When sending a big file (or using a small blocksize while testing), the TFTP server is not able to handle the rollover occurring after DATA 65535.
Usually, implementations restart with 0 by default, but some of them use 1.
It is sometimes also possible to choose 0 or 1 on the command line, and even to negociate with a non standard option as explained here:
https://www.compuphase.com/tftp.htm
When sending a big file (or using a small blocksize while testing), the TFTP server is not able to handle the rollover occurring after DATA 65535.
Usually, implementations restart with 0 by default, but some of them use 1.
It is sometimes also possible to choose 0 or 1 on the command line, and even to negociate with a non standard option as explained here:
https://www.compuphase.com/tftp.htm