IP Multicast Group Management
A multicast router periodically sends queries to all hosts participating in IP Multicast on the special 224.0.0.1 all-hosts group.
Each relevant host sets a random timer for each group it is a member of. When the timer expires, it sends a report message on that group multicast address.
Each host that gets a report message for a group cancel its local timer for that group.
When a host joins a group it announces that on the group multicast address.
Extensions to IP within one sub-net (IGMP)