Scan results show full list of all possible IP, all with the same MAC address

When I make a network scan, it shows the entire IP address range list (not just the real devices that I have), and each of those listed IPs has the same identical MAC address.

This typically happens because network scan sends out ARP requests to identify MAC addresses of devices and verify their online status. However, when scanning across subnets, the router often responds to all ARP requests with its own MAC address, which can lead to all IP addresses appearing as if they were active, even if they aren't assigned, and all appearing to have the same MAC address

To resolve this, try setting the ping method to "ICMP only" instead of "Both ICMP and ARP." Using just ICMP can help to resolve the issue by displaying only the actual devices, but the downside is that it can be blocked by the firewall, if you have one in your network.

Additionally, depending on the version you're using, ensure that "Allow ARP outside current subnet" is unchecked: