----- Original Message -----
From: "Steve Feldman" <feldman(_at_)TWINCREEKS(_dot_)NET>
To: "Robert Elz" <kre(_at_)munnari(_dot_)OZ(_dot_)AU>
Sent: Friday, July 27, 2001 1:29 PM
Subject: Re: IPv4 vs MAC
On Fri, Jul 27, 2001 at 03:40:53PM +0700, Robert Elz wrote:
Does no-one else still recall the world before ARP, where MAC addresses
(ie: the old 16 bit things that 3Mbit ethernet used) were embedded in
bottom 16 bits of your class B address (no-one had anything smaller than
that of course...)
Oh my, I remember writing drivers for those beasts
back in my UC Berkeley days. (We had a class A!)
And wondering how to deal with those new-fangled 48 bit
MAC adddresses in 10 Megabit Ethernet. I think I
started off just taking the low 16 bits, which worked
fine when there were only 100 or so Ethernet interfaces
in existence. (The first ARP RFC didn't come out until
after I graduated.)
As I recall, Xerox's XNS protocol used the entire MAC address
as the protocol address, which made translation easy but
I feel old...
Keep in mind that the entire ARP, MAC empire on the Ethernet
takes a "broadcast" medium and turns it into a "point-to-point circuit"
medium. This allows the 48 bit addresses to be used for "local"
send-receive end-points for the next layer up, IP protocol which
looks to many people to be a "broadcast" (NON-point-to-point)
protocol.....but it's next layer up, TCP....turns the whole thing
back into a NON-broadcast Poinit-toPoint Circuit focus......
In summary....we have Ethernet, which people think is a "send-to-all"
"receive-from-all" technology, but that is negated in order to create
an *illusion* of an IP send-to-all, receive-from-all layer [which we
all know it is not], and then on top of all this, reliable TCP circuits
are created....and for performance, people end up trying to stuff it
all through "circuit-mentality" ATM....which many people view as
*bad*(tm).....because they want to believe the Internet is NOT
circuit-based but packet-based....
packet-based Ethernet ---> circuit-based via MAC, ARP, etc.
packet-based IPv4 ----> circuit-based via TCP