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.
Read more about Application-level Gateway: Functions, ALG Service in Microsoft Windows
Famous quotes containing the word gateway:
“The whole fauna of human fantasies, their marine vegetation, drifts and luxuriates in the dimly lit zones of human activity, as though plaiting thick tresses of darkness. Here, too, appear the lighthouses of the mind, with their outward resemblance to less pure symbols. The gateway to mystery swings open at the touch of human weakness and we have entered the realms of darkness. One false step, one slurred syllable together reveal a man’s thoughts.”
—Louis Aragon (1897–1982)