SIP ALG (Application Layer Gateway) is a feature which is enabled by default in most Netgear routers and inspects VoIP traffic as it passes through and modifies the messages on-the-fly.

In few situations this is useful, but in most situations SIP ALG can cause problems using the service. Very often, SIP ALG is poorly implemented causing VoIP messages to be modified in a harmful way or simply corrupts them. In such cases you may experience issues registering your handset, one-way or no audio, unable to receive calls, and issues with BLF and Message Waiting Indicators.

For our Hosted VoIP service, including out Single User services, SIP ALG must be disabled on your Netgear router.

Although this guide was written with the Netgear DG834N router in mind, the guide below should be applicable to similar Netgear routers.

1. Fire up a browser (Firefox, Chrome etc) and go to 192.168.0.1 (this is the default IP address)
   The default username is admin and the default password is password
2. Under Advanced click on WAN Setup
3. Check the Disable SIP ALG option
4. Click Apply

Further information can be found at Netgear documentation.