----- Original Message -----
From: "Steve Feldman" <[EMAIL PROTECTED]>
To: "Robert Elz" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
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
the
> > 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
> routing difficult.
>
> I feel old...
>
> Steve
>
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
Jim Fleming
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