But the maximum for implementation is not necessarily the maximum for the
packet format.
Thus one could have started with a variable length address format, but said
"For the immediate future we will always pick a length of 32 bits". Then at
some point we could have said "in 5 years we are going to start assigning 64
bit addresses, you MUST update your implementations to support this as well --
same packet format and everything else stays the same".
We would have needed to be very careful to ensure that the packet formats
allowing variable lengths applied to all protocols that carry or use IP
addresses (such as DNS records, ...). Such architectural care is not easy to
enforce.
Whether everyone actually would have updated their implementations is another
issue -- but at least in theory it *might* have been simpler than upgrading to
a new version of IP.
Of course, since we don't have time machines, it is too late to change our past
(and we will note that other types of networks have run out of addresses /
digits / area codes also).
Ross
-----Original Message-----
From: ietf-bounces(_at_)ietf(_dot_)org
[mailto:ietf-bounces(_at_)ietf(_dot_)org] On Behalf Of Stephen Sprunk
Sent: Wednesday, February 15, 2012 4:10 PM
To: ietf(_at_)ietf(_dot_)org
Subject: Re: Variable length internet addresses in TCP/IP: history
On 15-Feb-12 08:42, Dave CROCKER wrote:
As I recall, there was essentially no experience with variable length
addresses -- and certainly no production experience -- then or even by
the early 90s, when essentially the same decision was made and for
essentially the same reason.[1]
It's not that variable length addressing is a bad idea; it's that it
didn't get the research work and specification detail it needed, for
introduction into what had become critical infrastructure. What I
recall during the IPng discussions of the early 90s was promotion of
the /concept/ of variable length addressing but without the
experiential base to provide assurance we knew how it would operate.
The problem with variable-length addressing that, in practice, one needs
to specify a maximum length. The result, therefore, is that you don't
have variable-length addresses at all but rather fixed-length addresses
with a shorthand encoding for unused bits.
S
--
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking
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