Special Use Domain Name 'ipv4only.arpa'
draft-cheshire-sudn-ipv4only-dot-arpa-10
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| Document | Type | Active Internet-Draft (individual) | |
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| Authors | Stuart Cheshire , David Schinazi | ||
| Last updated | 2018-07-02 | ||
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draft-cheshire-sudn-ipv4only-dot-arpa-10
Network Working Group S. Cheshire
Internet-Draft D. Schinazi
Updates: 7050 (if approved) Apple Inc.
Intended status: Standards Track July 2, 2018
Expires: January 3, 2019
Special Use Domain Name 'ipv4only.arpa'
draft-cheshire-sudn-ipv4only-dot-arpa-10
Abstract
The specification for how a client discovers its network's NAT64
prefix [RFC7050] defines the special name 'ipv4only.arpa' for this
purpose, but declares it to be a non-special name in that
specification's Domain Name Reservation Considerations section.
Consequently, despite the well articulated special purpose of the
name, 'ipv4only.arpa' was not recorded in the Special-Use Domain
Names registry as a name with special properties.
As a result of this omission, in cases where software needs to give
this name special treatment in order for it to work correctly, there
was no clear mandate authorizing software authors to implement that
special treatment. Software implementers were left with the choice
between not implementing the special behavior necessary for the name
queries to work correctly, or implementing the special behavior and
being accused of being noncompliant with some RFC.
This document formally declares the actual special properties of the
name, and adds similar declarations for 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."
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This Internet-Draft will expire on January 3, 2019.
Copyright Notice
Copyright (c) 2018 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
The specification for how a client discovers its network's NAT64
prefix [RFC7050] defines the special name 'ipv4only.arpa' for this
purpose, but declares it to be a non-special name in that
specification's Domain Name Reservation Considerations section.
Consequently, despite the well articulated special purpose of the
name, 'ipv4only.arpa' was not recorded in the Special-Use Domain
Names registry [SUDN] as a name with special properties.
This omission was discussed in the Special-Use Domain Names Problem
Statement [RFC8244].
As a result of this omission, in cases where software needs to give
this name special treatment in order for it to work correctly, there
was no clear mandate authorizing software authors to implement that
special treatment. Software implementers were left with the choice
between not implementing the special behavior necessary for the name
queries to work correctly, or implementing the special behavior and
being accused of being noncompliant with some RFC.
This document formally declares the actual special properties of the
name, and adds similar declarations for the corresponding reverse
mapping names.
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2. Conventions and Terminology Used in this Section
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY",
and "OPTIONAL" in this section are to be interpreted as described
in "Key words for use in RFCs to Indicate Requirement Levels",
when, and only when, they appear in all capitals, as shown here
[RFC2119] [RFC8174].
3. Specialness of 'ipv4only.arpa'
The hostname 'ipv4only.arpa' is peculiar in that it was never
intended to be treated like a normal hostname.
A typical client never looks up the IPv4 address records for
'ipv4only.arpa', because it is already known, by specification
[RFC7050], to have exactly two IPv4 address records, 192.0.0.170 and
192.0.0.171. No client ever has to look up the name in order to
learn those two addresses.
In contrast, clients often look up the IPv6 AAAA address records for
'ipv4only.arpa', which is contrary to general DNS expectations, given
that it is already known, by specification [RFC7050], that no such
IPv6 AAAA address records exist. And yet, clients expect to receive,
and do in fact receive, positive answers for these IPv6 AAAA address
records that are known to not exist.
This is clearly not a typical DNS name. In normal operation, clients
never query for the two records that do in fact exist; instead they
query for records that are known to not exist, and then get positive
answers to those abnormal queries. Clients are using DNS to perform
queries for this name, but they are certainly not using DNS to learn
legitimate answers from the name's legitimate authoritative server.
Instead, these clients have, in effect, co-opted the DNS protocol as
an impromptu client-to-middlebox communication protocol, to
communicate with the NAT64/DNS64 [RFC6146] [RFC6147] gateway, if
present, and request that it disclose the prefix it is using for IPv6
address synthesis.
It is this use of specially-crafted DNS queries as an impromptu
client-to-middlebox communication protocol that makes the name
'ipv4only.arpa' most definitely a special name, and one that needs to
be listed in IANA's registry along with other DNS names that have
special uses [SUDN].
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4. Consequences of 'ipv4only.arpa' previously being declared unspecial
As a result of the original specification [RFC7050] not formally
declaring 'ipv4only.arpa' to have special properties, there was no
mandate for any DNS software to treat this name specially.
Consequently, queries for this name had to be handled normally,
resulting in unnecessary queries to the authoritative 'arpa' name
servers.
Having millions of devices around the world issue these queries
generated pointless additional load on the authoritative 'arpa' name
servers, which was completely unnecessary when the name
'ipv4only.arpa' is defined, by Internet Standard, to have exactly two
IPv4 address records, 192.0.0.170 and 192.0.0.171, and no other IPv4
or IPv6 address records.
Also, at times, for reasons that remain unclear, the authoritative
'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 DNS64 [RFC6147] address
synthesis.
Even when the authoritative 'arpa' name servers are operating
correctly, having to perform an unnecessary query to obtain an answer
that is already known in advance can add precious milliseconds of
delay for no reason.
A more serious problem occurs when a device is configured to use a
recursive resolver other than the one it learned from the network.
Typically a device joining a NAT64 network will learn the recursive
resolver recommended for that network either via IPv6 Router
Advertisement Options for DNS Configuration [RFC6106] or via DNS
Configuration options for DHCPv6 [RFC3646]. On a NAT64 network it is
essential that the client use the DNS64 recursive resolver
recommended for that network, since only that recursive resolver can
be relied upon to know the appropriate prefix(es) to use for
synthesizing IPv6 addresses that will be acceptable to the NAT64
gateway.
However, it is increasingly common for users to manually override
their default DNS configuration because they wish to use some other
public recursive resolver on the Internet, which may offer better
speed, better reliability, or better privacy than the local network's
default recursive resolver. At the time of writing, examples of
widely known public recursive resolver services include 1.1.1.1,
8.8.8.8, and 9.9.9.9.
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Another common scenario is the use of corporate VPN client software,
which overrides the local network's default configuration to divert
DNS requests to the company's own private internal recursive
resolver, because the local network's recursive resolver will
typically be unable to provide answers for the company's private
internal host names. Similarly, the company's private internal
recursive resolver may not be able to synthesize IPv6 addresses
correctly for use with the local network's NAT64 gateway, because it
is unlikely to be aware of the NAT64 prefix in use on the local
network. It is clear that a single recursive resolver cannot meet
both needs. The local network's recursive resolver cannot give
answers for some company's private internal host names, and some
company's private internal recursive resolver cannot give correctly
synthesized IPv6 addresses suitable for the local network's NAT64
gateway.
The conflict here arises because DNS is being used for two unrelated
purposes. The first purpose is retrieving data from a (nominally)
global database -- generally retrieving the IP address(es) associated
with a hostname. The second purpose is using the DNS protocol as a
middlebox communication protocol, to interrogate the local network
infrastructure to discover the IPv6 prefix(es) in use by the local
NAT64 gateway for address synthesis.
Possibly this problem could have been avoided if we had forced all
NAT64 gateways to use the same Well-Known Prefix for IPv6 address
synthesis [RFC6052]. If the decision had been made to use a single
fixed Well-Known Prefix, then there would have been no need for
clients to discover the local network's NAT64 prefix, and no need for
the 'ipv4only.arpa' [RFC7050] query. However, that was not the
decision that was made.
This document leverages operational experience to update the Domain
Name Reservation Considerations [RFC6761] section of the earlier
specification [RFC7050] with one that accurately lists the actual
special properties of the name 'ipv4only.arpa', so that software can
legitimately implement the correct behavior necessary for better
performance, better reliability, and correct operation.
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5. Security Considerations
Hard-coding the known answers for 'ipv4only.arpa' queries in
recursive resolvers reduces the risk of malicious devices
intercepting those queries and returning incorrect answers,
particularly in the case of recursive resolvers that do not perform
DNSSEC validation.
One of the known concerns with DNS64 [RFC6147] is that it interferes
with DNSSEC. DNSSEC may cryptographically assert that a name has no
IPv6 AAAA records, while at the same time DNS64 address synthesis is
contradicting this and claiming that IPv6 AAAA records do exist.
Section 3 of the DNS64 specification [RFC6147] discusses this:
... DNS64 receives a query with the DO bit set and
the CD bit set. In this case, the DNS64 is supposed
to pass on all the data it gets to the query initiator.
This case will not work with DNS64, unless the
validating resolver is prepared to do DNS64 itself.
The NAT64 Prefix Discovery specification [RFC7050] provides the
mechanism for the query initiator to learn the NAT64 prefix so that
it can do its own validation and DNS64 synthesis as described above.
With this mechanism the client can (i) interrogate the local NAT64/
DNS64 gateway with an 'ipv4only.arpa' query to learn the IPv6 address
synthesis prefix, (ii) query for the (signed) IPv4 address records
itself, and then (iii) perform its own IPv6 address synthesis
locally, combining the IPv6 address synthesis prefix learned from the
local NAT64/DNS64 gateway with the secure DNSSEC-signed data learned
from the global Domain Name System.
It is conceivable that over time, if DNSSEC is successful, the
majority of clients could move to this validate-and-synthesize-
locally model, which reduces the DNS64 machinery to the vestigial
role of simply responding to the 'ipv4only.arpa' query to report the
local IPv6 address synthesis prefix. In no case does the client care
what answer(s) the authoritative 'arpa' name servers might give for
that query. The 'ipv4only.arpa' query is being used purely as a
local client-to-middlebox communication message.
This approach is even more attractive if it does not create an
additional dependency on the authoritative 'arpa' name servers to
answer a query that is unnecessary because the NAT64/DNS64 gateway
already knows the answer before it even issues the query. Avoiding
this unnecessary query improves performance and reliability for the
client, and reduces unnecessary load for the authoritative 'arpa'
name servers.
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Note that there are two security paths to consider here: The path
from the authoritative server to the DNS64 recursive resolver, and
the path from the DNS64 recursive resolver to the ultimate client.
On either or both paths there may be one or more DNS64-unaware
recursive resolvers.
The path from the authoritative server to the DNS64 recursive
resolver (queries for IPv4 address records) need not be protected by
DNSSEC, because the DNS64 recursive resolver already knows, by
specification, what the answers are. Run-time cryptographic
signatures are not needed to verify the value compile-time constants.
The path from the DNS64 recursive resolver to the ultimate client
(queries for IPv6 address records) *cannot* be protected by DNSSEC,
because the DNS64 recursive resolver is synthesizing IPv6 address
answers that cannot be assumed to be signed by the authoritative
server.
Consequently, the ipv4only.arpa zone MUST be an insecure delegation.
6. 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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7. Domain Name Reservation Considerations
7.1. Special Use Domain Name '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 [RFC6147] recursive resolver, the name
'ipv4only.arpa' is also defined to have IPv6 AAAA records, with rdata
synthesized from a combination of the NAT64 IPv6 prefix(es) and the
IPv4 addresses 192.0.0.170 and 192.0.0.171. This can return more
than one pair of IPv6 addresses if there are multiple NAT64 prefixes.
The name 'ipv4only.arpa' has no other IPv4 or IPv6 address records.
There are no subdomains of ipv4only.arpa. All names falling below
'ipv4only.arpa' are defined to be nonexistent (NXDOMAIN).
The name 'ipv4only.arpa' is special to
(a) client software wishing to perform DNS64 address synthesis,
(b) APIs responsible for retrieving the correct information, and
(c) the DNS64 recursive resolver responding to such requests.
These three considerations are listed in items 2, 3 and 4 below:
1. Normal users should never have reason to encounter the
'ipv4only.arpa' domain name. If they do, they should expect
queries for 'ipv4only.arpa' to result in the answers required by
the specification [RFC7050]. Normal users have no need to know
that 'ipv4only.arpa' is special.
2. Application software may explicitly use the name 'ipv4only.arpa'
for NAT64/DNS64 address synthesis, and expect to get the answers
required by the specification [RFC7050]. 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 MUST recognize 'ipv4only.arpa'
as special and MUST give it special treatment. Learning a
network's NAT64 prefix is by its nature an interface-specific
operation, and the special DNS query used to learn this
interface-specific NAT64 prefix MUST be sent to the DNS recursive
resolver address(es) the client learned via the configuration
machinery for that specific client interface. Regardless of any
manual client DNS configuration, DNS overrides configured by VPN
client software, or any other mechanisms that influence the
choice of the client's recursive resolver address(es) (including
client devices that run their own local recursive resolver and
use the loopback address as their configured recursive resolver
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address) all queries for 'ipv4only.arpa' and any subdomains of
that name MUST be sent to the recursive resolver learned from the
network interface in question via IPv6 Router Advertisement
Options for DNS Configuration [RFC6106] or via DNS Configuration
options for DHCPv6 [RFC3646]. Because DNS queries for
'ipv4only.arpa' are actually a special middlebox communication
protocol, it is essential that they go to the correct middlebox
for the interface in question, and failure to honor this
requirement would cause failure of the NAT64 Prefix Discovery
mechanism [RFC7050].
4. For the purposes of this section, recursive resolvers fall into
two categories. The first category is the traditional recursive
resolvers that are in widespread use today. The second category
is DNS64 recursive resolvers, whose purpose is to synthesize IPv6
address records.
Traditional recursive resolvers SHOULD NOT recognize
'ipv4only.arpa' as special or give that name, or subdomains of
that name, any special treatment. The rationale for this is that
a traditional recursive resolver, such as built in to a home
gateway, may itself be downstream of a DNS64 recursive resolver.
Passing though the 'ipv4only.arpa' queries to the upstream DNS64
recursive resolver will allow the correct NAT64 prefix to be
discovered.
All DNS64 recursive resolvers MUST recognize 'ipv4only.arpa' as
special and MUST NOT attempt to look up NS records for it, or
otherwise query authoritative name servers in an attempt to
resolve this name. Instead, DNS64 recursive resolvers MUST act
as authoritative for this domain and generate immediate responses
for all such queries.
DNS64 recursive resolvers 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 negative
("no error no answer") response for all other query types.
For all subdomains of 'ipv4only.arpa', DNS64 recursive resolvers
MUST generate immediate NXDOMAIN responses. All names falling
below 'ipv4only.arpa' are defined to be nonexistent.
An example configuration for BIND 9 showing how to achieve the
desired result is given in Appendix A.
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Note that this is *not* a locally served zone in the usual sense
of that term [RFC6303] because this rule applies *only* to DNS64
recursive resolvers, not *all* DNS recursive resolvers.
5. Traditional authoritative name server software need not recognize
'ipv4only.arpa' as special or handle it in any special way.
Recursive resolvers SHOULD routinely act as authoritative for
this name and return the results described above. Only the
administrators of the 'arpa' namespace need to explicitly
configure their actual authoritative 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 name servers need
not know anything about the name 'ipv4only.arpa', just as they do
not need to know anything about any other names they are not
responsible for. Operators of authoritative name servers who are
configuring their name servers to be authoritative for this name
MUST understand that 'ipv4only.arpa' is a special name, with
records rigidly 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 do not 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. In particular,
ipv4only.arpa MUST be created as an insecure delegation, to allow
DNS64 recursive resolvers to create synthesized AAAA answers
within that zone. Signing the ipv4only.arpa would make it
impossible for DNS64 recursive resolvers to create synthesized
AAAA answers that won't fail DNSSEC validation, thereby defeating
the entire purpose of ipv4only.arpa.
7.2. Names '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 one DNS record, type PTR, with rdata 'ipv4only.arpa'.
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The name '171.0.0.192.in-addr.arpa' is defined, by Internet Standard,
to have only one DNS record, type PTR, with rdata 'ipv4only.arpa'.
There are no subdomains of '170.0.0.192.in-addr.arpa' or
'171.0.0.192.in-addr.arpa'. All names falling below these names are
defined to be nonexistent (NXDOMAIN).
Practically speaking these two names are rarely used, but to the
extent that they may be, they are special only to recursive resolvers
as described in item 4 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 recognize these two
reverse mapping names as special and generate the required
responses locally. For the names '170.0.0.192.in-addr.arpa' and
'171.0.0.192.in-addr.arpa' PTR queries yield the result
'ipv4only.arpa'; all other query types yield a negative
("no error no answer") response. For all subdomains of these two
reverse mapping domains, all queries yield an NXDOMAIN response.
All names falling below these two reverse mapping domains are
defined to be nonexistent.
This local self-contained generation of these responses is to
avoid placing unnecessary load on the authoritative
'in-addr.arpa' name servers.
4. Recursive resolvers SHOULD NOT recognize these two reverse
mapping names as special and SHOULD NOT, by default, give them
any special treatment.
5. Traditional authoritative name 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
'192.in-addr.arpa' namespace will configure their name servers to
be authoritative for these names and to generate the appropriate
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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 name servers need
not know anything about these two reverse mapping names, just as
they do not need to know anything about any other names they are
not responsible for. Operators of authoritative name 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 '192.in-addr.arpa'
namespace).
7. DNS Registries/Registrars need not know anything about these two
reverse mapping names, just as they do not need to know anything
about any other name they are not responsible for. Only the
administrators of the '192.in-addr.arpa' namespace need to be
aware of the purpose of these two names.
7.2.1. ip6.arpa Reverse Mapping PTR Records
For all IPv6 addresses synthesized by a DNS64 recursive resolver, the
DNS64 recursive resolver is responsible for synthesizing the
appropriate 'ip6.arpa' reverse mapping PTR records too, if it chooses
to provide reverse mapping PTR records. 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 resolver synthesizes appropriate
'ip6.arpa' reverse mapping PTR records by extracting the embedded
IPv4 address from the encoded IPv6 address, performing a reverse
mapping PTR 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 resolver
does not issue reverse mapping queries for those IPv4 addresses, but
instead, according to rule 3 above, immediately returns the answer
'ipv4only.arpa'.
In the case of a client that uses the 'ipv4only.arpa' query to
discover the IPv6 prefixes in use by the local NAT64 gateway, and
then proceeds to perform its own address synthesis locally (which has
benefits such as allowing DNSSEC validation), that client MUST also
synthesize 'ip6.arpa' reverse mapping PTR records for those
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discovered prefix(es), according to the rules above: When a client's
name resolution APIs and libraries receive a request to look up an
'ip6.arpa' reverse mapping PTR record for an address that falls
within one of the discovered NAT64 address synthesis prefixes, the
software extracts the embedded IPv4 address and then, for IPv4
addresses 192.0.0.170 and 192.0.0.171, returns the fixed answer
'ipv4only.arpa', and for all other IPv4 addresses performs a reverse
mapping PTR query for the IPv4 address, and then synthesizes a
corresponding 'ip6.arpa' reverse mapping PTR record containing the
same rdata.
8. Acknowledgements
Thanks to Jouni Korhonen, Teemu Savolainen, and Dan Wing, for
devising the NAT64 Prefix Discovery mechanism [RFC7050], and for
their feedback on this document. Thanks to Geoff Huston for his
feedback on the draft, and to Erik Kline for pointing out that the
in-addr.arpa names are special too. Thanks particularly to Lorenzo
Colitti for an especially spirited hallway discussion at IETF 96 in
Berlin, which lead directly to significant improvements in how this
document presents the issues.
9. References
9.1. 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, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic
Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
DOI 10.17487/RFC3646, December 2003, <https://www.rfc-
editor.org/info/rfc3646>.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010, <https://www.rfc-
editor.org/info/rfc6052>.
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 6106, DOI 10.17487/RFC6106, November 2010,
<https://www.rfc-editor.org/info/rfc6106>.
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[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011, <https://www.rfc-
editor.org/info/rfc6147>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://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,
<https://www.rfc-editor.org/info/rfc7050>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163,
RFC 6303, DOI 10.17487/RFC6303, July 2011,
<https://www.rfc-editor.org/info/rfc6303>.
[RFC8244] Lemon, T., Droms, R., and W. Kumari, "Special-Use Domain
Names Problem Statement", RFC 8244, DOI 10.17487/RFC8244,
October 2017, <https://www.rfc-editor.org/info/rfc8244>.
[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 resolver can be configured to act as authoritative
for the necessary DNS64 names as described below.
In /etc/named.conf the following line is added:
zone "ipv4only.arpa" { type master; file "ipv4only"; };
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
@ IN AAAA 64:ff9b::192.0.0.170 ; If not using Well-Known Prefix
@ IN AAAA 64:ff9b::192.0.0.171 ; place actual NAT64 prefix here
Authors' Addresses
Stuart Cheshire
Apple Inc.
One Apple Park Way
Cupertino, California 95014
USA
Phone: +1 (408) 996-1010
Email: cheshire@apple.com
David Schinazi
Apple Inc.
One Apple Park Way
Cupertino, California 95014
USA
Email: dschinazi@apple.com
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