Windows 7 - Cisco VPN causes system choppiness for 3-5 seconds every few minutes when transferring large file over VPN in background

[ciscoguy999]

I have been using Cisco VPN Client 5.0.07.440 for several years now and it is rock solid most of the time.  The only issue I consistently have is when I am transferring one large file (~300 GB) over the VPN connection to my desktop.  It maxes out my internet connection (50 Mbps) and every few minutes the mouse gets super laggy and the PC is unusable for 3-5 seconds until it snaps out of it and is responsive again.  The keyboard also won't work and the display also seems to freeze.  This has happened on two different installations of Windows 7 Ultimate SP1 x64 so far.

The PC itself is no slouch - i7 4790K with 16GB of ram and an Intel gigabit NIC.

From what I can tell, the OS is having trouble with interrupts. When I experience system lag, the DPC latency spikes to insanely high levels.  This ONLY happens during file transfers.  The system has otherwise never had any DPC issues.

Is there a way to fix this?

[Aditya Ganjoo]

Hi,

You can try reducing the MSS size on the VPN server ( not sure if its an ASA or a router).

Try checking this link:

http://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-next-generation-firewalls/82444-fragmentation.html

You can check the respective commands for reducing the MSS size and then test if it makes any difference.

Regards,

Aditya

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[ciscoguy999]

How would this affect the responsiveness of the local machine?  The transfer seems to continue on just fine in the background, but using any sort of application (even ones that don't need network access like windows explorer) is super laggy and unusable.