Every Ethernet Network card that has ever been made is supposed to have a unique Hardware Address. The Hardware Address is customarily hard coded into the network card and is not normally allowed to change. Network switches use the Hardware Address to direct communications. Network routers track the relationship between IP Addresses and Hardware Addresses to direct communications.
A typical hardware address will look something like this ‘00:00:0C:0F:35:04′ - there are six pairs of hexadecimal (0-9,A-F) numbers in a hardware address, in this example they are separated by colons, but can also be separated by dashes or periods, or the hardware address can be presented in a single long string.
