Port Exhaustion

Hi!

I am hosting a server that clients can connect to using UDP packets.

The problem is that when using my router, only less than 4095 clients can be connected at a time, like some sort of port exhaustion.

When removing the router and connecting the modem directly to the computer, I can have around 16 700 clients connected (or more).

Setup:

Modem, HES-3109W2A(SM-10)-DR, with cable to ->

Router, NETGEAR WNR2200, Firmware Version V1.0.1.102, with cable to ->

Computer, Windows 10 Home 64-bit

My internet connection is 100/100 Mbps (I have also tried using speedtest).

What is it that is limiting the amount of clients connected so heavily when using the router?