Is the target replying to all pings?
Yes. And I can see the same in wireshark.
Ah. I see. Strange...
What is missing in the reassembly code (that is described in RFC815) is the timer. (quote from the RFC):
The final part of the algorithm is some sort of timer based mechanism which decrements the time to live field of each partially reassembled datagram, so that incomplete datagrams which have outlived their usefulness can be detected and deleted.
But I reassemble one packet only, so I don't need to timeout partly-filled packets to recover memory.
But it is for the state that you described - the user cntr-C a current transfer, and the reassembly algorithm doesn't know to throw away a partially accepted packet, when things are cancelled...
No, it's not like that. The old instance of the TFTP server resends the last packet of the aborted xfer, while the new server sends the new packet. Both packets are new, they just come as intermixed fragments. And none survives as there is only one reassembly buffer. Or something like that, but both are fresh fragmented packets, no timeout would solve this sporadic problem.
It seems to me that if we want a secure defagment system (one that can be use to net-boot production systems in hostile networks), it's going to be too complex. It could work well, however, as a faster tool for the interactive developer.
/alessandro