The traditional firewall of intelligent firewall is facing application problems.

At present, firewall has gone through five stages in technology and product development. The first generation firewall technology appeared almost at the same time as the router, using packet filtering technology. 1989, Dave Presotto and Howard Trickey of Bell Laboratories introduced the second generation firewall, that is, the circuit layer firewall, and proposed the initial structure of the third generation firewall-the application layer firewall (proxy firewall). 1992, BobBraden of USC Institute of Information Science developed the fourth generation firewall based on dynamic packet filtering technology, which later developed into the so-called state detection technology. 1994, Israel CheckPoint Company developed the first commercial product adopting this technology. 1998, NAI company introduced the adaptive proxy technology, and realized it in its product Gauntlet Firewall for NT, which gave the proxy firewall a brand-new meaning and could be called the fifth generation firewall.

The first five generations of firewall technologies all have the same characteristics, that is, they adopt a one-to-one matching method, which requires too much calculation. Packet filtering is to check the matching of IP packets. State detection packet filtering not only checks the matching of packets, but also checks the matching of state information. The application proxy checks the match between the application protocol and the application data. So everyone has the same defect-the higher the security, the more inspections and the lower the efficiency. Described by a law, the security of firewall is inversely proportional to its efficiency.

No one doubts that firewalls occupy the first place in the procurement of all security equipment. But the traditional firewall does not solve the main security problems of the network. At present, the three major problems of network security are: network attack with denial of access (DDOS) as the main purpose, virus spread with worms as the main representative, and content control with spam as the representative. These three security issues cover the vast majority of network security issues. And these three problems, the traditional firewall is powerless. There are three reasons, one is the limitation of traditional firewall computing power. Traditional firewall is at the cost of high-intensity inspection. The higher the inspection intensity, the greater the calculation cost. Second, the access control mechanism of traditional firewall is a simple filtering mechanism. It is a simple conditional filter, which has no intelligent function and cannot cope with complex attacks. Third, the traditional firewall can't distinguish between benign and malicious behaviors, which determines that the traditional firewall can't solve malicious attacks.