Leaving Your Neighborhood the Same Way, Every Time

Step 1: Leaving Your Neighborhood the Same Way, Every Time

For most people who have a car, when you leave your house or apartment, you can only drive one direction. Eventually, you'll get to some intersection, where you can make a choice of where to turn. If you know where you're going, you can go ahead and turn. If not, you can look for road signs at each intersection, with the road signs telling you which way to turn.

In Figure 11-1, Hannah is in the same basic situation. After Hannah's PC's IP software has built the IP packet that needs to be sent to the server, it needs to know where to send the packet first. As it turns out, because R1 is the only router attached to Hannah's IP network (network 8.0.0.0), she needs to send the packet to R1.

To send the packet to R1, Hannah needs to know R1's IP addressspecifically, the IP address of the router interface that's connected to the same Ethernet as Hannah. In TCP/IP terminology, R1 would be Hannah's default router, or default gateway. A PC's default router is simply the router to which that PC sends packets when the destination is in another network or subnet. As you can see in Figure 11-2, Hannah knows her default router is R1.