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Question 1,458 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Notices that internal hosts (192.168.1.0/24) can…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
Exhibit
R1# show ip nat translations Pro Inside global Inside local Outside local Outside global --- 203.0.113.10 192.168.1.10 198.51.100.1 198.51.100.1 --- 203.0.113.11 192.168.1.20 198.51.100.2 198.51.100.2 R1# show ip nat statistics Total active translations: 2 (0 static, 2 dynamic; 2 extended) Pool translations: 2 Outside interfaces: GigabitEthernet0/0 Inside interfaces: GigabitEthernet0/1 Hits: 5 Misses: 0 CEF Translated packets: 5, CEF Punted packets: 0 Expired translations: 0 Dynamic mappings: -- Inside Source [Id] ip nat pool POOL 203.0.113.10 203.0.113.20 netmask 255.255.255.0 access-list NAT permit 192.168.1.0 0.0.0.255 Refcount: 2
A network engineer notices that internal hosts (192.168.1.0/24) can reach external servers on the internet, but replies from external servers never reach the internal hosts. The router R1 is configured with dynamic NAT to translate the internal subnet to a pool of public IPs (203.0.113.10-203.0.113.20). The engineer runs 'show ip nat translations' and sees only a few stale translations. What is the most likely cause of the issue?
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.
Clue:
"never"Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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
✓
The outside interface (GigabitEthernet0/0) is missing the 'ip nat outside' command.
The issue is that the 'ip nat inside source list NAT pool POOL overload' command is missing the 'overload' keyword. Without 'overload', the router uses dynamic NAT (one-to-one mapping), which exhausts the pool of 11 addresses. However, the symptom of unreachable external replies typically points to a missing 'ip nat outside' interface command. The exhibit shows only 2 active translations, but the problem is that replies are not being translated back because the outside interface (GigabitEthernet0/0) lacks 'ip nat outside'. This prevents the router from performing inbound NAT on return traffic. Option B is correct: adding 'ip nat outside' on the outside interface fixes the issue. Option A is wrong because the access list is correct. Option C is wrong because overload is for PAT, but even without overload, dynamic NAT should work for the first 11 hosts. Option D is wrong because the pool size is sufficient for the current traffic.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 list 'NAT' is incorrect; it should permit only specific hosts, not the entire subnet.
Why it's wrong here
The access list permits the internal subnet, which is correct for dynamic NAT. The issue is not with the access list.
- ✓
The outside interface (GigabitEthernet0/0) is missing the 'ip nat outside' command.
Why this is correct
Without 'ip nat outside' on the outside interface, the router does not translate return packets from the outside to the inside. Adding this command enables NAT to work bidirectionally.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The NAT configuration lacks the 'overload' keyword, so the pool is exhausted quickly.
Why it's wrong here
While 'overload' is important for PAT, the immediate symptom of no reply traffic is not due to pool exhaustion but missing outside interface configuration.
- ✗
The NAT pool 'POOL' has too few addresses; it should be expanded to a /24 subnet.
Why it's wrong here
The pool has 11 addresses, which is sufficient for the current number of active translations (2). Expanding the pool would not fix the missing outside interface command.
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 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The outside interface (GigabitEthernet0/0) is missing the 'ip nat outside' command.Correct answer▾
Why this is correct
Without 'ip nat outside' on the outside interface, the router does not translate return packets from the outside to the inside. Adding this command enables NAT to work bidirectionally.
✗The access list 'NAT' is incorrect; it should permit only specific hosts, not the entire subnet.Wrong answer — click to see why▾
Why this is wrong here
The access list correctly matches the internal subnet, so this is not the root cause.
✗The NAT configuration lacks the 'overload' keyword, so the pool is exhausted quickly.Wrong answer — click to see why▾
Why this is wrong here
Even without overload, dynamic NAT should work for the first 11 hosts; the problem is that return packets are not being translated.
✗The NAT pool 'POOL' has too few addresses; it should be expanded to a /24 subnet.Wrong answer — click to see why▾
Why this is wrong here
The pool size is not the issue; the router is not translating return traffic due to missing 'ip nat outside'.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
The pool has 11 addresses, which is sufficient for the current number of active translations (2). Expanding the pool would not fix the missing outside interface command.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
CIDR notation defines the prefix length.
What is the correct answer to this question?
The correct answer is: The outside interface (GigabitEthernet0/0) is missing the 'ip nat outside' command. — The issue is that the 'ip nat inside source list NAT pool POOL overload' command is missing the 'overload' keyword. Without 'overload', the router uses dynamic NAT (one-to-one mapping), which exhausts the pool of 11 addresses. However, the symptom of unreachable external replies typically points to a missing 'ip nat outside' interface command. The exhibit shows only 2 active translations, but the problem is that replies are not being translated back because the outside interface (GigabitEthernet0/0) lacks 'ip nat outside'. This prevents the router from performing inbound NAT on return traffic. Option B is correct: adding 'ip nat outside' on the outside interface fixes the issue. Option A is wrong because the access list is correct. Option C is wrong because overload is for PAT, but even without overload, dynamic NAT should work for the first 11 hosts. Option D is wrong because the pool size is sufficient for the current traffic.
What should I do if I get this 200-301 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". 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?
CIDR notation defines the prefix length.
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