Symptom

Failed tftp file transfers, file transfer stops, in the case of the AP, AP sends the ACK for the previous block over end over indicating a malformed packet. With the Windows 10 tftp client, tftp ignores blocks received (doesn't send ACKs) (TFTP error: Undefined error code, TFTP: Illegal operation)

Conditions

The issue happens while trying to send files through tftp across an L2 domain (ie3300 switches) with tftp block size above 4448, (discovered with the block size of 8192)

Workaround

use tftp block size below 4448

Further Problem Description