Use Cable TDR Diagnostics on Cisco 3750 Switches

Cisco 3750 Switches now include a time domain reflectometer!

Historical platform note (updated July 2026): This Cisco 3750 cable-diagnostics example is retained for its troubleshooting concept. Confirm command availability and output on the exact supported switch and software release.

How many time have you wanted to know how long a cable run was? Now if you are running cisco 3750 switches you can find out by issuing the following commands you can see how long that cable run really is.

Switch# test cable-diagnostics tdr interface gigabitethernet0/2
TDR test started on interface Gi0/2

A TDR test can take a few seconds to run on an interface. Use "show cable-diagnostics tdr" to read the TDR results.

Switch#show cable-diagnostics tdr interface gigabitEthernet 0/2
TDR test last run on: Dec 10 09:05:10

         Interface Speed Local pair Pair length Remote pair Pair status 
         --------- ------ ---------- ------------ ------------ ---------- 
         Gi0/2 auto Pair A   22 +/- 4 m N/A Open 
           Pair B    21 +/- 4 m N/A Open 
           Pair C    5 +/- 4 m N/A Open 
           Pair D    20 +/- 4 m N/A Open