illumos gate

A viona instance is usually used with a VNIC but should work atop any MAC provider. But today it relies on private behaviour between the MAC layer and VNIC driver:

/*
 * mac_client.c:
 * 
 * When VNICs are created on top of an underlying MAC, this causes
 * a layering of two MAC instances. Since the lower MAC already
 * does the switching and demultiplexing to its MAC clients, the
 * upper MAC would simply have to pass packets to the layer below
 * or above it, which would introduce overhead. In order to avoid
 * this overhead, the MAC layer implements a pass-through mechanism
 * for VNICs. When a VNIC opens the lower MAC instance, it saves
 * the MAC client handle it optains from the MAC layer. When a MAC
 * client opens a VNIC (upper MAC), the MAC layer detects that
 * the MAC being opened is a VNIC, and gets the MAC client handle
 * that the VNIC driver obtained from the lower MAC. This exchange
 * is done through a private capability between the MAC layer
 * and the VNIC driver. The upper MAC then returns that handle
 * directly to its MAC client. Any operation done by the upper
 * MAC client is now done on the lower MAC client handle, which
 * allows the VNIC driver to be completely bypassed for the
 * performance sensitive data-path.
 */

The VNIC driver opens a MAC client handle to the lower MAC and configures it with a unicast address setting up a datapath. Viona implicitly relies on this so attempting to use a non-VNIC device will result in packets not being delivered from/to the underlying MAC provider.