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MTU and MRU settings

Nemo2000
Dabbler
Posts: 20
Thanks: 10
Registered: 21-12-2010

MTU and MRU settings

When I first started using broadband a few years ago I had to tweak the MRU and MTU settings on my router on a few occasions. IIRC it was the case that some sites (eg Yahoo ?) needed a higher value, whilst others (usually banking sites) needed something a bit lower.
In the end I finished up, by a process of trial and error, with MTU=1420 and MRU=1492. I left the router set at that when I switched to Plusnet recently.
Does anyone have any thoughts as to whether those settings are reasonably OK, or should they be changed? I don't want to spend unnecessary time 'tinkering' with the configuration if it is not necessary, but obviously I would like to optimise my connection if possible.
4 REPLIES
Moderator
Moderator
Posts: 17,534
Thanks: 1,081
Fixes: 126
Registered: 11-01-2008

Re: MTU and MRU settings

Mtu of 1500 should be fine in your router.
Will Moderate For Thanks
Community Veteran
Posts: 18,556
Thanks: 197
Registered: 12-08-2007

Re: MTU and MRU settings

I did a similar thing a few years ago.  Got some good help from a forum member who recommended running Dr TCP.  I downloaded it and gave me settings for RWIN and MTU which speeded up my broadband. Doesn't work on Vista.
http://www.dslreports.com/faq/578
Superuser
Superuser
Posts: 9,133
Thanks: 537
Fixes: 46
Registered: 06-04-2007

Re: MTU and MRU settings

The main thing is not to have a router MTU which is smaller than the value on your PC - doing so can lead to packet fragmentation and lower transmission speeds.
I think MTU=1500kbps is usually OK on both router and PC these days. RWIN is dynamically adjusted on Vista and Windows 7, but often requires increasing significantly on XP and earlier versions of Windows. This is where DrTCP, mentioned in the previous reply, comes in. RWIN values of about 100,000 are usually suitable on those earlier Operating systems.
David
Hary
Grafter
Posts: 90
Registered: 16-09-2009

Re: MTU and MRU settings

Another handy program is TCP Optimizer.
First of all set your pc and router MTU to 1500 for this to work, then click on the Largest MTU tab.This gives you the MTU for your setup.
This is the older version, the newer one for windows7 excludes RWIN window
http://www.speedguide.net/files/TCPOptimizer_v203.exe ;