Testing a cable from CLI

[Andy White]

Hello,

I recently foudn out you can test the physical cables on a switch to see if they are faulty or not, I used the command

'test cable tdr interface'

The results can back in a table, but does anyone know how to interpret them?

Interface Speed      Local pair   Pair length          Remote pair    Pair status

---------     -----          ----------      ------------------       -----------          --------------------

Gi0/24    100M       Pair A         N/A                         N/A                    Normal

                                  Pair B         N/A                         N/A                    Normal

                                  Pair C         N/A                         N/A                    Normal

                                  Pair D         0    +/- 2  meters  N/A                    Open

Thanks

[Sandeep Choudhary]

HI ,

You can test like this:

test cable-diagnostics tdr interface gigabitethernet0/24

and then

"show cable-diagnostics tdr" and press the "Enter" key to view the test results.

Regards

Please rate if it helps.

[Andy White]

Thanks but how can I interpret the results, what do the values mean in the results?

Regards

[Sandeep Choudhary]

HI Andy,

TDR Guidelines

The following guidelines apply to the use of TDR:

•If  you connect a port undergoing a TDR test to an Auto-MDIX enabled port,  the TDR result might be invalid. In those instances, the port on the Switch should be administratively down before the start of the  TDR test.

•If  you connect a port undergoing a TDR test to a 100BASE-T port such as  that on the WS-X4148-RJ45V, the unused pairs (4-5 and 7-8) is reported  as faulty because the remote end does not terminate these pairs.

•Do not change the port configuration while the TDR test is running.

•Due to cable characteristics, you should run the TDR test multiple times to get accurate results.

•Do not change port status (for example, remove the cable at the near or far end) because the results might be inaccurate.

•TDR  works best if the test cable is disconnected from the remote port.  Otherwise, it might be difficult for you to interpret results correctly.

•TDR  operates across four wires. Depending on the cable conditions, the  status might show one pair is OPEN or SHORT while all other wire pairs  display as faulty. This operaton is acceptable because you should  declare a cable faulty provided one pair of wires is found to be OPEN or  SHORT.

•TDR intent is to determine how poorlya cable is functioning rather than to locate a faulty cable.

•When TDR locates a faulty cable, you should still use an offline cable diagnosis tool to better diagnose the problem.

•TDR  results might differ between runs on different Catalyst modules  because of the resolution difference of TDR implementations. When this  occurs, you should refer to offline cable diagnosis tool.

follow this link see wt this status says:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2ZY/command/reference/show1.pdf

If you are satisfied then please mark this question as answered!

Regards

Please rate if it helps

[singhaam007]

hi Andy,

here is the explanation for

show cable-diagnostics td

Result	Explaination
Normal	Ideal result you want. If testing FastEthernet, you want Pair A and B as “Normal”. If testing GigabitEthernet, you want ALL as “Normal”.
Open	Open circuit. This means that one (or more) pair has “no pin contact”.
Short	Short circuit.
Impedance Mismatched	Bad cable.

Pair C represnt POE and its working because its shows normal but Pair D is not normal and support Gig interface

please check this link for more detail

https://supportforums.cisco.com/message/3741767#3741767

please rate if this helps

thanks