Mebbe.  I confess I didn't study the details of the competing proposals at the 
time because I was confident the people who were heavily involved surely had 
things under control.

Steve

On Oct 10, 2010, at 6:41 PM, Dave CROCKER wrote:

> 
> 
> On 10/10/2010 2:51 PM, Steve Crocker wrote:
>> A compatible solution would have been better, but I don't think IPv4... --
>> were designed in a way that permitted a compatible extension.
> 
> 
> Oh?
> 
> Perhaps:
> 
>   1.  Adopt an IPv6 as Steve Deering originally designed it[1]:  A basic 
> upgrade to the IPv4 header, with more address bits, an extensibility 
> mechanisms for adding fields later, and removal of some bits that weren't 
> needed.
> 
>   2.  Define the IPv6 address space as the IPv4 address space, with all 
> zeroes for the higher bits.  (In other words, defer more interesting schemes 
> until later.)
> 
>   3.  Design header translation devices to map between the two formats.
> 
>   4.  Start fielding these implementations.  (That could have started by 1994 
> or so.)
> 
> The "gateways" between v4 and v6 would initially be notably for having almost 
> no work to do and of not losing any information.  In particular, barely 
> qualifies as a "dual" stack.
> 
> With this approach, "incompatibility" between v4 and v6 would only occur when 
> additional addresses, beyond v4's limitations, start to be assigned.
> 
> We must deal with the current reality and make it work, but historical 
> considerations need to factor in the ambitions that dominated during the many 
> years of design.
> 
> The community got ambitious in a fashion that smacked of the overreaching 
> that is often called second system syndrome (although counting the Arpanet, 
> this was really a third system...)
> 
> d/
> 
> [1]  http://tools.ietf.org/html/draft-deering-sip-00
> -- 
> 
>  Dave Crocker
>  Brandenburg InternetWorking
>  bbiw.net

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