Question 1,263 of 2,152

MPLS Operations →hardMultiple ChoiceObjective-mapped

IPsec VPN Not Encrypting — Crypto Map on Wrong Interface | Cisco CCNP ENARSI 300-410 Explained

This 300-410 practice question tests your understanding of mpls operations. 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.

An engineer configures IPsec site-to-site VPN between two routers. The tunnel is established, but no traffic is encrypted. The engineer checks the crypto map and access-list and confirms they match the interesting traffic. What 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, and traffic is not being matched.
If the crypto map is applied to a different interface than the one carrying the interesting traffic, the traffic will not be encrypted even if the tunnel is up. The tunnel establishment only requires the crypto map to be present on the interface, but encryption only occurs for traffic matching the access-list on that specific interface.
B
The 'transform-set' is configured with ESP-NULL, which provides no encryption.
Why wrong: ESP-NULL provides authentication but no encryption; however, the question states no traffic is encrypted, which could be true, but the tunnel would still be established. This is a possible but less likely cause compared to interface mismatch.
C
The 'crypto isakmp key' is mismatched between the two routers.
Why wrong: A mismatched ISAKMP key would prevent the tunnel from establishing, not just encryption.
D
The 'crypto map' is not applied globally, so it does not affect traffic.
Why wrong: Crypto maps are applied per interface, not globally. This statement is incorrect.

Full breakdown with real-world context →

Quick Answer

The answer is that the crypto map is applied to the wrong interface, so traffic is not being matched for encryption. Even when an IPsec VPN tunnel is established, the crypto map must be applied to the specific interface through which the interesting traffic actually exits; if it is applied to a different interface—such as a subinterface while traffic flows through the main interface, or vice versa—the router will not attempt to encrypt that traffic, leaving it to pass in plaintext. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that tunnel establishment only proves IKE and IPsec negotiation succeeded, not that encryption is occurring on the correct data path. A common trap is assuming a working tunnel guarantees encryption, but the crypto map’s interface binding is what triggers the encryption engine. Remember the memory tip: “Tunnel up, traffic clear? Check the interface where the crypto map lives.”

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 crypto map is applied to the wrong interface, and traffic is not being matched.

A common edge case is that the crypto map is applied to the wrong interface or the access-list is not correctly referencing the traffic. However, if the tunnel is established, the issue may be that the crypto map is applied to a subinterface but the traffic is flowing through the main interface, or the 'crypto map' command is missing the 'local-address' option for multiple crypto maps. Another possibility is that the 'set peer' command is missing or the peer address is incorrect.

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, and traffic is not being matched.
Why this is correct
If the crypto map is applied to a different interface than the one carrying the interesting traffic, the traffic will not be encrypted even if the tunnel is up. The tunnel establishment only requires the crypto map to be present on the interface, but encryption only occurs for traffic matching the access-list on that specific interface.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The 'transform-set' is configured with ESP-NULL, which provides no encryption.
Why it's wrong here
ESP-NULL provides authentication but no encryption; however, the question states no traffic is encrypted, which could be true, but the tunnel would still be established. This is a possible but less likely cause compared to interface mismatch.
✗
The 'crypto isakmp key' is mismatched between the two routers.
Why it's wrong here
A mismatched ISAKMP key would prevent the tunnel from establishing, not just encryption.
✗
The 'crypto map' is not applied globally, so it does not affect traffic.
Why it's wrong here
Crypto maps are applied per interface, not globally. This statement is incorrect.

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.

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.

Related 300-410 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Layer 3 Technologies practice questions

Practise 300-410 questions linked to Layer 3 Technologies.

EIGRP Troubleshooting practice questions

Practise 300-410 questions linked to EIGRP Troubleshooting.

OSPF Troubleshooting (v2/v3) practice questions

Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).

BGP Troubleshooting practice questions

Practise 300-410 questions linked to BGP Troubleshooting.

Route Redistribution practice questions

Practise 300-410 questions linked to Route Redistribution.

Policy-Based Routing (PBR) practice questions

Practise 300-410 questions linked to Policy-Based Routing (PBR).

VRF-Lite practice questions

Practise 300-410 questions linked to VRF-Lite.

Route Maps and Route Filtering practice questions

Practise 300-410 questions linked to Route Maps and Route Filtering.

Administrative Distance practice questions

Practise 300-410 questions linked to Administrative Distance.

Route Summarization practice questions

Practise 300-410 questions linked to Route Summarization.

Bidirectional Forwarding Detection (BFD) practice questions

Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).

VPN Technologies practice questions

Practise 300-410 questions linked to VPN Technologies.

Practice this exam

Start a free 300-410 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

300-410 practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this 300-410 question test?

MPLS Operations — This question tests MPLS Operations — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: The crypto map is applied to the wrong interface, and traffic is not being matched. — A common edge case is that the crypto map is applied to the wrong interface or the access-list is not correctly referencing the traffic. However, if the tunnel is established, the issue may be that the crypto map is applied to a subinterface but the traffic is flowing through the main interface, or the 'crypto map' command is missing the 'local-address' option for multiple crypto maps. Another possibility is that the 'set peer' command is missing or the peer address is incorrect.

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.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Keep practising

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.