What is Application-Layer Gateway
Application-Layer Gateway (ALG) is a software component that manages specific application protocols such as SIP (Session Initiation Protocol) and FTP (File Transfer Protocol). An ALG acts an intermediary between the Internet and an application server that can understand the application protocol. The ALG appears as the end point server and controls whether to allow or deny traffic to the application server. It does this by intercepting and analysing the specified traffic, allocating resources, and defining dynamic policies to allow traffic to pass through the gateway.