CCNA Network Services and Security Practice Question
Exhibit
Configured: interface G0/0 ip nat inside interface G0/1 ip nat outside No translations appear in 'show ip nat translations'.
Exhibit: Users report no internet access after PAT was configured. The inside and outside interfaces are marked correctly. Which missing configuration is the most likely cause?
⚠ Common exam trap
A frequent exam trap is believing that configuring the inside and outside interfaces alone is enough for PAT to function correctly. Candidates may overlook the necessity of an ACL that explicitly identifies the inside local addresses for translation. Without this ACL and the corresponding NAT overload statement, the router cannot perform address translation, causing intermittent or failed internet connectivity. This mistake often occurs because the interface roles are visible and seem sufficient, but the translation logic depends on the ACL match. Understanding that PAT requires both interface roles and an ACL-based NAT overload rule is critical to avoid this pitfall.
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
✓
No ACL and nat overload statement identifying inside source addresses
PAT needs both the inside and outside interface roles and a NAT statement referencing an ACL that identifies the inside local addresses. Without the ACL match and NAT overload rule, translation does not occur for user traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
No ACL and nat overload statement identifying inside source addresses
Why this is correct
For PAT to be operational, the router must have an access list that identifies the inside local source addresses to be translated, along with an ip nat inside source list <ACL> interface <outside> overload statement that actually enables port address translation. Without this ACL and overload rule, the router has no dynamic translation entry, so private inside addresses are forwarded untranslated to the ISP and the return traffic cannot be routed back. This missing configuration directly causes the intermittent or complete loss of internet access, making it the correct root cause.
- ✗
No DHCP pool on the outside interface
Why it's wrong here
A DHCP pool is intended to dynamically assign IP addresses to hosts on the inside LAN, not to provide outbound internet access or to be placed on the outside interface. The outside interface typically receives a public IP address statically or via DHCP client, but it does not hand out addresses to other devices. Thus, whether a DHCP pool exists on the outside interface has no effect on PAT traffic flow, so its absence is unrelated to the intermittent internet access problem.
When this WOULD be correct
In a different scenario where the question specifies that users are trying to connect to the internet but are not receiving IP addresses, and the router's outside interface is expected to assign IP addresses dynamically, the absence of a DHCP pool would indeed be the correct answer.
- ✗
No CDP enabled on the router
Why it's wrong here
CDP (Cisco Discovery Protocol) operates at Layer 2 and is used only to advertise and discover directly connected Cisco neighbors, such as device names, platforms, and VLANs. Disabling CDP has no impact on the router's ability to route packets, perform NAT/PAT, or reach the internet, because CDP is not in the forwarding path. Therefore, the absence of CDP enabled on the router is a distractor and cannot contribute to intermittent internet access.
When this WOULD be correct
In a question focused on network topology discovery, where the scenario involves troubleshooting connectivity issues between Cisco devices, the absence of CDP could be identified as the cause of the problem. For example, if the question asked about issues with device visibility or neighbor discovery, then not having CDP enabled would be the correct answer.
- ✗
No syslog server configured
Why it's wrong here
A syslog server is purely a remote logging destination that collects router event messages for monitoring and troubleshooting; it is not a forwarding element or a dependency for NAT/PAT. Without syslog, the router simply has no remote logging facility, but packets still traverse the router and internet connectivity is not affected by the lack of logging. Therefore, configuring syslog would only help diagnose the root cause after the fact, not fix the actual PAT misconfiguration.
When this WOULD be correct
In a different scenario where a question focuses on network troubleshooting and monitoring, a candidate might be asked about missing configurations that affect logging and alerting. If the question specifies that logs are needed for troubleshooting connectivity issues, then not having a syslog server could be the correct answer.
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.
✓No ACL and nat overload statement identifying inside source addressesCorrect answer▾
Why this is correct
For PAT to be operational, the router must have an access list that identifies the inside local source addresses to be translated, along with an ip nat inside source list <ACL> interface <outside> overload statement that actually enables port address translation. Without this ACL and overload rule, the router has no dynamic translation entry, so private inside addresses are forwarded untranslated to the ISP and the return traffic cannot be routed back. This missing configuration directly causes the intermittent or complete loss of internet access, making it the correct root cause.
✗No DHCP pool on the outside interfaceWrong answer — click to see why▾
Why this is wrong here
This option is wrong because the issue relates to PAT configuration, which does not require a DHCP pool on the outside interface. DHCP pools are typically used for dynamic IP address assignment to clients, not for NAT operations.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that users are trying to connect to the internet but are not receiving IP addresses, and the router's outside interface is expected to assign IP addresses dynamically, the absence of a DHCP pool would indeed be the correct answer.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of NAT and DHCP roles, thinking that DHCP is necessary for any internet access configuration, leading to confusion about their specific functions.
✗No CDP enabled on the routerWrong answer — click to see why▾
Why this is wrong here
CDP (Cisco Discovery Protocol) is used for discovering information about directly connected Cisco devices and does not impact NAT or internet connectivity. Therefore, its absence would not cause intermittent internet access issues related to PAT configuration.
★ When this WOULD be the correct answer
In a question focused on network topology discovery, where the scenario involves troubleshooting connectivity issues between Cisco devices, the absence of CDP could be identified as the cause of the problem. For example, if the question asked about issues with device visibility or neighbor discovery, then not having CDP enabled would be the correct answer.
Why candidates choose this
Candidates may confuse the importance of CDP in network management with its relevance to NAT configurations, leading them to mistakenly believe that it could affect internet access.
✗No syslog server configuredWrong answer — click to see why▾
Why this is wrong here
No syslog server configured is not directly related to the intermittent internet access issue caused by PAT misconfiguration. Syslog servers are used for logging events and do not affect the NAT functionality or connectivity.
★ When this WOULD be the correct answer
In a different scenario where a question focuses on network troubleshooting and monitoring, a candidate might be asked about missing configurations that affect logging and alerting. If the question specifies that logs are needed for troubleshooting connectivity issues, then not having a syslog server could be the correct answer.
Why candidates choose this
Candidates may choose this option because they understand the importance of logging in network management and might mistakenly believe that logging issues could lead to connectivity problems, thus overlooking the specific NAT-related context of the question.
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?”
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Key term
NAT
NAT (Network Address Translation) is a method that allows multiple devices on a private network to share a single public IP address when accessing the internet.
Key term
NAT overload
NAT overload is a form of network address translation that allows many devices on a private network to share a single public IP address by using unique port numbers to track each connection.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.