350-401 Security Practice Question
A network engineer is configuring a site-to-site VPN between two Cisco IOS routers. The engineer wants to ensure that only traffic from the 10.1.1.0/24 subnet to the 10.2.2.0/24 subnet is encrypted, while all other traffic is sent unencrypted. Which IPsec configuration component defines this traffic?
⚠ Common exam trap
Watch out — candidates often confuse the role of the crypto map (which binds components) with the ACL (which actually defines the traffic).
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
✓
Access control list (ACL)
In Cisco IPsec configuration, the ACL (often called the crypto ACL) specifies the traffic that should be protected. The crypto map then references this ACL. Traffic that matches the ACL is encrypted; traffic that does not match is sent in clear text. Therefore, the ACL is the component that defines the interesting 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.
- ✗
Transform set
Why it's wrong here
A transform set defines the encryption and integrity algorithms (e.g., esp-aes 256 esp-sha-hmac) for the IPsec SA. It does not define which traffic is encrypted. The transform set is negotiated during IKE and applies to the protected traffic, but traffic selection is separate.
- ✗
Crypto map
Why it's wrong here
A crypto map ties together the ACL, transform set, and peer information, but it does not itself define the traffic to be encrypted. The crypto map references an ACL that defines interesting traffic. While the crypto map is essential, the specific traffic selection is done by the ACL.
- ✓
Access control list (ACL)
Why this is correct
The ACL in an IPsec configuration defines the interesting traffic that will be encrypted. In this scenario, an ACL permitting IP from 10.1.1.0/24 to 10.2.2.0/24 would ensure only that traffic is encrypted. The crypto map references this ACL to match traffic. Other traffic not matching the ACL is sent unencrypted.
- ✗
IKE policy
Why it's wrong here
An IKE policy defines the parameters for establishing the IKE SA (encryption, hash, authentication, DH group, lifetime). It does not define which traffic is encrypted. IKE policies are used for phase 1 negotiation and are independent of traffic selection.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 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 350-401 exam.