26.5.3 Protocol and trunk ports

Protocol ports identify the protocol for untagged frames. Ports used as protocol VLANs set a protocol port. Different VLANs over multiple protocols can be assigned to a protocol port. Trunk ports are used to connect multiple protocol VLANs to another LAN switch. Note that because trunk ports distinguish VLANs by their VLAN tag, they do not distinguish according to protocol.