Tutorials..

iP Port Probe.

How to use the iP Port Probe:

Port:
The port you specify here will be probed when you click the "Test" buttons.
The "Listening on Port" Light will show the status of the listening server when the "test" buttons are clicked.
If the light is red then the "server" could not be opened on that port, that means the port was in use by another "server".

LocalHost/127.0.0.1
LocalHost and 127.0.0.1 are two ways of refering directly to the computer that iP Port Probe is running on.
When a "test" of either of them is green it means that nothing on your computer is blocking the port.
If they are red then its possible a software firewall is blocking them.
However many software firewalls will not block direct connctions to the same computer.

Internal ip Address
This is the ip address of your computer on its internal network.
For example if you have internet connection sharing, or a cable/dsl router you will want to test this.
Enter your internal ip address and "test" this, if the light next to this appears red then you may have the wrong ip address, or your computer has a software firewall.
If this tests green then you will want to test your external ip address.

External ip address
To obtain your external ip address, click the "Get Ext ip" button.
If you test the external ip address and it results in a green light you are all set.
If it comes up red the most likely cause is a cable/dsl router or hardware firewall.
It is also possible your isp has blocked that particular port.
If you are sure you have no cable/dsl router blockage etc, try different ports and see if your isp has them opened.

Links to help solve blockage issues.

XP Firewall settings.
How to open ports on XP's firewall.

Cable/DSL Router Configurations.
How to open ports on many different kinds of cable/dsl routers.