collision vs. broadcast domain: Hub, Switch and Router


In an Ethernet network, a collision domain is a group of nodes that hear each other. When one node is talking, everyone is listening. When one node is using the hub, all other nodes must wait. Collision occurs when two nodes send signals at the same time. Thus, hub would create a collision domain.

If the collision domain gets too large, you’ll start running into traffic problems. If you try to daisy chain or cascade some hubs, you actually expand the collision domain.The more hubs we use on a local network, the larger collision domain we create.

A switch is much smarter than a hub because it gives every conversation the full bandwidth of the network. When node A is talking, only its receiver B can hear. When node C is talking, only its receiver D can hear. Now communications on a network become one-to-one conversations. If A and B are talking at the same time, no collision would occur. Thus, switch separates the collision domain.

Router operates at layer 3, or the network layer of the OSI model. Routers only forward IP packets based on IP address. Routers not only separate collision domains, but also separate broadcast domains.

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  1. Nicely presented! Just a comment for the last animation; even the links between two switches, or one switch and one router, or two routers are considered to be collision domains. Correct me if I'm wrong (:

  2. That was a great explanation. Was confused a bit reading Lammle’s CCNA book but your video cleared up my confusion right away. Thanks for this!

  3. Hello, sony. Thanks for this video about the broadcast domain and collision domain. You are explained well. It is very helpful to me understanding. One more I have not quite understand" broadcast domain " is a group of notes. So it means that all the data are transferred from switch. It became to a group of notes basically saying. Right?
    I almost get the broadcast domain but I have a little confusion. 😀

  4. I still need a bit more understanding. Great video. I want to take my CCNA composite in December. I still need to work on STP , routing table, some VLSM and other things from theory also.

  5. With the AR and VR being implemented into the new Web 3.0 upgrade, where would AR/VR fall under in the OSI model? Through presentation, transport, or strictly application? Just curious, but love your videos, just became a SUPER FAN!

  6. Sunny Thank you very much…You are simply too good…After reviewing a bund of materials all your explanations Topics are the only ones that I could remember even in my dreams…
    The visual graphics are simple and comprehensive.
    Thank you very much for changing the rhythm of networking from Theory to practical.


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