Hi,
What can I setup a multiple MAC on one interface?
I received five IP addresses from the operator.
Each of them is assigned to a given MAC address.
Is it possible to connect 5 DHCP clients on one interface?
I guess your ISP has given you static IP addresses right ?
If yes, why use DHCP ?
Just assign those static addresses to your interfaces.
Lets say you could connect 5 dhcp clients on one interface, tell me what address that dhcp client would take first? 
Some ISPs have strange ideas… If using dhcp is really required, then for the lack of better solutions, there’s vrrp hack.
My internet provider assigns me an internal IP by MAC address.
Then this address is translated to the external address.
If they assign you an Internal IP that mean that they have routed your public IP through this one, no need to DHCP client in WAN interface!
Well. How can I do it best on RB3011UiAS