Question 571 of 1,020

Network Configuration Concepts →hardMultiple ChoiceObjective-mapped

Why Can Guest Subnet Devices Not Reach the Internet?

This 220-1201 practice question tests your understanding of network configuration concepts. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A network administrator is configuring a small business network with two subnets: 192.168.1.0/24 for employees and 192.168.2.0/24 for guests. The router has two LAN interfaces with IPs 192.168.1.1 and 192.168.2.1. A technician connects a new access point to the guest subnet switch and configures it with a static IP of 192.168.2.50. The access point can ping the router's guest interface but cannot reach the internet. The router's default route points to an ISP modem at 203.0.113.1. What is the most likely missing configuration?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The access point's default gateway is set to 192.168.1.1.
Why wrong: If the gateway were set to the employee subnet, the access point would not be able to ping the router's guest interface (192.168.2.1), but it can, so the gateway is likely correct.
B
NAT is not enabled for the 192.168.2.0/24 subnet on the router.
Without NAT, the router will not translate private IPs from the guest subnet to the public IP, so traffic cannot reach the internet. The employee subnet works because NAT is likely enabled for it.
C
The access point has a duplicate IP address.
Why wrong: A duplicate IP would cause conflicts, but the access point can ping the router, so the IP is likely unique.
D
The ISP modem is blocking traffic from the guest subnet.
Why wrong: The ISP modem typically routes based on the router's public IP, not private subnets. The issue is on the router, not the modem.

Full breakdown with real-world context →

Quick Answer

The answer is that NAT is not enabled for the guest subnet. This is correct because the access point can ping the router’s guest interface at 192.168.2.1, proving Layer 3 connectivity is working, but it cannot reach the internet. Without Network Address Translation (NAT) on the 192.168.2.0/24 subnet, the router will forward guest traffic to the ISP modem using private IP addresses, which the modem cannot route back—it has no route to 192.168.2.x. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding that NAT is required for private IP ranges to access public networks; a common trap is assuming a default route alone is sufficient. The employee subnet works because NAT is likely already configured for 192.168.1.0/24. Memory tip: think “NAT for the net”—if a subnet can’t reach the internet, check that NAT is enabled for that specific subnet, not just the router’s WAN interface.

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

✓

NAT is not enabled for the 192.168.2.0/24 subnet on the router.

The access point can ping the router's guest interface (192.168.2.1), confirming Layer 2 and Layer 3 connectivity within the guest subnet. However, it cannot reach the internet, which indicates that the router is not performing Network Address Translation (NAT) for the 192.168.2.0/24 subnet. Without NAT, private IP addresses from the guest subnet are not translated to the router's public IP, so the ISP modem drops the return traffic because it has no route back to the private range.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The access point's default gateway is set to 192.168.1.1.
Why it's wrong here
If the gateway were set to the employee subnet, the access point would not be able to ping the router's guest interface (192.168.2.1), but it can, so the gateway is likely correct.
✓
NAT is not enabled for the 192.168.2.0/24 subnet on the router.
Why this is correct
Without NAT, the router will not translate private IPs from the guest subnet to the public IP, so traffic cannot reach the internet. The employee subnet works because NAT is likely enabled for it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The access point has a duplicate IP address.
Why it's wrong here
A duplicate IP would cause conflicts, but the access point can ping the router, so the IP is likely unique.
✗
The ISP modem is blocking traffic from the guest subnet.
Why it's wrong here
The ISP modem typically routes based on the router's public IP, not private subnets. The issue is on the router, not the modem.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a successful ping to the default gateway implies full internet connectivity, when in fact NAT misconfiguration is the hidden culprit that breaks traffic beyond the local router.

Detailed technical explanation

How to think about this question

NAT (specifically source NAT or IP masquerading) rewrites the source IP address of packets leaving the router's WAN interface to the router's public IP, and maintains a translation table to reverse the mapping for return traffic. On Cisco IOS routers, this is configured with 'ip nat inside' on the LAN interface, 'ip nat outside' on the WAN interface, and an access list defining which private subnets are eligible for translation. Without these commands, packets from 192.168.2.0/24 are forwarded with their private source IPs, which are not routable on the public internet, causing the ISP modem to drop them or send them to a black hole.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

Network Configuration Concepts — This question tests Network Configuration Concepts — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: NAT is not enabled for the 192.168.2.0/24 subnet on the router. — The access point can ping the router's guest interface (192.168.2.1), confirming Layer 2 and Layer 3 connectivity within the guest subnet. However, it cannot reach the internet, which indicates that the router is not performing Network Address Translation (NAT) for the 192.168.2.0/24 subnet. Without NAT, private IP addresses from the guest subnet are not translated to the router's public IP, so the ISP modem drops the return traffic because it has no route back to the private range.

What should I do if I get this 220-1201 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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