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Versions: (draft-nair-sip-dhcp) 00 01 02 03 04 05 RFC 3361

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


   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-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at

   To view the list Internet-Draft Shadow Directories, see


   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

1 Terminology

        DHCP client: A DHCP [1] client is an Internet host that uses
             DHCP to obtain configuration parameters such as a network

        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",
   "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


             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

6 Acknowledgements

   Robert Elz, Wenyu Jiang, Peter Koch, Erik Nordmark, Jonathan
   Rosenberg, Kundan Singh, Sven Ubik and Bernie Volz provided useful

7 Authors' Addresses

   Gautam Nair
   Dept. of Computer Science
   Columbia University 1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   electronic mail:  gnair@cs.columbia.edu

   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University 1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   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]

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