I recently discovered a really cool command on a Cisco 3560 switch.
It has a TDR (Time-domain reflectometer). It basically means you can test how long the cable is, if it has a short, pair of wires open and any other problem.
TDR works on 10/100/1000BaseTx. Fibre optic ports are not supported.
TDR has been available after Cisco IOS Release 12.2(25)SE or later.
This is a table of the different pair status results and their meanings.
|Pair Status||What does this mean?|
|Normal||Best result. No issues.|
|Impedance Mismatched||Bad cable.|
More info is available here from Cisco.
Here is an example:
Switch# test cable-diagnostics tdr interface g0/1 TDR test started on interface Gi0/1 A TDR test can take a few seconds to run on an interface Use 'show cable-diagnostics tdr' to read the TDR results. Switch# sh cable-diagnostics tdr int g0/1 TDR test last run on: March 01 00:09:06 Interface Speed Local pair Pair length Remote pair Pair status --------- ----- ---------- ------------------ ----------- -------------------- Gi0/1 auto Pair A 20 +/- 4 meters N/A Open Pair B 20 +/- 4 meters N/A Open Pair C 21 +/- 4 meters N/A Open Pair D 20 +/- 4 meters N/A Open
Have a read through TSF’s other networking articles here.
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