Netgear ships their routers so that out of the box they rewrite SIP (VoIP) packets due to their stateful packet inspection (SPI) firewall & SIP ALG. However, Netgear’s implementation of the SPI firewall and SIP ALG breaks the connection between VoIP phone endpoints and our services, so it’s best to simple disable them.
Disabling the stateful firewall
- 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
admin/password. - 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.
- Also under “WAN Setup” there should be an option to turn off “SIP ALG”, turn SIP ALG off 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.
Also you are going to want to check to ensure that your modem is in “bridge mode”. You may need to contact your Internet Service Provider to check.