[ppml] The myth of IPv6-IPv4 interoperation, was: Re: Legacy /24s

Paul Vixie paul at vix.com
Mon Sep 3 11:11:43 EDT 2007

> It looks like you suffer from the (fairly common) misconception

what an unnecessarily harsh way to phrase your difference of opinion.  "ouch."

> that goes along these lines:
>      "If only the IETF had made IPv6 interoperable with IPv4,
>      we wouldn't have any transition issues."
> (See http://cr.yp.to/djbdns/ipv6mess.html )

no.  we would still have transition issues.  just not this one.

> The assumption here of course is that it would have been POSSIBLE to  
> build IPv6 in such a way that an IPv6 host can talk to an IPv4 host.  

that was a design goal.  of the IPng candidates being proferred, the one we've
got now was chosen to become IPv6 on the basis of the features it offered.  if
it wasn't possible to deliver this, then it's possible a different choice
might have been made.  but more to the point, if the paragraph i quoted had
been true then IPv6 would be in wide deployment today and the IPv4 runout
would be a yawner.

> 	The IPng transition mechanisms ensures that IPv6 hosts can
> 	interoperate with IPv4 hosts anywhere in the Internet up until the
> 	time when IPv4 addresses run out, and allows IPv6 and IPv4 hosts
> 	within a limited scope to interoperate indefinitely after that.  This
> 	feature protects the huge investment users have made in IPv4 and
> 	ensures that IPv6 does not render IPv4 obsolete. Hosts that need only
> 	a limited connectivity range (e.g., printers) need never be upgraded
> 	to IPv6.
>	(From <http://playground.sun.com/ipv6/INET-IPng-Paper.html>.)

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