Deprecation of DNS64 for Discovery of IPv6 Prefix Used for IPv6 Address Synthesis
draft-buraglio-deprecate7050-00
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draft-buraglio-deprecate7050-00
dnsop N. Buraglio
Internet-Draft Energy Sciences Network
Intended status: Standards Track T. Jensen
Expires: 13 March 2025 Microsoft
J. Linkova
Google
9 September 2024
Deprecation of DNS64 for Discovery of IPv6 Prefix Used for IPv6 Address
Synthesis
draft-buraglio-deprecate7050-00
Abstract
RFC7050 describes a method for detecting the presence of DNS64 and
for learning the IPv6 prefix used for protocol translation (RFC6145).
This methodology depends on the existence of a well-known IPv4-only
fully qualified domain name "ipv4only.arpa.". Because newer methods
exist that lack the requirement of a higher level protocol, instead
using existing operations in the form of native router
advertisements, discovery of the IPv6 prefix used for protocol
translation using RFC7050 is deprecated to legacy status.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://buraglio.github.io/draft-buraglio-deprecate7050/draft-
buraglio-deprecate7050.html. Status information for this document
may be found at https://datatracker.ietf.org/doc/draft-buraglio-
deprecate7050/.
Discussion of this document takes place on the dnsop Working Group
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Source for this draft and an issue tracker can be found at
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Existing issues with RFC 7050 . . . . . . . . . . . . . . . . 4
3.1. Dependency on Network-Provided Recursive Resolvers . . . 4
3.2. Network Stack Initialization Delay . . . . . . . . . . . 4
3.3. Inflexibility . . . . . . . . . . . . . . . . . . . . . . 4
3.4. Security Implications . . . . . . . . . . . . . . . . . . 5
3.4.1. Definition of secure channel . . . . . . . . . . . . 5
3.4.2. Secure channel example of IPsec . . . . . . . . . . . 5
3.4.3. Secure channel example of link layer encryption . . . 6
4. Recommendations for PREF64 Discovery . . . . . . . . . . . . 6
4.1. Deployment Recommendations . . . . . . . . . . . . . . . 6
4.2. Clients Implementation Recommendations . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The DNS-based mechanism defined in [RFC7050] was the very first
mechanism available for nodes to discover the PREF64 information.
However since the publication of RFC7050, other methods have been
developed to address some of [RFC7050] limitations.
For example, [RFC8781] describes a Neighbor Discovery option to be
used in Router Advertisements (RAs) to communicate prefixes of
Network Address and Protocol Translation from IPv6 clients to IPv4
servers (NAT64) to hosts. This approach has the advantage of using
the same communication channel IPv6 clients use to discover other
network configurations such as the network's default route. This
means network administrators can secure this configuration along with
other configurations IPv6 requires using a single approach such as RA
Guard [RFC6105].
Taking into account some fundamental flaws of [RFC7050] mechanism, it
seems desirable to deprecate it and recommend new deployments and
implementations to use better methods to obtain PREF64 information.
2. Conventions and Definitions
NAT64: a mechanism for translating IPv6 packets to IPv4 packets and
vice versa. The translation is done by translating the packet
headers according to the IP/ICMP Translation Algorithm defined in
[RFC6145].
DNS64: a mechanism for synthesizing AAAA records from A records,
defined in [RFC6147].
Router Advertisement: A packet used by Neighbor Discovery [RFC4861]
and StateLess Address AutoConfiguration (SLAAC, [RFC4862]) to
advertize the presence of the routers, togther with other IPv6
configuration information.
PREF64 (or NAT64 prefix): An IPv6 prefix used for IPv6 address
synthesis and for network addresses and protocols translation from
IPv6 clients to IPv4 servers, [RFC6146].
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.
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3. Existing issues with RFC 7050
DNS-based method of discovering the NAT64 prefix introduces some
challenges, which make this approach less preferable than most
recently developed alternatives (such as PREF64 RA option,
[RFC8781]). This section outlines the key issues, associated with
[RFC7050].
3.1. Dependency on Network-Provided Recursive Resolvers
Fundamentally, the presence of the NAT64 and the exact value of the
prefix used for the translation are network-specific attributes.
Therefore, to discover the PREF64 the device needs to use the DNS
resolvers provided by the network. If the device is configured to
use other recursive resolvers, its name resolution APIs and libraries
are required to recognize 'ipv4only.arpa.' as a special name and give
it special treatment. This issue and remediation approach are
discussed in [RFC8880]. However, it has been observed that not all
[RFC7050] implementations support [RFC8880] requirements for special
treatment of 'ipv4only.arpa.'. As a result, configuring such systems
to use resolvers other than the one provided by the network might
break the PREF64 discovery, leading to degraded user experience.
3.2. Network Stack Initialization Delay
When using SLAAC ([RFC4862]), an IPv6 host usually needs just one
Router Advertisement (RA, [RFC4861]) packet to obtain all information
required to complete the host's network configuration. For an
IPv6-only host, the PREF64 information is essential, especially if
the host implements the customer-side translator (CLAT) ([RFC6877]).
The mechanism defined in [RFC7050] implies that the PREF64
information is not bundled with all other network configuration
parameters provided by RAs, and can only be obtained after the host
has configured the rest of its IPv6 stack. Therefore, until the
process described in Section 3 of [RFC7050] is completed, the CLAT
process can not start, which negatively impacts IPv4-only
applications which have alrady started.
3.3. Inflexibility
Section 3 of [RFC7050] requires that the node SHALL cache the replies
received during the PREF64 discovery and SHOULD repeat the discovery
process ten seconds before the TTL of the Well-Known Name's synthetic
AAAA resource record expires. As a result, once the PREF64 is
discovered, it will be used until the TTL expired, or until the node
disconnects from the network. There is no mechanism for an operator
to force the PREF64 rediscovery on the node without disconnecting the
node from the network. If the operator needs to change the PREF64
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value used in the network, they need to proactively reduce the TTL
value returned by the DNS64 server. This method has two significant
drawbacks:
* many networks utilize external DNS64 servers and therefore have no
control over the TTL value.
* the PREF64 changes need to be planned and executed at least TTL
seconds in advance. If the operator needs to notify nodes that a
particular prefix must not be used (e.g. during a network outage
or if the nodes learnt a rogue PREF64 as a result of an attack),
it might not be possible without interrupting the network
connectivity for the affected nodes.
3.4. Security Implications
As discussed in Section 7 of [RFC7050], the DNS-based PREF64
discovery is prone to DNS spoofing attacks. In addition to creating
a wider attack surface for IPv6 deployments, [RFC7050] has other
security challenges worth noting to justify declaring it legacy.
3.4.1. Definition of secure channel
[RFC7050] requires a node's communication channel with a DNS64 server
to be a "secure channel" which it defines to mean "a communication
channel a node has between itself and a DNS64 server protecting DNS
protocol-related messages from interception and tampering." This
need is redundant when another communication mechanism of
IPv6-related configuration, specifically Router Advertisements, can
already be defended against tampering by RA Guard [RFC6105].
Requiring nodes to implement two defense mechanisms when only one is
necessary when [RFC8781] is used in place of [RFC7050] creates
unnecessary risk.
3.4.2. Secure channel example of IPsec
One of the two examples [RFC7050] defines to qualify a communication
channel with a DNS64 server is the use of an "IPsec-based virtual
private network (VPN) tunnel". As of the time of this writing, this
is not supported as a practice by any common operating system DNS
client. While they could, there have also since been multiple
mechanisms defined for performing DNS-specific encryption such as
those defined in [RFC9499] that would be more appropriately scoped to
the applicable DNS traffic. These are also compatible with encrypted
DNS advertisement by the network using Discovery of Network-
designated Resolvers [RFC9463] that would ensure the clients know in
advance that the DNS64 server supported the encryption mechanism.
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3.4.3. Secure channel example of link layer encryption
The other example given by [RFC7050] that would allow a communication
channel with a DNS64 server to qualify as a "secure channel" is the
use of a "link layer utilizing data encryption technologies". As of
the time of this writing, most common link layer implementations use
data encryption already with no extra effort needed on the part of
network nodes. While this appears to be a trivial way to satisfy
this requirement, it also renders the requirement meaningless since
any node along the path can still read the higher-layer DNS traffic
containing the translation prefix. This seems to be at odds with the
definition of "secure channel" as explained in Section 2.2 of
[RFC7050].
4. Recommendations for PREF64 Discovery
4.1. Deployment Recommendations
Operators deploying NAT64 networks SHOULD provide PREF64 information
in Router Advertisements as per [RFC8781].
4.2. Clients Implementation Recommendations
Clients SHOULD obtain PREF64 information from Router Advertisements
as per [RFC8781] instead of using [RFC7050] method. In the absense
of the PREF64 information in RAs, a client MAY choose to fall back to
RFC7050.
5. Security Considerations
Obtaining PREF64 information from Router Advertisements improves the
overall security of an IPv6-only client as it mitigates all attack
vectors related to spoofed or rogue DNS response, as discussed in
Section 7 of [RFC7050]. Security considerations related to obtaining
PREF64 information from RAs are discussed in Section 7 of [RFC8781].
6. IANA Considerations
It is expected that there will be a long tail of both clients and
networks still relying on [RFC7050] as a sole mechanism to discover
PREF64 information. Therefore IANA still need to maintain
"ipv4only.arpa." as described in [RFC7050] and this document has no
IANA actions.
7. References
7.1. Normative References
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[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/rfc/rfc2119>.
[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/rfc/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/rfc/rfc8174>.
7.2. Informative References
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/rfc/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/rfc/rfc4862>.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
DOI 10.17487/RFC6105, February 2011,
<https://www.rfc-editor.org/rfc/rfc6105>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
<https://www.rfc-editor.org/rfc/rfc6145>.
[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/rfc/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/rfc/rfc6147>.
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[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/rfc/rfc6877>.
[RFC8781] Colitti, L. and J. Linkova, "Discovering PREF64 in Router
Advertisements", RFC 8781, DOI 10.17487/RFC8781, April
2020, <https://www.rfc-editor.org/rfc/rfc8781>.
[RFC8880] Cheshire, S. and D. Schinazi, "Special Use Domain Name
'ipv4only.arpa'", RFC 8880, DOI 10.17487/RFC8880, August
2020, <https://www.rfc-editor.org/rfc/rfc8880>.
[RFC9463] Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N.,
and T. Jensen, "DHCP and Router Advertisement Options for
the Discovery of Network-designated Resolvers (DNR)",
RFC 9463, DOI 10.17487/RFC9463, November 2023,
<https://www.rfc-editor.org/rfc/rfc9463>.
[RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
RFC 9499, DOI 10.17487/RFC9499, March 2024,
<https://www.rfc-editor.org/rfc/rfc9499>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Nick Buraglio
Energy Sciences Network
Email: buraglio@forwardingplane.net
Tommy Jensen
Microsoft
Email: tojens.ietf@gmail.com
Jen Linkova
Google
Email: furry13@gmail.com
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