Did you know most Cisco switches with 10/100/1000 RJ45 ports have TDR capabilities? Yes, it is true.
At the time of this writing it is my understanding that this feature is not supported on any 10/100 ports or SFP module ports.
So, what the TDR may help you with? Short answer: dealing with the physical problems outside of the switch. Long answer: it helps you detect certain types of twisted-pairs cabling problems. So you can troubleshoot:\
- Open wires
- Cut wires
- Broken wires
- Shorted wires
With the TDR functionallity you can find the length at which the twisted-pair wire is open.
Now, remember, since TDR is a port test, the port can will not handle any traffic for the duration of the test (generally, 1 minute). So, how do you run this feature? In two simple phases.
First run the diagnostic test and collect the results:
# test cable-diagnostics tdr interface GigabitEthernet 0/1
Second display the results:
# show cable-diagnostics tdr interface GigabitEthernet 0/1
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
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:
# show diagnostic result interface GigabitEthernet 0/1
So you better know both. You never know when you might need it.
Woah! I never knew Cisco switches have TDR capabilities. thanks for explaining the whole stuff now its crystal clear to me. Can u please update us more about cisco unidirectional link detection.
ReplyDeleteThank you for explaining this information in such a way.
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I am happy to see your post,
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