Re: Setting MTU Value

From: J.C. Hornbeck [MSFT] (jchornbe_at_online.microsoft.com)
Date: 03/30/04 

Date: Tue, 30 Mar 2004 13:00:19 -0600

The system isn't causing fragmentation, the intermediate devices are.
Article 826159 works for VPN connections but if you want to change MTU for a
specific NIC then follow 'Method 3' in this article:

314825 - How to Troubleshoot Black Hole Router Issues
(http://support.microsoft.com/?id=314825). 

-- 
J.C. Hornbeck, MCSE
Microsoft Product Support
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"Chips" <Chips.Fowler@InLightSolutions.com> wrote in message
news:9bef76ea.0403301035.30fb65a4@posting.google.com...
> I have read many messages concerning setting the MTU value have a
> couple of different questions.
>
> 1.  When trying to find the best MTU value for on laptop (W2K Pro) on
> our network, I have found the value to be less than 1400.  Everything
> above 1345 causes the packets to fragment.  For other systems on our
> network, the MTU value is 1472 before the packets start fragmenting
> (which is about the number I would expect).  The VPN performance at
> 1345 over cable is very poor for this user and I would hope to bump
> this up so the performance is better.
>
> Why would this one system start fragmenting at such a low value while
> everything I have read states the best MTU value should be between
> 1400-1500.
>
> 2.  What it the correct registry key to set the MTU value.
> Microsoft's page:
http://support.microsoft.com/default.aspx?scid=kb;en-us;826159&Product=win2000
> points to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\0
> as the correct key with the parameter TunnelMTU to set while other
> links in this group points to
> HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\
> and the parameter MTU to set.
>
> Thanks,
>
> Chips

Relevant Pages

  • Re: packet fragmentation
    ... > we have a unix box that receives ICMP fragmentation requests because ... > the MTU size is too large, but it continues to retransmit the packet ... > without changing the MTU size. ... You cannot stop a packet fragmenting if it is too big. ...
    (comp.unix.aix)
  • Setting MTU Value
    ... When trying to find the best MTU value for on laptop on ... Why would this one system start fragmenting at such a low value while ... What it the correct registry key to set the MTU value. ... as the correct key with the parameter TunnelMTU to set while other ...
    (microsoft.public.win2000.networking)
  • Re: MTU not found!
    ... PPP Connections or for VPN Connections ... > Recently when I ran a system check, it returned a message saying that "MTU ... > reasonable speed or download for long before any ...
    (microsoft.public.windowsxp.general)
  • Re: MTU Setting
    ... >RAS Uses Fixed TCP/IP MTU Size ... >PPP Connections or for VPN Connections ... >> Does anyone know how to view/modify the MTU setting? ...
    (microsoft.public.windowsxp.help_and_support)
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