Windows Firewall runs in the Windows Firewall/Internet Connection Sharing service and is dependent on several subsidiary services. If any of the subsidiary services are not running or cannot be started, Windows Firewall might not start or run properly. Windows Firewall depends on the following services.
Application Layer Gateway Service
The Application Layer Gateway Service (sometimes known as the ALG service) is required if you enable Windows Firewall on a computer that is an FTP client or FTP server that does not use PASV FTP. The Application Layer Gateway Service listens for outgoing FTP traffic from an FTP client. It then extracts the port from which the FTP client is expecting to receive data and creates an appropriate dynamic port mapping for the FTP data channel.
The Application Layer Gateway Service and Windows Firewall interact as follows:
* If the Application Layer Gateway Service is disabled and you try to enable Windows Firewall, Windows Firewall will start, but FTP traffic that does not use PASV FTP might fail.
* If you stop the Application Layer Gateway Service while Windows Firewall is running, Windows Firewall will continue to run, but FTP traffic that does not use PASV FTP might fail.
* If the Application Layer Gateway Service is stopped and its startup type is set to Manual, then the Application Layer Gateway Service will attempt to start when you enable Windows Firewall.