Collision and Broadcast Domain Count — Switch and Hub Scenario
A network technician is analyzing a small office network topology. An 8-port switch has 7 workstations directly connected. The remaining switch port is connected to a 4-port hub, which has 4 workstations attached. All devices are configured on the same VLAN and IP subnet. How many collision domains and broadcast domains are present in this network?
Quick Answer
The key rule this question is testing is that collision domains are created at the port level of a switch, while a hub does not add any new collision domains of its own - it simply extends the single collision domain of whichever switch port it's plugged into to every device attached to it. That's why the 8-port switch alone accounts for all 8 collision domains here: each of its ports, including the one connected to the hub, forms its own separate collision domain, and the four workstations sharing the hub all fall within that one shared domain rather than getting domains of their own. Broadcast domains work on a completely different boundary - they're determined by VLAN and Layer 3 segmentation, not by the physical device type, so since every device here sits on the same VLAN and IP subnet, a broadcast sent by any device reaches all of them, meaning there is only one broadcast domain regardless of how many switch ports or hub ports are involved. This distinction between hubs (no new collision domains, just extending an existing one) and switches (one collision domain per port) is exactly the pattern to watch for whenever a topology question mixes switches and hubs and asks you to count domains separately.
⚠ Common exam trap
The N10-009 exam often tests the distinction between hubs (Layer 1 repeaters that extend collision domains) and switches (Layer 2 devices that segment collision domains), and the trap here is assuming that each hub port creates its own collision domain, leading to overcounting collision domains, or confusing collision domains with broadcast domains by thinking hubs or switches create multiple broadcast domains.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
8 collision domains, 1 broadcast domain
Switches create a separate collision domain per port, so the 8-port switch provides 8 collision domains. The hub connected to one switch port extends that single collision domain to all its attached devices, but does not create new ones. All devices are on the same VLAN and IP subnet, so there is only one broadcast domain. Therefore, the network has 8 collision domains and 1 broadcast domain.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
8 collision domains, 1 broadcast domain
Why this is correct
Correct. Each switch port creates its own collision domain (8 total). The hub does not add separate collision domains; it connects all its ports into the collision domain of the switch port it is attached to. All devices are on the same VLAN, so there is one broadcast domain.
- ✗
11 collision domains, 1 broadcast domain
Why it's wrong here
Incorrect. This answer incorrectly counts each workstation on the hub as a separate collision domain. Hubs do not segment collision domains; they operate at Layer 1 and forward all signals, so all hub-attached devices belong to the same collision domain as the switch port.
When this WOULD be correct
If the question stated that each hub port was connected to a separate switch port (e.g., a 4-port hub connected to 4 different switch ports), then each hub port would be its own collision domain, giving 7 (switch workstations) + 4 (hub workstations) = 11 collision domains, all in one broadcast domain.
- ✗
12 collision domains, 5 broadcast domains
Why it's wrong here
Incorrect. There are not 12 collision domains; the total is 8 (one per switch port). Also, a broadcast domain is not determined by the number of devices. All devices share the same broadcast domain because they are on the same VLAN and no router is involved.
When this WOULD be correct
This option would be correct if the network had 5 separate VLANs (each with its own broadcast domain) and the switch ports were configured in access mode for different VLANs, with the hub connecting to a switch port in a trunk mode carrying multiple VLANs, and each hub port assigned to a different VLAN. Then collision domains would be 8 (switch ports) + 4 (hub ports) = 12, and broadcast domains would be 5 (one per VLAN).
- ✗
8 collision domains, 5 broadcast domains
Why it's wrong here
Incorrect. While 8 collision domains is correct, 5 broadcast domains is wrong. Broadcast domains are separated by Layer 3 devices (routers), or by VLANs if trunked. Since all devices are on the same VLAN and subnet without a router, there is only one broadcast domain.
When this WOULD be correct
This option would be correct if the question stated that the hub's 4 workstations are each directly connected to the switch (i.e., no hub), and the network had 5 VLANs (or 5 separate IP subnets). Then there would be 8 collision domains (one per switch port) and 5 broadcast domains (one per VLAN).
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓8 collision domains, 1 broadcast domainCorrect answer▾
Why this is correct
Correct. Each switch port creates its own collision domain (8 total). The hub does not add separate collision domains; it connects all its ports into the collision domain of the switch port it is attached to. All devices are on the same VLAN, so there is one broadcast domain.
✗11 collision domains, 1 broadcast domainWrong answer — click to see why▾
Why this is wrong here
The hub creates a single collision domain for its 4 ports, not 4 separate ones. The switch has 8 collision domains (one per port), but the hub's segment adds only 1, totaling 9, not 11. The correct count is 8 collision domains (7 switch ports + 1 hub segment) and 1 broadcast domain.
★ When this WOULD be the correct answer
If the question stated that each hub port was connected to a separate switch port (e.g., a 4-port hub connected to 4 different switch ports), then each hub port would be its own collision domain, giving 7 (switch workstations) + 4 (hub workstations) = 11 collision domains, all in one broadcast domain.
Why candidates choose this
Candidates mistakenly count each hub port as a separate collision domain, forgetting that a hub operates as a single collision domain for all its ports. They also may incorrectly add the hub's 4 ports to the switch's 7 ports without considering the hub's shared nature.
✗12 collision domains, 5 broadcast domainsWrong answer — click to see why▾
Why this is wrong here
A hub creates a single collision domain for all its ports, and a switch creates a separate collision domain per port. Here, the switch has 8 ports (7 workstations + 1 to hub), giving 8 collision domains. The hub adds 1 collision domain for its 4 workstations, but since it's connected to a switch port, that hub's collision domain is already counted within the switch port's collision domain. So total collision domains = 8 (switch ports) = 8. Option C incorrectly counts 12 collision domains and 5 broadcast domains, but all devices are on the same VLAN and IP subnet, so there is only 1 broadcast domain.
★ When this WOULD be the correct answer
This option would be correct if the network had 5 separate VLANs (each with its own broadcast domain) and the switch ports were configured in access mode for different VLANs, with the hub connecting to a switch port in a trunk mode carrying multiple VLANs, and each hub port assigned to a different VLAN. Then collision domains would be 8 (switch ports) + 4 (hub ports) = 12, and broadcast domains would be 5 (one per VLAN).
Why candidates choose this
Candidates often mistakenly count each hub port as a separate collision domain (adding 4 instead of 1) and think that a hub creates multiple broadcast domains, confusing collision and broadcast domain concepts.
✗8 collision domains, 5 broadcast domainsWrong answer — click to see why▾
Why this is wrong here
A switch creates a separate collision domain per port, so the 8-port switch provides 8 collision domains. The hub creates a single collision domain for its 4 workstations, but that hub port on the switch is already counted as one collision domain. Thus total collision domains = 8 (switch ports) = 8, not 8 + 4 = 12. Broadcast domain is one because all devices are on the same VLAN and IP subnet.
★ When this WOULD be the correct answer
This option would be correct if the question stated that the hub's 4 workstations are each directly connected to the switch (i.e., no hub), and the network had 5 VLANs (or 5 separate IP subnets). Then there would be 8 collision domains (one per switch port) and 5 broadcast domains (one per VLAN).
Why candidates choose this
Candidates often mistakenly count each hub-attached workstation as a separate collision domain, adding 4 to the switch's 8, and may also think that a hub creates multiple broadcast domains or confuse collision and broadcast domains.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Network Virtualization and VXLAN
Key term
Collision domain
A segment of a network where data packets can collide with one another when two or more devices transmit at the same time.
Key term
Hub
A hub is a basic networking device that connects multiple computers or devices together so they can communicate, but it sends all data to every connected port without filtering.
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Same concept, more angles
1 more way this is tested on N10-009
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which of the following best describes a broadcast domain?
easy- A.All devices connected to the same switch
- B.All devices that share the same IP subnet
- ✓ C.All devices that can receive a broadcast frame from any other device in the network segment
- D.All devices that have the same MAC address prefix
Why C: A broadcast domain is defined as the set of all devices that can receive a broadcast frame (destination MAC FF:FF:FF:FF:FF:FF) sent by any other device within the same network segment. This boundary is typically enforced by Layer 3 devices like routers, which do not forward broadcast frames, whereas Layer 2 switches forward broadcasts out all ports except the receiving port within the same VLAN.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.