6.5.2. Transparent and non-transparent traffic

Application-level Gateway can handle traffic both transparently and non-transparently. In transparent mode, the clients address the destination servers directly, without being aware that the traffic is handled by Application-level Gateway. In nontransparent mode, the clients address Application-level Gateway, that is, the destination address of the client's connection is an IP address of the firewall host, and Application-level Gateway determines the address of the destination server.

There are two methods to determine the destination address in nontransparent mode: