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rfc:rfc2937

Network Working Group C. Smith Request for Comments: 2937 Sun Microsystems, Inc. Category: Standards Track September 2000

              The Name Service Search Option for DHCP

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This document defines a new Dynamic Host Configuration Protocol
 (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 services 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.  To avoid the need for inventing and
 maintaining a separate name space for this option, we rely on the
 existence of previously-defined DHCP options that specify the IP
 address(es) of servers which provide name services whose order we
 wish to express.

Smith Standards Track [Page 1] RFC 2937 The Name Service Search Option for DHCP September 2000

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 117, and its minimum length is 2 bytes.
   A DHCP server SHOULD return, in its preferred order, the 16-bit,
   network byte order (big-endian [4]) integer option code for the
   name services (the earlier in the list, the more preferred the name
   service).
     Code            Length      Name Service Search Order in Sequence
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     117       |     Len       |             ns1               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             ns2               |             ...               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   In the above diagram, ns1 and ns2 are 16-bit integers corresponding
   to two DHCP options which specify the IP addresses of two different
   types of name server.  The current list of name services and their
   DHCP option codes, 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 Standards Track [Page 2] RFC 2937 The Name Service Search Option for DHCP September 2000

     A name service option code of 0 is used to indicate that the
     client should refer to local naming information (e.g., an
     /etc/hosts file on a UNIX machine).
   A DHCP server wishing to express that a client should first search
   DNS, then NIS+, would send
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     117       |      4        |              6                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              65               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 DHCP Client Behavior
   The DHCP client will use this option to create a search list for
   name resolution.  The client may receive name services in this
   option that it does not support or has not been configured to
   access.  Likewise, a client may receive an option that lists name
   services for which no corresponding DHCP option was supplied.
   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].

IANA Considerations

 IANA has assigned a value of 117 for the DHCP option code described
 in this document.

Smith Standards Track [Page 3] RFC 2937 The Name Service Search Option for DHCP September 2000

References

 [1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
     1997.
 [2] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
     Extensions", RFC 2132, March 1997.
 [3] Bradner, S., "Key words for use in RFCs to indicate requirement
     levels", BCP 14, RFC 2119, March 1997.
 [4] Cohen, D., "On Holy Wars and a Plea for Peace", Computer, IEEE,
     October 1981.

Author's Address

 Carl Smith
 Sun Microsystems, Inc.
 901 San Antonio Road
 Palo Alto, CA 94043
 EMail:  cs@Eng.Sun.COM

Smith Standards Track [Page 4] RFC 2937 The Name Service Search Option for DHCP September 2000

Full Copyright Statement

 Copyright (C) The Internet Society (2000).  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.

Smith Standards Track [Page 5]

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