The internal network firewall access rules on my Surf SOHO mk3 (firmware 8.0.1) are not working. For example, on my untagged LAN enabling a rule to block access (any protocol) from my mac laptop to my Synology NAS has no effect, and similarly for access rules to block access to any other device on the untagged LAN. I would like to block one device on my LAN from accessing other devices but cannot use VLANs at the moment because of a (known) problem they cause with wifi roaming on my AP One mini - so I would like to use internal network firewall access rules instead. Is there a fix for the internal network firewall access rule problem?
in a local network, you use the switching engine, not the routing (and firewall) engine of the Peplink router.
So the Firewall-roule cannot work in this case.
probably using Synology Firewall is the easiest way to solve your problem if VLANs are not a choice.
As you have control over your network you can create dhcp reservations for all of your devices.