Block a range of IP addresses from reaching your server

When your Linux server gets bombarded with malicious requests the quickest and easiest thing is to block the offending IP address (or the entire range) using iptables:

To block just one IP address:

$ sudo iptables -A INPUT -s 103.10.86.53 -j DROP

To block 103.10.86.* addresses:

$ sudo iptables -A INPUT -s 103.10.86.0/24 -j DROP

To block 103.10.*.* addresses:

$ sudo iptables -A INPUT -s 103.10.0.0/16 -j DROP

To block 103.*.*.* addresses:

$ sudo iptables -A INPUT -s 103.0.0.0/8 -j DROP

Note: Be careful not to unintentionally block legitimate traffic from reaching your server.

List the rules for the INPUT chain:

$ sudo iptables -L INPUT -v