hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures IPsec with a transform set…
An engineer configures IPsec with a transform set that includes ESP-SHA-HMAC and ESP-AES-256. The VPN tunnel fails to establish, and debug shows 'transform set mismatch'. 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 peer has the transform set with the same protocols but in a different order (ESP-AES-256 then ESP-SHA-HMAC), which is considered a mismatch.
The transform set must match exactly on both peers, including the order of protocols. ESP-SHA-HMAC is an authentication protocol, and ESP-AES-256 is encryption. If the peer has them in a different order or uses a different combination, the negotiation fails.
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 peer has the transform set with the same protocols but in a different order (ESP-AES-256 then ESP-SHA-HMAC), which is considered a mismatch.
Why this is correct
IPsec transform sets are matched exactly, including the order of protocols.
- ✗
The peer uses ESP-AES-256 with a different key length, such as 128-bit.
Why it's wrong here
AES-256 implies 256-bit key; AES-128 would be a different transform.
- ✗
The peer has 'crypto ipsec transform-set' with 'esp-sha-hmac' and 'esp-aes 256' but also includes 'comp-lzs'.
Why it's wrong here
Extra protocols would also cause a mismatch, but the order issue is more subtle and common.
- ✗
The peer uses 'esp-sha-hmac' as authentication and 'esp-aes 256' as encryption, but the mode is set to transport instead of tunnel.
Why it's wrong here
Mode mismatch is a separate issue and would show a different debug message.
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.