What is the purpose of a zone in JUNOS Software?
A.
A zone defines a group of security devices with a common management.
B.
A zone defines the geographic region in which the security device is deployed.
C.
A zone defines a group of network segments with similar security requirements.
D.
A zone defines a group of network segments with similar class-of-service requirements.
http://www.juniper.net/techpubs/software/junos-security/junos-security95/junos-security-swconfig-security/id-29204.html
On a single device, you can configure multiple security zones, dividing the network into segments to which you can apply various security options to satisfy the needs of each segment.