Question: what is tpid in vlan?
Answer: Tag protocol identifier (TPID) A 16-bit field set to a value of 0x8100 in order to identify the frame as an IEEE 802.1Q-tagged frame. This field is located at the same position as the EtherType field in untagged frames, and is thus used to distinguish the frame from untagged frames. Tag control information (TCI)