This 300-410 practice question tests your understanding of ipv6 tunneling techniques. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
What is the default tunnel mode for a tunnel interface on Cisco IOS?
tunnel mode ipv6ip
Why wrong: ipv6ip is not the default.
tunnel mode gre ip
GRE over IPv4 is the default.
tunnel mode gre ipv6
Why wrong: GRE over IPv6 is not the default.
tunnel mode mpls traffic-eng
Why wrong: MPLS TE is a different tunnel mode.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
tunnel mode gre ip
The default tunnel mode on Cisco IOS is GRE (Generic Routing Encapsulation) over IPv4, configured with the command `tunnel mode gre ip`. This mode encapsulates packets using the GRE protocol (RFC 2784) with an IPv4 transport header, and it is the default when no explicit tunnel mode is specified. GRE ip supports multiprotocol payloads (IPv4, IPv6, etc.) and is widely used for site-to-site VPNs and overlay networks.
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.
tunnel mode ipv6ip
Why it's wrong here
ipv6ip is not the default.
tunnel mode gre ip
Why this is correct
GRE over IPv4 is the default.
Related concept
Read the scenario before looking for a memorised answer.
tunnel mode gre ipv6
Why it's wrong here
GRE over IPv6 is not the default.
tunnel mode mpls traffic-eng
Why it's wrong here
MPLS TE is a different tunnel mode.
Common exam traps
Cisco often tests the assumption that the default tunnel mode is IPv6-in-IPv4 or GRE over IPv6, but the actual default is GRE over IPv4, which catches candidates who overlook the implicit IPv4 transport requirement.
Detailed technical explanation
When a tunnel interface is created without a `tunnel mode` command, Cisco IOS automatically sets it to `tunnel mode gre ip`, which uses protocol type 0x0800 for IPv4 transport and GRE protocol type 0x2F. Under the hood, GRE adds a 4-byte header (plus optional 4-byte key/sequence) between the payload and the outer IP header, allowing the tunnel to carry any Layer 3 protocol. In real-world scenarios, forgetting to change the tunnel mode when deploying IPv6-over-IPv4 or GRE-over-IPv6 can cause connectivity failures, as the default expects IPv4 transport.
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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: tunnel mode gre ip — The default tunnel mode on Cisco IOS is GRE (Generic Routing Encapsulation) over IPv4, configured with the command `tunnel mode gre ip`. This mode encapsulates packets using the GRE protocol (RFC 2784) with an IPv4 transport header, and it is the default when no explicit tunnel mode is specified. GRE ip supports multiprotocol payloads (IPv4, IPv6, etc.) and is widely used for site-to-site VPNs and overlay networks.
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
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.
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