Quickly Allowing/Denying IP’s Using Iptables

[Chris Luke]

How do you block an IP using iptables?

iptables -A INPUT -s xx.xx.xx.xx -j DROP

How do you block an IP from a specific port?

iptables -A INPUT -p tcp -s xx.xx.xx.xx --dport PORT -j DROP

(xx.xx.xx.xx is the remote IP address and PORT is the port number you wish to allow/deny access to.)

How do you allow access to an IP?

iptables -A INPUT -s xx.xx.xx.xx -j ACCEPT

How do you 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

(Again, xx.xx.xx.xx is the remote IP address and PORT is the port number you wish to allow/deny access to.)

How do you block a scanner on a server for example "blablabla.at.ISC.SANS" using iptables?

iptables -I INPUT -p tcp --dport 80 -m string --algo bm \
--string 'GET /blablabla.at.ISC.SANS.' -j DROP

More information can be found in our article about the most common iptables rules:
https://www.lcwhost.org/topic/21-basic-and-most-common-iptables-rules/