This 300-410 practice question tests your understanding of vrf-lite. 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.
A network engineer is troubleshooting a VRF-Lite configuration on a Cisco router. The router has two VRFs (VRF_CUSTOMER_A and VRF_CUSTOMER_B). The engineer notices that traffic from VRF_CUSTOMER_A is being routed to the wrong next-hop, causing connectivity issues. The 'show ip route vrf VRF_CUSTOMER_A' shows a route to the destination via a next-hop that belongs to VRF_CUSTOMER_B. What is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'route-target import' command in VRF_CUSTOMER_A is importing routes from VRF_CUSTOMER_B.
This issue is typically caused by route leaking between VRFs, which can happen if the route-target import/export commands are misconfigured or if there is a shared interface with incorrect VRF assignment.
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 'route-target import' command in VRF_CUSTOMER_A is importing routes from VRF_CUSTOMER_B.
Why this is correct
This causes routes from VRF_CUSTOMER_B to appear in VRF_CUSTOMER_A's routing table, leading to incorrect next-hop selection.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The router has a default route that points to the next-hop in VRF_CUSTOMER_B.
Why it's wrong here
A default route would only be used if no specific route exists, and the route in question is specific.
✗
The 'ip cef' command is disabled globally.
Why it's wrong here
Disabling CEF would affect performance but not cause cross-VRF route selection.
✗
The 'ip vrf forwarding' command is applied to the same physical interface for both VRFs.
Why it's wrong here
An interface can only belong to one VRF; applying it to both would cause an error.
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.
VRF-Lite — This question tests VRF-Lite — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The 'route-target import' command in VRF_CUSTOMER_A is importing routes from VRF_CUSTOMER_B. — This issue is typically caused by route leaking between VRFs, which can happen if the route-target import/export commands are misconfigured or if there is a shared interface with incorrect VRF assignment.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". 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?
Static NAT maps one inside address to one outside address.
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