Hi, I have a customer that uses windows 11 to access an L2TP vpn. The configuration worked up to about 10 days ago, now it does not work anymore.
The vpn is configured as split tunnel, so internet traffic stays out of the vpn.
He connects to his wifi at home, then to the vpn, and after just a few minutes (or even just one minute) his internet connection dies. It seems to be connected but he cannot do anything on the internet and of course inside the vpn too.
He connects to his wifi hotspot on his phone, same issue
He connects to his home router via a network cable, everything is fine.
So it seems that when he uses wifi and the vpn, his wifi somehow dies, traffic just stops.
I have tried setting up a win11 PC the same way (he’s VERY remote, so I’m not going to his home, I must solve this remotely) and my win11 PC has the same problem.
Googling “win 11 wifi l2tp vpn not working” or something similar gives no meaningful results, so I’m here asking if someone else is experiencing this issue.
EDIT:
my colleague ran some tests: installing KB5026372 broke his PC (very slow internet when the vpn is connected and WIFI is in use, no problems with cabled LAN).
Issuing powershell Get-NetAdapterRsc shows that wifi supports RSC and it’s enabled. Cabled adapter does not even show up in the list. Issuing powershell Disable-NetAdapterRsc -Name disabled RSC and after this we were able to run the VPN on wifi without issues. We are currently testing it for a longer time to see if it’s stable.
So, to recap:
KB5026372 breaks internet when vpn is connected only on the network adapter that supports Receive Segment Coalescing (RSC).
Disabling RSC seems to make it work again without the need to uninstall KB5026372, but not in all cases. I have seen cases where the only solution is to uninstall KB5026372. I have also seen a case where disabling RSC does nothing, and I cannot uninstall KB5026372 so I am fucked.
My bet would be that the user let their connection go to sleep causing it not to be closed out properly on the vpn side of things. Most of the time when L2TP mysteriously stops working it’s this.
However you’re going to need to capture logs and info to fully troubleshoot.
Other issues would be an ISP problem, someone else using L2TP at their location and the router not being able to handle it, configuration change by customer.
I can vouch that L2TP works on windows 11 with stable connectivity (as I accidentally left a link on my work PC connected for over 2 days recently trying to troubleshoot a company WAN issue from outside our network)
We have had similar issues with machines that have Dell Optimizer / Dell Express Connect installed. Once the shovelware is removed, the L2PN vpn & internet connections began working normally once again.
See if this fixes the issue: ‘windows 11 disable rsc.’ Look through the search results; the symptoms are similar to what you describe (no-or-terrible networking when the VPN is enabled, even local non-VPN traffic, but not when using a different adapter). This setting is per-adapter, so it may be that the drivers for the wifi adapter cannot do this but the LAN ones can, or some other such magic I don’t understand.
Make sure there is no conflict anywhere with VLANs and his home subnet.
I would recommend getting an exact timestamp, you may even want to have a ping cmd run in the background writing to a log file with timestamps for each ping.
Find the exact moment that pings stop responding, check your VPN/Firewall logs and also use a tool like nirsoft fulleventlogview and comb through the events on his computer.
Another thing to check is the ipv4 adapter for the VPN, somewhere in the advanced options there is a setting “use default gateway on remote connection” or something like that. Try toggling it off if it is on, or viceversa.
You may also want to go into device manager and look for some advanced settings on the wifi adapter to disable sleep/lowpower mode/shutting off the adapter to conserve power or any settings like that.
I’m quite sure it’s the combination of wifi and L2TP vpn. Any other combination works (wifi alone, VPN with a cabled network). And since it worked before, I suppose it might be some update that broke it. I was just hoping for someone to say “ehi, I had the same issued, solved it like this”, before diving into a lot of debugging.
Default gw is disabled (it’s the default config and I changed it). His local net is the classic 192.168.1.0/24 and the remote net is different, no conflicts at all. Power management is something to check, but if it was power management is should be malfunctioning even with the vpn switched off, instead it works fine when the vpn is off. Also, it fails even when the PC is actively used (I was connected with anydesk) so it’s not an issue with suspension or inactivity.