Re: IPv4 vs MAC

[Valdis . Kletnieks]

On Thu, 26 Jul 2001 18:52:50 CDT, Jose Manuel Arronte Garcia 
[EMAIL PROTECTED]  said:
 If the used 48-bit addresses in lower layer protocols, why they did not use
 48-bit routing-enabled addressing for the Internetwork layer? Not just use
 the very same addresses as I may have implied (I DO NOT mean that). After
 all, they were using 48-bit addresses already.

First off, 32 was probably chosen because it was a number of octets(*)
that fit nicely into a register.  Dealing with 48 gets more interesting.

Secondly, at the time, a 9600 baud leased line was a *high speed* link,
and 56KB was long haul backbone link.  The added 4 bytes/packet would
be noticable at that speed.

Third, they were doing a new design, and the old one (NCP) had a 256
host limit.   I wasn't there, but I bet '4 billion will be PLENTY' was a
common sentiment - and understanding the amount of address space wasted
by subnetting and the eventual need for CIDR so routing tables could be
aggregated were still a decade down the road.

Valdis Kletnieks
Operating Systems Analyst
Virginia Tech

Re: IPv4 vs MAC

[John Stracke]

Balaji H. Kasal wrote:

why we are going from IPv6 to IPv16? 

We aren't.

-- 
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|John Stracke| http://www.ecal.com |My opinions are my own.   |
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Re: IPv4 vs MAC

[J. Noel Chiappa]

 From: Jose Manuel Arronte Garcia [EMAIL PROTECTED]

 1. ARP's function is to resolve IPv4-MAC addresses (32-bit-48-bit)
 2. Ipv4 addresses are running out.

 Why the IPv4 development team did not implement a simpler mechanism for
 IP addresses? ... If they had done this .. we would have more
 addresses available for all us

You need to realize that when Ethernet came out, there were a lot of
machines already running TCP/IP, with other WAN/LAN technology interfaces.
They included various home-rolled LAN's (CHAOSNet, V1 LNI Ring, Experimental
Xerox Ethernet), as well as lots of other stuff. We had an entire working
infrastructure, with lots of routers, etc. 

So, converting IPv4 to have larger addresses (to allow a straight inclusion
of the IEEE address in the rest field) would have been a lot more work
than doing ARP for those few (at that point) machines that wanted to hook up
to an Ethernet.

Noel

Re: IPv4 vs MAC

[Jim Fleming]

- 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, TCPturns the whole thing
back into a NON-broadcast Poinit-toPoint Circuit focus..

In summarywe 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 createdand for performance, people end up trying to stuff it
all through circuit-mentality ATMwhich 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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