[DNSOP] AD sponsoring draft-cheshire-sudn-ipv4only-dot-arpa

Warren Kumari <warren@kumari.net> Wed, 04 July 2018 20:26 UTC

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From: Warren Kumari <warren@kumari.net>
Date: Wed, 4 Jul 2018 16:26:06 -0400
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Subject: [DNSOP] AD sponsoring draft-cheshire-sudn-ipv4only-dot-arpa
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Stuart Cheshire & David Schinazi have asked me to AD sponsor the
draft-cheshire-sudn-ipv4only-dot-arpa document

>From the document:
"The specification for how a client discovers its network's NAT64 prefix
[RFC7050] defines the special name 'ipv4only.arpa' for this purpose, but
declares it to be a non-special name in that specification Domain Name
Reservation Considerations section.
Consequently, despite the well articulated special purpose of the name,
'ipv4only.arpa' was not recorded in the Special-Use Domain Names registry
as a name with special properties.
This document formally declares the actual special properties of the name,
and adds similar declarations for the corresponding reverse mapping names."

RFC7050 ("Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis") is
worth reading before reading this. If you are mainly a DNS person,
​this may be...surprising.

When reading draft-cheshire-sudn-ipv4only-dot-arpa there are a few things
 keeping in mind:

1: This is a fairly specialized function - it is used by NAT64 clients to
discover the prefix used for synthesis ("normal" people / applications
never need to resolve this). The main people who will deal with this are
mobile / stack vendors, and NAT64 providers.
2: RFC7050 has a large amount of text around DNSSEC, what to do with
DNSSEC, etc. Note that this DNSSEC is for the FQDN of the *NAT64 device*,
not the ipv4only.arpa name.
3: Devices use this mechanism to discover the IPv6 prefix used for IPv6
address synthesis - different interfaces (e.g cellular and wifi) will have
different prefixes. This means that clients
​ ​
do this query using the resolver learned on / appropriate for that
interface. This is the main bit which is weird for a DNS person - the
response from the resolver for your cellular interface connected to
T-Mobile contains T-Mobile's NAT64 prefix; the response from the resolver
learnt over your wifi connection to the IETF network contains the NAT64
prefix you use on the IETF network. DNS isn't really being used here for
resolving names, rather DNS is being used a signalling mechanism (a rude
t-shirt springs to mind here).

What this draft does is:
1: record this in
​ ​
the SUDN registry; RFC7050 answered the RFC6761 questions, but didn't
actually ask the IANA to update the registry.
2: requests that the IANA make ipv4only.arpa be an insecure delegation (see
#2 above) -
​this removes some special handling and complexity.​

3: specifies that you have to use the resolvers learn on an interface for
these queries. The whole purpose of these queries is to learn the *local*
NAT64 prefix - asking a public recursive isn't going to help you here.
4: This is under .arpa (and is already in wide use) - it doesn't have the
sticky policy problems that many SUD names have.

 to AD sponsor this, but would really appreciate your review and input.
RFC7050 is deployed - this improves / clarifies things.

1: The authors have previously presented this document at DNSOP meetings -
there was some discussion, but no real interest in adopting or shouts of
outrage about it.
2: I've asked the DNSOP chairs if I can use the DNSOP list for discussion
of this
​ ​
(and they agreed)
3: This was originally a product of the (now closed) BEHAVE WG - I've
spoken with Spencer (the BEHAVE AD) who has no objections.
4: I've asked the IESG and there were no objections either.
5: As this touches .arpa I'm also asking the IAB for input.
6: Dave Thaler (who was the document shepherd for RFC7050) has kindly
agreed to be shepherd for this document too.


[0]: note that they asked this before the current "ipv4only.arpa's
delegation should be insecure." thread -

I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of