . . . . . . . . . . . 8 9

1.  Introduction

   DHCPv4 [RFC2131] was not designed with IPv6 consideration.  In
   particular, in mind: DHCPv4 cannot work
   operate on the an IPv6 network.  However, with
   IPv4-IPv6 coexistence coming to as dual-stack networks become a
   reality, the demand of allocating need arises to allocate IPv4 address under addresses in an IPv6 environment naturally arises.
   environment.  To meet this demand, this document extends DHCPv4 should be extended to run over
   allow the use of an IPv6 network. network for transport.

   A typical scenario that probably requires this feature is IPv4-over-
   IPv6 hub and spoke tunnel [RFC4925].  In this scenario, IPv4-over-
   IPv6 tunnel is used to provide IPv4 connectivity to end users (hosts
   or end networks) across an IPv6 network.  If the IPv4 addresses of
   the end users are provisioned by the concentrator side, then the
   provisioning process should be able to cross the IPv6 network, too.
   One such tunnel mechanism is demonstrated in
   [I-D.ietf-softwire-public-4over6].  DHCPv4 over IPv6 would be a
   generic solution for this scenario.

   Three main flavours of solutions may be considered:

   o  Use DHCPv6 instead of DHCPv4, to provision IPv4-related
      connectivity.  In DHCPv6, the provisioned IPv4 address can be
      embedded into IPv6 address, or carried within a new option.  Along
      with that, dedicated options are needed to convey IPv4-related
      information, such as the IPv4 address of DNS server, NTP server,
      etc.  Therefore it will put a certain amount of IPv6-unrelated
      information into DHCPv6 protocol.

   o  Use DHCPv4 and tunnel DHCPv4-in-IPv4 packets messages over IPv6.  Unlike
      the previous approach where DHCPv6 is used for both IPv4 and IPv6
      connectivity, this approach consists in preserving the separation
      between IPv4 and IPv6 connectivity information.  It allows to
      maintain the IPv4 service without major modification of IPv6-
      related provisioning resources, and sustains DHCPv4 to be the
      IPv4-related information carrier.  However, this approach enforces
      an IPv4-in-IPv6 tunnel onto on DHCP, and requires extra efforts to
      maintain tunnel endpoint information for encapsulation use.

   o  Use DHCPv4 and extend it to work over IPv6 transport.  This  Instead of
      relying on IPv4-in-IPv6 tunnel, this flavour uses IPv6 directly
      for DHCP packet transport instead of
      relying on IPv4-in-IPv6 tunnel, message transport, and it keeps the advantage of
      separation with IPv6 connectivity information.  This document
      focuses on this flavour.  The document will define the extensions
      of DHCPv4 protocol behavior, as well as a new suboption of the
      Relay Agent Information Option, to fully support DHCPv4 over IPv6.

2.  Requirements Language
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Terminology

   This document makes use of the following terms:

   o  DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131].

   o  Client Relay Agent(CRA): a special DHCPv4 Relay Agent that sits on
      the same, IPv6-accessable host with the DHCPv4 client.  CRA works
      as a "bridge" between DHCPv4 client and the IPv6 network, to
      convert between IPv4 transport and IPv6 transport.

   o  IPv6-Transport Server(TSV): a DHCPv4 Server that support supports IPv6
      transport.  TSV can listen on IPv6 for incoming DHCPv4 messages,
      and send DHCPv4 messages in IPv6 packets.

   o  IPv6-Transport Relay Agent(TRA): a DHCPv4 Relay Agent that
      supports IPv6 transport.  TRA sits on a machine which has both
      IPv6 and IPv4 connectivity, and relays DHCP packets messages between CRA
      and normal DHCPv4 server.

   o  Client Relay Agent IPv6 Address Sub-option(6ADDR Sub-option(CRA6ADDR suboption): a
      new suboption of DHCP Relay Agent Information Option [RFC3046]
      defined in this document. 6ADDR  CRA6ADDR suboption is used by TRA to
      carry the IPv6 address of a CRA.

4.  Protocol Summary

   The scenario for DHCPv4 over IPv6 transport is shown in Figure 1.
   DHCPv4 clients and DHCPv4 server/relay are separated by an IPv6
   network in the middle.  DHCP messages between a client and the
   server/relay cannot naturally be forwarded to each other because they
   are by default IPv4 UDP packets, either unicast or broadcast.  To
   bridge this gap, both the client side and the server/relay side
   should enable DHCPv4 over IPv6 transport.  To be more precise,  More precisely, they
   should support delivering and receiving DHCP messages in IPv6 UDP
   packets and thereby traverse the IPv6 network.

   On the client side, a special relay agent called Client Relay Agent
   is placed on the same machine with the client.  CRA is used to relay
   DHCP messages from the client to the server, and from the server to
   the client.  CRA sends DHCPv4 messages to the server through unicast
   IPv6 UDP, and receives unicast IPv6 UDP packets with the DHCPv4
   messages from the server.  By using CRA, no extension is required on
   the DHCP client.

     +------+                     |
     |DHCPv4|                     |
     |Client|                 +-------+
     +------+                 |DHCPv4 |
        |      IPv6 Network   |Server/|
     +------+                 |Relay  |
     |DHCPv4|                 +-------+
     |Client|                     |
     +------+                     |

   Figure 1 Scenario of DHCPv4 over IPv6 Transport

   The IPv6-Transport DHCPv4 server can receive DHCP messages delivered
   in IPv6 UDP from CRA, and send out DHCP messages to CRA using IPv6
   UDP(figure 2(a)).  TSV should send DHCP messages to the IPv6 address
   from which it receives relevant DHCP messages earlier.

   When CRAs communicate with an IPv6-Transport Relay Agent rather than
   with a server directly, the situation will become a little more
   complicated.  Besides the IPv6 communication with CRA, TRA also
   communicates with a regular DHCPv4 server through IPv4.  Therefore,
   when TRA relays DHCP messages between a CRA and the DHCPv4 server, it
   receives DHCP message from the CRA in IPv6 and sends it to the server
   in IPv4, while receives DHCP message from the server in IPv4 and
   sends it to the CRA in IPv6.  TRA has to use the DHCP Relay Agent
   Information Option(Option 82) to record the IPv6 address of a CRA,
   which will be used as forwarding destination when relaying DHCP a DHCP
   message from the server.  Since Option 82 doesn't has have an existing
   suboption that fits in the case, this document defines a new Client
   Relay Agent IPv6 Address Sub-option.

     +------+                +------+
     |client|  IPv6 network  |TSV   |
     |+CRA  |----------------|      |
     +------+                +------+
     (a)client--server case

     +------+                +------+              +------+
     |client|  IPv6 network  |TRA   | IPv4 network |server|
     |+CRA  |----------------|      |--------------|      |
     +------+                +------+              +------+
     (b)client--relay--server case

   Figure 2 Protocol Summary

5.  Client Relay Agent IPv6 Address Sub-option

   This suboption MUST be added by a DHCPv4 TRA.  It encodes the IPv6
   address of the host from which a DHCPv4-in-IPv6 CRA-to-TRA packet message
   was received.  It is intended for the TRA to relay DHCPv4 replies
   back to the proper CRA.  To be more specific, the TRA uses the IPv6
   address encoded in this suboption as the destination IPv6 address
   when relaying a DHCPv4 reply to IPv6 network.

   The CRA IPv6 address MUST be unique in the IPv6 domain.

   The 6ADDR CRA6ADDR suboption has a fixed length of 18 octets.  The SubOpt
   code is tbd by IANA, the length field should be 16, and the following
   16 octets contain the CRA IPv6 address.

   DHCP servers MAY use this suboption to select parameters specific to
   particular hosts.  Servers MAY parse this suboption and extract the
   semantic of IPv6 address.

             SubOpt   Len     Agent Remote ID
            +------+------+------+------+------+-     -+------+
            | tbd  |  16  |  a1  |  a2  |  a3  |  ...  |  a16 |
            +------+------+------+------+------+-     -+------+

   Figure 3 Client Relay Agent IPv6 Address Sub-option format

6.  Client Relay Agent Behavior

   A Client Relay Agent sits on the same machine with the DHCPv4 client.
   CRA is a special type of relay agent, which relays DHCPv4 messages
   between regular client and TSV/TRA.  The communication between CRA
   and the client happens within the machine using IPv4, and the
   communication between CRA and TSV/TRA happens on the IPv6 network
   using IPv6.

   A CRA is configured with one or more IPv6 addresses of TSV/TRA.  This
   configuration is provided before DHCPv4 process, for example through
   DHCPv6 option, or by some other mechanisms depending on the
   application scenarios.

   A CRA listens for DHCP packets messages on IPv4 UDP port 67.  When it
   receives from IPv4 any DHCP packet message with bootp op field = 1, it
   forwards the
   packet message using the standard DHCP relay agent format, but
   over UDPv6, with source port 67 and destination port 67.  Here the
   CRA MUST NOT include an option 82 or modify the giaddr field of the
   DHCP packet. message.  The CRA forwards the packet message to each of the DHCP
   server or relay agent with which it is configured.  The CRA MUST use
   a global IPv6 address if it has one.

   A CRA also listens for DHCP packets messages on IPv6 UDP port 68.  When it
   receives from IPv6 any DHCP packet message with bootp op field = 2, the CRA
   checks to see if the packet message contains option 82, and if so, it drops
   discards the packet. message.  Otherwise, it delivers the packet message to the DHCP
   client using IPv4.

7.  IPv6-Transport Server Behavior

   To support IPv6 transport, the behavior of DHCPv4 server should be
   extended.  The IPv6-Transport Server can listen on IPv6 port 67 for
   DHCPv4 packets, messages, and send DHCPv4 packets messages through IPv6.

   A TSV listens for DHCP packets messages on IPv6 UDP port 67.  When it
   receives from IPv6 a DHCP packet, message, it MUST record the IPv6 source
   address of that packet message and retain it as the return address of the packet.
   message.  That is to say, when sometime later the TSV responds to
   this packet, message, it MUST send the reply packet message to the IPv6 return
   address retained
   earlier. earlier, with destination port 68.  When the TSV
   receives an DHCP message with a CRA6ADDR option, the TSV handles it
   following the standard option 82 proceudure defined in [RFC3046].
   The rest of TSV DHCP process is the same with normal DHCPv4 server.
   A TSV can also listen on IPv4 UDP port 67 like a normal DHCPv4
   server, and process normally when receives IPv4 DHCPv4 packet. message.

   This document places no new requirements on DHCPv4 servers that do
   not listen on UDPv6--in order to use an IPv4-only DHCPv4 server
   through an IPv6 connection, a TRA is required.

8.  IPv6-Transport Relay Agent Behavior

   An IPv6-Transport Relay Agent sits between IPv6 network and IPv4
   network, and relays DHCPv4 message between CRAs and IPv4-only DHCPv4
   server.  The communication between CRAs and the TRA uses IPv6, while
   the communication between TRA and server uses IPv4.  A TRA listens on
   IPv6 UDP port 67 for DHCP packets messages with bootp op field = 1, as well
   as IPv4 UDP port 68 for DHCP packets messages with bootp op field = 2.

   When relaying a DHCP message from CRA to server, TRA MUST add an
   option 82 with a 6ADDR CRA6ADDR suboption.  This suboption contains the
   IPv6 source address of the message (the CRA's IPv6 address) which is
   retained when the message is received in IPv6.  The TRA MUST also
   store the IPv4 address of itself in the giaddr field of the DHCP
   message.  The TRA MAY include a Link Selection Suboption [RFC3527] to
   indicate to the DHCP server which link to use when choosing an IP

   When a TRA receives receiving a DHCP message from the DHCP server, if the
   packet option 82
   in the message contains no 6ADDR CRA6ADDR suboption, the TRA discards MUST discard
   the packet. message.  Otherwise, it processes it as required by [RFC3046],
   and forwards it to the IPv6 address recorded in the 6ADDR suboption. CRA6ADDR
   suboption, with source port 67 and destination port number 68.  TRA
   SHOULD drop DHCPv4-over-IPv6 traffic that is not originated from
   configured server address.

9.  Security Consideration

   This specification raises no particular security issues mechanism may rise a new form of DHCP protocol attack.  A
   malicious attacker in IPv6 can interference with the DHCPv4 process
   by inject fake DHCPv4-in-IPv6 messages which will be handled by TSV
   or TRA.  However, the damage is the same with the known DHCPv4 attack
   happened in IPv4.  The only difference is the attacker and the victim
   could locate in different address families.

   Another impact is DHCP filtering.  There are firewalls today capable
   of filtering DHCP traffic (DHCPv4 over IPv4 and DHCPv6 over IPv6
   packages).  The DHCP messages with the new, DHCPv4-in-IPv6 style may
   bypass these firewalls.  Nevertheless it is not difficult for them to
   make some slight modification and adapt to the new DHCPv4
   protocol model. message

10.  IANA consideration

   IANA is requested to assign one new suboption code from the registry
   of DHCP Agent Sub-Option Codes maintained in  This
   suboption code will be assigned to the Client Relay Agent IPv6
   Address Sub-option.

11.  References

11.1.  Normative References

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

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

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

   [RFC3527]                          Kinnear, K., Stapp, M., Johnson,
                                      R., and J. Kumarasamy, "Link
                                      Selection sub-option for the Relay
                                      Agent Information Option for
                                      DHCPv4", RFC 3527, April 2003.

   [RFC4925]                          Li, X., Dawkins, S., Ward, D., and
                                      A. Durand, "Softwire Problem
                                      Statement", RFC 4925, July 2007.

11.2.  Informative References

   [I-D.ietf-softwire-public-4over6]  Cui, Y., Wu, J., Wu, P., Metz, C.,
                                      Vautrin, O., and Y. Lee, "Public
                                      IPv4 over Access IPv6 Network", dr
                                      (work in progress),
                                      September 2011.

Authors' Addresses

   Yong Cui
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6260-3059

   Peng Wu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5822

   Jianping Wu
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5983

   Ted Lemon
   Nominum, Inc.
   2000 Seaport Blvd
   Redwood City  94063

   Phone: +1-650-381-6000