It has already been mentioned that group administration via IGMP is not the responsibility of the package sender. However, as with all other stations on the network (including the receiver) involved, this output host must support multicast connections. Receiving client requests for inclusion in a specific multicast group and notifying clients in the event of incoming multicast data streams is handled by the individual network routers on the path between the sender and receiver.
For this purpose, the Internet Group Management Protocol offers functions that a station can use to inform the router assigned to it that it is to be included in a multicast group. On the other hand, it enables the routers to remember outgoing interfaces of those receiver devices that are to receive certain IP multicast data streams to be able to send specific reports as soon as corresponding data is received. Multicast groups are characterized by their specific addresses from the 224.0.0x range. In most cases, the first point of contact for a device is the home internet router, which receives the membership application and forwards it to the next network node, typically the internet service provider’s router. This communication chain ends with the router of the data stream transmitter, which in turn duplicates the IP packet if required, if it has several outgoing interfaces to serve.