Question 1,791 of 2,152

DMVPN →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is the hub’s EIGRP summary route causing suboptimal spoke-to-spoke traffic in DMVPN Phase 3. This occurs because the hub advertises a less specific 10.0.0.0/16 summary route to spokes, which is installed in the routing table as the best match for destinations like 10.1.0.1, overriding the more specific /24 routes learned from other spokes via NHRP redirect. As a result, spoke-to-spoke direct tunnels are never used, and all traffic is forwarded through the hub, breaking the Phase 3 design goal of dynamic direct communication. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how EIGRP summary routes interact with NHRP Phase 3 redirects—a common trap is assuming more specific routes always win, but summary routes are preferred when they are the only entry in the routing table. Memory tip: “Summary steals the show—spokes go through the hub, not the spoke.”

300-410 DMVPN Practice Question

This 300-410 practice question tests your understanding of dmvpn. 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 EIGRP as the routing protocol experiences intermittent connectivity between spokes. R1 (hub) has 'ip summary-address eigrp 100 10.0.0.0 255.255.0.0' configured on the tunnel interface. R2 (spoke) shows 'show ip eigrp topology all-links' listing 10.1.0.0/24 as reachable via R1, but traffic from R2 to 10.1.0.1 (another spoke) is forwarded to R1 instead of directly via the spoke-to-spoke tunnel. What is the root cause?

Question 1hardmultiple choice

Study the full EIGRP explanation →

A
The summary route on the hub creates a less specific route that is preferred over the more specific /24 routes learned from other spokes, causing suboptimal routing.
Correct. EIGRP summary routes have administrative distance 5 by default, which is lower than the distance of learned routes (90/170). This causes spokes to prefer the summary route and forward traffic to the hub, even though more specific routes exist.
B
EIGRP stub configuration on spokes prevents them from learning routes from other spokes.
Why wrong: Incorrect. EIGRP stub configuration would limit route advertisement, but the issue is about route preference, not learning.
C
NHRP redirect is disabled on the hub, preventing spoke-to-spoke tunnel establishment.
Why wrong: Incorrect. NHRP redirect is required for Phase 3, but even if enabled, the summary route would still be preferred.
D
The spoke-to-spoke tunnel interface has a different MTU causing fragmentation.
Why wrong: Incorrect. MTU mismatch would cause packet drops, not suboptimal routing.

Full breakdown with real-world context →

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

✓

The summary route on the hub creates a less specific route that is preferred over the more specific /24 routes learned from other spokes, causing suboptimal routing.

The hub's summary route 10.0.0.0/16 is advertised to spokes, causing them to prefer the summary route over the more specific /24 routes learned from other spokes via NHRP redirect. This prevents spoke-to-spoke direct tunnels from being established or used, as traffic is forwarded to the hub based on the summary route.

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 summary route on the hub creates a less specific route that is preferred over the more specific /24 routes learned from other spokes, causing suboptimal routing.
Why this is correct
Correct. EIGRP summary routes have administrative distance 5 by default, which is lower than the distance of learned routes (90/170). This causes spokes to prefer the summary route and forward traffic to the hub, even though more specific routes exist.
Related concept
Read the scenario before looking for a memorised answer.
✗
EIGRP stub configuration on spokes prevents them from learning routes from other spokes.
Why it's wrong here
Incorrect. EIGRP stub configuration would limit route advertisement, but the issue is about route preference, not learning.
✗
NHRP redirect is disabled on the hub, preventing spoke-to-spoke tunnel establishment.
Why it's wrong here
Incorrect. NHRP redirect is required for Phase 3, but even if enabled, the summary route would still be preferred.
✗
The spoke-to-spoke tunnel interface has a different MTU causing fragmentation.
Why it's wrong here
Incorrect. MTU mismatch would cause packet drops, not suboptimal routing.

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.

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: The summary route on the hub creates a less specific route that is preferred over the more specific /24 routes learned from other spokes, causing suboptimal routing. — The hub's summary route 10.0.0.0/16 is advertised to spokes, causing them to prefer the summary route over the more specific /24 routes learned from other spokes via NHRP redirect. This prevents spoke-to-spoke direct tunnels from being established or used, as traffic is forwarded to the hub based on the summary route.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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