MAC uses a globally-unique OUI it doesn't own

[ramereth]

The MAC is built as:

mac[0] = 0xdc;  //the first mac octet must be even, otherwise it is a broadcast
mac[1] = 0xad;
mac[2] = 0xbe;

DC:AD:BE is not an IEEE-assigned OUI, and bit 1 of the first octet is clear,
which asserts the address is globally unique. It isn't.

Setting the locally-administered bit — 0xDE instead of 0xDC, giving
DE:AD:BE — is correct, costs nothing, and is what the address is obviously
meant to be anyway.

⚠ Changing this changes the MAC of every deployed board, so anything keyed
to it (DHCP reservations, switch port security, monitoring) needs updating in
the same maintenance window. Worth doing, worth not doing by surprise.

Upstream was aware of the neighbouring concern; commit ca4f739 is titled
"MAC address OUI bit is 0".