An office network consists of one two-port router connected to a 12-port switch. A four-port hub is also connected to the switch. On this particular network, which of the following is the number of collision domain that exist?
A. 3
B. 12
C. 13
D. 14
E. 15
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Except for the hub, each device has a collision domain.
1) Router has 2 interfaces = 2 collision domains.
2) Switch has 12 interfaces = 12 collision domains.
3) Hub has no collision domains
If you connect a router with a switch they share a collision domain. So the router has 1 left and the switch has another 11 left.
Since the HUB doesn’t have collision domains, then the hub in the 2nd collision domain of the switch.
———(Router)————–[Switch]————–[HUB]
1 CD 1CDv 11CD = 13CD
A 12 port switch creates 12 collision domains (one for each port) and 1 broadcast domain by default if only 1 VLAN is used. Routers don’t create collision domains and Hubs have a single collision domain regardless of port count. Two router ports and one hub port are wired to switch ports. Both router and hub will share collision domain with upstream switch port they are connected to. Therefore, total number of collision domains in this scenario would be 3 because there are 3 links from router and hub to the switch. So, based on what we see in question, there are total of 3 collision domains. If all switch ports are connected to client PCs, then there will be total of 12 collision domains.
Reference: CompTIA Network+ N10-007 book by Anthony Sequeira Ch.3 Figures 3.26, 3.27 & 3.28.
12-portswitch but the switch is connected to the router with its uplink port so the collisions are 13 along with the hub that also connected to the switch. And, at last the router’s other interface which is not connected with the switch. So, 13+1=14.
Answer is 14 100%.
You’re getting close to the right answer! I think the answer is 3 based on given scenario in the question. You missed the other 2 router connections to the switch. Total of 3 switch port links gives it 3 collision domains.
Since everyone has a comment on this, I am afraid I have to put my 2 cents in too.
the way i am looking at it is totally different than everyone else.
If you read the question carefully, it is saying just one hob is connected to the switch and nothing else. all other 11 ports are empty.
it could’ve been a 12 port switch or 24 ports switch, when it has just one device connected to it, therefore it has just one collision domain at any given time. and one from switch to router, there fore 2 only.
Maybe i am wrong, but it sure is confusing.
https://www.dropbox.com/s/dm2ttvlt6dw9yef/collision%20domain.jpg?dl=0
You’re getting close to the right answer! I think the answer is 3 based on given scenario in the question. You missed the other 2 router connections to the switch. Total of 3 switch port links gives it 3 collision domains.
I typically don’t rely on test dumps for certs…soooooo glad I did it this time. There are more problems with this exam than having wall to wall carpet in your shower
HHAHAAH WHAT
Logical network diagram = 13 collision domains
Physical network diagram = 14 collision domains
The problem is the question doesn’t specify for which its looking.
Should be 13
The router have 2 collision domain
one of these is connected to the switch which has 12 – 1 (for domain already counted at the router) = 11 other domains (2+11)
the hub is connected to one of the switch’s ports and form one domain (still 2+11)
answer is 13 collision domains
now if they said any extra ports that may change but they didn’t
I think the best way to understand this is to pretend as if computers and links are attached to the hubs and switches. If you count the collision domains based on the links you can count how many collision domains are there in total.
If you connect a hub to a port on a router, even if there are other links from the hub to the other computers, there’s 1 collision domain from that segment. Now, if you add 12 hypothetical computers and 12 links from those computers to the switch, you are effectively creating 12 collision domains. However, you also need to take into consideration the link from the switch to the router which also creates another collision domain.
If you count the links that you have in total, you would get:
1 Link from Router to Hub = 1 Collision Domain
1 Link from Router to Switch = 1 Collision Domain
12 Links from Switch to Hypothetical Computers = 12 Collision Domains
1 + 1 + 12 = 14 Links
I used this youtube video to try to help me understand
Mostly typing this here to help me remember and incase anyone else needs the explanation
It is 14 as the question makes you assume all ports are used and its a Managed switch
The router has 2 CD (Collision Domains), 1 is plugged into the switch on a dedicated port for the link. The switch than has 12 CDs that it shares one with the hub witch is used as CD.
So:
2 – Router
12 – for the switch (1 is connected to hub as 1 CD)
14
What Iget out of this is assume a 12 port switch is managed with an aditional port for the router for the sake of testing
Router has two, switch has twelve, hub has one. Subtract two for the interconnects. Answer is 2+12+1-2 = 13.
I disagree answer should be 13
It is 14 because you are only counting 1 port from the router that is plugged into the switch. Router to switch = 1 collision domain. Switch has 12 ports = 12 collision domains. Hub itself has 1 collision domain. Altogether you get 14.
Agreed!
lol no,
router to switch has 1 collision domain, and yet youre still going to add 12 more collision domains for the switch (including the one with the router)? makes no sense.
The hub connected to switch is only 1. The router to the Switch is 1. The sitch has 10 more ports which is 12… .then add on extra port on router equals 13. But is that second port even in that network or is it connecting a different network then making the answer actually 12????
Why is it not 13????