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
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