"iptables is a user-space utility program that allows a system administrator to configure the tables[2] provided by the Linux kernel firewall (implemented as different Netfilter modules) and the chains and rules it stores. Different kernel modules and programs are currently used for different protocols; iptables applies to IPv4, ip6tables to IPv6, arptables to ARP, and ebtables to Ethernet frames." - More on Wikipedia

Configuration

Show the current roles

iptables -L -n

Add a rule to reject traffic from 666.666.*.*

iptables -A INPUT -s 666.666.0.0/16 -j REJECT

Delete the role with -D not -A

iptables -D INPUT -s 666.666.0.0/16 -j REJECT

(Edited 12-11-19)