The answer is that the NAT pool is exhausted, and the fix is to configure PAT (Port Address Translation) to allow multiple internal hosts to share a single public IP address. This is correct because dynamic NAT allocates a unique public IP from a pool for each inside-to-outside session, and when the pool runs out, the router cannot create new translations, dropping new connection attempts while existing sessions continue. On the CCNA 200-301 v2 exam, this scenario tests your understanding of NAT scalability limits and the difference between dynamic NAT and PAT; a common trap is to confuse pool exhaustion with an ACL misconfiguration or routing issue. The key symptom is partial connectivity—users can reach some websites (those with established translations) but not new ones. Memory tip: think of a parking lot—dynamic NAT gives each car its own spot, but when the lot is full, new cars are turned away; PAT is like valet parking that stacks cars in one spot using different keys (port numbers).
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. 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
--- 192.0.2.10 10.0.0.10 --- ---
--- 192.0.2.11 10.0.0.11 --- ---
--- 192.0.2.12 10.0.0.12 --- ---
--- 192.0.2.13 10.0.0.13 --- ---
--- 192.0.2.14 10.0.0.14 --- ---
--- 192.0.2.15 10.0.0.15 --- ---
--- 192.0.2.16 10.0.0.16 --- ---
--- 192.0.2.17 10.0.0.17 --- ---
--- 192.0.2.18 10.0.0.18 --- ---
--- 192.0.2.19 10.0.0.19 --- ---
R1# show running-config | include ip nat
ip nat pool MYPOOL 192.0.2.10 192.0.2.19 netmask 255.255.255.240
ip nat inside source list 1 pool MYPOOL
A network administrator configured dynamic NAT on a Cisco router to allow internal hosts to access the internet. After the configuration, users report that they can access some websites but not others. The administrator checks the router and discovers that the NAT translation table is full, and new connection attempts are being dropped. What is the most likely cause of this 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.
R1# show ip nat translations
Pro Inside global Inside local Outside local Outside global
--- 192.0.2.10 10.0.0.10 --- ---
--- 192.0.2.11 10.0.0.11 --- ---
--- 192.0.2.12 10.0.0.12 --- ---
--- 192.0.2.13 10.0.0.13 --- ---
--- 192.0.2.14 10.0.0.14 --- ---
--- 192.0.2.15 10.0.0.15 --- ---
--- 192.0.2.16 10.0.0.16 --- ---
--- 192.0.2.17 10.0.0.17 --- ---
--- 192.0.2.18 10.0.0.18 --- ---
--- 192.0.2.19 10.0.0.19 --- ---
R1# show running-config | include ip nat
ip nat pool MYPOOL 192.0.2.10 192.0.2.19 netmask 255.255.255.240
ip nat inside source list 1 pool MYPOOL
A
The inside local addresses are not properly defined in the access list.
Why wrong: The access list is not shown, but the translations are present, indicating that the access list is matching the correct internal hosts.
B
The NAT pool is exhausted; configure PAT to allow multiple hosts to share a single public IP.
The pool has only 10 addresses, and once all are used, new translations fail. PAT allows many internal hosts to share a single public IP by using unique port numbers.
C
The outside interface is not configured with the ip nat outside command.
Why wrong: If the outside interface were missing this command, no translations would be created at all, but translations are present.
D
The inside interface is not configured with the ip nat inside command.
Why wrong: Similar to option C, translations are present, indicating that the inside interface is correctly configured.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The NAT pool is exhausted; configure PAT to allow multiple hosts to share a single public IP.
When the NAT pool is exhausted, no new translations can be created, so only hosts that already have established translations can continue to communicate, causing intermittent connectivity. A full NAT table means the pool of public IP addresses is completely allocated, preventing new sessions. Implementing PAT allows multiple inside hosts to share a single public IP by multiplexing port numbers, resolving the pool exhaustion.
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 inside local addresses are not properly defined in the access list.
Why it's wrong here
The access list is not shown, but the translations are present, indicating that the access list is matching the correct internal hosts.
✓
The NAT pool is exhausted; configure PAT to allow multiple hosts to share a single public IP.
Why this is correct
The pool has only 10 addresses, and once all are used, new translations fail. PAT allows many internal hosts to share a single public IP by using unique port numbers.
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 outside interface is not configured with the ip nat outside command.
Why it's wrong here
If the outside interface were missing this command, no translations would be created at all, but translations are present.
✗
The inside interface is not configured with the ip nat inside command.
Why it's wrong here
Similar to option C, translations are present, indicating that the inside interface is correctly configured.
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 NAT pool is exhausted; configure PAT to allow multiple hosts to share a single public IP.Correct answer▾
Why this is correct
The pool has only 10 addresses, and once all are used, new translations fail. PAT allows many internal hosts to share a single public IP by using unique port numbers.
✗The inside local addresses are not properly defined in the access list.Wrong answer — click to see why▾
Why this is wrong here
The access list is used to define which inside local addresses are eligible for NAT. If the access list were misconfigured, the router would not create translations for those hosts. However, the scenario states that translations are present, indicating that the access list is correctly matching the internal hosts.
Why candidates choose this
Students often confuse the role of the access list in NAT with other ACL functions. They might think that an incomplete translation is due to the ACL not permitting certain traffic, but the presence of translations shows the ACL is working.
✗The outside interface is not configured with the ip nat outside command.Wrong answer — click to see why▾
Why this is wrong here
If the outside interface were missing the 'ip nat outside' command, the router would not perform NAT on outbound traffic at all, resulting in no translations being created. Since translations are present, this command is correctly configured.
Why candidates choose this
Students may think that an incomplete translation could be due to a missing 'ip nat outside' command, but that would prevent any translation from being created, not just incomplete ones.
✗The inside interface is not configured with the ip nat inside command.Wrong answer — click to see why▾
Why this is wrong here
Similar to option C, if the inside interface were missing the 'ip nat inside' command, no translations would be created. The presence of translations indicates that the inside interface is correctly configured.
Why candidates choose this
Students might incorrectly attribute incomplete translations to a missing 'ip nat inside' command, but that would cause a complete failure of NAT, not partial functionality.
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: answer the scenario, not the keyword
Cisco often tests the distinction between dynamic NAT (one-to-one pool) and PAT (many-to-one), leading candidates to overlook pool exhaustion when symptoms show partial connectivity rather than total failure.
Trap categories for this question
Similar concept trap
Similar to option C, translations are present, indicating that the inside interface is correctly configured.
Command / output trap
The access list is not shown, but the translations are present, indicating that the access list is matching the correct internal hosts.
Detailed technical explanation
How to think about this question
Dynamic NAT allocates a one-to-one mapping from a pool of public IPs to private IPs. When the pool is exhausted, the router cannot create new translations, leading to 'incomplete' entries as the router attempts to establish a mapping but fails. PAT (NAT overload) extends this by multiplexing thousands of sessions through a single public IP using TCP/UDP port numbers (RFC 2663), which is why it is the standard solution for conserving public IPv4 addresses in enterprise networks.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Network Services and Security — This question tests Network Services and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The NAT pool is exhausted; configure PAT to allow multiple hosts to share a single public IP. — When the NAT pool is exhausted, no new translations can be created, so only hosts that already have established translations can continue to communicate, causing intermittent connectivity. A full NAT table means the pool of public IP addresses is completely allocated, preventing new sessions. Implementing PAT allows multiple inside hosts to share a single public IP by multiplexing port numbers, resolving the pool exhaustion.
What should I do if I get this 200-301 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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