随着计算机网络的不断发展,全球信息化已成为人类发展的大趋势,但由于计算机网络联结形式的多样性,致使网络系统的硬件、软件及网络上传输的信息易遭受偶然的或恶意的攻击、破坏。人为的网络入侵和攻击行为使得网络安全面临新的挑战。因此,无论是局域网还是广域网,都存在着自然和人为等诸多因素的脆弱性和潜在威胁,这也使我们不得不将网络的安全措施提高到一个新的层次,以确保网络信息的保密性、完整性和可用性。 With the continuous development of computer networks, the global informationization has become a general trend of human development. However, due to the diversity of computer network connections, the information transmitted on the network hardware, software and networks is vulnerable to accidental or malicious attacks ,damage. Artificial network intrusion and attacks make the network security is facing new challenges. Therefore, whether it is local area network or wide area network, there are natural and human factors such as vulnerability and potential threats, which also makes us have to take the network security measures to a new level to ensure the confidentiality of the network information, Integrity and availability.