Ubuntu - Firewall - Blocking an IP address using the route command

To add an IP to 127.0.0.1:

route add 192.16.1.100 gw 127.0.0.1 lo

Also it can be rejected by:

route add -host 192.168.1.100 reject

Block entire subnet 192.168.1.0/24:

route add -net 192.168.1.0/24 gw 127.0.0.1 lo

To delete this rule:

route del -host 192.168.1.100 reject