On sparc64 the gem driver respects the local-mac-address? system configuration variable which can be set in the Open Firmware boot monitor using the setenv command or by eeprom(8). If set to "false" (the default), the gem driver will use the systems default MAC address for all of its devices. If set to "true", the unique MAC address of each interface is used if present rather than the systems default MAC address.
Supported interfaces having their own MAC address include the on-board Sun ERI 10/100 Mbps and GEM gigabit Ethernet Interfaces on boards equipped with more than one Ethernet interface and the Sun GEM gigabit Ethernet add-on cards.
hme(4), miibus(4), netintro(4), eeprom(8), ifconfig(8)