- A
The crypto map is applied to the wrong interface; it should be applied to the VRF interface, not the physical interface.
Why wrong: The crypto map should be applied to the physical interface (or tunnel interface) that carries the traffic, but the issue is that the crypto engine does not see VRF traffic.
- B
The ACL for interesting traffic is not matching the VRF traffic because the ACL is evaluated in the global routing table, not the VRF.
IPsec crypto maps are evaluated in the global routing table. VRF traffic must be redirected to the global table using PBR or the crypto map must be VRF-aware.
- C
The IPsec transform set has a mismatch in the encryption algorithm, causing the tunnel to fail to establish.
Why wrong: The tunnel is established, so transform set mismatch is not the issue.
- D
The 'crypto isakmp key' command is missing the VRF keyword, causing IKE to fail.
Why wrong: IKE is used for tunnel establishment, and the tunnel is up, so this is not the problem.
Quick Answer
The answer is that the ACL for interesting traffic is not matching the VRF traffic because the ACL is evaluated in the global routing table, not the VRF. This occurs because IPsec crypto maps, by default, operate within the global routing table, even when applied to an interface that belongs to a VRF. In VRF-Lite, traffic is forwarded using the VRF’s routing table, but the crypto engine inspects packets against the ACL in the global table; if the source and destination addresses belong to the VRF, the ACL sees them as non-matching, so the traffic is never deemed interesting and remains unencrypted. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the boundary between VRF forwarding and IPsec policy enforcement—a common trap is assuming that applying the crypto map to the VRF interface is sufficient. To fix this, you must either apply the crypto map with the `vrf` keyword or use policy-based routing to redirect the traffic into the global table. Memory tip: “VRF routes the packet, but the crypto map sees the global map.”
300-410 VRF-Lite Practice Question
This 300-410 practice question tests your understanding of vrf-lite. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An engineer configures IPsec between two VRF-Lite routers using a site-to-site VPN. The tunnel is established, but no traffic is encrypted. The engineer verifies that the crypto map is applied to the correct interface and that the ACL for interesting traffic matches the VRF traffic. Which is the most likely explanation?
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 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
The ACL for interesting traffic is not matching the VRF traffic because the ACL is evaluated in the global routing table, not the VRF.
In VRF-Lite, traffic is forwarded based on the VRF routing table. However, IPsec crypto maps operate on the global routing table by default. If the traffic is in a VRF, the crypto map must be applied with the VRF keyword or the traffic must be redirected using a policy-based route (PBR) to the global table. Without this, the crypto engine does not see the traffic as interesting, so it is not encrypted.
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 crypto map is applied to the wrong interface; it should be applied to the VRF interface, not the physical interface.
Why it's wrong here
The crypto map should be applied to the physical interface (or tunnel interface) that carries the traffic, but the issue is that the crypto engine does not see VRF traffic.
- ✓
The ACL for interesting traffic is not matching the VRF traffic because the ACL is evaluated in the global routing table, not the VRF.
Why this is correct
IPsec crypto maps are evaluated in the global routing table. VRF traffic must be redirected to the global table using PBR or the crypto map must be VRF-aware.
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 IPsec transform set has a mismatch in the encryption algorithm, causing the tunnel to fail to establish.
Why it's wrong here
The tunnel is established, so transform set mismatch is not the issue.
- ✗
The 'crypto isakmp key' command is missing the VRF keyword, causing IKE to fail.
Why it's wrong here
IKE is used for tunnel establishment, and the tunnel is up, so this is not the problem.
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.
What to study next
Got this wrong? Here's your next step.
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.
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VRF-Lite — study guide chapter
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VRF-Lite practice questions
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FAQ
Questions learners often ask
What does this 300-410 question test?
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 ACL for interesting traffic is not matching the VRF traffic because the ACL is evaluated in the global routing table, not the VRF. — In VRF-Lite, traffic is forwarded based on the VRF routing table. However, IPsec crypto maps operate on the global routing table by default. If the traffic is in a VRF, the crypto map must be applied with the VRF keyword or the traffic must be redirected using a policy-based route (PBR) to the global table. Without this, the crypto engine does not see the traffic as interesting, so it is not encrypted.
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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Last reviewed: Jun 18, 2026
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