Ok, you have a router connected to a switch by Ethernet and a PC connected to each of the 8 switch ports, how many collision domains are there?
I originally thought 8 because each switch port with a PC is classed as it’s own collision domain.
Then i read something else that said 2 because a collision domain is a single CSMA/CD network in which there will be a collision if 2 PCs attached to the system transmit at the same time.
Any ideas what the correct answer is????
I seem to have started a war of words here!
Maybe it’s the way i worded the question, maybe i should have said a 24-port switch with 8 PCs and 1 connection to the router. Anyways, i dug out the CCNA books and according to them its 9.
Thanks for the input guys 
First, if you’re talking about a *switch*, and there are 8 computers connected to it *and* a router (so 9 switch ports), then there are 9 collision domains (one out of each port connecting to a computer, and one between the switch and the router).
CSMA/CD applies if you’re running in half-duplex configuration. If it’s a switch running at half-duplex, you’ll still have one collision domain for every switchport just the same (CSMA/CD is a channel access method for half-duplex ethernet networks, and doesn’t *directly* relate to the number of collision domains since you can still have multiple switched, half-duplex segments).
If the scenario includes a hub rather than a switch, however, then the answer is "one collision domain" because the hub cannot put each port onto its own segment. Unfortunetally "hub" and "switch" are frequently misused terms by those who aren’t aware of the differences, so if you are actually talking about a hub then the answer is 1.
If you have an 8port switch, you have 8 collision domains. Switches treat each port as a different bus, and provide the layer2 service of switching for each frame received.
EDIT:
The posters below me are both incorrect. If you have a 8 port switch, you have 8 collision domains. I’m not entirely sure how they’re magically plugging their routers into the switch if they have 8 computers connected to the switch.
If you have an 8 port switch, you have 8 collision domains. If you connect your router to your switch, you have 7 available ports left for your computers.
Re-read your CCNA books, and don’t give out false information.
"HEY BRENT, I’M JUST CONSIDERING THE ROUTER to SWITCH LINK SINCE THE ASKER SAYS THAT ALL 8 eth PORTS ARE OCCUPIED…. WHERE THE HELL IS HE GOING TO PLUG THE ROUTER UNLESS THE SWITCH HAS ANOTHER INTERFACE WHICH HE DOESN’t INCLUDE IN THE PORT COUNT….
…AND I DONT NEED TO REREAD MY BOOKS SINCE I’M ALREADY PUTTING THESE THINGS INTO PRACTICE, FUC7ER"
you might be confusing a switch from a hub.
A hub doesn’t split collision domains because each device use ONE virtual link to transmit/receive (a bus topology); a switch does, since it creates a virtual path to EACH device connected to it.
And you actually have 9 collision domains cause you said you have a router connected to your switch. (1 collision domain for the router-switch link)
As the others have pointed out, 9. Brent seems to have a misunderstanding, it happens though, it is a strange concept at first.