To enable fast startup of an audio/video receiver device and quick receipt of a first audio/video stream, is provided a method in an intermediate device in between a router device and the receiver device. The intermediate device snoops the communication between the audio/video receiver device and the router device to determine the protocol version of the router device to subscribe to a transmission of an audio/video stream and to determine that the receiver device is starting up. If the protocol version is a version not supporting Source Specific Multicast and the receiver device is booting, a message indicating the protocol version is transmitted to the receiver device during starting up of the receiver device so that the latter can switch to a protocol version supported by the IP multicast router device without further delay.