Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations Chriss Miller on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!
Uniqueness of MAC address?
- Thread starter Kressmark
- Start date
Ethernet uses special 48-bit addresses known as MAC addresses, which is used to identify individual computers on a network.
Therefore there are a possible 281, 474, 976, 710, 656 MAC addresses. However an Ethernet network could conceptually consist of more than 281 trillion machines.
Manufacturers apply to the IEEE for blocks of MAC addresses. These manufacturer IDs are unique. The potential difficulty is that this leaves only 4 bits for unique addresses.
A common MAC looks like this:
00:a0:cc:5d:78:15:00:30:80:ac:84:a8:08:00
which can also be represented as:
0da0:dc5d:7816:0030:80ac:84a8:0800
The regulating bodies give the vendor's the first half of the MAC address:
0da0:dc5d:7816
Which leaves the vendors the last 4 numbers for the addition of a unique serial. That is a huge number of possible unique permutations, but it is conceivable that you could get a duplication if the manufacturer is rather loose about things, and you order a huge quantity of adapters from a single manufacturer.
A more likely source of duplication is the feature of some adapters and devices to allow a software configurable MAC. In this case it would be a user mistake, but it would be a fairly easy one to make.
Therefore there are a possible 281, 474, 976, 710, 656 MAC addresses. However an Ethernet network could conceptually consist of more than 281 trillion machines.
Manufacturers apply to the IEEE for blocks of MAC addresses. These manufacturer IDs are unique. The potential difficulty is that this leaves only 4 bits for unique addresses.
A common MAC looks like this:
00:a0:cc:5d:78:15:00:30:80:ac:84:a8:08:00
which can also be represented as:
0da0:dc5d:7816:0030:80ac:84a8:0800
The regulating bodies give the vendor's the first half of the MAC address:
0da0:dc5d:7816
Which leaves the vendors the last 4 numbers for the addition of a unique serial. That is a huge number of possible unique permutations, but it is conceivable that you could get a duplication if the manufacturer is rather loose about things, and you order a huge quantity of adapters from a single manufacturer.
A more likely source of duplication is the feature of some adapters and devices to allow a software configurable MAC. In this case it would be a user mistake, but it would be a fairly easy one to make.
- Status
