I have read next guide: Sharing Connection to other PCs (Via Wired Ethernet)
Did everything as it is there and even more, with no success. I have next set-up: Optic Fiber + Modem -> Microtik -> 26port Switch -> my main Ubuntu PC -> second Ubuntu PC
The problem is that after I try to do a bridge or a simple share to that network, my main Ubuntu just refuse to connect to that network, auto switch off instantly. Second network between two PC works fine, ping go both directions.
How can I fix this problem?