there are some tools availble using which a fake mac address can be given to any NIC. What are the ways to control/avoid such fake MAC addresses to be relayed and get unathorized access to the network?
You can use the Secure DHCP feature where an IP address is assigned to a Mac address is recorded. This feature is called Secure DHCP. Refer URL http://cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ftdsiaa.html#wp1027188 for more information.