CCNP Security Practice Question
A network administrator is configuring IPsec VPN on a Cisco IOS router. The administrator 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 configuration element is required to define this traffic?
⚠ Common exam trap
A common mix-up: candidates confuse interface ACLs with crypto ACLs; only the crypto ACL referenced in the crypto map defines interesting traffic for encryption.
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
✓
A crypto ACL that permits IP traffic from 10.1.1.0/24 to 10.2.2.0/24.
IPsec uses a crypto ACL to define which traffic is protected. This ACL is referenced in a crypto map, which is applied to the interface. Traffic matching the ACL is encrypted; other traffic is not. The crypto ACL must permit the specific source and destination subnets. Other options do not correctly identify interesting traffic for IPsec.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A crypto ACL that permits IP traffic from 10.1.1.0/24 to 10.2.2.0/24.
Why this is correct
A crypto ACL (also called an encryption ACL) defines the interesting traffic that should be protected by IPsec. It is referenced in the crypto map. Permitting traffic from 10.1.1.0/24 to 10.2.2.0/24 ensures that only this traffic is encrypted. Other traffic falls through the implicit deny and is sent unencrypted, as desired. This is the standard method to specify VPN traffic.
- ✗
An ACL applied to the outside interface with 'ip access-group' to permit the traffic and enable encryption.
Why it's wrong here
Applying an ACL to an interface controls traffic flow but does not trigger encryption. IPsec encryption is initiated based on the crypto ACL referenced in the crypto map. Interface ACLs are for filtering, not for defining VPN interesting traffic. This approach would not ensure that the specified traffic is encrypted; it might even block it if not permitted.
- ✗
A prefix list that permits the source and destination subnets, applied to the crypto map.
Why it's wrong here
Prefix lists are used for route filtering and cannot be referenced in a crypto map to define interesting traffic. Crypto maps require an extended ACL to specify traffic. Prefix lists only match network prefixes, not protocol or port information. Therefore, this option fails to meet the requirement of selecting specific traffic for encryption.
- ✗
A route map that matches the source and destination subnets and sets the next-hop to the VPN peer.
Why it's wrong here
Route maps are used for routing policy, not for defining IPsec interesting traffic. While route maps can influence which traffic is routed, they do not trigger encryption. IPsec uses crypto ACLs to determine what to encrypt. Using a route map would not correctly define the encryption domain and could lead to traffic being sent unencrypted or dropped.
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.
About these practice questions
This 350-401 question is part of Courseiva's 1,923-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.