This 300-410 practice question tests your understanding of ipv6 tunneling techniques. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which authentication method is supported by default for GRE tunnels in Cisco IOS-XE?
MD5 authentication
Why wrong: MD5 is used in routing protocols like OSPF, not in GRE by default.
SHA-256 authentication
Why wrong: SHA-256 is not a default GRE authentication method.
No authentication by default
GRE tunnels have no authentication by default; a key must be configured manually.
Plain-text password authentication
Why wrong: While a key can be used, it is not enabled by default.
Answer choices
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
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
MD5 is used in routing protocols like OSPF, not in GRE by default.
SHA-256 authentication
Why it's wrong here
SHA-256 is not a default GRE authentication method.
No authentication by default
Why this is correct
GRE tunnels have no authentication by default; a key must be configured manually.
Related concept
Read the scenario before looking for a memorised answer.
Plain-text password authentication
Why it's wrong here
While a key can be used, it is not enabled by default.
Common exam traps
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.
Detailed technical explanation
GRE tunnels operate by encapsulating packets within a simple IP protocol (47) header, with no integrity checks or authentication fields in the base specification. The optional GRE key field (RFC 2890) is sometimes misconstrued as authentication, but it is merely a 32-bit identifier used for flow classification or to identify a tunnel endpoint, not a cryptographic or plain-text password. In real-world deployments, GRE tunnels are often combined with IPsec (e.g., using tunnel mode or transport mode) to provide authentication, integrity, and confidentiality, especially when traversing untrusted networks.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
IPv6 Tunneling Techniques — This question tests IPv6 Tunneling Techniques — Read the scenario before looking for a memorised answer..
The correct answer is: 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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