|  | 6.3 | MAC Addressing
| 6.3.5 | Limitations of MAC addressing
MAC addresses are vital to the functioning of a computer network. They provide a way for computers to identify themselves. They give hosts a permanent, unique name. The number of possible addresses is not going to run out anytime soon, since there are 16^12 (or over 2 trillion!) possible MAC addresses. MAC addresses do have one major disadvantage. They have no structure, and are considered flat address spaces. Different vendors have different OUIs, but they're like personal identification numbers. As soon as your network grows to more than just a few computers, this disadvantage becomes a real problem.