Network Working Group                                    J. Klensin, Ed.
Request for Comments: 3245                                           IAB
Category: Informational                                       March 2002


      The History and Context of Telephone Number Mapping (ENUM)
      Operational Decisions: Informational Documents Contributed
                     to ITU-T Study Group 2 (SG2)

Status of this Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

  RFC 2916 assigned responsibility for a number of administrative and
  operational details of Telephone Number Mapping (ENUM) to the IAB.
  It also anticipated that ITU would take responsibility for
  determining the legitimacy and appropriateness of applicants for
  delegation of "country code"-level subdomains of the top-level ENUM
  domain.  Recently, three memos have been prepared for the ITU-T Study
  Group 2 (SG2) to explain the background of, and reasoning for, the
  relevant decisions.  The IAB has also supplied a set of procedural
  instructions to the RIPE NCC for implementation of their part of the
  model.  The content of the three memos is provided in this document
  for the information of the IETF community.

Table of Contents

  1. Introduction: ENUM Background Information .....................  2
  2. Why one and only one domain is used in ENUM ...................  2
  3. Why .ARPA was selected as the top level domain for ENUM .......  4
  4. The selection of an operator for E164.ARPA ....................  7
  5. Procedures to be followed by RIPE NCC .........................  8
  6. References ....................................................  8
  6.1. Normative references ........................................  8
  6.2. Informative and explanatory references ......................  8
  7. Security Considerations .......................................  9
  8. IANA Considerations ...........................................  9
  9. Authors' Addresses ............................................  9
  10. Full Copyright Statement ..................................... 10




Klensin                      Informational                      [Page 1]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


1. Introduction: ENUM Background Information

  In January 2002, in response to questions from the ITU-T Study Group
  2 (referred to just as "SG2", below), specifically its group working
  on "Questions 1 and 2", and members of the IETF and
  telecommunications communities, Scott Bradner, as Area Director
  responsible for the ENUM work and ISOC Vice President for Standards,
  initiated an effort to produce explanations of the decisions made by
  the IETF about ENUM administration.  The effort to produce and refine
  those documents eventually involved him, Patrik Faltstrom (author of
  RFC 2916), and several members of the IAB.

  The documents have now been contributed to ITU-T, and are being
  published as internal SG2 documents.  This document provides the IETF
  community a copy of the information provided to SG2.  Section 2 below
  contains the same content as COM 2-11-E, section 3 contains the same
  content as COM 2-12-E, and section 4 contains the same content as SG2
  document COM 2-10-E.  The documents being published within SG2 show
  their source as "THE INTERNET SOCIETY ON BEHALF OF THE IETF", which
  is a formality deriving from the fact that ISOC holds an ITU sector
  membership on behalf of the IETF.

2. Why one and only one domain is used in ENUM

2.1. Introduction

  This contribution is one of a series provided by the IETF to ITU-T
  SG2 to provide background information about the IETF's ENUM Working
  Group deliberations and decisions.  This particular contribution
  addresses the IETF's decision that only a single domain could be
  supported in ENUM.

2.2. The need for a single root in the DNS

  In the Domain Name System (DNS), each domain name is globally unique.
  This is a fundamental fact in the DNS system and follows
  mathematically from the structure of that system as well as the
  resource identification requirements of the Internet.  Which DNS
  server is authoritative for a specific domain is defined by
  delegations from the parent domain, and this is repeated recursively
  until the so-called root zone, which is handled by a well-known set
  of DNS servers.  Note that words like "authoritative" and
  "delegation" and their variations are used here in their specific,
  technical, DNS sense and may not have the same meanings they normally
  would in an ITU context.






Klensin                      Informational                      [Page 2]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


  Given that one starts with the well-known root zone, every party
  querying the DNS system will end up at the same set of servers for
  the same domain, regardless of who is sending the query, when the
  query is sent and where in the network the query is initiated.  In
  May 2000 the IAB published a document on the need for a single root
  in the DNS.  This document explores the issues in greater detail.
  See RFC 2826 (http://www.ietf.org/rfc/rfc2826.txt).

2.3. Storing E.164 numbers in the DNS

  An E.164 number is also globally unique, and because of that it has
  most of the same properties as a domain name.  This was the reason
  why storing E.164 numbers in the DNS system is technically a simple
  mapping.  ENUM is just that, a way to store E.164 numbers in the DNS.
  Multiple ENUM trees in the DNS hierarchy would have the telephony
  equivalent of permitting every carrier to assign a different meaning
  to an E.164 country code, with each one potentially mapping a given
  number to a different circuit or rejecting it entirely.  For the
  Internet, if there were multiple trees, there would be no way to
  determine which domains might contain ENUM records.  Thus, each
  application that uses ENUM facilities would have to be manually
  configured with a list of domains to be searched.  This would incur
  the same problems of scaling and updates that led to the development
  of the DNS.

  The goal with ENUM is that one party should be able to look up
  information in DNS, which another party has stored in DNS.  This must
  be possible with only the E.164 number as input to the algorithm.

  If the party storing information in DNS has two (or more) places to
  choose from, and chooses one of them, how is a second party looking
  up things to know what place was selected?  An analogy would be if
  one knew only www.whitehouse, and not the TLD, and ask people to go
  to that website.  Is the correct domain name www.whitehouse.gov,
  www.whitehouse.com or www.whitehouse.se?  It should be noted that
  www.whitehouse.com exists and is a pornography site.

  Thus, the only way of knowing where to look up E.164/ENUM numbers in
  DNS is to use one and only one domain, and have everyone agree on
  what that domain is.  Note that ENUM is a system for use with E.164
  numbers in their general, global, context.  Nothing technical can, or
  should, try to prevent parties that wish to use ENUM-like mechanisms,
  or other systems that have the same general structure as telephone
  numbers, from working out private, out of band, agreements to support
  those applications.  However, such applications are neither E.164 nor
  ENUM, any more than internal extension numbers in a PBX are normally
  considered to be part of either.




Klensin                      Informational                      [Page 3]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


3. Why .ARPA was selected as the top level domain for ENUM

3.1. Introduction

  This memo is one of a series provided by the IETF to SG2 to provide
  background information about the IETF's ENUM Working Group
  deliberations and decisions.  This particular memo addresses the
  IETF's decision that the ENUM DNS tree would use the .ARPA top level
  domain.

3.2. IAB Statement on Infrastructure Domain and Subdomains

  (Taken from http://www.iab.org/iab/DOCUMENTS/iab-arpa-stmt.txt, May
  2000.)

  Over the last several months, the IAB has been reviewing, and
  discussing with ICANN and other parties, the handling of various
  Internet Protocol-related infrastructure components that the
  community has concluded should be placed into the DNS.

  Historically, the most visible infrastructure domain has been the
  IPv4 address reverse-mapping domain.  This domain was placed in "in-
  addr.arpa" as part of the initial ARPANET transition strategy from
  host table naming (see RFC 881-http://www.ietf.org/rfc/ rfc0881.txt).
  Other than the IPv4 reverse-mapping subdomain, it became the only
  active subdomain of that domain as the <host-table-name>.ARPA names
  that were also part of the transition were gradually removed.  Other
  infrastructure domains were, in the past, placed under the "INT" TLD
  and various organizational names.

  It is in the interest of general Internet stability, to pay adequate
  attention to the placement of secondary DNS servers, and
  administrative cleanliness, to start rationalizing this situation by
  locating new infrastructure subdomains in a single domain and
  migrating existing ones to it as appropriate.  It appears that our
  original infrastructure domain "ARPA", redesignated from an
  abbreviation for "ARPANET" to an acronym for "Address and Routing
  Parameters Area" is best suited for this purpose.

3.3. Infrastructure subdomains

  Operationally, it is easier to ensure good stability for DNS in
  general if we have as few DNS zones as possible that are used for
  parameters for infrastructure purposes.  Today, new infrastructure
  domains are put in ARPA and old assignments which were made in other
  domains are being migrated to ARPA.  Currently, ARPA is used for in-
  addr.arpa (for reverse mapping of IPv4 addresses), ip6.arpa, (for




Klensin                      Informational                      [Page 4]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


  reverse mapping of IPv6 addresses), and e164.arpa, (the subject of
  this memo).  In the future, URI schemes, URN namespaces and other new
  address families will be stored in ARPA.

  Theoretically, each set of infrastructure parameters could be stored
  in a separate domain as a TLD.  (For example, .URI, .UNI, .IPV6, new
  TLD, which only can be created via the ICANN process (which might
  take a year or more) and would unnecessarily and undesirably flatten
  the DNS tree.  It is much easier to have one TLD with easily created
  new subdomains (2nd level domains), one for each parameter.  Thus it
  was logical to store E.164 numbers in ARPA.

3.4. The ARPA domain (derived from RFC 3172, September 2001)

  The "arpa" domain was originally established as part of the initial
  deployment of the DNS, to provide a transition mechanism from the
  Host Tables that were previously standard in the ARPANET.  It was
  also used to provide a permanent home for IPv4 address to name
  mappings ("reverse mappings") which were previously also handled
  using the Host Table mechanism.  The Internet Architecture Board
  (IAB), in cooperation with the Internet Corporation for Assigned
  Names and Numbers (ICANN), is currently responsible for managing the
  Top Level Domain (TLD) name "arpa".  This arrangement is documented
  in Appendix A of RFC 3172.  This domain name provides the root of the
  name hierarchy of the reverse mapping of IP addresses to domain
  names.  More generally, this domain name undertakes a role as a
  limited use domain for Internet infrastructure applications, by
  providing a name root for the mapping of particular protocol values
  to names of service entities.  This domain name provides a name root
  for the mapping of protocol values into lookup keys to retrieve
  operationally critical protocol infrastructure data records or
  objects for the Internet.

  The IAB may add other infrastructure uses to the "arpa" domain in the
  future.  Any such additions or changes will be in accordance with the
  procedures documented in Section 2.1 and Section 3 of this document.
  [referring to RFC 3172] This domain is termed an "infrastructure
  domain", as its role is to support the operating infrastructure of
  the Internet.  In particular, the "arpa" domain is not to be used in
  the same manner (e.g., for naming hosts) as other generic Top Level
  Domains are commonly used.

  The operational administration of this domain, in accordance with the
  provisions described in this document, shall be performed by the IANA
  under the terms of the MoU between the IAB and ICANN concerning the
  IANA [RFC 2860].





Klensin                      Informational                      [Page 5]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


3.5. Assignment of the .ARPA top level domain

  As documented in appendix A of RFC 3172, on April 28, 2000 the US
  Department of Commerce, acting under the authority of its purchase
  order with ICANN, directed ICANN to operate the .ARPA TLD under the
  guidance of the IAB, as a limited use domain for internet
  infrastructure applications.

3.6. Name Server Requirements for .ARPA (from RFC 3172)

  As this domain is part of the operationally critical infrastructure
  of the Internet, the stability, integrity and efficiency of the
  operation of this domain is a matter of importance for all Internet
  users.

  The "arpa" domain is positioned as a top level domain in order to
  avoid potential operational instabilities caused by multiple DNS
  lookups spanning several operational domains that would be required
  to locate the servers of each of the parent names of a more deeply
  nested infrastructure name.  The maximal lookup set for ARPA is a
  lookup of the name servers for the "arpa" domain from a root server,
  and the query agent is then provided with a list of authoritative
  "arpa" name servers.

  The efficient and correct operation of the "arpa" domain is
  considered to be sufficiently critical that the operational
  requirements for the root servers apply to the operational
  requirements of the "arpa" servers.  All operational requirements
  noted in RFC 2870, as they apply to the operational requirements of
  the root servers, shall apply to the operation of the "arpa" servers.
  Any revision to RFC 2870 in relation to the operation of the root
  servers shall also apply to the operation of the "arpa" servers.

  Many of the servers that are authoritative for the root zone (or the
  "." zone) also currently serve as authoritative for the "arpa" zone.
  As noted in RFC 2870, this arrangement is likely to change in the
  future.

3.7. Summary: ENUM use of .ARPA

  The ARPA domain is the preferred TLD for infrastructure and parameter
  use.  The ENUM structure should be placed in a single domain subtree
  (see separate contribution, COM 2-11), and is expected to evolve into
  important Internet infrastructure, and hence should be placed there.
  This decision is facilitated by the MOU between ICANN and IETF and
  the instructions from the US Government to ICANN, which provide for
  IAB supervision of that domain.  Despite some confusion with the name
  of a US Department of Defense agency, DARPA, these uses are



Klensin                      Informational                      [Page 6]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


  consistent with all of the historical uses of the ARPA domain, which
  have been for infrastructure purposes (initially when the
  hierarchical DNS was created to replace the old flat namespace of
  ARPANET): the domain was never used for any internal or specific
  DARPA purpose.  Recognizing the potential difficulties with multiple
  infrastructure domains, the Internet Architecture Board concluded in
  May 2000 that all new infrastructure information was to be stored in
  the ARPA domain and existing infrastructure subtrees migrated there
  as feasible.  http://www.iab.org/iab/DOCUMENTS/iab-arpa-stmt.txt
  provides additional context for these decisions.

  The ENUM Working Group decided to follow that recommendation.

4. The selection of an operator for E164.ARPA

4.1. Introduction

  This contribution is one of a series provided by the IETF to SG2 to
  provide background information about the IETF's ENUM Working Group
  deliberations and decisions.  This particular contribution addresses
  the IETF's selection of an operator for the E164.ARPA domain.

4.2. Name server operator requirements

  RFC 2870 (http://www.ietf.org/rfc/rfc2780.txt) describes the
  requirements for operating DNS root servers.  Important DNS-based
  infrastructure services require that their servers be operated with
  the same level of attention to reliability and security that the root
  servers require.  In addition, for an infrastructure service such as
  E164.ARPA some additional requirements were felt by the IAB to be
  important.  Organizations that operate core services such as IN-
  ADDR.ARPA and E164.ARPA must have a history of reliable operation of
  DNS servers and be highly respected and known for both their relevant
  technical skills and their fairness and impartiality.  In addition,
  the IAB felt that the organization that operates such infrastructure
  domains must be a non-profit and public-service-oriented one to
  remove any incentive for exploitative behavior based on profit
  motives that depend on, e.g., the number of records in the database
  even if some reasonable registration fee is charged to recover costs.
  The IAB also felt that they wanted an organization with good (and
  extensive) experience working with governments when necessary and one
  with experience working with the IAB and the IETF more generally.









Klensin                      Informational                      [Page 7]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


4.3. Evaluating possible operators

  The IAB researched various options for operators and came to the
  conclusion that the regional IP address registries (RIRs) met all of
  the criteria.  They all had extensive experience providing and
  supporting infrastructure services reliably and securely and all
  three of them had a long history of working with the IETF.

4.4. Selecting a particular operator

  Given that all of the RIRs would have met the criteria, the selection
  of a particular RIR required looking at other factors.  The IAB
  concluded that RIPE NCC would be the best operator for E164.ARPA,
  based largely on their somewhat greater experience in running DNS
  servers and on their location in a neutral legal jurisdiction.

4.5. Country administration of cc subdomains

  Of course, once a subdomain associated with a country code is
  assigned for registration and operations to an appropriately-
  designated entity for the associated country or numbering plan,
  administration of that subdomain is entirely a National Matter, with
  no involvement anticipated from the IAB/IETF, the E164.ARPA registry,
  or from the ITU.

5. Procedures to be followed by RIPE NCC

  The IAB and the RIPE NCC have agreed on procedures for the latter to
  follow in making ENUM registrations at the country code level.  Those
  instructions are expected to evolve as experience is accumulated.
  Current versions will be posted on the IAB and/or RIPE NCC web sites.

6. References

6.1. Normative references

  None.  This document is intended to be self-contained and purely
  informational.

6.2.  Informative and explanatory references.

  [RFC 2860] Carpenter, B., Baker, F. and M.  Roberts, "Memorandum of
             Understanding Concerning the Technical Work of the
             Internet Assigned Numbers Authority", RFC 2860, June 2000.

  [RFC 2870] Bush, R., Karrenberg, D., Kosters, M. and R. Plzak, "Root
             Name Server Operational Requirements", BCP 40, RFC 2870,
             June 2000.



Klensin                      Informational                      [Page 8]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


  [RFC 2916] Faltstrom, P., "E.164 number and DNS", RFC 2916, September
             2000.

  [RFC 3172] Huston, G., Ed., "Management Guidelines & Operational
             Requirements for the Address and Routing Parameter Area
             Domain ('arpa')", BCP 52, RFC 3172, September 2001.

7. Security Considerations

  This document provides information only and raises no new security
  issues.  The security issues associated with the underlying protocols
  are described in RFC 2916.

8. IANA Considerations

  There are no IANA considerations regarding this document.  Sections 3
  and 4 contain a record of actions already performed by IANA and
  partial explanations for them.

9.  Authors' Addresses

  Internet Architecture Board EMail:  [email protected]

     Membership at time this document was completed:

     Harald Alvestrand
     Ran Atkinson
     Rob Austein
     Fred Baker
     Steve Bellovin
     Brian Carpenter
     Jon Crowcroft
     Leslie Daigle
     Steve Deering
     Sally Floyd
     Geoff Huston
     John Klensin
     Henning Schulzrinne

  Scott Bradner
  EMail: [email protected]

  Patrik Faltstrom
  EMail: [email protected]







Klensin                      Informational                      [Page 9]

RFC 3245   History and Context of ENUM Operational Decisions  March 2002


10. Full Copyright Statement

  Copyright (C) The Internet Society (2002).  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
  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.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.



















Klensin                      Informational                     [Page 10]


You are viewing proxied material from gopher.fnord.one. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.