Hi everyone. I have an question on how the collision handles on mmo games. 1. Does the client check all the collisions aswell the server? 2. How does the collision systems works? and what is the best way to make an collision system thats makes you be enable to walk ontop of objects?. 3. How does the server handle the collisions? I hope anyone have some intresting answers. Thanks.

If the collision system has impact on gameplay and not just on visuals then any online game will (should) do the calculations server sided.
This applies to anything that has any effect on gameplay.

All your client does is rendering the visuals and provide the server with your input (of course this is a very vague description).

About collision calculation, there is no real big difference between an online game and others, it all depends on the gametype and how it was being structured.

Collisions affect gameplay, as such the server should check collisions.
Collisions should also be done client side so that the use isn't walking through
walls while waiting for the server to confirm their position.
That said, the server's calculation should be the final athority.