How to setup and use iptables

What’s iptables?
Iptables is the current Linux firewall and routing service. It controls incoming and outgoing network

How to stop/start/restart iptables?
Basically just like any other Linux service:

# service iptables start
# service iptables stop
# service iptables restart

How to check if iptables is currently running?
Simply call service status and take a look at the result:

# service iptables status
Firewall is stopped.

If you run “service iptables status” and get “Firewall is stopped.” that means that iptables are not running and you should start it with “sertvice iptables start”. If you get some tables with bunch of geek stuff that means that iptables are running.

How to automatically start iptables service on Linux boot?
To enable iptables starting on boot run

# chkconfig iptables on

or run code below to disable it

# chkconfig iptables off

How to block IP address using iptables?
This will block IP from accessing your server. Be careful not to block your IP address.
In command below replace “192.168.0.4” with correct IP address.

# iptables -A INPUT -s 192.168.0.4 -j DROP

After blocking the IP address (adding it to the iptable rules) you must restart iptables calling:

# service iptables restart

How to unblock IP address using iptables?
Similar to blocking, just use ACCEPT instead of DROP:

# iptables -A INPUT -s 192.168.0.4 -j ACCEPT

And after allowing that IP you must also restart iptables:

# service iptables restart

You can also flush your iptables rules by using:

# iptables -F

This will remove all custom added rules.

How to see current rules?
Simply by running following command:

# iptables -L

How to save iptable rules?
Rules created with the iptables command are stored in memory. If the system is restarted before saving the iptables rule set, all rules are lost. For rules to persist through a system reboot, they need to be saved. To save rules, type the following command:

# iptables-save > /etc/iptables.rules

How to load iptable rules?
To load previously saved rules execute:

# iptables--restore < /etc/iptables.rules

How to load iptable rules on Linux boot?
There are few ways and can be different on different Linux distributions. This should work on CentOS. To load rules on system boot make file /etc/init.d/iptableslr

# vi /etc/init.d/iptableslr

and add these two lines to it:

#!/bin/bash
/sbin/iptables-restore < /etc/iptables.rules

The file needs to be executable so change the permissions:

# chmod +x /etc/init.d/iptables
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