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What is a MAC address?

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The answer can be found in here, pay attention to the chapter on Hexadecimal.
 
A two-digit hexadecimal number can range from 00 to FF, which is 256 possible values. Two hexadecimal digits can represent all the values for one 8-bit byte of binary memory (00000000 to 11111111). Hexadecimal is just a convenient way to represent all the possible values of a byte using only two characters.

Any MAC ID is represented with 6 bytes of memory, or 12 hexadecimal digits. The first 6 digits are typically assigned to a particular manufacturer by IEEE as the "organizationally unique identifier" or "OUI."

"MAC" means "Media Access Control," which is kinda obtuse.
 
Despoiler said:
The first 6 digits aren't a valid OUI.
Click to expand...
But that doesn't mean it is not a MAC address, especially in the wireless world. An option in Windows 10 is for it to generate a random MAC every time it connects to a wireless network. It is just not a registered OUI with the IEEE. Aside from a few special OUI's (broadcast and multicast) any 48-bit value can be a MAC address.
 
MtnMan said:
But that doesn't mean it is not a MAC address, especially in the wireless world. An option in Windows 10 is for it to generate a random MAC every time it connects to a wireless network. It is just not a registered OUI with the IEEE. Aside from a few special OUI's (broadcast and multicast) any 48-bit value can be a MAC address.
Click to expand...

You are right. I screwed up the binary conversion. A MAC can be UAA or LAA. Universal or local. Universal MACs are registered with IEEE and will show up in an OUI search. It could be set to private, but that is still valid. LAA are locally administered so unregistered. The LAA bit must be set in the MAC to designate it as LAA. The LAA is the second least significant bit in the first octet. 0=universal and 1=local
 
Why do you want to know? Are you trying to make a filter for your mac address for access to your router? MAC use to be called a MACHINE address back in the days. It's not as important as it was supposed to be a "UNIQUE" address but... as you know it's easy to clone a mac address.
 
I was upgrading all the PC's in a bank in the mid-90's which included installing NIC cards to connect to Novell servers I had installed. I had a bulk box of 100 3-Com NIC's and going from PC to PC installing the NICs and some software. This was back in the day when you had jumpers on the card to set the IRQ and I/O address. All was going fine, but then I had some really weird problems with a couple of PC's.

It took me 3 days to narrow it down, a manufacturing error. Two PC's had NICs with the same MAC address on the same network. If both PC's were on had some strange symptoms, login problems, applications hanging, just weird stuff.

Disconnect either and everything worked find.

Used the card in a different branch of the bank where it couldn't cause a conflict.
 
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