I have asked this question in a roundabout way recently, but I'm going to try be more specific this time 🙂
I have a 10 node ESX cluster, and each host has a virtual switch with various VM PortGroups on them. The Port Groups have a VLANID number set, which matches the VLANID of the physical ports which are trunked.
I now have to renumber these Physical VLANID's in preperation for a DataCentre move and am trying to predict the impact this will have.
I expect I am going to lose connectivity across the Port Groups until i can change the Port Group VLANID *affinity*.
The Service Console for the ESX Hosts also has a VLANID affinity to the Production server VLAN. SO, I expect that the ESX hosts will lose connectivity completely as well, until I can ILO onto them and set the new VLANID.
Have I got the basic gist of it right would you say? And has anyone done this of late and got some stories to share? I wish I could stage this but I don;t believe I can...
If you configue the physical switch trunk ports to include the new vlan id first when you change the vlan tag on the vswitch it should have minimal impact on connectivity -
That sounds right. You might want to power off the VM's if you can for the process just to keep them from freaking out. Adding both vlanid's in to phys port is a great idea.
As has been noted above, changing the actual VLAN id should be a fast move, if the new VLAN is already available in the "trunk port". When changing the VLAN id on the portgroup it should be a very fast switchover.
But... there are many other issues that you must consider. The VLAN is just a layer two construction (virtual switches if you like) and changing the VLAN numbers is like very fast moving the ethernet cables for some devices to another switch.
However, you must also think of layer three connectivity, that is: IP. The VMs has IP addresses and default gateways in a certain IP range and for example the default gateway must on your physical router be switched over to the new VLAN. At this moment you lose all access to your VMs from other subnets, until you have changed on all portgroups.
You must also know if there are VMs that have network communications with each other, like all servers to Domain controllers or application servers to database servers. If these are on the same VLAN, but running on multiple hosts and you change the VLAN id on the first host, then all connection will break until changed on the others.
So I am afraid that it might not be a very transparent switch if not handled very carefully.