The answer is that the NAT command is missing the required 'vrf A' keyword, which must be explicitly added as in *ip nat inside source list 100 interface GigabitEthernet0/1 vrf A overload*. This is correct because in a multi-VRF environment, NAT operations are VRF-aware; without the *vrf* keyword appended to the NAT configuration, the router applies the translation only to the global routing table, not to the specified VRF. As a result, traffic from VRF B to VRF A bypasses translation entirely, causing asymmetric routing or unreachability even when route leaking is working. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of VRF-aware services and the common trap of assuming NAT inherits the VRF context from the interface. A reliable memory tip: "NAT needs its own VRF tag—if you forget the keyword, the translation is deferred."
300-410 NAT and PAT Practice Question
This 300-410 practice question tests your understanding of nat and pat. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
In a multi-VRF environment, Router R1 is leaking routes between VRF A and VRF B using route-target import/export. Hosts in VRF A can ping hosts in VRF B, but traffic from VRF B to VRF A fails when NAT is applied on the VRF A egress interface. Configuration: ip nat inside source list 100 interface GigabitEthernet0/1 vrf A overload. Router R1 shows: show ip nat translations vrf A: no entries. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The NAT command is missing the 'vrf A' keyword; it should be ip nat inside source list 100 interface GigabitEthernet0/1 vrf A overload.
NAT configuration for VRF A requires the 'vrf' keyword to be specified in the NAT command. Without it, NAT does not operate within the VRF context. The missing 'vrf A' in the NAT configuration means that traffic from VRF B to VRF A is not translated, causing asymmetric routing or unreachability.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 NAT command is missing the 'vrf A' keyword; it should be ip nat inside source list 100 interface GigabitEthernet0/1 vrf A overload.
Why this is correct
Adding the VRF keyword ensures NAT operates within the correct VRF context.
Related concept
Static NAT maps one inside address to one outside address.
✗
The route leaking is misconfigured; use route-map to filter routes.
Why it's wrong here
Route leaking is working as hosts in VRF A can ping VRF B, so the issue is NAT-specific.
✗
The access-list 100 is blocking VRF B traffic.
Why it's wrong here
ACL 100 is used for NAT matching, not for filtering traffic.
✗
The interface GigabitEthernet0/1 is not in VRF A.
Why it's wrong here
If the interface were not in VRF A, NAT would not be attempted at all, but the configuration implies it is.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 300-410 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
NAT and PAT — This question tests NAT and PAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The NAT command is missing the 'vrf A' keyword; it should be ip nat inside source list 100 interface GigabitEthernet0/1 vrf A overload. — NAT configuration for VRF A requires the 'vrf' keyword to be specified in the NAT command. Without it, NAT does not operate within the VRF context. The missing 'vrf A' in the NAT configuration means that traffic from VRF B to VRF A is not translated, causing asymmetric routing or unreachability.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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