Before considering how to configure Cisco routers and switches, you must be
introduced to basic networking concepts you’ll need to understand in order to grasp
the advanced concepts discussed in later chapters. The OSI Reference Model is the
best place to start, since it will help you understand how information is transferred between
networking devices. Of the seven layers in the OSI Reference Model, be especially sure to
understand how the bottom three layers function, since most networking devices function at
these layers. This chapter discusses information flow, as well as Cisco’s three-tiered hierarchical
model, which is used to design scalable, flexible, and easy-to-troubleshoot-and-maintain networks....