Measure the cable lengths on a Catalyst switch
Ken McCoy sent me a short question:
At one point someone posted an article about a command you could run on the Catalyst switch that would give you back the distance of the cable between the switch and end device, but now I can't find it.I remembered reading the same article and after I've figured out the underlying technology is called TDR (Time Domain Reflectometer), uncle Google immediately provided a reader tip from Csaba Farkas.
This article is part of You've asked for it series.
c3560#sh cable-diagnostics tdr inter gi0/2
TDR test last run on: August 19 21:47:29
Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/2 100M Pair A 1 +/- 4 meters Pair A Normal
Pair B 1 +/- 4 meters Pair B Normal
Pair C 2 +/- 4 meters Pair C Short
Pair D 2 +/- 4 meters Pair D Short
The switch (actually part of the NIC hardware) sends a pulse into the cable and measures when the pulse returns. Calculating distance based on measured travel time and (known) propagation speed in cable is trivial.
http://supportwiki.cisco.com/ViewWiki/index.php/Tech_Insights:Cool_Tool_for_Solving_Layer_1_Cable_Issues