The answer is that the OSPF network type mismatch causes R1 to ignore Type 2 LSAs from R2, preventing route installation. This occurs because R1 is configured as point-to-point, which expects no DR/BDR election and uses Type 1 router LSAs exclusively, while R2 defaults to broadcast mode and generates Type 2 network LSAs to describe the multi-access link. Since R1 does not process Type 2 LSAs from a point-to-point interface, it cannot learn the prefixes R2 advertises, even though the neighbor state shows FULL due to the adjacency forming at Layer 2. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that OSPF adjacency does not guarantee route exchange—network type consistency is critical on multi-access links. A common trap is assuming FULL neighbor state means full routing convergence. Memory tip: "FULL neighbor, empty table—check the network type label."
300-410 MPLS Operations Practice Question
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.
In an MPLS network, OSPF network type mismatch causes routing issues. Router R1 and R2 are connected via a multi-access Ethernet link. R1 has 'interface GigabitEthernet0/0 ip ospf network point-to-point', while R2 has default OSPF network type broadcast. R1 shows 'show ip ospf neighbor' output: 'Neighbor 10.0.0.2, interface address 10.0.0.2, state FULL' but 'show ip route' does not include routes from R2. 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 OSPF network type mismatch causes R1 to ignore Type 2 LSAs from R2, preventing route installation.
OSPF network type mismatch on a multi-access link can cause adjacency to form but with different DR/BDR election behavior. With point-to-point on R1, it expects no DR/BDR, while broadcast on R2 expects DR election. The adjacency forms as FULL, but R1 does not accept routes from R2 because R2's LSA may have a different link type or R1 ignores them due to mismatch in network type handling.
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 OSPF network type mismatch causes R1 to ignore Type 2 LSAs from R2, preventing route installation.
Why this is correct
Point-to-point network type does not process Type 2 (network) LSAs, so routes advertised by R2 via network LSA are ignored.
The MTU mismatch between R1 and R2 causes OSPF database synchronization failure.
Why it's wrong here
Adjacency is FULL, so database sync is complete.
✗
R1 has a distribute-list blocking routes from R2.
Why it's wrong here
No distribute-list mentioned.
✗
R2 is not advertising any routes; need 'network' statement.
Why it's wrong here
Routes are expected to be advertised.
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.
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: The OSPF network type mismatch causes R1 to ignore Type 2 LSAs from R2, preventing route installation. — OSPF network type mismatch on a multi-access link can cause adjacency to form but with different DR/BDR election behavior. With point-to-point on R1, it expects no DR/BDR, while broadcast on R2 expects DR election. The adjacency forms as FULL, but R1 does not accept routes from R2 because R2's LSA may have a different link type or R1 ignores them due to mismatch in network type handling.
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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