Concept
MAC spoofing is a technique for changing a factory-assigned Media Access Control (MAC) address of a network interface on a networked device. The MAC address that is hard-coded on a network interface controller (NIC) cannot be changed. However, many drivers allow the MAC address to be changed. Additionally, there are tools which can make an operating system believe that the NIC has the MAC address of a user's choosing. The process of masking a MAC address is known as MAC spoofing. Essentially, MAC spoofing entails changing a computer's identity, for any reason. Changing the assigned MAC address may allow the user to bypass access control lists on servers or routers, either hiding a computer on a network or allowing it to impersonate another network device. It may also allow the user to bypass MAC address blacklisting to regain access to a Wi-Fi network. However, MAC spoofing does not work when trying to bypass parental controls if automatic MAC filtering is turned on. MAC spoofing is done for legitimate and illicit purposes alike. Many ISPs register the client's MAC address for service and billing services. Since MAC addresses are unique and hard-coded on network interface controller (NIC) cards, when the client wants to connect a new device or change an existing one, the ISP will detect different MAC addresses and might not grant Internet access to those new devices. This can be circumvented easily by MAC spoofing, with the client only needing to spoof the new device's MAC address so it appears to be the MAC address that was registered by the ISP. In this case, the client spoofs their MAC address to gain Internet access from multiple devices. While this is generally a legitimate case, MAC spoofing of new devices can be considered illegal if the ISP's user agreement prevents the user from connecting more than one device to their service. Moreover, the client is not the only person who can spoof their MAC address to gain access to the ISP. Computer crackers can gain unauthorized access to the ISP via the same technique.