The answer is that the outside interface is missing the ip nat outside command. This is the most likely issue when NAT overload translations never appear despite inside users browsing the internet, because NAT overload requires the router to explicitly identify which interfaces belong to the inside (private) and outside (public) domains. Without the ip nat outside command on the correct interface, the router has no context for translating traffic—it cannot determine which packets need source address translation or where to send them, so the NAT table remains empty. On the CCNA 200-301 v2 exam, this tests your understanding of NAT configuration fundamentals, often appearing as a troubleshooting scenario where translations fail despite correct access lists and pool definitions. A common trap is assuming the ip nat inside command alone is sufficient, or reversing the interface roles. Remember the memory tip: “Inside for source, outside for destination—both must be marked for NAT to start.”
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 overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session.. 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
ip nat inside source list 10 interface g0/0 overload
access-list 10 permit 192.168.10.0 0.0.0.255
!
interface g0/0
ip address 203.0.113.2 255.255.255.252
!
interface g0/1
ip address 192.168.10.1 255.255.255.0
ip nat inside
A router is configured for NAT overload, but translations never appear when inside users browse the internet. Which issue is most likely?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The outside interface is missing the ip nat outside command
NAT needs the inside and outside interfaces marked correctly. If those roles are missing or reversed, the router has no context for translating traffic and the NAT table stays empty.
Key principle: NAT overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The outside interface is missing the ip nat outside command
Why this is correct
Without inside and outside roles, overload translations will not build correctly.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
NAT overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session.
✗
The ACL used by NAT must deny inside addresses
Why it's wrong here
The NATACL should usually match the inside local addresses to be translated.
When this WOULD be correct
If the question were about restricting NAT to only certain inside hosts (e.g., 'Which ACL configuration would prevent inside users from being translated?'), then an ACL that denies those addresses would be correct.
If the question asked 'Which feature is required on the inside interface for NAT overload to translate private addresses when using dynamic addressing?', then DHCP would be correct because inside hosts need IP addresses from a DHCP server to communicate through NAT.
✗
NAT overload works only with OSPF-learned routes
Why it's wrong here
NAT is independent of the routing protocol choice.
When this WOULD be correct
In a scenario where the question specifies that NAT overload must only translate traffic for routes learned via OSPF (e.g., to restrict translation to specific destinations), then an ACL or route-map referencing OSPF-learned routes could be required. For example: 'A router must perform NAT overload only for traffic destined to networks learned via OSPF. Which configuration is needed?'
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.
✓The outside interface is missing the ip nat outside commandCorrect answer▾
Why this is correct
Without inside and outside roles, overload translations will not build correctly.
✗The ACL used by NAT must deny inside addressesWrong answer — click to see why▾
Why this is wrong here
The ACL used by NAT should match the inside local addresses that need to be translated, typically using a permit statement. If the ACL denies inside addresses, no traffic will be matched for translation, causing NAT to fail. The correct ACL should permit the inside network.
★ When this WOULD be the correct answer
If the question were about restricting NAT to only certain inside hosts (e.g., 'Which ACL configuration would prevent inside users from being translated?'), then an ACL that denies those addresses would be correct.
Why candidates choose this
Students might think that NAT should deny private addresses to prevent them from being translated, but in reality, NAT translates private addresses to public ones. The confusion arises from the idea of filtering traffic, but NAT ACLs are used to identify which addresses to translate, not to block them.
✗PAT requires DHCP on the inside interfaceWrong answer — click to see why▾
Why this is wrong here
PAT (Port Address Translation) does not require DHCP on any interface. PAT translates multiple private IP addresses to a single public IP using different port numbers, and it works independently of how IP addresses are assigned. DHCP is only needed if the interface needs to obtain an IP address dynamically.
★ When this WOULD be the correct answer
If the question asked 'Which feature is required on the inside interface for NAT overload to translate private addresses when using dynamic addressing?', then DHCP would be correct because inside hosts need IP addresses from a DHCP server to communicate through NAT.
Why candidates choose this
Some students may associate NAT with DHCP because both are often used together in home networks to provide internet access. However, they are separate functions; DHCP assigns IP addresses, while NAT translates them. PAT can work with static IPs or DHCP-assigned IPs.
✗NAT overload works only with OSPF-learned routesWrong answer — click to see why▾
Why this is wrong here
NAT overload (PAT) is independent of the routing protocol used. It works with static routes, OSPF, EIGRP, or any other routing protocol. The routing protocol only affects how packets are forwarded, not how NAT translates addresses.
★ When this WOULD be the correct answer
In a scenario where the question specifies that NAT overload must only translate traffic for routes learned via OSPF (e.g., to restrict translation to specific destinations), then an ACL or route-map referencing OSPF-learned routes could be required. For example: 'A router must perform NAT overload only for traffic destined to networks learned via OSPF. Which configuration is needed?'
Why candidates choose this
Students might think that because OSPF is a common protocol in enterprise networks, NAT might depend on it. However, NAT operates at Layer 3 and is not tied to any specific routing protocol. The confusion may come from the fact that NAT often works with routing to ensure return traffic reaches the correct inside host.
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
Ensure inside and outside interfaces are correctly set for NAT; misconfigurations here are a common oversight.
Detailed technical explanation
How to think about this question
Network Address Translation (NAT) overload, also known as Port Address Translation (PAT), allows multiple inside local IP addresses to be mapped to a single inside global IP address by using different port numbers. This technique conserves public IP addresses and enables multiple devices on a private network to access the internet simultaneously. For NAT overload to function correctly, the router must identify which interfaces are inside and which are outside to apply translation rules properly.
The router uses the commands ip nat inside and ip nat outside to designate interfaces accordingly. The inside interface connects to the private network, while the outside interface connects to the public network or internet. If the outside interface is not configured with ip nat outside, the router cannot correctly translate inside local addresses to inside global addresses, resulting in no NAT translations appearing. This misconfiguration prevents the router from building the NAT translation table, causing inside users to fail when browsing the internet.
A common exam trap is assuming that NAT overload will work without explicitly configuring inside and outside interface roles. Candidates might also confuse ACLs used for NAT with deny rules, or believe that routing protocols like OSPF affect NAT operation. In practice, NAT operates independently of routing protocols and DHCP presence. Correct interface role assignment is essential for NAT to function, and missing ip nat outside on the external interface is the most frequent cause of translation failures.
KKey Concepts to Remember
NAT overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session.
The router requires explicit configuration of inside and outside interfaces using ip nat inside and ip nat outside commands to correctly apply NAT translations.
Without the ip nat outside command on the external interface, the router cannot build NAT translation entries, causing inside users to fail internet access.
ACLs used in NAT configurations must permit inside local addresses for translation and should not deny them, ensuring proper NAT operation.
NAT overload operates independently of routing protocols such as OSPF and does not require DHCP on the inside interface to function.
The NAT translation table remains empty if interface roles are missing or reversed, preventing any NAT translations from occurring.
Correct interface role assignment is essential for NAT to identify traffic direction and perform address translation accurately.
Misconfiguring NAT interface roles is a common cause of NAT failures and a frequent exam trap in CCNA 200-301 scenarios.
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 overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
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 overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session., 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 overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session..
What is the correct answer to this question?
The correct answer is: The outside interface is missing the ip nat outside command — NAT needs the inside and outside interfaces marked correctly. If those roles are missing or reversed, the router has no context for translating traffic and the NAT table stays empty.
What should I do if I get this 200-301 question wrong?
Review nAT overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session., then practise related 200-301 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
NAT overload allows multiple inside local IP addresses to share a single inside global IP address by using unique port numbers for each session.
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