draft-ietf-dnsext-dhcid-rr-12.txt

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DNSEXT                                                          M. Stapp
Internet-Draft                                       Cisco Systems, Inc.
Expires: September 1, 2006                                      T. Lemon
                                                           Nominum, Inc.
                                                           A. Gustafsson
                                          Araneus Information Systems Oy
                                                       February 28, 2006


           A DNS RR for Encoding DHCP Information (DHCID RR)
                  <draft-ietf-dnsext-dhcid-rr-12.txt>

Status of this Memo

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   This Internet-Draft will expire on September 1, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   It is possible for DHCP clients to attempt to update the same DNS
   FQDN or attempt 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, "Resolution of DNS Name



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   Conflicts" [1] 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 RR type for this purpose
   for use by DHCP clients and servers, the "DHCID" RR.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  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 . . . . . . . . . .  5
       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  . . . . . . . . . . . . . . . . . . . . . .  6
       3.6.3.  Example 3  . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Use of the DHCID RR  . . . . . . . . . . . . . . . . . . . . .  7
   5.  Updater Behavior . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12


















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1.  Terminology

   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 [2].


2.  Introduction

   A set of procedures to allow DHCP [6] [10] clients and servers to
   automatically update the DNS (RFC 1034 [3], RFC 1035 [4]) is proposed
   in "Resolution of DNS Name Conflicts" [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, "Resolution of DNS Name
   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
   client as it is associated with various domain names.


3.  The DHCID RR

   The DHCID RR is defined with mnemonic DHCID and type code [TBD].  The
   DHCID RR is only defined in the IN class.  DHCID RRs cause no
   additional section processing.  The DHCID RR is not a singleton type.

3.1.  DHCID RDATA format

   The RDATA section of a DHCID RR in transmission contains RDLENGTH
   octets of binary data.  The format of this data and its
   interpretation by DHCP servers and clients are described below.

   DNS software should consider the RDATA section to be opaque.  DHCP
   clients or servers use the DHCID RR to associate a DHCP client's



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   identity with a DNS name, so that multiple DHCP clients and servers
   may deterministically perform dynamic DNS updates to the same zone.
   From the updater's perspective, the DHCID resource record RDATA
   consists of a 2-octet identifier type, in network byte order,
   followed by a 1-octet digest type, followed by one or more octets
   representing the actual identifier:

           < 2 octets >    Identifier type code
           < 1 octet >     Digest type code
           < n octets >    Digest (length depends on digest type)

3.2.  DHCID Presentation Format

   In DNS master files, the RDATA is represented as a single block in
   base 64 encoding identical to that used for representing binary data
   in RFC 3548 [7].  The data may be divided up into any number of white
   space separated substrings, down to single base 64 digits, which are
   concatenated to form the complete RDATA.  These substrings can span
   lines using the standard parentheses.

3.3.  The DHCID RR Identifier Type Codes

   The DHCID RR Identifier Type Code specifies what data from the DHCP
   client's request was used as input into the hash function.  The
   identifier type codes are defined in a registry maintained by IANA,
   as specified in Section 7.  The initial list of assigned values for
   the identifier type code is:

   0x0000 = htype, chaddr from a DHCPv4 client's DHCPREQUEST [6].
   0x0001 = The data octets (i.e., the Type and Client-Identifier
      fields) from a DHCPv4 client's Client Identifier option [9].
   0x0002 = The client's DUID (i.e., the data octets of a DHCPv6
      client's Client Identifier option [10] or the DUID field from a
      DHCPv4 client's Client Identifier option [12]).

   0x0003 - 0xfffe = Available to be assigned by IANA.

   0xffff = RESERVED

3.4.  The DHCID RR Digest Type Code

   The DHCID RR Digest Type Code is an identifier for the digest
   algorithm used.  The digest is calculated over an identifier and the
   canonical FQDN as described in the next section.

   The digest type codes are defined in a registry maintained by IANA,
   as specified in Section 7.  The initial list of assigned values for
   the digest type codes is: value 0 is reserved and value 1 is SHA-256.



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   Reserving other types requires IETF standards action.  Defining new
   values will also require IETF standards action to document how DNS
   updaters are to deal with multiple digest types.

3.5.  Computation of the RDATA

   The DHCID RDATA is formed by concatenating the 2-octet identifier
   type code with variable-length data.

   The RDATA for all type codes other than 0xffff, which is reserved for
   future expansion, is formed by concatenating the 2-octet identifier
   type code, the 1-octet digest type code, and the digest value (32
   octets for SHA-256).

       < identifier-type > < digest-type > < digest >

   The input to the digest hash function is defined to be:

       digest = SHA-256(< identifier > < FQDN >)

   The FQDN is represented in the buffer in unambiguous canonical form
   as described in RFC 4034 [8], section 6.1.  The identifier type code
   and the identifier are related as specified in Section 3.3: the
   identifier type code describes the source of the identifier.

   A DHCPv4 updater uses the 0x0002 type code if a Client Identifier
   option is present in the DHCPv4 messages and it is encoded as
   specified in [12].  Otherwise, the updater uses 0x0001 if a Client
   Identifier option is present and 0x0000 if not.

   A DHCPv6 updater always uses the 0x0002 type code.

3.5.1.  Using the Client's DUID

   When the updater is using the Client's DUID (either from a DHCPv6
   Client Identifier option or from a portion of the DHCPv4 Client
   Identifier option encoded as specified in [12]), the first two octets
   of the DHCID RR MUST be 0x0002, in network byte order.  The third
   octet is the digest type code (1 for SHA-256).  The rest of the DHCID
   RR MUST contain the results of computing the SHA-256 hash across the
   octets of the DUID followed by the FQDN.

3.5.2.  Using the Client Identifier Option

   When the updater is using the DHCPv4 Client Identifier option sent by
   the client in its DHCPREQUEST message, the first two octets of the
   DHCID RR MUST be 0x0001, in network byte order.  The third octet is
   the digest type code (1 for SHA-256).  The rest of the DHCID RR MUST



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   contain the results of computing the SHA-256 hash across the data
   octets (i.e., the Type and Client-Identifier fields) of the option,
   followed by the FQDN.

3.5.3.  Using the Client's htype and chaddr

   When the updater is using the client's link-layer address as the
   identifier, the first two octets of the DHCID RDATA MUST be zero.
   The third octet is the digest type code (1 for SHA-256).  To generate
   the rest of the resource record, the updater computes a one-way hash
   using the SHA-256 algorithm across a buffer containing the client's
   network hardware type, link-layer address, and the FQDN data.
   Specifically, the first octet of the buffer contains the network
   hardware type as it appeared in the DHCP 'htype' field of the
   client's DHCPREQUEST message.  All of the significant octets of the
   'chaddr' field in the client's DHCPREQUEST message follow, in the
   same order in which the octets appear in the DHCPREQUEST message.
   The number of significant octets in the 'chaddr' field is specified
   in the 'hlen' field of the DHCPREQUEST message.  The FQDN data, as
   specified above, follows.

3.6.  Examples

3.6.1.  Example 1

   A DHCP server allocating the IPv4 address 10.0.0.1 to a client with
   Ethernet MAC address 01:02:03:04:05:06 using domain name
   "client.example.com" uses the client's link-layer address to identify
   the client.  The DHCID RDATA is composed by setting the two type
   octets to zero, the 1-octet digest type to 1 for SHA-256, and
   performing an SHA-256 hash computation across a buffer containing the
   Ethernet MAC type octet, 0x01, the six octets of MAC address, and the
   domain name (represented as specified in Section 3.5).

     client.example.com.   A       10.0.0.1
     client.example.com.   DHCID   ( AAABxLmlskllE0MVjd57zHcWmEH3pCQ6V
                                     ytcKD//7es/deY= )

   If the DHCID RR type is not supported, the RDATA would be encoded
   [13] as:

     \# 35 ( 000001c4b9a5b249651343158dde7bcc77169841f7a4243a572b5c283
             fffedeb3f75e6 )

3.6.2.  Example 2

   A DHCP server allocates the IPv4 address 10.0.12.99 to a client which
   included the DHCP client-identifier option data 01:07:08:09:0a:0b:0c



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