all pix firewalls provide at least two interfaces, which by default, are called outside and inside, and are assigned a security level of 0 and 100, respectively. a lower security level indicates that the interface is relatively less protected than the higher security level. typically, the outside interface is connected to the public internet, while the inside interface is connected to your private network and is protected from public access.

    many pix firewall models provide up to eight interfaces, to allow you to create one or more perimeter networks, also called bastion networks or demilitarized zones (dmzs). a dmz is a network that is more secure than the outside interface but less secure than the inside interface. you can assign security levels to your perimeter networks from 0 to 100. typically, you put mail servers or web servers that need to be accessed by users on the public internet in a dmz to provide some protection, but without jeopardizing the resources on your internal network.