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Indirect connection works better

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Philip at Herlihy

May 14, 2009, 7:34 AM

Post #1 of 12 (2661 views)
Permalink

Indirect connection works better

Recent came across a situation again which has puzzled me in the past. I'm
trying to connect to a machine running VNC Free edition in an office. I can
make the connection (having set up port forwarding on the router) but it
hangs, with only the top third of the screen visible after several minutes.
Further attempts produced the same result.

That office has a workstation used as a simple workstation. Unlike the
"target" machine, which is wirelessly connected, this one is connected to
the router by cable. I can connect reliably to the fileserver PC. I found
that within my remote session I could start a new session from the
fileserver PC to the target PC, and this worked well.

Now that's using the same links, but in two jumps instead of one. What's
going on?

Phil, London
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jnw at realvnc

May 14, 2009, 8:20 AM

Post #2 of 12 (2559 views)
Permalink

RE: Indirect connection works better [In reply to]

Hi Philip,

Some Wi-Fi routers have trouble handling large numbers of small network packets, such as are produced when moving the mouse around in the VNC session, and that in turn can upset the Windows TCP stack and lead to the sort of behaviour you're seeing.

You can enable the "Pointer event rate-limiting" feature in the VNC Viewer to work around this problem.

Cheers,

--
Wez @ RealVNC Ltd

> -----Original Message-----
> From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> bounces [at] realvnc] On Behalf Of Philip Herlihy
> Sent: 14 May 2009 15:34
> To: vnc-list [at] realvnc
> Subject: Indirect connection works better
>
> Recent came across a situation again which has puzzled me in the past.
> I'm
> trying to connect to a machine running VNC Free edition in an office.
> I can
> make the connection (having set up port forwarding on the router) but
> it
> hangs, with only the top third of the screen visible after several
> minutes.
> Further attempts produced the same result.
>
> That office has a workstation used as a simple workstation. Unlike the
> "target" machine, which is wirelessly connected, this one is connected
> to
> the router by cable. I can connect reliably to the fileserver PC. I
> found
> that within my remote session I could start a new session from the
> fileserver PC to the target PC, and this worked well.
>
> Now that's using the same links, but in two jumps instead of one.
> What's
> going on?
>
> Phil, London
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

Philip at Herlihy

May 14, 2009, 9:09 AM

Post #3 of 12 (2547 views)
Permalink

RE: Indirect connection works better [In reply to]

Thanks, Wez - however, in response to guidance you gave me once before I
already have that setting enabled.

What puzzles me is that either route is using the same links, so it's hard
to understand what the difference might be.

Philip Herlihy

-----Original Message-----
From: vnc-list-bounces [at] realvnc [mailto:vnc-list-bounces [at] realvnc] On
Behalf Of James Weatherall
Sent: 14 May 2009 16:21
To: 'Philip Herlihy'; vnc-list [at] realvnc
Subject: RE: Indirect connection works better

Hi Philip,

Some Wi-Fi routers have trouble handling large numbers of small network
packets, such as are produced when moving the mouse around in the VNC
session, and that in turn can upset the Windows TCP stack and lead to the
sort of behaviour you're seeing.

You can enable the "Pointer event rate-limiting" feature in the VNC Viewer
to work around this problem.

Cheers,

--
Wez @ RealVNC Ltd

> -----Original Message-----
> From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> bounces [at] realvnc] On Behalf Of Philip Herlihy
> Sent: 14 May 2009 15:34
> To: vnc-list [at] realvnc
> Subject: Indirect connection works better
>
> Recent came across a situation again which has puzzled me in the past.
> I'm
> trying to connect to a machine running VNC Free edition in an office.
> I can
> make the connection (having set up port forwarding on the router) but
> it
> hangs, with only the top third of the screen visible after several
> minutes.
> Further attempts produced the same result.
>
> That office has a workstation used as a simple workstation. Unlike the
> "target" machine, which is wirelessly connected, this one is connected
> to
> the router by cable. I can connect reliably to the fileserver PC. I
> found
> that within my remote session I could start a new session from the
> fileserver PC to the target PC, and this worked well.
>
> Now that's using the same links, but in two jumps instead of one.
> What's
> going on?
>
> Phil, London
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
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jnw at realvnc

May 14, 2009, 9:23 AM

Post #4 of 12 (2550 views)
Permalink

RE: Indirect connection works better [In reply to]

Hi Philip,

Sorry to hear that. The difference you've highlighted is that the "target" machine is on Wi-Fi, not cable, which can cause issues. You might also check, for instance, what the target computer thinks the MTU of the Wi-Fi network is, and compare that to what it really is - if it's smaller than the server thinks it is then the connection is likely to stall as soon as a significant amount of data gets transferred.

Regards,

--
Wez @ RealVNC Ltd

> -----Original Message-----
> From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> bounces [at] realvnc] On Behalf Of Philip Herlihy
> Sent: 14 May 2009 17:09
> To: vnc-list [at] realvnc
> Subject: RE: Indirect connection works better
>
> Thanks, Wez - however, in response to guidance you gave me once before
> I
> already have that setting enabled.
>
> What puzzles me is that either route is using the same links, so it's
> hard
> to understand what the difference might be.
>
>
> Philip Herlihy
>
>
>
> -----Original Message-----
> From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> bounces [at] realvnc] On
> Behalf Of James Weatherall
> Sent: 14 May 2009 16:21
> To: 'Philip Herlihy'; vnc-list [at] realvnc
> Subject: RE: Indirect connection works better
>
> Hi Philip,
>
> Some Wi-Fi routers have trouble handling large numbers of small network
> packets, such as are produced when moving the mouse around in the VNC
> session, and that in turn can upset the Windows TCP stack and lead to
> the
> sort of behaviour you're seeing.
>
> You can enable the "Pointer event rate-limiting" feature in the VNC
> Viewer
> to work around this problem.
>
> Cheers,
>
> --
> Wez @ RealVNC Ltd
>
>
> > -----Original Message-----
> > From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> > bounces [at] realvnc] On Behalf Of Philip Herlihy
> > Sent: 14 May 2009 15:34
> > To: vnc-list [at] realvnc
> > Subject: Indirect connection works better
> >
> > Recent came across a situation again which has puzzled me in the
> past.
> > I'm
> > trying to connect to a machine running VNC Free edition in an office.
> > I can
> > make the connection (having set up port forwarding on the router) but
> > it
> > hangs, with only the top third of the screen visible after several
> > minutes.
> > Further attempts produced the same result.
> >
> > That office has a workstation used as a simple workstation. Unlike
> the
> > "target" machine, which is wirelessly connected, this one is
> connected
> > to
> > the router by cable. I can connect reliably to the fileserver PC. I
> > found
> > that within my remote session I could start a new session from the
> > fileserver PC to the target PC, and this worked well.
> >
> > Now that's using the same links, but in two jumps instead of one.
> > What's
> > going on?
> >
> > Phil, London
> > _______________________________________________
> > VNC-List mailing list
> > VNC-List [at] realvnc
> > To remove yourself from the list visit:
> > http://www.realvnc.com/mailman/listinfo/vnc-list
>
>
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list
>
>
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
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dalece at yahoo

May 14, 2009, 9:25 AM

Post #5 of 12 (2548 views)
Permalink

RE: Indirect connection works better [In reply to]

I find this interesting. I have seen this issue and did not know how to fix it. I do now.

The other issue I have seen is the screen saver stays on and the page does not refresh after connect. I have found adjusting to a lower resolution manually rather than the "let the server decide" option fixes this as well.

Dale

--- On Thu, 5/14/09, James Weatherall <jnw [at] realvnc> wrote:

> From: James Weatherall <jnw [at] realvnc>
> Subject: RE: Indirect connection works better
> To: "'Philip Herlihy'" <Philip [at] Herlihy>, vnc-list [at] realvnc
> Date: Thursday, May 14, 2009, 10:20 AM
> Hi Philip,
>
> Some Wi-Fi routers have trouble handling large numbers of
> small network packets, such as are produced when moving the
> mouse around in the VNC session, and that in turn can upset
> the Windows TCP stack and lead to the sort of behaviour
> you're seeing.
>
> You can enable the "Pointer event rate-limiting" feature in
> the VNC Viewer to work around this problem.
>
> Cheers,
>
> --
> Wez @ RealVNC Ltd
>
>
> > -----Original Message-----
> > From: vnc-list-bounces [at] realvnc
> [mailto:vnc-list-
> > bounces [at] realvnc]
> On Behalf Of Philip Herlihy
> > Sent: 14 May 2009 15:34
> > To: vnc-list [at] realvnc
> > Subject: Indirect connection works better
> >
> > Recent came across a situation again which has puzzled
> me in the past.
> > I'm
> > trying to connect to a machine running VNC Free
> edition in an office.
> > I can
> > make the connection (having set up port forwarding on
> the router) but
> > it
> > hangs, with only the top third of the screen visible
> after several
> > minutes.
> > Further attempts produced the same result.
> >
> > That office has a workstation used as a simple
> workstation.� Unlike the
> > "target" machine, which is wirelessly connected, this
> one is connected
> > to
> > the router by cable.� I can connect reliably to
> the fileserver PC.� I
> > found
> > that within my remote session I could start a new
> session from the
> > fileserver PC to the target PC, and this worked well.
> >
> > Now that's using the same links, but in two jumps
> instead of one.
> > What's
> > going on?
> >
> > Phil, London
> > _______________________________________________
> > VNC-List mailing list
> > VNC-List [at] realvnc
> > To remove yourself from the list visit:
> > http://www.realvnc.com/mailman/listinfo/vnc-list
>
>
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list
>

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

Philip at Herlihy

May 14, 2009, 9:56 AM

Post #6 of 12 (2547 views)
Permalink

RE: Indirect connection works better [In reply to]

Thanks, Wez,

In fact both routes use WiFi for the last leg, but your point about MTU is
an interesting one. How do I assess the "real and imaginary" MTUs?

(Offline for 24 hours from now, but still interested!)

Philip Herlihy

-----Original Message-----
From: James Weatherall [mailto:jnw [at] realvnc]
Sent: 14 May 2009 17:24
To: 'Philip Herlihy'; vnc-list [at] realvnc
Subject: RE: Indirect connection works better

Hi Philip,

Sorry to hear that. The difference you've highlighted is that the "target"
machine is on Wi-Fi, not cable, which can cause issues. You might also
check, for instance, what the target computer thinks the MTU of the Wi-Fi
network is, and compare that to what it really is - if it's smaller than the
server thinks it is then the connection is likely to stall as soon as a
significant amount of data gets transferred.

Regards,

--
Wez @ RealVNC Ltd

> -----Original Message-----
> From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> bounces [at] realvnc] On Behalf Of Philip Herlihy
> Sent: 14 May 2009 17:09
> To: vnc-list [at] realvnc
> Subject: RE: Indirect connection works better
>
> Thanks, Wez - however, in response to guidance you gave me once before
> I
> already have that setting enabled.
>
> What puzzles me is that either route is using the same links, so it's
> hard
> to understand what the difference might be.
>
>
> Philip Herlihy
>
>
>
> -----Original Message-----
> From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> bounces [at] realvnc] On
> Behalf Of James Weatherall
> Sent: 14 May 2009 16:21
> To: 'Philip Herlihy'; vnc-list [at] realvnc
> Subject: RE: Indirect connection works better
>
> Hi Philip,
>
> Some Wi-Fi routers have trouble handling large numbers of small network
> packets, such as are produced when moving the mouse around in the VNC
> session, and that in turn can upset the Windows TCP stack and lead to
> the
> sort of behaviour you're seeing.
>
> You can enable the "Pointer event rate-limiting" feature in the VNC
> Viewer
> to work around this problem.
>
> Cheers,
>
> --
> Wez @ RealVNC Ltd
>
>
> > -----Original Message-----
> > From: vnc-list-bounces [at] realvnc [mailto:vnc-list-
> > bounces [at] realvnc] On Behalf Of Philip Herlihy
> > Sent: 14 May 2009 15:34
> > To: vnc-list [at] realvnc
> > Subject: Indirect connection works better
> >
> > Recent came across a situation again which has puzzled me in the
> past.
> > I'm
> > trying to connect to a machine running VNC Free edition in an office.
> > I can
> > make the connection (having set up port forwarding on the router) but
> > it
> > hangs, with only the top third of the screen visible after several
> > minutes.
> > Further attempts produced the same result.
> >
> > That office has a workstation used as a simple workstation. Unlike
> the
> > "target" machine, which is wirelessly connected, this one is
> connected
> > to
> > the router by cable. I can connect reliably to the fileserver PC. I
> > found
> > that within my remote session I could start a new session from the
> > fileserver PC to the target PC, and this worked well.
> >
> > Now that's using the same links, but in two jumps instead of one.
> > What's
> > going on?
> >
> > Phil, London
> > _______________________________________________
> > VNC-List mailing list
> > VNC-List [at] realvnc
> > To remove yourself from the list visit:
> > http://www.realvnc.com/mailman/listinfo/vnc-list
>
>
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list
>
>
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

Philip at Herlihy

May 14, 2009, 9:57 AM

Post #7 of 12 (2548 views)
Permalink

RE: Indirect connection works better [In reply to]

Have tried lowering resolution, but to no avail.

Philip Herlihy

-----Original Message-----
From: vnc-list-bounces [at] realvnc [mailto:vnc-list-bounces [at] realvnc] On
Behalf Of Dale Eshelman
Sent: 14 May 2009 17:25
To: 'Philip Herlihy'; vnc-list [at] realvnc; james.weatherall [at] realvnc
Cc: dean.eshelman [at] gmail
Subject: RE: Indirect connection works better

I find this interesting. I have seen this issue and did not know how to fix
it. I do now.

The other issue I have seen is the screen saver stays on and the page does
not refresh after connect. I have found adjusting to a lower resolution
manually rather than the "let the server decide" option fixes this as well.

Dale

--- On Thu, 5/14/09, James Weatherall <jnw [at] realvnc> wrote:

> From: James Weatherall <jnw [at] realvnc>
> Subject: RE: Indirect connection works better
> To: "'Philip Herlihy'" <Philip [at] Herlihy>, vnc-list [at] realvnc
> Date: Thursday, May 14, 2009, 10:20 AM
> Hi Philip,
>
> Some Wi-Fi routers have trouble handling large numbers of
> small network packets, such as are produced when moving the
> mouse around in the VNC session, and that in turn can upset
> the Windows TCP stack and lead to the sort of behaviour
> you're seeing.
>
> You can enable the "Pointer event rate-limiting" feature in
> the VNC Viewer to work around this problem.
>
> Cheers,
>
> --
> Wez @ RealVNC Ltd
>
>
> > -----Original Message-----
> > From: vnc-list-bounces [at] realvnc
> [mailto:vnc-list-
> > bounces [at] realvnc]
> On Behalf Of Philip Herlihy
> > Sent: 14 May 2009 15:34
> > To: vnc-list [at] realvnc
> > Subject: Indirect connection works better
> >
> > Recent came across a situation again which has puzzled
> me in the past.
> > I'm
> > trying to connect to a machine running VNC Free
> edition in an office.
> > I can
> > make the connection (having set up port forwarding on
> the router) but
> > it
> > hangs, with only the top third of the screen visible
> after several
> > minutes.
> > Further attempts produced the same result.
> >
> > That office has a workstation used as a simple
> workstation.� Unlike the
> > "target" machine, which is wirelessly connected, this
> one is connected
> > to
> > the router by cable.� I can connect reliably to
> the fileserver PC.� I
> > found
> > that within my remote session I could start a new
> session from the
> > fileserver PC to the target PC, and this worked well.
> >
> > Now that's using the same links, but in two jumps
> instead of one.
> > What's
> > going on?
> >
> > Phil, London
> > _______________________________________________
> > VNC-List mailing list
> > VNC-List [at] realvnc
> > To remove yourself from the list visit:
> > http://www.realvnc.com/mailman/listinfo/vnc-list
>
>
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list
>

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
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John_Serink at Trimble

May 14, 2009, 5:36 PM

Post #8 of 12 (2546 views)
Permalink

Re: Indirect connection works better [In reply to]

You have an MTU issue.
If you have access to the router/gateway you need to put a tcp mssadjust xxxx command in the outgoing interface, usually eth0 or something like that where xxxx is the max mtu of you internet connection.

A more painful alternative is to change the mtu on the individual machine giving you problems.

Cheers,
John

----- Original Message -----
From: vnc-list-bounces [at] realvnc <vnc-list-bounces [at] realvnc>
To: vnc-list [at] realvnc <vnc-list [at] realvnc>
Sent: Fri May 15 02:34:03 2009
Subject: Indirect connection works better

Recent came across a situation again which has puzzled me in the past. I'm
trying to connect to a machine running VNC Free edition in an office. I can
make the connection (having set up port forwarding on the router) but it
hangs, with only the top third of the screen visible after several minutes.
Further attempts produced the same result.

That office has a workstation used as a simple workstation. Unlike the
"target" machine, which is wirelessly connected, this one is connected to
the router by cable. I can connect reliably to the fileserver PC. I found
that within my remote session I could start a new session from the
fileserver PC to the target PC, and this worked well.

Now that's using the same links, but in two jumps instead of one. What's
going on?

Phil, London
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

eshelmand at gmail

May 15, 2009, 7:45 AM

Post #9 of 12 (2535 views)
Permalink

Re: Indirect connection works better [In reply to]

I understand what you are talking about; but, do not follow how one
would go about fixing the issue.

Dale

On May 14, 2009, at 7:36 PM, John Serink wrote:

> You have an MTU issue.
> If you have access to the router/gateway you need to put a tcp
> mssadjust xxxx command in the outgoing interface, usually eth0 or
> something like that where xxxx is the max mtu of you internet
> connection.
>
> A more painful alternative is to change the mtu on the individual
> machine giving you problems.
>
> Cheers,
> John
>
> ----- Original Message -----
> From: vnc-list-bounces [at] realvnc <vnc-list-bounces [at] realvnc>
> To: vnc-list [at] realvnc <vnc-list [at] realvnc>
> Sent: Fri May 15 02:34:03 2009
> Subject: Indirect connection works better
>
> Recent came across a situation again which has puzzled me in the
> past. I'm
> trying to connect to a machine running VNC Free edition in an
> office. I can
> make the connection (having set up port forwarding on the router)
> but it
> hangs, with only the top third of the screen visible after several
> minutes.
> Further attempts produced the same result.
>
> That office has a workstation used as a simple workstation. Unlike
> the
> "target" machine, which is wirelessly connected, this one is
> connected to
> the router by cable. I can connect reliably to the fileserver PC.
> I found
> that within my remote session I could start a new session from the
> fileserver PC to the target PC, and this worked well.
>
> Now that's using the same links, but in two jumps instead of one.
> What's
> going on?
>
> Phil, London
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list
> _______________________________________________
> VNC-List mailing list
> VNC-List [at] realvnc
> To remove yourself from the list visit:
> http://www.realvnc.com/mailman/listinfo/vnc-list

Dale Eshelman
eshelmand [at] gmail

ShopToEarn (Dist ID 105985)
http://www.ShopToEarn.net/DaleEshelman

MonaVie (Distr ID 1316953)
http://www.monavie.com/Web/US/en/product_overview.dhtml

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Philip at Herlihy

May 18, 2009, 12:10 PM

Post #10 of 12 (2477 views)
Permalink

RE: Indirect connection works better [In reply to]

Thanks to John, and James, for very interesting pointers.

I'll experiment on the affected systems and see what I can demonstrate, but
I'd like some feedback on these ideas first, if anyone has any!

As I understand it, MTU (Maximum Transmission Unit) describes the size of
the largest packet to (be expected to) get through the network without being
fragmented. Different types of network (e.g. dial-up) work best with
different sizes of MTU. The default (if there is one) is 1500, with other
sizes down to 1400 being suggested for different situations. Netgear
suggest trying 1400 to "solve most problems":
http://kb.netgear.com/app/answers/detail/a_id/1153

This article describes an empirical way of checking what MTU works best in a
given situation:
http://www.dslreports.com/faq/5793

Now, in the situation I'm most concerned about, I have my machine, my router
(on which I can change the MTU at will), the office router (ditto), two
wireless access points (neither have an MTU setting) and the destination
machine(s). Changing the MTU on the end machines will involve a registry
hack after identifying the interface:
http://help.expedient.com/broadband/mtu.shtml
Am I right in thinking that if I lower the MTU on any one of them, it'll be
effective across the entire connection? Which one should I change first?

I've also remembered a situation I encountered some years ago when a
firewall was found to be blocking ICMP packets. For anyone following this,
ICMP is a collection (as I understand it) of "control" protocols which can
be necessary for a TCP connection to "tune" itself. See:
http://technet.microsoft.com/en-us/library/cc758065(WS.10).aspx
I found (can't remember the details) that allowing ICMP unblocked this
particular jam. See: http://www.dslreports.com/faq/2520

Is this likely to be relevant here? I could do with someone who actually
knows more than I can find on Google to share some experience!

Philip Herlihy

-----Original Message-----
From: vnc-list-bounces [at] realvnc [mailto:vnc-list-bounces [at] realvnc] On
Behalf Of John Serink
Sent: 15 May 2009 01:37
To: vnc-list [at] realvnc
Subject: Re: Indirect connection works better

You have an MTU issue.
If you have access to the router/gateway you need to put a tcp mssadjust
xxxx command in the outgoing interface, usually eth0 or something like that
where xxxx is the max mtu of you internet connection.

A more painful alternative is to change the mtu on the individual machine
giving you problems.

Cheers,
John

----- Original Message -----
From: vnc-list-bounces [at] realvnc <vnc-list-bounces [at] realvnc>
To: vnc-list [at] realvnc <vnc-list [at] realvnc>
Sent: Fri May 15 02:34:03 2009
Subject: Indirect connection works better

Recent came across a situation again which has puzzled me in the past. I'm
trying to connect to a machine running VNC Free edition in an office. I can
make the connection (having set up port forwarding on the router) but it
hangs, with only the top third of the screen visible after several minutes.
Further attempts produced the same result.

That office has a workstation used as a simple workstation. Unlike the
"target" machine, which is wirelessly connected, this one is connected to
the router by cable. I can connect reliably to the fileserver PC. I found
that within my remote session I could start a new session from the
fileserver PC to the target PC, and this worked well.

Now that's using the same links, but in two jumps instead of one. What's
going on?

Phil, London
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
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Philip at Herlihy

May 18, 2009, 12:24 PM

Post #11 of 12 (2482 views)
Permalink

RE: Indirect connection works better [In reply to]

Something else I found: Try this in a command prompt (XP SP1+):

Netsh firewall show icmpsetting
Netsh firewall set icmpsetting, REM doesn't change anything, just shows
options.

See: http://support.microsoft.com/kb/875357

Philip Herlihy

-----Original Message-----
From: Philip Herlihy [mailto:Philip [at] Herlihy]
Sent: 18 May 2009 20:11
To: 'vnc-list [at] realvnc'
Subject: RE: Indirect connection works better

Thanks to John, and James, for very interesting pointers.

I'll experiment on the affected systems and see what I can demonstrate, but
I'd like some feedback on these ideas first, if anyone has any!

As I understand it, MTU (Maximum Transmission Unit) describes the size of
the largest packet to (be expected to) get through the network without being
fragmented. Different types of network (e.g. dial-up) work best with
different sizes of MTU. The default (if there is one) is 1500, with other
sizes down to 1400 being suggested for different situations. Netgear
suggest trying 1400 to "solve most problems":
http://kb.netgear.com/app/answers/detail/a_id/1153

This article describes an empirical way of checking what MTU works best in a
given situation:
http://www.dslreports.com/faq/5793

Now, in the situation I'm most concerned about, I have my machine, my router
(on which I can change the MTU at will), the office router (ditto), two
wireless access points (neither have an MTU setting) and the destination
machine(s). Changing the MTU on the end machines will involve a registry
hack after identifying the interface:
http://help.expedient.com/broadband/mtu.shtml
Am I right in thinking that if I lower the MTU on any one of them, it'll be
effective across the entire connection? Which one should I change first?

I've also remembered a situation I encountered some years ago when a
firewall was found to be blocking ICMP packets. For anyone following this,
ICMP is a collection (as I understand it) of "control" protocols which can
be necessary for a TCP connection to "tune" itself. See:
http://technet.microsoft.com/en-us/library/cc758065(WS.10).aspx
I found (can't remember the details) that allowing ICMP unblocked this
particular jam. See: http://www.dslreports.com/faq/2520

Is this likely to be relevant here? I could do with someone who actually
knows more than I can find on Google to share some experience!

Philip Herlihy

-----Original Message-----
From: vnc-list-bounces [at] realvnc [mailto:vnc-list-bounces [at] realvnc] On
Behalf Of John Serink
Sent: 15 May 2009 01:37
To: vnc-list [at] realvnc
Subject: Re: Indirect connection works better

You have an MTU issue.
If you have access to the router/gateway you need to put a tcp mssadjust
xxxx command in the outgoing interface, usually eth0 or something like that
where xxxx is the max mtu of you internet connection.

A more painful alternative is to change the mtu on the individual machine
giving you problems.

Cheers,
John

----- Original Message -----
From: vnc-list-bounces [at] realvnc <vnc-list-bounces [at] realvnc>
To: vnc-list [at] realvnc <vnc-list [at] realvnc>
Sent: Fri May 15 02:34:03 2009
Subject: Indirect connection works better

Recent came across a situation again which has puzzled me in the past. I'm
trying to connect to a machine running VNC Free edition in an office. I can
make the connection (having set up port forwarding on the router) but it
hangs, with only the top third of the screen visible after several minutes.
Further attempts produced the same result.

That office has a workstation used as a simple workstation. Unlike the
"target" machine, which is wirelessly connected, this one is connected to
the router by cable. I can connect reliably to the fileserver PC. I found
that within my remote session I could start a new session from the
fileserver PC to the target PC, and this worked well.

Now that's using the same links, but in two jumps instead of one. What's
going on?

Phil, London
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

Philip at Herlihy

May 19, 2009, 6:07 AM

Post #12 of 12 (2455 views)
Permalink

RE: Indirect connection works better [In reply to]

Correction (sorry):

Netsh firewall set icmpsetting, REM doesn't change anything, just shows
options

... Should be:

Netsh firewall set icmpsetting & REM doesn't change anything, just shows
options

(ampersand, not comma)

Philip Herlihy

-----Original Message-----
From: vnc-list-bounces [at] realvnc [mailto:vnc-list-bounces [at] realvnc] On
Behalf Of Philip Herlihy
Sent: 18 May 2009 20:24
To: vnc-list [at] realvnc
Subject: RE: Indirect connection works better

Something else I found: Try this in a command prompt (XP SP1+):

Netsh firewall show icmpsetting
Netsh firewall set icmpsetting, REM doesn't change anything, just shows
options.

See: http://support.microsoft.com/kb/875357

Philip Herlihy

-----Original Message-----
From: Philip Herlihy [mailto:Philip [at] Herlihy]
Sent: 18 May 2009 20:11
To: 'vnc-list [at] realvnc'
Subject: RE: Indirect connection works better

Thanks to John, and James, for very interesting pointers.

I'll experiment on the affected systems and see what I can demonstrate, but
I'd like some feedback on these ideas first, if anyone has any!

As I understand it, MTU (Maximum Transmission Unit) describes the size of
the largest packet to (be expected to) get through the network without being
fragmented. Different types of network (e.g. dial-up) work best with
different sizes of MTU. The default (if there is one) is 1500, with other
sizes down to 1400 being suggested for different situations. Netgear
suggest trying 1400 to "solve most problems":
http://kb.netgear.com/app/answers/detail/a_id/1153

This article describes an empirical way of checking what MTU works best in a
given situation:
http://www.dslreports.com/faq/5793

Now, in the situation I'm most concerned about, I have my machine, my router
(on which I can change the MTU at will), the office router (ditto), two
wireless access points (neither have an MTU setting) and the destination
machine(s). Changing the MTU on the end machines will involve a registry
hack after identifying the interface:
http://help.expedient.com/broadband/mtu.shtml
Am I right in thinking that if I lower the MTU on any one of them, it'll be
effective across the entire connection? Which one should I change first?

I've also remembered a situation I encountered some years ago when a
firewall was found to be blocking ICMP packets. For anyone following this,
ICMP is a collection (as I understand it) of "control" protocols which can
be necessary for a TCP connection to "tune" itself. See:
http://technet.microsoft.com/en-us/library/cc758065(WS.10).aspx
I found (can't remember the details) that allowing ICMP unblocked this
particular jam. See: http://www.dslreports.com/faq/2520

Is this likely to be relevant here? I could do with someone who actually
knows more than I can find on Google to share some experience!

Philip Herlihy

-----Original Message-----
From: vnc-list-bounces [at] realvnc [mailto:vnc-list-bounces [at] realvnc] On
Behalf Of John Serink
Sent: 15 May 2009 01:37
To: vnc-list [at] realvnc
Subject: Re: Indirect connection works better

You have an MTU issue.
If you have access to the router/gateway you need to put a tcp mssadjust
xxxx command in the outgoing interface, usually eth0 or something like that
where xxxx is the max mtu of you internet connection.

A more painful alternative is to change the mtu on the individual machine
giving you problems.

Cheers,
John

----- Original Message -----
From: vnc-list-bounces [at] realvnc <vnc-list-bounces [at] realvnc>
To: vnc-list [at] realvnc <vnc-list [at] realvnc>
Sent: Fri May 15 02:34:03 2009
Subject: Indirect connection works better

Recent came across a situation again which has puzzled me in the past. I'm
trying to connect to a machine running VNC Free edition in an office. I can
make the connection (having set up port forwarding on the router) but it
hangs, with only the top third of the screen visible after several minutes.
Further attempts produced the same result.

That office has a workstation used as a simple workstation. Unlike the
"target" machine, which is wirelessly connected, this one is connected to
the router by cable. I can connect reliably to the fileserver PC. I found
that within my remote session I could start a new session from the
fileserver PC to the target PC, and this worked well.

Now that's using the same links, but in two jumps instead of one. What's
going on?

Phil, London
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list
_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

_______________________________________________
VNC-List mailing list
VNC-List [at] realvnc
To remove yourself from the list visit:
http://www.realvnc.com/mailman/listinfo/vnc-list

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