TFTP

Trivial File Transfer Protocol (TFTP), which is defined in RFC 1350 (obsoletes RFC 783). Its name says it all; it is trivial in comparison with its more robust relative, FTP. Its trivial nature can be seen in the following limitations:

• Runs on top of UDP (port 69), unlike FTP
• Provides no user authentication
• Cannot list directories
• Limited header

 TFTP uses a 2-byte op-code header that follows immediately after the IP and UDP headers. 

Figure 4.

There are five types of operational codes:

• RRQ Read Request
• WRQ Write Request
• DATA
• ACK Acknowledgement
• ERROR

If an error occurs, there will also be an error number given. There are three bits reserved for error codes, giving values 0 - 7.
0 - Not defined
1 - File not found
2 - Access violation
3 - Disk full
4 - Illegal operation
5 - Unknown transfer id
6 - File already exists
7 - No such user