We currently see no way to apply the request-response filtering policy for IP multicast applications. In most multicast applications, it is not even meaningful to attempt to classify packets as either requests or responses.
Different applications can use the same multicast address simultaneously without restriction.
Even within a single application, a single multicast address can be used simultaneously for different purposes. A packet filter cannot discriminate between these different uses of the multicast address without having considerable application-specific knowledge. Furthermore, filtering any of these three classes of packets would significantly disrupt a wb session. If the dissemination packets are dropped, then local clients only see the locally-contributed whiteboard data. If the retransmission request packets are dropped and only local hosts possess the requested data, then no outside participant will ever see that data.