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Positioning Leased Lines with LANs and Routers

The vast majority of end-user devices in an enterprise or small office/home office (SOHO)
network connect directly into a LAN. Many PCs use an Ethernet network interface card
(NIC) that connects to a switch. More and more, devices use 802.11 wireless LANs, with
some devices like phones and tablets supporting only wireless LAN connections.

Now think about a typical company that has many different locations. From a human
resources perspective, it might have lots of employees that work at many locations. From
a facilities perspective, the company might have a few large sites, with hundreds or even
thousands of individual branch offices, stores, or other small locations. However, from a
networking perspective, think of each site as being one or more LANs that need to communicate
with each other, and to communicate, those LANs need to be connected to each
other using a WAN.

To connect LANs using a WAN, the internetwork uses a router connected to each LAN,
with a WAN link between the routers. First, the enterprise’s network engineer would order
some kind of WAN link. A router at each site connects to both the WAN link and the LAN,
as shown in Figure 3-1. Note that a crooked line between the routers is the common way to
represent a leased line when the drawing does not need to show any of the physical details
of the line.
Free CISCO CCNA Routing and Switching ICND1 Study Guide
Figure 3-1 Small Enterprise Network with One Leased Line
The world of WAN technologies includes many different options in addition to the leased
line shown in the figure. WAN technology includes a large number of options for physical
links, as well as the data-link protocols that control those links. By comparison, the wired
LAN world basically has one major option today—Ethernet—because Ethernet won the
wired LAN battle in the marketplace back in the 1980s and 1990s.

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