Re: TFTP mode strings

Mon, 11 Jul 88 21:06:21 EDT

> From: dcatla! (William C. VerSteeg)
> Subject: TFTP mode strings

> There appears to be some discrepancy between the TFTP document (IEN
> 133) and the packages that I have seen in use.

Um, try reading RFC783 (June 1981) for the definitive (ugh) tftp

> Basically, the IEN calls for three type of files- netascii, binary, and mail.

TFTP encodes "netascii", "octet" or "mail" into the request packet. I've
never seen "mail" implemented. Image, binary & test were never encoded
in the packet and were just used for user-interface/debugging purposes.

The thing to watch out for are retransmit wars. You can get into a mode
where you are transmitting two packets for each packet you really want
to send if you blindly ack all the packets that are retransmitted. I wound up
just relying on a timer and ignoring the retransmits.

Be careful of some older TFTP implementations. There was a bug in the
4.2 TFTP that made it confused when it received retransmitted packets.
Since 4.2 begat such a large amount of derivitives, some implementations
may still exhibit this problem. The problem was fixed in 4.3.

There are lots of implementations existing to test against. Have fun.

                            Joe Herman
                            PC/IP @ Maryland

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