CCNP Infrastructure Practice Question
A network engineer is configuring a Cisco IOS router to establish a site-to-site VPN using IPsec. The engineer wants to ensure that the VPN tunnel only carries traffic for the subnet 10.1.1.0/24 to 10.2.2.0/24. Which configuration element is required to define the interesting traffic?
⚠ Common exam trap
It's easy for candidates to confuse the roles of the various IPsec components; the crypto ACL defines interesting traffic, while the crypto map applies the policies.
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
✓
crypto ACL (extended access list)
The crypto ACL, an extended access list, defines the interesting traffic that should be protected by IPsec. It specifies the source and destination addresses and ports. The crypto map then references this ACL to apply the IPsec policies. Without the crypto ACL, the router would not know which packets to encrypt and send through the tunnel.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ISAKMP policy
Why it's wrong here
The ISAKMP policy defines the parameters for phase 1 IKE negotiation, such as encryption, hash, authentication, and Diffie-Hellman group. It does not define which traffic is interesting for the VPN tunnel. Traffic selection is handled by the crypto ACL.
- ✗
crypto map
Why it's wrong here
A crypto map ties together the IPsec parameters and is applied to an interface, but it does not define which traffic is interesting. The crypto map references an access list or a crypto ACL that defines the traffic. Without the ACL, the crypto map has no traffic selection criteria.
- ✗
IPsec transform set
Why it's wrong here
The IPsec transform set defines the encryption and authentication algorithms used to protect the data traffic, such as esp-aes and esp-sha-hmac. It does not specify the traffic that should be encrypted; that is the role of the crypto ACL.
- ✓
crypto ACL (extended access list)
Why this is correct
The crypto ACL, typically an extended access list, defines the interesting traffic that should be encrypted and sent through the VPN tunnel. It specifies the source and destination subnets, such as permit ip 10.1.1.0 0.0.0.255 10.2.2.0 0.0.0.255. This ACL is referenced by the crypto map.
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.