- A
The 'metric weights' (k-values) are mismatched between the two routers, causing query propagation to fail.
Correct. EIGRP requires matching k-values between neighbors. If they differ, the adjacency may form but queries can be dropped, leading to SIA.
- B
The 'auto-summary' command is enabled on one router, causing route summarization to break the adjacency.
Why wrong: Incorrect. Auto-summary is disabled by default in named mode and would not cause SIA; it would cause routing loops or missing routes.
- C
The 'passive-interface' command is applied to the interface, preventing the adjacency from forming.
Why wrong: Incorrect. A passive interface would prevent the adjacency from forming at all, not cause SIA after forming.
- D
The 'bandwidth' setting on the interface is set to a very low value, causing the EIGRP metric to be too high for the route to be installed.
Why wrong: Incorrect. Low bandwidth would affect metric calculation but not cause SIA; SIA is related to query propagation.
Quick Answer
The answer is a mismatch in the metric weights (k-values) between the two routers. In EIGRP named mode, the metric weights must be identical on both sides for query propagation to function correctly; if they differ, the routers will form an adjacency but fail to process queries, leading to a stuck-in-active (SIA) state for certain routes. This edge case is a classic trap on the Cisco CCNP ENARSI 300-410 exam, especially in the context of MPLS L3VPNs, where engineers often overlook that named mode defaults to wide metrics but still requires consistent k-values—commonly K1=1, K3=1, and all others 0. The exam tests your ability to distinguish this from other SIA causes like interface flapping or route redistribution loops. A quick memory tip: “K-values must kiss—if they don’t match, queries miss.”
300-410 MPLS L3VPN Practice Question
This 300-410 practice question tests your understanding of mpls l3vpn. 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 configures EIGRP named mode on two routers in an MPLS L3VPN. The routers are directly connected and can ping each other. The engineer notices that the EIGRP adjacency forms but then the neighbor relationship goes down and the routers become stuck-in-active (SIA) for certain routes. The engineer checks the logs and sees no errors. What is the most likely explanation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 'metric weights' (k-values) are mismatched between the two routers, causing query propagation to fail.
In EIGRP named mode, the default hello interval and hold time are different from classic mode. Named mode uses a default hello interval of 5 seconds and hold time of 15 seconds, while classic mode uses 5 and 15 as well, but the key difference is that named mode uses a different metric calculation (wide metrics) by default. However, the most common edge case causing SIA in named mode is that the 'metric weights' or 'k-values' must match between neighbors. If one router is using named mode with default k-values (1,0,1,0,0) and the other is using classic mode with different k-values (e.g., 1,0,1,0,0), the adjacency will form but queries may not be processed correctly, leading to SIA. Additionally, named mode requires the 'address-family' configuration to be consistent. A more specific edge case is that named mode uses a different 'graceful-restart' mechanism by default, which can cause issues if not supported on both sides.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 'metric weights' (k-values) are mismatched between the two routers, causing query propagation to fail.
Why this is correct
Correct. EIGRP requires matching k-values between neighbors. If they differ, the adjacency may form but queries can be dropped, leading to SIA.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The 'auto-summary' command is enabled on one router, causing route summarization to break the adjacency.
Why it's wrong here
Incorrect. Auto-summary is disabled by default in named mode and would not cause SIA; it would cause routing loops or missing routes.
- ✗
The 'passive-interface' command is applied to the interface, preventing the adjacency from forming.
Why it's wrong here
Incorrect. A passive interface would prevent the adjacency from forming at all, not cause SIA after forming.
- ✗
The 'bandwidth' setting on the interface is set to a very low value, causing the EIGRP metric to be too high for the route to be installed.
Why it's wrong here
Incorrect. Low bandwidth would affect metric calculation but not cause SIA; SIA is related to query propagation.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
MPLS L3VPN — This question tests MPLS L3VPN — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The 'metric weights' (k-values) are mismatched between the two routers, causing query propagation to fail. — In EIGRP named mode, the default hello interval and hold time are different from classic mode. Named mode uses a default hello interval of 5 seconds and hold time of 15 seconds, while classic mode uses 5 and 15 as well, but the key difference is that named mode uses a different metric calculation (wide metrics) by default. However, the most common edge case causing SIA in named mode is that the 'metric weights' or 'k-values' must match between neighbors. If one router is using named mode with default k-values (1,0,1,0,0) and the other is using classic mode with different k-values (e.g., 1,0,1,0,0), the adjacency will form but queries may not be processed correctly, leading to SIA. Additionally, named mode requires the 'address-family' configuration to be consistent. A more specific edge case is that named mode uses a different 'graceful-restart' mechanism by default, which can cause issues if not supported on both sides.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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