Network Security Principles and Practices

Adaptive Security Algorithm

Adaptive Security Algorithm (ASA) is the foundation on which the PIX Firewall is built. It defines how PIX examines traffic passing through it and applies various rules to it. The basic concept behind ASA is to keep track of the various connections being formed from the networks behind the PIX to the public network. Based on the information collected about these connections, ASA allows packets to come back into the private network through the firewall. All other traffic destined for the private network and coming to the firewall is blocked.

ASA also defines the information PIX saves for any given connection made through it (this is called state information in the case where TCP is being used as the transport protocol). ...