Blocking an IP address using route command.

To add an IP to 127.0.0.1:
root# route add 192.16.1.100 gw 127.0.0.1 lo

Also it can be rejected by:
root# route add -host 192.168.1.100 reject

Block entire subnet 192.168.1.0/24:
root# route add -net 192.168.1.0/24 gw 127.0.0.1 lo

To delete this rule:
root# route del -host 192.168.1.100 reject