- A
The router's DNS proxy is misconfigured, preventing resolution of website names.
Why wrong: DNS issues would cause failures when pinging by name, but the symptom states users can ping public IP addresses successfully. This points to the problem being at the transport layer, not DNS.
- B
The PAT translation table is full, causing new TCP connection requests to be dropped.
PAT uses source port translation to map many internal addresses to a single public IP. ICMP (ping) does not consume a port mapping and can still be translated even when the table is exhausted. New TCP connections, required for web traffic, will fail when no free source port is available.
- C
The 'overload' keyword was omitted, causing the router to use dynamic NAT with a single-address pool.
Why wrong: The configuration shown includes the 'overload' keyword. Even if it were missing, dynamic NAT without overload would not allow any internal host other than the first one to use the IP, but pings would also fail from other hosts. This does not match the symptom.
- D
A static NAT entry for a web server is using the same public IP address as the PAT overload.
Why wrong: Configuring a static NAT entry with the same IP as the overloaded outside interface would typically cause a conflict or prevent the PAT translation from working correctly for all traffic, including ping. The router would likely generate an error or reject the command.
Quick Answer
The answer is PAT port exhaustion, where the translation table fills up and drops new TCP connections while ICMP still works. This occurs because PAT uses unique port numbers to map multiple internal IPs to a single public IP, and when all available ports are consumed—often by many short-lived TCP sessions like web browsing—the router cannot create new translations for HTTP or HTTPS traffic. ICMP traffic, however, uses a different identifier (the ICMP query ID) and typically consumes fewer entries, so pings succeed even when TCP ports are exhausted. On the CCNA 200-301 v2 exam, this scenario tests your understanding of NAT overload behavior and the distinction between TCP and ICMP translation resources; a common trap is to suspect ACL misconfiguration or missing overload keyword when the real issue is table capacity. Remember the memory tip: “Pings pass, pages fail—ports are full, TCP’s in jail.”
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.
A network administrator configures PAT on a router to allow internal hosts in the 10.10.10.0/24 subnet to access the Internet. Afterward, users report that they can ping public IP addresses but cannot access any websites. The administrator verifies that the access list for NAT matches the correct subnet, and the 'ip nat inside source list 1 interface GigabitEthernet0/1 overload' command is applied. 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.
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 PAT translation table is full, causing new TCP connection requests to be dropped.
The ability to ping public IP addresses confirms that IP routing and PAT translation are working for ICMP traffic. However, the failure to access websites (HTTP/HTTPS) while ping succeeds indicates that the PAT translation table is likely exhausted, preventing the router from creating new translations for TCP connections. The 'overload' keyword is correctly configured, so the issue is not a missing keyword but rather resource exhaustion in the NAT table.
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 router's DNS proxy is misconfigured, preventing resolution of website names.
Why it's wrong here
DNS issues would cause failures when pinging by name, but the symptom states users can ping public IP addresses successfully. This points to the problem being at the transport layer, not DNS.
- ✓
The PAT translation table is full, causing new TCP connection requests to be dropped.
Why this is correct
PAT uses source port translation to map many internal addresses to a single public IP. ICMP (ping) does not consume a port mapping and can still be translated even when the table is exhausted. New TCP connections, required for web traffic, will fail when no free source port is available.
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 'overload' keyword was omitted, causing the router to use dynamic NAT with a single-address pool.
Why it's wrong here
The configuration shown includes the 'overload' keyword. Even if it were missing, dynamic NAT without overload would not allow any internal host other than the first one to use the IP, but pings would also fail from other hosts. This does not match the symptom.
- ✗
A static NAT entry for a web server is using the same public IP address as the PAT overload.
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 PAT translation table is full, causing new TCP connection requests to be dropped.Correct answer▾
Why this is correct
PAT uses source port translation to map many internal addresses to a single public IP. ICMP (ping) does not consume a port mapping and can still be translated even when the table is exhausted. New TCP connections, required for web traffic, will fail when no free source port is available.
✗The router's DNS proxy is misconfigured, preventing resolution of website names.Wrong answer — click to see why▾
Why this is wrong here
The scenario explicitly mentions successful pings to IP addresses, so name resolution is not the cause.
✗The 'overload' keyword was omitted, causing the router to use dynamic NAT with a single-address pool.Wrong answer — click to see why▾
Why this is wrong here
The command output explicitly shows 'overload', and the symptom (ping works, TCP fails) is inconsistent with a missing overload keyword.
✗A static NAT entry for a web server is using the same public IP address as the PAT overload.Wrong answer — click to see why▾
Why this is wrong here
A static NAT conflict would affect all traffic (including ICMP), not just web traffic.
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 ICMP and TCP behavior under PAT exhaustion—candidates assume that if ping works, all IP connectivity is fine, but the trap is that PAT table exhaustion selectively drops new TCP sessions while allowing existing or low-volume ICMP traffic.
Trap categories for this question
Keyword trap
The configuration shown includes the 'overload' keyword. Even if it were missing, dynamic NAT without overload would not allow any internal host other than the first one to use the IP, but pings would also fail from other hosts. This does not match the symptom.
Command / output trap
The configuration shown includes the 'overload' keyword. Even if it were missing, dynamic NAT without overload would not allow any internal host other than the first one to use the IP, but pings would also fail from other hosts. This does not match the symptom.
Detailed technical explanation
How to think about this question
PAT (Port Address Translation) uses a single public IP address and multiplexes multiple internal connections by assigning unique source port numbers. The NAT translation table has a finite size (typically thousands of entries, e.g., 4,096 or more depending on platform), and when it fills up, the router cannot create new translations for TCP SYN packets, causing connection timeouts. ICMP traffic uses a separate identifier field and may still succeed if the table has room for a few ICMP entries, but TCP connections for web browsing quickly exhaust the table under heavy load.
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.
What to study next
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FAQ
Questions learners often ask
What does this 200-301 question test?
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 PAT translation table is full, causing new TCP connection requests to be dropped. — The ability to ping public IP addresses confirms that IP routing and PAT translation are working for ICMP traffic. However, the failure to access websites (HTTP/HTTPS) while ping succeeds indicates that the PAT translation table is likely exhausted, preventing the router from creating new translations for TCP connections. The 'overload' keyword is correctly configured, so the issue is not a missing keyword but rather resource exhaustion in the NAT table.
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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Last reviewed: Jun 25, 2026
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