easyMultiple ChoiceObjective-mapped
Default Tunnel Mode for IPv6 Tunnels
What is the default tunnel mode for an IPv6 tunnel configured on Cisco IOS-XE?
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.
⚠ Common exam trap
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.
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
✓
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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Same concept, more angles
1 more way this is tested on 300-410
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Variation 1. What is the default tunnel mode for a tunnel interface on Cisco IOS?
easy- A.tunnel mode ipv6ip
- ✓ B.tunnel mode gre ip
- C.tunnel mode gre ipv6
- D.tunnel mode mpls traffic-eng
Why 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.
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.