I looked up 11:0:0 range in the online databases after the first post mentioning mac addr, and its not got any manufacturer associated with it on the ones I searched and instead I get this for the 11:00: range-
Group address (multicast MAC address). Multicast addresses do not contain OUIs.
And :-
Ethernet frames with a value of 1 in the least-significant bit of the first octet[note 2] of the destination address are treated as multicast frames and are flooded to all points on the network.

I've set the config item to a valid entry two up to a value cribbed off some pc to hand and now its working fine.

Could be someone having set the mac via the nvram in the past, but great, its working now on the onboard! Thanks for the help.