I'm having the same problem. So adjusting the MTU for the server is the solution because VPN was mixed up in the topic. In my case, it is Win2K3.
Thanks On 4/27/06, James Weatherall <[EMAIL PROTECTED]> wrote: > > Hi Alex, > > I didn't think that you were - I was just trying to advise you on the best > course of action to see a resolution to the VPN/MTU problem, it being a > pain > to have to configure these things manually! > > It sounds from what you say as though there is a manual-configuration > component to the VPN setup that is the source of the connection hang > problem. I think you are correct in asserting that this results from > over-large do-not-fragment packets, which result from the server system's > TCP stack using the underlying network MTU rather than the VPN's > MTU. (The > VPN's MTU is obviously slightly smaller due to VPN headers.) TCP has > end-to-end Maximum Segment Size handling which is supposed to take care of > this sort of thing, but it sounds like it's not in your case, or in SB's. > Retransmission won't help (in fact, it can make things worse), because TCP > will keep trying to retransmit with the same MSS/MTU and so the > retransmissions will be dropped in the same way as the original packets. > > Thanks for the recommendation, much appreciated! :) > > Cheers, > > Wez @ RealVNC Ltd. > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Alex Pelts > > Sent: 26 April 2006 18:44 > > To: James Weatherall > > Cc: 'S B'; [email protected] > > Subject: Re: VNC freezing on Win XP Media Center Edition SP2 > > > > James, > > I am not trying to ask help on the forum. I am just telling what I > > observed and how I fixed it. My VPN software made by cisco > > and I think > > it is one of the better pieces of vpn out there or at least > > comparable > > to any other vpn. > > Note that I am not blaming VNC for my problems at all in fact > > I am very > > happy with it and recommend anyone to upgrade to EE or > > personal edition > > if they are running VNC on windows. > > > > I think that default MTU in some vpn setups is too high and it is > > causing the problems I described. Unfortunately I don't have > > the time or > > desire to investigate the cause of this problem. It baffles > > me as well, > > because I know that TCP is connection based protocol and packets are > > retransmitted. But I do observe the problem and that was how I solved > > it. I will be happy to provide more details if you want them. > > > > Regards, > > Alex > > > > > > James Weatherall wrote: > > > Hi Alex, > > > > > > Yes, TCP sends packets, but VNC doesn't - VNC sends a > > stream of bytes and > > > the TCP stack is then responsible for splitting that stream > > into a sequence > > > of packets of an appropriate size for the underlying network. > > > > > > The problems you're seeing are most likely caused by faulty > > VPN software not > > > indicating the MTU correctly to the two ends of the > > connection, resulting in > > > TCP splitting the data stream into chunks that are too > > large for the VPN. > > > Your best bet is therefore to contact your VPN vendor for > > support for their > > > product. > > > > > > Cheers, > > > > > > Wez @ RealVNC Ltd. > > > > > > > > > > > >> -----Original Message----- > > >> From: Alex Pelts [mailto:[EMAIL PROTECTED] > > >> Sent: 26 April 2006 16:50 > > >> To: James Weatherall > > >> Cc: 'S B'; [email protected] > > >> Subject: Re: VNC freezing on Win XP Media Center Edition SP2 > > >> > > >> Well tcp stack sends packets. It all has to do with the > > single write > > >> length that most likely goes out as a packet. If the write is > > >> large it > > >> will fill one or more full vpn packets that can't be > > >> fragmented and will > > >> be dropped. You can try it yourself. To tell you the truth > > I am not a > > >> TCP expert so I cant tell you the exact reason. I am sure > > that if you > > >> run ethereal you can find some clues rather quickly. > > >> > > >> All I know that lowering MTU on my VPN interface fixed > > these problems. > > >> > > >> Regards, > > >> Alex > > >> > > >> > > >> James Weatherall wrote: > > >>> Hi Alex, > > >>> > > >>> VNC doesn't send packets at all - it runs over TCP. > > >>> > > >>> Cheers, > > >>> > > >>> Wez @ RealVNC Ltd. > > >>> > > >>> > > >>>> -----Original Message----- > > >>>> From: [EMAIL PROTECTED] > > >>>> [mailto:[EMAIL PROTECTED] On Behalf Of Alex Pelts > > >>>> Sent: 25 April 2006 19:14 > > >>>> To: James Weatherall > > >>>> Cc: 'S B'; [email protected] > > >>>> Subject: Re: VNC freezing on Win XP Media Center Edition SP2 > > >>>> > > >>>> The VPN has MTU larger than MTU of physical network. Lots of > > >>>> packets are > > >>>> dropped as somehow VNC sends rather large packets. I had > > >> this problem > > >>>> myself until I lowered MTU to below of the physical network MTU. > > >>>> > > >>>> The symptoms were: > > >>>> 1. screen would render half way and then stop. > > >>>> 2. screen updates were extremely slow > > >>>> 3. Connection would go for some short time and then would > > >> be dropped. > > >>>> I am not sure why MTU is causing that effect. I think that > > >>>> VPN packets > > >>>> can not be fragmented so they are dropped and there is a > > >> large packet > > >>>> loss. I am not sure how VNC reacts to large packet loss. > > >>>> > > >>>> Regards, > > >>>> Alex > > >>>> > > >>>> > > >>>> James Weatherall wrote: > > >>>>> Hi Alex, > > >>>>> > > >>>>> Can you provide any more information on why that causes the > > >>>> effect SB is > > >>>>> seeing? > > >>>>> > > >>>>> Cheers, > > >>>>> > > >>>>> Wez @ RealVNC Ltd. > > >>>>> > > >>>>> > > >>>>>> -----Original Message----- > > >>>>>> From: [EMAIL PROTECTED] > > >>>>>> [mailto:[EMAIL PROTECTED] On Behalf Of Alex Pelts > > >>>>>> Sent: 25 April 2006 07:07 > > >>>>>> To: S B > > >>>>>> Cc: [email protected] > > >>>>>> Subject: Re: VNC freezing on Win XP Media Center Edition SP2 > > >>>>>> > > >>>>>> MTU is too large on your vpn connection. > > >>>>>> > > >>>>>> Regards, > > >>>>>> Alex > > >>>>>> > > >>>>>> > > >>>>>> S B wrote: > > >>>>>>> Hi, > > >>>>>>> > > >>>>>>> I just bought a new computer from Dell (Intel dual core > > >>>>>> 2.8GHz, 1GB RAM > > >>>>>>> running Win XP Media Center w/ SP2), and downloaded VNC 4.4 > > >>>>>> viewer on it. > > >>>>>>> When I VNC to my work machine, VNC viewer freezes > > >>>>>> intermittently. Some times > > >>>>>>> immediately after logging in and some times after 10-15 > > >>>>>> minutes of work. Did > > >>>>>>> anyone here faced a similar problem? How do I fix > > this problem. > > >>>>>>> > > >>>>>>> Thanks, > > >>>>>>> - SB > > >>>>>>> _______________________________________________ > > >>>>>>> VNC-List mailing list > > >>>>>>> [email protected] > > >>>>>>> To remove yourself from the list visit: > > >>>>>>> http://www.realvnc.com/mailman/listinfo/vnc-list > > >>>>>> _______________________________________________ > > >>>>>> VNC-List mailing list > > >>>>>> [email protected] > > >>>>>> To remove yourself from the list visit: > > >>>>>> http://www.realvnc.com/mailman/listinfo/vnc-list > > >>>>> _______________________________________________ > > >>>>> VNC-List mailing list > > >>>>> [email protected] > > >>>>> To remove yourself from the list visit: > > >>>>> http://www.realvnc.com/mailman/listinfo/vnc-list > > >>>> _______________________________________________ > > >>>> VNC-List mailing list > > >>>> [email protected] > > >>>> To remove yourself from the list visit: > > >>>> http://www.realvnc.com/mailman/listinfo/vnc-list > > >>> _______________________________________________ > > >>> VNC-List mailing list > > >>> [email protected] > > >>> To remove yourself from the list visit: > > >>> http://www.realvnc.com/mailman/listinfo/vnc-list > > _______________________________________________ > > VNC-List mailing list > > [email protected] > > To remove yourself from the list visit: > > http://www.realvnc.com/mailman/listinfo/vnc-list > _______________________________________________ > VNC-List mailing list > [email protected] > To remove yourself from the list visit: > http://www.realvnc.com/mailman/listinfo/vnc-list > -- {Celia} _______________________________________________ VNC-List mailing list [email protected] To remove yourself from the list visit: http://www.realvnc.com/mailman/listinfo/vnc-list
