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 no traffic is encrypted. The engineer verifies that the crypto map is applied to the outgoing interface and that the ACL defining interesting traffic is correct. Which 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 ACL is not mirrored on both sides, so the SA is not established for the traffic
A common edge case is that the ACL defining interesting traffic is applied in the wrong direction. For IPsec, the ACL should match traffic that will be encrypted, and it must be applied to the crypto map. However, if the ACL is configured with the source and destination reversed (e.g., source is local network and destination is remote network on one router, but on the other router the ACL should also have source as local network), the traffic may not match. Additionally, if the ACL is not mirrored on both sides, the tunnel may come up but traffic will not be encrypted because the SA is not established for that traffic.
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 is not mirrored on both sides, so the SA is not established for the traffic
Why this is correct
Correct. IPsec requires that the crypto ACLs be mirror images of each other for bidirectional traffic to be encrypted.
- ✗
The transform-set is missing encryption or authentication
Why it's wrong here
A missing transform-set would prevent the tunnel from coming up at all.
- ✗
The crypto map is applied to the wrong interface
Why it's wrong here
If the crypto map is applied to the wrong interface, the tunnel would not come up.
- ✗
The IKE policy is not configured
Why it's wrong here
Without IKE policy, the tunnel would not establish.
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.