Troubleshooting guide

2-4
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter2 Troubleshooting Tools
Third-Party Troubleshooting Tools
Using the extended command mode of the privileged EXEC mode ping command, you can specify the
supported IP header options, which allow the switch router to perform a more extensive range of test
options. To enter ping extended command mode, enter the ping command at the command prompt
followed by a return.
To see how the command works under normal conditions, use the ping command when the network is
functioning properly. When you are troubleshooting, you can then see the difference between normal and
abnormal operation.
For detailed information about using the ping and extended ping commands, refer to the
Cisco IOS Configuration Fundamentals Command Reference publication.
traceroute Command
The traceroute user EXEC command discovers the routes packets follow when traveling to their
destinations. With the traceroute privileged EXEC command, the supported IP header options are
specified, and the switch router can perform a more extensive range of test options.
The traceroute command works by using the error message generated by switch routers when a
datagram exceeds its time-to-live (TTL) value. First, probe datagrams are sent with a TTL value of one.
This causes the first switch router to discard the probe datagrams and send back “time exceeded” error
messages. The traceroute command then sends several probes, and displays the round-trip time for each.
After every third probe, the TTL increases by one.
Each outgoing packet can result in one of two error messages. A “time exceeded” error message
indicates that an intermediate switch 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 traceroute
command displays an asterisk (*).
The traceroute command terminates when the destination responds, when the maximum TTL is
exceeded, or when the user interrupts the traceroute command with the escape sequence.
To see how the command works under normal conditions, use the traceroute command when the
network is functioning properly. When you are troubleshooting, you can then see the difference between
normal and abnormal operation.
For detailed information about using the traceroute and extended traceroute commands, refer to the
ATM Switch Router Command Reference.
Third-Party Troubleshooting Tools
In many situations, third-party diagnostic tools can be helpful. For example, attaching a network
analyzer to a network is less intrusive and is more likely to yield useful information, without interrupting
the operation of the switch router, than using the debug commands, which are processor intensive.
Some typical third-party tools used for troubleshooting internetworks are described in the following
sections:
• Volt-Ohm Meters, Digital Multimeters, and Cable Testers, page 2-5
• TDRs and OTDRs, page 2-5
• Network Monitors, page 2-5
• Network Analyzers, page 2-6