In order to enable an AIX host to use one virtual Ethernet adapter to communicate on multiple VLANs, what is required?

Assigning IP addresses from different subnets does not enable multi-VLAN operation; the underlying VLAN devices with the correct VLAN IDs must be created first before IP addressing is even relevant.

The duplex setting of a virtual Ethernet adapter governs link negotiation behavior and has no bearing on the adapter's ability to handle multiple VLAN-tagged traffic streams.

In AIX, VLAN devices are logical network interfaces layered on top of a physical or virtual Ethernet adapter, each associated with a specific VLAN ID, created using mkvdev or smit vlan. These devices allow the adapter to send and receive IEEE 802.1Q-tagged frames for each configured VLAN independently. Without creating these VLAN devices within the AIX host, the adapter has no mechanism to classify or process traffic belonging to multiple distinct VLANs.

Configuring the adapter as a trunk adapter is a hypervisor or VIO Server level setting that permits tagged frames to reach the partition, but it is not sufficient on its own - VLAN devices inside the AIX host are still required to process that traffic.