Nullroute IP using route command

Suppose that bad IP is, type following command at shell:

# route add gw lo

You can verify it with following command:
# netstat -nr

# route -n

You can also use reject target (thanks to Gabriele):
# route add -host IP-ADDRESS reject
# route add -host reject

To confirm the null routing status, use ip command as follows:
# ip route get

RTNETLINK answers: Network is unreachable

Drop entire subnet
# route add -net gw lo

You can also use ip command to null route network or ip, enter:
# ip route add blackhole
# route -n
How do I remove null routing? How do I remove blocked IP address?

Simple use router delete command,
# route delete

This is cool, as you do not have to play with iptables rules.