@MatthiasL22 I had to install a new OpenVPN server with TCP to get it to work, so I think this is the only option on ER8411. and the server was installed in 2.4 or older compatibility to get it to...

@MatthiasL22 there is somthing with UDP on this router, try and configure OpenVPN server with TCP. for me this work, very slow and far away from the spec on this device. OpenVPN is also very oudated,...

@Carlootje OK, I misunderstood you a bit, you are going to use the router as an L2TP Client, then there is no need for a public wan ip. the fact that you cannot set up usb as wan in vpn is probably a...

@Carlootje I try enable USB on a site, but there is no option to use this as wan in any vpn configuguration,, so it look like that usb is primary for failover to give internet when main line is down....

@Carlootje Carlootje wrote @MR.S dear sir, when I connect also my laptop on the LAN I can make the same L2TP connection without a problem. So then the proble, I think isn't at the provider is it?...

@Carlootje You are problably behind a cgnat. very common on 4g. you have to speak with your 4g provider and ask for apn with public ip