Network Working Group Bernard Aboba INTERNET-DRAFT Microsoft Category: Standards Track 19 October 2000 DHCP Domain Search Option 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. The distribution of this memo is unlimited. 1. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. 2. Abstract The Dynamic Host Configuration Protocol (DHCP) provides a mechanism for host configuration. RFC 2132 allows DHCP servers to specify configuration information for various kinds of name services to be passed to DHCP clients. In some circumstances, it is useful for the DHCP client to be configured with the domain search list. This is particularly useful for cases where the client may be configured to use multicast DNS (mDNS). This document defines a new DHCP option which is passed from the DHCP Server to the DHCP Client to specify the domain seach list when resolving hostnames. Aboba Standards Track [Page 1] INTERNET-DRAFT DHCP Domain Search Option 19 October 2000 3. Introduction The Dynamic Host Configuration Protocol (DHCP) [2] provides a mechanism for host configuration. RFC 2132 [3] allows DHCP servers to specify configuration information for various kinds of name services to be passed to DHCP clients. In some circumstances, it is useful for the DHCP client to be configured with the domain search list. This is particularly useful for cases where the client may be configured to use multicast DNS (mDNS) [5]. This document defines a new DHCP option which is passed from the DHCP Server to the DHCP Client to specify the domain seach list when resolving hostnames. 3.1. Terminology This document uses the following terms: DHCP client A 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. 3.2. Requirements language In this document, the key words "MAY", "MUST, "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [1]. 4. Domain Search Option Format The code for this option is TBD. 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 | Len | SearchString... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Searchstring... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In the above diagram, Searchstring is a string specifying the searchlist. If the length of the searchlist exceeds the maximum permissible within a single option (256 octets), then multiple options may be used, as described in [6]. Aboba Standards Track [Page 2] INTERNET-DRAFT DHCP Domain Search Option 19 October 2000 To enable the searchlist to be encoded compactly, searchstrings in the searchlist are concatenated and encoded using the technique described in section 4.1.4 of [7]. In this scheme, an entire domain name or a list of labels at the end of a domain name is replaced with a pointer to a prior occurance of the same name. In this case, the pointer refers to the offset within the searchlist option starting with the SearchString portion of the option. 5. References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [3] Alexander, S., Droms, R., "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. [4] Droms, R., Arbaugh, W., "Authentication for DHCP Messages", Internet draft (work in progress), draft-ietf-dhc- authentication-14.txt, July 2000. [5] Esibov, L., Aboba, B., Thaler, D., "Multicast DNS", Internet draft (work in progress), draft-aboba-dnsext-mdns-03.txt, October 2000. [6] Arbaugh, W. A., Keromytis, A. D.,"DHCP Continuation Option Code", Internet draft (work in progress), draft-ietf-dhc-options- cont-01.txt, January 2000. [7] Mockapetris, P., "DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION", RFC 1035, November 1987. 6. Security Considerations Potential attacks on DHCP are discussed in section 7 of the DHCP protocol specification [2], as well as in the DHCP authentication specification [4]. Since the domain search option may be used to control the use of mDNS as described in [5], it is possible for a host masquerading as a DNS server to return a domain search option enabling use of mDNS. Since mDNS uses only linklocal multicast, such an attack would not have repercussions beyond the local segment. However, on a heavily populated segment, it might result in increased multicast traffic levels and some degradation in host performance. Aboba Standards Track [Page 3] INTERNET-DRAFT DHCP Domain Search Option 19 October 2000 7. IANA Considerations This draft does not create any new number spaces for IANA administration. 8. Acknowledgments The authors would like to thank Stuart Cheshire, Michael Patton, Erik Guttman, Olafur Gudmundsson, Thomas Narten, Mark Andrews, Erik Nordmark, Myron Hattig and Bill Manning for comments on this draft, provided at the mDNS lunch in Adelaide, Australia on 3/29/00. 9. Authors' Addresses Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: +1 (425) 936-6605 EMail: bernarda@microsoft.com 10. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards- related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 11. Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to Aboba Standards Track [Page 4] INTERNET-DRAFT DHCP Domain Search Option 19 October 2000 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." 12. Expiration Date This memo is filed as , and expires May 1, 2001. Aboba Standards Track [Page 5]