Should distributors disable IPv4-mapped IPv6?

Posted Jun 10, 2016 14:06 UTC (Fri) by paulj (subscriber, #341)
In reply to: Should distributors disable IPv4-mapped IPv6? by farnz
Parent article: Should distributors disable IPv4-mapped IPv6?

I've explained it several times... A transition strategy that starts with a completely new, disjoint address space and builds a logically distinct Internet has *fundamental* routing issues _if_ it tries to re-use the existing connectivity. And re-use the existing connectivity _was_ /often/ tried, once the sheer scale of the "build a new, logically distinct Internet" became clear - witness the multiple tunneling and 6to4-ish protocols. Except, by that time, it was *too late*.

Had the _initial_ transition strategy - designed and agreed on in the early 90s - been a "re-use the existing connectivity" one, and the disjoint-address-space avoided (at least, till closer to the exhaustion of the old) then that /might/ have allowed a faster rollout, and we might nearly all have had working, efficiently-routed, IPng more than a decade ago. Can't say for sure of course, but it couldn't have been worse.

Would such an approach have been the most aesthetically pleasing? No. Would such an approach have come with packet header overheads? Yes. Might stupid middle-boxes have caused for some at times, yes. But there would have been ways around those with (with additional packet overheads), also stupid middle-boxes will continue to cause problems for some at times, regardless :(.

Also, NAT is *not* local-only. Many hosts connect to lots of sites far away on the Internet through NAT - not local at all. And even NATed hosts can often exchange packets directly with other NATed hosts, using 3rd parties to setup the initial mapping state.

Should distributors disable IPv4-mapped IPv6?

Posted Jun 10, 2016 14:13 UTC (Fri) by farnz (subscriber, #17727) [Link]

Then you're not addressing the points I'm making at all about why any transition was doomed to failure - fundamentally, there's nothing about the transition state that makes it worth people's while taking any pain from IPvN (no matter how minimal) until they cannot get IPv4. Multiply that by the fact that IPvN on its own is not helpful until everyone you wish to communicate with has IPvN, and you get exactly the outcome we see - no-one cares until IANA runs out.

And it absolutely could be much worse than it is - other transitions in network land (e.g. the move to SS7) have taken even longer than the move to IPv6; if IPv6 is a failure, please point to another, faster, global network transition.

You're also misunderstanding what I mean by local-only; NAT is local only in the sense that if I wish to use it, I do not need you to take any action to continue communicating with me. If I want to use IPvN, I need you to understand IPvN, regardless of whether IPvN is an extension atop IPv4 (like MPTCP or SCTP), or whether it's a disjoint network (like IPv6). In other words, I can transition to NAT without any of my peers needing to know or care; the same is definitionally false of a larger address space.