The dash in between those two numbers means its opens all the ports in that range or numbers. Best to have them all open if a bunch of people are trying to connect at once. As far as I understand it, port 16261 is used to connect to the server. Every other port is used by the server to send data to the players, ie each player is assigned a port upon connection. So if dont have all those open, there will be issues when more than one person is trying to get on.