When you deploy a new instance of the virtual
ION device on ESXi with v5.5.1, the default driver is vmxnet3. When
you upgrade the virtual ION from 5.2.x or 5.4.x to 5.5.1, the default
driver is retained as e1000. If you change the driver from
e1000 to vmxnet3 (which is supported as the default on 5.5.1) by
removing and adding interfaces after powering off the VM, the interface
ordering will need to be corrected. | For virtual ION devices deployed on ESXi
that are launched with the 5.5.1 ova image, you cannot downgrade
to an earlier version. The downgrade is not supported because
the default driver in v5.5.1 is vmxnet3 and was e1000 for
the earlier versions. | 
