[MX64] The L2TP connection attempt failed because the security layer encountered a processing error

[BFrança]

Hey guys.

I'm having difficulties connecting to a client-to-site VPN on some firewalls. This, specifically, is the MX64 but I'm also having the same problem on the MX84, however, this one I managed to get around the problem using VPN Client AnyConnect. When trying to connect to the VPN the message "The L2TP connection attempt failed because the security layer encountered a processing error" is displayed. I've already tested all the procedures I found available on the internet and nothing worked so I appealed to you hahaha.

Could someone who has faced this problem help me?

Thanks in advance for everyone's attention.

[BrandonS · Accepted solution]

I assume you are using Windows and missed this thread 😉

https://community.meraki.com/t5/Security-SD-WAN/Client-VPN-Error-After-January-Windows-Updates/m-p/1...

Short answer, you need to remove a recent Windows update.

[AllianceTech]

THANK YOU! I was going insane, I have 20+ MX at different customers, made the mistake to not test VPN prior to installing since have never had an issue.

Was on hold waiting for support, removed the update, recreated the VPN, not thinking would work, and by my shock it did. 

Craziest thing is, I have an MX80 and Z1 that i was testing with, they never stopped working, this was a Z3. 

Signed up for meraki community to post this, thanks again.

[BFrança]

Thank you Brandon! It really helped.

[jfvick]

I'm still having the same connection error, even after removing the recent Windows Update. Any other suggestions, possibilities? 

[Dipen]

@jfvick What exactly the error is ? If it is related to L2TP connection then you need to remove 2 security updates.

[OJA]

I have a brand new Windows install with this same issue. Neither update is installed, and when trying to install the update that is supposed to fix this; KB5010793 (it worked for me back in January) it tells me that update isn't applicable with my computer.

Windows 10 19045.2193 v 22H2

[OJA]

I discovered it was because I was connecting to the VPN from the same network.

[NwIndiana]

Same exact Issue ... any luck ?

[OJA]

My issue was that I was connecting to the VPN from inside the network. Are you connecting from inside or outside the network?

Meraki may not support connections from the inside.

I also had to dance with the advanced adapter options. For every failure, something in the settings would change - such as MS- CHAP would be checked or the connection option would change back to "General"

[Dipen]

Try uninstalling latest windows update most of the time Windows release patch update that screws L2TP connection. 

[NwIndiana]

Outside .. Noticed the settings keep changing

[OJA]

Yeah, that's the "dance" I was referring to. Are you Windows 10? Are you up to date? Did you check for the Windows Updates mentioned earlier ib BrandonS's link?

https://community.meraki.com/t5/Security-SD-WAN/Client-VPN-Error-After-January-Windows-Updates/m-p/1...

After every failure, check the settings before you try again. Once you connect, those settings will stick.