Linux Iptables Setup Firewall For a Web Server

The default iptables configuration on CentOS or RHEL does not allow access to the HTTP (TCP PORT # 80) and HTTPS (TCP PORT # 443) ports used by the Apache web server. You can modify settings using any one of the following three methods:

1. /etc/sysconfig/iptables : Edit this file to allow or deny access to the Apache Web Server IPv4. You also need to edit the /etc/sysconfig/ip6tables file to allow or deny access to the Apache Web Server IPv6 ports.
2. system-config-firewall-tui command (runs on ssh text based session) or system-config-firewall command (run on GUI based session) : This is a graphical user interface for setting basic firewall rules. This tool will always overwrite /etc/sysconfig/iptables file.
3. /sbin/iptables command : Use iptables command directly to modify/append/add firewall rules. The rules can be saved to /etc/sysconfig/iptables file with /sbin/service iptables save command.
4. /usr/sbin/lokkit command : This is a basic firewall configuration tool, designed for ease of use and configuration. This tool also supports SELinux config option. This tool is considered as deprecated and not covered in this faq.

Method # 1: Edit /etc/sysconfig/iptables file (recommend for advanced users)

Edit the IPv4 /etc/sysconfig/iptables, enter:
# vi /etc/sysconfig/iptables
Add the following lines, ensuring that they appear before the final LOG and DROP lines for INPUT chain:

## allow everyone to access port 80 and 443 (IPv4 Only)##   -A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT -A INPUT -m state --state NEW -p tcp --dport 443 -j ACCEPT

Save and close the file. Restart the IPv4 iptables service:
# service iptables start
Edit the IPv6 /etc/sysconfig/ip6tables, enter:
# vi /etc/sysconfig/ip6tables
Add the following lines, ensuring that they appear before the final LOG and DROP lines for INPUT chain:

## allow everyone to access port 80 and 443 (IPv6 Only)##   -A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT -A INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT

Save and close the file. Restart the IPv6 iptables service:
# service ip6tables restart

Method # 2: Firewall configuration GUI/TUI tool (recommend for new users)

The system-config-firewall command is a graphical user interface for setting basic firewall rules. You need to have KDE or Gnome installed on the system. Open a terminal and type the following command as root user:
# system-config-firewall
Sample outputs:

Fig.01: GUI tool in action

Select services such as WWW, SSH, HTTPS to open port for everyone. Click on Apply button. This tool will generate /etc/sysconfig/iptables as follows:

Sample RHEL CentOS Linux /etc/sysconfig/iptables files

A note about text based config tool (recommend for remote server with ssh access)

The sysystem-config-firewall-tui is a command line tool without having the GUI installed on the server:
# system-config-firewall-tui
Sample outputs:

Fig.02: system-config-firewall-tui in action

Select Enabled and Press Tab to select “Customization” :

Fig.03: Opening a port 80

Scroll down/up and select SSH, WWW, Secure WWW (HTTPS) and other required ports you wish to open. Finally, select Close button. Finally, press OK button to activate new firewall settings.

Method # 3: /sbin/iptables command line utility (recommend for advanced/expert users only)

Type the following iptables command as root user to open port 80 / 443:

## open port 80 and 443 for everyone ## /sbin/iptables -A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT /sbin/iptables -A INPUT -m state --state NEW -p tcp --dport 443 -j ACCEPT   ## save newly added firewall rules ## /sbin/service iptables save   ## verify new firewall settings /sbin/iptables -L -n -v /sbin/iptables -L INPUT -n -v /sbin/iptables -L INPUT -n -v | grep :80 /sbin/iptables -L INPUT -n -v | grep :443

The following rule allows access to port 80 and 443 only to 192.168.1.0/24

## Find an appropriate network block, and network mask ## representing the machines on your network which should operate as ## clients of the Apache Web-server   ## Open port 80 and 443 for 192.168.1.0/24 subnet only ## /sbin/iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 80 -j ACCEPT /sbin/iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 443 -j ACCEPT   ## save newly added firewall rules ## /sbin/service iptables save   ## verify new firewall settings /sbin/iptables -L -n -v /sbin/iptables -L INPUT -n -v /sbin/iptables -L INPUT -n -v | grep :80 /sbin/iptables -L INPUT -n -v | grep :443

You can block/drop the IP address 202.54.1.1 or subnet 202.54.1.2/29 as follows using iptables:

## Block access to port 80 ## iptables -A INPUT -s 202.54.1.1 -p tcp --dport 80 -j DROP iptables -A INPUT -s 202.54.1.2/29 -p tcp --dport 80 -j DROP   ## block and drop access to port 443 (secure apache web-server) iptables -A INPUT -s 202.54.1.1 -p tcp --dport 443 -j DROP iptables -A INPUT -s 202.54.1.2/29 -p tcp --dport 443 -j DROP   ## save newly added firewall rules ## /sbin/service iptables save   ## verify new firewall settings /sbin/iptables -L -n -v /sbin/iptables -L INPUT -n -v | grep 202.54.1.1

Note: To unblock an IP i.e. delete the IP address 202.54.1.1 listed in iptables type the following command:
iptables -D INPUT -s 202.54.1.1 -j DROP