If your switch does IGMP Snooping, and your host OSes play along, IP multicast should only go to the ports that care. Caveat: I've never done much with multicast.

> * If IPV4 UDP multi-cast is used, the switch is obliged to forward all mcast packets to all 50 machines.

Nope. The switch (i've only used cisco/arista so ymmv) will keep a map of resolved macs that have made IGMP subscriptions and only forward to hosts thus subscribed to ip:port groups. View on your subscribing host (netstat -g). This is done in switch hardware, however new subs/changing macs is done in software.

Secondly there is/was (i might be out of date) a bug/wontfix in mcast subs in Linux that no matter the group unique IP, if you subbed on a port it would be forwarded to any group with the same port number. So isolate all services using unique port numbers if you have multiple consumers on one host. (see `man 7 ip` setsockopt IP_ADD_MEMBERSHIP)

Not really, if you use IPv4 BROADCAST the traffic will go to all machines. If you use multicast and IGMP support is turned on in the switch the data will only be forwarded to receivers that care about it.