We are supporting customer with central datacenter and plenty production nodes (factories) connected via WAN. Internal setup of each node/factory is totally independent and IT in factory is able to work when WAN connection is not working for the factory. From monitoring perspective we have central PRTG server in datacenter and remote probes in local nodes (currently we are adding second probe for each node). WAN and local LANs are operated by third party. When WAN is not working - we cannot see status of local node - means we cannot distinguish between "just WAN" or "factory down" situation. As we are responsible for customer application operation, it would be nice to be able to get positive (or negative) alert from disconnected island (e.g via SMS) - like "application works" or at minimum "database server is visible from app server" . If I understand PRTG architecture well - the remote probe cannot do such work. Also clustering over WAN looks like not good solution - we have 14 factory nodes there. What solution would you recommend ?