The answer is the redistribution of the static Null0 route into EIGRP, which causes spoke-to-spoke tunnel failure by blackholing traffic. When the hub redistributes a static route to Null0 for the 10.0.0.0/8 summary, all spokes learn this route and forward traffic destined for remote spoke networks toward the hub’s Null0 interface instead of using the direct NHRP shortcut. This prevents dynamic spoke-to-spoke tunnels from forming because the routing table on each spoke lacks a valid path to the other spoke’s tunnel IP, forcing all inter-spoke traffic to be dropped. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how DMVPN phase 3 and EIGRP interact, particularly the danger of redistributing summary or default routes that can override NHRP-learned direct paths. A common trap is assuming the DMVPN tunnel state is UP means traffic flows correctly, but the routing table tells the real story. Memory tip: “Null0 kills the shortcut” — if you see a Null0 route redistributed from the hub, expect spoke-to-spoke failure.
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. 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 network uses EIGRP as the routing protocol. After redistributing a static route into EIGRP on the hub, spoke-to-spoke tunnels fail to form. Hub configuration:
router eigrp 100
redistribute static metric 10000 100 255 1 1500
!
ip route 10.0.0.0 255.0.0.0 Null0
Spoke1# show dmvpn
Interface: Tunnel0, IPv4 NHRP Details
Type:Spoke, NHRP Peers:2,
# Ent Peer NBMA Addr Peer Tunnel Addr State UpDn Tm Attrb
1 192.168.1.1 10.1.1.1 UP 00:01:00 D
2 192.168.1.2 10.1.1.2 UP 00:00:30 D
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The static Null0 route is redistributed, causing spokes to send traffic to the hub instead of directly to other spokes.
The static route to Null0 for 10.0.0.0/8 is redistributed into EIGRP, causing all spokes to learn a summary route pointing to Null0 on the hub. This blackholes traffic destined to other spokes, preventing dynamic spoke-to-spoke tunnel establishment. The fix is to use a more specific static route or filter the Null0 route from redistribution.
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 static Null0 route is redistributed, causing spokes to send traffic to the hub instead of directly to other spokes.
Why this is correct
The Null0 route blackholes traffic, preventing spoke-to-spoke communication.
Related concept
Read the scenario before looking for a memorised answer.
✗
The EIGRP metric is too low, causing the route to be preferred over NHRP.
Why it's wrong here
Metric does not affect NHRP; the issue is the route itself.
✗
The DMVPN tunnel is misconfigured with mismatched authentication.
Why it's wrong here
Tunnel is up; authentication is not the issue.
✗
The redistribute static command is missing the route-map to set the next-hop.
Why it's wrong here
Missing route-map does not cause spoke-to-spoke failure; the Null0 route is the problem.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
Route Redistribution — This question tests Route Redistribution — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The static Null0 route is redistributed, causing spokes to send traffic to the hub instead of directly to other spokes. — The static route to Null0 for 10.0.0.0/8 is redistributed into EIGRP, causing all spokes to learn a summary route pointing to Null0 on the hub. This blackholes traffic destined to other spokes, preventing dynamic spoke-to-spoke tunnel establishment. The fix is to use a more specific static route or filter the Null0 route from redistribution.
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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