Iptables firewall rule chains configuration guide on linux with examples for beginners

In this article we learn how to create iptables rules on linux operating system, how to listing configured iptables rules and how to flush all listing rules of iptables. By default iptables is preinstalled for all linux distribution. If iptables is absent we execute the following command .

#yum install iptables

Iptables firewall rule chains configuration guide on linux with examples for beginners

What is iptables

Iptables is the command line firewall utility for linux operating system. We can create the chain rule on firewall based on the rule when system try to establish connection it checks the list of the rules if the rule does not found it takes the default action. Basically iptables uses to allow or block the traffic based on the iptables chain rules .

Action For the iptables

Three types of actions can be performed on linux by setting the iptables.

Accept: Allow the traffic
Drop: Drop the traffic
Reject: Don’t allow the traffic.

Types of chains in iptables

Three types of chains are available for iptables rules .

Input: Input chain uses for the incoming connection.
Forward: Forward chain uses to forward the traffic .
Output: Output chain uses for the outgoing connection.

Allow/deny the traffic configuration on iptables

Suppose we have source ipaddress that is 192.168.1.2 and network is 192.168.1.0/24.We want to drop traffic from source ipaddress that is 192.168.1.2.To do this activity we execute the below command.

#iptables -A INPUT –s 192.168.1.2 –j DROP

Now we want to drop the traffic the whole source network we con execute the below command.

#iptables -A INPUT –s 192.168.1.0/24 –j DROP

Allow/deny the traffic for the particular port configuration on iptables

Now we are going to allow the ssh port for the source ipaddress 192.168.1.2.To do this we mention the protocol that is tcp and the port no or port name by executing the below commad.

#iptables -A INPUT –p tcp –s 192.168.1.2 --dport 22 –j ACCEPT

On iptables at the booting time

To start the iptables after the booting automatically we execute the below command.

#chkconfig iptables on

Start/Save/listing the iptables rules

To start iptables we execute the below command .

#service iptables start

After configured the iptables rule we need to save the iptables configuration to do this we execute the follwing command.

#/etc/init.d/iptables save

To listing the iptables rule we execute the below command.

#iptables –L

To get the packet and byte information we use “-v” switch and to get all information numerically we use “-n” switch and to flush all information we use “-F” switch.

Conclusion

You can get many switch function of the iptables command. To know all switches function go to the man page of the iptables command using “man iptables”.

Iptables firewall rule chains configuration guide on linux with examples for beginners

Iptables firewall rule chains configuration guide on linux with examples for beginners