Posted on Friday, 21st December 2007 by sean
The 3750 (and it would appear, the 3560s, 4500s, and 6500s) have an integrated Time Domain Reflector which is used to test cables associated with a port.
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_see/command/reference/cli3.html#wp2168243
Today I was troubleshooting a problem at a newly renovated remote office with an IP phone that would power up but not boot. After swapping cables and phones, I remembered the TDR and tried it out:
Switch# test cable-diagnostics tdr interface g1/0/14
TDR test started on interface Gi1/0/14
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 1/0/14
TDR test last run on: March 04 22:31:09
Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/14 auto Pair A 19 +/- 4 meters N/A Open
Pair B 4 +/- 4 meters N/A Open
Pair C 20 +/- 4 meters N/A Open
Pair D 20 +/- 4 meters N/A Open
Looks like a problem on Pair B! You should have heard the suprise from the (telecom) guy on the other end of the line when I finally said "looks like a problem in the cabling, get the contractor to check pair B.
Posted in Switching | Comments (2)
March 6th, 2009 at 2:53 pm
This works on a 2960 too.
e-
August 16th, 2010 at 10:20 am
They only let you do it on the gigabit ports, the Fast Ethernet ports don’t have TDR built in.
From Cisco’s website:-
Q. Does Cisco Catalyst 3750 Series support TDR?
A. Yes. Cisco Catalyst 3750 Series Switches support TDR on its 10/100/1000 interfaces. TDR is not supported on 10/100 or 1000base SFP ports.