In computing, a Firewall is a network security system that controls the incoming and outgoing network traffic based on an applied rule set. A firewall establishes a barrier between a trusted, secure internal network and another network (for example Internet) that is assumed not to be trusted and secure.

FirewallFirewalls can be a dedicated hardware devices or can also be a software service.

Cisco PIX (Private Internet eXchange) is a popular IP firewall and network address translation (NAT) appliance. It was one of the first product in market in Network security segment.

Cisco introduced the newer Cisco Adaptive Security Appliance (ASA) in 2005 which inherited many features of the PIX, and in 2008 PIX was announced end-of-sale. The PIX technology is still sold in FireWall Services Module (FWSM), for the Cisco Catalyst 6500 series switches and the 7600 series routers.

In this section, we will discuss about Cisco Adaptive Security Appliance (ASA). The ASA provides advanced Stateful Firewall and VPN concentrator functionality in one device, and for some models, an integrated Intrusion Prevention System (IPS) module or an integrated Content Security and Control (CSC) module. The ASA includes many advanced features, such as multiple security contexts, transparent (Layer 2) firewall or routed (Layer 3) firewall operation, advanced inspection engines, IPsec VPN, SSL VPN, clientless SSL VPN support, and many more features.