Operation Manual

58
Application Layer Gateway
In the context of computer networking, an application-level gateway
(also known as ALG or application layer gateway) consists of a security
component that augments a firewall or NAT employed in a computer network.
It allows customized NAT traversal filters to be plugged into the gateway to
support address and port translation for certain application layer "control/data"
protocols such as FTP, BitTorrent, SIP, RTSP, file transfer in IM applications etc.
In order for these protocols to work through NAT or a firewall, either the
application has to know about an address/port number combination that allows
incoming packets, or the NAT has to monitor the control traffic and open up port
mappings (firewall pinhole) dynamically as required.
Legitimate application data can thus be passed through the security checks of the
firewall or NAT that would have otherwise restricted the traffic for not meeting its
limited filter criteria.
To Enable/Disable special support for any of the applications in the list. You can
Simply check or uncheck the corresponding checkbox and Click “Apply” for the
settings to take effect.