First, I'm not really good at networking terminologies, So I'll explain the case as simple as possible.
I have a PFSense set up, my PFsense gets its internet through its WAN IP 192.168.10.2 and disperse to clients on its DHCP LAN IPS 192.168.20.100~150
Everything works, 20.xx has internet access, problem is they also can ping the ip groups in 10.x example PC outside pfsense with IP 192.168.10.50
How do I stop this from happening? This also applies to routers.