In this chapter, we will begin to configure services that require communication between hosts over the network. Most Linux distributions will default to running a host-based firewall, iptables. If you want your hosts to communicate with each other, you have two options: turn off iptables or configure iptables to allow the communication.

I prefer to leave iptables turned on and configure access. Keeping iptables is just another layer on your defense across the network. iptables isn't a magic bullet that will make your system secure, but it will block access to services you didn't intend to expose to the network.

Configuring iptables properly is a complicated task, which requires deep knowledge of networking. The example presented here is a simplification. If you are unfamiliar with iptables, I suggest you research iptables before continuing. More information can be found at http://wiki.centos.org/HowTos/Network/IPTables or https://help.ubuntu.com/community...