The answer is an OSPF network type mismatch between the two VRF-Lite interfaces. In a VRF-Lite setup, when one router’s interface is configured as point-to-point and the other remains as the default broadcast type, the OSPF neighbor adjacency fails because the two sides disagree on how to form the neighbor relationship. On a broadcast network, OSPF requires a Designated Router (DR) and Backup Designated Router (BDR) election, while a point-to-point link bypasses this election entirely and uses a different Hello packet format. This mismatch causes each router to ignore the other’s Hello packets, as the interface parameters—such as Hello and Dead intervals—are no longer compatible. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of OSPF operation within VRF-Lite and the critical rule that both sides of a link must share the same network type. A common trap is assuming a direct Ethernet link defaults to point-to-point; it does not. Memory tip: “One side votes, the other doesn’t—neighbors won’t.”
300-410 VRF-Lite Practice Question
This 300-410 practice question tests your understanding of vrf-lite. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 a VRF-Lite setup, Router R1 and R2 are running OSPF in VRF-A. R1 has interface Gig0/0 in VRF-A with ip ospf network point-to-point. R2 has interface Gig0/1 in VRF-A with default network type (broadcast). The link between them is a direct Ethernet connection. OSPF neighbors are not forming. 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 types are mismatched: one side is point-to-point, the other is broadcast, causing neighbor adjacency failure.
OSPF network type mismatch prevents neighbor formation. On a broadcast network, OSPF expects DR/BDR elections, while point-to-point expects no election. The mismatch causes hello packets to be ignored because the OSPF interface parameters (like hello interval, dead interval, and network type) differ. Specifically, on a point-to-point link, the neighbor state machine expects a different packet format and does not process broadcast hellos.
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 types are mismatched: one side is point-to-point, the other is broadcast, causing neighbor adjacency failure.
Why this is correct
Correct: OSPF requires matching network types on the same link; mismatch leads to no neighbor formation.
The VRF names must match for OSPF to form neighbors.
Why it's wrong here
Incorrect: VRF names are local; OSPF process is per VRF, but network type mismatch is the issue.
✗
The OSPF process ID must be the same on both routers.
Why it's wrong here
Incorrect: OSPF process ID is local and does not need to match.
✗
The interface must be configured with the same IP subnet mask.
Why it's wrong here
Incorrect: While IP subnet mismatch can cause issues, the primary problem here is network type mismatch.
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.
VRF-Lite — This question tests VRF-Lite — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The OSPF network types are mismatched: one side is point-to-point, the other is broadcast, causing neighbor adjacency failure. — OSPF network type mismatch prevents neighbor formation. On a broadcast network, OSPF expects DR/BDR elections, while point-to-point expects no election. The mismatch causes hello packets to be ignored because the OSPF interface parameters (like hello interval, dead interval, and network type) differ. Specifically, on a point-to-point link, the neighbor state machine expects a different packet format and does not process broadcast hellos.
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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