How to check which port allow incoming Connection?

[iwod]

I am behind a firewall and it had listed all the avalible port. 80 being one of them ( of course because we need to surf the web ).

However i am trying to use Skype but it doesn't work. And Skype has an alternative port 80 option which doesn't work either. So i am wondering what is that and if any thing check to tell which port i could use.

[GlobalForce]

Your question provoked my interest. See if any of these pages feed your quest Iwod, I learned something searching.
First one's a pretty good info article at WindowSecurity.com (http://www.windowsecurity.com/articles/Port_Scanning_ISA_Server.html).

http://netsecurity.rutgers.edu/ports_tools.htm

http://lists.gpick.com/pages/Port_Tools.htm

Too bad symantec bought @stake. I've heard lots about their "NetCat"...


GF

[meneer]

-{ Quote: "I am behind a firewall and it had listed all the avalible port. 80 being one of them ( of course because we need to surf the web ).

However i am trying to use Skype but it doesn't work. And Skype has an alternative port 80 option which doesn't work either. So i am wondering what is that and if any thing check to tell which port i could use." }-If you're behind a firewall, port 80 must be closed on the internet side. When you surf, your pc uses another outgoing port number above 1023. Your request tries to connect to port 80 of the system that you want to connect to. So, if you have an open port 80 on your firewall, this can only mean that there is a public webserver somewhere on your network. You better check, no firewall needs an open port, unless there's a service that has to be published.
Skype uses a filesharing like connection. I don't know what port it uses. I suppose it will hide behind a http request.