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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 27 Troubleshooting
Using the show forward Command
Enabling All-System Diagnostics
Beginning in privileged EXEC mode, enter this command to enable all-system diagnostics:
Switch# debug all
Caution
Because debugging output takes priority over other network traffic, and because the debug all
privileged EXEC command generates more output than any other debug command, it can severely
diminish switch performance or even render it unusable. In virtually all cases, it is best to use more
specific debug commands.
The no debug all privileged EXEC command disables all diagnostic output. Using the no debug all
command is a convenient way to ensure that you have not accidentally left any debug commands
enabled.
Redirecting Debug and Error Message Output
By default, the network server sends the output from debug commands and system error messages to the
console. If you use this default, you can use a virtual terminal connection to monitor debug output
instead of connecting to the console port.
Possible destinations include the console, virtual terminals, internal buffer, and UNIX hosts running a
syslog server. The syslog format is compatible with 4.3 Berkeley Standard Distribution (BSD) UNIX
and its derivatives.
Note
Be aware that the debugging destination you use affects system overhead. Logging messages to the
console produces very high overhead, whereas logging messages to a virtual terminal produces less
overhead. Logging messages to a syslog server produces even less, and logging to an internal buffer
produces the least overhead of any method.
For more information about system message logging, see
Chapter 17, “Configuring System Message
Logging.”
Using the show forward Command
The output from the show forward privileged EXEC command provides some useful information about
the disposition of a packet entering an interface. Depending upon the parameters entered about the
packet, the output provides lookup table results, maps and masks used to calculate forwarding
destinations, bitmaps, and egress information.
Note
For more syntax and usage information for the show forward command, refer to the Catalyst 3550
Multilayer Switch Command Reference for this release.
