When you add a USB device connection from an ESXi host to a virtual machine, the autoconnect feature is enabled for the device connection. It is not disabled until you remove the device connection from the virtual machine.

With autoconnect enabled, the device reconnects in the following cases:
  • The virtual machine is cycling through power operations, such as Power Off/Power On, Reset, Pause/Resume.
  • The device is unplugged from the host, and then plugged back in to the same USB port.
  • The device is power cycled but has not changed its physical connection path.
  • The device is mutating identity while it is in use.
  • A new virtual USB device is added.

The USB passthrough autoconnect feature identifies the device by using the USB path of the device on the host. It uses the physical topology and port location instead of the device identity.

If you plug the same device back in to a different USB port on the host, it cannot reestablish the connection with the virtual machine. If you unplug the device from the host and plug in a different device to the same USB path, the new device appears. It is connected to the virtual machine by the autoconnect feature that you enabled in the previous device connection.

Autoconnect is useful when devices mutate during usage. For example, for iPhones and other similar devices, the device VID/PID changes during software or firmware upgrades. The upgrade process disconnects and reconnects the devices to the USB port.

The USB port is speed-specific. If you change a USB device with another USB device that works with different speed, the autoconnect feature might not work. For example, you might connect a USB 2.0 high-speed device to a port and connect that device to the virtual machine. If you unplug the device from the host and plug in a USB 1.1, USB 3.1 SuperSpeed, or 3.1 SuperSpeedPlus device to the same port, the device might not connect to the virtual machine.

For a list of supported USB devices for passthrough from an ESXi host to a virtual machine, see Supported USB device models for passthrough from an ESX or ESXi host to a virtual machine.