Nepal: a path query language for communication networks

Communication networks are typically large, dynamic and extremely complicated. To deploy, maintain, and trouble-shoot 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 be able to discover communication paths between them. 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. This problem is becoming more acute with the advent of software defined networks, where network functions are virtualized and managed in a cloud infrastructure. We represent a communication network inventory as a graph where the nodes are network entities and edges represent relationships between them, e.g. hosted-on, communicates-with, etc. Querying such a graph, e.g. for troubleshooting, using existing graph query languages is too cumbersome for network analysts. Thus, in this paper we present Nepal---a network path query language, which is designed to effectively retrieve desired paths from a network graph. The main novelty of Nepal is to consider paths as first-class citizens of the language, which achieves closure under composition while maintaining simplicity. We demonstrate the capabilities of Nepal by examples and discuss query evaluation. We illustrate how path queries can simplify the extraction of information from a dynamic inventory of a multi-layer network and can be used for troubleshooting.