::. Kitz - Tweaking MTU settings .::

Tweaking your MTU may help resolve some problems such as slow adsl speeds and problems connecting to certain sites. I have a specific page dedicated to MTU problems, and a page which gives a more in depth view on how to calculate your MTU and RWIN settings to optimise your connection and get better speeds.

This page is more of an introduction to tweaking your MTU and RWIN with some suggested settings that have worked for many. The best way to tweak your settings is to download and use Dr TCP.

My speed increased by about 30kb after tweaking a 512 kbps connection (to 478/250kbps). When on 2Mb I got a speed increase of around an extra 50 kbps. The amount of speed increases can and does vary - sometimes with remarkable results.

So if you are looking for the basics of MTU tweaking and some suggested settings then read on:-

How to tweak your MTU and RWIN

Note: Dr TCP does not work with Windows Vista and you will need to manually adjust your MTU value - See Changing your MTU in Vista

Instructions

MTU - RWIN Calculator

Download Dr TCP
unzip to folder and run from your desktop.
Select your Connection Speed from the MTU/RWin calculator on the right.
Choose an MTU value. 1458 works well, 1430 is a personal preference of mine. AOL users should choose 1400. (TT users should also try 1400).
Change the relevant settings in Dr TCP using the image as a guide.
Make sure you choose the correct Adapter Settings from the pull down menu *
Save the changes.
Reboot your PC.

Connection Speed

Select MTU

RWIN:

* Under "Adapter Settings" select the following options:-
For a usb modem select Dial up RAS
When using a router select your Ethernet Card (NIC)
For Laptops and Wireless select your Wireless adapter.

More Information

Dr TCP is provided by dslreports, who also provide a tweak tester where you can check your results.
When imputting your information into the tweak tester if on adsl you should use the following settings:

MTU test results

|| Tweaking History || Understanding MTU and RWIN || MTU Problems|| Vista MTU ||

Some more recommended settings.

Different people tend to get best results with different settings,
so it may be worth spending a bit of time to find the best for you.

512kb connections
MTU	RWin	Comments
1458	12762	BT original suggested setting.
1430	13900	Pengbo + Tams recommendations. * probably the best settings for most 512 users.
1478	14380	Another of Tams, that works best for some.
1458	14180
1472	14320
1500	14600
1Mb connections (Use 2x the rwin)
MTU	RWin	Comments
1430	27800	If you found 1430/13900 worked best for you on 512kb then this may well be the best setting for you on 1MB
1478	28760	Doubled rwin for tams 1478/14380
1458	28360
1472	28640
1478	25884	Guest_SO's recommended settings.
1458	9000	This supposedly weird setting was discovered by nickvid. It sucessfully managed to increase speeds for users who were previously having problems with 1Mb connections. This sparked a few more low rwin suggestions.
1478	8628	Another weird recommended setting
1500	8760	Best settings for one user (cjtc)
2Mb connections (Use 4x the rwin)
MTU	RWin	Comments
1430	55600	Best setting based on the 4x theory.
1458	56720	" "
1472	57280	" "
1478	57520	" "
1478	51768	Guest_Again's recommended setting for 2MB.
1458	64512	MHC's recommended setting.
8Mb connections
MTU	RWin	Comments
1478	75020	Guest_Again's recommended setting for 8MB.
1478	75060	Twitch's recommended setting
1478	78840	Guest_Again's
1430	65535	TriGGa's recommended setting.
1430	84300
1430	166800	What Im currently using and seems to work best for me on a stable 8Mb connection
1430	111200	Another setting that works pretty well for me and should work well with 4Mb speeds.

AOL Suggested Settings
MTU	RWin	Comments
1400	13600	512kb connection
1400	27200	1Mb connection
1400	54400	2Mb connection

With the advent of maxDSL higher speeds, we are now seeing various sync speeds and users may be unsure what settings to use. The following information kindly provided by Guest_Again will be useful in these circumstances.

Non standard sync speed settings.

First, set your rWin [Top Receive Window] in DRTCP to 1000000, save this setting and RESTART your PC. (it's way to high but you'll see why in a minute).
Next, go to http://www.broadbandreports.com/tweaks and start the Tweak Tester, when it's finished, press the Results button.
On the next page enter the following in the 'Final Step' window: Service - DSL, Speed - [*See Below], OS - XP, Connection - WinXPpppoe, now click Recommend...
On this page you will see on the middle left hand side " Choose RWIN between 'xxxxx' and 'xxxxxx' (FAQ #586)" - choose the lowest setting and put that into the Top Receive Window in DRTCP, click Save and then restart your PC again.
Now try another speed test.

* Enter the speed that your modem / router is synced at.

RWIN = n * (MTU - 40)
where n is a whole number.

n can be 2, 4, 6, 8 or 16 (8 is the Win9x default),
although 9 is recommended by pengbo

ping -f -l [size] [url]

Tweaking your MTU settings.