Subject: Info: MAC Numbers: All you wanted to know, but were afraid to ask.
From: Mac_Numbers@a
Sender: Mac_Numbers@b
DRAFT By JHS
You mentioned not knowing what MAC numbers are:
First: A MAC number is not an Ethernet IP number.
- An Ethernet IP number is usually a 4 byte number of form:
[0-255].[0-255].[0-255].[0-255] it is not unique to a PC, there
are not enough to go round in the world, so they get re-issued by
internet providers on new connections. So they are not used for
software licencing. (A bit like in Germany, where if you move to
a house in a new town, you have to change your car registered
number plates, but the chassis number remains unchanged).
0 to 255 is 256 possibilities.
Comes from the 8 bits in a byte, all 8 bits can be in any of 2 states:
0 or 1, so
2 x 2 x 2 x 2 = 16 states in a 4 bit nibble.
2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 states in an 8 bit byte.
With 4 bytes, 256 x 256 x 256 x 256 = 4,294,967,296 states.
Yes, 4 billion is not enough numbers for all the world's ethernet ports,
particularly as blocks are pre reserved.
Occasionally IP numbers have not just 4 bytes (in IPV4 standard),
but have 8 bytes (in IPV6 standard, that is about 16 billion billion.
but not in wide use yet. )
A MAC (MAchine) number is actually:
- not one per machine
- but 1 per ethernet interface
(so a router would sometimes have 4, &
my gateway PCs have 2: 1 for internal net, & 1 to router)
- MAC number is more like a chassis number embossed on a car,
actually, if individual windows on a car had individual different
serial numbers on each window, that would be an exact analogy.
- MAC numbers are very hard if not impossible to change, dependent
on hardware, so used for licensing.
- MAC is a 6 byte number in hexa-decimal arithmetic (base 16),
In decimal base 10 we use digits in range 0 1 2 3 4 5 6 7 8 9
In hexadecimal base 16 we use digits in range 0 1 2 3 4 5 6 7 8 9 A B C D E F
(A=10, B=11, C=12, D=13, E=14, F=15)
Each of the 6 bytes is comprised of 2 nibbles,
Each nibble is comprises 4 bits,
So you see some numbers like: 05:7A:B9:34:CD:E8
There are 256 x 256 x 256 x 256 x 256 x 256 = 281,474,976,710,656