A DNS Resource Record (RR) for Encoding Dynamic Host Configuration Protocol (DHCP) Information (DHCID RR)
RFC 4701

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Network Working Group                                           M. Stapp
Request for Comments: 4701                           Cisco Systems, Inc.
Category: Standards Track                                       T. Lemon
                                                           Nominum, Inc.
                                                           A. Gustafsson
                                          Araneus Information Systems Oy
                                                            October 2006

                A DNS Resource Record (RR) for Encoding
   Dynamic Host Configuration Protocol (DHCP) Information (DHCID RR)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   It is possible for Dynamic Host Configuration Protocol (DHCP) clients
   to attempt to update the same DNS Fully Qualified Domain Name (FQDN)
   or to update a DNS FQDN that has been added to the DNS for another
   purpose as they obtain DHCP leases.  Whether the DHCP server or the
   clients themselves perform the DNS updates, conflicts can arise.  To
   resolve such conflicts, RFC 4703 proposes storing client identifiers
   in the DNS to unambiguously associate domain names with the DHCP
   clients to which they refer.  This memo defines a distinct Resource
   Record (RR) type for this purpose for use by DHCP clients and
   servers:  the "DHCID" RR.

Stapp, et al.               Standards Track                     [Page 1]
RFC 4701                      The DHCID RR                  October 2006

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. The DHCID RR ....................................................3
      3.1. DHCID RDATA Format .........................................3
      3.2. DHCID Presentation Format ..................................4
      3.3. The DHCID RR Identifier Type Codes .........................4
      3.4. The DHCID RR Digest Type Code ..............................4
      3.5. Computation of the RDATA ...................................5
           3.5.1. Using the Client's DUID .............................5
           3.5.2. Using the Client Identifier Option ..................6
           3.5.3. Using the Client's htype and chaddr .................6
      3.6. Examples ...................................................6
           3.6.1. Example 1 ...........................................6
           3.6.2. Example 2 ...........................................7
           3.6.3. Example 3 ...........................................7
   4. Use of the DHCID RR .............................................8
   5. Updater Behavior ................................................8
   6. Security Considerations .........................................8
   7. IANA Considerations .............................................9
   8. Acknowledgements ................................................9
   9. References ......................................................9
      9.1. Normative References .......................................9
      9.2. Informative References ....................................10

Stapp, et al.               Standards Track                     [Page 2]
RFC 4701                      The DHCID RR                  October 2006

1.  Introduction

   A set of procedures to allow DHCP [7] [11] clients and servers to
   automatically update the DNS ([3], [4]) is proposed in [1].

   Conflicts can arise if multiple DHCP clients wish to use the same DNS
   name or a DHCP client attempts to use a name added for another
   purpose.  To resolve such conflicts, [1] proposes storing client
   identifiers in the DNS to unambiguously associate domain names with
   the DHCP clients using them.  In the interest of clarity, it is
   preferable for this DHCP information to use a distinct RR type.  This
   memo defines a distinct RR for this purpose for use by DHCP clients
   or servers: the "DHCID" RR.

   In order to obscure potentially sensitive client identifying
   information, the data stored is the result of a one-way SHA-256 hash
   computation.  The hash includes information from the DHCP client's
   message as well as the domain name itself, so that the data stored in
   the DHCID RR will be dependent on both the client identification used
   in the DHCP protocol interaction and the domain name.  This means
   that the DHCID RDATA will vary if a single client is associated over
   time with more than one name.  This makes it difficult to 'track' a