Education – Australia / New Zealand

Reply
This is an open group. Sign in and click the "Join Group" button to become a group member and start posting.
Highlighted
Aruba Employee

Cable Testing with TDR to the Rescue!

Cable and cable plant are perhaps the most under-appreciated part of any network. Once run and connected, they are often forgotten about, sometimes for decades.

 

The problem is, sometimes they degrade or fail completely.  A cable can look perfectly fine, but after one too many footsteps, office chairs, filing cabinets, rack doors, etc, it stops working as it should.

 

Like this one.

2017-05-25 20.59.42.jpg

 

I needed to test a POE phone, so I plugged it in using the cable shamed in the picture above. It worked perfectly well for - as best I can estimate - over 15 years. It powers on the phone, but doesn't provide connectivity.

 

This is where the TDR (time domain reflectometer) comes into play. The TDR is built-in to most of the new Aruba-branded switches (previously known as ProCurve, E-Series, ProVision). That includes:

  • 2930F
  • the brand new 2930M
  • 3810M
  • 5400R V3 modules

I plugged both ends of the cable into a 2930M (yes, STP was configured properly), and ran these commands from the console.

2930M(config)# test cable-diagnostics 1/3-1/4
This command will cause a loss of link on all tested ports and will take
several seconds per port to complete.  Use the 'show cable-diagnostics'
command to view the results.

Continue (y/n)?  y
2930M(config)# show cable-diagnostics

 Cable Diagnostic Status - Copper Ports

       MDI    Cable       Cable Length or
  Port Pair   Status      Distance to Fault
  ---- ------ ----------- ---------------------
  1/3  1-2    OK          5m
       3-6    OK          4m
       4-5    OK          5m
       7-8    OK          4m
  1/4  1-2    OK          5m
       3-6    OK          0m
       4-5    OK          4m
       7-8    OK          5m

Note the "0m" for the 3-6 pair on port 1/4. Straight into the special box of broken bits used for testing and demos (after proper marking as "faulty" of course)!

Richard Litchfield
Network Solution Architect, HPE Aruba
Search Airheads
cancel
Showing results for 
Search instead for 
Did you mean: