Scenario:

Suppose you have several Virtual Machines running in a VLAN of which you decide they should be migrated to a new VLAN because of infrastructural changes in your network. Mind you this is only handy if the machines you are about to migrate use DHCP to get their network addresses.

Approach:

First of all you need to make sure all the ESX-servers in your cluster have the ability to use that VLAN so you need to have your your switchports/trunks tagged with it.

Secondly you need to add the new VLAN (portgroup) to the complete cluster, in this example I’m using vSwitch0 as your Virtual Switch name, make sure you change it into what applies to you in case if it’s different.

Get-Cluster "Your Cluster" | Get-VMHost | Get-VirtualSwitch -Name "vSwitch0"`
| New-VirtualPortGroup -Name "New VLAN" -VLanId 123

This will add the “New VLAN” to all of the ESX Servers in “Your Cluster” with VLAN ID 123 on vSwitch0.

Since all the ESX Server are provided with access to the new VLAN to place their Virtual Machines in it’s time to migrate them to the new VLAN. There are two ways you can do this:

The first is to configure all the network adapters of all VM’s from the old to the new VLAN/Portgroup and the second is to do exactly the same but to shortly disconnect/reconnect the network adapters of the Virtual Machines to initiate a DHCP request for your VM’s.

First method:

Get-Cluster "Your Cluster" | Get-VM | Get-NetworkAdapter | `
Where { $_.NetworkName -eq "Old VLAN" } | `
Set-NetworkAdapter -NetworkName "New VLAN"

Second method:

Get-Cluster "Your Cluster" | Get-VM | Get-NetworkAdapter | `
Where { $_.NetworkName -eq "Old VLAN" } | `
Set-NetworkAdapter -NetworkName "New VLAN" -Connected:$false | `
Set-NetworkAdapter -Connected:$True

Note:

Then again if you do use static addresses for your Virtual Machines you will need to configure them within the Operating Systems afterwards. Although that might be scriptable I haven’t found a way to do this.

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