The basic premise of this document is to give any person a way to tell if their ISP is blocking any incoming ports.
1. Attach a PC directly to your service provider's modem. There should not be a router or any other device between the PC and the ISP's modem.
2. Open a web browser (IE) and in the address bar enter www.grc.com.
3. Once at the Gibson Research Corporation's website, click on the ShieldsUP! banner.
4. When you are taken to the next page, scroll down about half way. You will see the title Hot Spots. Under this heading is a link for the ShieldsUP! test. It is the link in the middle.
5. Once you have selected this link, please read the box and then click the proceed button.
6. The next page is where you will begin the test. Look for the text box in the center of the page. This is where you enter the port you want examined. You should enter 500 here and press enter.
7. When you press enter it will take you to another page and explain the details about the port you are about to probe. At the top of this page is a green button labeled "Probe THIS Port".
8. At this point, you need to turn off all firewall and anti-virus software. If you do not, it could give you a false reading from the probing. Once the test is complete you should re-enable the software you disabled.
9. Click that button and wait for the test to complete. The test should reveal "Open", "Closed", or "Stealth". If it is closed or stealth, the ISP is blocking it. Also, if you are trying to get a VPN tunnel to establish, the only way to get this to work is with the status open.