will be understood that typically there will be many more nac servers each controlling access by its own corresponding group of client devices the nac server e g server 16 or 22 provides service to and control access by a group of client devices such as client device 18 or 24 each of the servers 16 and 22 and each of all other nac servers not shown in fig1 controlling access to the same ip network has a unique identifier a media access layer domain identifier or mdi in the case of cable systems which is different from the identifier of all other nac servers in the ip network as noted above when a customer using client device 18 signs up for a service a customer service representative will authorize the physical address such as a mac address in the case of cable systems of the client device and this authorized physical address and the nac server identifier of server 16 are then stored in database 12 the physical addresses of other client devices controlled by server 16 not shown in fig1 are authorized in a similar manner and are stored in database 12 with the identifier of server 16 similarly when a customer using client device 24 signs up for a service a customer service representative will authorize the physical address of the client device and this authorized physical address and the identifier of nac server 22 are then.