Cable-diagnostics command

Routing & Switching
1

Hi

How does the ‘cable-diagnostics’ command work?

Can you explain differences between tdr and prbr ?

SW#show cable-diagnostics ?   
  prbs  show PRBS result
  tdr   show TDR result

Also how should i read this output?

SW#test cable-diagnostics tdr interface gigabitEthernet 0/4
TDR test started on interface Gi0/4
A TDR test can take a few seconds to run on an interface
Use 'show cable-diagnostics tdr' to read the TDR results.
SW#show cable-diagnostics tdr interface gigabitEthernet 0/4
TDR test last run on: May 30 09:12:38

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/4     1000M Pair A     22   +/- 10 meters Pair B      Normal              
                Pair B     22   +/- 10 meters Pair A      Normal              
                Pair C     22   +/- 10 meters Pair D      Normal              
                Pair D     22   +/- 10 meters Pair C      Normal

Thanks

2

Hello Giovanni

Take a look at this NetworkLessons note on cable diagnostics for more information.

The output shows the length of the cable (22 +/- 10 meters in your case) and it shows that the status is normal, which means the pair is terminated and functioning correctly.

Keep in mind that the results of such tests are a best-effort affair. The switch should not replace specialized equipment that performs these tests more accurately, but should only be used to initially diagnose possible cable faults.

I hope this has been helpful!

Laz