[ih] IPv4 address size debate

[John Day]

At 2:41 +0000 2009/11/14, Jack Haverty wrote:
>Answering a few messages...
>
>I don't recall any significant discussion of variable-length addresses.
>There was discussion of the fixed size of the address field, and
>especially of the way to split it up into class A/B/C/etc, which was I
>guess a form of variable addressing.  There weren't all that many
>computers around, but a new concern was the number of *networks* that
>could be handled (256 wasn't enough), and the number of hosts that could
>be on a particular net.  So IP4 *does* have variable-length addresses.
>Sort of.
>
>This also was I think when the need for ARP surfaced, since there wasn't
>enough "host" space left in the IP address to contain a full lower-layer
>address for the then-new LANs.  I think that the limitation to 32 bits
>may have partially been to force the issue of dealing with physical nets
>whose addresses were "too big" to just stuff into the IP address host
>part.  If the IP address had been 64 bits, you can bet that 48 of them
>would have held Ethernet MACs...it would have been too tempting.

ARP is required any time the layer below is either multiple access or 
there are multiple paths to the next hop.

It is just as well there was no room to put the MAC address in the IP 
address.  That way we avoided a mistake we didn't need to make. 
Although as long as IP names the same thing the MAC address does, 
i.e. the interface, it doesn't matter.

This is all consistent with Noel's point that IP is a subnet access 
(interface) protocol.

>
>Lastly, there was some real concern about efficiency.  A lot of traffic
>was Telnet, much of it character-at-a-time, which meant each TCP/IP
>packet often carried exactly one byte of user data, reaching an
>astounding wire efficiency of less than 5%.  So 95+% of the $$$s buying
>those expensive leased lines was for overhead.  More if you considered
>that you never wanted to run lines at 100%.  If you took an analyzer and
>snooped on the IMP/IMP circuits, it was sometimes really hard to see any
>actual user data for all the headers and control packets (TCP ACKs).
>Not so good.

Yea, I remember most people outside the Internet community i.e. in 
the commercial world, would take one look at the header overhead even 
without the Tenex insistence on character at a time and scoff.  There 
was no way they could sell that to customers that were working over 
much slower links at the time.

Snip

Take care,
John