The answer is that the tunnel interface lacks a global unicast address, which prevents it from routing IPv6 traffic beyond the local link. This is correct because the output shows only a link-local address (FE80::) is present, and without a global unicast address, the router cannot participate in IPv6 routing or forward packets to other networks. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of IPv6 tunneling fundamentals and the distinction between link-local and global addresses—a common trap is assuming a tunnel source/destination alone provides global reachability. Remember that a tunnel interface, like any IPv6 interface, requires an explicit global unicast address for routing to function. A useful memory tip: "No GUA, no routing beyond the link"—if you see only FE80 in the show output, check the tunnel configuration for a missing global unicast address.
300-410 IPv6 Tunneling Techniques Practice Question
This 300-410 practice question tests your understanding of ipv6 tunneling techniques. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network engineer runs the following command on Router R1:
R1# show ipv6 interface tunnel 0
Tunnel0 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::A8BB:CCFF:FE00:1
No global unicast address is configured
Joined group address(es):
FF02::1
FF02::2
FF02::1:FF00:1
MTU is 1480 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds
ND advertised reachable time is 0 milliseconds
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfiguration for addresses.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The tunnel is not configured with a global IPv6 address, which may prevent routing of IPv6 traffic.
The output shows that the tunnel interface has no global unicast address configured, only a link-local address. Without a global IPv6 address, the router cannot route IPv6 traffic beyond the local link, as global reachability requires a globally routable address. This is a common misconfiguration in IPv6 tunneling scenarios where the tunnel source and destination are set but the interface itself lacks a global IPv6 address.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The tunnel interface is down.
Why it's wrong here
The interface is up, line protocol is up.
✓
The tunnel is not configured with a global IPv6 address, which may prevent routing of IPv6 traffic.
Why this is correct
No global unicast address means the tunnel cannot be used for IPv6 routing beyond link-local.
Related concept
Read the scenario before looking for a memorised answer.
✗
The MTU is too small for IPv6.
Why it's wrong here
1480 bytes is typical for tunnels; not a problem.
✗
IPv6 is not enabled on the tunnel.
Why it's wrong here
IPv6 is enabled as shown.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a link-local address alone is sufficient for IPv6 routing, but in fact, global unicast addresses are required for traffic to be routable beyond the local segment.
Trap categories for this question
Command / output trap
IPv6 is enabled as shown.
Detailed technical explanation
How to think about this question
IPv6 tunneling techniques like GRE or IPv6-in-IPv4 require a global unicast address on the tunnel interface for routing traffic across the tunnel; the link-local address is only used for neighbor discovery and local communication. The absence of a global address means the router cannot participate in IPv6 routing protocols (e.g., OSPFv3, EIGRP for IPv6) or forward packets to remote destinations, as the routing table lacks a valid next-hop. In real-world scenarios, this often occurs when an engineer configures the tunnel source/destination but forgets to assign an IPv6 address to the tunnel interface itself.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPv6 Tunneling Techniques — This question tests IPv6 Tunneling Techniques — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The tunnel is not configured with a global IPv6 address, which may prevent routing of IPv6 traffic. — The output shows that the tunnel interface has no global unicast address configured, only a link-local address. Without a global IPv6 address, the router cannot route IPv6 traffic beyond the local link, as global reachability requires a globally routable address. This is a common misconfiguration in IPv6 tunneling scenarios where the tunnel source and destination are set but the interface itself lacks a global IPv6 address.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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