|  | 8.4 | The Network Layer
| 8.4.5 | The reason for employing unique network ids
Each device, which participates on a network, must have a unique id: A MAC address (also known as layer 2 address, hardware address, or physical address). MAC addresses can be easily identified and maintained for LANs up to a certain size; however, the addresses become unmanagemable for large unsegmented LANs or WANs. The layer 3 or network addressing scheme, which is hierarchical, was created because a new addressing scheme was needed. By requiring that all networks connected to the router have their own network id number, the router can refer to a group of hosts with one network layer (often IP) address. The router builds tables of device hardware and network addresses (typically MAC and IP addresses) and by which interface these networks can be reached. Thus the routers use the network id address to efficiently make best path selection and switching decisions.