A piece of hardware I am working for contains a small network, which includes about 13 devices. This network is dedicated and only internal available.

Due a factory error, a certain type of those devices all have the same MAC address, which obviously causes problems.

I am just working on patch to rewrite the MAC addresses and correct the situation.

My question is: Due reasons, I cannot access our reserved MAC address pool during this patch. Am I allowed, in a private local network, to assign any random mac address? Or are there legal issues?

  • 2
    Just pay attention to the U/L and I/G bits. You need to set the U/L bit to indicate that this is s locally configured address, and you need to make sure that the I/G bit is not set, otherwise any traffic sent to the address will go to all hosts.
    – Ron Maupin
    Jul 13, 2018 at 14:23
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin
    Jan 5, 2021 at 23:00

1 Answer 1


Officially, you may assign any locally administered address (LAA), ie. an address that has bit 1 (the 2nd lowest bit) in its first octet set to 1.

Practically, you can assign any adress that isn't already used in the local segment.

If you're going to sell the hardware you might want to apply for an official OUI prefix with IEEE.

Edit as per Martin's comment: make sure bit 0 in the first octet is set to 0 to indicate a unicast address.

  • 5
    Don't forget that the "individual/group" bit (the lowest bit in the first octet ??) must be zero. I'm not sure about this but switches should broadcast data if this bit is set. Jul 13, 2018 at 12:09
  • @MartinRosenau Absolutely, thx!
    – Zac67
    Jul 13, 2018 at 19:10
  • So this includes, that I may, theoretically, even assign existing vendor mac addresses inside my own network onto my devices?
    – Herr Derb
    Jul 17, 2018 at 11:52
  • You can but officially you may not. Vendor OUIs have the LAA/UAA bit set to zero to indicate global/universal validity. Of course, no one will be stopping you...
    – Zac67
    Jul 17, 2018 at 12:39

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