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I am trying to test a VLAN-related networking issue, so I thought that firing up a couple virtual machines would be the easiest and cleanest method to test the problem. On the vSphere server I created a new vSwitch with no adapters bound, then created a new VM Network with VLAN tag 0 (disabled.)

I created two VMs and put those VMs on the new VM Network. They can talk to each other so long as VLAN tagging is not involved, but as soon as I assign their interfaces to a specific VLAN inside the operating system, they cannot communicate on the VLAN.

It appears that vSphere is stripping the VLAN tags somehow. Does anyone know if there's a way to make vSphere NOT strip VLANs it's not expecting at the vSwitch?

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up vote 7 down vote accepted

You need to check this VMware KB about VM VLAN Tagging Mode. This explains what to do on ESX 3.X but applies to 4 and 5 too.

Basically you need to enable trunk mode on the vSwitch by using VLAN ID 4095 to let your guests do the tagging.

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Thanks pfo! I tried this and it did exactly what I was looking for. Kudos! – Peter Grace Dec 2 '11 at 19:07

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