Black screen/error 10054/VPN
jnw "at" realvnc.com
Tue Nov 15 12:27:00 2005
The problem is probably that your VPN has an MTU smaller than the underlying
network, but that your servers are not detecting that correctly - this is a
very common flaw in many VPN setups, and will affect any protocol that
transfers non-trivial amounts of data, e.g. FTP, HTTP, etc.
You will find that VNC can connect and will attempt to authenticate you, but
that you'll then get a blank screen and an eventual disconnect error - this
is because your server's TCP/IP stack is sending network data segments that
are larger than the VPN can support, so it's simply dropping them. To the
TCP/IP stacks at both ends, it appears that the connection has been lost, as
a result. Because connecting & authenticating involve small amounts of
data, they don't exhibit this problem.
Wez @ RealVNC Ltd.
> -----Original Message-----
> From: vnc-list-admin "at" realvnc.com
> [mailto:vnc-list-admin "at" realvnc.com] On Behalf Of Garry Dunn
> Sent: 15 November 2005 01:20
> To: vnc-list "at" realvnc.com
> Subject: Black screen/error 10054/VPN
> To all,
> I've been trying to get RealVNC (4.1.1) running through a VPN and I'm
> having no luck. Could someone give me ideas as to what's
> going wrong?
> Here is the setup:
> Computer A is in the main office. It sits behind a
> firewall/VPN device.
> Computer B is in a remote office. It sits behind a
> firewall/VPN device.
> Computer C is in a second remote office. It sits behind a
> Computer D is in a test site. It sits behind a firewall
> without a VPN
> I've got a public IP address I can hit for Computer A, B and
> C and I can
> get control over any of those VNC terminals from Computer D.
> The same
> goes for Computer A to Computers B or C (through the public
> IP address).
> If I try from Computer A to Computer B or C through the VPN
> (using the
> private IP), I will be asked for the VNC password, which it
> will accept
> and bring up a black remote screen. I never get the remote
> desktop (the
> screen is the correct size, but black). After roughly 15
> seconds I'll
> get the error code 10054 and the connection is lost. The remote user
> tells me they can see the mouse moving on their screen. The
> remote end
> lists a 'timeout' as the reason for the connectionn being dropped.
> It seems obvious the problem is related to the VPN (remember:
> I can use
> the public IP addresses without issues). But what is the
> problem? I've
> run a ping in the background while I'm trying to connect
> through the VPN
> and the computer will ping consistently (even after the error 10054).
> The ping times are roughly 40ms to Computer B and 70ms to Computer C.
> All the internet connections are DSL (1Mbit/s or greater--not
> I've run through the archives and I think I've got everything covered
> that is suggested there:
> 1) fast user switching is off
> 2) the rate limiting is on for mouse movements
> I'm running Windows XP SP2 on Computer A and B. Computer C
> is Windows
> XP SP1. Computer D is Windows 98. I've tried RealVNC 3.7.7, 4.0 and
> 4.1.1. They all do virtually the same thing. I can telnet to the
> private IP address (port 5900) and get the RFB response.
> I've been playing with the firewall configurations to make sure that
> port 5900 is passed through the firewall and it is. Based on the VNC
> authentication being granted, I'd say that is true. But why do I not
> get screen updates and lose the connection 15 seconds later?
> Any ideas would be greatly appreciated.
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