concept broadcast domain in category system administration
This is an excerpt from Manning's book Learn Cisco Network Administration in a Month of Lunches.
All of these devices that receive the frame are members of the same broadcast domain. A broadcast domain isn’t a thing or a directly configurable setting but rather an emergent property of a network. To better understand this, consider the following analogy.
When you stand alone in the middle of a street, you’re not a crowd. But as a few people gather around you, you become part of a small crowd. As more people gather around you, you become part of a larger crowd. You don’t change, but you become part of a crowd by virtue of how many others gather around you. Similarly, a device becomes part of a broadcast domain by virtue of which devices it receives flooded frames from.
As the size of the broadcast domain grows, communication becomes more difficult. Consequently, a broadcast domain containing hundreds of devices performs poorly. But modern organizations require network connectivity among thousands of devices. And just having connectivity isn’t good enough. The network still has to be fast and reliable.
The solution is to limit the size of the broadcast domain. This means breaking it into multiple, small broadcast domains that somehow can still communicate with each other.
Going back to our example, the simplest way to split the broadcast domain is to remove the Ethernet cable connecting Switch1 and Switch2, as shown in figure 2.7. Note that the switches aren’t connected in any way. That’s the easy part. Here’s the hard part: My computer and the database server reside on two separate broadcast domains. There’s no way my computer and the server can communicate. What do you do? You can’t just plug the switches back together because that would re-create the original, single broadcast domain.