mediumMultiple ChoiceObjective-mapped
Implementing VLAN Network Segmentation
A small company with 50 employees uses a flat network with no VLANs. They recently experienced a ransomware attack that spread from an infected workstation to a file server. The IT manager wants to implement network segmentation to prevent future lateral movement. The company uses a single /24 subnet (192.168.1.0/24) with a single switch and a router/firewall. They have three departments: Sales, HR, and IT. Each department has about 15-20 computers. The file server is in the IT department. The company has a limited budget and cannot purchase new hardware. Which of the following is the MOST effective and practical approach to segment the network given these constraints?
Quick Answer
The correct answer is to create three VLANs on the switch, one for each department, and configure ACLs on the router to allow only necessary inter-VLAN traffic. This approach directly implements network segmentation with VLANs by dividing the flat /24 subnet into three isolated broadcast domains on the existing single switch, which prevents ransomware from moving laterally between departments by default. The ACLs on the router then act as a firewall between VLANs, permitting only essential traffic—like Sales and HR accessing the IT file server—without requiring any new hardware. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your understanding of how VLANs enforce segmentation at Layer 2 and how ACLs control inter-VLAN routing at Layer 3, a common trap being to suggest buying a new switch or using separate physical networks, which violates the budget constraint. Remember the mnemonic “VLANs block, ACLs unlock”—VLANs stop the spread, ACLs open only what’s needed.
⚠ Common exam trap
ISC2 often tests the misconception that physical separation (Option A) is always required for segmentation, when in fact VLANs provide logical separation at no extra cost, and that MAC filtering (Option C) or host-based firewalls (Option D) can substitute for network-level segmentation, which they cannot because they fail to isolate broadcast domains or prevent Layer 2 attacks.
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
✓
Create three VLANs on the switch, one for each department, and configure ACLs on the router to allow only necessary inter-VLAN traffic.
Creating three VLANs on the existing switch segments the flat /24 network into separate broadcast domains, preventing lateral movement by default. Configuring ACLs on the router allows only necessary inter-VLAN traffic (e.g., Sales and HR can access the file server in IT), which stops the ransomware from spreading across departments without requiring new hardware.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace the switch with three separate physical switches, each connected to a separate router interface.
Why it's wrong here
This requires new hardware and additional configuration, exceeding the budget constraint.
- ✓
Create three VLANs on the switch, one for each department, and configure ACLs on the router to allow only necessary inter-VLAN traffic.
Why this is correct
VLANs logically separate traffic, and ACLs enforce policy; uses existing hardware if the switch supports VLANs (most do).
- ✗
Implement MAC address filtering on the switch to only allow authorized devices to communicate with the file server.
Why it's wrong here
MAC filtering does not isolate departments; devices within the same subnet can still communicate.
- ✗
Install a software firewall on each workstation to block traffic from other subnets.
Why it's wrong here
Host-based firewalls are inconsistent and difficult to manage; they do not prevent all lateral movement.
Visual reference
Go deeper
Related to this question
Learn chapter
Access Control Fundamentals
Key term
Lateral movement
Lateral movement is the technique attackers use to move through a network from one compromised system to another, seeking sensitive data or higher privileges.
Key term
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
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Same concept, more angles
1 more way this is tested on CC
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. A small company has a single flat network with no segmentation. They recently experienced a malware outbreak that spread quickly across all devices. The IT manager wants to implement network segmentation to contain future outbreaks with minimal cost and complexity. The company currently has a single switch and a router/firewall appliance. The network consists of three departments: Sales, HR, and Engineering. After analyzing the requirements, what is the best course of action?
easy- A.Deploy a next-generation firewall between the switch and the router to inspect traffic
- ✓ B.Replace the single switch with multiple managed switches and create VLANs for each department, then connect them to the firewall
- C.Implement 802.1X authentication on the switch to control device access
- D.Install host-based firewalls on all endpoints
Why B: VLANs logically segment the flat network into separate broadcast domains for Sales, HR, and Engineering, containing malware spread at Layer 2. Using multiple managed switches with VLANs and trunking to the firewall allows inter-VLAN traffic to be inspected and controlled by the firewall, providing segmentation with minimal cost and complexity. This approach leverages existing hardware (router/firewall) and avoids the expense of additional appliances.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CC practice question is part of Courseiva's free ISC2 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 CC exam.