Application Level Gateway #2

With a packet filter firewall authorized packets are allowed to pass through, after verifying they conform to the security policy.

The application level gateway stops all packets trying to pass through it. It then checks them against its security policy. Packets which fail the security check are simply dropped by the gateway, just as in the packet filter firewall.

However, packets which pass the security check are not simply passed on. They are unpackaged and repackaged by the application level gateway.