Question 235 of 2,152

DMVPN →hardMultiple ChoiceObjective-mapped

BGP Local Preference in DMVPN Spoke-to-Spoke Path

This 300-410 practice question tests your understanding of dmvpn. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 uses BGP for routing between hubs and spokes. R1 (hub) and R2 (spoke) have an eBGP peering. R2 advertises a prefix 192.168.1.0/24 to R1. R3 (another spoke) receives this prefix via R1 but with a higher local preference than expected, causing R3 to prefer the path through R1 even though a direct spoke-to-spoke tunnel exists. What is the root cause?

A
R1 has a route-map that sets local preference to 200 for prefixes received from R2, causing R3 to prefer the path through R1 over the direct path.
Correct. BGP local preference is propagated to iBGP peers. If R1 sets a high local preference on routes from R2, R3 will prefer the path via R1, even if a direct spoke-to-spoke tunnel is available.
B
R3 has a static route pointing to R1 for 192.168.1.0/24, overriding BGP.
Why wrong: Incorrect. Static routes have higher administrative distance than BGP, but the issue is about BGP path selection, not static routes.
C
NHRP redirect is disabled on R1, preventing spoke-to-spoke tunnel establishment.
Why wrong: Incorrect. NHRP redirect is needed for Phase 3, but the issue is BGP path selection, not tunnel establishment.
D
R2 is advertising the prefix with a MED of 0, causing R3 to prefer the path through R1.
Why wrong: Incorrect. MED is compared only when paths are from the same AS, and local preference is evaluated before MED. The issue is local preference manipulation.

Full breakdown with real-world context →

Quick Answer

The answer is that R1 has a route-map setting local preference to 200 for prefixes received from R2, which overrides the normal BGP path selection. This is because BGP local preference is a well-known mandatory attribute that is propagated throughout the autonomous system, and when the hub (R1) manipulates it via a route-map, the higher value (200) is advertised to other spokes like R3. In a DMVPN Phase 3 network, spoke-to-spoke tunnels are established dynamically, but BGP’s best-path algorithm will always prefer the path with the highest local preference, forcing R3 to route through the hub instead of using the direct spoke-to-spoke path. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how BGP path attributes interact with DMVPN overlay routing, and a common trap is forgetting that local preference is transitive within the AS—it affects all iBGP peers, not just the immediate neighbor. Memory tip: “Local pref is king in the AS—if it’s higher, the hub becomes the middleman.”

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

✓

R1 has a route-map that sets local preference to 200 for prefixes received from R2, causing R3 to prefer the path through R1 over the direct path.

BGP local preference is manipulated on the hub (R1) using route-maps or policy, causing the prefix to have a higher local preference when advertised to other spokes. This overrides the normal BGP path selection and forces traffic through the hub, even if a direct spoke-to-spoke tunnel is available.

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.

✓
R1 has a route-map that sets local preference to 200 for prefixes received from R2, causing R3 to prefer the path through R1 over the direct path.
Why this is correct
Correct. BGP local preference is propagated to iBGP peers. If R1 sets a high local preference on routes from R2, R3 will prefer the path via R1, even if a direct spoke-to-spoke tunnel is available.
Related concept
Read the scenario before looking for a memorised answer.
✗
R3 has a static route pointing to R1 for 192.168.1.0/24, overriding BGP.
Why it's wrong here
Incorrect. Static routes have higher administrative distance than BGP, but the issue is about BGP path selection, not static routes.
✗
NHRP redirect is disabled on R1, preventing spoke-to-spoke tunnel establishment.
Why it's wrong here
Incorrect. NHRP redirect is needed for Phase 3, but the issue is BGP path selection, not tunnel establishment.
✗
R2 is advertising the prefix with a MED of 0, causing R3 to prefer the path through R1.
Why it's wrong here
Incorrect. MED is compared only when paths are from the same AS, and local preference is evaluated before MED. The issue is local preference manipulation.

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: R1 has a route-map that sets local preference to 200 for prefixes received from R2, causing R3 to prefer the path through R1 over the direct path. — BGP local preference is manipulated on the hub (R1) using route-maps or policy, causing the prefix to have a higher local preference when advertised to other spokes. This overrides the normal BGP path selection and forces traffic through the hub, even if a direct spoke-to-spoke tunnel is available.

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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