Network Working Group C. Smith
Internet Draft Sun Microsystems, Inc.
October 1999
Expires April 2000
The Name Service Search Option for DHCP
<draft-ietf-dhc-nsso-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 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.
To view the entire list of current Internet-Drafts, please check the
1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern
Europe), ftp.nic.it (Southern Europe), munnari.oz.au (Pacific Rim),
ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
Abstract
This document defines a new DHCP option which is passed from the DHCP
Server to the DHCP Client to specify the order in which name services
should be consulted when resolving hostnames and other information.
Introduction
The Dynamic Host Configuration Protocol (DHCP)[1] provides a
framework for passing configuration information to hosts on a TCP/IP
network. RFC 2132 [2] allows DHCP servers to specify configuration
information for various kinds of name servers to be passed to DHCP
clients. Many clients use multiple name services and have crafted
their own conventions that allow an individual host to express the
order among the various name services with which lookups are done.
However, no search order can be specified via DHCP. The purpose of
this document is to allow DHCP servers to specify the search order to
be used by DHCP clients.
Smith [Page 1]
RFC DRAFT October 1999
Definitions
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 [3]. This
document also uses the following terms:
"DHCP client"
DHCP client or "client" is an Internet host using DHCP to
obtain configuration parameters such as a network address.
"DHCP server"
A DHCP server or "server" is an Internet host that returns
configuration parameters to DHCP clients.
Name Service Search Option Format
The code for this option is TBD, and its minimum length is 1 byte. A
DHCP server SHOULD return, in its preferred order, the integer option
code for the name services (the earlier in the list, the more
preferred the name service).
Code Len Name Service Search Order in Sequence
+-------+-------+-------+--------+-
| TBD | n | ns1 | ns2 | ...
+-------+-------+-------+--------+-
In the above example, ns1 & ns2 are integers corresponding to the name
service servers option (this allows for evolution without the need for a
separate table translating between these integers and the name services
they represent). For example, the current list, taken from RFC 2132,
includes
Name Service Value
Domain Name Server Option 6
Network Information Servers Option 41
NetBIOS over TCP/IP Name Server Option 44
Network Information Service+ Servers Option 65
Smith [Page 2]
RFC DRAFT October 1999
A DHCP server wishing to express that a client should first search DNS,
then NIS+, would send
+-------+-------+-------+--------+-
| TBD | 2 | 6 | 65 |
+-------+-------+-------+--------+-
DHCP Client Behavior
The DHCP client will use this option to create a search list for name
resolution. The client SHOULD ignore any name services appearing in
this option that it does not support or has not been configured to
access. Clients will interpret this option in a system-specific
manner whose specification is outside the scope of this document.
Security Considerations
DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification [1].
References
[1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
1997.
[2] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[3] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
Author Information
Carl Smith
Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA 94043
email: cs@Eng.Sun.COM
Expiration
This document will expire on December 31, 1999.
Full Copyright Statement
Copyright (C) The Internet Society (1999). 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
Smith [Page 3]
RFC DRAFT October 1999
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.
Smith [Page 4]