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So I am having rather an odd issue that I do not know how to investigate.

I installed Asterisk with FreeBPX on a raspberry pi and configured it to use IAX, used a softphone to connect and everything is working great on my local network.

Then I opened the needed IAX port in my router and tried to test it from another network but it did not work, my phone simply could not reach the Asterisk server. This strikes me as a NAT issue, but I used a UDP sender program to send a packet to the IAX port, and in the logs chan_iax2 acknowledged receiving a midget packet, this tells me that there are no NAT problems.

My biggest fear now is that my ISP is somehow blocking IAX and SIP traffic, but I can't think of a way to debug this. So my question is: How can I debug this issue? How can I know if my ISP is blocking IAX traffic?

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  • Do the logs on your router confirm that your external request on that port is being received? If not, it may be denied at the ISP's level. However, if you can confirm that your requests are hitting your internal network's border, you should be able to continue the troubleshooting process.
    – root
    Commented Apr 4, 2016 at 19:56
  • Unfortunately I have a basic router that does not log access attempts, I will try to get a more robust router with dd-wrt or tomato and try this.
    – Hisham Abdel-Hafez
    Commented Apr 7, 2016 at 12:05

1 Answer 1

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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. e g : 4569

  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.

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  • Thank you for your answer, I will test this when I get back home in a couple of days and I will let you how it goes.
    – Hisham Abdel-Hafez
    Commented Apr 7, 2016 at 12:33

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