300-410 IPv6 Tunneling Techniques Practice Question
This 300-410 practice question tests your understanding of ipv6 tunneling techniques. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 DMVPN phase 3 network with IPv6 over IPv4 tunnels is experiencing spoke-to-spoke tunnel failures. Hub router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source GigabitEthernet0/0 tunnel mode gre multipoint ip nhrp network-id 1 ip nhrp map multicast dynamic ipv6 nhrp map multicast dynamic. Spoke router R2 shows: R2# show dmvpn detail Legend: Attrb -> S: Static, D: Dynamic, I: Incomplete NHRP domain: 1 Interface: Tunnel0, IPv4 NHRP Details Type:Spoke, Total NBMA Peers: 1 # Ent Peer NBMA Addr Peer Tunnel Add State UpDn Tm Attrb 1 192.0.2.2 2001:DB8:1::2 UP 00:10:00 D. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The hub is missing the ip nhrp redirect command under Tunnel0.
In DMVPN Phase 3, spoke-to-spoke tunnels rely on the hub to send NHRP Redirect messages to trigger shortcut creation. The hub's configuration is missing the `ip nhrp redirect` command under Tunnel0, which prevents it from informing the spoke that a better path exists directly to another spoke. Without this redirect, the spoke never initiates an NHRP Resolution Request to build a direct tunnel, causing spoke-to-spoke communication to fail.
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 hub is missing the ip nhrp redirect command under Tunnel0.
Why this is correct
This command enables NHRP redirect messages, which are essential for phase 3 spoke-to-spoke shortcut establishment.
Related concept
Read the scenario before looking for a memorised answer.
✗
The spoke is missing the ip nhrp shortcut command under Tunnel0.
Why it's wrong here
While the spoke also needs this command, the hub's missing redirect is the primary cause here.
✗
The tunnel mode should be gre multipoint on the spokes.
Why it's wrong here
Spokes can use point-to-point GRE tunnels; multipoint is only required on the hub.
✗
IPv6 NHRP is not supported on DMVPN phase 3.
Why it's wrong here
IPv6 NHRP is supported on DMVPN phase 3 with appropriate configuration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between Phase 2 (where `ip nhrp map multicast dynamic` alone enables spoke-to-spoke tunnels) and Phase 3 (which additionally requires `ip nhrp redirect` on the hub and `ip nhrp shortcut` on spokes), causing candidates to overlook the missing redirect command.
Trap categories for this question
Command / output trap
While the spoke also needs this command, the hub's missing redirect is the primary cause here.
Detailed technical explanation
How to think about this question
DMVPN Phase 3 uses NHRP Redirect (RFC 2332) to offload traffic from the hub: when the hub forwards a packet between two spokes, it sends an NHRP Redirect message to the source spoke, which then sends an NHRP Resolution Request to the destination spoke's NBMA address. The `ip nhrp redirect` command on the hub enables this behavior; without it, the hub silently forwards traffic but never triggers shortcut creation, forcing all spoke-to-spoke traffic through the hub even in Phase 3.
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 hub is missing the ip nhrp redirect command under Tunnel0. — In DMVPN Phase 3, spoke-to-spoke tunnels rely on the hub to send NHRP Redirect messages to trigger shortcut creation. The hub's configuration is missing the `ip nhrp redirect` command under Tunnel0, which prevents it from informing the spoke that a better path exists directly to another spoke. Without this redirect, the spoke never initiates an NHRP Resolution Request to build a direct tunnel, causing spoke-to-spoke communication to fail.
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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Question Discussion
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