MAC address

Media Access Control address. Also known as adapter address. A 12-digit alphanumeric string, written in six chunks of two characters each, that uniquely identifies a network device. For example, 00-20-78-A3-49-5E is a valid MAC address.

MACs are almost always hardcoded and cannot be changed. Consequently, they have become a popular tool in the fight against service theft. If the MAC of the NIC connected to a cable modem does not match the MAC on record, the cable company assumes that an unauthorized computer has been connected, and service is denied. While this prevents seedy neighbors from sharing a cable modem, it also prevents legitimate users from connecting the service to multiple computers in their own home.

Because of this MAC control, most cable/DSL routers now offer the option to “spoof” a MAC; in other words, to have the router report something other than its true MAC. This allows users to spoof the MAC of the NIC that was originally connected to the cable modem, which makes it appear as if nothing about the network configuration has changed.


Megabits per second. A measure of data transfer speed, equal to 1,000 Kbps.


The physical connection between network devices. Usually a Cat-5 cable.


A chunk of data equal to 1,000 kilobits. The unit of measure for higher data transfer rates, especially over LANs (rather than over the Internet). In terms of data storage, it is often considered to be equal to 1,024 kilobits.