A network monitoring system monitors a data network and enables observation of the data network state in the present or any arbitrary previous time. The system maintains an object-oriented network model that mirrors the state of network devices. A network data repository stores and maintains the network model. The network model retains a history of network events, enabling the system to reconstruct the state of all or a portion of the devices in the network at any previous time. The network data repository detects network devices on the data network to be monitored, communicates with network devices, monitors the state of network devices, receives and records network events, provides device and network state information to client applications, and manages data storage. Client applications can rewind and replay the history of the network model, allowing the observation of network devices and all of their state data at any prior time.