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New Member

Loss of network connectivity

Hi all,

I am experiencing a problem on a single machine on our network. For some unexplained reason this machine unpredictable goes offline and the only way it appears to bring it back is to do a shut/no shut on the port.

Any ideas how I can troubleshoot?


New Member

Re: Loss of network connectivity

Have you checked the logs on the switch? Check the int stats on the port? Does it go into an err-disable state?

New Member

Re: Loss of network connectivity

Which logs should I check?

this is the 2nd port on the switch to which I have patched the infrastructure cable. We saw the same problems on the other port.

From other testing we have done we have narrowed it down to the infrastructure cabling. Is there a way to monitor the port which will prove that it is aproblem in the cable?

New Member

Re: Loss of network connectivity

So if you have narrowed it down to the infrastructure cabling, does it mean that its the cabling issue? What happens if you plug in this computer into another port?

New Member

Re: Loss of network connectivity

The cabling I am referring to is in a remote part of the building (200 feet away). I have 2 cables goiing there. Each one goes to a patch panel port at each end. The other cable seems to be ok sonce the machine patched into the switch does not lose its connectivity.

I have just swapped the patch leads at the machine end to isolate whether its a machine or this infrastructure cabling. I have done this in the past as well and found that it was the infrastructure cabling. Since then it has been re-terminated and was operating ok. Now the problem has re-emerged and we have changed the machines in the meantime as well.

So, what would be ideal is if I can capture (from the switch) the loss of connectivity and see if we can trace the problem to the installed cable run. If we can I can ask the contractor who installed the cable to re-install or replace.

What are the commands I can use on the switch to monitor this? What should I be looking for?

How can I configure the switch to automatically reset the port if it goes into the err-disable state?


New Member

Re: Loss of network connectivity

Do the following:

Show int status err-disabled

This will show which port(s) are disabled if any.

Show int fa

This will show if there are any errors on the port (crc, etc.)

Show log

This may show the reason. Sometimes port security will put a port into err-disable state.

Is it possible to test the cable end to end with a cable tester? If the cable is bad you would have to reterminate or replace. I'm assuming you have changed patch cords? It may also be bad nic on your pc?

Bringing the port back automatically can be done, but I would advise finding the source of the problem and correcting. Not much use in having the port go err-disable and back up again. Performance for this pc will obviously suffer.


New Member

Re: Loss of network connectivity


Thanks for the detailed commands. I will run them when the machine loses connectivity again.

I have already re-terminated this cable, and each time I run a cable tester against it it seems fine. I have changed patch cords but the problem remains.

Currently I have swapped the 2 machines patch cords to see if the problem is machine-specific. Stay tuned.


Re: Loss of network connectivity

I agree it is going into a err-disable state for some reason , check in the logs for the reason .When it happens , do a show interface status and i bet the interface says err-disable. Probably a link flapping or similar reason. You can also configure the switch so it will automatically bring the interface back up after a err-disable state , default is 5 minutes. You should figure out why it is going err-disable though.

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