Internet Engineering Task Force SIP WG Internet Draft H.Schulzrinne draft-ietf-sip-dhcpv6-00.txt Columbia University November 24, 2001 Expires: May 2002 DHCPv6 Options 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 DHCPv6 option that contains a list of domain names or IPv6 addresses 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 This document uses the DHCP terminology defined in [1]. A SIP server is 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. H.Schulzrinne [Page 1] Internet Draft November 24, 2001 A SIP client is defined in RFC 2543 [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. In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULD NOT", "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 two DHCPv6 options [1] 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 DHCPv6 Option This document defines The SIP server DHCP option carries either a 128-bit (binary) IPv6 address or, preferably, a DNS (RFC 1035 [5]) fully-qualified domain name to be used by the SIP client to locate a SIP server. 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 H.Schulzrinne [Page 2] Internet Draft November 24, 2001 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 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 accomodate future internationalized domain name mechanisms. The option MAY contain multiple domain names, but these SHOULD refer to different SRV records, rather than different A records. Domain names SHOULD be listed in order of preference. A SIP client obtains a domain name through the DHCP 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 domain name is used first in a DNS SRV lookup and, if that fails because of a lack of matching DNS SRV records, the domain name is used in an address record lookup. Normative details are contained in RFC XXXX [3]. Use of multiple domain names is not meant to replace SRV records, but rather to allow a single DHCP server to indicate outbound proxy servers operated by multiple providers. An encoding according to section 4.1.4 of "Domain Names - Implementation And Specification" [5] does not seem appropriate here, since the domain names are supposed to be different domains, so that compression will have little effect. The DHCPv6 option has the following format: 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 H.Schulzrinne [Page 3] Internet Draft November 24, 2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_SIP_SERVER_D | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SIP Server Domain List | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: OPTION_SIP_SERVER_D (TBD) option-length: variable SIP Server Domain List: The list of SIP servers the client should use. 3.2 SIP Servers IPv6 Address List This option specifies a list of IPv6 addresses indicating SIP outbound proxy servers available to the client. Servers SHOULD be listed in order of preference. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_SIP_SERVER_A | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SIP server (IP address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SIP server (IP address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: OPTION_SIP_SERVER_A (TBD) option-length: variable SIP server: IPv6 address of a SIP server for the client to use. The servers are listed in the order of preference for use H.Schulzrinne [Page 4] Internet Draft November 24, 2001 by the client. 4 Security Consideration There are no security considerations beyond those described in RFC XXXX [1], RFC 2543 [2] and RFC YYYY [3]. 5 IANA Considerations IANA has assigned a DHCPv6 option number of TBD for the "SIP Servers Domain Name List" and the DHCPv6 option number of TBD for the "SIP Servers IPv6 Address List" defined in this document. 6 Acknowledgements TBD. 7 Authors' Addresses 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] J. Bound, M. Carney, C. Perkins, and R. Droms, "Dynamic host configuration protocol for IPv6 (DHCPv6)," Internet Draft, Internet Engineering Task Force, Oct. 2001. Work in progress. [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, Mar. 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] P. V. Mockapetris, "Domain names - implementation and specification," Request for Comments 1035, Internet Engineering Task Force, Nov. 1987. H.Schulzrinne [Page 5] Internet Draft November 24, 2001 [6] G. Nair and H. Schulzrinne, "DHCP option for SIP servers," Internet Draft, Internet Engineering Task Force, Mar. 2001. Work in progress. H.Schulzrinne [Page 6]