Answer:
iptables
Explanation:
On a Linux system, iptables command allows us to modify settings of the built-in packet filtering firewall.
Iptables is used to set up, maintain, inspect and update the tables of IP packet filtering rules on Linux.
For example,
# iptables -L -n -v
# iptables -I INPUT <rule number> -s <source-ip address> -j DROP