Why does TFTP timeout after 33,553,920 bytes received

TWS
TWS used Ask the Experts™
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TFTP times out after transmitting / receiving 33,553,920
bytes between two Windows 2000 PCs.  Have set
GlobalMaxTcpWindowSize = 256920 , TcpWindowSize = 256920 , and Tcp1323Opts = 1 in the registry of both PCs.  Using SolarWinds TFTP server on one Windows 2000 PC and command line TFTP on the other Windows 2000 PC.  However, cannot transmit a file larger than 33,553,920 using TFTP between the two W2K PCs.  Anyone know a solution to this?  Thanks,  TWS
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Les MooreSr. Systems Engineer
Top Expert 2008

Commented:
Try a different TFTP server. I've had issues with Solar Winds weak server.
Try Pumpkin
http://www.klever.net/kin/pumpkin.html

Commented:
Well it obviously has a 32Mb limit (33,554,432).  I seem to recall seeing something saying it often has a 64kbyte counter for no. of packets and they are 512bytes each...

rmoore is probably right, maybe another server will allow more ...

Steve

Commented:
The RFC as far as I could see states that there are two bytes to store the packet number giving a total of... nearly 32Mb.  I suppose if the data packet size was more than 512 you could increase the limit to 80-90Mb - maybe another server/client combination will support that?

http://www.faqs.org/rfcs/rfc1350.html

Steve
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Commented:
I'm Curious, Did you manage to get a TFTP Server/Client combination that works with more than 32Mb (using bigger block sizes)?

Steve
TWS

Author

Commented:
No, I changed to FTP and am now transferring files greater than 32 Meg just fine.  I found out the following on the Microsoft Windows 2000 Networking Community Newsgroup:
"TFTP usually uses a blocksize of 512 bytes, and 33,553,920 / 512 is 65535, the largest number that can be specified in two bytes.  Since the block number is represented in two bytes, this is the largest file you can send through vanilla TFTP.  RFC 1783 added the TFTP blocksize option in 1995 (and it was updated in RFC 2348, in 1998), but this is obviously too recent to have
been included in Windows TFTP client implementation, since it defaults to a blocksize of 512, and has no option to change this.  However, even a change of blocksize won't give you a complete solution - after
all, you can still only transfer ~65536 blocks, so even if you double, triple, the blocksize, you still only double or triple your file size.  TFTP really isn't the transport for such large files."
Commented:
Yup, as I thought. I'd read the RFC's for bigger block sizes but couldn't see anything that showed any configuration for Windows TFTP.  You've probably made a wise move there with FTP....

You either need to accept an answer or post a comment in the Community Support area for 0 points if you want the question removed.

"How do I know what grade to give?":
http://www.experts-exchange.com/jsp/cmtyQuestAnswer.jsp#3

Steve

Commented:
Hi,

As it appears this question is abandoned if you don't say otherwise within 7 days I will ask the community support to close it and award the points to dragon-it.

thanks

Steve
TWS

Author

Commented:
Steve, I will post a comment in the Community Support area for 0 points to have the question removed. Thanks, Tom

Commented:
Dear expert(s),

A request has been made to close this Q in CS:
http://www.experts-exchange.com/Community_Support/CleanUp/Q_20483528.html

Without a response in 72 hrs, a moderator will finalize this question by:

 - Saving this Q as a PAQ and refunding the points to the questionner

When you agree or disagree, please add a comment here.

Thank you.

modulo

Community Support Moderator
Experts Exchange

Commented:
Well unfair since I looked into his problem for him but whatever...

Steve
Les MooreSr. Systems Engineer
Top Expert 2008

Commented:
dragon-it should get the points

Commented:
Thanks lrmoore, needed your comment for a "fair trial" :-)

I'll change my proposal from "PAQ" to "accept dragon-it's comment" on 01-30-2003.

modulo

Community Support Moderator
Experts Exchange
TWS

Author

Commented:
Steve, even though I found the solution on another website, you looked into this for me and I appreciate it, so it's fair that you get the points. Tom
Grade changed to a B.

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