Network Working Group P. Gupta
Internet Draft IBM Corporation
Obsoletes: draft-ietf-dhc-domsrch-01.txt November 1998
Expires May 1999
The Domain Search Option for DHCP
<draft-ietf-dhc-domsrch-02.txt>
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Abstract
This document defines a new DHCP option which is passed form the DHCP
Server to the DHCP Client to configure the domain search list which
is used by the clients to resolve hostnames in the Domain Name
System[3].
Introduction
The Dynamic Host Configuration Protocol (DHCP)[1] provides a
framework for passing configuration information to hosts on a TCP/IP
network. RFC 2132 allows the Domain Name (option 15) and the Domain
Name Server (option 6) to be passed to the DHCP client. This
information is used to resolve names in the Domain Name System. These
options are usually placed in the resolv.conf file on most operating
systems. The name resolution routines on the client are also capable
of using a domain search list that allows name resolution to be
attempted in a number of domains in sequence. The Domain Search
Option allows a list of domain names, in order of preference, to be
passed to the DHCP client such that the search directive can be
specified for name resolution.
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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 [4].
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.
Domain Search Option Format
The code for this option is TBD, and its minimum length is 2 bytes.
This option can contain multiple domain names separated by the ASCII
space character.
Code Len Domain Names in Sequence
+-------+-------+-------+--------+---------+-
| TBD | n | d1 | 0x20 | d2 |
+-------+-------+-------+--------+---------+-
In the above example, d1 & d2 are domain names specified as NVT ASCII
strings. An ASCII space character (0x20) is used as a separator
between the domain names.
DHCP Client Behavior
The DHCP client will use this option to create a domain search list
for name resolution. If a DHCP client is given both a Domain Name
Option and a Domain Search Option, the Domain Search Option will
take precedence.
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]. The Domain Search Option can be used to
misdirect domain name resolution on a client and thus misdirect
network traffic based on DNS names.
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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] Mockapetris, P. V., "Domain names - implementation and
specification", RFC 1035, November 1987.
[4] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
Author Information
Pratik Gupta
IBM Corporation
4205 S.Miami Blvd
Research Triangle Park, NC 27709
Phone: (919)254-5654
email: pratikg@us.ibm.com
Expiration
This document will expire on May 31, 1999.
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