Hello,
I've banged my head a few days ago trying to debug an issue with a TFTP transfer hanging in the middle.
I'm testing U-Boot 2022-rc5 on a Toradex Verdin i.MX8MP module (using the verdin-imx8mp defconfig). My local network MTU is 1500 bytes, and the board uses the EQoS ethernet controller.
The problem started occurring after rebuilding a kernel image. U-Boot started transferring the image, and stopped in the middle, eventually timing out. Capture network traffic showed that U-Boot was continuously asking for retransmit of the same block, and eventually timed out.
U-Boot is configured with a default TFTP block size of 4096 bytes, which results in the TFTP blocks being sent in one UDP packet split in three IP packets. U-Boot is configured with IP fragmentation supprot enabled. This works fine for all TFTP blocks until a paticular one in the middle of the kernel image.
I've narrowed it down to a file of 1472 that can't be transferred at all (I have attached the binary to this e-mail). Changing the value of any of the last two bytes of the file allows transferring it correctly, so I suspect a CRC issue, likely related to IP fragmentation. Lowering the TFTP block size to avoid fragmentation works around the problem.
Arguably a TFTP block size of 4096 bytes should probably not be used with a 1500 bytes MTU network, but I thought it would be useful to fix the issue nonetheless.
I can test patches.