A very useful tool for determining simple wiring problems (Layer 1) without having to leave your desk is the Time Domain Reflector testing built in to some of the Catalyst switches including the 3750E.

One caveat is that it may cause connectivity problems for the particular tested interface.

Start the test by issuing the command:

Switch#test cable-diagnostics tdr interface gi2/0/2

After a few seconds the test results will be available by issuing this command:

Switch#show cable-diagnostics tdr interface gi2/0/2
TDR test last run on: February 22 10:00:46

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi2/0/2   auto  Pair A     N/A                Pair B      Normal              
                Pair B     N/A                Pair A      Open                
                Pair C     64   +/- 1  meters N/A         Normal              
                Pair D     65   +/- 1  meters N/A         Normal   
Jonathan Voss - Feb 22, 2012

For a while now, security scanning software and users have been triggering an onslaught of %SNMP-3-AUTHFAIL messages in our device logs. This rather annoying message often obscures other events that may be more important. Old mentality would tell you to simply create a logging discriminator and be done with it. However, I recently learned of a little undocumented gem in IOS that saves the day:

hostname(config)#no logging snmp-authfail

Do not trust the almighty ‘?‘ command. It will not show up as a valid option. However, when actually executing the command, it has worked in every IOS case I have tried.

Jonathan Voss - Mar 23, 2011