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Is there any functional difference between:

A) Broadcasting to a range of addresses

B) Putting the range of addresses into a subnet and broadcasting to that subnet

Would it matter if there was a layer 2 switch in the network?

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Multicasts are only forwarded to ports/nodes that have subscribed to that specific multicast (if everything is set up correctly). In contrast, broadcasts are forwarded to all ports.

If you configure multiple IP subnets within a single layer-2 segment, even directed broadcasts will still be forwarded to all ports: IP broadcasts are translated to Ethernet broadcasts, no matter if they are limited (255.255.255.255) or directed (e.g. 192.168.0.255 for 192.168.0.0/24). The only difference a directed broadcast makes is that non-subnet members will ignore it (at the IP stack).

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Broadcast is sent to a single broadcast address to which all hosts must listen and process anything sent to that address. This interrupts every host on the LAN, and it uses bandwidth on every LAN link. Switches will flood a broadcast frame to every other switch interface.

Multicast is sending something to a multicast group address to which only some LAN hosts may subscribe, and it only interrupts the hosts which have subscribed to the multicast group. Modern switches can snoop on the IGMP messages sent by hosts to a multicast router and use the information to limit where the multicast frames are sent, only using bandwidth and sending multicast frames to the interfaces where there are hosts that have subscribed to the multicast group.

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