Client and server on different LANs connected through a WAN.

We show the client and server on different LANs, with both LANs connected to a wide area network (WAN) using routers.

Figure 1.4. Client and server on different LANs connected through a WAN.
Routers are the building blocks of WANs. The largest WAN today is the Internet. Many companies build their own WANs and these private WANs may or may not be connected to the Internet.