online or lan multiplayer co op game

Hi guys im looking into adding a co op mode to my game im currently working on and i want the ability to have it so players can play single player or player multiplayer over lan if ther in the same house or online if there far apart. i dont mean like a mmo i just mean like portal 2 co op mode that type of thing is ther any way to do this in blender thanks.

ok thanks.

ok i have looked at this and played around with it but what i dont understand is how to make it so you can play with another pearson
because it is set to localhost and i dont know how to set everything up.

Ill make a tutorial!