The Network layer is used by the Transport layer to provide the best end-to-end services and
path for PDU delivery. This means that the Network layer also uses protocols to accomplish this task. This section discusses protocols that are used within layer 3 of the OSI model. Some of
these protocols use other protocols within them for finer granularity of certain functions.
There is a significant difference between routing protocols and routed protocols. Routing
protocols are used to exchange route information and to create a network topology, thus
enabling routing decisions to be made. The routed protocols, on the other hand, contain information
regarding the end systems, how communication is established, and other information
relevant to the transfer of data. The routing protocols will be covered in Chapter 38, “TCP/IP
Routing Protocol Troubleshooting.”