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Old 08-01-2004, 01:06 PM   #1
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Question Question About TFTP !!!

Question !

How TFTP works for files bigger than 32Mb ?!?
What happends with the field BLOCK NUMBER when it becomes 65535 witch is the biggest number supported by 2 bytes format ???

Thank you and sorry for my english !
[daniel]
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Old 08-03-2004, 04:16 AM   #2
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Default Re: Question About TFTP !!!

TFTP (Trivial File Transfer Protocol) work much the same as the FTP protocol with only a slight technical difference.
FTP uses TCP/IP as it's carrier, TCP is transmission control protocol, the TCP part of the protocol suit ensures a connection is made and carriers out error checking on the transission.
TFTP works on the UDP (user datagram protocol), no connection is guarenteed, since no connection is guarenteed, if a a packet is dropped it will not be resent, certainly I wouldn't use TFTP for any large files, the law of averages means that youd expect at least one packet to be dropped somewhere when file sizes get extreemly large.
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Old 08-03-2004, 07:17 AM   #3
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Default Re: Question About TFTP !!!

root ?!?
TFTP and FTP works much the same ???
They serve to the same purpose : to transfer files over net but thei are pretty much different !
TFTP is a very very simple one !
I agree on that TFTP is encapsulated in UDP and FTP it uses TCP and i know pretty much the difference. (no offence).
I read a lot of documents about protocols this time now and what i did not found on any of those was something regardind the maximum size of a file trasferred using TFTP witch is 31.9 Mb !
TFTP it uses fixed size blocks of 512 bytes !
It also uses a field in the header called "Block #" witch is 2 bytes number ( 65536 values)
Value 0 is used for acknowledgment so it remains 65535 posible values ! If you multiply 65535 and 512 it comes out that the maximum size of a file trasfered using TFTP is 33553920 bytes !
If you try to send any file bigger than that value it will fail !

read the RFC0783 and RFC1350 ! is nothing there about this !

Anyway thank you again !
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Old 08-03-2004, 08:17 AM   #4
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Default Re: Question About TFTP !!!

when I say works pretty much the same I means that when you write a TFTP program in C it will look pretty much the same as a FTP program,
you'll set up the connection, open the file and read byte by byte, on the other end you'll assemble it back byte by byte.
the biggest difference will be how you open the connection, (because you won't be using TCP).
Yes, I did mean the had simillar functions.
There isn't anything in the RFC's about a maximum file size of 32MB because (as far as I know) that wouldn only be the maximum file saize if the block size was left at 512, how ever the block size can be changed.
Read here
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Old 08-04-2004, 01:56 AM   #5
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Default Re: Question About TFTP !!!

Now i got it !
...but i tried to send a file bigger than 31.9 Mb using windows tftp implicit client and the implementation of TFTP protocol does not work.
Anyway...thank you very much !!!
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