Internet Engineering Task Force                                   SIP WG
Internet Draft                                     H.Schulzrinne, G.Nair
draft-ietf-sip-dhcp-04.txt                           Columbia University
March 24, 2001
Expires: September 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.

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   This document defines a DHCP option that contains a single name that
   can be mapped 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

        DHCP server: A DHCP server is an Internet host that returns
             configuration parameters to DHCP clients.

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Internet Draft                                            March 24, 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", "MUST NOT", "REQUIRED",
   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 SIP Server DHCP Option

   The SIP server DHCP option carries a DNS (RFC 1035 [6]) fully-
   qualified domain name to be used by the SIP client to locate a SIP
   server. The FQDN is 16-bit Unicode text encoded into an octet stream
   using UTF-8 (RFC 2044 [7]). The FQDN in the SIP server option MUST
   NOT be null-terminated. It MUST NOT end with a period.

   A SIP client obtains a FQDN through the SIP server option, which the
   client then uses to locate the outbound proxy server by the mechanism
   described in RFC XXXX [3]. In summary, the FQDN is used first in a
   DNS SRV lookup and, if that fails because of a lack of matching DNS
   SRV records, the FQDN is used in an address record lookup. Normative
   details are contained in RFC XXXX [3].

   It is possible, but NOT RECOMMENDED that the string is the textual
   representation of a network address, e.g., a "dotted quad" for IPv4

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   and the hexadecimal representation of RFC 2373 [8].  Implementations
   MUST detect this case by checking whether all characters are decimal
   digits or periods.

   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

             Code  Len      DNS name of SIP server
           | TBD |  n  | s1  | s2  | s3  | s4  | s5  |  ...

4 Security Consideration

   There are no security considerations beyond those described in RFC
   2131 [1], RFC 2543 [2] and RFC XXXX [3].

5 IANA Considerations

   IANA has assigned a DHCP option number of TBD for the "SIP Servers
   DHCP Option" defined in this document.

6 Acknowledgements

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

7 Authors' Addresses

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

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

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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
   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.

   [7] F. Yergeau, "UTF-8, a transformation format of unicode and ISO
   10646," Request for Comments 2044, Internet Engineering Task Force,
   Oct. 1996.

   [8] R. Hinden and S. Deering, "IP version 6 addressing architecture,"
   Request for Comments 2373, Internet Engineering Task Force, July

H.Schulzrinne, G.Nair                                         [Page 4]