Normally port 80 so you'll probably have to turn off your firewall. Also for working an MP session through a router, don't join the session until you are in your kite and on the ramp, otherwise you can get weird problems like sinking underground.
Ozzy
There are two types of aeroplane, Spitfires and everything else that wishes it was a Spitfire!
Yes. All of them. Other than VATSIM. I assume that FS host connect and normal ip would use the same ports, right? Probably most of what I do online involves fshost but some ip connect and on rare occasions zone launch.