hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures IPsec site-to-site VPN…
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?
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.
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.
- ✗
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.
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.