Network Working Group A. Gustafsson
Internet-Draft T. Lemon
Expires: January 12, 2001 Nominum, Inc.
M. Stapp
Cisco Systems, Inc.
July 14, 2000
A DNS RR for encoding DHCP information
<draft-ietf-dnsext-dhcid-rr-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on January 12, 2001.
Copyright Notice
Copyright (C) The Internet Society (2000). 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'[7] 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.
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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 . . . . . . . . . . . . . . . . . . . . . 4
References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 5
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 6
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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[1].
2. Introduction
A set of procedures to allow DHCP [RFC2131] clients and servers to
automatically update the DNS (RFC1034[2], RFC1035[3]) is proposed in
Resolution of DNS Name Conflicts[7].
A situation can arise where multiple DHCP clients wish to use the
same DNS name. To resolve such conflicts, Resolution of DNS Name
Conflicts[7] 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 DHCP 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 as a hexadecimal string with
an optional "0x" or "0X" prefix. Periods (".") may be inserted
anywhere after the "0x" for readability. This format is identical
to that of the NSAP RR (RFC1706[4]). The number of hexadecimal
digits MUST be even.
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. There are two possible forms
for a DHCID RR - one that is used when the DHCP server is using the
client's link-layer address to identify it, and one that is used
when the DHCP server is using some DHCP option that the DHCP client
sent to identify it. When the link-layer address is used as the
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identifier, the first two bytes of the RRDATA are set to 0. When a
DHCP option is used as the identifier, the first two bytes of the
RRDATA contain the option number, in network byte order. The two
bytes 0xffff are reserved. In both cases, the remainder of the
RRDATA is the result of performing a one-way hash across the
identifier.
The details of the method used to generate the data in the RR and
the use to which a DHCP client or server may put this association
are beyond the scope of this draft, and are discussed in the draft
that specifies the DNS update behavior, 'Resolution of DNS Name
Conflicts'[7]. This RR MUST NOT be used for any purpose other than
that detailed in the DHC document. Althought this RR contains data
that is opaque to DNS servers, the data is meaningful to DHCP
updaters. Therefore, new data formats may only be defined through
actions of the DHC Working Group.
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
00.00.18.29.11.17.22.0a.ad.c1.88.10.a3.dd.ff.c8.d9.49
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 00.61.92.71.22.da.01.88.dd.3a.11.8c.1c.a0.ff.94.9d.81
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.
6. IANA Considerations
The IANA is requested to allocate an RR type number for the DHCP
record type.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
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[2] Mockapetris, P., "Domain names - Concepts and Facilities", RFC
1034, Nov 1987.
[3] Mockapetris, P., "Domain names - Implementation and
Specification", RFC 1035, Nov 1987.
[4] Manning, B. and R. Colella, "DNS NSAP Resource Records", RFC
1706, Oct 1994.
[5] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, Mar
1997.
[6] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, Mar 1997.
[7] Stapp, M., "Resolution of DNS Name Conflicts Among DHCP Clients
(draft-ietf-dhc-dns-resolution-*)", July 2000.
Authors' Addresses
Andreas Gustafsson
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
USA
EMail: gson@nominum.com
Ted Lemon
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
USA
EMail: mellon@nominum.com
Mark Stapp
Cisco Systems, Inc.
250 Apollo Dr.
Chelmsford, MA 01824
USA
Phone: 978.244.8498
EMail: mjs@cisco.com
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Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
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