Dynamic Host Configuration Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) Servers
RFC 3319

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Network Working Group                                     H. Schulzrinne
Request for Comments: 3319                           Columbia University
Category: Standards Track                                        B. Volz
                                                                Ericsson
                                                               July 2003

         Dynamic Host Configuration Protocol (DHCPv6) Options
             for Session Initiation Protocol (SIP) Servers

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document defines a Dynamic Host Configuration Protocol version 6
   (DHCPv6) option that contains a list of domain names or IPv6
   addresses that can be mapped to one or more Session Initiation
   Protocol (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

   This document uses the DHCP terminology defined in [1].

   A SIP server is defined in RFC 3261 [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 outbound SIP proxy
   server is running on.

   A SIP client is defined in RFC 3261 [2].  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.

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   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in BCP 14, 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 document specifies two DHCPv6 options [1] that allow 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, such as
   when firewalls are present, or local dialing plans, local emergency
   and other services need to be provided, 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 DHCPv6 Option

   This document defines two DHCPv6 options that describe a local
   outbound SIP proxy: one carries a list of domain names (Section 3.1),
   the other a list of 128-bit (binary) IPv6 addresses (Section 3.2).

      Since DHCPv6 does not suffer from a shortage of option codes, we
      avoid the encoding byte found in the IPv4 DHCP option for SIP
      servers [6].  This makes the option shorter, easier to parse,
      simplifies appropriate word alignment for the numeric addresses
      and allows the client to request either numeric or domain name
      options using the "option request option".

   An implementation implementing this specification MUST support both
   options.

3.1  SIP Servers Domain Name List

   The option length is followed by a sequence of labels, encoded
   according to Section 3.1 of RFC 1035 [5], quoted below:

      "Domain names in messages are expressed in terms of a sequence of
      labels.  Each label is represented as a one octet length field
      followed by that number of octets.  Since every domain name ends

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      with the null label of the root, a domain name is terminated by a
      length byte of zero.  The high order two bits of every length
      octet must be zero, and the remaining six bits of the length field
      limit the label to 63 octets or less.  To simplify
      implementations, the total length of a domain name (i.e., label
      octets and label length octets) is restricted to 255 octets or
      less."

      RFC 1035 encoding was chosen to accommodate future
      internationalized domain name mechanisms.