HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 07:53:17 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Mon, 28 Feb 2000 15:33:00 GMT ETag: "30502c-3037-38ba952c" Accept-Ranges: bytes Content-Length: 12343 Connection: close Content-Type: text/plain Internet Engineering Task Force SIP WG Internet Draft G.Nair, H.Schulzrinne draft-ietf-sip-dhcp-00.txt Columbia University February 27, 2000 Expires: August 2000 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 The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document defines DHCP options that contain one or more pointers to one or more SIP servers. This is one of the many methods that a SIP client can use to obtain the addresses of the SIP servers. 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. SIP server: As defined in RFC 2543 [2]. In the context of this document, a SIP server refers to the host the application is running on. G.Nair, H.Schulzrinne [Page 1] Internet Draft February 27, 2000 SIP client: As defined in RFC 2543. In the context of this document, a SIP client refers to the host the application is running on. 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 RFC 2119 [3]. 2 Introduction The Session Initiation Protocol (SIP) [2] is an application-layer control protocol that can establish, modify and terminate multimedia sessions or calls. In particular, it is used for signalling of Internet telephony calls. A SIP system has two components: user agents and servers. The user agent is the SIP end system that acts on behalf of someone who wants to participate in a SIP call. This draft specifies a DHCP option [1,4] that allows SIP user agents (clients) to locate a local SIP server that is to be used for all outbound SIP requests. (SIP clients MAY contact the address identified in the SIP URL directly, without involving a local SIP server. However in some circumstances, in particular with firewalls, SIP clients need to use a local server for outbound requests.) This is one of many possible solutions for locating the outbound SIP server. 3 Overview We identify two methods of notifying the client of the servers' location: 1. DNS [5] SRV records: The host name can be resolved by the client, using DNS and the name string obtained via a DHCP option. The client first uses the SRV [6] resource records to resolve the host name. If this fails the A resource records are tried. 2. List of IP addresses: Used in case there is no DNS server OR in the case that the client host is not DNS capable. Either or both of these methods MAY be used to notify the client of the servers' location through DHCP. 4 SIP server DHCP options We propose two new DHCP options. Our approach is defined in the following sections. G.Nair, H.Schulzrinne [Page 2] Internet Draft February 27, 2000 4.1 SIP server DNS name option This option specifies the DNS [5] name of the SIP server The client SHOULD first use this string to send an SRV query to the DNS server. If the client is not SRV-cognizant OR the SRV query fails, the client sends the same string in an A record query. 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. Code Len DNS name of SIP server +-----+-----+-----+-----+-----+-----+-----+-- | TBD | n | s1 | s2 | s3 | s4 | s5 | ... +-----+-----+-----+-----+-----+-----+-----+-- Clients SHOULD use this method to locate the SIP server. The reason to list the SRV string and use DNS to resolve the address is that load sharing can be implemented more readily by an SRV-cognizant client. 4.2 SIP server IP address option This option specifies the list of IP addresses indicating SIP servers available to the client. The option SHOULD only be used if the client does not implement DNS (as in the case of some emebedded systems) OR if the DNS server is not responding. We duplicate relevant parts of the SRV record [6] in this option. Each item of the list consists of an ASCII string with 5 fields separated by a single space (ASCII 0x20) as shown below: IP address: This field contains the IP address of the SIP server in dotted quad notation. prio: This field indicates the priority of this target host. A client MUST attempt to contact the target host with the lowest-numbered priority it can reach; target hosts with the same priority SHOULD be tried in a round-robin fashion starting with a randomly chosen address. The range of G.Nair, H.Schulzrinne [Page 3] Internet Draft February 27, 2000 priorities is 0-65535. wt: This field is used by the load balancing mechanism. When selecting a target host among those that have the same priority, the chance of trying this one first SHOULD be proportional to its weight. The range of this number is 1- 65535. Domain administrators are urged to use Weight 0 when there isn't any load balancing to do, to make the option easier to read for humans (less noisy). port: This field indicates the port on this target SIP server. The range is 0-65535. This is often 5060 - as specified in the IANA Assigned Numbers, but need not be. prot: This field indicates the protocol used by the SIP server. This can be either `TCP' or `UDP'. The protocol name is case sensitive. The code for this option is TBD. The length of this option is specified in `Len'. The minimum length of this option is 17 octets. The maximum length of this option is 255 octets. Code Len string 1 string 2 +-----+-----+-----+-----+-----+-- --+-----+-----+-- | TBD | n | s1 | s2 | s3 | ... | s13 | s14 | ... +-----+-----+-----+-----+-----+-- --+-----+-----+-- 5 Multiple options More than one SIP server option MAY be returned by the DHCP server. More than one of any option types MAY be present. This permits the client to select the option that suits its capabilities (DNS-SRV, DNS-A, or no DNS capability). 6 Security Consideration There are no security considerations beyond those described in RFC 2132. 7 Acknowledgements We would like to thank Jonathan Rosenberg, Bernie Volz, Kundan Singh, Sven Ubik and Wenyu Jiang for their contributions. 8 Authors' Addresses G.Nair, H.Schulzrinne [Page 4] Internet Draft February 27, 2000 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 9 Bibliography [1] R. Droms, "Dynamic host configuration protocol," Request for Comments (Draft Standard) 2131, Internet Engineering Task Force, Mar. 1997. [2] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: session initiation protocol," Request for Comments (Proposed Standard) 2543, Internet Engineering Task Force, Mar. 1999. [3] S. Bradner, "Key words for use in RFCs to indicate requirement levels," Request for Comments (Best Current Practice) 2119, Internet Engineering Task Force, Mar. 1997. [4] S. Alexander and R. Droms, "DHCP options and BOOTP vendor extensions," Request for Comments (Draft Standard) 2132, Internet Engineering Task Force, Mar. 1997. [5] P. V. Mockapetris, "Domain names - implementation and specification," Request for Comments (Standard) 1035, Internet Engineering Task Force, Nov. 1987. [6] A. Gulbrandsen and P. Vixie, "A DNS RR for specifying the location of services (DNS SRV)," Request for Comments (Experimental) 2052, Internet Engineering Task Force, Oct. 1996. Full Copyright Statement Copyright (c) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published G.Nair, H.Schulzrinne [Page 5] Internet Draft February 27, 2000 and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. 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Table of Contents 1 Terminology ......................................... 1 2 Introduction ........................................ 2 3 Overview ............................................ 2 4 SIP server DHCP options ............................. 2 4.1 SIP server DNS name option .......................... 3 4.2 SIP server IP address option ........................ 3 5 Multiple options .................................... 4 6 Security Consideration .............................. 4 7 Acknowledgements .................................... 4 8 Authors' Addresses .................................. 4 9 Bibliography ........................................ 5 G.Nair, H.Schulzrinne [Page 6]