介绍ARP 协议、Windows 系统中ARP 实现,设计了一个非法入网检测及阻止系 统。该系统通过ARP 扫描,实时检测非法主机(未知主机)接入内部网络的企图,并 通过发送冲突包和其它伪造数据包,阻止与内部网络的其它主机进行信息交换,从而 有效地保护了内部网络的信息安全。 Abstract: The paper introduces ARP protocol, the implement of ARP in Windows system, and designs the system of the detection and block on illegal connection to LAN. The system can detect the illegal host connecting to LAN in real time by scanning LAN, and block the swap of information between the illegal(unknown) host and other host in LAN by sending ARP packets resulting in conflicting or error. So the system can protect the security of information in LAN in effect. Key words: ARP; illegal connection to LAN; detection; block