I am researching the possibilities for a new iOS game. It's going to be a run-n-gun type platformer, and I'm looking into the possibility of co-op multiplayer.

The game itself wouldn't be very physics intensive, there will most likely be 20-30 physics bodies at any given time. For the multiplayer, I think I would have one player "hosting" and up to 3 other connecting via the Internet.

Here's my first question, are there any 2D physics engines that work over a network(preferably open source)?

My second question, Does anyone have any thoughts on using a non-networked engine (like Box2D or Chipmunk) and adding the networking component? Since there would not be very much information sent, do you think it would cause a lot of lag?