E.164 number and DNS
RFC 2916

Document Type RFC - Proposed Standard (September 2000; Errata)
Obsoleted by RFC 3761
Author Patrik Fältström 
Last updated 2020-01-21
Replaces draft-faltstrom-e164
Stream IETF
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Network Working Group                                        P. Faltstrom
Request for Comments: 2916                             Cisco Systems Inc.
Category: Standards Track                                  September 2000

                          E.164 number and DNS

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 (2000).  All Rights Reserved.


   This document discusses the use of the Domain Name System (DNS) for
   storage of E.164 numbers.  More specifically, how DNS can be used for
   identifying available services connected to one E.164 number.
   Routing of the actual connection using the service selected using
   these methods is not discussed.

1. Introduction

   Through transformation of E.164 numbers into DNS names and the use of
   existing DNS services like delegation through NS records, and use of
   NAPTR [1] records in DNS [2] [3], one can look up what services are
   available for a specific domain name in a decentralized way with
   distributed management of the different levels in the lookup process.

1.1 Terminology

   The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
   in this document are to be interpreted as described in RFC2119 [4].

2. E.164 numbers and DNS

   The domain "e164.arpa" is being populated in order to provide the
   infrastructure in DNS for storage of E.164 numbers.  In order to
   facilitate distributed operations, this domain is divided into
   subdomains.  Holders of E.164 numbers which want to be listed in DNS

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RFC 2916                  E.164 number and DNS            September 2000

   should contact the appropriate zone administrator in order to be
   listed, by examining the SOA resource record associated with the
   zone, just like in normal DNS operations.

   Of course, as with other domains, policies for such listings will be
   controlled on a subdomain basis and may differ in different parts of
   the world.

   To find the DNS names for a specific E.164 number, the following
   procedure is to be followed:

  1.  See that the E.164 number is written in its full form, including
      the countrycode IDDD.  Example: +46-8-9761234

  2.  Remove all non-digit characters with the exception of the leading
      '+'.  Example: +4689761234

  3.  Remove all characters with the exception of the digits.  Example:

  4.  Put dots (".") between each digit.  Example:

  5.  Reverse the order of the digits.  Example:

  6.  Append the string ".e164.arpa" to the end.  Example:

2.1 Special note about the '+'

   The '+' is kept in stage 2 in section 2 to flag that the number which
   the regular expression is operating on is a E.164 number.  Future
   work will be needed to determine how other numbering plans (such as
   closed ones) might be identified.  It is possible, but not definite,
   that they would use a similar mechanism as the one described in this

3. Fetching URIs given an E.164 number

   For a record in DNS, the NAPTR record is used for identifying
   available ways of contacting a specific node identified by that name.
   Specifically, it can be used for knowing what services exists for a
   specific domain name, including phone numbers by the use of the
   e164.arpa domain as described above.

   The identification is using the NAPTR resource record defined for use
   in the URN resolution process, but it can be generalized in a way
   that suits the needs specified in this document.

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RFC 2916                  E.164 number and DNS            September 2000

   It is the string which is the result of step 2 in section 2 above
   which is input to the NAPTR algorithm.

3.1 The NAPTR record

   The key fields in the NAPTR RR are order, preference, service, flags,
   regexp, and replacement.  For a detailed description, see:

   o  The order field specifies the order in which records MUST be
      processed when multiple NAPTR records are returned in response to
      a single query.

   o  The preference field specifies the order in which records SHOULD
      be processed when multiple NAPTR records have the same value of

   o  The service field specifies the resolution protocol and resolution
      service(s) that will be available if the rewrite specified by the
      regexp or replacement fields is applied.

   o  The flags field contains modifiers that affect what happens in the
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