Classic zones are primarily intended for backward compatibility with older versions of the Centrify agent. If you upgrade the agent to version 5.x or later, you can migrate any or all of your classic zone information into one or more hierarchical zones.
Migrating a classic zone to a hierarchical zone is a multi-step process that requires some initial planning. For example, the first step in the migration changes the zone type but does not change any existing zone information, including the computer accounts that are joined to the zone. To take full advantage of the hierarchical zone after migration, however, it is likely that you will need to modify some of your existing zone information and move computer accounts into different zones.