- A
Check the OSPF hello and dead intervals on R1 and R2.
Why wrong: While timer mismatches can prevent adjacency, the technician has not yet confirmed basic IP connectivity parameters. The default timers are rarely changed, and it is more efficient to rule out a subnet mask mismatch first.
- B
Verify the OSPF area ID configured on R2's interface.
Why wrong: Area mismatches are a common cause of adjacency failure, but the technician has already confirmed that R1's interface is in area 0. Checking R2's area is a valid step, but it does not address the possibility that R2's interface may have a wrong IP subnet mask, which would also prevent adjacency.
- C
Check whether R2's interface is configured as a passive interface.
Why wrong: The technician verified that R1's interface is not passive, but R2 could be passive. However, a passive interface on R2 would suppress OSPF hello packets and prevent adjacency. While this is a plausible next step, the scenario provides no indication of a passive configuration on R2, and the subnet mask mismatch is a more common misconfiguration to rule out first.
- D
Verify the subnet mask configured on R2's connecting interface.
OSPF on a broadcast network requires an exact subnet mask match; a mismatch will prevent neighbor relationships. Given that R1's interface is properly added to OSPF, is not passive, and is in the correct area, the most likely cause is a misconfigured subnet mask on R2. Checking this resolves a basic Layer 3 requirement before investigating any OSPF-specific parameters.
Quick Answer
The answer is to verify the subnet mask configured on R2's connecting interface. This is correct because OSPF, when operating on a broadcast multi-access network like Ethernet, requires both neighbors to agree on the exact subnet mask for the link; a subnet mask mismatch causes OSPF to reject incoming hello packets, directly preventing adjacency formation. On the CCNA 200-301 v2 exam, this scenario tests your understanding of OSPF neighbor requirements beyond just area and passive interface settings—a common trap is to immediately check OSPF timers or router IDs, but the fundamental Layer 3 mismatch is the first logical step. Remember that OSPF treats a subnet mask mismatch as a fatal hello parameter error, so always verify the mask on both sides before diving into OSPF-specific configurations. A useful memory tip: "Mask must match, or the neighbor won't catch."
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. 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.
A technician configures OSPF on R1 using the command network 10.0.0.0 0.0.0.255 area 0. R1's GigabitEthernet0/0 interface has IP address 10.0.0.1/30 and is included in the OSPF process. The technician confirms the interface is not passive using the show ip ospf interface GigabitEthernet0/0 command. However, R2 is not forming an OSPF adjacency with R1. What should the technician do next?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Verify the subnet mask configured on R2's connecting interface.
On broadcast multi-access networks like Ethernet, OSPF requires both neighbors to agree on the exact subnet mask; a mismatch causes the hello packets to be rejected. R1's interface is already confirmed to be in the correct area and not passive, so the next logical step is to check R2's interface configuration. Verifying the subnet mask on R2's connecting interface addresses a fundamental Layer 3 misconfiguration that would directly prevent adjacency formation, before investigating OSPF-specific parameters.
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.
- ✗
Check the OSPF hello and dead intervals on R1 and R2.
Why it's wrong here
While timer mismatches can prevent adjacency, the technician has not yet confirmed basic IP connectivity parameters. The default timers are rarely changed, and it is more efficient to rule out a subnet mask mismatch first.
- ✗
Verify the OSPF area ID configured on R2's interface.
Why it's wrong here
Area mismatches are a common cause of adjacency failure, but the technician has already confirmed that R1's interface is in area 0. Checking R2's area is a valid step, but it does not address the possibility that R2's interface may have a wrong IP subnet mask, which would also prevent adjacency.
- ✗
Check whether R2's interface is configured as a passive interface.
Why it's wrong here
The technician verified that R1's interface is not passive, but R2 could be passive. However, a passive interface on R2 would suppress OSPF hello packets and prevent adjacency. While this is a plausible next step, the scenario provides no indication of a passive configuration on R2, and the subnet mask mismatch is a more common misconfiguration to rule out first.
- ✓
Verify the subnet mask configured on R2's connecting interface.
Why this is correct
OSPF on a broadcast network requires an exact subnet mask match; a mismatch will prevent neighbor relationships. Given that R1's interface is properly added to OSPF, is not passive, and is in the correct area, the most likely cause is a misconfigured subnet mask on R2. Checking this resolves a basic Layer 3 requirement before investigating any OSPF-specific parameters.
Related concept
OSPF neighbours must agree on key parameters.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Verify the subnet mask configured on R2's connecting interface.Correct answer▾
Why this is correct
OSPF on a broadcast network requires an exact subnet mask match; a mismatch will prevent neighbor relationships. Given that R1's interface is properly added to OSPF, is not passive, and is in the correct area, the most likely cause is a misconfigured subnet mask on R2. Checking this resolves a basic Layer 3 requirement before investigating any OSPF-specific parameters.
✗Check the OSPF hello and dead intervals on R1 and R2.Wrong answer — click to see why▾
Why this is wrong here
Skips the more likely and fundamental subnet mask check, which would render timer issues irrelevant until resolved.
✗Verify the OSPF area ID configured on R2's interface.Wrong answer — click to see why▾
Why this is wrong here
Ignores the more foundational IP addressing check that could also cause the issue, and area troubleshooting would be misleading if the subnet mask is incorrect.
✗Check whether R2's interface is configured as a passive interface.Wrong answer — click to see why▾
Why this is wrong here
Jumps to an OSPF-specific command without first verifying the fundamental IP subnet configuration, which is a more direct cause of failed adjacencies on broadcast links.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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
Scenario analysis trap
The technician verified that R1's interface is not passive, but R2 could be passive. However, a passive interface on R2 would suppress OSPF hello packets and prevent adjacency. While this is a plausible next step, the scenario provides no indication of a passive configuration on R2, and the subnet mask mismatch is a more common misconfiguration to rule out first.
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.
What to study next
Got this wrong? Here's your next step.
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 200-301 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 200-301 question test?
IP Routing — This question tests IP Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Verify the subnet mask configured on R2's connecting interface. — On broadcast multi-access networks like Ethernet, OSPF requires both neighbors to agree on the exact subnet mask; a mismatch causes the hello packets to be rejected. R1's interface is already confirmed to be in the correct area and not passive, so the next logical step is to check R2's interface configuration. Verifying the subnet mask on R2's connecting interface addresses a fundamental Layer 3 misconfiguration that would directly prevent adjacency formation, before investigating OSPF-specific parameters.
What should I do if I get this 200-301 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 200-301 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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Last reviewed: Jun 14, 2026
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