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

John Curran jcurran at istaff.org
Fri Mar 25 19:31:32 UTC 2022

On 25 Mar 2022, at 2:27 PM, Philip Homburg <pch-nanog-2 at u-1.phicoh.com> wrote:
>> If by ?straightforward transition plan? one means a clear and rational set of 
>> options that allows networks to plan their own migration from IPv4-only to IPv
>> 6, while maintaining connectivity to IPv4-only hosts and with a level of effor
>> t reasonable comparable to just running IPv4, then I would disagree, as such a
>> n "IPng transition plan? was achievable, expected, and we collectively failed 
>> to deliver on it (as noted below) 
> I'm a bit confused about the achievable part.
> Obviously, the adoption of IPv6 without a clear transition plan was a process
> failure. However, it is not clear to me that waiting a few years would 
> have brought something much better. And waiting more than a decade would
> mean that today there would not be a mature IPv6.
> ...
> The big issue is 3). If we look at the current internet, there are parties
> who lack IPv4 addresses and want to switch to IPv6. Obviously, they
> want to be IPv6-only. The lack of IPv4 address makes dual stack even harder.
> On the other hand, there are parties who have enough IPv4 addresses and
> have no reason to switch to IPv6.
> So we are clearly in the situation of 'migration from IPv4-only to IPv6,
> while maintaining connectivity to IPv4-only hosts'

Correct (although I will also point out that having zero IPv4 addresses isn’t really the problem but rather “not enough IPv4 space for their networking needs” – in the ARIN region, for example, organizations can obtain a small amount of IPv4 address space specifically for purposes of IPv6 transition technology use - it’s quite necessary for nearly any IPv6/IPv6 interoperability solution since they need to have an IPv4-facing interfaces)

> It should be clear that an IPv4-only host only speaks IPv4. This means that
> communication with an IPv4-only host has to be IPv4. So either the
> IPv6-only host or something in the network has to speak IPv4. If the
> IPv6 host speaks IPv4 then we get dual stack, which has been rejected
> as a broken solution. Technically, it is also possible to tunnel IPv4
> packets, then the host is in some sense dual stack, but most of the network
> is not. However, automatic tunnel configuration is hard, and tunnels
> tend to be fragile.
> So the only option is a device in the network that translates between
> IPv6 and IPv4. Currently we have such a protocol, NAT64. And from
> a technical point of view it is a disaster.

We actually have an abundance of technical solutions that provide some degree of IPv6/IPv4 interoperability, all with various tradeoffs, and which address various deployment scenarios such as whether the network service has involvement in the individual CPE, DNS resolution, ability to alter/profile applications, etc…  it’s a rather complex mess, and there’s far more solutions in use that just NAT64.  

> Looking back, we can say that the only feature of IPv6 that makes people
> invest in IPv6 is the bigger address space. So it is safe to say that
> most of the internet would have waited to invest in IPv6 until we were
> (almost) out of IPv4 addresses. So by its very nature this transation 
> between IPv6 and IPv4 would have NAT component.

<chuckle> Full agreement there…  one would have expected a strong focused effort in making a small number of standard NAT-based interoperability protocols for IPng, including working through the transition scenario implications. 

> In my opinion, It is clear that during the time IPv6 was developed, any
> solution involving NAT would have been rejected.

Pretty much correct…  As you may be aware, there was a large focus on tunnel-bases solutions (so that various islands of IPv6 exploration could be interconnected) but actual NAT-based interoperability wasn’t in the cards.

> So I'm confused, what transition technology was achievable (also in the
> political sense) but not delivered?

Well, I think you’ve hit the nail on the head - we certainly could have delivered on the actual IPng technical requirements for a straightforward transition plan (and ended up with a short finite number of well-tested protocols with far more attention paid to them starting 10 years earlier in the process) rather than present cornucopia of last-minute solutions of various technical strength – alas, taking that path of actually working on NAT-based interoperability solutions did not align with the culture/politics of the IETF. 

> If there is a magical transition technology that allows an IPv6-only host to
> 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...)


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