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weird packet loss

one of customer is having weird problem. they can connect either over vpn or on citrix(LAN).
we use xml for communication betwn server and client.

for eg..

<reason>hello world</reason>


if reason tag has text that is more than 5 characters, we are not able to save the data when connected over the vpn. but on citrix it works fine.

i have determined, when xml leaves the client, data is well formed but by the time it has reached server, the xml has turned into null.

so i think, some thing is happening in between either a problem with ISP or vpn tunnel do i determine/ find out where its dropping the data?

Saturday, October 07, 2006
You're not passing over a network with different MTUs? And a firewall that won't let fragmented packets through?

That's what it was last time I had something like that.
Katie Lucas
Sunday, October 08, 2006
"if reason tag has text that is more than 5 characters, we are not able to save the data when connected over the vpn."

I'm suspicious.  If you save the data locally, do you have the same problem.  And if not, are you sure the "saving of data" is going through the same logic/code.

Years of experience has taught me that VPNs are not deterministic -- that is to say they don't selectively decide to drop traffic or data after a certain amount has passed or what type it is (XML or otherwise).
Monday, October 09, 2006
thanks were right on the money.. this particular VPN set up had MTU of 1392 bytes. once i changed the registry entry on the machine to reflect this MTU, it worked like a charm.

of course it would have been better if i could change the VPN setting so that it would allow default bytes but since i didn't have access to the router's etc.. this was the best solution i could come up with.

  locally ( a citrix server sitting right next to app server), we were able to save data with out any problem..


How to find MTU for a network:

how to change MTU on xp machine

to find the adapter ID

Monday, October 09, 2006

When these issues occur, try using Ethereal to trace the raw data at both ends.  It will show you quite a bit and should show you the xml, retransmissions, etc.  I've spent a lot of time on issues like these, and this tool is a life saver.

Hope that helps,
Jon from Proactive Logic Send private email
Thursday, October 12, 2006

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