I'm trying to send a file to a device using TFTP.exe in Windows 7. The transfer worked successfully on Windows XP every time (many times). I'm listening to the connection using Wireshark. It seems that the device gets some packets, but occasionally the Don't fragment flag is set and the transfer fails. If it isn't set, the transfer works. The device doesn't drop such packets.
I tried the following things: - Turning off the firewall. - Allowing all ports in and out UDP and TCP. (Especially 69 and 1023) - Allowing TFTP.exe in the firewall - Programming a short script in Python using TFTPY and setting using setsockopt the "Don't Frag" flag in IPv6 (there is no IPv4 DF flag option in the Python version I'm using for sockets). [less relevant, as I want to use the built TFTP.exe feature] - (The windows feature TFTP has been enabled obviously...)
The computer sends an error packets saying "unexpected port number" to the device repeatedly even when it works.
I'm not sure if it's relevant, but the port that the file is sent on XP is usually one of the known ports while on Win7 it's a dynamic port (50k-60k...).
Does anyone know how to unset the DF flag by any chance in Win7 in the regular TFTP.exe?