On 2/13/2012 7:53 PM, Noel Chiappa wrote:
> From: Brian E
Carpenter<brian(_dot_)e(_dot_)carpenter(_at_)gmail(_dot_)com>
> The design error was made in the late 1970s, when Louis Pouzin's advice
> that catenet addresses should be variable length, with a format prefix,
> was not taken during the design of IPv4.
Ironically, TCP/IP had variable length addresses put in _twice_, and they were
removed both times! (You can't make this stuff up! :-)
Noel,
You probably remember this, but...
Within the ARPA-funded Internet research program that designed IP and
TCP, Jon Postel and
Danny Cohen argued strenuously for variable length addresses. (This must
have been
around 1979. I cannot name most of the other 10 people in the room, but
I have
a clear mental picture of Jon, in the back of the room, fuming over this
issue. Jon believed
intensely in protocol extensibility.)
However, Vint Cerf, the ARPA program manager, rules against variable
length addresses and
decreed the fixed length 32 bit word-aligned addresses of RFC 791. His
argument was that
TCP/IP had to be simple to implement if it were to succeed (and survive
the juggernaut
of the ISO OSI protocol suite).
System programmers of that day were familiar with word-aligned data
structures with fixed offsets, and variable length addresses seemed to
be (and in fact
would be) harder to program and would make packet dumps harder to interpret.
It was a political as much as a technical judgment, and Vint may have
been right ... we
can never know. We do know that IP eventually succeeded and OSI failed,
but it
was a near thing for awhile. Of course, there were other factors in the
success
of IP, such as Berkeley Unix.
It is to be noted that when it came time to define IPv6 some 20 years
later, the IETF
stuck with fixed length internet addresses.
Bob Braden
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