Chapter 15. Manually directing traffic using the IP routing table
Connecting two switches that are in the same physical location is easy. All you have to do is string a couple of Ethernet cables between them, configure the interfaces, and you’re finished. But now imagine that your switches sit in separate offices hundreds of miles apart. How do you connect them?
In chapter 8 I said that you have a few options when it comes to connecting geographically separated sites. Private T1/E1 lines and MPLS virtual private networks (VPNs) are two popular methods. With both of these methods, the telecom carrier provides you physical connectivity between your sites. But it’s still up to you to configure IP routing between those sites.
In the last chapter, you got a glimpse of how IP routing works when you set up your “router-on-a-stick” topology. Figure 15.1 illustrates the topology you have right now.
Recall that you didn’t have to explicitly tell Router1 how to route between IP subnets. All you had to do was create a couple of subinterfaces, configure an IP address on each one, and the router took care of the rest.
But that’s with just one router. When you connect geographically separated sites, you’ll have multiple routers. Take a look at figure 15.2; you’ll reconfigure your network to look like this in this chapter.
