VLAN tag

A 32-bit label (ethertype x'8100') inserted into a frame, by originating station or relaying bridge, immediately following the layer 2 source address (or, if a source routed frame, immediately following the RIF), 12 bits of which identifies its VLAN association by VLAN number. Although not all frames need be tagged, sufficient tagging should be done so that there is no ambiguity regarding VLAN membership when a frame is received by a 802.1q-compliant bridge. It is also desirable to isolate non-802.1q-compliant nodes from the possibility of receiving tagged frames, as the tags would make the layer 3+ information unreadable to them and the frames would be dropped.