Multiplayer MOD question

[kattana]

so..as long as everyone has a specific mod loaded on their machine already, they all can use it in a multiplayer game, correct?

now what if one person doesnt have said mod, has does the game handle that when they are trying to join a MP game where they are using that MOD?

i willnt get the chance until this weekend to test out myself, but im sure someone here already knows

thanks