Internet DRAFT - draft-ietf-v6ops-nat64-deployment
draft-ietf-v6ops-nat64-deployment
v6ops J. Palet Martinez
Internet-Draft The IPv6 Company
Intended status: Informational July 11, 2019
Expires: January 12, 2020
Additional NAT64/464XLAT Deployment Guidelines in Operator and
Enterprise Networks
draft-ietf-v6ops-nat64-deployment-08
Abstract
This document describes how NAT64 (including 464XLAT) can be deployed
in an IPv6 network, whether cellular ISP, broadband ISP, or
enterprise, and possible optimizations. The document also discusses
issues to be considered when having IPv6-only connectivity,
regarding: a) DNS64, b) applications or devices that use literal IPv4
addresses or non-IPv6 compliant APIs, and c) IPv4-only hosts or
applications.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 12, 2020.
Copyright Notice
Copyright (c) 2019 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. NAT64 Deployment Scenarios . . . . . . . . . . . . . . . . . 5
3.1. Known to Work . . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. Service Provider NAT64 with DNS64 . . . . . . . . . . 6
3.1.2. Service Provider Offering 464XLAT, with DNS64 . . . . 8
3.1.3. Service Provider Offering 464XLAT, without DNS64 . . 12
3.2. Known to Work Under Special Conditions . . . . . . . . . 14
3.2.1. Service Provider NAT64 without DNS64 . . . . . . . . 14
3.2.2. Service Provider NAT64; DNS64 in the IPv6 hosts . . . 16
3.2.3. Service Provider NAT64; DNS64 in the IPv4-only
remote network . . . . . . . . . . . . . . . . . . . 16
3.3. Comparing the Scenarios . . . . . . . . . . . . . . . . . 17
4. Issues to be Considered . . . . . . . . . . . . . . . . . . . 19
4.1. DNSSEC Considerations and Possible Approaches . . . . . . 19
4.1.1. Not using DNS64 . . . . . . . . . . . . . . . . . . . 20
4.1.2. DNSSEC validator aware of DNS64 . . . . . . . . . . . 21
4.1.3. Stub validator . . . . . . . . . . . . . . . . . . . 22
4.1.4. CLAT with DNS proxy and validator . . . . . . . . . . 22
4.1.5. ACL of clients . . . . . . . . . . . . . . . . . . . 22
4.1.6. Mapping-out IPv4 addresses . . . . . . . . . . . . . 23
4.2. DNS64 and Reverse Mapping . . . . . . . . . . . . . . . . 23
4.3. Using 464XLAT with/without DNS64 . . . . . . . . . . . . 23
4.4. Foreign DNS . . . . . . . . . . . . . . . . . . . . . . . 24
4.4.1. Manual Configuration of DNS . . . . . . . . . . . . . 25
4.4.2. DNS Privacy/Encryption Mechanisms . . . . . . . . . . 25
4.4.3. Split DNS and VPNs . . . . . . . . . . . . . . . . . 26
4.5. Well-Known Prefix (WKP) vs Network-Specific Prefix (NSP) 26
4.6. IPv4 literals and non-IPv6 Compliant APIs . . . . . . . . 26
4.7. IPv4-only Hosts or Applications . . . . . . . . . . . . . 27
4.8. CLAT Translation Considerations . . . . . . . . . . . . . 27
4.9. EAM Considerations . . . . . . . . . . . . . . . . . . . 28
4.10. Incoming Connections . . . . . . . . . . . . . . . . . . 28
5. Summary of Deployment Recommendations for NAT64/464XLAT . . . 28
6. Deployment of 464XLAT/NAT64 in Enterprise Networks . . . . . 31
7. Security Considerations . . . . . . . . . . . . . . . . . . . 33
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33
10. ANNEX A: Example of Broadband Deployment with 464XLAT . . . . 34
11. ANNEX B: CLAT Implementation . . . . . . . . . . . . . . . . 37
12. ANNEX C: Benchmarking . . . . . . . . . . . . . . . . . . . . 38
13. ANNEX D: Changes from -00 to -01/-02 . . . . . . . . . . . . 38
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14. ANNEX E: Changes from -02 to -03 . . . . . . . . . . . . . . 38
15. ANNEX F: Changes from -03 to -04 . . . . . . . . . . . . . . 39
16. ANNEX G: Changes from -04 to -05 . . . . . . . . . . . . . . 39
17. ANNEX H: Changes from -05 to -06 . . . . . . . . . . . . . . 39
18. ANNEX H: Changes from -06 to -07 . . . . . . . . . . . . . . 39
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 39
19.1. Normative References . . . . . . . . . . . . . . . . . . 39
19.2. Informative References . . . . . . . . . . . . . . . . . 42
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction
Stateful NAT64 ([RFC6146]) describes a stateful IPv6 to IPv4
translation mechanism, which allows IPv6-only hosts to communicate
with IPv4-only servers using unicast UDP, TCP, or ICMP, by means of
IPv4 public addresses sharing, among multiple IPv6-only hosts.
Unless otherwise stated, references in the rest of this document to
NAT64 (function) should be interpreted as to Stateful NAT64.
The translation of the packet headers is done using the IP/ICMP
translation algorithm defined in [RFC7915] and algorithmically
translating the IPv4 addresses to IPv6 addresses and vice versa,
following [RFC6052].
DNS64 ([RFC6147]) is in charge of the synthesis of AAAA records from
the A records, so only works for applications making use of DNS. It
was designed to avoid changes in both, the IPv6-only hosts and the
IPv4-only server, so they can use a NAT64 function. As discussed in
Section 5.5 of [RFC6147], a security-aware and validating host has to
perform the DNS64 function locally.
However, the use of NAT64 and/or DNS64 present three drawbacks:
a. Because DNS64 ([RFC6147]) modifies DNS answers, and DNSSEC is
designed to detect such modifications, DNS64 ([RFC6147]) may
potentially break DNSSEC, depending on a number of factors, such
as the location of the DNS64 function (at a DNS server or
validator, at the end host, ...), how it has been configured, if
the end-hosts is validating, etc.
b. Because the need of using DNS64 ([RFC6147]) or an alternative
"host/application built-in" mechanism for address synthesis,
there may be an issue for NAT64 ([RFC6146]), as it doesn't work
when IPv4 literal addresses or non-IPv6 compliant APIs are being
used.
c. NAT64 alone, was not designed to provide a solution for IPv4-only
hosts or applications located within a network which are
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connected to a service provider IPv6-only access, as it was
designed for a very specific scenario ([RFC6144], Section 2.1).
Above drawbacks may be true if part of, an enterprise network, is
connected to other parts of the same network or third-party networks
by means of IPv6-only connectivity. This is just an example which
may apply to many other similar cases. All them are deployment
specific.
According to that, across this document, the use of "operator",
"operator network", "service provider", and similar ones, are
interchangeable with equivalent cases of enterprise networks (and
similar ones). This may be also the case for "managed end-user
networks".
Note that if all the hosts in a network were performing the address
synthesis, as described in Section 7.2 of [RFC6147], some of the
drawbacks may vanish. However, it is unrealistic today to expect
that, considering the high number of devices and applications that
aren't yet IPv6-enabled. So, in this document, this will be
considered only for specific scenarios that can guarantee it.
An analysis of stateful IPv4/IPv6 mechanisms is provided in
[RFC6889].
This document looks into different possible NAT64 ([RFC6146])
deployment scenarios, including IPv4-IPv6-IPv4 (464 for short) and
similar ones, which were not documented in [RFC6144], such as 464XLAT
([RFC6877]), in operator (broadband and cellular) and enterprise
networks, and provides guidelines to avoid operational issues.
Towards that, this document first looks into the possible NAT64
deployment scenarios (split in "known to work" and "known to work
under special conditions"), providing a quick and generic comparison
table among them. Then the document describes the issues that an
operator need to understand on different matters that will allow to
define what is the best approach/scenario for each specific network
case. A summary provides some recommendations and decision points.
A section with clarifications on the usage of this document for
enterprise networks, is also provided. Finally, an annex provides an
example of a broadband deployment using 464XLAT and another annex
provides hints for a CLAT implementation.
[RFC7269] already provides information about NAT64 deployment options
and experiences. Both, this document and [RFC7269] are
complementary; they are looking into different deployment
considerations and furthermore, this document is considering the
updated deployment experience and newer standards.
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The target deployment scenarios in this document may be covered as
well by other IPv4-as-a-Service (IPv4aaS) transition mechanisms.
Note that this is true only for the case of broadband networks, as in
the case of cellular networks the only supported solution is the use
of NAT64/464XLAT. So, it is out of scope of this document to provide
a comparison among the different IPv4aaS transition mechanisms, which
is being analyzed already in [I-D.lmhp-v6ops-transition-comparison].
Consequently, this document should not be understood as a guide for
an operator or enterprise to decide which IPv4aaS is the best one for
its own network. Instead it should be used as a tool for
understanding all the implications, including relevant documents (or
even specific parts of them), for the deployment of NAT64/464XLAT and
facilitate the decision process regarding specific deployment
details.
2. Requirements Language
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. NAT64 Deployment Scenarios
Section 7 of DNS64 ([RFC6147]), provides three scenarios, depending
on the location of the DNS64 function. However, since the
publication of that document, other deployment scenarios and NAT64
use cases need to be considered in actual networks, despite some of
them were specifically ruled out by the original NAT64/DNS64 work.
Consequently, the perspective in this document is to broaden those
scenarios, including a few new ones. However, in order to be able to
reduce the number of possible cases, we work under the assumption
that typically, the service provider wants to make sure that all the
customers have a service without failures. This means considering
the following assumptions for the worst possible case:
a. There are hosts that will be validating DNSSEC.
b. IPv4 literal addresses and non-IPv6 compliant APIs are being
used.
c. There are IPv4-only hosts or applications beyond the IPv6-only
link (e.g., tethering in cellular networks).
The document uses a common set of possible "participant entities":
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1. An IPv6-only access network (IPv6).
2. An IPv4-only remote network/server/service (IPv4).
3. A NAT64 function (NAT64) in the service provider.
4. A DNS64 function (DNS64) in the service provider.
5. An external service provider offering the NAT64 function and/or
the DNS64 function (extNAT64/extDNS64).
6. 464XLAT customer side translator (CLAT).
Note that the nomenclature used in parenthesis is the one that, for
short, will be used in the figures. Note also that for simplicity,
the boxes in the figures don't mean they are actually a single
device; they just represent one or more functions as located in that
part of the network (i.e. a single box with NAT64 and DNS64 functions
can actually be several devices, not just one).
The possible scenarios are split in two general categories:
1. Known to work.
2. Known to work under special conditions.
3.1. Known to Work
The scenarios in this category are known to work, as there are well-
known existing deployments from different operators using them. Each
one may have different pros and cons, and in some cases the trade-
offs, maybe acceptable for some operators.
3.1.1. Service Provider NAT64 with DNS64
In this scenario (Figure 1), the service provider offers both, the
NAT64 and the DNS64 functions.
This is the most common scenario as originally considered by the
designers of NAT64 ([RFC6146]) and DNS64 ([RFC6147]), however also
may have the implications related the DNSSEC.
This scenario also may fail to solve the issue of IPv4 literal
addresses or non-IPv6 compliant APIs, as well as the issue of
IPv4-only hosts or applications behind the IPv6-only access network.
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+----------+ +----------+ +----------+
| | | NAT64 | | |
| IPv6 +--------+ + +--------+ IPv4 |
| | | DNS64 | | |
+----------+ +----------+ +----------+
Figure 1: NAT64 with DNS64
A similar scenario (Figure 2) will be if the service provider offers
only the DNS64 function, and the NAT64 function is provided by an
outsourcing agreement with an external provider. All the
considerations in the previous paragraphs of this section, are the
same for this sub-case.
+----------+ +----------+
| | | |
| extNAT64 +--------+ IPv4 |
| | | |
+----+-----+ +----------+
|
|
+----------+ +----+-----+
| | | |
| IPv6 +--------+ DNS64 +
| | | |
+----------+ +----------+
Figure 2: NAT64 in external service provider
This is equivalent to the scenario (Figure 3) where the outsourcing
agreement with the external provider is to provide both the NAT64 and
DNS64 functions. Once more, all the considerations in the previous
paragraphs of this section are the same for this sub-case.
+----------+ +----------+
| extNAT64 | | |
| + +-------+ IPv4 |
| extDNS64 | | |
+----+-----+ +----------+
|
+----------+ |
| | |
| IPv6 +-------------+
| |
+----------+
Figure 3: NAT64 and DNS64 in external provider
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One additional equivalent scenario (Figure 4) will be if the service
provider offers the NAT64 function only, and the DNS64 function is
from an external provider with or without a specific agreement among
them. This is a scenario already common today, as several "global"
service providers provide free DNS/DNS64 services and users often
configure manually their DNS. This will only work if both the NAT64
and the DNS64 functions are using the WKP (Well-Known Prefix) or the
same NSP (Network-Specific Prefix). All the considerations in the
previous paragraphs of this section, are the same for this sub-case.
Of course, if the external DNS64 function is agreed with the service
provider, then we are in the same case as in the previous ones
already depicted in this scenario.
+----------+
| |
| extDNS64 |
| |
+----+-----+
|
|
+----------+ +----+-----+ +----------+
| | | | | |
| IPv6 +--------+ NAT64 +--------+ IPv4 |
| | | | | |
+----------+ +----------+ +----------+
Figure 4: NAT64; DNS64 by external provider
3.1.2. Service Provider Offering 464XLAT, with DNS64
464XLAT ([RFC6877]) describes an architecture that provides IPv4
connectivity across a network, or part of it, when it is only
natively transporting IPv6. [RFC7849] already suggest the need to
support the CLAT function in order to ensure the IPv4 service
continuity in IPv6-only cellular deployments.
In order to do that, 464XLAT ([RFC6877]) relies on the combination of
existing protocols:
1. The customer-side translator (CLAT) is a stateless IPv4 to IPv6
translator (NAT46) ([RFC7915]) implemented in the end-user device
or CE (Customer Edge Router), located at the "customer edge" of
the network.
2. The provider-side translator (PLAT) is a stateful NAT64
([RFC6146]), implemented typically at in the operator network.
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3. Optionally, DNS64 ([RFC6147]), may allow an optimization: a
single translation at the NAT64, instead of two translations
(NAT46+NAT64), when the application at the end-user device
supports IPv6 DNS (uses AAAA Resource Records).
Note that even if in the 464XLAT ([RFC6877]) terminology, the
provider-side translator is referred as PLAT, for simplicity and
uniformity, across this document is always referred as NAT64
(function).
In this scenario (Figure 5) the service provider deploys 464XLAT with
a DNS64 function.
As a consequence, the DNSSEC issues remain, unless the host is doing
the address synthesis.
464XLAT ([RFC6877]) is a very simple approach to cope with the major
NAT64+DNS64 drawback: Not working with applications or devices that
use literal IPv4 addresses or non-IPv6 compliant APIs.
464XLAT ([RFC6877]) has been used initially mainly in IPv6-only
cellular networks. By supporting a CLAT function, the end-user
device applications can access IPv4-only end-networks/applications,
despite those applications or devices use literal IPv4 addresses or
non-IPv6 compliant APIs.
In addition to that, in the same example of the cellular network
above, if the User Equipment (UE) provides tethering, other devices
behind it will be presented with a traditional NAT44, in addition to
the native IPv6 support, so clearly it allows IPv4-only hosts behind
the IPv6-only access network.
Furthermore, as discussed in [RFC6877], 464XLAT can be used in
broadband IPv6 network architectures, by implementing the CLAT
function at the CE.
The support of this scenario in a network, offers two additional
advantages:
o DNS load optimization: A CLAT should implement a DNS proxy (as per
[RFC5625]), so that only IPv6 native queries and only for AAAA
records are sent to the DNS64 server. Otherwise doubling the
number of queries may impact the DNS infrastructure.
o Connection establishment delay optimization: If the UE/CE
implementation is detecting the presence of a DNS64 function, it
may issue only the AAAA query, instead of both the AAAA and A
queries.
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In order to understand all the communication possibilities, let's
assume the following representation of two dual-stack peers:
+-------+ .-----. .-----.
| | / \ / \
.-----. | Res./ | / IPv6- \ .-----. / IPv4- \
/ Local \ | SOHO +--( only )---( NAT64 )---( only )
/ \ | | \ flow /\ `-----' \ flow /
( Dual- )--+ IPv6 | \ / \ / \ /
\ Stack / | CE | `--+--' \ .-----. / `--+--'
\ Peer / | with | | \ / Remote\/ |
`-----' | CLAT | +---+----+ / \ +---+----+
| | |DNS/IPv6| ( Dual- ) |DNS/IPv4|
+-------+ | with | \ Stack / +--------+
| DNS64 | \ Peer /
+--------+ `-----'
Figure A: Representation of 464XLAT among two peers with DNS64
The possible communication paths, among the IPv4/IPv6 stacks of both
peers, in this case, are:
a. Local-IPv6 to Remote-IPv6: Regular DNS and native IPv6 among
peers.
b. Local-IPv6 to Remote-IPv4: DNS64 and NAT64 translation.
c. Local-IPv4 to Remote-IPv6: Not possible unless the CLAT
implements EAM (Explicit Address Mappings) as indicated by
Section 4.9. In principle, it is not expected that services are
deployed in Internet using IPv6-only, unless there is certainty
that peers will also be IPv6-capable.
d. Local-IPv4 to Remote-IPv4: DNS64, CLAT and NAT64 translations.
e. Local-IPv4 to Remote-dual-stack using EAM optimization: If the
CLAT implements EAM as indicated by Section 4.9, instead of using
the path d. above, NAT64 translation is avoided and the flow will
use IPv6 from the CLAT to the destination.
The rest of the figures in this section show different choices for
placing the different elements.
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+----------+ +----------+ +----------+
| IPv6 | | NAT64 | | |
| + +--------+ + +--------+ IPv4 |
| CLAT | | DNS64 | | |
+----------+ +----------+ +----------+
Figure 5: 464XLAT with DNS64
A similar scenario (Figure 6) will be if the service provider offers
only the DNS64 function, and the NAT64 function is provided by an
outsourcing agreement with an external provider. All the
considerations in the previous paragraphs of this section are the
same for this sub-case.
+----------+ +----------+
| | | |
| extNAT64 +--------+ IPv4 |
| | | |
+----+-----+ +----------+
|
|
+----------+ +----+-----+
| IPv6 | | |
| + +--------+ DNS64 +
| CLAT | | |
+----------+ +----------+
Figure 6: 464XLAT with DNS64; NAT64 in external provider
As well, is equivalent to the scenario (Figure 7) where the
outsourcing agreement with the external provider is to provide both
the NAT64 and DNS64 functions. Once more, all the considerations in
the previous paragraphs of this section are the same for this sub-
case.
+----------+ +----------+
| extNAT64 | | |
| + +--------+ IPv4 |
| extDNS64 | | |
+----+-----+ +----------+
|
+----------+ |
| IPv6 | |
| + +-------------+
| CLAT |
+----------+
Figure 7: 464XLAT with DNS64; NAT64 and DNS64 in external provider
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3.1.3. Service Provider Offering 464XLAT, without DNS64
The major advantage of this scenario (Figure 8), using 464XLAT
without DNS64, is that the service provider ensures that DNSSEC is
never broken, even in case the user modifies the DNS configuration.
Nevertheless, some CLAT implementations or applications may impose an
extra delay, which is induced by the dual A/AAAA queries (and wait
for both responses), unless Happy Eyeballs v2 ([RFC8305]) is also
present.
A possible variation of this scenario is the case when DNS64 is used
only for the discovery of the NAT64 prefix. The rest of the document
is not considering it as a different scenario, because once the
prefix has been discovered, the DNS64 function is not used, so it
behaves as if the DNS64 synthesis function is not present.
In this scenario, as in the previous one, there are no issues related
to IPv4-only hosts (or IPv4-only applications) behind the IPv6-only
access network, neither related to the usage of IPv4 literals or non-
IPv6 compliant APIs.
The support of this scenario in a network, offers one advantage:
o DNS load optimization: A CLAT should implement a DNS proxy (as per
[RFC5625]), so that only IPv6 native queries are sent to the DNS64
server. Otherwise doubling the number of queries may impact the
DNS infrastructure.
As indicated earlier, the connection establishment delay optimization
is achieved only in the case of devices, Operating Systems, or
applications that use Happy Eyeballs v2 ([RFC8305]), which is very
common.
Let's assume the representation of two dual-stack peers as in the
previous case:
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+-------+ .-----. .-----.
| | / \ / \
.-----. | Res./ | / IPv6- \ .-----. / IPv4- \
/ Local \ | SOHO +--( only )---( NAT64 )---( only )
/ \ | | \ flow /\ `-----' \ flow /
( Dual- )--+ IPv6 | \ / \ / \ /
\ Stack / | CE | `--+--' \ .-----. / `--+--'
\ Peer / | with | | \ / Remote\/ |
`-----' | CLAT | +---+----+ / \ +---+----+
| | |DNS/IPv6| ( Dual- ) |DNS/IPv4|
+-------+ +--------+ \ Stack / +--------+
\ Peer /
`-----'
Figure B: Representation of 464XLAT among two peers without DNS64
The possible communication paths, among the IPv4/IPv6 stacks of both
peers, in this case, are:
a. Local-IPv6 to Remote-IPv6: Regular DNS and native IPv6 among
peers.
b. Local-IPv6 to Remote-IPv4: Regular DNS, CLAT and NAT64
translations.
c. Local-IPv4 to Remote-IPv6: Not possible unless the CLAT
implements EAM as indicated by Section 4.9. In principle, it is
not expected that services are deployed in Internet using
IPv6-only, unless there is certainty that peers will also be
IPv6-capable.
d. Local-IPv4 to Remote-IPv4: Regular DNS, CLAT and NAT64
translations.
e. Local-IPv4 to Remote-dual-stack using EAM optimization: If the
CLAT implements EAM as indicated by Section 4.9, instead of using
the path d. above, NAT64 translation is avoided and the flow will
use IPv6 from the CLAT to the destination.
It needs to be noticed that this scenario works while the local
hosts/applications are dual-stack (which is the current situation),
because the connectivity from a local-IPv6 to a remote-IPv4 is not
possible without an AAAA synthesis. This aspect is important only
when in the LANs behind the CLAT there are IPv6-only hosts and they
need to communicate with remote IPv4-only hosts. However, it doesn't
look a sensible approach from an Operating System or application
vendor perspective, to provide IPv6-only support unless, similarly to
case c above, there is certainty of peers supporting IPv6 as well. A
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solution approach to this is also presented in
[I-D.palet-v6ops-464xlat-opt-cdn-caches].
The following figures show different choices for placing the
different elements.
+----------+ +----------+ +----------+
| IPv6 | | | | |
| + +--------+ NAT64 +--------+ IPv4 |
| CLAT | | | | |
+----------+ +----------+ +----------+
Figure 8: 464XLAT without DNS64
This is equivalent to the scenario (Figure 9) where there is an
outsourcing agreement with an external provider for the NAT64
function. All the considerations in the previous paragraphs of this
section are the same for this sub-case.
+----------+ +----------+
| | | |
| extNAT64 +--------+ IPv4 |
| | | |
+----+-----+ +----------+
|
+----------+ |
| IPv6 | |
| + +-------------+
| CLAT |
+----------+
Figure 9: 464XLAT without DNS64; NAT64 in external provider
3.2. Known to Work Under Special Conditions
The scenarios in this category are known to not work unless
significant effort is devoted to solve the issues, or are intended to
solve problems across "closed" networks, instead of as a general
Internet access usage. In addition to the different pros, cons and
trade-offs, which may be acceptable for some operators, they have
implementation difficulties, as they are beyond the original
expectations of the NAT64/DNS64 original intent.
3.2.1. Service Provider NAT64 without DNS64
In this scenario (Figure 10), the service provider offers a NAT64
function, however there is no DNS64 function support at all.
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As a consequence, an IPv6 host in the IPv6-only access network, will
not be able to detect the presence of DNS64 by means of [RFC7050],
neither to learn the IPv6 prefix to be used for the NAT64 function.
This can be sorted out as indicated in Section 4.1.1.
However, despite that, because the lack of the DNS64 function, the
IPv6 host will not be able to obtain AAAA synthesized records, so the
NAT64 function becomes useless.
An exception to this "useless" scenario will be manually configure
mappings between the A records of each of the IPv4-only remote hosts
and the corresponding AAAA records, with the WKP (Well-Known Prefix)
or NSP (Network-Specific Prefix) used by the service provider NAT64
function, as if they were synthesized by a DNS64 function.
This mapping could be done by several means, typically at the
authoritative DNS server, or at the service provider resolvers by
means of DNS RPZ (Response Policy Zones, [I-D.vixie-dns-rpz]) or
equivalent functionality. DNS RPZ, may have implications in DNSSEC,
if the zone is signed. Also, if the service provider is using an
NSP, having the mapping at the authoritative server, may create
troubles to other parties trying to use different NSP or the WKP,
unless multiple DNS "views" (split-DNS) is also being used at the
authoritative servers.
Generally, the mappings alternative, will only make sense if a few
set of IPv4-only remote hosts need to be accessed by a single network
(or a small number of them), which support IPv6-only in the access.
This will require some kind of mutual agreement for using this
procedure, so it doesn't care if they become a trouble for other
parties across Internet ("closed services").
In any case, this scenario doesn't solve the issue of IPv4 literal
addresses or non-IPv6 compliant APIs, neither it solves the problem
of IPv4-only hosts within that IPv6-only access network.
+----------+ +----------+ +----------+
| | | | | |
| IPv6 +--------+ NAT64 +--------+ IPv4 |
| | | | | |
+----------+ +----------+ +----------+
Figure 10: NAT64 without DNS64
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3.2.2. Service Provider NAT64; DNS64 in the IPv6 hosts
In this scenario (Figure 11), the service provider offers the NAT64
function, but not the DNS64 function. However, the IPv6 hosts have a
built-in DNS64 function.
This may become common if the DNS64 function is implemented in all
the IPv6 hosts/stacks. However, commonly this is not the actual
situation, even if it may happen in the medium-term. At this way,
the DNSSEC validation is performed on the A record, and then the host
can use the DNS64 function so to be able to use the NAT64 function,
without any DNSSEC issues.
This scenario fails to solve the issue of IPv4 literal addresses or
non-IPv6 compliant APIs, unless the IPv6 hosts also supports Happy
Eyeballs v2 ([RFC8305], Section 7.1), which may solve that issue.
However, this scenario still fails to solve the problem of IPv4-only
hosts or applications behind the IPv6-only access network.
+----------+ +----------+ +----------+
| IPv6 | | | | |
| + +--------+ NAT64 +--------+ IPv4 |
| DNS64 | | | | |
+----------+ +----------+ +----------+
Figure 11: NAT64; DNS64 in IPv6 hosts
3.2.3. Service Provider NAT64; DNS64 in the IPv4-only remote network
In this scenario (Figure 12), the service provider offers the NAT64
function only. The remote IPv4-only network offers the DNS64
function.
This is not common, and looks like doesn't make too much sense that a
remote network, not deploying IPv6, is providing a DNS64 function.
As in the case of the scenario depicted in Section 3.2.1, it will
only work if both sides are using the WKP or the same NSP, so the
same considerations apply. It can be also tuned to behave as in
Section 3.1.1
This scenario still fails to solve the issue of IPv4 literal
addresses or non-IPv6 compliant APIs.
This scenario also fails to solve the problem of IPv4-only hosts or
applications behind the IPv6-only access network.
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+----------+ +----------+ +----------+
| | | | | IPv4 |
| IPv6 +--------+ NAT64 +--------+ + |
| | | | | DNS64 |
+----------+ +----------+ +----------+
Figure 12: NAT64; DNS64 in the IPv4-only
3.3. Comparing the Scenarios
This section compares the different scenarios, including the possible
variations (each one represented in the precedent sections by a
different figure), looking at the following criteria:
a. DNSSEC: Are there hosts validating DNSSEC?
b. Literal/APIs: Are there applications using IPv4 literals or non-
IPv6 compliant APIs?
c. IPv4-only: Are there hosts or applications using IPv4-only?
d. Foreign DNS: Is the scenario surviving if the user, Operating
System, applications or devices change the DNS?
e. DNS load opt. (DNS load optimization): Are there extra queries
that may impact DNS infrastructure?
f. Connect. opt. (Connection establishment delay optimization): Is
the UE/CE issuing only the AAAA query or also an A query and
waiting for both responses?
In the next table, the columns represent each of the scenarios from
the previous sections, by the figure number. The possible values
are:
o "-" Scenario "bad" for that criteria.
o "+" Scenario "good" for that criteria.
o "*" Scenario "bad" for that criteria, however it is typically
resolved, with the support of Happy Eyeballs v2 ([RFC8305]).
In some cases, "countermeasures", alternative or special
configurations, may be available for the criteria designated as
"bad". So, this comparison is considering a generic case, as a quick
comparison guide. In some cases, a "bad" criterion is not
necessarily a negative aspect, all it depends on the specific needs/
characteristics of the network where the deployment will take place.
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For instance, in a network which has only IPv6-only hosts and apps
using only DNS and IPv6-compliant APIs, there is no impact using only
NAT64 and DNS64, but if the hosts may validate DNSSEC, that item is
still relevant.
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| Item / Figure | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| DNSSEC | - | - | - | - | - | - | - | + | + | + | + | + |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| Literal/APIs | - | - | - | - | + | + | + | + | + | - | - | - |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| IPv4-only | - | - | - | - | + | + | + | + | + | - | - | - |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| Foreign DNS | - | - | - | - | + | + | + | + | + | - | + | - |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| DNS load opt. | + | + | + | + | + | + | + | + | + | + | + | + |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
| Connect. opt. | + | + | + | + | + | + | + | * | * | + | + | + |
+----------------+---+---+---+---+---+---+---+---+---+----+----+----+
Figure 13: Scenario Comparison
As a general conclusion, we should note that, if the network must
support applications using any of the following:
o IPv4 literals
o non-IPv6-compliant APIs
o IPv4-only hosts or applications
Then, only the scenarios with 464XLAT, a CLAT function, or equivalent
built-in local address synthesis features, will provide a valid
solution. Further to that, those scenarios will also keep working if
the DNS configuration is modified. Clearly also, depending on if
DNS64 is used or not, DNSSEC may be broken for those hosts doing
DNSSEC validation.
All the scenarios are good in terms of DNS load optimization, and in
the case of 464XLAT it may provide an extra degree of optimization.
Finally, all them are also good in terms of connection establishment
delay optimization. However, in the case of 464XLAT without DNS64,
it requires the usage of Happy Eyeballs v2. This is not an issue, as
commonly it is available in actual Operating Systems.
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4. Issues to be Considered
This section reviews the different issues that an operator needs to
consider towards a NAT64/464XLAT deployment, as they may bring to
specific decision points about how to approach that deployment.
4.1. DNSSEC Considerations and Possible Approaches
As indicated in Section 8 of [RFC6147] (DNS64, Security
Considerations), because DNS64 modifies DNS answers and DNSSEC is
designed to detect such modifications, DNS64 may break DNSSEC.
If a device connected to an IPv6-only access network, queries for a
domain name in a signed zone, by means of a recursive name server
that supports DNS64, and the result is a synthesized AAAA record, and
the recursive name server is configured to perform DNSSEC validation
and has a valid chain of trust to the zone in question, it will
cryptographically validate the negative response from the
authoritative name server. This is the expected DNS64 behavior: The
recursive name server actually "lies" to the client device. However,
in most of the cases, the client will not notice it, because
generally, they don't perform validation themselves and instead, rely
on the recursive name servers.
A validating DNS64 resolver in fact, increase the confidence on the
synthetic AAAA, as it has validated that a non-synthetic AAAA for
sure, doesn't exists. However, if the client device is
NAT64-oblivious (most common case) and performs DNSSEC validation on
the AAAA record, it will fail as it is a synthesized record.
The best possible scenario from DNSSEC point of view, is when the
client requests the DNS64 server to perform the DNSSEC validation (by
setting the DO bit to 1 and the CD bit to 0). In this case, the
DNS64 server validates the data, thus tampering may only happen
inside the DNS64 server (which is considered as a trusted part, thus
its likelihood is low) or between the DNS64 server and the client.
All other parts of the system (including transmission and caching)
are protected by DNSSEC ([Threat-DNS64]).
Similarly, if the client querying the recursive name server is
another name server configured to use it as a forwarder, and is
performing DNSSEC validation, it will also fail on any synthesized
AAAA record.
All those considerations are extensively covered in Sections 3, 5.5
and 6.2 of [RFC6147].
A solution to avoid DNSSEC issues, will be that all the signed zones
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also provide IPv6 connectivity, together with the corresponding AAAA
records. However, this is out of the control of the operator needing
to deploy a NAT64 function. This has been proposed already in
[I-D.bp-v6ops-ipv6-ready-dns-dnssec].
An alternative solution, which was the one considered while
developing [RFC6147], is that validators will be DNS64-aware, so
could perform the necessary discovery and do their own synthesis.
That was done under the expectation that it was sufficiently early in
the validator-deployment curve that it would be ok to break certain
DNSSEC assumptions for networks who were really stuck in a NAT64/
DNS64-needing world.
As already indicated, the scenarios in the previous section, are in
fact somehow simplified, looking at the worst possible case. Saying
it in a different way: "trying to look for the most perfect
approach". DNSSEC breach will not happen if the end-host is not
doing validation.
Existing previous studies seems to indicate that the figures of
DNSSEC actually broken by using DNS64 will be around 1.7%
([About-DNS64]) of the cases. However, we can't negate that this may
increase, as DNSSEC deployment grows. Consequently, a decision point
for the operator must depend on "do I really care for that percentage
of cases and the impact in my helpdesk or can I provide alternative
solutions for them?". Some possible solutions may be taken, as
depicted in the next sections.
4.1.1. Not using DNS64
A solution will be to avoid using DNS64, but as already indicated
this is not possible in all the scenarios.
The use of DNS64 is a key component for some networks, in order to
comply with traffic performance metrics, monitored by some
governmental bodies and other institutions ([FCC], [ARCEP]).
One drawback of not having a DNS64 at the network side, is that is
not possible to heuristically discover the NAT64 ([RFC7050]).
Consequently, an IPv6 host behind the IPv6-only access network, will
not be able to detect the presence of the NAT64 function, neither to
learn the IPv6 prefix to be used for it, unless it is configured by
alternative means.
The discovery of the IPv6 prefix could be solved, as described in
[RFC7050], by means of adding the relevant AAAA records to the
ipv4only.arpa. zone, of the service provider recursive servers, i.e.,
if using the WKP (64:ff9b::/96):
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ipv4only.arpa. SOA . . 0 0 0 0 0
ipv4only.arpa. NS .
ipv4only.arpa. AAAA 64:ff9b::192.0.0.170
ipv4only.arpa. AAAA 64:ff9b::192.0.0.171
ipv4only.arpa. A 192.0.0.170
ipv4only.arpa. A 192.0.0.171
An alternative option to the above, is the use of DNS RPZ
([I-D.vixie-dns-rpz]) or equivalent functionalities. Note that this
may impact DNSSEC if the zone is signed.
One more alternative, only valid in environments with PCP support
(for both the hosts or CEs and for the service provider network), is
to follow [RFC7225] (Discovering NAT64 IPv6 Prefixes using PCP).
Other alternatives may be available in the future. All them are
extensively discussed in [RFC7051], however the deployment evolution
has evolved many considerations from that document. New options are
being documented, such using Router Advertising
([I-D.ietf-6man-ra-pref64]) or DHCPv6 options
([I-D.li-intarea-nat64-prefix-dhcp-option]).
It may be convenient the simultaneous support of several of the
possible approaches, in order to ensure that clients with different
ways to configure the NAT64 prefix, successfully obtain it. This is
also convenient even if DNS64 is being used.
Of special relevance to this section is also
[I-D.cheshire-sudn-ipv4only-dot-arpa].
4.1.2. DNSSEC validator aware of DNS64
In general, by default, DNS servers with DNS64 function will not
synthesize AAAA responses if the DNSSEC OK (DO) flag was set in the
query.
In this case, as only an A record is available, if a CLAT function is
present, it means that the CLAT will take the responsibility, as in
the case of literal IPv4 addresses, to keep that traffic flow end-to-
end as IPv4, so DNSSEC is not broken.
However, this will not work if a CLAT function is not present as the
hosts will not be able to use IPv4 (which is the case for all the
scenarios without 464XLAT).
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4.1.3. Stub validator
If the DO flag is set and the client device performs DNSSEC
validation, and the Checking Disabled (CD) flag is set for a query,
the DNS64 recursive server will not synthesize AAAA responses. In
this case, the client could perform the DNSSEC validation with the A
record and then synthesize the AAAA ([RFC6052]). For that to be
possible, the client must have learned beforehand the NAT64 prefix
using any of the available methods ([RFC7050], [RFC7225],
[I-D.ietf-6man-ra-pref64],
[I-D.li-intarea-nat64-prefix-dhcp-option]). This allows the client
device to avoid using the DNS64 function and still use NAT64 even
with DNSSEC.
If the end-host is IPv4-only, this will not work if a CLAT function
is not present (scenarios without 464XLAT).
Some devices or Operating Systems may implement, instead of a CLAT,
an equivalent function by using Bump-in-the-Host ([RFC6535]),
implemented as part of Happy Eyeballs v2 (Section 7.1 of [RFC8305]).
In this case, the considerations in the above paragraphs are also
applicable.
4.1.4. CLAT with DNS proxy and validator
If a CE includes CLAT support and also a DNS proxy, as indicated in
Section 6.4 of [RFC6877], the CE could behave as a stub validator on
behalf of the client devices. Then, following the same approach
described in the Section 4.1.3, the DNS proxy actually will "lie" to
the client devices, which in most of the cases will not notice it,
unless they perform validation by themselves. Again, this allow the
client devices to avoid using the DNS64 function and still use NAT64
with DNSSEC.
Once more, this will not work without a CLAT function (scenarios
without 464XLAT).
4.1.5. ACL of clients
In cases of dual-stack clients, the AAAA queries typically take
preference over A queries. If DNS64 is enabled for those clients,
will never get A records, even for IPv4-only servers.
As a consequence, in cases where there are IPv4-only servers, and
those are located in the path before the NAT64 function, the clients
will not be able to reach them. If DNSSEC is being used for all
those flows, specific addresses or prefixes can be left-out of the
DNS64 synthesis by means of ACLs.
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Once more, this will not work without a CLAT function (scenarios
without 464XLAT).
4.1.6. Mapping-out IPv4 addresses
If there are well-known specific IPv4 addresses or prefixes using
DNSSEC, they can be mapped-out of the DNS64 synthesis.
Even if this is not related to DNSSEC, this "mapping-out" feature is
actually, quite commonly used to ensure that [RFC1918] addresses (for
example used by LAN servers) are not synthesized to AAAA.
Once more, this will not work without a CLAT function (scenarios
without 464XLAT).
4.2. DNS64 and Reverse Mapping
When a client device, using DNS64 tries to reverse-map a synthesized
IPv6 address, the name server responds with a CNAME record pointing
the domain name used to reverse-map the synthesized IPv6 address (the
one under ip6.arpa), to the domain name corresponding to the embedded
IPv4 address (under in-addr.arpa).
This is the expected behavior, so no issues need to be considered
regarding DNS reverse mapping.
4.3. Using 464XLAT with/without DNS64
In the case the client device is IPv6-only (either because the stack
or application is IPv6-only, or because it is connected via an
IPv6-only LAN) and the remote server is IPv4-only (either because the
stack is IPv4-only, or because it is connected via an IPv4-only LAN),
only NAT64 combined with DNS64 will be able to provide access among
both. Because DNS64 is then required, DNSSEC validation will be only
possible if the recursive name server is validating the negative
response from the authoritative name server and the client is not
performing validation.
Note that is not expected at this stage of the transition, that
applications, devices or Operating Systems are IPv6-only. It will
not be a sensible decision for a developer to work on that direction,
unless it is clear that the deployment scenario fully supports it.
On the other hand, an end-user or enterprise network may decide to
run IPv6-only in the LANs. In case there is any chance for
applications to be IPv6-only, the Operating System may be responsible
either for doing a local address synthesis, or alternatively, setting
up some kind of on-demand VPN (IPv4-in-IPv6), which need to be
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supported by that network. This may become very common in enterprise
networks, where "Unique IPv6 Prefix per Host" [RFC8273] is supported.
However, when the client device is dual-stack and/or connected in a
dual-stack LAN by means of a CLAT function (or has a built-in CLAT
function), DNS64 is an option.
1. With DNS64: If DNS64 is used, most of the IPv4 traffic (except if
using literal IPv4 addresses or non-IPv6 compliant APIs) will not
use the CLAT, so will use the IPv6 path and only one translation
will be done at the NAT64. This may break DNSSEC, unless
measures as described in the precedent sections are taken.
2. Without DNS64: If DNS64 is not used, all the IPv4 traffic will
make use of the CLAT, so two translations are required (NAT46 at
the CLAT and NAT64 at the PLAT), which adds some overhead in
terms of the extra NAT46 translation. However, this avoids the
AAAA synthesis and consequently will never break DNSSEC.
Note that the extra translation, when DNS64 is not used, takes place
at the CLAT, which means no extra overhead for the operator. It
however adds potential extra delays to establish the connections, and
no perceptible impact for a CE in a broadband network, while it may
have some impact in a battery powered device. This cost for a
battery powered device, is possibly comparable to the cost when the
device is doing a local address synthesis (see Section 7.1 of
[RFC8305]).
4.4. Foreign DNS
Clients, devices or applications in a service provider network, may
use DNS servers from other networks. This may be the case either if
individual applications use their own DNS server, the Operating
System itself or even the CE, or combinations of the above.
Those "foreign" DNS servers may not support DNS64, which as a
consequence, will mean that those scenarios that require a DNS64 may
not work. However, if a CLAT function is available, the
considerations in Section 4.3 will apply.
In the case that the foreign DNS supports the DNS64 function, we may
be in the situation of providing incorrect configurations parameters,
for example, un-matching WKP or NSP, or a case such the one described
in Section 3.2.3.
Having a CLAT function, even if using foreign DNS without a DNS64
function, ensures that everything will work, so the CLAT must be
considered as an advantage even against user configuration errors.
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The cost of this, is that all the traffic will use a double
translation (NAT46 at the CLAT and NAT64 at the operator network),
unless there is support for EAM (Section 4.9).
An exception to that is the case when there is a CLAT function at the
CE, which is not able to obtain the correct configuration parameters
(again, un-matching WKP or NSP).
However, it needs to be emphasized, that if there is not a CLAT
function (scenarios without 464XLAT), an external DNS without DNS64
support, will disallow any access to IPv4-only destination networks,
and will not guarantee the correct DNSSEC validation, so will behave
as in the Section 3.2.1.
In summary, it can be said, that the consequences of the use of
foreign DNS depend very much in each specific case. However, in
general, if a CLAT function is present, most of the time, there will
not be any. In the other cases, generally, the access to
IPv6-enabled services is still guaranteed for IPv6-enabled hosts, but
not for IPv4-only hosts, neither the access to IPv4-only services for
any hosts in the network.
The causes of "foreign DNS" could be classified in three main
categories, as depicted in the following sub-sections.
4.4.1. Manual Configuration of DNS
It is becoming increasingly common that end-users or even devices or
applications configure alternative DNS in their Operating Systems,
and sometimes in CEs.
4.4.2. DNS Privacy/Encryption Mechanisms
Clients or applications may use mechanisms for DNS privacy/
encryption, such as DNS over TLS ([RFC7858]), DNS over DTLS
([RFC8094]), DNS queries over HTTPS ([RFC8484]) or DNS over QUIC
([I-D.huitema-quic-dnsoquic]). Those are commonly cited as DoT, DoH
and DoQ.
Those DNS privacy/encryption options, currently are typically
provided by the applications, not the Operating System vendors. At
the time of writing this document, at least DoT and DoH standards
have declared DNS64 (and consequently NAT64) out of their scope, so
an application using them may break NAT64, unless a correctly
configured CLAT function is used.
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4.4.3. Split DNS and VPNs
When networks or hosts use "split-DNS" (also called Split Horizon,
DNS views or private DNS), the successful use of the DNS64 is not
guaranteed. Section 4 of [RFC6950], analyses this case.
A similar situation may happen in case of VPNs that force all the DNS
queries through the VPN, ignoring the operator DNS64 function.
4.5. Well-Known Prefix (WKP) vs Network-Specific Prefix (NSP)
Section 3 of [RFC6052] (IPv6 Addressing of IPv4/IPv6 Translators),
discusses some considerations which are useful to decide if an
operator should use the WKP or an NSP.
Taking in consideration that discussion and other issues, we can
summarize the possible decision points as:
a. The WKP MUST NOT be used to represent non-global IPv4 addresses.
If this is required because the network to be translated use non-
global addresses, then an NSP is required.
b. The WKP MAY appear in inter-domain routing tables, if the
operator provides a NAT64 function to peers. However, in this
case, special considerations related to BGP filtering are
required and IPv4-embedded IPv6 prefixes longer than the WKP MUST
NOT be advertised (or accepted) in BGP. An NSP may be a more
appropriate option in those cases.
c. If several NAT64 use the same prefix, packets from the same flow
may be routed to different NAT64 in case of routing changes.
This can be avoided either by using different prefixes for each
NAT64 function, or by ensuring that all the NAT64 coordinate
their state. Using an NSP could simplify that.
d. If DNS64 is required and users, devices, Operating Systems or
applications may change their DNS configuration, and deliberately
choose an alternative DNS64 function, most probably alternative
DNS64 will use by default the WKP. In that case, if an NSP is
used by the NAT64 function, clients will not be able to use the
operator NAT64 function, which will break connectivity to
IPv4-only destinations.
4.6. IPv4 literals and non-IPv6 Compliant APIs
A host or application using literal IPv4 addresses or older APIs,
which aren't IPv6 compliant, behind a network with IPv6-only access,
will not work unless any of the following alternatives is provided:
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o CLAT (or equivalent function).
o Happy Eyeballs v2 (Section 7.1, [RFC8305]).
o Bump-in-the-Host ([RFC6535]) with a DNS64 function.
Those alternatives will solve the problem for an end-host. However,
if that end-hosts is providing "tethering" or an equivalent service
to other hosts, that needs to be considered as well. In other words,
in a case of a cellular network, it resolves the issue for the UE
itself, but may be not the case for hosts behind it.
Otherwise, the support of 464XLAT is the only valid and complete
approach to resolve this issue.
4.7. IPv4-only Hosts or Applications
An IPv4-only hosts or application behind a network with IPv6-only
access, will not work unless a CLAT function is present.
464XLAT is the only valid approach to resolve this issue.
4.8. CLAT Translation Considerations
As described in Section 6.3 of [RFC6877] (IPv6 Prefix Handling), if
the CLAT function can be configured with a dedicated /64 prefix for
the NAT46 translation, then it will be possible to do a more
efficient stateless translation.
Otherwise, if this dedicated prefix is not available, the CLAT
function will need to do a stateful translation, for example
performing stateful NAT44 for all the IPv4 LAN packets, so they
appear as coming from a single IPv4 address, and then in turn,
stateless translated to a single IPv6 address.
A possible setup, in order to maximize the CLAT performance, is to
configure the dedicated translation prefix. This can be easily
achieved automatically, if the broadband CE or end-user device is
able to obtain a shorter prefix by means of DHCPv6-PD ([RFC8415]), or
other alternatives. The CE can then use a specific /64 for the
translation. This is also possible when broadband is provided by a
cellular access.
The above recommendation is often not possible for cellular networks,
when connecting smartphones (as UEs), as generally they don't use
DHCPv6-PD ([RFC8415]). Instead, a single /64 is provided for each
PDP context and prefix sharing ([RFC6877]) is used. So, in this
case, the UEs typically have a build-in CLAT function which is
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performing a stateful NAT44 translation before the stateless NAT46.
4.9. EAM Considerations
Explicit Address Mappings for Stateless IP/ICMP Translation
([RFC7757]) provide a way to configure explicit mappings between IPv4
and IPv6 prefixes of any length. When this is used, for example in a
CLAT function, it may provide a simple mechanism in order to avoid
traffic flows between IPv4-only nodes or applications and dual-stack
destinations to be translated twice (NAT46 and NAT64), by creating
mapping entries with the GUA of the IPv6-reachable destination. This
optimization of the NAT64 usage is very useful in many scenarios,
including CDNs and caches, as described in
[I-D.palet-v6ops-464xlat-opt-cdn-caches].
In addition to that, it may provide as well a way for IPv4-only nodes
or applications to communicate with IPv6-only destinations.
4.10. Incoming Connections
The use of NAT64, in principle, disallows IPv4 incoming connections,
which may be still needed for IPv4-only peer-to-peer applications.
However, there are several alternatives that resolve this issue:
a. STUN ([RFC5389]), TURN ([RFC5766]) and ICE ([RFC8445]) are
commonly used by peer-to-peer applications in order to allow
incoming connections with IPv4 NAT. In the case of NAT64, they
work as well. RFC editor note: If in time, replace STUN and TURN
with [I-D.ietf-tram-stunbis] / [I-D.ietf-tram-turnbis].
b. PCP ([RFC6887]) allows a host to control how incoming IPv4 and
IPv6 packets are translated and forwarded. A NAT64 may implement
PCP to allow this service.
c. EAM ([RFC7757]) may also be used in order to configure explicit
mappings for customers that require them. This is used for
example by SIIT-DC ([RFC7755]) and SIIT-DC-DTM ([RFC7756]).
5. Summary of Deployment Recommendations for NAT64/464XLAT
NAT64/464XLAT has demonstrated to be a valid choice in several
scenarios (IPv6-IPv4 and IPv4-IPv6-IPv4), being the predominant
mechanism in the majority of the cellular networks, which account for
hundreds of millions of users ([ISOC]). NAT64/464XLAT offer
different choices of deployment, depending on each network case,
needs and requirements. Despite that, this document is not an
explicit recommendation for using this choice versus other IPv4aaS
transition mechanisms. Instead, this document is a guide that
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facilitates evaluating a possible implementation of NAT64/464XLAT and
key decision points about specific design considerations for its
deployment.
Depending on the specific requirements of each deployment case, DNS64
may be a required function, while in other cases the adverse effects
may be counterproductive. Similarly, in some cases a NAT64 function,
together with a DNS64 function, may be a valid solution, when there
is a certainty that IPv4-only hosts or applications do not need to be
supported (Section 4.6 and Section 4.7). However, in other cases
(i.e. IPv4-only devices or applications need to be supported), the
limitations of NAT64/DNS64, may suggest the operator to look into
464XLAT as a more complete solution.
In the case of broadband managed networks (where the CE is provided
or suggested/supported by the operator), in order to fully support
the actual user needs (IPv4-only devices and applications, usage of
IPv4 literals and non-IPv6 compliant APIs), the 464XLAT scenario
should be considered. In that case, it must support a CLAT function.
If the operator provides DNS services, in order to increase
performance by reducing the double translation for all the IPv4
traffic, they may support a DNS64 function and avoid, as much as
possible, breaking DNSSEC. In this case, if the DNS service is
offering DNSSEC validation, then it must be in such way that it is
aware of the DNS64. This is considered the simpler and safer
approach, and may be combined as well with other recommendations
described in this document:
o DNS infrastructure MUST be aware of DNS64 (Section 4.1.2).
o Devices running CLAT SHOULD follow the indications in
Section 4.1.3 (Stub Validator). However, this may be out of the
control of the operator.
o CEs SHOULD include a DNS proxy and validator (Section 4.1.4).
o Section 4.1.5 (ACL of clients) and Section 4.1.6 (Mapping-out IPv4
addresses) MAY be considered by operators, depending on their own
infrastructure.
This "increased performance" approach has the disadvantage of
potentially breaking DNSSEC for a small percentage of validating end-
hosts versus the small impact of a double translation taking place in
the CE. If CE performance is not an issue, which is the most
frequent case, then a much safer approach is to not use DNS64 at all,
and consequently, ensure that all the IPv4 traffic is translated at
the CLAT (Section 4.3).
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If DNS64 is not used, at least one of the alternatives described in
Section 4.1.1, must be followed in order to learn the NAT64 prefix.
The operator needs to consider that if the DNS configuration can be
modified (Section 4.4, Section 4.4.2, Section 4.4.3), which most
probably is impossible to avoid, there are chances that instead of
configuring a DNS64 a foreign non-DNS64 is used. In a scenario with
only a NAT64 function IPv4-only remote host will no longer be
accessible. Instead, it will continue to work in the case of
464XLAT.
Similar considerations need to be taken regarding the usage of a
NAT64 WKP vs NSP (Section 4.5), as they must match with the
configuration of the DNS64. In case of using foreign DNS, they may
not match. If there is a CLAT and the configured foreign DNS is not
a DNS64, the network will keep working only if other means of
learning the NAT64 prefix are available.
As described in Section 4.8, for broadband networks, the CEs
supporting a CLAT function, SHOULD support DHCPv6-PD ([RFC8415]), or
alternative means for configuring a shorter prefix. The CE SHOULD
internally reserve one /64 for the stateless NAT46 translation. The
operator must ensure that the customers get allocated prefixes
shorter than /64 in order to support this optimization. One way or
the other, this is not impacting the performance of the operator
network.
Operators may follow Section 7 of [RFC6877] (Deployment
Considerations), for suggestions in order to take advantage of
traffic engineering requirements.
In the case of cellular networks, the considerations regarding DNSSEC
may appear as out-of-scope, because UEs Operating Systems, commonly
don't support DNSSEC. However, applications running on them may do,
or it may be an Operating System "built-in" support in the future.
Moreover, if those devices offer tethering, other client devices
behind the UE, may be doing the validation, hence the relevance of a
proper DNSSEC support by the operator network.
Furthermore, cellular networks supporting 464XLAT ([RFC6877]) and
"Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis"
([RFC7050]), allow a progressive IPv6 deployment, with a single APN
supporting all types of PDP context (IPv4, IPv6, IPv4v6). This
approach allows the network to automatically serve every possible
combinations of UEs.
If the operator chooses to provide validation for the DNS64 prefix
discovery, it must follow the advice from Section 3.1. of [RFC7050]
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(Validation of Discovered Pref64::/n).
One last consideration, is that many networks may have a mix of
different complex scenarios at the same time, for example, customers
requiring 464XLAT, others not requiring it, customers requiring
DNS64, others not, etc. In general, the different issues and the
approaches described in this document can be implemented at the same
time for different customers or parts of the network. That mix of
approaches don't present any problem or incompatibility, as they work
well together, being just a matter of appropriate and differentiated
provisioning. In fact, the NAT64/464XLAT approach facilitates an
operator offering both cellular and broadband services, to have a
single IPv4aaS for both networks while differentiating the deployment
key decisions to optimize each case. It even makes possible using
hybrid CEs that have a main broadband access link and a backup via
the cellular network.
In an ideal world we could safely use DNS64, if the approach proposed
in [I-D.bp-v6ops-ipv6-ready-dns-dnssec] is followed, avoiding the
cases where DNSSEC may be broken. However, this will not solve the
issues related to DNS Privacy and Split DNS.
The only 100% safe solution, which also resolves all the issues, will
be, in addition to having a CLAT function, not using a DNS64 but
instead making sure that the hosts have a built-in address synthesis
feature. Operators could manage to provide CEs with the CLAT
function, however the built-in address synthesis feature is out of
their control. If the synthesis is provided either by the Operating
System (via its DNS resolver API) or by the application (via its own
DNS resolver), in such way that the prefix used for the NAT64
function is reachable for the host, the problem goes away.
Whenever feasible, using EAM ([RFC7757]) as indicated in Section 4.9,
provides a very relevant optimization, avoiding double-translations.
Applications that require incoming connections, typically already
provide means for that. However, PCP and EAM, as indicated in
Section 4.10, are valid alternatives, even for creating explicit
mappings for customers that require them.
6. Deployment of 464XLAT/NAT64 in Enterprise Networks
The recommendations of this document can be used as well in
enterprise networks, campus and other similar scenarios (including
managed end-user networks).
This include scenarios where the NAT64 function (and DNS64 function,
if available) are under the control of that network (or can be
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configured manually according to that network specific requirements),
and for whatever reasons, there is a need to provide "IPv6-only
access" to any part of that network or it is IPv6-only connected to
third party-networks.
An example of that is the IETF meetings network itself, where both
NAT64 and DNS64 functions are provided, presenting in this case the
same issues as per Section 3.1.1. If there is a CLAT function in the
IETF network, then there is no need to use DNS64 and it falls under
the considerations of Section 3.1.3. Both scenarios have been tested
and verified already in the IETF network itself.
Next figures are only meant to represent a few of the possible
scenarios, not pretending to be the only feasible ones.
Figure 14 provides an example of an IPv6-only enterprise network
connected with dual-stack to Internet and using local NAT64 and DNS64
functions.
+----------------------------------+
| Enterprise Network |
| +----------+ +----------+ | +----------+
| | IPv6 | | NAT64 | | | IPv4 |
| | only +--------+ + | +-------+ + |
| | LANs | | DNS64 | | | IPv6 |
| +----------+ +----------+ | +----------+
+----------------------------------+
Figure 14: IPv6-only enterprise with NAT64 and DNS64
Figure 15 provides an example of a dual-stack (DS) enterprise network
connected with dual-stack (DS) to Internet and using a CLAT function,
without a DNS64 function.
+----------------------------------+
| Enterprise Network |
| +----------+ +----------+ | +----------+
| | IPv6 | | | | | IPv4 |
| | + +--------+ NAT64 | +-------+ + |
| | CLAT | | | | | IPv6 |
| +----------+ +----------+ | +----------+
+----------------------------------+
Figure 15: DS enterprise with CLAT, DS Internet, without DNS64
Finally, Figure 16 provides an example of an IPv6-only provider with
a NAT64 function, and a dual-stack (DS) enterprise network by means
of their own CLAT function, without a DNS64 function.
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+----------------------------------+
| Enterprise Network |
| +----------+ +----------+ | +----------+
| | IPv6 | | | | IPv6 | |
| | + +--------+ CLAT | +--------+ NAT64 |
| | IPv4 | | | | only | |
| +----------+ +----------+ | +----------+
+----------------------------------+
Figure 16: DS enterprise with CLAT, IPv6-only Access, without DNS64
7. Security Considerations
This document does not have new specific security considerations
beyond those already reported by each of the documents cited. For
example, DNS64 ([RFC6147]) already describes the DNSSEC issues.
Note that, as already described in Section 4.4, there may be
undesirable interactions, specially if using VPNs or DNS privacy,
which may impact in the correct performance of DNS64/NAT64.
It should be remarked that the use of a DNS64 function has equivalent
privacy considerations as in the case of a regular DNS, either
located in the service provider or an external one.
8. IANA Considerations
This document does not have any new specific IANA considerations.
Note: This section is assuming that https://www.rfc-
editor.org/errata/eid5152 is resolved, otherwise, this section may
include the required text to resolve the issue.
Alternatively, this could be fixed also by
[I-D.cheshire-sudn-ipv4only-dot-arpa].
9. Acknowledgements
The author would like to acknowledge the inputs of Gabor Lencse,
Andrew Sullivan, Lee Howard, Barbara Stark, Fred Baker, Mohamed
Boucadair, Alejandro D'Egidio, Dan Wing, Mikael Abrahamsson and Eric
Vyncke.
Conversations with Marcelo Bagnulo, one of the co-authors of NAT64
and DNS64, as well as several emails in mailing lists from Mark
Andrews, have been very useful for this work.
Christian Huitema inspired working in this document by suggesting
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that DNS64 should never be used, during a discussion regarding the
deployment of CLAT in the IETF network.
10. ANNEX A: Example of Broadband Deployment with 464XLAT
This section summarizes how an operator may deploy an IPv6-only
network for residential/SOHO customers, supporting IPv6 inbound
connections, and IPv4-as-a-Service (IPv4aaS) by using 464XLAT.
Note that an equivalent setup could also be provided for enterprise
customers. In case they need to support IPv4 inbound connections,
several mechanisms, depending on specific customer needs, allow that,
for instance [RFC7757].
Conceptually, most part of the operator network could be IPv6-only
(represented in the next pictures as "IPv6-only flow"), or even if
this part of the network is actually dual-stack, only IPv6-access is
available for some customers (i.e. residential customers). This part
of the network connects the IPv6-only subscribers (by means of
IPv6-only access links), to the IPv6 upstream providers, as well as
to the IPv4-Internet by means of the NAT64 (PLAT in the 464XLAT
terminology).
The traffic flow from and back to the CE to services available in the
IPv6 Internet (or even dual-stack remote services, when IPv6 is being
used), is purely native IPv6 traffic, so there are no special
considerations about it.
Looking at the picture from the DNS perspective, there are remote
networks with are IPv4-only, and typically will have only IPv4 DNS
(DNS/IPv4), or at least will be seen as that from the CE perspective.
At the operator side, the DNS, as seen from the CE, is only IPv6
(DNS/IPv6) and has also a DNS64 function.
In the customer LANs side, there is actually one network, which of
course could be split in different segments. The most common setup
will be those segments being dual-stack, using global IPv6 addresses
and [RFC1918] for IPv4, as usual in any regular residential/SOHO IPv4
network. In the figure, it is represented as tree segments, just to
show that the three possible setups are valid (IPv6-only, IPv4-only
and dual-stack).
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.-----. +-------+ .-----. .-----.
/ IPv6- \ | | / \ / \
( only )--+ Res./ | / IPv6- \ .-----. / IPv4- \
\ LANs / | SOHO +--( only )--( NAT64 )--( only )
`-----' | | \ flow / `-----' \ flow /
.-----. | IPv6 | \ / \ /
/ IPv4- \ | CE | `--+--' `--+--'
( only )--+ with | | |
\ LANs / | CLAT | +---+----+ +---+----+
`-----' | | |DNS/IPv6| |DNS/IPv4|
.-----. +---+---+ | with | +--------+
/ Dual- \ | | DNS64 |
( Stack )------| +--------+
\ LANs /
`-----'
Figure 17: CE setup with built-in CLAT with DNS64
In addition to the regular CE setup, which will be typically access-
technology dependent, the steps for the CLAT function configuration
can be summarized as:
1. Discovery of the PLAT (NAT64) prefix: It may be done using
[RFC7050], or in those networks where PCP is supported, by means
of [RFC7225], or other alternatives that may be available in the
future, such as Router Advertising ([I-D.ietf-6man-ra-pref64]) or
DHCPv6 options ([I-D.li-intarea-nat64-prefix-dhcp-option]).
2. If the CLAT function allows stateless NAT46 translation, a /64
from the pool typically provided to the CE by means of DHCPv6-PD
[RFC8415], need to be set aside for that translation. Otherwise,
the CLAT is forced to perform an intermediate stateful NAT44
before the a stateless NAT46, as described in Section 4.8.
A more detailed configuration approach is described in [RFC8585].
The operator network needs to ensure that the correct responses are
provided for the discovery of the PLAT prefix. It is highly
recommended to follow [RIPE-690], in order to ensure that multiple
/64s are available, including the one needed for the NAT46 stateless
translation.
The operator needs to understand other issues, described across this
document, in order to take the relevant decisions. For example, if
several NAT64 functions are needed in the context of scalability/
high-availability, an NSP should be considered (Section 4.5).
More complex scenarios are possible, for example, if a network offers
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multiple NAT64 prefixes, destination-based NAT64 prefixes, etc.
If the operator decides not to provide a DNS64 function, then this
setup turns into the one in the following Figure. This will be also
the setup that "will be seen" from the perspective of the CE, if a
foreign DNS is used and consequently is not the operator-provided
DNS64 function.
.-----. +-------+ .-----. .-----.
/ IPv6- \ | | / \ / \
( only )--+ Res./ | / IPv6- \ .-----. / IPv4- \
\ LANs / | SOHO +--( only )--( NAT64 )--( only )
`-----' | | \ flow / `-----' \ flow /
.-----. | IPv6 | \ / \ /
/ IPv4- \ | CE | `--+--' `--+--'
( only )--+ with | | |
\ LANs / | CLAT | +---+----+ +---+----+
`-----' | | |DNS/IPv6| |DNS/IPv4|
.-----. +---+---+ +--------+ +--------+
/ Dual- \ |
( Stack )------|
\ LANs /
`-----'
Figure 18: CE setup with built-in CLAT without DNS64
In this case, the discovery of the PLAT prefix needs to be arranged
as indicated in Section 4.1.1.
In this case, the CE doesn't have a built-in CLAT function, or the
customer can choose to setup the IPv6 operator-managed CE in bridge
mode (and optionally use an external router), or for example, there
is an access technology that requires some kind of media converter
(ONT for FTTH, Cable-Modem for DOCSIS, etc.), the complete setup will
look as in Figure 19. Obviously, there will be some intermediate
configuration steps for the bridge, depending on the specific access
technology/protocols, which should not modify the steps already
described in the previous cases for the CLAT function configuration.
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+-------+ .-----. .-----.
| | / \ / \
| Res./ | / IPv6- \ .-----. / IPv4- \
| SOHO +--( only )--( NAT64 )--( only )
| | \ flow / `-----' \ flow /
| IPv6 | \ / \ /
| CE | `--+--' `--+--'
| Bridge| | |
| | +---+----+ +---+----+
| | |DNS/IPv6| |DNS/IPv4|
+---+---+ +--------+ +--------+
|
.-----. +---+---+
/ IPv6- \ | |
( only )--+ IPv6 |
\ LANs / | Router|
`-----' | |
.-----. | with |
/ IPv4- \ | CLAT |
( only )--+ |
\ LANs / | |
`-----' | |
.-----. +---+---+
/ Dual- \ |
( Stack )------|
\ LANs /
`-----'
Figure 19: CE setup with bridged CLAT without DNS64
It should be avoided that several routers (i.e., the operator
provided CE and a downstream user provided router) enable
simultaneously routing and/or CLAT, in order to avoid multiple NAT44
and NAT46 levels, as well as ensuring the correct operation of
multiple IPv6 subnets. In those cases, it is suggested the use of
HNCP ([RFC8375]).
Note that the procedure described here for the CE setup, can be
simplified if the CE follows [RFC8585].
11. ANNEX B: CLAT Implementation
In addition to the regular set of features for a CE, a CLAT CE
implementation requires support of:
o [RFC7915] for the NAT46 function.
o [RFC7050] for the PLAT prefix discovery.
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o [RFC7225] for the PLAT prefix discovery if PCP is supported.
o [I-D.ietf-6man-ra-pref64] for the PLAT prefix discovery by means
of Router Advertising.
o [I-D.li-intarea-nat64-prefix-dhcp-option] for the PLAT prefix
discovery by means of DHCP.
o If stateless NAT46 is supported, a mechanism to ensure that
multiple /64 are available, such as DHCPv6-PD [RFC8415].
There are several OpenSource implementations of CLAT, such as:
o Android: https://github.com/ddrown/android_external_android-clat.
o Jool: https://www.jool.mx.
o Linux: https://github.com/toreanderson/clatd.
o OpenWRT: https://github.com/openwrt-
routing/packages/blob/master/nat46/files/464xlat.sh.
o VPP: https://git.fd.io/vpp/tree/src/plugins/nat.
12. ANNEX C: Benchmarking
[RFC8219] has defined a benchmarking methodology for IPv6 transition
technologies. NAT64 and 464XLAT are addressed among the single and
double translation technologies, respectively. DNS64 is addressed in
Section 9, and the methodology is more elaborated in [DNS64-BM-Meth].
Several documents provide references to benchmarking results, for
example in the case of DNS64, [DNS64-Benchm].
13. ANNEX D: Changes from -00 to -01/-02
Section to be removed after WGLC. Significant updates are:
1. Text changes across all the document.
14. ANNEX E: Changes from -02 to -03
Section to be removed after WGLC. Significant updates are:
1. Added references to new cited documents.
2. Reference to RFC8273 and on-demand IPv4-in-IPv6 VPN for IPv6-only
LANs w/o DNS64.
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3. Overall review and editorial changes.
15. ANNEX F: Changes from -03 to -04
Section to be removed after WGLC. Significant updates are:
1. Added text related to EAM considerations.
16. ANNEX G: Changes from -04 to -05
Section to be removed after WGLC. Significant updates are:
1. Added cross references to EAM section.
2. Reworded "foreing DNS section".
3. Overall editorial review of text, pictures and nits correction.
17. ANNEX H: Changes from -05 to -06
Section to be removed after WGLC. Significant updates are:
1. Corrected EAMT to EAM.
2. Typos and nits.
3. New considerations regarding incoming connections.
18. ANNEX H: Changes from -06 to -07
Section to be removed after WGLC. Significant updates are:
1. Inputs/clarifications from IESG review.
19. References
19.1. Normative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
<https://www.rfc-editor.org/info/rfc1918>.
[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>.
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[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<https://www.rfc-editor.org/info/rfc5389>.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
<https://www.rfc-editor.org/info/rfc5625>.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766,
DOI 10.17487/RFC5766, April 2010,
<https://www.rfc-editor.org/info/rfc5766>.
[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>.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, DOI 10.17487/RFC6144,
April 2011, <https://www.rfc-editor.org/info/rfc6144>.
[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>.
[RFC6535] Huang, B., Deng, H., and T. Savolainen, "Dual-Stack Hosts
Using "Bump-in-the-Host" (BIH)", RFC 6535,
DOI 10.17487/RFC6535, February 2012,
<https://www.rfc-editor.org/info/rfc6535>.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation",
RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
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[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>.
[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>.
[RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
Port Control Protocol (PCP)", RFC 7225,
DOI 10.17487/RFC7225, May 2014,
<https://www.rfc-editor.org/info/rfc7225>.
[RFC7757] Anderson, T. and A. Leiva Popper, "Explicit Address
Mappings for Stateless IP/ICMP Translation", RFC 7757,
DOI 10.17487/RFC7757, February 2016,
<https://www.rfc-editor.org/info/rfc7757>.
[RFC7915] Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
"IP/ICMP Translation Algorithm", RFC 7915,
DOI 10.17487/RFC7915, June 2016,
<https://www.rfc-editor.org/info/rfc7915>.
[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>.
[RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
<https://www.rfc-editor.org/info/rfc8273>.
[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/info/rfc8305>.
[RFC8375] Pfister, P. and T. Lemon, "Special-Use Domain
'home.arpa.'", RFC 8375, DOI 10.17487/RFC8375, May 2018,
<https://www.rfc-editor.org/info/rfc8375>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
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[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
19.2. Informative References
[About-DNS64]
Linkova, J., "Let's talk about IPv6 DNS64 & DNSSEC", 2016,
<https://blog.apnic.net/2016/06/09/
lets-talk-ipv6-dns64-dnssec/>.
[ARCEP] ARCEP, "Service client des operateurs : les mesures de
qualite de service", 2018, <https://www.arcep.fr/
cartes-et-donnees/nos-publications-chiffrees/
service-client-des-operateurs-mesures-de-la-qualite-de-
service/service-client-des-operateurs-les-mesures-de-
qualite-de-service.html>.
[DNS64-Benchm]
Lencse, G. and Y. Kadobayashi, "Benchmarking DNS64
Implementations: Theory and Practice", Computer
Communications , vol. 127, no. 1, pp. 61-74,
DOI 10.1016/j.comcom.2018.05.005, September 2018.
[DNS64-BM-Meth]
Lencse, G., Georgescu, M., and Y. Kadobayashi,
"Benchmarking Methodology for DNS64 Servers", Computer
Communications , vol. 109, no. 1, pp. 162-175,
DOI 10.1016/j.comcom.2017.06.004, September 2017.
[FCC] FCC, "Measuring Broadband America Mobile 2013-2018
Coarsened Data", 2018, <https://www.fcc.gov/reports-
research/reports/measuring-broadband-america/
measuring-broadband-america-mobile-2013-2018>.
[I-D.bp-v6ops-ipv6-ready-dns-dnssec]
Byrne, C. and J. Palet, "IPv6-Ready DNS/DNSSSEC
Infrastructure", draft-bp-v6ops-ipv6-ready-dns-dnssec-00
(work in progress), October 2018.
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[I-D.cheshire-sudn-ipv4only-dot-arpa]
Cheshire, S. and D. Schinazi, "Special Use Domain Name
'ipv4only.arpa'", draft-cheshire-sudn-ipv4only-dot-arpa-14
(work in progress), November 2018.
[I-D.huitema-quic-dnsoquic]
Huitema, C., Shore, M., Mankin, A., Dickinson, S., and J.
Iyengar, "Specification of DNS over Dedicated QUIC
Connections", draft-huitema-quic-dnsoquic-06 (work in
progress), March 2019.
[I-D.ietf-6man-ra-pref64]
Colitti, L. and J. Linkova, "Discovering PREF64 in Router
Advertisements", draft-ietf-6man-ra-pref64-01 (work in
progress), June 2019.
[I-D.ietf-tram-stunbis]
Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
D., Mahy, R., and P. Matthews, "Session Traversal
Utilities for NAT (STUN)", draft-ietf-tram-stunbis-21
(work in progress), March 2019.
[I-D.ietf-tram-turnbis]
K, R., Johnston, A., Matthews, P., and J. Rosenberg,
"Traversal Using Relays around NAT (TURN): Relay
Extensions to Session Traversal Utilities for NAT (STUN)",
draft-ietf-tram-turnbis-27 (work in progress), June 2019.
[I-D.li-intarea-nat64-prefix-dhcp-option]
Li, L., Cui, Y., Liu, C., Wu, J., Baker, F., and J. Palet,
"DHCPv6 Options for Discovery NAT64 Prefixes", draft-li-
intarea-nat64-prefix-dhcp-option-02 (work in progress),
April 2019.
[I-D.lmhp-v6ops-transition-comparison]
Lencse, G., Palet, J., Howard, L., Patterson, R., and I.
Farrer, "Pros and Cons of IPv6 Transition Technologies for
IPv4aaS", draft-lmhp-v6ops-transition-comparison-03 (work
in progress), July 2019.
[I-D.palet-v6ops-464xlat-opt-cdn-caches]
Palet, J. and A. D'Egidio, "464XLAT Optimization", draft-
palet-v6ops-464xlat-opt-cdn-caches-02 (work in progress),
June 2019.
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[I-D.vixie-dns-rpz]
Vixie, P. and V. Schryver, "DNS Response Policy Zones
(RPZ)", draft-vixie-dns-rpz-04 (work in progress),
December 2016.
[ISOC] ISOC, "State of IPv6 Deployment 2018", 2018,
<https://www.internetsociety.org/resources/2018/
state-of-ipv6-deployment-2018/>.
[RFC6889] Penno, R., Saxena, T., Boucadair, M., and S. Sivakumar,
"Analysis of Stateful 64 Translation", RFC 6889,
DOI 10.17487/RFC6889, April 2013,
<https://www.rfc-editor.org/info/rfc6889>.
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in
the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013,
<https://www.rfc-editor.org/info/rfc6950>.
[RFC7051] Korhonen, J., Ed. and T. Savolainen, Ed., "Analysis of
Solution Proposals for Hosts to Learn NAT64 Prefix",
RFC 7051, DOI 10.17487/RFC7051, November 2013,
<https://www.rfc-editor.org/info/rfc7051>.
[RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64
Deployment Options and Experience", RFC 7269,
DOI 10.17487/RFC7269, June 2014,
<https://www.rfc-editor.org/info/rfc7269>.
[RFC7755] Anderson, T., "SIIT-DC: Stateless IP/ICMP Translation for
IPv6 Data Center Environments", RFC 7755,
DOI 10.17487/RFC7755, February 2016,
<https://www.rfc-editor.org/info/rfc7755>.
[RFC7756] Anderson, T. and S. Steffann, "Stateless IP/ICMP
Translation for IPv6 Internet Data Center Environments
(SIIT-DC): Dual Translation Mode", RFC 7756,
DOI 10.17487/RFC7756, February 2016,
<https://www.rfc-editor.org/info/rfc7756>.
[RFC7849] Binet, D., Boucadair, M., Vizdal, A., Chen, G., Heatley,
N., Chandler, R., Michaud, D., Lopez, D., and W. Haeffner,
"An IPv6 Profile for 3GPP Mobile Devices", RFC 7849,
DOI 10.17487/RFC7849, May 2016,
<https://www.rfc-editor.org/info/rfc7849>.
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[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/info/rfc8094>.
[RFC8219] Georgescu, M., Pislaru, L., and G. Lencse, "Benchmarking
Methodology for IPv6 Transition Technologies", RFC 8219,
DOI 10.17487/RFC8219, August 2017,
<https://www.rfc-editor.org/info/rfc8219>.
[RFC8585] Palet Martinez, J., Liu, H., and M. Kawashima,
"Requirements for IPv6 Customer Edge Routers to Support
IPv4-as-a-Service", RFC 8585, DOI 10.17487/RFC8585, May
2019, <https://www.rfc-editor.org/info/rfc8585>.
[RIPE-690]
RIPE, "Best Current Operational Practice for Operators:
IPv6 prefix assignment for end-users - persistent vs non-
persistent, and what size to choose", October 2017,
<https://www.ripe.net/publications/docs/ripe-690>.
[Threat-DNS64]
Lencse, G. and Y. Kadobayashi, "Methodology for the
identification of potential security issues of different
IPv6 transition technologies: Threat analysis of DNS64 and
stateful NAT64", Computers & Security , vol. 77, no. 1,
pp. 397-411, DOI 10.1016/j.cose.2018.04.012, August 2018.
Author's Address
Jordi Palet Martinez
The IPv6 Company
Molino de la Navata, 75
La Navata - Galapagar, Madrid 28420
Spain
Email: jordi.palet@theipv6company.com
URI: http://www.theipv6company.com/
Palet Martinez Expires January 12, 2020 [Page 45]
