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Network Working Group                                            B. Volz
Internet-Draft                                                  Ericsson
Expires: October 24, 2002                                       J. Bound
                                             Compaq Computer Corporation
                                                                R. Droms
                                                           Cisco Systems
                                                                T. Lemon
                                                           Nominum, Inc.
                                                          April 25, 2002


                         DSTM Options for DHCP
                 draft-ietf-dhc-dhcpv6-opt-dstm-01.txt

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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   This Internet-Draft will expire on October 24, 2002.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   The DSTM Global IPv4 Address option and the DSTM Tunnel Endpoint
   Option provide DSTM (Dual Stack Transition Mechanism) configuration
   information to DHCPv6 hosts.






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1. Introduction

   This document describes two options for DHCPv6 [2] that provide
   information for hosts using the "Dual Stack Transition Mechanism"
   (DSTM) [3].

2. Requirements

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in RFC2119 [1].

3. Terminology

   This document uses terminology specific to IPv6 and DHCPv6 as defined
   in section "Terminology" of the DHCPv6 specification.

4. Identity Association for DSTM Global IPv4 Addresses

   The Identity Association for DSTM Global IPv4 Addresses (IA_DSTM)
   option is used to carry an IA, the parameters associated with the IA
   and the addresses associated with the IA.  All of the addresses in
   this option are used by the client as DSTM Global IPv4 Addresses [3].

   The format of the IA_DSTM option is:

         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_IA_DSTM        |          option-len           |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        IAID (4 octets)                        |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                              T1                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                              T2                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        .                           IA-options                          .
        .                                                               .
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code: OPTION_IA_DSTM (TBD)

   option-len:  12 + length of IA-options field

   IAID:        The unique identifier for this IA; the IAID must be
      unique among the identifiers for all of this client's IAs



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   T1:          The time at which the client contacts the server from
      which the addresses in the IA were obtained to extend the
      lifetimes of the addresses assigned to the IA; T1 is a time
      duration relative to the current time expressed in units of
      seconds

   T2:          The time at which the client contacts any available
      server to extend the lifetimes of the addresses assigned to the
      IA; T2 is a time duration relative to the current time expressed
      in units of seconds

   IA-options:  Options associated with this IA.

   The IA-options field encapsulates those options that are specific to
   this IA.  For example, all of the Address Options carrying the
   addresses associated with this IA are in the IA-options field.

   An IA_DSTM option may only appear in the options area of a DHCP
   message.  A DHCP message may contain multiple IA_DSTM options.

   The status of any operations involving this IA is indicated in a
   Status Code option in the IA-options field.

   Note that an IA has no explicit "lifetime" or "lease length" of its
   own.  When the lifetimes of all of the addresses in an IA have
   expired, the IA can be considered as having expired.  T1 and T2 are
   included to give servers explicit control over when a client
   recontacts the server about a specific IA.

   In a message sent by a client to a server, values in the T1 and T2
   fields indicate the client's preference for those parameters.  The
   client may send 0 if it has no preference for T1 and T2.  In a
   message sent by a server to a client, the client MUST use the values
   in the T1 and T2 fields for the T1 and T2 parameters.  The values in
   the T1 and T2 fields are the number of seconds until T1 and T2.

   The server selects the T1 and T2 times to allow the client to extend
   the lifetimes of any addresses in the IA before the lifetimes expire,
   even if the server is unavailable for some short period of time.
   Recommended values for T1 and T2 are .5 and .8 times the shortest
   preferred lifetime of the addresses in the IA, respectively.  If the
   server does not intend for a client to extend the lifetimes of the
   addresses in an IA, the server sets T1 and T2 to 0.

   T1 is the time at which the client begins the lifetime extension
   process by sending a Renew message to the server that originally
   assigned the addresses to the IA.  T2 is the time at which the client
   starts sending a Rebind message to any server.



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   T1 and T2 are specified as unsigned integers that specify the time in
   seconds relative to the time at which the messages containing the
   option is received.

   A DSTM Tunnel End Point option (Section 5) MAY be encapsulated in an
   IA_DSTM option to specify one or more tunnel endpoints.

5. DSTM Tunnel Endpoint Option

   The DSTM Tunnel Endpoint option carries an IP address that is to be
   used as a tunnel endpoint (TEP) to encapsulate IP datagrams within
   IP.

   The format of the DSTM Tunnel Endpoint option is:

          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_DSTM_TEP        |         option-length         |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         .                                                               .
         .                              tep                              .
         .                          (16 octets)                          .
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:   OPTION_DSTM_TEP (TBD)

   option-length: 16

   tep:           Tunnel endpoint

   A DSTM Tunnel EndPoint Option MUST NOT be used except when
   encapsulated in an IA_DSTM option.

6. Appearance of these options

   The IA_DSTM option may appear in the same messages as the IA option
   and the IA_TA option [2].

   A server may send a Reconfigure with an IA_DSTM option number in the
   Option Request option (see sections 19 and 22.7 of the DHCP
   specification [2]) to request that the client send a IA_DSTM option,
   with an IAID, in the Renew message the client subsequently sends to
   the server.

   The DSTM Tunnel Endpoint option MUST only appear as an encapsulated
   option in an IA_DSTM option.




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7. Security Considerations

   The DSTM Global IPv4 Address option may be used by an intruder DHCP
   server to assign an invalid IPv4-mapped address to a DHCPv6 client in
   a denial of service attack.  The DSTM Tunnel Endpoint option may be
   used by an intruder DHCP server to configure a DHCPv6 client with an
   endpoint that would cause the client to route packets thorugh an
   intruder system.

   To avoid these security hazards, a DHCPv6 client MUST use
   authenticated DHCPv6 to confirm that it is exchanging the DSTM
   options with an authorized DHCPv6 server.

8. IANA Considerations

   IANA is requested to assign an option code to this option from the
   option-code space defined in section "DHCPv6 Options" of the DHCPv6
   specification [2].

References

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

   [2]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", draft-ietf-dhc-dhcpv6 (work in progress), April 2002.

   [3]  Bound, J., "Dual Stack Transition Mechanism (DSTM)", draft-ietf-
        ngtrans-dstm (work in progress), November 2001.

   [4]  Hinden, R. and S. Deering, "IP Version 6 Addressing
        Architecture", RFC 2373, July 1998.


Authors' Addresses

   Bernie Volz
   Ericsson
   959 Concord Street
   Framingham, MA  01701
   USA

   Phone: +1 508 875 3162
   EMail: bernie.volz@ericsson.com






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   Jim Bound
   Compaq Computer Corporation
   ZK3-3/W20
   110 Spit Brook Road
   Nashua, NH  03062-2698
   USA

   Phone: +1 603 884 0062
   EMail: Jim.Bound@compaq.com


   Ralph Droms
   Cisco Systems
   250 Apollo Drive
   Chelmsford, MA  01824
   USA

   Phone: +1 978 497 4733
   EMail: rdroms@cisco.com


   Ted Lemon
   Nominum, Inc.
   950 Charter Street
   Redwood City, CA  94043
   USA

   EMail: mellon@nominum.com























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Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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