L2TP on Windows 10, Zyxel VPN100 cannot connect error 788

TecIpso · September 2021

Hello,

I configured an L2TP vpn (to connect iOS clients) according to the "https://support.zyxel.eu/hc/fr/articles/360001390914-Configuration-L2TP-sur-un-USG-Firewall-à-l-aide-du-client-intégré-Windows" link.

When trying to connect on my Win10 client I got an error 788, The L2TP connection attempt failed because the security layer could not negotiate compatible parameters with the remote computer.

Could you help me please?
Gérald

mMontana · September 2021

Behind NAT for both endpoint?

Did you edited the registry?

TecIpso · September 2021

Hello, thanks.

.

Client game: Win10 or Android, behind an internet box or 3G.
Server Part: Zywall VPN100, access via WAN direct connection of box in mode bridge.
below the logs.
You speak to me edited the registry?

mMontana · September 2021

As stated from zyxel documentation...

https://support.zyxel.eu/hc/en-us/articles/360003503440-L2TP-behind-NAT-on-a-Windows-client

Zyxel_Stanley · September 2021

Hi @TecIpso
As your log entry, VPN100 sent "No Proposal Chosen" to client.
It means your configuration is not correct.
You can refer to FAQ for L2TP VPN setting.

L2TP on Windows 10, Zyxel VPN100 cannot connect error 788

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