Win7 problems with VPN copying large files
I've had a VPN issues with both Vista and Win7 (x64) editions over the last two years, where copying large files up to a mapped drive over the VPN causes the link to drop. Scenario: I regularly copy files up to my office using a VPN - this is currently a windows PPTP VPN over the internet, on a Windows 2003 server. The VPN works fine for TCPIP e.g. SQL and remote desktop, but when SMB and large files are copied up it drops. This does not happen when I copy from XP over the same VPN, so there is obviously some sort of dynamic networking in the Vista and Win7 network stacks which are kicking in and causing the VPN to fail. If I copy a small file (say 64k) it will work - but anything much larger will start and then fail. As it only seems to happen with file copying I assume it is SMB related, whereas SQL and RDP seem to be unaffected. Howard
October 11th, 2009 7:35pm

Hi, Based on my research, I would like to suggest the following: 1. Disable the security software such as firewall and Anti-virus software on the Windows 7 or Windows Vista computer to see how it works. 2. Perform a clean boot to check the issue: How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7 After booting into the clean boot environment, please establish the VPN connection and cope the large files to see how it works. 3. If the issue persists, please adjust the following registry keys in Windows 2003 Server. Note: please perform a full system backup first. Increase the SizReqBuf value How to modify the default SizReqBuf value in Windows 2000 and Windows Server 2003 Hope this helps. Nicholas Li - MSFT
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October 19th, 2009 11:20am

Thanks for the response.I tried a clean boot, and disabled firewall and anti-virus software.Same problem - a 12MB copy failed after about 100k.Adjusting the settings on the destination 2003 server seems to make no difference. It works if I copy Win2003 to Win2003 without any changes.As I had exactly the same problems with Vista as Win7 I assume it is the changes to the Win7/Vista IP stack.Howard
October 21st, 2009 7:20pm

Hi, At this time, please try the following: 1. Please check the following: How to Troubleshoot Black Hole Router Issues 2. Disable SNP in Windows Vista or Windows 7 by setting Registry as following: Note: Please perform a full-system backup first. [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters] EnableTCPChimney=dword:00000000 EnableTCPA=dword:00000000 EnableRSS=dword:00000000 An update to turn off default SNP features is available for Windows Server 2003-based and Small Business Server 2003-based computers 3. If possible, please establish the VPN connection on another network and then copy files to see how it works. If the issue persists, please also capture a netmon trace for our further research: 1. Download the Microsoft Network Monitor 3.3. 2. Install the network monitor on a Windows 7 or Windows Vista computer and start to capture. 3. Establish the VPN connection on this computer and start to copy a large file. 4. When the issue occurs, just stop capturing and save the netmon trace files to check the related network activations. You can use Windows Live SkyDrive to upload the file and share its URL with us. Thanks. Nicholas Li - MSFT
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October 22nd, 2009 12:25pm

Thanks for the reply. 1. I checked the router and it seems my Netgear DGFV338 has an MTU of 1492 - I wasn't able to get this to change to 1500, which may be related. I tried the fix setting EnablePMTUBHDetect but it had no effect.2. This seems to work - the copy over the VPN now works more reliably - the VPN still drops out occassionally but it's less frequent than it was (and may be network problems with remote servers more than bug in tcppip)cheersHoward
October 27th, 2009 1:41pm

Hi, Thank you for your update. I am glad to know that this helped. Lets keep monitoring the issue. If there is an update, please also let us know. Thanks again. Nicholas Li - MSFT
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October 29th, 2009 5:58am

Hmmm.. it is still having problems. It gets further than it used to but often fails about half way through the copy.I have captured the network traffic during the upload and uploaded to Skydrive as requested.URL is http://u4hwjw.blu.livefilestore.com/y1pMqV_0e7GFiVFa1kQSqa-6axMxHngh7b_cS2cX9jt2LTzzRj52r8aTpB0JVwAOae8Stein-QKIPP7PfxxGc7x449col-K5sD5/cap2.zip?downloadplease let me know when you have downloaded this as I want to delete it afterwards.Layout:Workstation (win7) 192.168.55.4 connectedto internetvia router Netgear DGFV338 at 192.168.55.1 (uses NAT)running dialup IP VPN via 62.24.204.44Firewall on DGFV permits all traffic outboundHoward
October 29th, 2009 2:21pm

Any input on this? Or do we assume Win7 networking is as much of a joke as Vista's was?Howard
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November 3rd, 2009 5:37pm

Hi, I am sorry that I could not get the file you shared. If possible, could you please share it with me again? Once we get the information, we willperform some further researches and update with you. Thanks again for your time and efforts. Nicholas Li - MSFT
November 4th, 2009 3:07pm

Can you try this URL: only one file in this folder: http://cid-ac44601e5195662b.skydrive.live.com/browse.aspx/Win7%20copyHoward
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November 4th, 2009 4:27pm

Hi, After researching, I would like to suggest you try the following to narrow down the issue: 1. Take the Windows 7 client to another network and see how it works. 2. Adjust the MTU values referring to the following Knowledge Base: HOW TO: Change the Default Maximum Transmission Unit (MTU) Size Settings for PPP Connections or for VPN Connections 3. Please also check the following: How to Troubleshoot Black Hole Router Issues Hope this helps. Thanks. Nicholas Li - MSFT
November 5th, 2009 10:45am

An update on this issue and some thanks for your assistance. Having tried all these fixes and still having the problems, I was able to push the company whose VPN I was connecting to (a big corporate here in the UK). Their network engineers monitored the firewall at their endduring aVPN session and have made some tweaks to their firewall setup.Unfortunately I don't know the details of the firewall config or how the manage PPTP VPNpass-thruso I cannot share the actual solution (and they are the securityparanoid types who would probablynot release such info!).Suffice to say that Vista/Win7 VPN connectivity and TCPIP packets can cause a firewall to drop a VPN session incorrectly. Thanks again.Howard
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November 17th, 2009 6:52pm

Hi, Thank you for your update. I am glad to know it worked. In the future, if you experience any issues regarding our products or if you have any feedbacks, you are welcome to post a new thread in our forum. It is always our pleasure to be of assistance. Thanks again for your time and efforts. Nicholas Li - MSFT
November 18th, 2009 10:48am

Hi Nicholas,The link above (HOW TO: Change the Default Maximum Transmission Unit (MTU) Size Settings for PPP Connections or for VPN Connections) is according to "APPLIES TO" only for Server 2000, Server 2003 and XP Pro. But you're referring to it for a Win7 problem. Does it also apply to Vista and Win7?
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February 23rd, 2010 10:41am

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