Why does the Netgear WGT624 v3 cause problems for your VoIP service?
Unfortunately, Netgear has decided to ship their routers so that out of the box they rewrite SIP packets due to their stateful packet inspection (SPI) firewall. In this short tutorial I will show you how to disable the SPI firewall. Covering what SPI is and why it exists in the router is outside the scope of this document, instead I suggest reading this wikipedia article on SPI.
Before you begin this tutorial it is highly recommended that you upgrade your router to the latest and "greatest" firmware for your WGT624 v3. To do that, go to this Netgear webpage and download the latest firmware for the router. You may follow their instructions for upgrading. When you've completed that process then continue with this tutorial.
After deciding whether or not disabling the firewall is for you and upgrading to the latest firmware, follow these simple steps to complete the process. At the time of this writing the latest firmware for the WGT624 v3 was Version 2.0.26_1.0.1, any other version of the firmware may change the steps required to complete this process.
- Log in to the routers administration page through your web browser, by default the page should be located at http://192.168.1.1 and the username and password are
- On the left menu under "Advanced" click the "WAN Setup" link.
- In the content area of the page under "WAN Setup" there should be a checkbox labeled "Disable SPI Firewall". Check that box and click the apply button.
- Important: After the router finishes its update, be sure that you force all of your SIP devices behind the firewall to reregister. Failing to do so will only complicate matters further!
Completing this process should fix the issues that your SIP phones face when behind a Netgear router.