Hello everyone...

In short, assuming a router board with 3 ethers, i want to make ether1 a master one, who can see and communicate with other ethers, while ether2 and ether 3 isolated from each other but no from ether1 (ether2 communicate with ether1 but not with ether3 - ether 3 also communicate with ether1 but not with ether2 - ether 1 communicate with both)

I'd appreciate answering me as soon as possible with details

Thanks in advance

Assuming that you are talking about layer 3 check the use of filters in the forwarding chain.

http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/Filter