No there is no firewall.
But I have to tell windows, that incoming signals on the ports 2000 - 5000 have to be rerouted to my computer in the network.
Because if I start a server in the network, I have the same ip as the ICS server, because of the sharing of the internet connection.
If now someone wants to connect to the ah server, the signals go to the ICS server and not to my computer. Thats why I have to say the ICS server, that it has to reroute the ports.