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

Philip Homburg pch-nanog-2 at u-1.phicoh.com
Fri Mar 25 18:27:38 UTC 2022

>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.

Transition to IPv6 so far seems to have consisted of 3 phases:
1) Lots of tunnels due lack of a wide spread IPv6 backbone.
2) Early adopters being happy that they can run IPv6 native, usually as
   dual stack.
3) Lots of people looking into IPv6-only.

I'd say 1) mostly worked. 6to4 was a bit of mess. But otherwise tunnels
worked. Obviously, deploying IPv6 using tunnels is a lot more complex
than deploying native IPv4 without NAT. 
>From a technical perspective 2) just works. From an operational perspective
it is about twice as expensive as IPv4-only. So 2) is popular with people
who really want 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'

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.

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.

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

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

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.

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