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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