Chapter11.Knowing Where to Turn at Each Intersection (Router)

Chapter 11. Knowing Where to Turn at Each Intersection (Router)

What You Will Learn

After reading this chapter, you should be able to

• Explain the process of routing an IP packet from one computer to another

• Describe the purpose of a default gateway

• Explain how to encapsulate IP packets inside an Ethernet frame for delivery

• Describe the contents of a router's IP routing table

• Define the logic that a router uses when it makes a forwarding decision

In Chapter 10, "Delivering the Goods to the Right Street (IP) Address," you learned about IP addresses and the basics of IP routing. You can understand addressing better if you understand routing. This chapter takes the routing concepts a little deeper, now that you understand the basics of IP addressing.

In many ways, IP routing works like driving somewhere in your car. You leave the house, and generally leave your neighborhood to get to the main road. After you get to the first intersection, you make a decision of whether to turn left, right, or keep going straight. Every time you get to another intersection, you make a choice of where to turn, until you eventually get to your destination.

With IP routing, a PC sends an IP packet to some nearby router. That router chooses the interface that the router uses to forward the packet. The packet travels across the physical network, for instance, over a LAN switch, to the next router. Eventually, the packet arrives at the last router, which routes the packet to the destination address.

The routing process is actually pretty simple, and you've already seen the basics in Chapter 10. This chapter covers more details of the routing process that pull some important concepts together.