MAC learning: Ethernet switching family, qualified MAC learning

Typically, during MAC learning on an ingress packet, the outer tag is removed, and MAC learning happens based on the inner VLAN tag. Qualified MAC learning enables a device to learn the MAC addresses of network nodes by determining the innermost VLAN tag of single-tagged, 2-tagged, or 3-tagged ingress packets, and VLAN learning happens at each level without popping the outer tags.