> I know that many hardware devices have MAC numbers. What are the
> significances of these numbers. Why are they these particular numbers?
MAC numbers are used to address Ethernet packets. http://en.wikipedia.org/wiki/File:Et...ame_format.svg
Here, you can see the IP address, is carried separately from
the MAC source and destination addresses. The addresses are at
different layers in the protocol stack. http://www.laneye.com/network/how-ne...lationship.htm
The MAC address has significance, between point to point devices.
The IP address has network wide significance, as the IP address
can be preserved as a packet is forwarded from one point to the next.
MAC #1 MAC #2 MAC#3
Device ------------ Device --------------- Device
IP #1 IP #2
And, of course, Windows activation places a significant weight
on the value of the MAC address, on the assumption the Ethernet
chip is soldered to the motherboard, and the MAC address can be
used to detect a hardware change :-) MAC addresses are sometimes
used with cable modems, as a user validation mechanism (so change
the device connected to the cable modem, and it stops working -
this can be fixed with MAC address spoofing).
This HFS24Tusermanual2.1.pdf document, on page 8, shows another purpose
for the MAC address. It allows a network switch to more efficiently
forward packets, instead of sending them to all ports on the
switch. Using address learning, the packet is sent to a destination
port, based on storing MAC addresses and learning who has what
As for the particular values, if you're manufacturing Ethernet cards,
you buy MAC addresses in blocks. Some of the digits, are intended to
identify the hardware manufacturer. The purpose of buying MAC address blocks,
and the attendant registration, is to guarantee the numbers are unique.
Using unique values is important for identifying local devices (since
the MAC address doesn't travel across the entire Internet). For example,
that Hawking switch, if two Ethernet cards had the same MAC address, is
going to do a poor job of forwarding packets.
So that is what I've learned so far.