The word alignment issue was very strong and the router people had considerably more influence than the host folks. I tried to propose variable length addressing using four bit nibbles in August 1974 and I got no traction at all. Steve Sent from my iPhone On Feb 14, 2012, at 6:31 PM, Bob Braden <braden@xxxxxxx> wrote: > On 2/13/2012 7:53 PM, Noel Chiappa wrote: >> > From: Brian E Carpenter<brian.e.carpenter@xxxxxxxxx> >> >> > 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 > > _______________________________________________ > Ietf mailing list > Ietf@xxxxxxxx > https://www.ietf.org/mailman/listinfo/ietf _______________________________________________ Ietf mailing list Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf