What are broadcast domains?

A broadcast domain is like a big room where everyone can hear the same message when someone shouts it out.

Imagine you're in a classroom full of kids. If one kid yells, “Who wants to play tag?”, everyone in that room hears them, even if they’re not sitting right next to them. That whole classroom is like a broadcast domain because all the kids can hear the same shout.

Now imagine there are two classrooms connected by a hallway. If the kid from the first class yells, only the kids in that first classroom hear it, the second classroom doesn’t know what’s going on. But if you put up a loudspeaker in the hallway, then both classes can hear the same message at once. That's like connecting broadcast domains.

If more kids come into the classroom, they still all hear the same shout, the broadcast domain gets bigger. But if someone moves to another classroom and starts shouting there, that’s a new broadcast domain.

So, in simple terms: A broadcast domain is where everyone can hear the same message, just like a big room full of kids listening to one kid yell.