Install Iptables Firewall in Redhat / CentOS Linux

How do I install iptables under Redhat (RHEL) or CentOS or Fedora Linux operating systems?

In most Linux distros including Redhat / CentOS / Fedora Linux installs iptables by default. It has become a standard option in all distros. So there is a good chance that iptables is already installed in your server or workstation. But, you can use the following procedure to verify that iptables has been installed. Open a terminal Window or login using the ssh client to remote server. Make sure you logged in as root user. Type the following command:
# iptables
OR for IPv6 firewall, enter:
# ip6tables
Sample outputs:

ip6tables v1.3.5: no command specified
Try `ip6tables -h' or 'ip6tables --help' for more information.

If iptables is installed, you should get the above message. You can use the following command to view the status of iptables command, enter:
# yum info iptables
Sample outputs:

Loaded plugins: downloadonly, rhnplugin, security
Installed Packages
Name       : iptables
Arch       : x86_64
Version    : 1.3.5
Release    : 5.3.el5_4.1
Size       : 653 k
Repo       : installed
Summary    : Tools for managing Linux kernel packet filtering capabilities.
URL        : http://www.netfilter.org/
License    : GPL
Description: The iptables utility controls the network packet filtering code in the
           : Linux kernel. If you need to set up firewalls and/or IP masquerading,
           : you should install this package.

If the above message does not appear, then type the following command to install iptables, enter:
# yum install iptables
OR to install IPv6 firewall, enter:
# yum install ip6tables