【正文】 o broadcast the technical basis for Ether, any two nodes of munication between the data packet is not only these two nodes by the card receipt, were also at the same Ether to the nodes of a work card by the interception, As long as hackers access to the Ether nodes for an interception, can capture the Ether in the data packet and all its packet analysis solution, thereby stealing critical information, This is the Ether inherent security risks. In fact, many on the Inter free of the hacking tools are put Ether interception as the most fundamental means. A firewall is a work device that enforces security policy for work traffic. The term originates from firewall, a fireproof wall used as a barrier to prevent the spread of fire. An Inter firewall creates a barrier between separate works by imposing a point of control that traffic needs to pass before it can reach a different work. A firewall may limit the exposure of hosts to malicious work traffic, ., 2 remote adversaries attempting to exploit security holes in vulnerable applications, by preventing certain packets from entering works protected by the firewall. When inspecting a work packet, a firewall decides if it should drop or forward the packet. The decision is based on a firewall39。s content. Packet inspection may occur at several different layers: (1)The link layer provides physical addressing of devices on the same work. Firewalls operating on the link layer usually drop packets based on the media access control (MAC) addresses of municating hosts. (2)The work layer contains the Inter protocol (IP) headers that support addressing across works so that hosts not on the same physical work can municate with each other. (3)The transport layer provides data flows between hosts. On the Inter, the transmission control protocol (TCP) and the user datagram protocol (UDP) are used for this purpose. Most firewalls operate at the work and transport layer. TCP provides reliable data flow between hosts. UDP is a much simpler but unreliable transport protocol. (4)The application layer contains application specific protocols like the hypertext transfer protocol (HTTP). Inspection of application specific protocols can be putationally expensive because more data needs to be inspected and more states are required. A firewall is a piece of software or hardware that helps screen out hackers, viruses, and worms that try to reach your puter over the Inter. If you are a home user or smallbusiness user, using a firewall is the most effective and important first step you can take to help protect your puter. It is important to have a firewall and antivirus software turned on before you connect to the Inter. If your puter is not protected when you connect to the Inter, hackers can gain access to personal information on your puter. They can install code on your puter that destroys files or causes malfunctions. They can also use your puter to cause problems on other home and business puters connected to the Inter. A firewall helps to screen out many kinds of malicious Inter traffic before it reaches your system. Some firewalls can also help to prevent other people from using your puter to attack other puters without your knowledge. Using a firewall is important no matter how you connect to the Inter — dialup modem, cable modem, or digital subscriber line (DSL or ADSL). The firewall product main bastion of the mainframe, packetfiltering router, Application Layer Gateway (Proxy), and Circuit Gateway, shielding mainframe firewalls, and other mainframetype places. Although the firewall is to protect the work from hacker attacks effective means, but there are clearly inadequate: unable to prevent outside the firewall through other means of attack, not prevent defection from within and not attentive to the customers who brought the threat, able to pletely prevent transmission of the 3 virus has infected software or documents, and can not prevent datadriven attacks. Since 1986 digital panies in the United States to install the Inter world, a mercial fire Wall system, the concept of a fi