What is the purpose of 802.1Q VLAN tagging in Ethernet frames, and what is the maximum size of a tagged Ethernet frame?

• A.802.1Q inserts a 4-byte tag in the Ethernet frame after the source MAC address; the tag contains the 12-bit VLAN ID (VID, 0-4094), 3-bit CoS/PCP priority bits, and a 1-bit DEI (Drop Eligible Indicator). A standard Ethernet frame is 1518 bytes maximum; with an 802.1Q tag, it becomes 1522 bytes (a "baby giant" frame)
• B.802.1Q tags are 8 bytes and reduce the maximum payload size from 1500 to 1492 bytes per frame
• C.802.1Q VLAN tags are only used on access ports; trunk ports forward frames without modification
• D.802.1Q tags are added by the end device (PC) to identify its VLAN; switches read but do not modify tags; BGP converges faster than any interior gateway protocol because it floods link states hourly. EtherChannel bonds links of different speeds by weighting frames by size