Packets freeze/stall for several seconds on Windows 7 with NDIS 6

[nstf-cvb]

I'm on Windows 7 x64, using commercial anonymous VPN services with OpenVPN, and for a few days I've been trying to track down an issue where every once in a while all packets sent or received from OpenVPN would not be delivered. I was eventually able to find a simple trigger event which reproduces it 100% of the time:

1. Run the NXT RuneScape Launcher.
2. When the Launcher's progress bar says "loading application resources" and the progress bar is about one-fifth of the way across, all packets across the entire system will be stalled.
3. After 5-10 seconds, packets get delivered again. The packets seem to be queued; if I send a ping before the stall, often I will receive the reply after it, several seconds later.

I have also observed it:

• Sometimes when the Battle.net launcher starts, though not always.
• Every few minutes in-game in RuneScape.

It does not occur merely under heavy activity; I can get a pretty good download speed, for example, without an excessive amount of packet loss. I also tested that it is not brought on by high CPU or GPU activity. I tried two different anonymous VPN services, and many different servers within each, with no change. I tried all sorts of MTU-related fixes, even though my MTU appears by testing to be the normal 1472. I tried disabling all security software.

It seems to be triggered by some very particular situation either with a series of packets or some action of the OS which freezes the TAP-Windows thread. Eventually I found this forum thread which describes a similar problem, and as recommended there I downgraded to TAP-Windows NDIS 5. This fixes it. Therefore, it seems to be a bug in Tap-Windows NDIS 6

[faern]

This is still a problem. The NDIS6 driver works really bad under Windows 7 if you apply any load (network traffic) to the system. The NDIS5 driver is much faster and more stable.

[schwabe]

As Windows 7 is not supported any more, it is very unlikely that someone will look into this issue.

[faern]

Yeah. We (Mullvad VPN) have been installing the NDIS5 driver for win7 users all the time because of this issue. In our latest release we upgraded everyone to the latest NDIS6 as a test. This bit us in the ass instantly. Many many users report the app became a lot worse.

So we will go back to conditionally install NDIS5 if the user is on Windows 7 and keep it like that until we stop supporting that OS.