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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →An IP multicast address identifies a destination group, not a single receiving interface. A sender transmits to the group address, and hosts that have joined the group are the intended recipients. This differs from unicast, which addresses one interface.
What an IP multicast address means
In IPv4, RFC 1112 describes a multicast group as a “host group”: a set of zero or more hosts identified by one IP destination address. The address therefore names the group as a whole; it does not identify a particular member or specify how many members there are.
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Hosts can request to receive traffic for a group, then join or leave it over time. Membership is dynamic, so the intended recipients may change while a sender continues transmitting to the same destination address.
How to recognize multicast addresses
IPv4
IPv4 multicast addresses occupy the range 224.0.0.0 through 239.255.255.255, represented by the prefix 224.0.0.0/4. An IPv4 destination in this range denotes a multicast group rather than an individual receiving interface.
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IPv6
IPv6 multicast addresses begin with the prefix FF00::/8; their first eight bits are all ones. The remaining address fields encode multicast properties, including flags and scope.
What membership and scope mean
Membership indicates which hosts have requested reception for a multicast group. It is not a guarantee that every member will receive every datagram.
Scope limits where multicast traffic is intended to be delivered. IPv6 includes a scope value in the multicast address itself, such as link-local or wider scopes. IPv4 has designated ranges for different uses, including addresses intended for local network control. Scope is not the same thing as membership: one describes the intended reach of traffic, while the other describes interested receivers.
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IP multicast delivery is best effort. A sender can address a group, but the IP service does not promise that every member receives every datagram, nor that datagrams arrive in the same order in which they were sent. Applications that require reliability, acknowledgments, or ordering must provide those features separately.
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