The answer is that the route via R3 is preferred because it has a lower EIGRP composite metric than the route learned via the tunnel from R1. When two EIGRP routes share the same administrative distance—in this case, AD 90 for both internal routes—the router selects the path with the better metric, which is calculated from bandwidth, delay, load, and reliability. In a DMVPN phase 3 network, the tunnel interface on R2 introduces significantly higher delay values than a physical interface, making the tunnel route’s metric worse even though both routes are internal. This scenario tests your understanding of EIGRP metric preference over tunnel and physical routes, a common trap on the Cisco CCNP ENARSI 300-410 exam where candidates mistakenly focus on split-horizon or distance changes instead of the composite metric calculation. Remember: when AD ties, the metric decides—tunnel delay kills the metric every time.
300-410 Administrative Distance Practice Question
This 300-410 practice question tests your understanding of administrative distance. 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.
In a DMVPN phase 3 network, Router R1 (hub) and R2 (spoke) have an mGRE tunnel. R1 has EIGRP configured over the tunnel with 'no ip split-horizon' and 'distance eigrp 90 100'. R2 has default EIGRP configuration. R2 learns a route to 192.168.1.0/24 via the tunnel with AD 90. Later, R2 also learns the same route via a physical interface from another spoke R3 using EIGRP with AD 90. R2's 'show ip route 192.168.1.0' shows the route via R3. 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 route via R3 has a better metric (lower composite) than the route via R1, so it is preferred.
EIGRP uses metric (composite) to choose between routes with equal AD. The route via R3 might have a better metric. However, if the distance is changed on R1 to 100 for external routes, the route via R1 might have AD 100, but the question says AD 90. The correct answer is that the route via R3 is an internal route (AD 90) with a lower metric than the route via R1 (also AD 90), so metric decides. But the trick is that the tunnel interface on R2 might have a higher delay, causing a worse metric.
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 route via R3 has a better metric (lower composite) than the route via R1, so it is preferred.
Why this is correct
Equal AD routes are compared by metric; the tunnel may have higher delay/bandwidth.
Related concept
Read the scenario before looking for a memorised answer.
✗
R2's EIGRP process has 'variance 2' configured, causing load balancing.
Why it's wrong here
Variance does not cause preference; it allows unequal-cost load balancing.
✗
The route via R1 is an external route (AD 100) due to redistribution, so it is less preferred.
Why it's wrong here
The distance is set to 90 for internal and 100 for external; if the route is external, AD 100 > 90.
✗
R2 has a static route with AD 1 that overrides both.
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.
Administrative Distance — This question tests Administrative Distance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The route via R3 has a better metric (lower composite) than the route via R1, so it is preferred. — EIGRP uses metric (composite) to choose between routes with equal AD. The route via R3 might have a better metric. However, if the distance is changed on R1 to 100 for external routes, the route via R1 might have AD 100, but the question says AD 90. The correct answer is that the route via R3 is an internal route (AD 90) with a lower metric than the route via R1 (also AD 90), so metric decides. But the trick is that the tunnel interface on R2 might have a higher delay, causing a worse metric.
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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