Prevent reverse DNS of angry IP with firewall

Hello. I have a guest net, say 3.1/24, and I set "forwarding" only to wan on my router. But with Angry IP on my macbook Pro on 3.1/24, I can see the hostnames of the clients on 1.1/24 net. What kind of firewall rule do I need on router to prevent an Angry IP user on 3.1/24-net to browse the hostnames on other nets, without causing other inconvenience? Hostnames are sometimes related to the names of the person, and I feel that privacy is not sufficiently protected. I set "drop" for 192.168.0.0/16 from 3.1/24, then it did have a desired effect, but I think it's over-killing. I would apprecite your advice!