A LAN connects network devices
over a relatively short distance. A
networked office building, school, or
home usually contains a single LAN,
though sometimes one building will
contain a few small LANs, and
occasionally a LAN will span a group of
nearby buildings. In IP networking, one
can conceive of a LAN as a single IP
subnet (though this is not necessarily
true in practice).
Besides operating in a limited space,
LANs include several other distinctive
features. LANs are typically owned,
controlled, and managed by a single
person or organization. They also use
certain specific connectivity
technologies, primarily Ethernet and
the term implies, a wide-area network
spans a large physical distance. A WAN
like the Internet spans most of the
WAN is a geographically dispered
collection of LANs. A network device
called a router connects LANs to a WAN.
In IP networking, the router maintains
both a LAN address and a WAN address.
differ from LANs in several important
ways. Like the Internet, most WANs are
not owned by any one organization but
rather exist under collective or
distributed ownership and management.
WANs use technology like ATM, Frame
Relay and X.25 for connectivity.
and WANs at Home:
networkers with cable modem or DSL
service already have encountered LANs
and WANs in practice, though they may
not have noticed. A cable/DSL router
like those in the Linksys family join
the home LAN to the WAN link maintained
by one's ISP . The ISP provides a WAN IP
address used by the router, and all of
the computers on the home network use
private LAN addresses. On a home
network, like many LANs, all computers
can communicate directly with each
other, but they must go through a
central gateway location to reach
devices outside of their local area.