Integrate AC86 as VPN gateway into existing network?

[phunky]

Hello all,

I use an AC86U with Merlin 386.5_2 as a VPN gateway so that the Internet access is censorship-free and reasonably secure. But now the question arises how I can integrate the router into the existing LAN. It would be nice if I could specify the AC86U as gateway on all possible devices.

Currently it looks like this my main network is a Fritzbox 7590 and a TP-Link switch TL-SG1016DE the subnet is 192.168.80.0. The Fritzbox provides direct internet access.
The AC86U is connected to the switch via the WAN interface, the subnet is 192.168.81.0.

In the Fritzbox as well as in the AC86U I have created corresponding static IP V4 routes.
From the AC86U network I can reach all devices in the main network 192.168.80.0. From the main network I can only reach the AC86U directly when the firewall is switched off, but no devices behind it. Also I can't use the AC86U as a gateway from the main network, I can ping it on the WAN IP of the main network as well as on the IP of its own network. But it probably does not allow a passthrough on the WAN side.

Is there any way to change this?
- Bridging
- IP Forwarding