- A
It is translated using PAT to 203.0.113.1.
Why wrong: The ACL does not include 172.16.0.0/24, so no translation occurs.
- B
It is not translated and will be forwarded with its original source IP.
Traffic not matching the ACL is not subject to NAT; it is routed normally.
- C
It is dropped because NAT is required for all inside interfaces.
Why wrong: NAT is not mandatory; unmatched traffic is forwarded without translation.
- D
It is translated using a different pool because it is on a separate inside interface.
Why wrong: No other NAT rule exists; the only rule uses ACL 1, which does not match 172.16.0.0/24.
Question 832 of 2,152
How to Fix NAT ACL Mismatches for Multiple Inside Networks
This 300-410 practice question tests your understanding of nat and pat. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Consider this partial configuration:
ip nat inside source list 1 interface GigabitEthernet0/1 overload access-list 1 permit 192.168.1.0 0.0.0.255
!
interface GigabitEthernet0/0 ip address 192.168.1.1 255.255.255.0 ip nat inside
!
interface GigabitEthernet0/1 ip address 203.0.113.1 255.255.255.0 ip nat outside
!
interface GigabitEthernet0/2 ip address 172.16.0.1 255.255.255.0 ip nat inside
What is true about traffic from the 172.16.0.0/24 network?
Quick Answer
The answer is that traffic from the 172.16.0.0/24 network is not translated and will be forwarded with its original source IP address. This occurs because the NAT ACL mismatch prevents the router from matching the 172.16.0.0/24 subnet against access-list 1, which only permits 192.168.1.0/24. In Cisco NAT configuration, the `ip nat inside source list` command ties translation eligibility directly to the ACL; any inside network not explicitly permitted by that ACL is simply not translated, even if the interface is configured as `ip nat inside`. On the CCNP ENARSI 300-410 exam, this scenario tests your understanding of how ACLs control NAT policy—a common trap is assuming that all inside interfaces automatically get translated, when in fact the ACL is the sole gatekeeper. A useful memory tip: “The ACL is the bouncer—if your network isn’t on the list, it doesn’t get translated.”
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
✓
It is not translated and will be forwarded with its original source IP.
The NAT configuration uses an access-list (list 1) that only matches traffic from the 192.168.1.0/24 network. Traffic sourced from the 172.16.0.0/24 network does not match this access-list, so it is not subject to NAT translation. As a result, the router forwards packets from 172.16.0.0/24 with their original source IP address unchanged.
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.
- ✗
It is translated using PAT to 203.0.113.1.
Why it's wrong here
The ACL does not include 172.16.0.0/24, so no translation occurs.
- ✓
It is not translated and will be forwarded with its original source IP.
- ✗
It is dropped because NAT is required for all inside interfaces.
Why it's wrong here
NAT is not mandatory; unmatched traffic is forwarded without translation.
- ✗
It is translated using a different pool because it is on a separate inside interface.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that all traffic on an interface marked 'ip nat inside' is automatically translated, but in reality, translation only occurs for traffic that matches the access-list referenced in the NAT command.
Detailed technical explanation
How to think about this question
The 'ip nat inside source' command binds a specific access-list to define which source IPs are eligible for translation. When multiple inside interfaces exist, each with different subnets, the access-list must explicitly include those subnets for NAT to apply. Under the hood, the Cisco NAT engine checks the source IP against the access-list; if there is no match, the packet bypasses the translation process entirely and is routed based on the routing table. In real-world scenarios, this allows selective NAT for certain subnets while others retain their original addressing, which is common in multi-homed or DMZ designs.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
NAT and PAT — This question tests NAT and PAT — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: It is not translated and will be forwarded with its original source IP. — The NAT configuration uses an access-list (list 1) that only matches traffic from the 192.168.1.0/24 network. Traffic sourced from the 172.16.0.0/24 network does not match this access-list, so it is not subject to NAT translation. As a result, the router forwards packets from 172.16.0.0/24 with their original source IP address unchanged.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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