Network Working Group C. Smith Internet Draft Sun Microsystems, Inc.
OctoberDecember 1999 Expires AprilJune 2000 The Name Service Search Option for DHCP <draft-ietf-dhc-nsso-01.txt><draft-ietf-dhc-nsso-02.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) provides a framework for passing configuration information to hosts on a TCP/IP network. RFC 2132  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. 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 . 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.2 bytes. A DHCP server SHOULD return, in its preferred order, the 16-bit, network order (big-endian ) integer option code for the name services (the earlier in the list, the more preferred the name service). Code LenLength 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TBD | nLen | ns1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ns2 | ... +-------+-------+-------+--------+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In the above example, ns1 & ns2 are 16-bit 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 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TBD | 24 | 6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 65 | +-------+-------+-------+--------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A name service option code of 0 is used to indicate that the client should refer to local configuration information. 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 . References  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997.  Bradner, S., "Key words for use in RFCs to indicate requirement levels", RFC 2119, March 1997.  Cohen, D., "On Holy Wars and a Plea for Peace", Computer, IEEE, October 1981. 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.June 30, 2000. 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