Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A router is configured with PAT for inside users. Which symptom most strongly suggests the NAT inside/outside roles are reversed on the interfaces?
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
Outbound traffic still shows private inside source addresses where translated public addresses should appear.
This is correct because reversed inside/outside roles break the normal PAT translation direction.
B
Distractor review
The switch elects a new STP root bridge.
This is wrong because STP root election is unrelated to NAT interface roles.
C
Distractor review
The router changes its hostname automatically.
This is wrong because NAT configuration does not affect router hostname behavior.
D
Distractor review
DHCP clients stop requesting leases on every VLAN.
This is wrong because DHCP leasing behavior is not the clearest symptom of reversed NAT roles.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that NAT translation problems are caused by ACL or overload command errors, while overlooking the inside/outside interface roles. Candidates may see private IP addresses in outbound traffic and mistakenly focus on ACL syntax or NAT pool definitions. However, the root cause is often reversed interface roles, which prevent the router from applying PAT correctly. This trap leads to wasted time troubleshooting unrelated configurations and missing the fundamental NAT directionality requirement.
Technical deep dive
How to think about this question
Port Address Translation (PAT) is a form of Network Address Translation (NAT) that allows multiple inside hosts to share a single public IP address by using different source port numbers. PAT requires correct identification of inside and outside interfaces on a router to properly translate private IP addresses to public IP addresses when traffic flows from the internal network to the external network. The inside interface is connected to the private network, and the outside interface connects to the public or external network. The router uses these roles to determine which packets to translate and how to apply the translation rules. When configuring PAT on Cisco routers, the 'ip nat inside' and 'ip nat outside' interface commands explicitly define the direction of NAT translation. The router translates source addresses of packets originating from the inside interface to the outside interface's public address. If these roles are reversed, the router attempts to translate packets in the wrong direction, causing the translation to fail. Consequently, private IP addresses remain visible in outbound traffic instead of being translated to public addresses, which breaks connectivity and defeats the purpose of NAT. This misconfiguration is a common exam trap because the NAT configuration commands and ACLs may appear correct, but the fundamental interface roles are swapped. The router does not automatically detect this error, so the symptom is that outbound packets still carry private source IP addresses. Understanding this behavior helps troubleshoot NAT issues practically and is critical for passing the CCNA exam, where recognizing the impact of reversed inside/outside roles on PAT is essential for NAT troubleshooting scenarios.
KKey Concepts to Remember
- PAT requires the router to correctly identify inside and outside interfaces to translate private IP addresses to public IP addresses for outbound traffic.
- The 'ip nat inside' command marks interfaces connected to the private network where source addresses are translated from.
- The 'ip nat outside' command marks interfaces connected to the public network where translated addresses are sent out.
- If inside and outside roles are reversed, the router fails to translate source addresses correctly, leaving private IPs visible in outbound packets.
- PAT uses port numbers to distinguish multiple inside hosts sharing a single public IP address during translation.
- Correct NAT interface role assignment is essential for the router to apply translation rules in the proper direction.
- Reversed NAT roles cause translation failures even if ACLs and overload commands are configured correctly.
- Troubleshooting NAT issues often involves verifying that inside and outside interfaces are assigned correctly to ensure proper PAT operation.
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?
PAT requires the router to correctly identify inside and outside interfaces to translate private IP addresses to public IP addresses for outbound traffic.
What is the correct answer to this question?
The correct answer is: Outbound traffic still shows private inside source addresses where translated public addresses should appear. — If the NAT inside/outside roles are reversed, internal clients may send traffic out but the translation logic will not behave correctly, often leaving private source addresses visible where a translated public address should appear. In plain language, the router knows traffic is moving, but it is applying NAT in the wrong direction, so the sessions do not get translated the way PAT expects. This is a classic NAT troubleshooting issue. The ACL and overload command might look fine, but the interface role assignment still matters. The strongest clue is that inside private addresses remain visible on traffic that should have been translated.
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.
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