application level firewall (security) (ALF)

An application level firewall( ALF) or application layer firewall (ALF) evaluates data packets on the application layer with regard to valid data and only permits a connection after evaluation.

ALF firewalls ensure network security and check each individual data packet according to application-specific specifications. They act as intermediary components between the Internet and an application server that can understand the application protocol. An example of an application layer firewall is a web application firewall, which sits between the web server and the web client. As software components, ALF firewalls manage specific application protocols such as Session Initiation Protocol( SIP) and File Transfer Protocol( FTP).