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Application-Level-Gateway (ALG)

What does Application-Level-Gateway mean?

A Application gateway or Application-level gateway is a firewall proxy that provides network security. It filters incoming traffic according to certain specifications so that only the transmitted network application data is filtered.


Such network applications include FTP (File Transfer Protocol), Telnet, RTSP (Real Time Streaming Protocol), and BitTorrent.

Why is a ALG useful?

  • Application level gateways provide secure, high-level network system communications. For example, when a Client requests access to server resources such as files, web pages, and databases, the Client first connects to the proxy server, which then connects to the main server.
  • The Application level gateway is located on the Client- and server firewall. The proxy server hides IP addresses and other information on behalf of the client. A computer’s internal system can communicate with an external computer using firewall protection. The Application level gateway and the external computer function without Clientinformation or knowledge of the proxy server’s IP address.

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