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How to test (tdr) your cable on a Cisco Catalyst Switch?

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How to test (tdr) your cable on a Cisco Catalyst Switch?

Postby admin » Thu Aug 09, 2012 7:39 am

Cisco has added a cable diagnostics command into some of their Catalyst switches. I have not used this on a working link, so I don't know if it is service impacting. I have only used this command on links that were already having an issue.

Switch#test cable-diagnostics tdr interface gigabitEthernet <slot/port> --> This starts the test
Switch#show cable-diagnostics tdr interface gigabitEthernet <slot/port> --> This displays the test results


Example:

Switch#test cable-diagnostics tdr interface gigabitEthernet 1/0/23
Link state may be affected during TDR test
TDR test started on interface Gi1/0/23
A TDR test can take a few seconds to run on an interface
Use 'show cable-diagnostics tdr' to read the TDR results.

Switch#show cable-diagnostics tdr interface gig 1/0/23
TDR test last run on: February 18 09:48:08

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/23 100M Pair A N/A Pair B Fail ---> This cable is bad, or the device on the other end.
Pair B N/A Pair A Normal
Pair C N/A Pair D Normal
Pair D N/A Pair C Normal
icon


Here are the results of a good cable

Switch#show cable-diagnostics tdr interface gig 1/0/23
TDR test last run on: February 18 10:06:49

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/23 auto Pair A N/A Pair B Normal
Pair B N/A Pair A Normal
Pair C N/A Pair D Normal
Pair D N/A Pair C Normal

Here are the results of a bad cable with no end user device connected

Switch#show cable-diagnostics tdr interface fa 0/27
TDR test last run on: August 16 11:24:56

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Fa0/27 auto Pair A 3 +/- 1 meters N/A Open ------> This pair is about 3 Meters long
Pair B 48 +/- 1 meters N/A Open ------> This pair is about 48 Meters long
Pair C N/A N/A Not Supported
Pair D N/A N/A Not Supported


Reference: http://www.cisco.com/en/US/docs/switche ... /show1.pdf

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