For most clients, its more effective to set the following registry key: HKLM\System\CCS\Services\TCP\Parameters EnablePMTUDiscovery to 1 (doesn't exist by default)
More info on that particular tweak (plus a few others) is available here: http://support.microsoft.com/default.aspx?scid=kb;en-us;q315669&sd=tech -------------------------------------------------------------- Roger D. Seielstad - MTS MCSE MS-MVP Sr. Systems Administrator Inovis Inc. > -----Original Message----- > From: Dave Vantine [mailto:[EMAIL PROTECTED] > Sent: Friday, May 21, 2004 7:43 AM > To: Exchange Discussions > Subject: RE: Latency Issue Exch03 - Outlook > > Most people probably know this but I ran across this information on > TechRepublic a few months ago on determining the ideal MTU > size and was > surprised to see the results when I followed the instructions > and tested > some connections. Thought I would pass it on for what its worth. > > -Dave Vantine > > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> > > Adjusting the Maximum Transmission Unit size > Of all the registry tweaks that I've found for TCP/IP, > perhaps the most > useful is the ability to adjust the Maximum Transmission Unit (MTU) > size. MTU size dictates the maximum packet size (in bytes) that the > TCP/IP transport will attempt to transmit over the underlying network. > Networks that use Internet Connection Sharing (ICS) or Point-to-Point > Protocol over Ethernet (PPPoE) for their broadband > connections must have > an MTU size of 1,492 or lower to run efficiently. > > An incorrect MTU size can make your network run slowly. Administrators > tend to dismiss this problem as low bandwidth on the ISP's > end, and that > might be a source of the problem. But you'd be surprised at the > difference an MTU adjustment can make. > > The MTU is such a factor because, by default, Windows 2000 and Windows > XP set the MTU size to 1,500. It's been my experience that if > a network > is running slowly, even the 1,492 value I mentioned earlier > is too high. > I usually have the best luck by setting the MTU to around 1,454. > > You can check the MTU size for your environment by opening a command > prompt on your administration workstation and typing > PING -F -I <MTUsize> <gateway> > > where MTUsize is the size you want to experiment with and > gateway is the > gateway of your network. Start out by using an MTU size of > 1,454. Doing > so will make the command look something like this: > PING -F -I 1454 147.100.100.50 > > When you enter the command, the PING will either be successful or it > will fail with a message stating that the data must be fragmented. If > you receive the error message, decrease the MTU value and keep trying > until you find a value that works. If the PING command works the first > time, try incrementing the value by five or 10 until you see the error > message. You can then narrow down to the appropriate value. > > Once you've discovered an MTU size that works, the next trick is to > embed the value into the registry. The key's actual location > within the > registry varies depending on the version of Windows you're using. If > you're using Windows NT, the MTU key is located at: > HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services > \Parameters\Tcpip > > If you're using Windows 2000 or higher, the MTU key is located at: > HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services > \Tcpip\Parameters\Interfaces\adapter ID > > There's a good chance that the MTU key doesn't presently exist in your > system and that you'll have to create it at the specified location. To > do so, open the Registry Editor and create a new DWORD value > called MTU. > The minimum value for this key is 68, and the maximum value is the MTU > for the underlying network. > > > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > >>>>>>>>>> > >>>> > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Horner, Josh > Sent: Thursday, May 20, 2004 1:38 PM > To: Exchange Discussions > Subject: RE: Latency Issue Exch03 - Outlook > > The VPN is most likely using an MTU Size Outlook doesn't like. This > might be useful. > > http://support.microsoft.com/default.aspx?scid=kb;EN-US;329918 > > > Josh > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > David, Andy > Sent: Thursday, May 20, 2004 1:11 PM > To: Exchange Discussions > Subject: RE: Latency Issue Exch03 - Outlook > > > MTU size is often a culprit with VPNs. > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Crista > Murphy > Sent: Thursday, May 20, 2004 1:12 PM > To: Exchange Discussions > Subject: Latency Issue Exch03 - Outlook > > We have a large WAN with remote offices connecting to the > exch03 office > via > PIX 501 to Sonicwall VPN. We are noticing severe latency problems in > 90% of > our remote offices when trying to use Outlook (2k std & pro and XP) > which > has shown up in conjunction with the move from the PIX to PIX > VPN to the > current configuration. > > Anyone have any suggestions on which diag logging to turn up > on the exch > server that might help diagnose this problem? The people in charge of > the > vpn's are 100% blaming the exch server for dropping sessions. > > Exch works fine in the local office and via webmail, it is only when > connecting thru the VPN with Outlook. > > Thanks! > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&t > ext_mode=& > lang > =english > To unsubscribe send a blank email to > %%email.unsub%% > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&t > ext_mode=& > lang > =english > To unsubscribe send a blank email to > %%email.unsub%% > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&t > ext_mode=& > lang=english > To unsubscribe send a blank email to > %%email.unsub%% > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > > This email and any files transmitted with it are confidential > and intended solely for the use of the individual or entity > to whom they are addressed. If you have received this email > in error please notify the system manager. This message > contains confidential information and is intended only for > the individual named. If you are not the named addressee you > should not disseminate, distribute or copy this e-mail. > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&t ext_mode=&lang=english > To unsubscribe send a blank email to > %%email.unsub%% > Exchange List admin: [EMAIL PROTECTED] > To unsubscribe via postal mail, please contact us at: > Jupitermedia Corp. > Attn: Discussion List Management > 475 Park Avenue South > New York, NY 10016 > > Please include the email address which you have been contacted with. > _________________________________________________________________ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Web Interface: http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&text_mode=&lang=english To unsubscribe send a blank email to [EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] To unsubscribe via postal mail, please contact us at: Jupitermedia Corp. 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