hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures an IPsec site-to-site VPN…
An engineer configures an IPsec site-to-site VPN between two routers. The tunnel comes up, but traffic is not encrypted. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the misconception that a tunnel being up guarantees traffic encryption, but the crypto ACL is the gatekeeper for which traffic gets encrypted, and candidates may overlook this distinction.
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 ACL does not match the traffic that is being sent.
The most likely reason traffic is not encrypted despite the tunnel being up is that the crypto ACL (access-list) applied to the IPsec configuration does not match the actual traffic being sent. The crypto ACL defines which traffic should be protected by IPsec; if the ACL does not permit the specific source/destination or protocol/port of the traffic, the router will not attempt to encrypt it, even though the IKE and IPsec security associations (SAs) are established.
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 ACL does not match the traffic that is being sent.
Why this is correct
Correct. Interesting traffic must match the ACL for encryption.
- ✗
The transform set uses ESP with null encryption.
Why it's wrong here
Null encryption would still encrypt (with null algo), but traffic would be encapsulated.
- ✗
The ISAKMP policy has the wrong authentication method.
Why it's wrong here
ISAKMP policy affects phase 1, not encryption of data.
- ✗
The pre-shared key is incorrect.
Why it's wrong here
Incorrect PSK would prevent phase 1 from completing.
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.
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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.