How to block an IP using iptables?
iptables -A INPUT -s xx.xx.xx.xx -j DROP
How to block an IP for a specific port:
iptables -A INPUT -p tcp -s xx.xx.xx.xx --dport PORT -j DROP
How to allow access to an IP?
iptables -A INPUT -s xx.xx.xx.xx -j ACCEPT
How to allow access to an IP to a specific port using iptables?
iptables -A INPUT -p tcp -s xx.xx.xx.xx --dport PORT -j ACCEPT
where, xx.xx.xx.xx is the remote IP address and PORT is the port number you wish to allow/deny access to.
How to block a scanner on your server for example “w00tw00t.at.ISC.SANS” using iptables?
iptables -I INPUT -p tcp --dport 80 -m string --algo bm  \
--string 'GET /w00tw00t.at.ISC.SANS.' -j DROP