Chapter12.Painting the Road Signs on Your Interstate (Internetwork)

Chapter 12. Painting the Road Signs on Your Interstate (Internetwork)

What You Will Learn

After reading this chapter, you should be able to

• Explain how a router learns to put routes in its routing table for networks or subnets that are connected directly to the router

• Describe how a network engineer can configure a router to use static routes so that it adds routes to its routing table

• Explain the basic idea of how multiple routers can use a routing protocol to exchange routing information with each other

• List several IP routing protocols

If you take a trip in your car and you don't use a map, you can still get where you're going by just reading the road signs. Routing, as covered in Chapter 11, "Knowing Where to Turn at Each Intersection (Router)," works a lot like taking a trip and relying on road signs. Think of the IP packets as cars, each intersection as a router, and the routers' routing tables as the road signs. Just like a driver might rely on good information found on the road signs, IP packets rely on the routers' routing tables having good information in them. When a router receives a packet, it must match the destination IP address of the packet to the routing table to figure out where to send the packet next. Similar to cases in which you might see a road sign when driving and turn off onto another road, a router directs the packet down the next network roadway to get to its destination. (Note that the router forwards the packet and makes the decision of where to send the packet, which is a slight departure from the analogy with driving, in which the driver of the car decides where to turn.)

In short, IP packets rely on the routers having good, complete routing information in their routing tables. This brief chapter covers the most basic concepts of how a router creates and fills its routing table.