Abstract:The Dynamic Host Configuration Protocol (DHCP) is an Internet protocol designed by IETF for automating the configuration of computers.DHCP can be used to automatically assign IP addresses,subnet mask,default gateway and other TCP/IP parameters.Acquainting the working principle of DHCP can help us deal with problems on LAN DHCP service effectively.The article analyzes the working principle and working flow of DHCP in-depth by the packets crawled on real network.