The answer is to swap the inside and outside NAT roles on the two interfaces. This is correct because Port Address Translation (PAT) requires the interface facing the private LAN to be marked as `ip nat inside` and the interface facing the public WAN to be marked as `ip nat outside`. In the given configuration, GigabitEthernet0/0 holds the private IP 192.168.10.1 but is incorrectly set as outside, while GigabitEthernet0/1 holds the public IP 203.0.113.10 but is set as inside, reversing the translation logic and breaking return traffic for PAT sessions. On the CCNA 200-301 v2 exam, this scenario tests your understanding of NAT directionality—a common trap where candidates focus on ACLs or the overload keyword instead of verifying interface roles. A reliable memory tip is to think of "inside" as your home network and "outside" as the internet; the private address always belongs on the inside interface.
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. A key principle to apply: nAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa.. 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
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
Refer to the exhibit. Users on the inside network can browse the web, but return traffic is failing for some sessions. A partial configuration shows:
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
ip nat outside
!
interface GigabitEthernet0/1
ip address 203.0.113.10 255.255.255.0
ip nat inside
!
ip nat inside source list 1 interface GigabitEthernet0/1 overload
access-list 1 permit 192.168.10.0 0.0.0.255
Based on this configuration, which change is required to make PAT work correctly?
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
A
Apply ip nat enable on both interfaces.
Why wrong: `ip nat enable` is not the normal Cisco IOS syntax used for classic inside/outside NAT in this scenario. The directional role assignment is what needs correction.
B
Replace overload with pool.
Why wrong: Using a pool is another NAT design option, but it is not required for PAT to work. The current command already uses interface overload, which is valid. The failure is caused by reversed inside and outside roles.
C
Swap the inside and outside NAT roles on the two interfaces.
This is correct because NAT depends on the router knowing which side is private and which side is public. The current configuration labels them the wrong way round. PAT with overload on the WAN interface is fine, but the interface roles must match the traffic direction.
D
Change access-list 1 to a standard ACL numbered 100.
Why wrong: Standard ACL 1 is already valid for identifying inside local addresses. There is no requirement to use ACL 100 for this kind of NAT rule. The bigger issue is that the interfaces are assigned the wrong NAT roles.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Swap the inside and outside NAT roles on the two interfaces.
The problem is that the router has the NAT directions backwards. In simple terms, the interface facing the private LAN should be marked as inside, and the interface facing the public or WAN side should be marked as outside. Here, GigabitEthernet0/0 uses the private address 192.168.10.1, but it is configured as outside. GigabitEthernet0/1 uses the public address 203.0.113.10, but it is configured as inside. That reverses the translation logic and breaks normal PAT behavior.
Technically, the command `ip nat inside source list 1 interface GigabitEthernet0/1 overload` is otherwise reasonable for dynamic PAT using the WAN interface address. The ACL also correctly identifies the inside local subnet. The essential fix is to mark G0/0 as `ip nat inside` and G0/1 as `ip nat outside`. Once the directions are corrected, PAT can create and track translations properly for outbound traffic and returning sessions.
Key principle: NAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Apply ip nat enable on both interfaces.
Why it's wrong here
`ip nat enable` is not the normal Cisco IOS syntax used for classic inside/outside NAT in this scenario. The directional role assignment is what needs correction.
When this WOULD be correct
In a different scenario, if the question asked about enabling NAT on both interfaces for a basic NAT setup without specifying PAT, then applying 'ip nat enable' on both interfaces would be correct to allow NAT functionality on both sides of the router.
✗
Replace overload with pool.
Why it's wrong here
Using a pool is another NAT design option, but it is not required for PAT to work. The current command already uses interface overload, which is valid. The failure is caused by reversed inside and outside roles.
When this WOULD be correct
In a different scenario where the question specifies that a static NAT configuration is required for a specific set of internal hosts to have unique public IP addresses, replacing overload with a pool would be correct. This would indicate that each internal host needs a dedicated public IP rather than sharing one.
✓
Swap the inside and outside NAT roles on the two interfaces.
Why this is correct
This is correct because NAT depends on the router knowing which side is private and which side is public. The current configuration labels them the wrong way round. PAT with overload on the WAN interface is fine, but the interface roles must match the traffic direction.
Related concept
NAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa.
✗
Change access-list 1 to a standard ACL numbered 100.
Why it's wrong here
Standard ACL 1 is already valid for identifying inside local addresses. There is no requirement to use ACL 100 for this kind of NAT rule. The bigger issue is that the interfaces are assigned the wrong NAT roles.
When this WOULD be correct
In a different scenario, if the question asked about configuring NAT for a specific set of protocols or services that require a standard ACL to permit traffic, then changing access-list 1 to a standard ACL numbered 100 could be correct if the original ACL was misconfigured or insufficient for the required traffic.
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.
✓Swap the inside and outside NAT roles on the two interfaces.Correct answer▾
Why this is correct
This is correct because NAT depends on the router knowing which side is private and which side is public. The current configuration labels them the wrong way round. PAT with overload on the WAN interface is fine, but the interface roles must match the traffic direction.
✗Apply ip nat enable on both interfaces.Wrong answer — click to see why▾
Why this is wrong here
Applying 'ip nat enable' on both interfaces does not address the issue of return traffic failing in a Port Address Translation (PAT) setup, as PAT requires specific configurations on the inside and outside interfaces rather than just enabling NAT.
★ When this WOULD be the correct answer
In a different scenario, if the question asked about enabling NAT on both interfaces for a basic NAT setup without specifying PAT, then applying 'ip nat enable' on both interfaces would be correct to allow NAT functionality on both sides of the router.
Why candidates choose this
Candidates may choose this option because they recognize that NAT must be enabled on interfaces for translation to occur, leading them to mistakenly believe that enabling it on both interfaces is a necessary step for any NAT configuration.
✗Replace overload with pool.Wrong answer — click to see why▾
Why this is wrong here
Replacing overload with pool is incorrect because overload is necessary for Port Address Translation (PAT) to allow multiple internal hosts to share a single public IP address. In this scenario, the issue is related to NAT roles, not the type of NAT configuration used.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that a static NAT configuration is required for a specific set of internal hosts to have unique public IP addresses, replacing overload with a pool would be correct. This would indicate that each internal host needs a dedicated public IP rather than sharing one.
Why candidates choose this
Candidates may find this option tempting because they might confuse the need for a pool of addresses with the functionality of PAT, thinking that changing the configuration type could resolve the NAT issues without considering the role assignments.
✗Change access-list 1 to a standard ACL numbered 100.Wrong answer — click to see why▾
Why this is wrong here
Changing access-list 1 to a standard ACL numbered 100 does not address the issue of return traffic failing for sessions using Port Address Translation (PAT). The problem lies in the NAT configuration roles, not in the access control list numbering.
★ When this WOULD be the correct answer
In a different scenario, if the question asked about configuring NAT for a specific set of protocols or services that require a standard ACL to permit traffic, then changing access-list 1 to a standard ACL numbered 100 could be correct if the original ACL was misconfigured or insufficient for the required traffic.
Why candidates choose this
Candidates may be tempted by this option because they understand that access lists are crucial for controlling traffic flow, leading them to believe that modifying the ACL could resolve NAT issues without considering the specific roles of the NAT interfaces.
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
A frequent exam trap is confusing the NAT inside and outside interface roles. Candidates may see the private IP on an interface and mistakenly assign it as 'ip nat outside' or vice versa. This reverses the translation direction, causing return traffic to fail despite correct ACLs and overload commands. The trap exploits the assumption that the public IP must be inside or that the interface with the ACL is always inside. Understanding that NAT roles depend on network topology, not just IP addresses, is crucial to avoid this error.
Trap categories for this question
Command / output trap
Using a pool is another NAT design option, but it is not required for PAT to work. The current command already uses interface overload, which is valid. The failure is caused by reversed inside and outside roles.
Scenario analysis trap
`ip nat enable` is not the normal Cisco IOS syntax used for classic inside/outside NAT in this scenario. The directional role assignment is what needs correction.
Detailed technical explanation
How to think about this question
Network Address Translation (NAT) is a fundamental technology in Cisco networking that allows private IP addresses within an internal network to be translated into public IP addresses for communication over the internet. Port Address Translation (PAT), a form of dynamic NAT, enables multiple devices on a LAN to share a single public IP address by differentiating sessions using TCP/UDP port numbers. This is essential for conserving public IP addresses and enabling outbound internet access from private networks.
For PAT to function correctly, the router must know which interfaces are inside (private) and which are outside (public). The 'ip nat inside' command marks interfaces connected to the private network, while 'ip nat outside' marks those connected to the public network. The NAT translation rule, such as 'ip nat inside source list 1 interface GigabitEthernet0/1 overload', uses an ACL to identify inside local addresses and translates them to the IP address of the outside interface. If these roles are reversed, the router cannot correctly translate and track sessions, causing return traffic to fail.
A common exam trap is misconfiguring the NAT roles on interfaces, such as marking the private LAN interface as outside and the public WAN interface as inside. This reverses the translation logic and breaks PAT functionality. Practically, this causes outbound sessions to initiate but return traffic to be dropped, as the router cannot match return packets to existing NAT translations. Correctly assigning 'ip nat inside' to the LAN-facing interface and 'ip nat outside' to the WAN-facing interface resolves this issue and ensures proper PAT operation.
KKey Concepts to Remember
NAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa.
Port Address Translation (PAT) uses a single public IP address with port numbers to allow multiple inside hosts to share one outside IP address.
The command 'ip nat inside source list <ACL> interface <interface> overload' enables PAT by translating inside local addresses to the IP of the specified outside interface.
Access Control Lists (ACLs) define which inside local IP addresses are eligible for NAT translation by matching source IP addresses.
Incorrectly assigning 'ip nat inside' and 'ip nat outside' to interfaces reverses the translation logic and causes return traffic to fail.
The inside interface should face the private LAN subnet, while the outside interface should face the public or WAN network.
Using 'overload' in NAT configuration enables PAT, allowing multiple sessions to share a single public IP address by differentiating ports.
Standard ACLs such as ACL 1 can be used to identify inside local addresses for NAT, and changing ACL numbers does not fix interface role misconfiguration.
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
NAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa.
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.
Review nAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — NAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa..
What is the correct answer to this question?
The correct answer is: Swap the inside and outside NAT roles on the two interfaces. — The problem is that the router has the NAT directions backwards. In simple terms, the interface facing the private LAN should be marked as inside, and the interface facing the public or WAN side should be marked as outside. Here, GigabitEthernet0/0 uses the private address 192.168.10.1, but it is configured as outside. GigabitEthernet0/1 uses the public address 203.0.113.10, but it is configured as inside. That reverses the translation logic and breaks normal PAT behavior.
Technically, the command `ip nat inside source list 1 interface GigabitEthernet0/1 overload` is otherwise reasonable for dynamic PAT using the WAN interface address. The ACL also correctly identifies the inside local subnet. The essential fix is to mark G0/0 as `ip nat inside` and G0/1 as `ip nat outside`. Once the directions are corrected, PAT can create and track translations properly for outbound traffic and returning sessions.
What should I do if I get this 200-301 question wrong?
Review nAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
NAT requires correct designation of inside and outside interfaces to properly translate private IP addresses to public IP addresses and vice versa.
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