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In Cisco IOS Release 12.1(19)EA1 or later, you can use the Time Domain Reflector (TDR) feature to diagnose and resolve cabling problems. When running TDR, a local device sends a signal through a cable and compares the reflected signal to the initial signal.
TDR is supported only on 10/100/100 copper Ethernet ports. It is not supported on 10/100 ports, 10-Gigabit module ports, or on SFP module ports.
TDR can detect these cabling problems:
•Open, broken, or cut twisted-pair wires—The wires are not connected to the wires from the remote device.
•Shorted twisted-pair wires—The wires are touching each other or the wires from the remote device. For example, a shorted twisted pair can occur if one wire of the twisted pair is soldered to the other wire.
If one of the twisted-pair wires is open, TDR can find the length at which the wire is open.
Use TDR to diagnose and resolve cabling problems in these situations:
•Replacing a switch
•Setting up a wiring closet
•Troubleshooting a connection between two devices when a link cannot be established or when it is not operating properly
core-switch#test cable-diagnostics tdr interface gi0/24 TDR test started on interface Gi0/24 A TDR test can take a few seconds to run on an interface Use 'show cable-diagnostics tdr' to read the TDR results.
core-switch#show cable-diagnostics tdr interface gigabitEthernet 0/24 TDR test last run on: November 19 14:54:18
Interface Speed Local pair Pair length Remote pair Pair status -------- ----- ----------- -------------- -------------- --------------- Gi0/24 1000M Pair A 4 +/- 4 meters Pair A Normal Pair B 4 +/- 4 meters Pair B Normal Pair C 5 +/- 4 meters Pair D Normal Pair D 4 +/- 4 meters Pair C Normal
It means Gi0/24 is running on 1000 Mbps speed, All four pairs have cable length of 4 meters & corresponding remote pair side (for local pair) is working Normally.
The previous command is set to be deprecated sometime in the future and will be replaced by:
" show diagnostic result interface GigabitEthernet 0/24 "