Cisco Systems 3550 Using the show forward Command

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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter27 Troubleshooting Using the show forward Command
Enabling All-System Diagnostics
Beginning in privileged EXEC mode, enter this command to ena ble al l-syste m diagnos tic s:
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 sev erel y
diminish switch performance or even render it unusable. In virtually all ca ses, i t is be st to use mor e
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 acc ide nta lly le ft a ny 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. Lo ggin g messa ge s to the
console produces very high overhead, whereas logging messag es to a virtual terminal produces less
overhead. Logging messages to a syslog server produces even less, and logging t o an internal buffer
produces the least overhead of any method.
For more information about system message logging, see Chapter 1 7, “Conf iguring Syst em Message
Logging.”
Using the show forward Command
The output from the show forward privileged EXEC command provides so me useful information about
the disposition of a packet entering an interface. Depending upon the parameters ent ered abou t the
packet, the output provides lookup table results, maps and ma sks used to c a lcula te fo rwar ding
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.