Connection from the same place on the same table are forbidden (comparaison between address is done on hashed ip's)

If only there were some way for them to communicate remotely without being in the same room together.

Highly hashed IPs. Highly. Hashed. That made my day.

Sorry, not used to speak about that with competent people :D

There are few enough IPv4 addresses that just about any hash forms an injective mapping which can be completely reversed: the best you can do is use something like HMAC and "pepper" it, but that only works if the clients can't verify or generate them.

They are server side, salted, and use multiple round hashing :)

My poker buddies from college are now all over the world. You can't identify us and ban us from playing at the same tables.

No, but you can definitely identify collusion. It's really very simple. When you see the guy with JJ fold preflop and the two remaining players have, say, AA and AQ, it suggests that JJ and AA have colluded to keep AQ in the pot. So you build a pipeline to process and detect this sort of thing. It doesn't have to be realtime. Same day would suffice. Besides, you will need hundreds, maybe thousands of hands to classify it reliably.

And you can be certain that none of that is happening in this example and I'd never play there -- unless I wanted to collude with friends.

Trivially circumvented with a proxy server, or simply, some other machine on a different network.