It's a performance thing, really. The lower the MTU the higher the percentage of overhead due to the packet header.
-------------------------------------------------------------- Roger D. Seielstad - MTS MCSE MS-MVP Sr. Systems Administrator Inovis Inc. > -----Original Message----- > From: Jim Richards [mailto:[EMAIL PROTECTED] > Sent: Monday, July 21, 2003 8:15 AM > To: Exchange Discussions > Subject: RE: Outlook/Exchange/VPN connectivity problem > > > Why would technet say not to adjust the MTU? I have found it > is neccesary to adjust this setting in a number of instances > (probably depending on routers in the path). I have dumped > it all the way down to 576, and have not had a difficulty > that I can remember. > > Jim > > -----Original Message----- > From: Roger Seielstad [mailto:[EMAIL PROTECTED] > Sent: Monday, July 21, 2003 12:10 PM > To: Exchange Discussions > Subject: RE: Outlook/Exchange/VPN connectivity problem > > > Hmm. Technet's wrong. We run 1300 all over the place (it's the Cisco > client). > > Are you still receiving the need to fragment message? > > -------------------------------------------------------------- > Roger D. Seielstad - MTS MCSE MS-MVP > Sr. Systems Administrator > Inovis Inc. > > > > -----Original Message----- > > From: Warren Cundy [mailto:[EMAIL PROTECTED] > > Sent: Friday, July 18, 2003 4:15 PM > > To: Exchange Discussions > > Subject: RE: Outlook/Exchange/VPN connectivity problem > > > > > > Thanks for this Roger. > > > > However the ping still doesn't work at 1400. Technet says > > not to set this > > below 1400, what else can I do? > > > > Thanks > > > > -Warren > > > > -----Original Message----- > > From: Roger Seielstad [mailto:[EMAIL PROTECTED] > > Sent: Friday, July 18, 2003 10:54 AM > > To: Exchange Discussions > > Subject: RE: Outlook/Exchange/VPN connectivity problem > > > > > > Nope. Not DNS. > > > > MTU size. Do a technet search on MTU (or check with your VPN > > client vendor > > if you're not using the built in client) and find out how to > > set the MTU to > > <1500 (we use 1400). > > > > Outlook has a nasty habit of setting the Do Not Fragment bit on > > communications, and sends it at the existing MTU size. The > > VPN client then > > encapulates the packet and adds to the packet size, exceeding > > the network's > > MTU. The first hop router then generates an ICMP reply > > basically saying the > > packet needs to be fragmented by DF flag is set (Don't > Fragment Flag). > > > > You can test it with the following command while connected via VPN. > > ping -l 1536 -f ipaddress > > > > 1536 is the standard Ethernet MTU. Try dropping that to 1400 > > and seeing if > > it works. I'd bet that's your culprit. > > > > -------------------------------------------------------------- > > Roger D. Seielstad - MTS MCSE MS-MVP > > Sr. Systems Administrator > > Inovis Inc. > > > > > > > -----Original Message----- > > > From: Warren Cundy [mailto:[EMAIL PROTECTED] > > > Sent: Friday, July 18, 2003 1:06 PM > > > To: Exchange Discussions > > > Subject: Outlook/Exchange/VPN connectivity problem > > > > > > > > > Hi guys, > > > > > > A few users are having an intermittent connectivity problem > > > to Exchange > > > server over a VPN connection. Here's what we're using: > > > Exchange 2000 Sp3, > > > Outlook 2002 Sp2 on the clients. > > > > > > When these users connect to our VPN, they can see/ping > > > everything, including > > > Exchange, but always have problems opening outlook. First > > > they have to set > > > their profile to manually control the connection and > force an online > > > connection. Even then they have to hit "retry" a few times, > > > but it finally > > > connects, although very slowly. > > > > > > I know DNS DNS DNS, but they can ping the Exchange server by > > > name, and I > > > even gave them entries in the HOSTS file for the local > > (internal VPN) > > > address of the Exchange server... any thoughts here? Its > > > driving me crazy. > > > > > > -W > > > > > > _________________________________________________________________ > > > 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: mailto:[EMAIL PROTECTED] > > Exchange List admin: [EMAIL PROTECTED] > > > > _________________________________________________________________ > > 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: mailto:[EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > > _________________________________________________________________ > 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: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] _________________________________________________________________ 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: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] _________________________________________________________________ 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: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] _________________________________________________________________ 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: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED]
