Network Layer

The third layer of the OSI Reference Model is network layer. The network layer provides quite a few functions. First it provides for a logical topology of your network using logical or layer 3 addresses. These addresses are used to group machines together. As you will see in chapter 3 these addresses have two components a network component and a host component. The network component is used to group devices together. Layer 3 addresses allow devices that are on the same or different media types to communicate with each other. Media types define types of connections such as Ethernet Token Ring or serial. These are discussed in the section Data Link Layer later in this chapter. To move information between devices that have different network numbers a router is used. Routers use information in the logical address to make intelligent decisions about how to reach a destination. Routing is discussed in more depth in chapter 9, 10 and 11. Examples of network layer protocols include Apply Talk DEC net IPX, TCP/IP (or IP for short), Vines and XNS. The network layer is discussed in much more depth in the section Network Layer later in this chapter