How much must the MTU be increased when configuring the 802.

When configuring the 802.1q VLAN tag, the MTU must be increased by 4 bytes. This is because the 802.1Q tag adds an additional header to the Ethernet frame, which includes information such as the VLAN ID and priority. To accommodate this extra header without fragmenting the packet, the MTU must be increased accordingly2. References: Configure 802.1Q VLAN Tagging, 802.1q and MTU.