When you learn networking and network software programming, you learn various aspects of networking. Along with datacom concepts such as network switches, routers and so on. As you learn Ethernet and networking packet protocols and so on, you eventually learn about packets which are destined for single or multiple devices and so based on this criteria packets are classified as unicast packets (or frames L2 context), multicast packets/frames, and broadcast packets/frames.
Usually such a thing can exist in L2 (Layer-2) context say at Ethernet level, and the same it can exist in L3 (Layer-3 or network layer) context say at IP level. For example L2 control packets (actually you are supposed to call them as frames) are usually L2 multicast frames. We can identify these frames from their destination mac addresses. These frames are also called as “slow protocols”.
Here is my detailed multi-episode YouTube Video series on L2 Multicast Frames:
Refer:
Multicast address – Wiki ↗