LevelOne FGP-2472 - Manual (Page 87)

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Drop Untag:
Drop untagged frame. You can configure a given port to accept all
frames (Tagged and Untagged) or just receive tagged frame. If the
former is the case, then the packets with tagged or untagged will be
processed. If the later is the case, only the packets carrying VLAN tag
will be processed, the rest packets will be discarded.