Application Layer Gateway Service (ALG) Defaults in Windows XP

Provides support for 3rd party protocol plug-ins for Internet Connection Sharing and the Windows Firewall.

Default Settings

Startup type: Manual
Display name:Application Layer Gateway Service
Service name:ALG
Service type:own
Error control:normal
Object:NT AUTHORITY\LocalService
Registry key:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ALG

Default Behavior

Application Layer Gateway Service is a Win32 service. In Windows XP it won't start until the current user starts it. When the Application Layer Gateway Service is started, it is running as NT AUTHORITY\LocalService in its own process of alg.exe. If the Application Layer Gateway Service fails to start, the technical information about the error is added to the Event Log. Windows XP startup should proceed, but a message box should be displayed informing the user that the ALG service has failed to start.


The Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS) depends on the Application Layer Gateway Service service.

Restore Default Startup Configuration of Application Layer Gateway Service

1. Run the Command Prompt.

2. Copy the command below, paste it into the command window and press ENTER:

sc config ALG start= demand

3. Close the command window and restart the computer.

The ALG service is using the alg.exe file that is located in the C:\Windows\System32 directory. If the file is removed or corrupted, read this article to restore its original version from Windows XP installation media.