Internet Engineering Task Force C. Perkins INTERNET DRAFT IBM 27 August 1996 DHCP Options for Service Location Protocol draft-ietf-dhc-slp-00.txt Status of This Memo This document is a submission to the Dynamic Host Configuration Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the dhcp@bucknell.edu mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft. 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract The Dynamic Host Configuration Protocol provides a framework for passing configuration information to hosts on a TCP/IP network. Entities using the Service Location Protocol need to find out the address of Directory Agents in order to transact messages. In certain other instances they may need to discover the correct scope and naming authority to be used in conjunction with the service attributes and URLS which are exchanged using the Service Location Protocol. Perkins Expires 27 February 1997 [Page i] Internet Draft DHCP Options for Service Location 27 August 1996 1. Directory Agent Extension This extension specifies a Directory Agent (DA) [3], along with zero or more Naming Authorities [2] known to that DA and zero or more scopes supported by that DA. The code for this extension is 78. Each Naming Authority and each scope MUST be a null-terminated string of ASCII characters. The lengths of the strings are only indicated implicitly by their null termination and the overall length of the extension. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Length |D| NA count | scope count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (if present) | | Directory Agent address (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NA list ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | scope list ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 78 Length variable D If the 'D' bit is set, the Directory Agent address is present. NA count The number of Naming Authorities indicated by strings in the NA list following. scope count The number of scopes indicated by strings in the scope list following. NA list A list of strings denoting Naming Authorities. scope list A list of strings denoting scopes. Note that more than one Directory Agent extension may be present in a DHCP message. Each such extension may have the same or different lists of Naming Authorities and scopes. The client may request a Perkins Expires 27 February 1997 [Page 1] Internet Draft DHCP Options for Service Location 27 August 1996 Directory Agent with a particular scope, and/or knowledgeable about schemes defined by a particular Naming Authority, by including the Directory Agent extension in a DHCP Request message with no Directory Agent address included (the 'D' bit set to zero), and the appropriate strings in the NA list and/or scope list. 2. Service Scope Extension This extension indicates a scope that should be used by a Service Agent (SA) [3], when responding to Service Request messages as specified by the Service Location Protocol. Code Len +-----+-----+-----+----- | 79 | n | Scope ... +-----+-----+-----+----- Scope is a null-terminated ASCII string, of length 'n' including the terminating null character. 3. Naming Authority Extension This extension indicates a naming authority (which specifies the syntax for schemes that may be used in URLs [1]) for use by entities with the Service Location Protocol. Code Len +-----+-----+-----+-----+-----+----- | 80 | n | Naming Authority ... +-----+-----+-----+-----+-----+----- Naming Authority is a null-terminated ASCII string, of length 'n' including the terminating null character. 4. Security Considerations If a malicious host is able to insert fraudulent information in DHCPOFFER packets sent to a prospective client of the Service Location Protocol, then the client will be unable to obtain service, and vulnerable to disclosing information to unauthorized service agents. Likewise, a service agent would find that it might rely on fraudulent or otherwise malicious directory agents to advertise its services. Many opportunities for denial of service exist. Perkins Expires 27 February 1997 [Page 2] Internet Draft DHCP Options for Service Location 27 August 1996 This difficulty is inherited from the much larger and more serious problem, viz. securing or authenticating any information whatsoever from a DHCP server (or client!) is not possible in common DHCP deployments. 5. Acknowledgements Thanks to Erik Guttman for his helpful suggestions in the creation of this draft. References [1] T. Berners-Lee, L. Masinter, and M. McCahill. Uniform Resource Locators (URL). RFC 1738, December 1994. [2] Paul E. Hoffman and Ron Daniel, Jr. Generic URN Syntax. draft-ietf-uri-urn-syntax-00.txt -- work in progress, April 1995. [3] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service Location Protocol. draft-ietf-svrloc-protocol-14.txt - work in progress, June 1996. Author's Address Questions about this memo can be directed to: Charles Perkins Room J1-A25 T. J. Watson Research Center IBM Corporation 30 Saw Mill River Rd. Hawthorne, NY 10532 Work: +1 914 7847350 Fax: +1 914 7847007 E-mail: perk@watson.ibm.com Perkins Expires 27 February 1997 [Page 3]