Cisco TDR (Time Domain Reflectometer)

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Using Cisco's Integrated TDR

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.

Helps with troubleshooting: 

   * Open wires
   * Cut wires
   * Broken wires
   * Shorted wires

With the TDR functionallity you can find the length of individual wires.


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 Cable length Remote channel Status

Gi0/1 0Mbps 1-2 102 +-2m Unknown Fault

3-6 100 +-2m Unknown Fault

4-5 102 +-2m Unknown Fault

7-8 102 +-2m Unknown Fault


The previous command is set to be deprecated sometime in the future and will be replaced by:

  1. show diagnostic result interface GigabitEthernet 0/1
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