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Network Working Group                                        S. Cheshire
Internet-Draft                                               D. Schinazi
Updates: 7050 (if approved)                                   Apple Inc.
Intended status: Standards Track                            May 24, 2016
Expires: November 25, 2016


                Special Use Domain Name 'ipv4only.arpa'
                draft-cheshire-sudn-ipv4only-dot-arpa-02

Abstract

   The document "Discovery of the IPv6 Prefix Used for IPv6 Address
   Synthesis" [RFC7050] specifies the Special Use Domain Name
   'ipv4only.arpa', with certain precise special properties, but,
   perversely, the Domain Name Reservation Considerations section
   [RFC6761] in that document then goes on to deny the specialness of
   that name, and (as of May 2016) the name 'ipv4only.arpa' does not
   appear in the Special-Use Domain Names registry.

   This document updates RFC 7050 with a more appropriate summary of the
   legitimate and useful special properties of the name 'ipv4only.arpa',
   and the corresponding reverse mapping names.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 25, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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1.  Introduction

   The document "Discovery of the IPv6 Prefix Used for IPv6 Address
   Synthesis" [RFC7050] specifies the Special Use Domain Name
   'ipv4only.arpa', with certain precise special properties, but,
   perversely, the Domain Name Reservation Considerations section
   [RFC6761] in that document denies the specialness of that name, and
   (as of May 2016) the name 'ipv4only.arpa' does not appear in the
   Special-Use Domain Names registry [SUDN].

   As a result of the name 'ipv4only.arpa' being formally declared to
   have no special properties, there was no mandate for software to
   treat this name specially.  Consequently, queries for this name have
   to be handled normally, and result in a large volume of unnecessary
   queries to the 'arpa' name servers.

   Having millions of devices around the world issue these queries
   generates pointless additional load on the 'arpa' name servers, which
   is completely unnecessary when the name 'ipv4only.arpa' is defined,
   by Internet Standard, to have only two IPv4 address records,
   192.0.0.170 and 192.0.0.171, and no other records of any type.

   At times, for reasons that are as yet unclear, the 'arpa' name
   servers have been observed to be slow or unresponsive.  The failures
   of these 'ipv4only.arpa' queries result in unnecessary failures of
   software that depends on them for NAT64 address synthesis.

   To remedy this situation, this document updates RFC 7050 with a more
   appropriate Domain Name Reservation Considerations section [RFC6761]
   that properly lists the desirable and beneficial special handling for
   'ipv4only.arpa'.


2.  Conventions and Terminology Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].



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3.  Security Considerations

   Hard-coding the answers for 'ipv4only.arpa' queries avoids the risk
   of malicious devices intercepting those queries and returning
   incorrect answers.

   DNSSEC signing issues for the 'ipv4only.arpa' address records don't
   apply, since the only use of the 'ipv4only.arpa' name is to trigger
   synthesis of NAT64 AAAA records, which aren't signed by arpa anyway.


4.  IANA Considerations

   [Once published, this should say]

   IANA has recorded the following names in the
   Special-Use Domain Names registry [SUDN]:
      ipv4only.arpa
      170.0.0.192.in-addr.arpa
      171.0.0.192.in-addr.arpa

   IANA has recorded the following IPv4 addresses in the
   IPv4 Special-Purpose Address Registry [SUv4]:
      192.0.0.170
      192.0.0.171


























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5.  Domain Name Reservation Considerations

5.1.  ipv4only.arpa

   The name 'ipv4only.arpa' is defined, by Internet Standard, to have
   two IPv4 address records with rdata 192.0.0.170 and 192.0.0.171.

   When queried via a DNS64 recursive/caching server, the name
   'ipv4only.arpa' is defined to also have two IPv6 AAAA records, with
   rdata synthesized from a combination of the NAT64 IPv6 prefix, and
   the IPv4 addresses 192.0.0.170 and 192.0.0.171.  This can return more
   than one pair of v6 addresses if there are multiple NAT64 prefixes.

   The name 'ipv4only.arpa' has no other DNS records of any type.

   The name 'ipv4only.arpa' is special only to
   (a) client software wishing to perform NAT64 address synthesis, and
   (b) the DNS64 server responding to such requests.
   These two considerations are listed in items 2 and 4 below:

   1.  Normal users should never have reason to encounter the
       'ipv4only.arpa' domain name.  If they do, queries for
       'ipv4only.arpa' should result in the answers specified in RFC
       7050.
       Normal users have no need to know that 'ipv4only.arpa' is
       special.

   2.  Application software may explicitly use the name 'ipv4only.arpa'
       for NAT64 address synthesis, and expect to get the answers
       specified in RFC 7050.  If application software encounters the
       name 'ipv4only.arpa' in the normal course of handling user input,
       the application software should resolve that name as usual and
       need not treat it in any special way.

   3.  Name resolution APIs and libraries SHOULD NOT recognize
       'ipv4only.arpa' as special and SHOULD NOT treat it differently.
       Name resolution APIs SHOULD send queries for this name to their
       configured recursive/caching DNS server(s).













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   4.  Recursive/caching DNS servers SHOULD recognize 'ipv4only.arpa' as
       special and SHOULD NOT, by default, attempt to look up NS records
       for it, or otherwise query authoritative DNS servers in an
       attempt to resolve this name.  Instead, recursive/caching DNS
       servers SHOULD, by default, act as authoritative and generate
       immediate responses for all such queries.

       Traditional recursive/caching DNS servers that act as
       authoritative for this name MUST generate only the 192.0.0.170
       and 192.0.0.171 responses for IPv4 address queries (DNS qtype
       "A"), and a "no error no answer" response for all other query
       types.  An example configuration for BIND 9 to achieve this
       result is given in Appendix A.

       All DNS64 recursive/caching DNS servers MUST generate the
       192.0.0.170 and 192.0.0.171 responses for IPv4 address queries
       (DNS qtype "A"), the appropriate synthesized IPv6 address record
       responses for IPv6 address queries (DNS qtype "AAAA"), and a
       "no error no answer" response for all other query types.
       This local self-contained generation of these responses is to
       avoid placing unnecessary load on the 'arpa' name servers.

   5.  Traditional authoritative DNS server software need not recognize
       'ipv4only.arpa' as special or handle it in any special way.
       As a practical matter, only the administrators of the 'arpa'
       namespace will configure their name servers to be authoritative
       for this name and to generate the appropriate answers; all other
       authoritative name servers will not be configured to know
       anything about this name and will reject queries for it as they
       would reject queries for any other name about which they have no
       information.

   6.  Generally speaking, operators of authoritative DNS servers need
       not know anything about the name 'ipv4only.arpa', just as they
       don't need to know anything about any other names they are not
       responsible for.  Operators of authoritative DNS servers who are
       configuring their name servers to be authoritative for this name
       MUST understand that 'ipv4only.arpa' is a special name, with
       answers specified by Internet Standard (generally this applies
       only to the administrators of the 'arpa' namespace).

   7.  DNS Registries/Registrars need not know anything about the name
       'ipv4only.arpa', just as they don't need to know anything about
       any other name they are not responsible for.  Only the
       administrators of the 'arpa' namespace need to be aware of this
       name's purpose and how it should be configured.





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5.2.  170.0.0.192.in-addr.arpa and 171.0.0.192.in-addr.arpa

   Since the IPv4 addresses 192.0.0.170 and 192.0.0.171 are defined to
   be special, and are listed in the IPv4 Special-Purpose Address
   Registry [SUv4], the corresponding reverse mapping names in the
   in-addr.arpa domain are similarly special.

   The name '170.0.0.192.in-addr.arpa' is defined, by Internet Standard,
   to have only a single DNS record, type PTR, with rdata
   'ipv4only.arpa'.

   The name '171.0.0.192.in-addr.arpa' is defined, by Internet Standard,
   to have only a single DNS record, type PTR, with rdata
   'ipv4only.arpa'.

   Practically speaking these two names are rarely used, but to the
   extent that they may be, they are special only to recursive/caching
   DNS servers as described in item 3 below:

   1.  Normal users should never have reason to encounter these two
       reverse mapping names.  However, if they do, queries for these
       reverse mapping names should return the expected answer
       'ipv4only.arpa'.  Normal users have no need to know that these
       reverse mapping names are special.

   2.  Application software SHOULD NOT recognize these two reverse
       mapping names as special, and SHOULD NOT treat them differently.
       For example, if the user were to issue the Unix command
       "host 192.0.0.170" then the "host" command should issue the query
       as usual and display the result that is returned.

   3.  Name resolution APIs and libraries SHOULD NOT recognize these two
       reverse mapping names as special and SHOULD NOT treat them
       differently.  Name resolution APIs SHOULD send queries for these
       names to their configured recursive/caching DNS server(s).

   4.  Recursive/caching DNS servers SHOULD recognize these two reverse
       mapping names as special and SHOULD NOT, by default, attempt to
       look up NS records for them, or otherwise query authoritative DNS
       servers in an attempt to resolve them.  Instead, recursive/
       caching DNS servers SHOULD, by default, act as authoritative and
       generate immediate responses for all such queries.

       Recursive/caching DNS servers that act as authoritative for these
       names MUST generate only the 'ipv4only.arpa' response for PTR
       queries, and a "no error no answer" response for all other query
       types.  This local self-contained generation of these responses
       is to avoid placing unnecessary load on the 'in-addr.arpa' name



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       servers.

   5.  Traditional authoritative DNS server software need not recognize
       these two reverse mapping names as special or handle them in any
       special way.
       As a practical matter, only the administrators of the
       'in-addr.arpa' namespace will configure their name servers to be
       authoritative for these names and to generate the appropriate
       answers; all other authoritative name servers will not be
       configured to know anything about these names and will reject
       queries for them as they would reject queries for any other name
       about which they have no information.

   6.  Generally speaking, operators of authoritative DNS servers need
       not know anything about these two reverse mapping names, just as
       they don't need to know anything about any other names they are
       not responsible for.  Operators of authoritative DNS servers who
       are configuring their name servers to be authoritative for this
       name MUST understand that these two reverse mapping names are
       special, with answers specified by Internet Standard (generally
       this applies only to the administrators of the 'in-addr.arpa'
       namespace).

   7.  DNS Registries/Registrars need not know anything about these two
       reverse mapping names, just as they don't need to know anything
       about any other name they are not responsible for.  Only the
       administrators of the 'in-addr.arpa' namespace need to be aware
       of the purpose of these two names.

5.3.  ip6.arpa Reverse Mapping PTR Records

   For all IPv6 addresses synthesized by the NAT64 gateway, the DNS64
   recursive/caching server is responsible for synthesizing the
   appropriate ip6.arpa reverse mapping PTR records, if it chooses to do
   so.  The same applies to the synthesized IPv6 addresses corresponding
   to the IPv4 addresses 192.0.0.170 and 192.0.0.171.

   Generally a DNS64 recursive/caching server synthesizes appropriate
   ip6.arpa reverse mapping PTR records by extracting the embedded IPv4
   address from the encoded IPv6 address, performing a reverse mapping
   query for that IPv4 address, and then synthesizing a corresponding
   ip6.arpa reverse mapping PTR record containing the same rdata.

   In the case of synthesized IPv6 addresses corresponding to the IPv4
   addresses 192.0.0.170 and 192.0.0.171, the DNS64 recursive/caching
   server does not issue mapping queries for those IPv4 addresses, but
   instead, according to rule 3 above, immediately returns the answer
   'ipv4only.arpa'.



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6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <http://www.rfc-editor.org/info/rfc6761>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <http://www.rfc-editor.org/info/rfc7050>.

6.2.  Informative References

   [SUDN]     "Special-Use Domain Names Registry", <https://
              www.iana.org/assignments/special-use-domain-names/>.

   [SUv4]     "IANA IPv4 Special-Purpose Address Registry", <https://
              www.iana.org/assignments/iana-ipv4-special-registry/>.


























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Appendix A.  Example BIND 9 Configuration

   A BIND 9 recursive/caching DNS server could be configured to act as
   authoritative for the appropriate names as follows.


   In /etc/named.conf the following lines are added:

    zone "ipv4only.arpa"            { type master; file "ipv4only"; };
    zone "170.0.0.192.in-addr.arpa" { type master; file "ipv4only-r"; };
    zone "171.0.0.192.in-addr.arpa" { type master; file "ipv4only-r"; };


   The file /var/named/ipv4only is created with the following content:

    $TTL 86400               ; Default TTL 24 hours
    @ IN SOA nameserver.example. admin.nameserver.example. (
             2016052400      ; Serial
             7200            ; Refresh ( 7200 = 2 hours)
             3600            ; Retry   ( 3600 = 1 hour)
             15724800        ; Expire  (15724800 = 6 months)
             60              ; Minimum
             )
    @ IN NS  nameserver.example.

    @ IN A   192.0.0.170
    @ IN A   192.0.0.171


   The file /var/named/ipv4only-r is created with the following content:

    $TTL 86400               ; Default TTL 24 hours
    @ IN SOA nameserver.example. admin.nameserver.example. (
             2016052400      ; Serial
             7200            ; Refresh ( 7200 = 2 hours)
             3600            ; Retry   ( 3600 = 1 hour)
             15724800        ; Expire  (15724800 = 6 months)
             60              ; Minimum
             )
    @ IN NS  nameserver.example.

    @ IN PTR ipv4only.arpa.









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Authors' Addresses

   Stuart Cheshire
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   USA

   Phone: +1 408 974 3207
   Email: cheshire@apple.com


   David Schinazi
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   USA

   Phone: +1 669 227 9921
   Email: dschinazi@apple.com































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