TFTP ACK (Acknowledge) Packet

The TFTP ACK (Acknowledge) packet is used to acknowledge the receipt of a DATA packet. The TFTP ACK (Acknowledge) packet is 4 bytes long. Following images shows the structure of TFTP ACK (Acknowledge) packet.

Following are the fields of TFTP ACK (Acknowledge) Packet.

• Opcode : Opcode field of TFTP ACK (Acknowledge) packet is 2-bytes (16-bits) in length. TFTP ACK (Acknowledge) Packets have an opcode of "4".


• Block Number : The Block Number field of TFTP ACK (Acknowledge) packet is also 2-bytes (16-bits) in size. Block Number field of TFTP ACK (Acknowledge) packet contains the number of the DATA block received. The Block Number of the ACK of a TFTP WRQ packets is 0.

Following image shows a Wireshark packet capture screeshot of TFTP ACK packet.