IP address example

Let’s extend our example to include a serial link between two routers, as shown in Figure 2.1.
FIGURE 2 . 1 IP address example
Because these are routers and not switches, each interface on the same router belongs to a
different network. The facing interfaces on opposing routers need to share a network to talk.
How many IP numbers do we really need on the network interconnecting the two routers?
Because a point-to-point link will never have anything but two devices, we need only two IP
numbers, one for each serial interface, as shown in Figure 2.1. Unfortunately, we have an
eight-bit subnet mask (i.e., 255.255.255.0), so we are wasting 252 of the 254 available numbers
on the subnet. One possible solution to this dilemma is to use VLSMs.