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 203.0.113.2 255.255.255.252 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
Hosts on the inside network can reach the internet, but return traffic is failing after a new router was installed. Based on the exhibit, what configuration mistake is the most likely cause?
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 NAT inside and outside interface roles are reversed.
That is the key problem shown.
B
Distractor review
The ACL must deny RFC1918 traffic before NAT can work.
The ACL is being used to match inside addresses for translation, not for packet filtering.
C
Distractor review
PAT cannot use an interface address for overload.
Using the outside interface address for PAT is standard.
D
Distractor review
The inside subnet must be configured as /24 on both interfaces.
The WAN interface should not use the inside subnet.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is reversing the NAT inside and outside interface roles. Candidates may see that hosts can initiate traffic to the internet and mistakenly assume NAT is correctly configured. However, if the router’s interfaces are misassigned, return traffic from the internet will not be translated back to the inside hosts, causing connectivity failures. This trap exploits the partial functionality of NAT where outbound packets appear to succeed but inbound packets fail, leading to confusion during troubleshooting and exam scenarios.
Technical deep dive
How to think about this question
Network Address Translation (NAT) is a fundamental technology in Cisco routing that allows multiple devices on a private inside network to access external networks like the internet using a single public IP address. NAT overload, also known as Port Address Translation (PAT), enables many inside hosts to share one outside IP address by tracking port numbers. For NAT to function correctly, the router interfaces must be explicitly designated as 'inside' or 'outside' using the commands 'ip nat inside' and 'ip nat outside'. This classification informs the router which traffic should be translated from private to public addresses and vice versa. The correct configuration requires the LAN-facing interface to be marked as 'ip nat inside' and the WAN-facing interface as 'ip nat outside'. This setup ensures that packets originating from the inside network are translated when they exit the router towards the internet, and return traffic from the internet is properly translated back to the inside hosts. If these roles are reversed, the router will not perform NAT translations correctly, causing return traffic to fail, even though outbound traffic appears to work. A common exam trap is confusing the NAT inside and outside interface roles, especially since the router can still forward packets without proper NAT translation. This misconfiguration leads to asymmetric traffic flow where outbound packets are translated, but inbound packets are dropped or not translated back. Practically, this results in inside hosts being unable to receive responses from the internet, causing connectivity failures. Understanding and verifying interface roles is critical in troubleshooting NAT issues in Cisco environments.
KKey Concepts to Remember
- NAT overload allows multiple inside hosts to share a single outside IP address by translating source ports for simultaneous connections.
- Cisco routers require explicit configuration of interfaces as 'ip nat inside' or 'ip nat outside' to determine the direction of NAT translation.
- The LAN-facing interface must be configured as 'ip nat inside' to identify private IP addresses for translation.
- The WAN-facing interface must be configured as 'ip nat outside' to represent the public IP address used for NAT translations.
- If the NAT inside and outside interface roles are reversed, return traffic from the internet will fail because translations are not applied correctly.
- Access Control Lists (ACLs) used in NAT configurations match inside local addresses but do not filter traffic or deny RFC1918 addresses.
- Using the outside interface IP address for PAT overload is standard and supported in Cisco NAT implementations.
- The inside subnet must be correctly configured only on the LAN interface; the WAN interface uses a different subnet and should not share the inside subnet.
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 overload allows multiple inside hosts to share a single outside IP address by translating source ports for simultaneous connections.
What is the correct answer to this question?
The correct answer is: The NAT inside and outside interface roles are reversed. — NAT overload requires the LAN-facing interface to be marked as ip nat inside and the WAN-facing interface as ip nat outside. The exhibit shows those roles reversed, so translations will not occur correctly. The ACL itself is fine for matching the inside subnet.
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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