I have Mikrotik 2.8.10
My configuration is quite simple right now. An internet connection on cable and a private network of 20 computers.
So, right now, I have two nic's in my Mikrotik box
ether1 - Public IP (Internet)
ether2 - Private IP (192.168.4.x)
The clients are masqueraded, using src-nat.

I want to give internet to another private network, say 192.168.3.x, but I don't want them to see each other, no trafic is allowed between the two private networks.

I've installed a third nic, for the second network.
What should I do next?

Some firewall rules inthe Forward Chain to restrict traffic between the two networks should do it. You just need to specify 'anything that enters on interface Private 1 can't exit on Private 2' and vice versa.

Regards

Andrew

Ok, I think it works, I'll do some more tests anyway.
Thank you