OpenVPN server and LAN routing query

[Steve Hoare]

Hi,

I need a little expert advice...and despite trying lots of different things I'm still a bit lost with this specific problem.

I'm running an OpenVPN (TUN) server on my Asus AC86U router, which is running the latest Merlin firmware, and I'm allowing just LAN access. The aim is to access the GUIs of various LAN devices for remote configuration but (relatively) securely as it's all over OpenVPN.

The problem is I can connect to my OpenVPN server, getting a 10.0.8.x address, and see my router (192.168.2.1) and NAS box (192.168.2.2) but I can't see my fibre modem (192.168.2.101).

However, I can see this device and all of the others when I'm sat on WiFi at home despite using the same 192.168.2.X IPs.

Am I missing something really obvious as I suspect I am with how the Asus routes incoming OpenVPN traffic for the LAN, or is it perhaps the firewall on the fibre modem. It's a Huawei HG612 which is unlocked in case that is relevant.

The only, perhaps relevant difference, is that the NAS is on the LAN via a WiFi dongle and the fibre modem itself is hooked up directly to a LAN port on the back of the router.

Any help really appreciated...