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Re: [LUG] MAc address changing was Re: MAC address on Android


On Mon, 13 Jan 2014, Tom wrote:

In the early days your MAC address was hardwired into the 'ethernet' card by the manufacturer.

Having had 1st hand experience of this ... (admittedly this was 25 years ago though)... Both allocating MACs for a company that had its own prefix (the first 3 bytes) and writing the driver...

An Ethernet card would have a PROM of some sorts on it "hardwiring" it to the card - so that the operating system would then read and use in all subsequent transactions. It was maintained in RAM after that. Nothing other than a "gentlemans agreement" to stop the OS changing it...

Conceivably there may now be systems with the MAC "fixed" into the hardware - I suspect these are the sort of cards that have TCP offload engines on the card or other microcontrollers to assist with the data flow, however I suspect that even these can be altered.

Sun 4's were no different - they had a PROM that was read by the firmware (in Forth) as well as a unique "hostid" that was used in various license servers - latterly they just used the MAC, however it was changeable - especially on the boards I wrote the boot code for... But again it was just held in RAM by the OS once it was loaded, so changable.

If you want to change the MAC on your Linux pc, simply become root then

  ifconfig eth0 hw ether aa:bb:cc:dd:ee:ff

where aa:bb... is the new MAC address. If you want to play, then you can freely use 00:00:fc:x.y.z if you like - I can guarantee that you will never see that prefix in the wild. (and if you do, please let me know ;-)


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