TCP/IP Guide

Network Layer (Layer 3)

The third-lowest layer of the OSI Reference Model is the network layer. If the data link layer defines the boundaries of what is considered a network, the network layer defines how internetworks (interconnected networks) function. The network layer is the lowest one in the OSI model that is concerned with actually getting data from one computer to another even if it is on a remote network; in contrast, the data link layer only deals with devices that are local to each other.

While layers 2 through 6 all act as fences between the layers above and below them, the network layer is particularly important in terms of separating higher and lower-layer functions. It is here that the transition really begins from the more abstract ...