I need to forward UDP ports 10000 to 20000 to an internal IP.
Do you really need 10000 open ports for one client?
instead of doing it 1 for 1 in the server-manager..... is there a quicker way of doing it?
It depends what server you are runnning, but AFAIK you can use the hyphen (-) to forward a range of ports. You could have read this in the server-manager portforwarding panel yourself:
If you wish to specify a port range, enter the lower and upper boundaries separated by a hyphen.
Did you try that already?