A straightforward transition plan (was: Re: V6 still not supported)

Mark Andrews marka at isc.org
Wed Mar 30 23:32:01 UTC 2022

> On 26 Mar 2022, at 21:51, Philip Homburg <pch-nanog-2 at u-1.phicoh.com> wrote:
>>> If there is a magical transition technology that allows an IPv6-only host t
>> o
>>> talk to an IPv4-only host, then let's deploy it.
>> DNS64/NAT64, DS-Lite, 6rd, 464XLAT, MAP-T, MAP-E, ? pick a transition
>> protocol and see what happens!  (with more coming every year...)
> The problem with these is that they are not full solutions. That's why we
> get new ones every year: everybody picks the subset of the problem they
> want solve.
> To go over the ones you listed:
> - 6rd. That's the odd one out here. 6rd privdes IPv6 over an IPv4
> infrastructure. Very useful when there was not a lot of IPv6 native. Not a
> good approach for organisations that lack IPv4 addresses. Also not a good
> approach if you want to switch off IPv4 at some point.
> - DS-Lite, MAP-T, MAP-E. Good for connecting CPEs to IPv4aaS over an IPv6-only
> backbone. Downstream from the CPE is dual stack. For this reason those
> protocols do not see much use outside ISP networks. Got a great transition
> technology because hosts will keep IPv4 until the last IPv4 on
> the internet is gone. It is a bit of an IETF failure that we have so
> many ways to connect a CPE to IPv4aaS.
> - NAT64/DNS64. This is the closest to an actual transition technology.
> Unfortunately it is completely flawed in too many ways. 
> - 464XLAT fixes many issues with NAT64/DNS64. The downside is again that
> hosts have to have an IPv4 stack until forever and in addition to that
> a complex IPv4-to-IPv6 translation module. That fails the requirement
> that an IPv6 stack should have roughly the same complexity as IPv4 and
> talk to IPv4-only.
> Basically, there is no solution to the transition problem. There are
> lots of partial solutions, each with their own advantages and disadvantages.
> If we could go back in time, then developing NAT64 along with IPv6 and
> making sure the translation really works including edge cases like IPv4
> literals, DNS A records, NAT traversal, etc. would have made a 
> difference.
> I don't know if such translation gateways were considered, I can't recall
> much discussion about them. By the time the IPv6 socket API was created
> it was already too late to get things like IPv4 literals right.

DS-Lite was designed to be implemented in the node.  You can run IPv6-only
everywhere in your network.  It is simple IPv4 in IPv6 encapsulation.  There
was a DHCPv6 option to tell the node how to configure the remote IPv6 tunnel
end point and everything else had defaults.  You could implement this in stack
that only presented IPv6 to the application using IPv4 mapped address.  You use
getaddrinfo with AI_V4MAPPED set for domain names and address literals which
should preference IPv6 over mapped IPv4 moving the traffic to IPv6.  Yes, you
still have a stub IPv4 implementation.  All this was available before DNS64/NAT64,
MAP-E, MAP-T, and 464XLAT.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org

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