Application Layer Gateway
The Application Layer Gateway (abbreviated ALG) forms the “last resort” of a multi-level security control, before any external content is allowed to cross the border to a shielded network. Therefore all incoming or outgoing data streams are each assigned to individual control programmes ,so-called security proxies. The security proxies briefly interrupt, analyse and send forward the content to an available Port or reject them. The data traffic is handled via a comparatively small number of released Ports. The network's security is increased by the fact that few transitions have to be kept open.