Quick Answer
The answer is GRE, or Generic Routing Encapsulation, which is the default tunnel mode for an IPv6 tunnel configured on Cisco IOS-XE. When you create a tunnel interface and specify an IPv6 tunnel source and destination without explicitly setting the mode, the router automatically applies the 'tunnel mode gre ipv6' command, defaulting to GRE encapsulation. This is because GRE provides a multiprotocol transport that can carry both IPv4 and IPv6 payloads, making it the flexible, standards-based choice for IPv6 tunneling. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of tunnel interface defaults and configuration nuances—a common trap is assuming IPv6 tunnels default to IPv6IP (protocol 41) encapsulation, which is actually a non-default option. Remember that GRE is the universal carrier: if you see a tunnel with an IPv6 source and destination but no mode set, think GRE first. A helpful memory tip is "GRE for the default, IPv6IP for the specific"—GRE handles both address families out of the box.
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 an IPv6 tunnel configured on Cisco IOS-XE?
IPv6IP
Why wrong: IPv6IP is not a default mode; it must be explicitly configured.
GRE
GRE is the default tunnel mode for IPv6 tunnels in IOS-XE.
ISATAP
Why wrong: ISATAP is a specific tunneling technique, not the default mode.
6to4
Why wrong: 6to4 is an automatic tunneling method, not the default 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
GRE
The default tunnel mode for an IPv6 tunnel on Cisco IOS-XE is GRE (Generic Routing Encapsulation), as specified by the 'tunnel mode gre ipv6' command. When you create a tunnel interface and configure an IPv6 tunnel source and destination without explicitly setting the tunnel mode, the router defaults to GRE encapsulation, which provides a multiprotocol transport capable of carrying both IPv4 and IPv6 payloads.
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.
IPv6IP
Why it's wrong here
IPv6IP is not a default mode; it must be explicitly configured.
GRE
Why this is correct
GRE is the default tunnel mode for IPv6 tunnels in IOS-XE.
Related concept
Read the scenario before looking for a memorised answer.
ISATAP
Why it's wrong here
ISATAP is a specific tunneling technique, not the default mode.
6to4
Why it's wrong here
6to4 is an automatic tunneling method, not the default mode.
Common exam traps
Cisco often tests the misconception that the default tunnel mode for IPv6 tunnels is 'ipv6ip' (manual IPv6-over-IPv4) because of its simplicity, but the actual default is GRE, which is a more feature-rich encapsulation.
Detailed technical explanation
Under the hood, GRE encapsulation adds an 8-byte GRE header (with a 4-byte protocol type field) and a 20-byte outer IPv4 header, allowing the tunnel to carry not only IPv6 but also other Layer 3 protocols like IPX or AppleTalk. In real-world scenarios, using GRE for IPv6 tunneling is common when you need to transport IPv6 across an IPv4-only network infrastructure while also supporting multicast or non-IP protocols, whereas simpler modes like IPv6IP are limited to unicast IPv6 traffic. A subtle behavior is that GRE tunnels require the 'tunnel mode gre ipv6' command to be explicitly shown in the running configuration, but if omitted, the router defaults to GRE for IPv6 tunnels, which can confuse administrators who expect a different default.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
IPv6 Tunneling Techniques — study guide chapter
Learn the concepts, then practise the questions
IPv6 Tunneling Techniques practice questions
Targeted practice on this topic area only
All 300-410 questions
2,152 questions across all exam domains
Cisco CCNP ENARSI 300-410 study guide
Full concept coverage aligned to exam objectives
300-410 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 300-410 questions linked to Layer 3 Technologies.
Practise 300-410 questions linked to EIGRP Troubleshooting.
Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).
Practise 300-410 questions linked to BGP Troubleshooting.
Practise 300-410 questions linked to Route Redistribution.
Practise 300-410 questions linked to Policy-Based Routing (PBR).
Practise 300-410 questions linked to VRF-Lite.
Practise 300-410 questions linked to Route Maps and Route Filtering.
Practise 300-410 questions linked to Administrative Distance.
Practise 300-410 questions linked to Route Summarization.
Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).
Practise 300-410 questions linked to VPN Technologies.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
IPv6 Tunneling Techniques — This question tests IPv6 Tunneling Techniques — Read the scenario before looking for a memorised answer..
The correct answer is: GRE — The default tunnel mode for an IPv6 tunnel on Cisco IOS-XE is GRE (Generic Routing Encapsulation), as specified by the 'tunnel mode gre ipv6' command. When you create a tunnel interface and configure an IPv6 tunnel source and destination without explicitly setting the tunnel mode, the router defaults to GRE encapsulation, which provides a multiprotocol transport capable of carrying both IPv4 and IPv6 payloads.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. What is the default tunnel mode for a tunnel interface on Cisco IOS?
easyWhy B: 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.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.