Just for the sake of completeness, if anyone else has this requirement of blocking the LAN for the Synology VPN and comes across this post:
When using OpenVPN in the Synology VPNServer, you can specify whether the clients are allowed to have access to the server lane segment or not. ‘Allow clients to access server LAN’ is disabled by default (DSM 5.2)
This would mean that all the ‘tinkering’ wouldn’t have been necessary - but the implemented solution also has some new great advantages 🙂
For home applications, Sophos has a bootable ISO ‘Sophos UTM Home Edition’ which creates a nice UTM solution with a lot of possibilities from a PC with 2 network cards. If you don’t want to/can’t use a PC or don’t have a PC virtualized, you can also use an entry-level version of Sophos. Solve UTM 110/120 and a free home license and install it on the box. This means you have web access, spam/phishing email filters, VPN, but also 10 licenses for Endpoint included - these licenses include the complete virus scanner for the PC/MAC/Android. The license allows networks with up to 50 IP addresses. That should usually be enough.