The MTU is the maximum payload length for a particular transmission media. For example, the MTU frame size (payload size) for Ethernet is typically 1500 bytes. The maximum packet length for Ethernet is typically 1518 bytes, but that includes 14 bytes of Ethernet header and 4 bytes of CRC, leaving 1500 bytes of payload.
When a VLAN tag is involved the packet length is increased to 1522 bytes.

Probably needs to be handled by hand if using UDP