I'd like to stop others from seeing my ports as filtered in the nmap standard scan (unprivileged). Let's say that I have the following ports open: 22, 3306, 995 and a firewall configured like this:
-A INPUT -p tcp -m tcp --dport 22 -j DROP -A INPUT -p tcp -m tcp --dport 3306 -j DROP -A INPUT -p tcp -m tcp --dport 995 -j DROP
This is the result of an nmap scan:
[+] Nmap scan report for X.X.X.X Host is up (0.040s latency). Not shown: 90 closed ports PORT STATE SERVICE 22/tcp filtered ssh 995/tcp filtered pop3s 3306/tcp filtered mysql
It displays these ports as filtered, because my server didn't reply RST for SYN. Is there a way to modify this behaviour? For example: if the iptables firewall blocks a port, reply RST for SYN, instead of remaining silent (not replying anything)?