A packet forwarding apparatus for connecting a plurality of user terminals to an ISP management server has a management table indicating the relationship between a connection port identifier and specific header information in association with the MAC address of each of the user terminals so that, in a communication protocol procedure executed between each of the user terminals and the ISP management server prior to communication with a wide-area network, the packet forwarding apparatus discards a packet for the user terminal when it is determined that the specific header information cannot be assigned to the user terminal based on the management table.