Traffic must pass through the firewall in order for the firewall to manage and control it. Physically, traffic enters and exits the firewall through interfaces. The firewall determines how to act on a packet based on whether the packet matches a Security policy rule. At the most basic level, each Security policy rule must identify where the traffic came from and where it is going. On a Palo Alto Networks next-generation firewall, Security policy rules are applied between zones. A zone is a grouping of interfaces (physical or virtual) that represents a segment of your network that is connected to, and controlled by, the firewall. Because traffic can only flow between zones if there is a Security policy rule to allow it, this is your first line of defense. The more granular the zones you create, the greater control you have over access to sensitive applications and data and the more protection you have against malware moving laterally throughout your network. For example, you might want to segment access to the database servers that store your customer data into a zone called Customer Data. You can then define security policies that only permit certain users or groups of users to access the Customer Data zone, thereby preventing unauthorized internal or external access to the data stored in that segment.