Hi all! 
So... i have maybe same problem ... everything what you say here is nice, but ... i playing DCS from October 2014, i played a lot of multiplayer games, i stop maybe on end of November... but im back from Christmas...    
and i CANT join on every server  (including where I formerly played ...  durring loading i get Connection interrupt ) 
and i CANT join to server created by my friend 
and i CANT CREATE server ( durring loading and joining to my server game just kick me to menu and my friend joint the server, and say " hey, i see you here and now you left " )  
my friend have port 10308 closed too and completely same version like me.   
I try turn offline my windows FW ( i will try avast's FW and router's ), completely reinstal game, deleting temp, reset of my router, changing MP settings in MP menu :(   
So this bug is here maybe from patch 2.1.14 ? :(