300-410 VPN Technologies Practice Question
A network administrator is configuring a site-to-site IPsec VPN between two Cisco IOS XE routers. The administrator wants to ensure that the VPN tunnel only encrypts traffic from the 10.1.1.0/24 subnet to the 10.2.2.0/24 subnet. Which configuration element defines the traffic to be encrypted?
⚠ Common exam trap
It's easy for candidates to confuse the role of the crypto ACL with the crypto map or transform set, which are used to apply protection but do not define the traffic itself.
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
In a site-to-site IPsec VPN, the crypto ACL (an extended access list) is used to define interesting traffic that should be encrypted and sent through the tunnel. The crypto map references this ACL to match packets. The transform set and ISAKMP policy define how to protect the traffic and negotiate the tunnel, but they do not select the 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
The transform set defines the encryption and authentication algorithms used to protect the traffic, such as esp-aes and esp-sha-hmac. It does not define which traffic is encrypted; that is the role of the crypto ACL. The transform set is applied within the crypto map or IPsec profile.
- ✗
ISAKMP policy
Why it's wrong here
The ISAKMP policy defines the parameters for IKE phase 1 negotiations, such as encryption, hash, authentication, and Diffie-Hellman group. It does not specify the traffic to be encrypted. That is determined by the crypto ACL referenced in the crypto map.
- ✓
crypto ACL
Why this is correct
The crypto ACL (extended access list) defines which traffic is interesting and should be protected by the IPsec VPN. In this scenario, an ACL permitting traffic from 10.1.1.0/24 to 10.2.2.0/24 and vice versa would be referenced by the crypto map. This ACL is the element that specifies the traffic to be encrypted.
- ✗
crypto map
Why it's wrong here
The 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 specifies the interesting traffic. Without the ACL, the crypto map has no traffic definition.
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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