Can't reach my machine using TCPClient

[9to5]

I've got a little rudimentary client-server app. One runs a server
listening to 'any' ip on a given port and the client attempts to
connect to the external ip of my app. I am on a LAN behind a router
and, undoubtedly, a firewall.

If I make the IP I am trying to connect to 127.0.0.1 everything works
fine but as long as I am using the external IP I can't get through and
I get an exception which states that the host is actively refusing the
connection.

Is this because I am behind a router? More importantly, if this is the
case how do applications manage to get around this. For example, if I
install some new random application, it seems to have no problem
connecting to a peer-to-peer server on some random port. But my app...
gets refused.

What am I missing?

Thanks!

 

[Mr. Arnold]

What am I missing?

http://www.homenethelp.com/web/explain/port-forwarding-dmz.asp

If you have a personal firewall running on the computer, you would need to
set a FW rule there too, to open the required port.

Keep the machine out of the DMZ