Troubleshooting guide

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Cisco PGW 2200 Softswitch Release 9.8 Operations, Maintenance, and Troubleshooting Guide
OL-0800-14
Chapter 4 Maintenance and Troubleshooting Overview
Troubleshooting Strategy Overview
For detailed information on using the ping command and extended ping commands, see the Cisco IOS
Configuration Fundamentals Command Reference.
Using the Trace Command
The trace user command in EXEC mode discovers the routes that packets follow when traveling to their
destinations. The trace command in privileged EXEC mode enables you to specify the supported IP
Header options, which enable the router to perform a more extensive range of test options. The trace
command uses the error message that a router generates when a datagram exceeds its time-to-live (TTL)
value. First probe datagrams are sent with a TTL value of 1, which causes the first router to discard the
probe datagrams and send back “time exceeded” error messages. The trace command then sends several
probes and displays the round-trip time for each. After every third probe, the TTL increases by 1.
Each outgoing packet can result in one of two error messages. A “time exceeded” error message
indicates that an intermediate router has seen and discarded the probe. A “port unreachable” error
message indicates that the destination node has received the probe and discarded it, because it could not
deliver the packet to an application. If the timer goes off before a response comes in, the trace command
prints an asterisk (*).
The trace command terminates when the destination responds, when the maximum TTL is exceeded, or
when the user interrupts the trace with the escape sequence.
It is a good idea to use the trace command when the network is functioning properly under normal
conditions. Compare the information that the command returns when the network is performing as
expected with the information returned by the command when you are troubleshooting a problem.
For detailed information on using the trace and extended trace commands, see Cisco IOS Configuration
Fundamentals Command Reference.
Third-Party Troubleshooting Tools
In many situations, third-party diagnostic tools can be more useful than system commands that are
integrated into the router. For example, issuing a processor-intensive debug command can contribute to
the overloading of an environment that is already experiencing excessively high traffic levels. Attaching
a network analyzer to the suspect network is less intrusive and is more likely to yield useful information
without interrupting the operation of the router.
Some useful third-party tools for troubleshooting internetworks include the following:
• Volt-ohm meters, digital multimeters, and cable testers
• Breakout boxes, fox boxes, bit error rate testers (BERTs), and block error rate testers (BLERTs)
• Network analyzers and network monitors
• Time domain reflectometers (TDRs) and optical time domain reflectometers (ODTRs)
Volt-Ohm Meters, Digital Multimeters, and Cable Testers
Volt-ohm meters and digital multimeters are at the lower end of the spectrum of cable testing tools. These
devices can measure basic parameters such as alternating current (AC) and direct current (DC) voltage,
current, resistance, capacitance, and cable continuity. They are used primarily to check physical
connectivity.
Cable testers (scanners) can also be used to check physical connectivity. Cable testers are available for
shielded twisted-pair, unshielded twisted-pair, 10BASE-T, and coaxial and twinax cables.