Question 1,483 of 2,152

VRF-Lite →hardMultiple ChoiceObjective-mapped

IPsec VPN in VRF-Lite: Why Traffic is Not Encrypted

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.

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.

Full breakdown with real-world context →

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.”

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: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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
Standard ACLs match source addresses.
✗
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: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

Visual reference

Quick reference

VPN Protocol Comparison

Protocol	Port	Encryption	Authentication	Use Case
IKEv2 / IPsec	UDP 500 / 4500	AES-256	Certificates / PSK	Site-to-site & remote access
SSL / TLS VPN	TCP 443	TLS 1.3	Certificates / MFA	Clientless remote access
L2TP / IPsec	UDP 1701	AES (IPsec)	PSK / Certificates	Legacy remote access
WireGuard	UDP 51820	ChaCha20	Public keys	Modern high-performance VPN
PPTP	TCP 1723	MPPE (weak)	MS-CHAPv2	Legacy — avoid in production

PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this 300-410 question test?

VRF-Lite — This question tests VRF-Lite — Standard ACLs match source addresses..

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?

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?

Standard ACLs match source addresses.

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