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    Hello,

    Forgive me if this is in the wrong forum, this seemed the most appropriate site for this. I have written a TFTP client, now I need to be able to graphically represent packet flow, for several of the packets.
    I have read various books in addition to TFTP RFC 1350, but still am confused regarding packet exchange (Acknowledgement sequence numbers).

    Attached are the results of my code, detailing packets sent to the client from the server, and also the Word document containing the graphical representation (so far) of these results.
    Would someone be kind enough to check if what I am doing thus far is correct? It would be much appreciated.
    Attached Files
  1. File Type: txtTFTP Packet Exchange Results.txt (1.6 KB, 42 views)
  2. File Type: docxTFTP Packet Exchange.docx (13.2 KB, 55 views)
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    what in particular are you asking about? I thought it was supposed to be game over when you recieved an error packet tbh... I can't even open your second file in word.
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    Hello,

    Thanks for replying.I am stuck on the acknowledgement sequence numbers, do the have to be incremented or not? There is 1 occasion when receiving an error packet doesn't result in termination.
    Re-attached is the Word file.

    Thanks again!
    Attached Files
  3. File Type: docTFTP Packet Exchange.doc (32.5 KB, 78 views)
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    This is probably down to what the TFTP protocol specifies and what the server expects. Remember TFTP is udp based (rather than TCP) so any sequence and acnowledgements will be dealt with at that layer.

    You might find it easier to debug if you get a packet capture of the data on the wire so you can see what's in there. tcpdump / wireshark are among the most useful tools when doing network programming.
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    Packet sniffing's good - but I don't know how you'd simulate errors if you haven't got the code written yet. Or look at what someone else has done http://www.codeproject.com/KB/IP/TFTPclientCS.aspx

    I've had a look at the RFC now and in protocol terms I don't think an error should be acked - you could optionally log or display the human readable part of the error if you wanted I guess but in terms of the protocol afaict it's no different from just simply not getting the next packet you were expecting within your timeout afaict. Fwiw the guy above seems to just ignore error packets and rely on a timeout with fixed number of retries.
    Either way it'll either recover or not, and if not you'll just eventually time out and go again from the initial request.

    not that I'm any sort of expert
 
 
 
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