WAN Access Problems
323
WAN Access Problems
T
he function of a wide area network (WAN) is to connect multiple
local area networks (LANs). There are several technologies and topologies
for connecting LANs. Here are a few examples:
Serial lines
HSSI (High-Speed Serial Lines)
ATM
ISDN
Frame Relay
DDR
POSIP (Packet over Sonet IP)
No matter what physical media, technology, or topology is used, one
thing remains constant: For information to get from one LAN to another, the
data has to be routed.
In order for data to be routed, certain components must be configured
and must work properly. The components that will be discussed are default
gateways, and static and dynamic routing. Troubleshooting methods for
each of these components will be addressed in their corresponding sections.
Default Gateways
The capability of a router to route or forward data depends on its knowledge
of the world around it. This knowledge comes in the form of a route table.
The route table is populated by the router's own networks, as well as by
advertisements received from neighboring routers. This will be covered in
detail when static and dynamic routing is discussed.
What happens if a router doesn't have a route to a destination? There are
two possibilities. If the router is configured to do so, it will send the packet
to a neighboring router that is considered to be the default gateway, with the
hope that the default gateway will know where to send the packet. If the
router is not configured to do that, it will simply drop the packet.
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