According to an example aspect of the present invention, there is provided a method comprising receiving, by a network repository function, a request from a network function, wherein the request comprises a string associated with an instance identity of the network function, determining, by the network repository function, a type of the instance identity of the network function from a set of instance identity types, determining, by the network repository function, the instance identity of the network function based on the string associated with the instance identity of the network function and the type of the instance identity of the network function and transmitting, by the network repository function, a response to the network function, wherein the response depends on whether the instance identity of the network function was found in a list of network function instances registered at the network repository function.