In this section, we will continue our work on the Apache2 Web Server we started in the last section, so as to make it accessible for other computers in our subnetwork. Also, we will give you a brief introduction to Linux firewalls in CentOS 7.
As briefly mentioned in the first section of this chapter, a network connection is always made through a combination of an IP address and the port, which together is called a socket address. Now, every Linux network service, such as a mail or web server, must be connected to an IP address and the port so that we can establish a connection to it at all from a different computer in the network or from the same local one:
When we are talking about network communication, we often refer to this as "a service is listening to IP address a port b". For example, our web server is listening on...