Each domain always has an assigned interface zone with the same name. This is an object zone.
This zone is the only interface that makes the domain available to higher-level domains, so-called parent domains. Any object zones from the parent domain can receive the interface zone as a subordinate sub-zone.
You can link this interface zone to other object zones in the same domain. This allows you to pass on the content of individual object zones to higher-level domains via the interface zone.
All zones that are linked to the interface zone are called shared zones, as these zones are available in a higher-level domain. The zones that are not linked to the interface zone and are therefore not available in a higher-level domain are called local zones.