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    Cisco: TDR Cable Diagnostic On Cisco Switch Port

    Posted on 3 mins

    Netadmin

    Table of Contents

    Overview

    These are notes I pickedup on how to test the cables connected to Cisco switch ports. A series of commands can be executed to check on the pairs of the switch.

    Although it’s not always accurate. It can save time to just inform them that they will lose connection for a few seconds. Then run the commands. It can take the load off of your other techs to confirm the pairs from the switch because they don’t have to go on site later. But, there are occurances where these diags aren’t accurate. So, you end up sending them anyway.

    Generally, when there are issues with port negotiation or connections drop off randomly. This is my first test because it tells you that the cable was terminated properly.

    Performing The Test

    You can initiate the command like the following as long as your account has the appropriate permissions for it. Make sure to change the tw1/0/13 portion with your interface name.

    This will initiate the TDR test on the interface and as long as there’s something on the other side. You should see some interesting results when they’re checked.

    We’ll just need to remember to give the switch, at most, 30 seconds to complete its test before we check the results

    show cable-diagnostics tdr interface tw1/0/13

    The following command will check the interface we just tested. Again, the twoGigabitEthernet 1/0/13 input will need to be swapped out for the port we’re testing.

    show cable-diagnostics tdr interface twoGigabitEthernet 1/0/13

    Once that’s executed we should see something similar to the following. This tells us that Pair A-C are in a Normal state on interface Tw1/0/13.

    Anything that would be considered abnormal would be seeing a pair that was open. When we see that. Either:

    There are any number of reasons. But, generally I will go with a broken termination. Especially if the organization utilizes 8P8C punch down patch panels. You’ll see this if someone wasn’t careful (even when careful) terminating a new cable.

    TDR test last run on:  June 02 01:59:04

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------

Tw1/0/13     1000M Pair A     8    +/- 10 meters Pair B      Normal             
                   Pair B     8    +/- 10 meters Pair A      Normal             
                   Pair C     8    +/- 10 meters Pair D      Normal             
                   Pair D     8    +/- 10 meters Pair C      Normal

    Some Things To Expect

    Some things to expect when you perform this test is for the switch to log it as shown below. The user will also log it into the void; telling you their port went down. As long as your transparent with them. No one will be angry. But, if you were to do this while a user was on a call. Not a good move…

    *Jun  2 01:59:05.231: %LINEPROTO-5-UPDOWN: Line protocol on Interface TwoGigabitEthernet1/0/13, changed state to down
*Jun  2 01:59:06.238: %LINK-3-UPDOWN: Interface TwoGigabitEthernet1/0/13, changed state to down
*Jun  2 01:59:12.772: %LINK-3-UPDOWN: Interface TwoGigabitEthernet1/0/13, changed state to up
*Jun  2 01:59:13.779: %LINEPROTO-5-UPDOWN: Line protocol on Interface TwoGigabitEthernet1/0/13, changed state to up