A method (30) is provided for a first network node (22) of ensuring validity of a service request. The method (30) comprises receiving (31), from a second network node (13), a first piece of information relating to a destination identifier of the service request; receiving (32), from a communication device (12), a request for the service, the request comprising a second piece of information relating to the destination identifier; and determining (33) the service request to be valid if establishing a correspondence of the first piece of information with the second piece of information, else determining the service request to be invalid. Methods in a second network node (13) and in a communications device (12) are also provided and corresponding devices.