VLAN-tagged Layer 3 subinterfaces

A Layer 3 subinterface is a logical division of a physical interface that operates at the network level and therefore can receive and forward 802.1Q VLAN tags. You can use Layer 3 subinterfaces to route traffic among multiple VLANs along a single trunk line that connects an EX Series switch to a Layer 2 switch. This topology is often called a "router on a stick" or a "one-armed router" when the Layer 3 device is a router.