I got 28000 open and canyouseeme says it is, but in the console heres what it says:
--------- Starting Dedicated Server ---------
Destroying NET Server
Exporting server prefs...
%
Starting Internet Server
Binding server port to default IP
Unable to initialize UDP - error 5
Port init failed on port 28000 trying next port.
Binding server port to default IP
UDP initialized on port 28001
%
Initializing UPnP...
--------------------
Why does it go to 28001?