|  | 10.1 | Importance of a Network Layer
| 10.1.1 | Identifiers
The network layer is responsible for moving data through a set of networks (internetwork). The network layer's addressing scheme is used by devices to determine the destination of data as it moves through the networks. Protocols that have no network layer can only be used on small internal networks. These protocols usually use only a name (i.e. MAC address) to identify the computer on a network. The problem with this approach is that, as the network grows in size, it becomes increasingly difficult to organize all the names, such as making sure that two computers aren't using the same name. Protocols that support the network layer use an identification technique for devices that guarantees a unique identifier. So how does this identifier differ from a MAC address, which is also unique? MAC addresses use a flat addressing scheme that makes it difficult to locate devices on other networks. Network layer addresses use a hierarchical addressing scheme that allows for unique addresses across network boundaries, along with a method for finding a path for data to travel between networks. Hierarchical addressing schemes enable information to traverse an internetwork, along with a method to find the destination in an efficient fashion. The telephone network is an example of the use of hierarchical addressing. The telephone system uses an area code that designates a geographical area for the call's first stop (hop). The next three digits represent the local exchange (second hop). The final digits represent the individual destination telephone (which is, or course, the final hop). Network devices need an addressing scheme that allows them to forward data packets through the internetwork (a set of networks composed of multiple segments using the same type of addressing). There are several network layer protocols with different addressing schemes that allow devices to forward data throughout an internetwork.
| Web Links
| RFC 941
| Routing and the Network Layer
| Network Layer Functions