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Chapter 7
Troubleshooting Serial Line and Frame Relay Connectivity
Summary
S
everal troubleshooting methods presented in this chapter can be used
to resolve many different types of serial line problems.
show interface
can be used to provide information relevant to serial
line, X.25, and Frame Relay interfaces. The command output varies,
depending on the way the interface was configured.
debug serial interface
is similar because it can provide informa-
tion that is relevant to all types of serial troubleshooting scenarios.
CSU/DSU loopback tests can be used in many scenarios to isolate hard-
ware and software problems encountered with serial lines.
debug
commands can be very useful, but it is important to use them
with caution because of the large amount of output that they generate.
Some information provided by the debug commands is hard to under-
stand, so knowledge of the protocol is necessary.
Summary tables were provided for serial, X.25, and Frame Relay
troubleshooting. The problems listed in these tables are common ones and
should be straightforward to resolve.
Many times, it will be necessary to contact the local service provider to aid
in troubleshooting failed links. It is important that you run all of the diag-
nostics available to you to isolate the problem before you call. If you have
done a lot of the groundwork, the carrier will be more willing to run tests
within its network.
Commands Used in This Chapter
T
he following list contains a summary of all the commands used in this
chapter.
Command
Description
clear counters serial
Clears the statistical counters on
the interface.
debug frame-relay events
Gives details about protocols and
applications using the DLCI.
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