C H A P T E R 5
• Learn the basics of routing protocols.
• Learn the differences between link-state and distance vector routing protocols.
• Learn about the metrics used by routing protocols to determine path selection.
• Learn the basics of how data travels from end stations through intermediate stations and on to the
destination end station.
• Understand the difference between routed protocols and routing protocols.
This chapter introduces the underlying concepts widely used in routing protocols. Topics summarized
here include routing protocol components and algorithms. In addition, the role of routing protocols is
briefly contrasted with the role of routed or network protocols. Subsequent chapters in Part VII,
“Routing Protocols,” address specific routing protocols in more detail, while the network protocols that
use routing protocols are discussed in Part VI, “Network Protocols.”
What Is Routing?
Routing is the act of moving information across an internetwork from a source to a destination. Along
the way, at least one intermediate node typically is encountered. Routing is often contrasted with
bridging, which might seem to accomplish precisely the same thing to the casual observer. The primary
difference between the two is that bridging occurs at Layer 2 (the link layer) of the OSI reference model,
whereas routing occurs at Layer 3 (the network layer). This distinction provides routing and bridging
with different information to use in the process of moving information from source to destination, so the
two functions accomplish their tasks in different ways.
The topic of routing has been covered in computer science literature for more than two decades, but
routing achieved commercial popularity as late as the mid-1980s. The primary reason for this time lag
is that networks in the 1970s were simple, homogeneous environments. Only relatively recently has
large-scale internetworking become popular.
rnetworking Technologies Handbook