- A
Add the command 'ip nhrp shortcut' under interface Tunnel0.
Why wrong: Incorrect. 'ip nhrp shortcut' is configured on spokes, not on the hub. The hub uses 'ip nhrp redirect'.
- B
Add the command 'ip nhrp nhs 10.0.0.1' under interface Tunnel0.
Why wrong: Incorrect. 'ip nhrp nhs' is used on spokes to point to the hub. The hub does not need this command.
- C
Add the command 'ip nhrp map multicast dynamic' under interface Tunnel0.
Correct. This command allows the hub to dynamically learn the NBMA addresses of spokes for multicast forwarding, which is required for routing protocol updates.
- D
Add the command 'no ip split-horizon eigrp 100' under interface Tunnel0.
Correct. In DMVPN Phase 3, the hub must disable EIGRP split horizon so that routes learned from one spoke can be advertised to other spokes, enabling spoke-to-spoke communication.
- E
Add the command 'ip nhrp authentication cisco123' under interface Tunnel0.
Why wrong: Incorrect. Authentication is optional and not required for spoke-to-spoke tunnels; it is used for security but not a mandatory change for the scenario.
Quick Answer
The answer is to add the commands 'ip nhrp map multicast dynamic' and 'no ip split-horizon eigrp 100' under interface Tunnel0. In DMVPN Phase 3, the hub already uses 'ip nhrp redirect' to trigger spokes to install a /32 shortcut route, but it must also accept dynamic NHRP registrations from spokes via 'ip nhrp map multicast dynamic' so the hub can forward multicast traffic like EIGRP hellos. Additionally, EIGRP split horizon on the hub prevents routes learned from one spoke from being advertised to another, which would block spoke-to-spoke tunnel establishment; disabling it with 'no ip split-horizon eigrp 100' allows the hub to propagate spoke routes correctly. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of the hub’s role in Phase 3—specifically that the hub does not need 'ip nhrp shortcut' (that is for spokes) but must handle multicast registration and routing updates. A common trap is forgetting that split horizon must be disabled for EIGRP, even though Phase 3 uses NHRP redirects. Memory tip: "Hub handles redirects, multicast maps, and no split—spokes handle shortcuts."
300-410 DMVPN Practice Question
This 300-410 practice question tests your understanding of dmvpn. 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.
An engineer is configuring a DMVPN Phase 3 network with EIGRP as the routing protocol. The hub router has the following configuration snippet:
interface Tunnel0 ip address 10.0.0.1 255.255.255.0 ip nhrp network-id 1 ip nhrp redirect
tunnel source GigabitEthernet0/1 tunnel mode gre multipoint !
router eigrp 100 network 10.0.0.0 0.0.0.255
Which TWO additional configuration changes are required on the hub to ensure that spokes can establish direct spoke-to-spoke tunnels? (Choose TWO.)
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
Add the command 'ip nhrp map multicast dynamic' under interface Tunnel0.
In DMVPN Phase 3, the hub must have 'ip nhrp redirect' to send redirect messages, and spokes need 'ip nhrp shortcut' to install the /32 route. However, the question asks about the hub. The hub already has 'ip nhrp redirect'. To allow spokes to learn the hub's NBMA address, the hub needs 'ip nhrp map multicast dynamic' to accept dynamic registrations. Also, the hub must have a valid tunnel source IP and the tunnel interface must be up. The hub does not need 'ip nhrp shortcut' (that's for spokes). The hub does not need 'ip nhrp nhs' (that's for spokes). The hub does not need 'no ip split-horizon' for EIGRP if using Phase 3 with BGP or if the hub is configured correctly; but in Phase 3, EIGRP split horizon can prevent spoke routes from being advertised to other spokes. Actually, to allow spokes to learn routes from other spokes, the hub must disable EIGRP split horizon on the tunnel interface. So the two correct changes are: add 'ip nhrp map multicast dynamic' and 'no ip split-horizon eigrp 100'.
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.
- ✗
Add the command 'ip nhrp shortcut' under interface Tunnel0.
Why it's wrong here
Incorrect. 'ip nhrp shortcut' is configured on spokes, not on the hub. The hub uses 'ip nhrp redirect'.
- ✗
Add the command 'ip nhrp nhs 10.0.0.1' under interface Tunnel0.
Why it's wrong here
Incorrect. 'ip nhrp nhs' is used on spokes to point to the hub. The hub does not need this command.
- ✓
Add the command 'ip nhrp map multicast dynamic' under interface Tunnel0.
Why this is correct
Correct. This command allows the hub to dynamically learn the NBMA addresses of spokes for multicast forwarding, which is required for routing protocol updates.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Add the command 'no ip split-horizon eigrp 100' under interface Tunnel0.
Why this is correct
Correct. In DMVPN Phase 3, the hub must disable EIGRP split horizon so that routes learned from one spoke can be advertised to other spokes, enabling spoke-to-spoke communication.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Add the command 'ip nhrp authentication cisco123' under interface Tunnel0.
Why it's wrong here
Incorrect. Authentication is optional and not required for spoke-to-spoke tunnels; it is used for security but not a mandatory change for the scenario.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
Incorrect. 'ip nhrp nhs' is used on spokes to point to the hub. The hub does not need this command.
Scenario analysis trap
Incorrect. Authentication is optional and not required for spoke-to-spoke tunnels; it is used for security but not a mandatory change for the scenario.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 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
Got this wrong? Here's your next step.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this 300-410 question test?
DMVPN — This question tests DMVPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add the command 'ip nhrp map multicast dynamic' under interface Tunnel0. — In DMVPN Phase 3, the hub must have 'ip nhrp redirect' to send redirect messages, and spokes need 'ip nhrp shortcut' to install the /32 route. However, the question asks about the hub. The hub already has 'ip nhrp redirect'. To allow spokes to learn the hub's NBMA address, the hub needs 'ip nhrp map multicast dynamic' to accept dynamic registrations. Also, the hub must have a valid tunnel source IP and the tunnel interface must be up. The hub does not need 'ip nhrp shortcut' (that's for spokes). The hub does not need 'ip nhrp nhs' (that's for spokes). The hub does not need 'no ip split-horizon' for EIGRP if using Phase 3 with BGP or if the hub is configured correctly; but in Phase 3, EIGRP split horizon can prevent spoke routes from being advertised to other spokes. Actually, to allow spokes to learn routes from other spokes, the hub must disable EIGRP split horizon on the tunnel interface. So the two correct changes are: add 'ip nhrp map multicast dynamic' and 'no ip split-horizon eigrp 100'.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 18, 2026
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