Troubleshoot vmnic malfunction

Malfunction is worse than failure

Redundancy is key in virtual environments. If one component fails, another will jump in and take over. But what happens if a component does not really fail but isn’t working properly any more. In this case it isn’t easy to detect a failure.

I recently got a call by a friend, that he has suddenly lost all file shares on his (virtual) file server. I opened a connection to a service machine and started some troubleshooting. These were the first diagnostic results:

  • Fileserver did not respond to ping.
  • Ping to gateway was successful.
  • Name resolution against virtual DC was successful.
  • A browser session to vCenter failed and vCenter did not respond to ping.

It is a little two-node cluster running on vSphere 6.5 U2. Maybe one ESX has failed? But then HA should have restarted all affected VMs. That was not the case. So I’ve pinged both hosts and got instant reply. No, it did not look like a host crash.
Next I’ve opened the host client to have a look on VMs. All VMs were running.
I’ve opened a console session to the file server and could not login with domain credentials, but with a local account. The file server looked healthy from inside.
Now it became obvious that there was a problem with networking. But all vmnics were active and link status was “up”. The virtual standard switch on which the VM-Network portgroup resided had 3 redundant uplinks with status “up”. So where’s the problem?
I’ve found another VM that responded to ping and had internet connectivity on the same host as vCenter and the fileserver.
I opened a RDP session and from there I was able to ping every VM on the same host. Even vCenter could be connected by browser. Now the picture became clearer. One of the uplinks must have a problem, although it didn’t fail. But which one? Continue reading “Troubleshoot vmnic malfunction”

Pockethernet hands on

The Swiss Army knife of network troubleshooting

Have you ever been in a situation where you had to follow a network cable through a mesh (or should I say mess?) of hundreds of other cables, just to find out which switchport it is connected to? If your answer is no, please tell me your secret! 🙂

Cool tool

Last week I got a packet with a handy new tool inside. It’s called Pockethernet. Once started as a crowdfunding project, it is now a mature, full featured network analyzer that easily fits into one hand or the pocket of your shirt.

Continue reading “Pockethernet hands on”