Introduction
Forget to bring your cable tester to site? Did you know you can test your cable from a Cisco Switch? Want to know more? Carry on reading below.
Before we start…
It’s important to know before using these commands that it will briefly down the port whilst running the test, so if any users are active on these ports we’ll need them to be aware.
It’s also important to note that Cisco have only included these commands with Gigabit switches. Switches with 100Mbit ports will not have this functionality.
Also worth pointing out that the port cannot be in a shutdown state and it will generate a warning.
Command Usage
The commands for testing an Ethernet cable are:-
test cable-diagnostics TDR Interface [Interface]
And once the test has ran…
Show cable-diagnostics TDR Interface [Interface]
How to interpret the output
From the above output – It shows as Open as there are no devices connected to the end of the cable.
This is also confirmed by speed being as normal, As you’ll see from the next example, It shows the speed that’s been negotiated if it’s in use.
We can see 3 of the 4 pairs are showing as 8 meters in length and so would suggest there is an issue with the 3rd pair of wires.
From this example, The device connected has negotiated 1000M, One of the pairs is showing as being longer then the other three so possibly some wiring issues here but all pairs are showing as normal status which is “good”.
We can also confirm by running a check on errors on this interface, And this suggests no issues here.
Hopefully this has been helpful to someone. It’s a tool I use occasionally to rule out issues on my network. If you have any comments please add them below.