Internet Engineering Task Force SIP WG Internet Draft G.Nair, H.Schulzrinne draft-ietf-sip-dhcp-02.txt Columbia University January 15, 2001 Expires: June 2001 DHCP Option for SIP Servers 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 To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Abstract This document defines a DHCP option that contains a pointers to one or more SIP outbound proxy servers. This is one of the many methods that a SIP client can use to obtain the addresses of such a local SIP server. 1 Terminology DHCP client: A DHCP [1] client is an Internet host that uses DHCP to obtain configuration parameters such as a network address. DHCP server: A DHCP server is an Internet host that returns configuration parameters to DHCP clients. G.Nair, H.Schulzrinne [Page 1]
Internet Draft January 15, 2001 SIP server: As defined in RFC 2543 [2]. This server MUST be an outbound proxy server, as defined in [3]. In the context of this document, a SIP server refers to the host the SIP server is running on. SIP client: As defined in RFC 2543. The client can be a user agent client or the client portion of a proxy server. In the context of this document, a SIP client refers to the host the SIP client is running on. In this document, the key words "MUST", "MUSTNOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULDNOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [4]. 2 Introduction The Session Initiation Protocol (SIP) [2] is an application-layer control protocol that can establish, modify and terminate multimedia sessions or calls. A SIP system has a number of logical components: user agents, proxy servers, redirect servers and registrars. User agents MAY contain SIP clients, proxy servers always do. This draft specifies a DHCP option [1,5] that allows SIP clients to locate a local SIP server that is to be used for all outbound SIP requests, a so-called outbound proxy server. (SIP clients MAY contact the address identified in the SIP URL directly, without involving a local SIP server. However in some circumstances, when firewalls are present, SIP clients need to use a local server for outbound requests.) This is one of many possible solutions for locating the outbound SIP server; manual configuration is an example of another. 3 Overview The SIP client obtains a DNS [6] string via a DHCP option. This string is then used by the mechanism described in [3] to locate the outbound proxy server. In summary, the domain name encoded in the string is used first in a DNS SRV lookup and, if that fails because of a lack of matching DNS SRV records, in an address record lookup. Normative details are contained in [3]. 4 SIP server DHCP options This option specifies the DNS [6] string that is passed to the client. This string SHOULD be the domain name of the SIP server (rather than a textual representation of the network address). The code for this option is TBD. The length of the DNS name string is specified in `Len'. The maximum length of this string is 255 octets and minimum length is 1 octet. For example, a value may be G.Nair, H.Schulzrinne [Page 2]
Internet Draft January 15, 2001 "sip.example.com". Code Len DNS name of SIP server +-----+-----+-----+-----+-----+-----+-----+-- | TBD | n | s1 | s2 | s3 | s4 | s5 | ... +-----+-----+-----+-----+-----+-----+-----+-- 5 Security Consideration There are no security considerations beyond those described in RFC 2132. 6 Acknowledgements Robert Elz, Wenyu Jiang, Peter Koch, Erik Nordmark, Jonathan Rosenberg, Kundan Singh, Sven Ubik and Bernie Volz provided useful feedback. 7 Authors' Addresses Gautam Nair Dept. of Computer Science Columbia University 1214 Amsterdam Avenue, MC 0401 New York, NY 10027 USA electronic mail: gnair@cs.columbia.edu Henning Schulzrinne Dept. of Computer Science Columbia University 1214 Amsterdam Avenue, MC 0401 New York, NY 10027 USA electronic mail: schulzrinne@cs.columbia.edu 8 Bibliography [1] R. Droms, "Dynamic host configuration protocol," Request for Comments 2131, Internet Engineering Task Force, Mar. 1997. [2] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: session initiation protocol," Request for Comments 2543, Internet Engineering Task Force, Mar. 1999. [3] H. Schulzrinne and J. Rosenberg, "SIP: session initiation protocol -- locating SIP servers," Internet Draft, Internet G.Nair, H.Schulzrinne [Page 3]
Internet Draft January 15, 2001 Engineering Task Force, Jan. 2001. Work in progress. [4] S. Bradner, "Key words for use in RFCs to indicate requirement levels," Request for Comments 2119, Internet Engineering Task Force, Mar. 1997. [5] S. Alexander and R. Droms, "DHCP options and BOOTP vendor extensions," Request for Comments 2132, Internet Engineering Task Force, Mar. 1997. [6] P. V. Mockapetris, "Domain names - implementation and specification," Request for Comments 1035, Internet Engineering Task Force, Nov. 1987. G.Nair, H.Schulzrinne [Page 4]
