300-410 VPN Technologies Practice Question
A network engineer is configuring a GRE over IPsec tunnel between two Cisco IOS routers. The engineer wants to ensure that the GRE tunnel traffic is encrypted by IPsec. Which of the following configurations is required to achieve this?
⚠ Common exam trap
The trap here is assuming that the crypto ACL should match the private traffic that traverses the GRE tunnel, but in GRE over IPsec, the crypto ACL must match the GRE protocol 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
✓
The crypto ACL must permit GRE traffic (protocol 47) between the tunnel source and destination IP addresses.
In a GRE over IPsec configuration, the GRE tunnel encapsulates the private traffic, and then IPsec encrypts the GRE packets. Therefore, the crypto ACL must match GRE traffic (protocol 47) between the tunnel endpoints. This ensures that the entire GRE packet, including the original private IP packet, is encrypted. Permitting the private IP traffic in the crypto ACL would cause IPsec to encrypt the private packets before GRE encapsulation, which is not desired.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The transform set must include the GRE protocol as the encapsulation mode.
Why it's wrong here
Transform sets define encryption and authentication algorithms, not encapsulation protocols. GRE is not a transform set option. IPsec can use transport or tunnel mode, but GRE is a separate encapsulation. The transform set does not need to specify GRE; it just needs to match on both peers.
- ✗
The crypto map must be applied to the GRE tunnel interface instead of the physical interface.
Why it's wrong here
Crypto maps are applied to physical interfaces, not tunnel interfaces. Applying a crypto map to a tunnel interface is not supported. The crypto map should be applied to the physical interface that carries the GRE traffic. Therefore, this option is incorrect.
- ✗
The crypto ACL must permit IP traffic between the private networks that are routed over the GRE tunnel.
Why it's wrong here
If the crypto ACL permits IP traffic between the private networks, IPsec would encrypt the original IP packets before they are encapsulated in GRE. This would result in double encryption or incorrect encapsulation, as GRE would then encapsulate the encrypted packets, which is not the intended design. The correct approach is to encrypt the GRE packets themselves.
- ✓
The crypto ACL must permit GRE traffic (protocol 47) between the tunnel source and destination IP addresses.
Why this is correct
For GRE over IPsec, the crypto ACL must match the GRE packets, which are protocol 47. The ACL should permit GRE between the tunnel source and destination IPs. This ensures that the GRE-encapsulated packets are encrypted by IPsec. Without matching GRE, the tunnel traffic would not be encrypted.
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.
Go deeper
Related to this question
About these practice questions
Courseiva writes every 300-410 question from scratch — 1,401 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or 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 300-410 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 300-410 exam.