Ever decreasing MTU

I have been getting the problem of my MTU value having to be decreased, every now & again my browser won't open any pages so I check the ping value using the 'ping -f -l #### 192.168.1.1' I am now having to set the value to 700 to get a ping response that doesn't fragment the packets. I am running on W2K through a Draytek vigor 2600 router, I have 2 other PC's on the same router so I know the problem must be on the PC & probably a registry entry. Does anybody know what I can do to to remove any rouge entries from my registry which effect the MTU?

In answer to the general PC question I use Registry Mechanic and it's a brilliant program (

Try using the 'Tweak Test' on this site to diagnose/recommend settings.

http://www.dslreports.com/tools

Then use 'Doctor TCP' - download from the same page - to change your settings to those advised.

I think I may have found the problem, I was using DRtcp & also DSLreports to try & find the problem. I found that to reset to the default values just set everything in DRtcp to blank then reboot. I did this & I can now ping at 1472. It seems that DRtcp was causing the problem probably there were other settings that were conflicting. What I need now is a way of checking what MTU setting I am actually using. I do have a copy of System Mechanic I will have a look to see if that can help.

I prefer to find the MTU this way,
Finding the largest MTU by EXPERIMENT version 2

First reset windows with Dr TCP to MTU 1500.
Then reset modem/router to MTU 1500 save it, reboot PC and modem/router.

Next from windows, go to Start/Run and type in, cmd (click OK)
At the MSDOS-PROMPT type,

ping -f -l 1472 www.bbc.co.uk

Then reduce 1472 by 10 until you no longer get the "packet needs to be fragmented" error message or

This is what I had done, the problem was the MTU would every so often decrease?? Sometimes I could check it & increase it back, all the time I was using DRtcp to change it. Lately though I was unable to open any webpages without checking the MTU using 'ping -f -l .....' then set it using DRtcp. Now I've wiped all the settings from DRtcp - saved then rebooted I can now 'ping -f -l .....' at 1472. I don't know what was happening but DRtcp seemed to be causing the problem, I was having to set the MTU to 700 before I could get it not to fragment. I would like to find out though how I can check what my MTU is now set to, I'm sure I used to have a dos comand for checking this & also changing it but I can't remember what it was.

Sorry to drag back this old thread. Just found out that pctools via element 5 may have set up an annual cca for this product, whereas I made a one-off purchase. In the light of that I withdraw my recommendation for this product, apologies to anyone who may have been inconvenienced by my recommedation

Edited by themidgieman (Thu 08-Feb-07 12:55:37)