I'm currently learning IPv6 and they mentioned broadcast is gone in IPv6 and replaced with multicast and unicast.
Are there some situations where multicast or unicast is better over the other in setups?
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"broadcast" was replaced with more specific multicast methods. All-station-broadcast would become a huge mess given the available size of IPv6 LANs -- imagine thousands of nodes broadcasting ARPs looking for each other. (it falls apart in IPv4 already) Multicast Neighbor Discovery limits who hears the requests and answers, in a network with multicast aware hardware.
And there are specific link-local addresses to speak to everyone on the link in the same manner as IPv4 broadcast, without using globally routable addresses.
There is so much different multicast possible in IPv6... are you talking about multicast traffic (for streaming) or generic multicasts?
FF:: is the multicast range....
FF02:: is Link Local scope, with FF02::1 being the equivalent of the Broadcast Address of a subnet in IPv4 FF02::2 is Link Local, All routers FF05:: is Site Local, again ::1 for All Node, ::2 for All Routers...
Basically, IPv6 multicasr permits a better targetting of many types of traffic.
Now, for Using Multicast for streaming, it's a lot like in IPv4, with PIM Sparse Mode (no more Dense Mode), MLD (replacing IGMP), Rendez-Vous Points, etc. There are differences, but not as much as replacing Broadcasts by Scoped Multicasts
When a node issues a broadcast packet, the packet is replicated to all other hosts on the medium or subnet. So if you have a 32 port switch, and one node issues a broadcast, it goes out each of the 32 ports. This takes away potential bandwidth from everyone else, especially if it is overused.
Multicast requires that interested parties "subscribe" to a multicaster. Multicasted traffic only replicates to previously identified subscribed parties, so there is less bandwidth consumed by unwanted traffic.
So multicast is really the better way to go if it is possible and supported by the software and hardware.