What exactly is a "Collision Domain" and "Broadcast Domain"? I'm a bit confused

Hi! Criminal IP Forums!
What exactly is a “Collision Domain” and “Broadcast Domain”? I’m a bit confused.

CD= Is all devices connected to a hub?
Broadcast domain = All devices connected to a switch?


They are separate beasts. Collision domain refers to communication collisions - transmission and receiving. If more than one device transmits at the same time in particular network segment, collision will occur. That is why CSMA/CD was invented, and that is why switches were brought into play because each port in switch is a separate collision domain. Wifi still works this way, all devices connected to one wifi network will cause collisions if they will transmit at the same time.
Hubs are not used anymore really.

shatteredglassedge is right. and more I want to say that Broadcast domain is a segment of network in which layer2 broadcast traffic can reach all devices. So yes, in the flat network it will be all devices connected to certain switch, but broadcast domains can be bridged together. They can also be divided using vlans, and then you can have many broadcast domains on one switch, so I would not use that blunt division. Do not look at CD and BD as device dependent. They are different things, have different features and tasks. They co-exists in networks.

Ahhhh ok thank you. Vlans can be used to both bridge and divide Broadcast domains?

No, they divide them.

Trunking connects multiple Vlans?

It does not really connect them, it allows traffic from multiple vlans pass the same link.

You can bridge BDs with unmanaged switch, for example, or with old school bridges, but nobody does it anymore. I used it as example that it is not that blunt that one switch is for sure one BD. And vlans divide BDs, the same as routers divide BDs.

Ok. Each interface on a switch though has its on BD? Guess I need to do some more studying haha

No, each interface on a switch is separate collision domain. broadcast domain on the switch can be one, if you choose to, or there can be many if you set vlans. Yeah, it will be helpful for you to read around :slight_smile: N+ unfortunetelly simplifies some stuff to the point of distortion :confused: And some COmptia teachers do it to. They introduce these blunt descriptions, and it only confuses people…

Ahhh all ports on a switch are part of a BD. But each port has its own CD

Yes! Remember however that there can be many DBs in one switch. You can have one, you can have 3, you can set it to be each port in different vlan… But each port is a separate collision domain always. Broadcast domains you ‘build’ the way you want them to be.

Ok. Thanks for your help. Apparently I need to hit the books lol

Yeah, you are mixing a lot. It is fine, nobody knows stuff right away, but it will be easier for you if you understand these things. :slight_smile: