When mobile node moves into the different IP address area, the mobile node can be set the proper environment parameters automatically by DHCP. If we extend the DHCP option field to support the roles of home agent and foreign agent in mobile IP protocol, mobile node can perform the foreign address registration process of mobile IP protocol when DHCP IP environment is achieved automatically, too. DHCP is supplied in the PC with a series of Windows NT. This paper proposes and implements the functional blocks of extended DHCP nodes and this enables the DHCP node have a role of mobile IP agents without another protocol functional blocks.