Address Resolution for Instant Messaging and Presence
RFC 3861

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• 04

Network Working Group                                        J. Peterson
Request for Comments: 3861                                       NeuStar
Category: Standards Track                                    August 2004

         Address Resolution for Instant Messaging and Presence

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 (2004).

Abstract

   Presence and instant messaging are defined in RFC 2778.  The Common
   Profiles for Presence and Instant Messaging define two Universal
   Resource Identifier (URI) schemes: 'im' for INSTANT INBOXes and
   'pres' for PRESENTITIES.  This document provides guidance for
   locating the resources associated with URIs that employ these
   schemes.

Table of Contents

   1.  Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Address Resolution. . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Domain Name Lookup. . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Processing SRV RRs. . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Processing Multiple Addresses . . . . . . . . . . . . . . . . . 5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   9.  Contributors. . . . . . . . . . . . . . . . . . . . . . . . . . 6
   10. Normative References. . . . . . . . . . . . . . . . . . . . . . 6
   11. Author's Address. . . . . . . . . . . . . . . . . . . . . . . . 7
   12. Full Copyright Statement. . . . . . . . . . . . . . . . . . . . 8

Peterson                    Standards Track                     [Page 1]
RFC 3861                        IM&P SRV                     August 2004

1.  Introduction

   Presence and instant messaging are defined in RFC 2778 [5].  The
   Common Profiles for Presence (CPP) [2] and Instant Messaging (CPIM)
   [1] define two Universal Resource Identifier (URI) schemes: 'im' for
   INSTANT INBOXes and 'pres' for PRESENTITIES.  This document provides
   rules for locating the resources associated with URIs that employ
   these schemes via the Domain Name Service (DNS) [4].  These rules
   could no doubt be applied to the resolution of other URI schemes that
   are unrelated to instant messaging and presence.

   CPIM and CPP both specify operations that have 'source' and
   'destination' attributes.  While only the semantics, not the syntax,
   of these attributes are defined by CPIM and CPP, many instant
   messaging and presence protocols today support the use of URIs to
   reflect the source and destination of their operations.  The 'im' and
   'pres' URI schemes allow such protocols to express the identities of
   the principals associated with a protocol exchange.  When these
   operations pass through a CPIM or CPP gateway, these URIs could be
   relayed without modification, which has a number of desirable
   properties for the purposes of interoperability.

   These URI schemes are also useful in cases where no CPIM/CPP
   gatewaying will occur.  If a particular principal's endpoint supports
   multiple instant messaging applications, for example, then a domain
   that identifies that host might use the sort of DNS records described
   in this document to provide greater compatibility with clients that
   support only one instant messaging protocol.  A client would look up
   the corresponding record to the supported protocol, and learn how to
   contact the endpoint for that protocol.  The principal in this
   instance would use an IM URI as their canonical address.

   In some architectures, these URIs might also be used to locate a CPIM
   or CPP gateway that serves a particular domain.  If a particular IM
   service provider wishes to operate CPIM/CPP gateways in its own
   domain that map standard Internet protocols to an internal
   proprietary protocol, that gateway could be identified by an IM URI.
   In that case, the DNS records used to dereference the IM URI would
   serve a purpose similar to that of Mail Exchange (MX) records.

   The system described in this document relies on the use of DNS
   service (SRV) [7] records and address (A) records.

Peterson                    Standards Track                     [Page 2]
RFC 3861                        IM&P SRV                     August 2004

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in BCP 14, RFC 2119 [3] and indicate requirement levels for