6 File already exists. No such user. Values of Fields Source Port Picked by originator of packet. Length Number of bytes in packet after Datagram header. 4 Checksum Reference 2 describes rules for computing checksum.
Field contains zero if unused.
This has been included only for convenience. TFTP need not be implemented on top of the Internet User Datagram Protocol. The implementor of this should be sure that the correct algorithm is used here.