Failure to add ESXi 5.1 host to DVS of vCenter 6.0

Hi,

I am trying to migrate VM guests from ESXi 5.1 to ESXi 6.0.

First of all, I have removed ESXi 5.1 host from vCenter 5.5 and added to vCenter 6.0.

Now I was failure to migrate VM guests to ESXi 6.0.

Below is my finding.

• Failure to add host to vDS. Incompatible host.

• Failure to process vMotion to ESXi 6 host. Incompatible host

May anyone give me some advice.

Thanks