This read-write TruthValue, defaulting to true, controls whether 802.1Q/802.1p tagged frames are accepted on the interface; when set to false, such frames are dropped instead. Admins toggle this to enforce whether a port should participate in VLAN tagging at all, which is useful for locking down access ports that should never see tagged traffic. For example, setting the value to false on an end-user access port causes any unexpectedly tagged frames arriving on it to be discarded rather than processed.