Most current kernels and available routers do support IP multicast technology, although service providers are sometimes reluctant to deploy it. A general discussion of IP multicast technology is beyond the scope here. There is no intrinsic limit on the number of senders or receivers and senders can be receivers and vice versa. The IANA has assigned multicast group address 224.0.1.1 to NTP, but this address should be used only where the multicast span can be reliably constrained to protect neighbor networks. However, there is a subtle difference between broadcasting and multicasting.
Broadcasting is specific to each interface and local subnet address.
If more than one interface is attached to a machine, a separate broadcast command applies to each one separately. This provides a way to limit exposure in a firewall, for example. IP multicasting is a different paradigm. A multicast message has the same format as a broadcast message and is configured with the same broadcast command, but with a multicast group address instead of a local subnet address. By design, multicast messages travel from the sender via a shortest-path or shared tree to the receivers, which may require these messages emit from one or all interfaces, but carry a common source address.