Declarative Networking has been recently promoted as a high-level programming paradigm to more conveniently describe and implement systems that run in a distributed fashion over a computer network. It has already been used to implement various networked systems, e.g., network overlays, Byzantine fault tolerance protocols, and distributed hash tables. Declarative Networking relies upon a rule-based programming language that resembles Datalog and allows one to declaratively specify the flow of networking events. However, the presence of asynchronous communication, distribution, and imperative modification of the program state in Declarative Networking applications have been an obstacle for defining its semantics. Currently, the reference semantics is determined by the runtime environment only, which hinders further application development and makes any efforts to develop program analysis and verification tools impossible. In this paper, we propose an operational semantics for Declarative Networking that addresses these problems. The semantics is parameterized to keep open a design space required at the current stage of the language development. We also report on our first experience with an interpreter for Declarative Networking applications that implements the proposed semantics.