This 300-410 practice question tests your understanding of mpls operations. 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.
EIGRP stuck-in-active (SIA) occurs in a large network. Router R1 shows 'show ip eigrp topology 10.0.0.0/24' output: 'P 10.0.0.0/24, 1 successors, FD is 128000, Q is 0, SIA is 00:01:00' and 'show ip eigrp neighbors' shows neighbor R2 in state 'Active'. R1 configuration includes 'router eigrp 100 network 10.0.0.0 passive-interface default'. 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
✓
R2 has 'passive-interface default' configured, which prevents it from sending query replies back to R1.
EIGRP SIA occurs when a query is not replied within the active timer. The 'passive-interface default' command makes all interfaces passive, preventing EIGRP hellos and queries from being sent on those interfaces. If R1 has a passive interface to R2, no queries are sent, but if R1 is the query originator and R2 is not responding due to passive interface on R2's side, SIA can occur. However, the scenario shows R1's neighbor R2 is in Active state, meaning R1 sent a query to R2 but R2 did not reply. This could be because R2 has a passive interface to R1, blocking the query reply.
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.
✓
R2 has 'passive-interface default' configured, which prevents it from sending query replies back to R1.
Why this is correct
Passive interface on R2 blocks EIGRP packets, including replies, causing SIA on R1.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
MPLS Operations — This question tests MPLS Operations — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: R2 has 'passive-interface default' configured, which prevents it from sending query replies back to R1. — EIGRP SIA occurs when a query is not replied within the active timer. The 'passive-interface default' command makes all interfaces passive, preventing EIGRP hellos and queries from being sent on those interfaces. If R1 has a passive interface to R2, no queries are sent, but if R1 is the query originator and R2 is not responding due to passive interface on R2's side, SIA can occur. However, the scenario shows R1's neighbor R2 is in Active state, meaning R1 sent a query to R2 but R2 did not reply. This could be because R2 has a passive interface to R1, blocking the query reply.
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.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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