But aren't all packets late because they have to travel to the server? The problem is the latency, an input packet could come in quickly but the second input packet that has mouse button up could come in late enough to have the server fire the weapon more times than the client wanted it to.

If I timestamp packets, isn't that open for speed hacking because anyone could spoof that data.

Also I'm a bit wary of running the simulation at a fixed time step, wouldn't that make it frame rate dependant?

But aren't all packets late because they have to travel to the server? The problem is the latency, an input packet could come in quickly but the second input packet that has mouse button up could come in late enough to have the server fire the weapon more times than the client wanted it to.

If I timestamp packets, isn't that open for speed hacking because anyone could spoof that data.