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  Network Working Group                                  S. Daniel Park
  Internet Draft                                                 P. Kim
  Expires : September 2004                          Samsung Electronics
                                                             March 2004
              DHCP Option for Configuring IPv6-over-IPv4 Tunnels
  Status of this Memo
     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026.
     Internet-Drafts are working documents of the Internet Engineering
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  Copyright Notice
     Copyright (C) The Internet Society (2004).  All Rights Reserved.
     This document provides a mechanism by which the DHCPv4 servers can
     provide information about the configured IPv6-over-IPv4 tunnel
     end-point.  The IPv4/IPv6 dual-stack nodes can use this
     information to set up a configured tunnel to the tunnel end-point
     to obtain IPv6 connectivity.
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  Internet Draft       CTEP Option for IP6over4 Tunnel         March 2004
  Table of Contents
     1.  Introduction.................................................2
     2.  Requirements.................................................2
     3.  Configured Tunnel End Point Option...........................2
     4.  Multiple Tunnel End Point Considerations.....................3
     5.  Security Considerations......................................4
     6.  IANA Considerations..........................................4
     7.  References...................................................4
         7.1  Normative References....................................4
         7.2  Informative Reference...................................4
     8.  Authors' Addresses...........................................5
     9.  Acknowledgements.............................................5
  1. Introduction
     In the initial deployment of IPv6, the IPv6 nodes may need to
     communicate with the other IPv6 nodes via IPv4 tunnel service. The
     connectivity can be obtained by setting up an IPv6-over-IPv4
     configured tunnel between a client and a tunnel router.
     This document defines a new option by which the DHCPv4 [1] server
     can notify the client with the list of end-points of the possible
     configured tunnels.
     Particularly, this mechanism is useful where the ISP is providing
     the IPv6 services but is doing it using tunneling over IPv4 to avoid
     upgrading all their infrastructure to support IPv6 on day one.
  2. Requirements
     SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
     document, are to be interpreted as described in RFC 2119 [2].
  3. Configured Tunnel End Point Option
     This option specifies the configured tunnel end-point that client
     should use when discovering the IPv4 address of the ISP's tunnel
     router somehow via the Dynamic Host Configuration Protocol.
     Once the IPv4 address has been learned, it is configured as the
     tunnel end-point for the configured IPv6-over-IPv4 tunnel.
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     The format of the Configured Tunnel End Point Option is shown as
     The code for this option is TBD.  The length of this option is 4.
          Code            Length             CTEP Order in Sequence
      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_CTEP  |     Len       |           CTEP Addr1          |
     |        CTEP Addr 1            |
     In the above diagram, CTEP Addr is 32-bit integers corresponding to
     DHCP options which specify the IP address of different configured
     tunnel end-point.
     As described in [4], the dual node received CTEP option MUST store
     the tunnel end-point address and this address is used as destination
     address for the encapsulating IPv4 header.
     The determination of which packets to tunnel is usually made by
     routing information on the encapsulator.  This is usually done via a
     routing table, which directs packets based on their destination
     address using the prefix mask and match technique.  For more
     information, refer to section 4. Configured Tunneling in [4].
  4. Multiple Tunnel End Point Considerations
     For the simple configured tunnel, one tunnel end-point is generally
     used and it assumes that all the networks will be reached through
     the same end-point.  In this case, one CTEP Addr field in the CTEP
     option is used for configured tunnel service.
     The list of end-points can be installed as the default routes and
     the routes will be tried in a round robin fashion if the IPv6 host
     load-sharing is honored [5].  Instead there can be specific default
     routes for the different destination.
     Generally, there may not be a need for installing multiple
     configured tunnel end-points unless administrator wants two for
     redundancy purposes.  It is out of scope of this draft.
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  5. Security Considerations
     A rouge DHCP server can issue invalid or incorrect configured tunnel
     end-point.  This may cause denial of service due to unreachability
     or makes the client to reach incorrect destination.
     The latter has very severe security issues as the tunnel end-point
     is on-the-path towards all the IPv6 destinations, and can trivially
     act as a man-in-the-middle attacker.
  6. IANA Considerations
     IANA is requested to an assign value for the Configured Tunnel End
     Point option code in accordance with RFC 2939 [3].
     Option Nam         Value     Described in
     OPTION_CTE          TBD        Section 3.
  7. References
  7.1 Normative References
     [1]   Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
           Bucknell University, March 1997.
     [2]   Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.
     [3]   Droms, R.,"Procedures and IANA Guidelines for Definition of
           New DHCP Options and Message Types", RFC 2939, September 2000.
  7.2 Informative Reference
     [4]   Nordmark, E. and Gilligan, R.E., "Basic Transition Mechanisms
           for IPv6 Hosts and Routers", RFC 2893, August 2000.
     [5]   Hinden B. and Thaler D., "IPv6 Host to Router Load Sharing",
           Internet-Draft (work in progress), January 2004.
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  8. Authors' Addresses
     Soohong Daniel Park
     Mobile Platform Laboratory
     Samsung Electronics.
     Phone: +81 31 200 4508
     Email: soohong.park@samsung.com
     Pyungsoo Kim
     Mobile Platform Laboratory
     Samsung Electronics.
     Phone: +81 31 200 4635
     Email: kimps@samsung.com
  9. Acknowledgements
     Special thanks to Pekka Savola, Vijayabhaskar A K, Eric Nordmark and
     Alain Durand for their many valuable revisions and comments.  In
     particular, Pekka Savola kindly clarified the multiple tunnel end
     point considerations with his good experience as well.
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