Securing the Perimeter
First, Tom had to establish some basic defenses to protect his network from the outside so he could direct his time to securing the servers and the inside of the network. He built a firewall for their Internet connections using a program called Turtle Firewall (covered in Chapter 3). Using this software and an old server that wasn't being used for anything else, he configured this machine to allow connections only from the inside of the network out wards; all incoming connections not requested from the inside were blocked. He made some exceptions for the public servers operated by his new employer that needed access from the outside. He was even able to set up a Virtual Private Network (VPN) through the firewall so that his users could connect securely from the outside (see Chapter 3). Now he was able to repel most of the basic attacks coming from the Internet and focus on closing up the other holes in the network.