@Phaedrux said in Duet Ethernet MAC address:

it reminds me that there are 2 ways to express a mac address

much more than 2 when it comes to formatting of MACs. Microsoft uses - instead of : to separate hex bytes, pluss countless variations on binary hexadecimal and octal representations

I'd discourage using MAC addresses with the unique/local but set to unique for an address outside your organisations control as it could (theoretically) break networks. If deemed absolutely necessary for testing try using an address for equipment you own and know is not connected to avoid problems. Even if you know the address isn't on your broadcast domain you rarely have control over the other broadcast domains of neighboring layer 3 devices which could be affected. And make sure to revert the address to the original or a locally administered one as soon as possible.