Owen DeLong owen at
Mon Dec 21 21:29:48 UTC 2015

Not quite true…

"What happens when we have to make an incompatible change to the fundamental packet header?” is the real challenge.

It happens that in the case of IPv4, we didn’t hit that particular wall until we needed a larger address.

In IPv6, it will probably be something related to the ability to scale the number of routing destinations if I had to guess, but it’s so far in the future that predicting it now is somewhere between highly suspect and utterly impossible.

There will be a next time… There is _ALWAYS_ a next time with any human system. We always end up changing how we use things and then needing to adapt those things to those changes. That’s not a bad thing. Hopefully we will learn some lessons from this process and make the next transition somewhat less painful. However, most of those lessons are behavioral and judging by our progress on climate change, I’m not convinced we’ve learned anything at all about addressing problems before they reach crisis status.

> I’m only going to say one more thing on this subject because this is essentially a side bar that has very little to do with the subject matter of the OP.  
> If we hadn’t run out of address space we’d still be trying to fix IPv4.  The numbers don’t lie.  It’s not very likely that we’re going to be space constrained on the IPv6 Internet like we are on the IPv4 internet.  Nobody is going to want to repeat the pain of the last 17 years of trying to convince people to run IPv6.
> Just about every technical challenge with the underlying protocol stack is fixable.  Except for one: what happens when we run out addresses.  For all of its flaws, IPv6 addresses this one particular issue quite well.

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