ENUM (E.164 Number Mapping, RFC 3761 [2]) is a system that transforms
E.164 numbers [3] into domain names and that then uses DNS (Domain
Name Service, RFC 1034 [4]) services such as delegation through NS
records and NAPTR records to look up what services are available for
a specific domain name.
This document registers 'Enumservices' according to the guidelines
given in RFC 3761 [2] to be used for provisioning in the services
field of an NAPTR [7] resource record to indicate what class of
functionality a given end point offers. The registration is defined
within the DDDS (Dynamic Delegation Discovery System [5][6][7][8][9])
hierarchy, for use with the "E2U" DDDS Application, defined in RFC
3761 [2].
The following 'Enumservices' are registered with this document: 'web'
and 'ft'. These share a common feature in that they each indicate
that the functionality of the given end points and the associated
resources are primarily sources of information.
According to RFC 3761 [2], the 'Enumservice' registered must be able
to function as a selection mechanism when one chooses between one
NAPTR resource record and another. This means that the registration
MUST specify what is expected when that NAPTR record is used, and the
URI scheme that is the outcome of use.
Therefore an 'Enumservice' acts as a hint, indicating the kind of
service with which the URI constructed by using the regexp field is
associated. More than one 'Enumservice' can be included within a
single NAPTR; this indicates that there is more than one service that
can be achieved by using the associated URI scheme.
The common thread with this set of definitions is that they reflect
the kind of service that the end user will hope to achieve with the
communication by using the associated URI.
The services specified here are NOT intended to specify the protocol
or even the method of connection that MUST be used to achieve each
service. Instead, we define the kind of interactive behavior that an
end user will expect, leaving the end system to decide (based on
policies outside the scope of this specification) how to execute the
service.
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As the same URI scheme may be used for different services (e.g.,
'tel:') and the same kind of service may use different URI schemes
(e.g., for VoIP, 'sip:', 'h323:', and 'tel:' may be used), it is
necessary in some cases to specify the service and the URI scheme
used.
The service parameters defined in RFC 3761 [2] therefore allow a
'type' and a 'subtype' to be specified. Within this set of
specifications, it is assumed that the 'type' (being the more generic
term) defines the service and the 'subtype' defines the URI scheme.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 [1].
Enumservice Name: "web"
Enumservice Type: "web"
Enumservice Subtype: "http"
URI Scheme: 'http:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of being a source of information.
Note that the kind of information retrieved can be manifold.
Usually, contacting a resource by an 'http:' [11] URI provides a
document. This document can contain references that will trigger the
download of many different kinds of information, such as audio,
video, or executable code. Thus, one cannot be more specific about
the kind of information expected when contacting the resource.
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Security Considerations:
There are no specific security issues with this 'Enumservice'.
However, the general considerations of Section 5 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author contact
detail, see the Authors' Addresses section)
Any other information the author deems interesting:
None
Enumservice Name: "web"
Enumservice Type: "web"
Enumservice Subtype: "https"
URI Scheme: 'https:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is capable of being a source of information,
which can be contacted by using TLS or the Secure Socket Layer
protocol.
Note that the kind of information retrieved can be manifold.
Usually, contacting a resource by an 'https:' URI [12] provides a
document. This document can contain many different kinds of
information, such as audio, video, or executable code. Thus, one
cannot be more specific about what information to expect when
contacting the resource.
Security Considerations:
There are no specific security issues with this 'Enumservice'.
However, the general considerations of Section 5 apply.
Intended Usage: COMMON
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Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author contact
detail, see the Authors' Addresses section)
Any other information the author deems interesting:
None
Enumservice Name: "ft"
Enumservice Type: "ft"
Enumservice Subtype: "ftp"
URI Scheme: 'ftp:'
Functional Specification:
This Enumservice indicates that the resource identified by the
associated URI scheme is a service usable in the manner specified for
ftp: in RFC 1738 [10], for instance, file retrieval.
Security Considerations:
There are no specific security issues with this 'Enumservice'.
However, the general considerations of Section 5 apply.
Intended Usage: COMMON
Authors:
Rudolf Brandner, Lawrence Conroy, Richard Stastny (for author contact
detail, see the Authors' Addresses section)
Any other information the author deems interesting:
None
As used by ENUM, DNS is a global, distributed database. Thus any
information stored there is visible to anyone anonymously. Although
this is not qualitatively different from publication in a telephone
directory, it does expose the data subject to having "their"
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information collected automatically without any indication that this
has been done, or by whom.
Data harvesting by third parties is often used to generate lists of
targets for unrequested information; in short, it is used to address
"spam". Anyone who uses a Web-archived mailing list is aware that
the volume of "spam" email they receive increases when they post to
the mailing list; publication of a telephone number in ENUM is no
different and may be used to send "junk faxes" or "junk SMS", for
example.
Many mailing list users have more than one email address and use
"sacrificial" email accounts when they post to these lists to help
filter out unrequested emails. This is not so easy with published
telephone numbers; the PSTN E.164 number assignment process is much
more involved, and usually a single E.164 number (or a fixed range of
numbers) is associated with each PSTN access. Thus, providing a
"sacrificial" phone number in any publication is not possible.
Due to the implications of publishing data on a globally accessible
database, as a principle the data subject MUST give explicit informed
consent when data is published in ENUM.
In addition, the data subject should be made aware that, due to
storage of such data during harvesting by third parties, removal of
the data from publication will not remove any copies that have been
taken; in effect, any publication may be permanent.
However, regulations in many regions will require that the data
subject can at any time request that the data is removed from
publication, and that consent for its publication is explicitly
confirmed at regular intervals.
The user SHOULD be asked to confirm opening a web page or starting an
ftp session (particularly if the ftp client is configured to send the
user's email address as an "anonymous" user password).
Using a web:http or ft:ftp service is not secure, so the user should
apply the same caution when entering personal data as they would do
if using a client application started with any other method.
Although this is not a feature of ENUM or these Enumservices, the
ENUM-using application on the end system may appear different from
the user's "normal" browser, so the user SHOULD receive an indication
of whether their communication is secured.
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As evaluating a web page can involve execution of embedded (or
linked) content that may include executable code, evaluating a web
URL involves risks. If automatic evaluation of a web link were to be
used, the querying user would be exposed to risks associated with
that automatic download and execution of content. Thus, the client
MUST ask the querying user for confirmation before evaluating the web
URL; the client MUST NOT download and evaluate the web content
automatically.
An analysis of threats specific to the dependence of ENUM on the DNS,
(threats against which are covered in [14]) and the applicability of
DNSSEC [13] to these, is provided in RFC 3761 [2].
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", RFC 3761, April 2004.
[3] ITU-T, "The International Public Telecommunication Number
Plan", Recommendation E.164 , May 1997.
[4] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[5] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
One: The Comprehensive DDDS", RFC 3401, October 2002.
[6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Two: The Algorithm", RFC 3402, October 2002.
[7] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database", RFC 3403,
October 2002.
[8] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Four: The Uniform Resource Identifiers (URI)", RFC 3404,
October 2002.
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[9] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Five: URI.ARPA Assignment Procedures", BCP 65, RFC 3405,
October 2002.
[10] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
[11] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,
L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol
-- HTTP/1.1", RFC 2616, June 1999.
[12] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[13] Arends, R. and et al., "Protocol Modifications for the DNS
Security Extensions", Work in Progress.
[14] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
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Authors' Addresses
Rudolf Brandner
Siemens AG
Hofmannstr. 51
81359 Munich
Germany
Phone: +49-89-722-51003
EMail: rudolf.brandner@siemens.com
Lawrence Conroy
Siemens Roke Manor Research
Roke Manor
Romsey
United Kingdom
Phone: +44-1794-833666
EMail: lwc@roke.co.uk
Richard Stastny
Oefeg
Postbox 147
1103 Vienna
Austria
Phone: +43-664-420-4100
EMail: richard.stastny@oefeg.at
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Full Copyright Statement
Copyright (C) The Internet Society (2005).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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Brandner, et al. Standards Track [Page 10]