The TFTP DATA packet is used for sending blocks of data, belongs to a file. The format of TFTP DATA packet is as shown below.
Following are the fields of TFTP DATA packet.
- Opcode : Opcode field of TFTP DATA packet is 16-bits (2-bytes) in length. TFTP DATA packets have an opcode value of "3".
- Block Number : The Block Number field on Data Packets starts with one and then increase sequentially by one for each new packets. This type of numbering allows TFTP applications to identify between new DATA packets and duplicates.
- DATA : The DATA field size is from 0 to 512 bytes. DATA field size of all the packets are 512 bytes in length, except the last packet. If the size of the DATA field is between 0 to 511 bytes, that is the last DATA packet belongs to the current transmission.
Following image shows a Wireshark packet capture screeshot of TFTP WRQ packet.