The Catalyst 2960, 2970, 3560/3560-E, and 3750/3750-E switches have an integrated Time Domain Reflector (TDR), which is used to test cables associated with a port. TDR is supported only on 10/100/1000 and some 10/100 (Catalyst 2960) copper Ethernet ports. It is not supported on 10 GigabitEthernet or SFP module ports.
Switch# test cable-diagnostics tdr interface gigabitethernet0/2 TDR test started on interface Gi0/2
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 gigabitEthernet 0/2 TDR test last run on: Dec 10 09:05:10
Interface Speed Local pair Pair length Remote pair Pair status --------- ------ ---------- ----------- ----------- ----------- Gi0/2 auto Pair A 22 +/- 4 m N/A Open Pair B 21 +/- 4 m N/A Open Pair C 5 +/- 4 m N/A Open Pair D 20 +/- 4 m N/A Open
The above example output shows the results of a TDR test, which was run while the other end of the cable was disconnected(Open). Because the other end of the cable is open, the "Remote pair" mapping is N/A (not available). From the results, we can see that Pair C has a "Pair length" that is much shorter than pair A, B, and D. This suggests there is an open (break) in pair C at the 5 meter point (+/- 4 meters) before the end of the cable (approximately 20 meters +/- 4 meters) is reached.
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