L2TP server stopped working properly

ANTONBORODA · Wed Feb 16, 2022 10:23 am

Hello,
I have an L2TP server setup and it was working correctly for quite some time (a year at least). Recently I updated to RouterOS 7.1.2 and after the update the L2TP works only once after the router has been restarted. After the connection was terminated, the new one cannot be established anymore.
Logs are

respond new phase 1
ISAKMP-SA established
purging ISAKMP-S
ISAKMP-SA deleted

Does anyone have and idea what might be wrong?

Thank you.

oliee0 · Wed May 11, 2022 12:06 am

Any solution?
Same situation in my networks today.
That's strange, few Mikrotik routers (RB5009 and RB4011 models) in different locations (and different ISPs), very similar L2TP configuration on each of them.
~20 PCs here! About 1/2 computers can't connect to any Mikrotik via L2TP from any internet source (LTE, fibre etc.). All PCs with clear and updated Windows 10/11. Connection from Android/iOS without any problems, tested on several smartphones, so...
That's Windows' fault? Help!

own3r1138 · Wed May 11, 2022 5:07 am

Any solution?
That's Windows' fault? Help!

A few months ago Windows devices had an issue with "Disabling Vendor ID", I don't know if your clients are affected by this issue or not.
viewtopic.php?t=182163

oliee0 · Wed May 11, 2022 5:35 am

I have all computers updated to W10 21H2

own3r1138 · Wed May 11, 2022 5:41 am

enable logging to check what is going on.

ANTONBORODA · Wed May 11, 2022 10:44 am

Any solution?
Same situation in my networks today.
That's strange, few Mikrotik routers (RB5009 and RB4011 models) in different locations (and different ISPs), very similar L2TP configuration on each of them.
~20 PCs here! About 1/2 computers can't connect to any Mikrotik via L2TP from any internet source (LTE, fibre etc.). All PCs with clear and updated Windows 10/11. Connection from Android/iOS without any problems, tested on several smartphones, so...
That's Windows' fault? Help!

I poked around for about a month and decided to do a reset/restore of the configuration, since the reset everything is working normally.
It wasn't windows fault because non of the clients (including other mikrotik devices) couldn't connect and the only solution was to restart the router. And after restart it happened randomly, it could work for a week just fine and then die, or could die instantly after a first client connection. I couldn't find a cause or a stable pattern to reproduce the issue to report properly.

oliee0 · Wed May 11, 2022 12:06 pm

Reset to factory and configure all 10 Mikrotik's in ~10 localizations is unreal for me...
It's not seems to be Mikrotik fault, Why I can't connect to all L2TP VPN from Windows? Difference Mikrotik's devices, each one of them has a different firmware number, different models.

A little example about my situation:
- 20 pieces PC Windows 10 21H2 - half of them can't connect to any Mikrotik router with VPN L2TP enabled
- any device with iOS or Android is connected successfully, with the same login credentials
- all Windows' computers has latest updates
- tested lots of internet connection method

Simple firewall config:

ANTONBORODA · Wed May 11, 2022 12:12 pm

Reset to factory and configure all 10 Mikrotik's in ~10 localizations is unreal for me...
It's not seems to be Mikrotik fault, Why I can't connect to all L2TP VPN from Windows? Difference Mikrotik's devices, each one of them has a different firmware number, different models.

A little example about my situation:
- 20 pieces PC Windows 10 21H2 - half of them can't connect to any Mikrotik router with VPN L2TP enabled
- any device with iOS or Android is connected successfully, with the same login credentials
- all Windows' computers has latest updates
- tested lots of internet connection method

Simple firewall config:

You have a different problem then.
I had problems with ANY type of client, sometimes, it broke with only mikrotik connected (as a client), sometimes after an iOS connected, etc.
It was a mikrotik fault in my case.

evince · Wed May 11, 2022 1:02 pm

Hello,

Take a look at this, maybe it is the solution. https://docs.microsoft.com/en-us/troubl ... t-t-device

Regards,

oliee0 · Wed May 11, 2022 1:27 pm

Tried, no effect.
All Mikrotik routers are not behind NAT. On all localizations I have static, public IP without any restrictions.
Today another funny situation, 2 pieces of factory new notebooks, same model. Clear W10 install with all updates, on one of them I can connect, second laptop next to me can't connect with same credentials...
Madness.

oliee0 · Wed May 11, 2022 9:30 pm

Solution! Problem resolved!
I can't believe... problem is service in Windows, running and named "Xbox Live Networking Service".
Randomly turned off/on on lots of computers.

ANTONBORODA · Fri May 13, 2022 9:15 am

And the issue happened again today!

I just noticed, that while this is happening the CPU load is almost 100%.
Profile says it's "networking" but there's close to 0 network operations at the moment.

MikrotikIssue.jpg

Log gives no info other than failed attempts of L2TP connection to the router and IPSec data.

L2TP server stopped working properly

L2TP server stopped working properly

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Re: L2TP server stopped working properly

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Re: L2TP server stopped working properly

Re: L2TP server stopped working properly

Re: L2TP server stopped working properly

Re: L2TP server stopped working properly