The root cause is the OSPF network type mismatch, which prevents R1 from generating a Network LSA, leaving R2 unable to install routes that depend on it. When R1’s interface is configured as point-to-point, it skips the DR/BDR election and never creates a Type 2 LSA, while R2, using the default broadcast type, expects that LSA to complete its link-state database for the segment. Although the adjacency reaches FULL and R2 receives R1’s Router LSA, the missing Network LSA blocks R2 from installing routes for networks beyond the direct link. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how OSPF network types affect LSA generation and route installation—a common trap is assuming FULL adjacency guarantees full routing. Remember the memory tip: “FULL neighbor, missing LSA means no route; point-to-point skips the DR, so no Type 2 appears.”
300-410 Device Access Control Practice Question
This 300-410 practice question tests your understanding of device access control. 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.
Two OSPF routers R1 and R2 are connected via a GigabitEthernet link in area 0. R1 has interface GigabitEthernet0/0 ip ospf network point-to-point, while R2 has the default OSPF network type broadcast. R1's show ip ospf neighbor shows R2 in FULL state, but R2's show ip ospf neighbor shows R1 in FULL state. However, routes from R1 are not appearing in R2's routing table. Show ip ospf database on R2 shows the router LSA from R1 but not the network LSA. 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 not generate a network LSA, and R2 cannot install routes that rely on that LSA.
When R1 has the OSPF network type set to point-to-point on the GigabitEthernet link, it does not elect a DR/BDR and therefore does not generate a Type 2 (Network) LSA. R2, with the default broadcast network type, expects a Network LSA to build complete routing information for the segment. Although the adjacency reaches FULL and R2 receives R1's Type 1 (Router) LSA, the missing Network LSA prevents R2 from installing routes that depend on that LSA, such as those for networks advertised by R1 that are not directly connected to the link.
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 OSPF network type mismatch causes R1 to not generate a network LSA, and R2 cannot install routes that rely on that LSA.
Why this is correct
R1's point-to-point network type does not elect a DR or generate Type 2 LSAs, so R2 lacks the necessary topology information for transit.
Related concept
Read the scenario before looking for a memorised answer.
✗
The OSPF adjacency is stuck in EXSTART state due to MTU mismatch.
OSPF LSAs are not blocked by firewalls in this context; the issue is protocol behavior.
✗
R1's router LSA has an incorrect metric, causing R2 to ignore it.
Why it's wrong here
The metric is not the issue; the LSA type mismatch is.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a FULL adjacency guarantees full route exchange, but the trap here is that OSPF network type mismatch can break route installation even when neighbor state is FULL and Router LSAs are exchanged.
Detailed technical explanation
How to think about this question
In OSPF, the network type determines LSA generation behavior: on a broadcast network, the DR generates a Type 2 LSA listing all attached routers, while on a point-to-point link, no DR is elected and no Type 2 LSA is created. This mismatch can cause partial reachability issues even when the adjacency is FULL, because R2's SPF calculation may require the Network LSA to determine that R1 is a transit router for certain prefixes. In real-world scenarios, this often occurs when one side is misconfigured as point-to-point on a multi-access segment, leading to silent route loss.
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.
TExam Day Tips
→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 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.
Device Access Control — This question tests Device Access Control — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The OSPF network type mismatch causes R1 to not generate a network LSA, and R2 cannot install routes that rely on that LSA. — When R1 has the OSPF network type set to point-to-point on the GigabitEthernet link, it does not elect a DR/BDR and therefore does not generate a Type 2 (Network) LSA. R2, with the default broadcast network type, expects a Network LSA to build complete routing information for the segment. Although the adjacency reaches FULL and R2 receives R1's Type 1 (Router) LSA, the missing Network LSA prevents R2 from installing routes that depend on that LSA, such as those for networks advertised by R1 that are not directly connected to the link.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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