300-410 Infrastructure Security Practice Question
A network engineer is configuring IPsec VPN on a Cisco IOS router. The engineer wants to ensure that only traffic from the 192.168.1.0/24 subnet is encrypted and sent through the tunnel, while other traffic is sent unencrypted. Which configuration element is required to define the interesting traffic?
⚠ Common exam trap
Many candidates confuse the role of the crypto map with the ACL; the crypto map references the ACL but does not itself define 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-list
In Cisco IOS IPsec configuration, an access list (ACL) is used to define interesting traffic that should be encrypted and sent through the VPN tunnel. The ACL specifies the source and destination subnets. The crypto map then references this ACL to apply IPsec to matching traffic. Other components like transform set and ISAKMP policy handle encryption algorithms and key exchange, but not traffic selection.
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 authentication algorithms used to protect the data, such as ESP-AES and ESP-SHA-HMAC. It does not specify which traffic is encrypted; that is the role of the ACL. The transform set is referenced in the crypto map along with the ACL.
- ✗
crypto map
Why it's wrong here
A crypto map ties together the various IPsec configuration components, such as the ACL, transform set, and peer. However, it does not define the interesting traffic itself; it references an ACL that does. The crypto map is applied to an interface to enable IPsec, but the traffic selection is done by the ACL.
- ✗
ISAKMP policy
Why it's wrong here
An ISAKMP policy defines the parameters for IKE Phase 1 negotiation, such as encryption, hash, authentication, and Diffie-Hellman group. It does not define interesting traffic. The ACL is used for traffic selection, while ISAKMP policy is for establishing the secure channel.
- ✓
access-list
Why this is correct
An access list (ACL) is used to define which traffic is considered interesting and should be encrypted. For example, an ACL permitting IP traffic from 192.168.1.0/24 to the remote subnet will match that traffic for encryption. The crypto map references this ACL to determine what to protect.
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
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