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.
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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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