MTU Problem

[Chris]

Check this one out, hopefully someone has some ideas on this...

I have a bunch of XP Pro machines in one office where I had to lower the MTU
setting to 1362 to allow traffic to work across a hardware VPN to the main
office. The correct MTU size was determined by finding the max size packet
that worked and then subtracting 10 (so in this case, 1372 was the largest
size packet that would work). Anyway, this was working fine for all of the
computers for months. All of a sudden, one computer quit working and it is
displaying a very strange behavior...

With the 1362 MTU size set, all of a sudden the largest packet that would go
through from this PC only was 1334, so I lowered the MTU down to 1324.
Reboot, and then the largest packet that would go through is 1282, so I
lowered the MTU to 1272 and rebooted. This goes on and on -- you enable the
correct setting, reboot, and then you have to go lower again. It literally
never ends.

I think that the registry has been tampered with as someone had set the TCP
Receive Window setting to 1100. I tried setting it back to 64512, and even
reset TCP/IP back to defaults with the guided help from this article:
http://support.microsoft.com/kb/299357

After resetting TCP/IP, the TCP Receive Window setting is fine, but I still
am running into the same MTU issue. I do believe it is something whacked
with this particular machine. Has anyone seen this before or have any ideas?

Thanks,
Chris

 

[Jack \(MVP-Networking\).]

Hi
You can try to use this application (make sure to check Modify all network
adapter).
http://www.speedguide.net/downloads.php
BTW, if you are using Broadband connection you can benefit from much large
RCwin),
Jack (MVP-Networking).