Modern communication networks are large, dynamic, and complex. To deploy, maintain, and troubleshoot such networks, it is essential to understand how network elements such as servers, switches, virtual machines, and virtual network functions are connected to one another, and to be able to discover communication paths between them. For network maintenance applications such as troubleshooting and service quality management it is also essential to understand how connections change over time, and be able to pose time-travel queries to retrieve information about past network states. With the industry-wide move to SDNs and virtualized network functions [13], maintaining these inventory databases becomes a critical issue.