Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
interface GigabitEthernet0/0 ip address 192.168.10.1 255.255.255.0 ip nat outside ! interface GigabitEthernet0/1 ip address 203.0.113.10 255.255.255.252 ip nat inside ! access-list 1 permit 192.168.10.0 0.0.0.255 ip nat inside source list 1 interface GigabitEthernet0/1 overload
Based on the exhibit, what is the most likely reason PAT is not working correctly?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The inside and outside NAT interface roles are reversed.
This is correct because the private interface should be inside and the public interface should be outside.
B
Distractor review
PAT requires OSPF to be enabled on the WAN link.
This is wrong because PAT does not depend on OSPF.
C
Distractor review
The ACL must be numbered 100 instead of 1.
This is wrong because a standard ACL such as 1 is valid for this NAT rule.
D
Distractor review
The router must use GRE before PAT can overload.
This is wrong because PAT does not require GRE tunneling.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is confusing the NAT inside and outside interface roles. Candidates might overlook that reversing these roles causes PAT to fail silently, as translation direction depends on correct interface designation. Misunderstanding this can lead to incorrect troubleshooting steps, such as focusing on routing protocols or ACL numbering, which do not impact PAT functionality directly.
Technical deep dive
How to think about this question
Port Address Translation (PAT) relies heavily on correct NAT interface role assignments to function properly. The 'ip nat inside' command marks interfaces connected to the private network, while 'ip nat outside' marks those connected to the public network. When these roles are reversed, the router attempts to translate traffic in the wrong direction, causing PAT to fail. This misconfiguration prevents the router from correctly mapping private IP addresses and ports to the public IP address and ports. Unlike routing protocols such as OSPF or GRE tunneling, PAT does not depend on these technologies for operation. Additionally, the ACL used to identify traffic for NAT translation can be either standard or extended and does not require a specific number like 100; any valid ACL number is acceptable. Understanding the directional nature of NAT and the importance of interface roles is critical for troubleshooting NAT-related issues on Cisco devices.
KKey Concepts to Remember
- NAT interface roles (inside vs outside)
- Port Address Translation (PAT) functionality
- Access Control Lists (ACL) in NAT
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
NAT interface roles (inside vs outside)
What is the correct answer to this question?
The correct answer is: The inside and outside NAT interface roles are reversed. — PAT is not working correctly because the inside and outside NAT roles are reversed on the interfaces. In practical terms, the private LAN-facing interface should be marked as inside, and the public-facing WAN interface should be marked as outside. In the exhibit, the router has those roles backwards, so translation logic is applied in the wrong direction. This is a very realistic NAT troubleshooting item because the configuration is close to correct and the failure comes from one directional mistake.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
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