NetNotes

cable testing on a cisco 3750

Catalyst 2960, 2970, 3560/3560-E, и 3750/3750-E switches have a built-in Time-Domain Reflectometer that can be used to test cabling directly from the switchports. TDR is not supported neither on 10Gig interfaces, nor FastEthernet or SFP interfaces.

Example:

SW01#test cable-diagnostics tdr interface gigabitethernet2/1
TDR test started on interface Gi2/1

A TDR test can take a few seconds to run on an interface

Use ’show cable-diagnostics tdr’ to read the TDR results.
SW01#

SW01#sh cable-diagnostics tdr interface gig2/1
TDR test last run on: March 02 00:31:15

Interface Speed Local pair Pair length Remote pair Pair status
——— —– ———- —————— ———– ——————–
Gi2/1 100M Pair A 47 +/- 4 meters Pair A Normal
Pair B 48 +/- 4 meters Pair B Normal
Pair C 48 +/- 4 meters Pair C Open
Pair D 48 +/- 4 meters Pair D Open
SW01#

The output shows the outgoing interface, the working bandwidth of the interface, and also which local pair corresponds to which remote one, approximated length of the cabling pair, and the pair status:

• Normal;
• Open - not connected;
• Not Completed - TDR testing was unsuccessful;
• Not supported - TDR testing not supported on the interface;
• Shorted - cable short ;);

Tags: cable testing, Catalyst 3750, Switching, TDR