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<pre>Network Working Group R. Mahy
Request for Comments: 5028 Plantronics
Category: Standards Track October 2007
<span class="h1">A Telephone Number Mapping (ENUM) Service Registration for</span>
<span class="h1">Instant Messaging (IM) Services</span>
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.
Abstract
This document registers a Telephone Number Mapping (ENUM) service for
Instant Messaging (IM). Specifically, this document focuses on
provisioning 'im:' URIs (Uniform Resource Identifiers) in ENUM.
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
ENUM (E.164 Number Mapping, <a href="./rfc3761">RFC 3761</a> [<a href="#ref-1" title=""The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)"">1</a>]) is a system that uses DNS
(Domain Name Service, <a href="./rfc1034">RFC 1034</a> [<a href="#ref-2" title=""Domain names - concepts and facilities"">2</a>]) to translate telephone numbers,
such as '+12025550100', into URIs (Uniform Resource Identifiers, <a href="./rfc3986">RFC</a>
<a href="./rfc3986">3986</a> [<a href="#ref-3" title=""Uniform Resource Identifier (URI): Generic Syntax"">3</a>]), such as 'im:user@example.com'. ENUM exists primarily to
facilitate the interconnection of systems that rely on telephone
numbers with those that use URIs to identify resources.
Instant Messaging (IM) is a service defined in <a href="./rfc2778">RFC 2778</a> [<a href="#ref-6" title=""A Model for Presence and Instant Messaging"">6</a>] that
allows users to send and receive typically short, often textual
messages in near real-time. The IETF has defined a generic URI used
to identify an IM service for a particular resource: the 'im:' URI
scheme (defined in <a href="./rfc3861">RFC 3861</a> [<a href="#ref-4" title=""Address Resolution for Instant Messaging and Presence"">4</a>]). <a href="./rfc3861">RFC 3861</a> [<a href="#ref-4" title=""Address Resolution for Instant Messaging and Presence"">4</a>] also defines rules
for discovering service running specific protocols, such as SIP (the
Session Initiation Protocol, <a href="./rfc3261">RFC 3261</a> [<a href="#ref-8" title=""SIP: Session Initiation Protocol"">8</a>]) and XMPP (the eXtensible
Messaging and Presence Protocol, <a href="./rfc3921">RFC 3921</a> [<a href="#ref-9" title=""Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence"">9</a>]) from a specific 'im:'
URI.
<a href="./rfc3953">RFC 3953</a> [<a href="#ref-10" title=""Telephone Number Mapping (ENUM) Service Registration for Presence Services"">10</a>] already defines an enumservice for presence services,
which returns 'pres:' URIs (also defined in <a href="./rfc3861">RFC 3861</a> [<a href="#ref-4" title=""Address Resolution for Instant Messaging and Presence"">4</a>]). This
document registers an enumservice for advertising IM information
associated with an E.164 number.
<span class="grey">Mahy Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc5028">RFC 5028</a> IM Enumservice October 2007</span>
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. ENUM Service Registration - im</span>
As defined in <a href="./rfc3761">RFC 3761</a> [<a href="#ref-1" title=""The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)"">1</a>], the following is a template covering
information needed for the registration of the enumservice specified
in this document:
Enumservice Name:
"im"
Enumservice Type:
"im"
Enumservice Subtypes:
N/A
URI scheme(s):
"im:"
Functional Specification:
This Enumservice indicates that the resource identified is an
'im:' URI. The 'im:' URI scheme does not identify any particular
protocol that will be used to handle instant messaging receipt or
delivery, rather the mechanism in <a href="./rfc3861">RFC 3861</a> [<a href="#ref-4" title=""Address Resolution for Instant Messaging and Presence"">4</a>] is used to discover
whether an IM protocol supported by the party querying ENUM is
also supported by the target resource.
Security considerations:
See <a href="#section-3">section 3</a>.
Intended usage:
COMMON
Author:
Rohan Mahy (rohan@ekabal.com)
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Security Considerations</span>
The Domain Name System (DNS) does not make policy decisions about
which records it provides to a DNS resolver. All DNS records must be
assumed to be available to all inquirers at all times. The
information provided within an ENUM record set must therefore be
considered open to the public -- which is a cause for some privacy
considerations.
Revealing an 'im:' URI by itself is unlikely to introduce many
privacy concerns, although, depending on the structure of the URI, it
might reveal the full name or employer of the target. The use of
anonymous URIs mitigates this risk.
As ENUM uses DNS, which in its current form is an insecure protocol,
there is no mechanism for ensuring that the answer returned to a
query is authentic. An analysis of threats specific to the
dependence of ENUM on the DNS is provided in <a href="./rfc3761">RFC 3761</a>, and a thorough
analysis of threats to the DNS itself is covered in <a href="./rfc3833">RFC 3833</a> [<a href="#ref-11" title=""Threat Analysis of the Domain Name System (DNS)"">11</a>].
Many of these problems are prevented when the resolver verifies the
<span class="grey">Mahy Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc5028">RFC 5028</a> IM Enumservice October 2007</span>
authenticity of answers to its ENUM queries via DNSSEC [<a href="#ref-5" title=""Protocol Modifications for the DNS Security Extensions"">5</a>] in zones
where it is available.
More serious security concerns are associated with potential attacks
against an underlying Instant Messaging system (for example, message
forgery and tampering). For this reason, IM protocols have a number
of security requirements (detailed in <a href="./rfc2779">RFC 2779</a> [<a href="#ref-7" title=""Instant Messaging / Presence Protocol Requirements"">7</a>]) that call for
authentication, integrity and confidentiality properties, and similar
measures to prevent such attacks. Any instant messaging protocol
used in conjunction with the 'im:' URI scheme is required to meet
these requirements.
Unlike a traditional telephone number, the resource identified by an
'im:' URI may require that callers provide cryptographic credentials
for authentication and authorization before instant messages are
exchanged. In concert with instant messaging protocols, ENUM can
actually provide far greater protection from unwanted callers than
does the existing PSTN, despite the public availability of ENUM
records.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. IANA Considerations</span>
This document requests registration of the "im" Enumservice according
to the definitions in this document and <a href="./rfc3761">RFC 3761</a> [<a href="#ref-1" title=""The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)"">1</a>].
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. References</span>
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. Normative References</span>
[<a id="ref-1">1</a>] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", <a href="./rfc3761">RFC 3761</a>, April 2004.
[<a id="ref-2">2</a>] Mockapetris, P., "Domain names - concepts and facilities", STD
13, <a href="./rfc1034">RFC 1034</a>, November 1987.
[<a id="ref-3">3</a>] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, <a href="./rfc3986">RFC 3986</a>,
January 2005.
[<a id="ref-4">4</a>] Peterson, J., "Address Resolution for Instant Messaging and
Presence", <a href="./rfc3861">RFC 3861</a>, August 2004.
[<a id="ref-5">5</a>] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Protocol Modifications for the DNS Security Extensions", <a href="./rfc4035">RFC</a>
<a href="./rfc4035">4035</a>, March 2005.
<span class="grey">Mahy Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc5028">RFC 5028</a> IM Enumservice October 2007</span>
<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. Informative References</span>
[<a id="ref-6">6</a>] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence
and Instant Messaging", <a href="./rfc2778">RFC 2778</a>, February 2000.
[<a id="ref-7">7</a>] Day, M., Aggarwal, S., Mohr, G., and J. Vincent, "Instant
Messaging / Presence Protocol Requirements", <a href="./rfc2779">RFC 2779</a>, February
2000.
[<a id="ref-8">8</a>] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", <a href="./rfc3261">RFC 3261</a>, June 2002.
[<a id="ref-9">9</a>] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence", <a href="./rfc3921">RFC 3921</a>,
October 2004.
[<a id="ref-10">10</a>] Peterson, J., "Telephone Number Mapping (ENUM) Service
Registration for Presence Services", <a href="./rfc3953">RFC 3953</a>, January 2005.
[<a id="ref-11">11</a>] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
System (DNS)", <a href="./rfc3833">RFC 3833</a>, August 2004.
Author's Address
Rohan Mahy
Plantronics
EMail: rohan@ekabal.com
<span class="grey">Mahy Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc5028">RFC 5028</a> IM Enumservice October 2007</span>
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
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Copies of IPR disclosures made to the IETF Secretariat and any
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such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
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The IETF invites any interested party to bring to its attention any
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rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Mahy Standards Track [Page 5]
</pre>
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