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Application Layer Gateway Service (System Services for the Windows Server 2003 Family and Windows XP Operating Systems)

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Service Name: ALG

Executable Name: ALG.EXE

Log On As: LocalService

Description: This subcomponent of the Internet Connection Sharing (ICS) / Internet Connection Firewall (ICF) service provides support for independent software vendors (ISVs) to write protocol plug-ins that allow their proprietary network protocols to pass through the firewall and work behind ICS. Application Layer Gateway plug-ins have the power to open ports and change data (such as ports and IP addresses) embedded in packets. File Transfer Protocol (FTP) is the only network protocol that has a plug-in shipping with Windows Server 2003 Standard Edition and Windows Server 2003 Enterprise Edition.

The service listens for outgoing FTP traffic from an FTP client. It extracts the port that the FTP client is expecting to receive data from and creates an appropriate dynamic port mapping for the FTP data channel

If this service is disabled, the Internet Connection Firewall and Internet Connection Sharing service will not start. The ALG service will start when set to manual if the Internet Connection Firewall and Internet Connection Sharing service is started.

Available on: Windows XP Home, Windows XP Professional; Windows Server 2003, Standard Edition; Windows Server 2003, Enterprise Edition; Windows Server 2003, Datacenter Edition and Windows Server 2003, Web Edition.

Installed through: Default operating system installation

Startup type: Manual

Service status: Stopped

This service depends on the following system components:

None

The following system components depend on this service:

Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS)

IP Port Numbers used:

TCP: 21, dynamically allocated

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