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+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.
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+Smith Standards Track [Page 1]
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+RFC 2937 The Name Service Search Option for DHCP September 2000
+
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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 [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
+
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+Smith Standards Track [Page 2]
+
+RFC 2937 The Name Service Search Option for DHCP September 2000
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+
+ 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.
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+Smith Standards Track [Page 3]
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+RFC 2937 The Name Service Search Option for DHCP September 2000
+
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+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
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+Smith Standards Track [Page 4]
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+RFC 2937 The Name Service Search Option for DHCP September 2000
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+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.
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+Smith Standards Track [Page 5]
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