DNSEXT Working Group M. Stapp
Internet-Draft Cisco Systems, Inc.
Expires: August 31, 2001 T. Lemon
A. Gustafsson
Nominum, Inc.
March 2, 2001
A DNS RR for Encoding DHCP Information
<draft-ietf-dnsext-dhcid-rr-02.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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 31, 2001.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
A situation can arise where multiple DHCP clients request the same
DNS name from their (possibly distinct) DHCP servers. To resolve
such conflicts, 'Resolution of DNS Name Conflicts'[6] proposes
storing client identifiers in the DNS to unambiguously associate
domain names with the DHCP clients "owning" them. This memo defines
a distinct RR type for use by DHCP servers, the "DHCID" RR.
Stapp, et. al. Expires August 31, 2001 [Page 1]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The DHCID RR . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. DHCID RDATA format . . . . . . . . . . . . . . . . . . . . . . 3
4.1 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Appendix A: Base 64 Encoding . . . . . . . . . . . . . . . . . 5
References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8
Stapp, et. al. Expires August 31, 2001 [Page 2]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
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[1].
2. Introduction
A set of procedures to allow DHCP[2] clients and servers to
automatically update the DNS (RFC1034[4], RFC1035[5]) is proposed in
"Resolution of DNS Name Conflicts"[6].
A situation can arise where multiple DHCP clients wish to use the
same DNS name. To resolve such conflicts, Resolution of DNS Name
Conflicts[6] proposes storing client identifiers in the DNS to
unambiguously associate domain names with the DHCP clients using
them. In the interest of clarity, it would be preferable for this
DHCP information to use a distinct RR type.
This memo defines a distinct RR type for this purpose for use by
DHCP clients or servers, the "DHCID" RR.
3. The DHCID RR
The DHCID RR is defined with mnemonic DHCID and type code [TBD].
4. DHCID RDATA format
The RDATA section of a DHCID RR in transmission contains RDLENGTH
bytes 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. In DNS
master files, the RDATA is represented in base 64 encoding (see
Appendix A (Section 7)) and may be divided up into any number of
white space separated substrings, down to single base 64 digits,
which are concatenated to obtain the full signature. These
substrings can span lines using the standard parenthesis. This
format is identical to that used for representing binary data in
DNSSEC (RFC2535[7]).
DHCP clients or servers use the DHCID RR to associate a DHCP
client's identity with a DNS name, so that multiple DHCP clients and
servers may safely perform dynamic DNS updates to the same zone.
From the updater's perspective, the DHCID resource record consists
of a 16-bit identifier type, followed by one or more bytes
representing the actual identifier.
The type code can have one of three classes of values. The first
Stapp, et. al. Expires August 31, 2001 [Page 3]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
class contains just the value zero. This type indicates that the
remaining contents of the DHCID record encode an identifier that is
based on the client's link-layer network address.
The second class of types contains just the value 0xFFFF. This type
code is reserved for future extensibility.
The third class of types contains all the values not included in the
first two - that is, every value other than zero or 0xFFFF. Types in
this class indicate that the remaining contents of the DHCID record
encode an identifier that is based on the DHCP option whose code is
the same as the specified type. The most common value in this class
at the time of the writing of this draft is 61, which is the DHCP
option code[3] for the Client Identifier option.
The data following the type code (for type codes other than 0xFFFF)
is derived by running a one-way hash across the identifying
information. The details of this are specified in "Resolution of
DNS Name Conflicts"[6].
This RR MUST NOT be used for any purpose other than that detailed in
"Resolution of DNS Name Conflicts"[6]. Althought this RR contains
data that is opaque to DNS servers, the data must be consistent
across all entities that update and interpret this record.
Therefore, new data formats may only be defined through actions of
the DHC Working Group, as a result of revising [6].
4.1 Example
A DHCP server allocating the IPv4 address 10.0.0.1 to a client
"client.org.nil" might use the client's link-layer address to
identify the client:
client.org.nil. A 10.0.0.1
client.org.nil. DHCID AAAYKREXIgqtwYgQo93/yNlJ
A DHCP server allocating the IPv4 address 10.0.12.99 to a client
"chi.org.nil" might use the DHCP client identifier option to
identify the client:
chi.org.nil. A 10.0.12.99
chi.org.nil. DHCID AGGScSLaAYjdOhGMHKD/lJ2B
5. Security Considerations
The DHCID record as such does not introduce any new security
problems into the DNS. In order to avoid exposing private
information about DHCP clients to public scrutiny, a one-way-hash is
used to obscure all client information.
Stapp, et. al. Expires August 31, 2001 [Page 4]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
6. IANA Considerations
IANA is requested to allocate an RR type number for the DHCID record
type.
7. Appendix A: Base 64 Encoding
The following encoding technique is taken from RFC 2045[8] by N.
Borenstein and N. Freed. It is reproduced here in an edited form
for convenience.
A 65-character subset of US-ASCII is used, enabling 6 bits to be
represented per printable character. (The extra 65th character, "=",
is used to signify a special processing function.)
The encoding process represents 24-bit groups of input bits as
output strings of 4 encoded characters. Proceeding from left to
right, a 24-bit input group is formed by concatenating 3 8-bit input
groups. These 24 bits are then treated as 4 concatenated 6-bit
groups, each of which is translated into a single digit in the base
64 alphabet.
Each 6-bit group is used as an index into an array of 64 printable
characters. The character referenced by the index is placed in the
output string.
The Base 64 Alphabet
Value Encoding Value Encoding Value Encoding Value Encoding
0 A 17 R 34 i 51 z
1 B 18 S 35 j 52 0
2 C 19 T 36 k 53 1
3 D 20 U 37 l 54 2
4 E 21 V 38 m 55 3
5 F 22 W 39 n 56 4
6 G 23 X 40 o 57 5
7 H 24 Y 41 p 58 6
8 I 25 Z 42 q 59 7
9 J 26 a 43 r 60 8
10 K 27 b 44 s 61 9
11 L 28 c 45 t 62 +
12 M 29 d 46 u 63 /
13 N 30 e 47 v
14 O 31 f 48 w (pad) =
15 P 32 g 49 x
16 Q 33 h 50 y
Special processing is performed if fewer than 24 bits are available
Stapp, et. al. Expires August 31, 2001 [Page 5]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
at the end of the data being encoded. A full encoding quantum is
always completed at the end of a quantity. When fewer than 24 input
bits are available in an input group, zero bits are added (on the
right) to form an integral number of 6-bit groups. Padding at the
end of the data is performed using the '=' character. Since all
base 64 input is an integral number of octets, only the following
cases can arise: (1) the final quantum of encoding input is an
integral multiple of 24 bits; here, the final unit of encoded output
will be an integral multiple of 4 characters with no "=" padding,
(2) the final quantum of encoding input is exactly 8 bits; here, the
final unit of encoded output will be two characters followed by two
"=" padding characters, or (3) the final quantum of encoding input
is exactly 16 bits; here, the final unit of encoded output will be
three characters followed by one "=" padding character.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, Mar
1997.
[3] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, Mar 1997.
[4] Mockapetris, P., "Domain names - Concepts and Facilities", RFC
1034, Nov 1987.
[5] Mockapetris, P., "Domain names - Implementation and
Specification", RFC 1035, Nov 1987.
[6] Stapp, M., "Resolution of DNS Name Conflicts Among DHCP Clients
(draft-ietf-dhc-dns-resolution-*)", July 2000.
[7] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[8] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
Stapp, et. al. Expires August 31, 2001 [Page 6]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
Authors' Addresses
Mark Stapp
Cisco Systems, Inc.
250 Apollo Dr.
Chelmsford, MA 01824
USA
Phone: 978.244.8498
EMail: mjs@cisco.com
Ted Lemon
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
USA
EMail: mellon@nominum.com
Andreas Gustafsson
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
USA
EMail: gson@nominum.com
Stapp, et. al. Expires August 31, 2001 [Page 7]
Internet-Draft A DNS RR for Encoding DHCP Information March 2001
Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
Stapp, et. al. Expires August 31, 2001 [Page 8]
