At present, The management IP range can only be expanded under the same subnet. According to existing range, either the last IP can be forward extended or the first IP can be backward extended. But we cannot add an entirely different range from the same subnet. So the expansion of range is subnet bound, which is fixed. But when the range gets exhausted and a user wants to deploy more system VMs, then the operation would fail. The purpose of this feature is to expand the range of management network IPs within the existing subnet. It can also delete and list the IP ranges.
Please find the FS here : https://cwiki.apache.org/confluence/display/CLOUDSTACK/Expansion+of+Management+IP+Range