Patent ID: 7996537

Claim:
A method for preventing illegitmate use of an Internet Protocol (IP) address by a subscriber device in an IP network, the network including a switch node and at least one DHCP server, said subscriber device in communication with the switch node, the method including the steps of: creating a list of trusted ones of the DHCP servers in said switch node; transmitting by the subscriber device a DHCP request message for an IP address; receiving a reply message by said switch node which carries an assigned subscriber IP address; analysing the reply message by said switch node to be a DHCP message and having a source address from one of the trusted DHCP servers; updating a filter dynamically in the switch node, the filter storing an identification of the subscriber device and the assigned subscriber IP address; transmitting a frame from the subscriber device using a source IP address; comparing in the filter said source IP address with the stored subscriber IP address; and, discarding said frame when said source IP address differs from the stored subscriber IP address.