====== How to Disable SIP ALG on the WatchGuard® XTM 3 Series Firewall ======
SIP ALG (Application Layer Gateway) is a feature which is available on most WatchGuard® network security appliances 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 [[features:blf|BLF]] and Message Waiting Indicators.

For our Hosted VoIP service, including out Single User services, SIP ALG must be disabled on your WatchGuard® XTM security appliance.

This guide explains how to to disable SIP ALG on the following WatchGuard® models:
  * **WatchGuard® XTM 2 Series**
  * **WatchGuard® XTM 3 Series**

Even if your particular WatchGuard® XTM model is not listed, these instructions should still apply if your model is in the same series.