mediumMultiple Choice
300-410 Practice Question: Which authentication method is supported by…
Which authentication method is supported by default for GRE tunnels in Cisco IOS-XE?
⚠ Common exam trap
Cisco often tests the misconception that the GRE key field provides authentication, but it is only an optional identifier and does not offer any security; candidates may incorrectly assume that a key or password is required or that GRE has built-in authentication.
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
✓
No authentication by default
GRE tunnels in Cisco IOS-XE do not include any built-in authentication mechanism by default. The GRE protocol (RFC 2784) defines a simple encapsulation method without authentication or encryption; any security features must be added externally, such as using IPsec to protect the tunnel traffic. Therefore, the correct answer is that no authentication is enabled by default.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
MD5 authentication
Why it's wrong here
GRE itself defines no authentication field, and IOS-XE enables none by default; MD5 is configured only through IPsec protection or a tunnel key. MD5 would be the answer where IPsec or a keyed tunnel is explicitly required.
- ✗
SHA-256 authentication
Why it's wrong here
SHA-256 is an IPsec integrity algorithm, not a native GRE feature, and IOS-XE enables no tunnel authentication by default. It becomes relevant when the GRE tunnel is protected by IPsec, where SHA-256 can secure the ESP payload.
- ✓
No authentication by default
Why this is correct
GRE tunnels in Cisco IOS-XE carry no authentication mechanism unless explicitly configured, so traffic passes without peer verification. This satisfies the stem's "by default" constraint: IPsec or tunnel key configuration must be added manually for any authentication to occur.
- ✗
Plain-text password authentication
Why it's wrong here
GRE itself carries no authentication mechanism; it encapsulates payloads without verifying peers, so plain-text password authentication is not a default option. Such passwords belong to protocols like OSPF or HSRP. GRE confidentiality and integrity are provided by layering IPsec over the tunnel.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.