Comprehensive and Detailed In-Depth Explanation:

IEEE 802.1Q defines VLAN tagging in Ethernet frames by inserting a 4-byte VLAN tag between the source MAC address and the EtherType field.

VLAN Tagging Format (IEEE 802.1Q):

2 Bytes → Tag Protocol Identifier (TPID)

2 Bytes → Tag Control Information (TCI)

Thus, the VLAN frame is extended by 4 bytes.