Newbie: First Time Altering MTU Settings, Checking I'm On The Right Track

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xenithon

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Hi All. New user to iBurst here. Thus far running smoothly without problems. I believe it is partly because I connect to Linksfield which seems very stable (It was similar when I was on Sentech - many guys had problems but Linksfield was stable).

Anyways, I would like to optimize my connection and after quite a few weeks of research on reading many threads here, I will try to optimize MTU settings. I currently have ICS running 100% at home (just 2 PC's), all settings are default. This is what I plan to do:

- Use cmd and use the 'ping -f www.iburst.com -l xxxx' command until it does not say truncated and add 28 to the minimum number I can use.
- I will use DrTCP, and on the host PC set dialup ras to this MTU and the MTU for the iBurst Terminal to this too.
- Use the formula "max multiple of (MTU-40) less than 65535*4" to calculate the value for TCP Receive Window
- Leave the other options in DrTCP untouched. Save settings and reboot
- Use DrTCP on the client PC and set the TCP Receive window to the same value as calculated before; and set the optimum MTU found for the NIC which connects the PC to the LAN.
- Reboot the PC. Connect to iBurst like normal and all 'should' be working and hopefully optimized :)

Two queries though:
1. I opened DrTCP on the host PC and in the drop down box there are a number of NIC's listed as well as 2-3 iBurt Terminal's listed for some reason. Should I just set the MTU for all the iBurst Terminals just in case? There is no way to tell which one is actually being used, is there? I opened DrTCP on the client PC and just saw my Yukon NIC (built onto motherboard) to which I connect to the LAN, so no worries that side, only the host PC.
2. Is there a way to backup my current settings in case I run into problems? Or should I just write down what they are currently are and set them back to these if any hassles arise?

Thanks for all the help and the great forum,
X
 
Ok, this is just my opinion.
I dont really like DRTCP.

Instead I use

http://www.speedguide.net/
and use their program
http://www.speedguide.net/files/TCPOptimizer.exe

It does a lot of the calculation for you, does pings until they fragment, etc.
And if you go in the menu, under broadband -> Broadband Tools -> analyzer, it actually tells you the values for the Rwin and all the other options.

I think it allows backup of the registry as well...

I think I just changed all of my iBurst Terminals to the same values.

Hope it helps...
 
Thanks for the info! Is there much difference between DrTCP and TCPOptimizer other than the latter being automated? Does it yield better results? I was reading up on it now and like the fact that you can backup and restore settings as well as rever to default windows settings.

Would I use it on both PC's though? I assume I would use it on the host first, reboot, and then the client PC.

X
 
I'm not sure if the client will need it. You are trying to tweak your internet connection, not your LAN... So as long as the host can connect to the internet faster, the client will automatically see the benefit.

There is no realy difference between the two programs. They both simply update registry settings with different interfaces. If you were hardcore you could do the same thing with regedit :)
 
I actually tried playing around with the registry - didn't get very far as I could not find any keys with the name 'MTU' which were supposed to be there :p

The reason I am thinking about using the proggy on both PC's is since the DrTCP documentation mentions that both PC's need to have the same MTU to prevent errors, but I will try double check that :o

X
 
You need to add the registry key. I created one called 'MTU'
 
Will DrTCP or TCPOptimizer add them for me automatically if they do not exist? I cannot find those details in their docs :(
 
Not sure, however one prog I used Wingate 6 did it on my machine by itself after installation and detecting the iBurst modem
 
xenithon said:
Will DrTCP or TCPOptimizer add them for me automatically if they do not exist? I cannot find those details in their docs :(
Click to expand...
)

DrTCP will add the entry if you change any setting from default.

DrTCP doesn't actually look at your hardware, it only looks at the registry. So any NICs that have been installed in the past will show up. So either clean up the registry, or just set them all the same.

Dial-up RAS will not be used in pppoe. Keep it at 1500. Just change the inidvidual NIC MTU's.
 
Will do, thanks. How do I go about fixing the registry though? I use norton system works quite often as well as reg mechanic. Is the only other way to do it manually? Or is there some usefull app I can use.

X
 
There probably are some useful apps...

But generally, it is best to leave it well alone. Don't fix what isn't broken.

If there are very specific entries/references that you want to get rid of, just search for and remove them in regedit.

The most useful section of your registry to be familiar with are the various "Run" and "Run Once" sections, that's were computer nasties love to hang out. But that's a whole other topic altogether...
 
A question for those of you who are guru's with MTU settings.

I am using System mechanic and in the setup Netbooster advanced optimization setting you can select the option of "enable automatic MTU detection".

After using it I must say my speed is back to nornal.

Any comments on this?
 
Some more info needed here:

Blackhole detection

A blackhole, in relation to the Internet, is a situation where your system attempts to automatically determine the MTU of a system on the other end, and is unable to do so because the system on the other end is not able to respond to MTU requests with the proper information. If blackhole detection is enabled, your system attempts to discover whether connected systems support automatic MTU discovery. If they do not support automatic MTU discovery, the MTU will be detected using alternate and less efficient methods, causing performance degradation.

To enable blackhole detection, check the box labeled Enable blackhole detection.
To disable blackhole detection, uncheck the box labeled Enabled blackhole detection.

Suggested blackhole detection value

Automatic MTU detection

Enabling this setting causes your system to attempt to discover the MTU over the path to a remote host. By discovering the remote host’s MTU and limiting TCP segments to this size, TCP can automatically eliminate fragmentation at routers along the path that connect networks with different MTUs. As outlined above, fragmentation adversely affects TCP throughput and network congestion.

To enable automatic MTU detection, check the box labeled Enable automatic MTU detection.

To disable automatic MTU detection, uncheck the box labeled Enable automatic MTU detection.

Will it help to select "Enable Blackhole Detection"?
 
Right, I used DrTCP as TCP Optimizer was giving me hassles for some reason. I checked using ping what MTU I should use. I could do 1372 without fragmentation. Hence optimum MTU should be 1400.

So in DrTCP I set RAS to 1400, iBurt Terminal to 1400 and Receive Window to 261120. Saved settings and rebooted host PC. Then I set the same on the client PC, with MTU of 1400 set for the NIC connecting to the LAN. Oh, and TTL was set to 64 as suggested. I then saved that and rebooted. Difference - none :confused:

Is there ALWAYS meant to be some difference or do some people not find a difference at all? When I download often the max I can get is around 90k/s. I always download the same file as a test - the FireFox installation file (4.6MB) from tucows.saix.net, using DAP which uses 14 threads I think. It starts out around 40k/s and after a while stabilises between 80-90k/s. This was the same both before and after MTU alterations. Anything I did wrong or should try do differently?

X
 
OK where to begin, hmmm

first of all 1400 is actually the default MTU, so if you went through all that to set it to 1400... you wasted a bit of your time :p

DAP does 10 threads at most

MTU won't always make a difference no, most people with healthy connections won't notice any difference at all. MTU to optimize broadband is awesome for services like cable where you can have larger packets sent but with iBurst it only helps if your connection is cruddy to begin with (and in which case you'll probably be setting it smaller than what it was, not bigger)

If you want to optimize your connection, watch the frame error rate and get it as low as possible, thats the big factor. You say you get 90KB/s well then realistically you have 30 or 40 KB/s (multithread on international) to gain by tweaking, so try spend a bit of time findign your sweet spot, low frame error and high signal, also make your connection active while you do it, download something and move the modem around bit by bit untill you find the peak.

Your connection looks reasonably healthy so I'd say in my personal opinion you have nothing to gain by playing with MTU. Oh another thign that may help you in your quest for speedier internet is use firefox and set it to multithread
 
Will do, thanks for the great info! Well I got a pretty good signal and it hovers between 75-98% :D What should I look for when it comes to frame error rates? Is there anything I can do to reduce them in terms of a setting or software change?

BTW I used TCPOptimizer to set everything back to windows defaults on both machines just in case DrTCP did anything nasty :p

Will be installing firefox this weekend and giving it a go. I use DAP Premium, latest version (7.4.1 I think and I was almost sure it was 14 thread, but will double check later tonite when I am at home).

Cheers once again,
X
 
no you can only tweak frame error rate by moving your modem, try put 20 minutes into finding that sweet spot, 120KB/s will make a world of difference, also when you install firefox remember to tweak the settings to allow for multithreading
 
Windows XP SP2. I am not sure what the default is. I do not have an MTU entry in my registry :p
 
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