VM displays to two port groups after migrating to a distributed vSwitch

Do you ever encounter the same issue over and over again and forget how you solved it the first time, or what caused it to happen in the first place?!?

It happened to me today on a customer site….. we were migrating a couple hundred VMs off a standard vSwitch onto a newly created Cisco Nexus 1000v switch and several VMs were showing to be connected to the old port group on the standard vSwitch as well as the new port group on the distributed vSwitch.
The VM Summary showed connections to 2 port groups even though there was only 1 vNIC and what made it more confusing was if you went and edited the VM hardware settings the vNIC was configured with the correct port group….. hmmm…..

It was a case of Déjà vu…. I sat there thinking “Damn, I’ve seen this before… but for the life of me I can’t remember what’s causing the problem!”

After a quick “Google”, I stumbled across the following KB and my foggy brain suddenly cleared!!

……If the virtual machine has snapshots associated with the old network, when you reconfigure the virtual machine to use a new network configuration, both old and new networks are associated with the virtual machine……”

“Doh…. Snapshots!!!”……. it’s all down to the VMs possibly having a snapshot attached to it!!


Basically someone had taken a few snapshots of the affected VMs, and because it’s a “snap shot” of the VMs state at that point in time, the snap shot had the old vSwitch port group whilst the new ‘delta’ VMs had been re-configured with the new 1000v port groups!
Kinda makes sense right? If you wanted to roll back to the old snapshot then it must have the configuration of the VM from the point in time when the snapshot was taken – ie with the old vSwitch port group!

Anyways, a quick check with the client and after a lengthy consolidation process all the VMs were happily only showing connections to the 1000v port group!


….. and so to make sure I don’t forget that I’ve encountered this issue millions of times before, I’ve decided to post up a blog entry about it….
(Which was one of the reasons I started blogging in the first place – a place where I can not only share my knowledge but also somewhere I can access solutions to past problems!)

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