Cisco ASA 5500 Series Adaptive Security Appliances, or simply Cisco ASA, is Cisco's line of network security devices introduced in 2005. Cisco ASA has generally been intended for the small-to-medium business market as a higher-end product with more features than entry-level products. Expansions are available for anti-virus/malware (dubbed Anti-X), and intrusion detection.
This video will explain you how to configure an ASA 8 firewall in GNS3.
