The answer is an OSPF network type mismatch, which prevents proper LSA exchange and causes R1 to ignore routes from R2. Although the two routers form a FULL adjacency, the mismatch between R1’s point-to-point configuration and R2’s default broadcast network type creates an inconsistency in how link-state advertisements are generated and processed. On the point-to-point side, R1 expects Type 1 LSA formats without DR/BDR election, while the broadcast side treats R1 as the DR despite its priority of 0, leading to a silent failure where routes are not installed. This scenario is a classic trap on the Cisco CCNP ENARSI 300-410 exam, testing your ability to recognize that a FULL neighbor state does not guarantee correct route propagation when network types differ. A quick memory tip: “FULL does not mean functional—match the type to make the route type stick.”
300-410 Network Logging and Syslog Practice Question
This 300-410 practice question tests your understanding of network logging and syslog. 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 routers R1 and R2 are connected via Ethernet. R1 has:
interface GigabitEthernet0/0
ip ospf network point-to-point
R2 has default OSPF network type (broadcast). R1 shows:
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 0 FULL/ - 00:00:35 10.1.1.2 GigabitEthernet0/0
R2 shows:
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.1.1.1 1 FULL/DR 00:00:30 10.1.1.1 GigabitEthernet0/0
R1 is not installing OSPF 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
✓
OSPF network type mismatch prevents proper LSA exchange, causing R1 to ignore routes from R2.
OSPF network type mismatch: R1 is point-to-point, R2 is broadcast. On the point-to-point side, R1 expects no DR/BDR election and uses a different LSA format. The broadcast side sees R1 as DR (because R1's priority is 0? Actually R1 has priority 0? Output shows R1's neighbor has priority 0, but R2 shows R1 as DR. This inconsistency causes adjacency but routes are not exchanged properly due to LSA type mismatch. The fix is to match network types.
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.
✓
OSPF network type mismatch prevents proper LSA exchange, causing R1 to ignore routes from R2.
Why this is correct
R1 is configured as point-to-point, R2 as broadcast. This causes R1 to not process Type 2 LSAs from R2.
R1 has a higher OSPF priority, causing it to become DR and not accept routes.
Why it's wrong here
R1's priority is 0 (shown in neighbor output), so it cannot be DR.
✗
The dead timer mismatch causes adjacency to be unstable.
Why it's wrong here
Dead timers are consistent (35 and 30 seconds are within tolerance).
✗
R2 is not configured with the same OSPF process ID.
Why it's wrong here
Process ID does not need to match for adjacency.
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.
Trap categories for this question
Command / output trap
R1's priority is 0 (shown in neighbor output), so it cannot be DR.
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.
Network Logging and Syslog — This question tests Network Logging and Syslog — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: OSPF network type mismatch prevents proper LSA exchange, causing R1 to ignore routes from R2. — OSPF network type mismatch: R1 is point-to-point, R2 is broadcast. On the point-to-point side, R1 expects no DR/BDR election and uses a different LSA format. The broadcast side sees R1 as DR (because R1's priority is 0? Actually R1 has priority 0? Output shows R1's neighbor has priority 0, but R2 shows R1 as DR. This inconsistency causes adjacency but routes are not exchanged properly due to LSA type mismatch. The fix is to match network types.
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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