A network security zone is an administrative name for a collection of systems that require the same access control policy. IP addresses are used to map systems into security zones. This requires that the IP addresses used in your multilevel secure network be predictably associated with a single system or group of systems with the same access control policy. A network security zone can contain a single IP address or any combination of IP addresses and subnetworks. All of the IP addresses in a security zone must have the same security label, though all IP addresses with the same security label do not have to be in the same security zone.