- A
The OSPF network type on R1's interface differs from the network type on R2's interface.
Why wrong: By default, Ethernet interfaces use the broadcast network type. Unless explicitly changed, both routers will have the same type, so this is unlikely to be the cause. The configuration shown does not indicate any network type changes.
- B
R1's network statement does not include the subnet of the link connecting R1 and R2.
The command 'network 192.168.1.0 0.0.0.255 area 0' only enables OSPF on interfaces with an IP address in the 192.168.1.0/24 range. The link uses the 10.1.1.0/30 subnet, so R1's interface (e.g., 10.1.1.2/30) is not matched. Consequently, OSPF is inactive on that interface, and no neighbor relationship can form.
- C
R1's router ID is not manually set and duplicates the router ID of R2.
Why wrong: A duplicate router ID would cause adjacency problems and log an error, but the scenario provides no evidence of this. The immediate and direct cause based on the configuration snippet is the network command mismatch.
- D
Mismatched OSPF hello and dead intervals between the routers.
Why wrong: Hello and dead interval mismatches prevent adjacency, but the question does not indicate that any timers have been modified from their default values. The most likely cause given the explicit network command is the missing subnet match.
Quick Answer
The answer is the OSPF adjacency failure is caused by R1’s network statement not covering the link subnet. OSPF only activates on interfaces whose primary IP address falls within a configured network statement and its wildcard mask; R1’s statement uses 192.168.1.0 0.0.0.255, which matches only the 192.168.1.0/24 range, while the link between R1 and R2 uses the 10.1.1.0/30 subnet. Because R1’s connecting interface is not included, OSPF does not run on that interface, no Hello packets are sent, and the adjacency cannot form—even though physical connectivity and R2’s OSPF configuration are correct. On the CCNA 200-301 v2 exam, this scenario tests your understanding that OSPF network statements are interface-selection tools, not routing advertisements; a common trap is assuming any network statement enables OSPF globally. Remember the memory tip: “Match the link, or no hello—network statements pick interfaces, not routes.”
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is troubleshooting an OSPF adjacency problem: R1 and R2 are not forming a neighbor relationship. R1's OSPF configuration includes the command 'network 192.168.1.0 0.0.0.255 area 0'. R2's GigabitEthernet0/0 is configured with IP address 10.1.1.1/30 and is participating in OSPF area 0. The engineer verifies that physical connectivity is fine and OSPF is enabled on R2. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
R1's network statement does not include the subnet of the link connecting R1 and R2.
R1's network statement uses a wildcard mask of 0.0.0.255, which exactly matches interfaces with IP addresses in the 192.168.1.0/24 range. The link between R1 and R2 uses the 10.1.1.0/30 subnet, so R1's interface on that link will have an IP address that does not fall within the network command. Because OSPF only activates on interfaces whose primary IP is covered by a network statement, OSPF is not running on R1's connecting interface; no Hello packets are sent, and the adjacency cannot form. The other options describe possible causes but do not align with the given configuration: no explicit network type change is mentioned, duplicate router-IDs are not indicated, and no timer modification is described.
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 on R1's interface differs from the network type on R2's interface.
Why it's wrong here
By default, Ethernet interfaces use the broadcast network type. Unless explicitly changed, both routers will have the same type, so this is unlikely to be the cause. The configuration shown does not indicate any network type changes.
- ✓
R1's network statement does not include the subnet of the link connecting R1 and R2.
Why this is correct
The command 'network 192.168.1.0 0.0.0.255 area 0' only enables OSPF on interfaces with an IP address in the 192.168.1.0/24 range. The link uses the 10.1.1.0/30 subnet, so R1's interface (e.g., 10.1.1.2/30) is not matched. Consequently, OSPF is inactive on that interface, and no neighbor relationship can form.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
R1's router ID is not manually set and duplicates the router ID of R2.
Why it's wrong here
A duplicate router ID would cause adjacency problems and log an error, but the scenario provides no evidence of this. The immediate and direct cause based on the configuration snippet is the network command mismatch.
- ✗
Mismatched OSPF hello and dead intervals between the routers.
Why it's wrong here
Hello and dead interval mismatches prevent adjacency, but the question does not indicate that any timers have been modified from their default values. The most likely cause given the explicit network command is the missing subnet match.
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.
✓R1's network statement does not include the subnet of the link connecting R1 and R2.Correct answer▾
Why this is correct
The command 'network 192.168.1.0 0.0.0.255 area 0' only enables OSPF on interfaces with an IP address in the 192.168.1.0/24 range. The link uses the 10.1.1.0/30 subnet, so R1's interface (e.g., 10.1.1.2/30) is not matched. Consequently, OSPF is inactive on that interface, and no neighbor relationship can form.
✗The OSPF network type on R1's interface differs from the network type on R2's interface.Wrong answer — click to see why▾
Why this is wrong here
Candidates assume that OSPF adjacency failures on Ethernet links are often due to network type mismatches, without considering that the default settings match.
✗R1's router ID is not manually set and duplicates the router ID of R2.Wrong answer — click to see why▾
Why this is wrong here
Candidates may remember that duplicate router‑IDs break OSPF and jump to this conclusion without first analyzing the simpler configuration issue.
✗Mismatched OSPF hello and dead intervals between the routers.Wrong answer — click to see why▾
Why this is wrong here
Many students learn that timer mismatches are a common OSPF problem and may incorrectly assume they are the cause when the real issue is a basic configuration oversight.
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
Command / output trap
By default, Ethernet interfaces use the broadcast network type. Unless explicitly changed, both routers will have the same type, so this is unlikely to be the cause. The configuration shown does not indicate any network type changes.
Scenario analysis trap
A duplicate router ID would cause adjacency problems and log an error, but the scenario provides no evidence of this. The immediate and direct cause based on the configuration snippet is the network command mismatch.
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: R1's network statement does not include the subnet of the link connecting R1 and R2. — R1's network statement uses a wildcard mask of 0.0.0.255, which exactly matches interfaces with IP addresses in the 192.168.1.0/24 range. The link between R1 and R2 uses the 10.1.1.0/30 subnet, so R1's interface on that link will have an IP address that does not fall within the network command. Because OSPF only activates on interfaces whose primary IP is covered by a network statement, OSPF is not running on R1's connecting interface; no Hello packets are sent, and the adjacency cannot form. The other options describe possible causes but do not align with the given configuration: no explicit network type change is mentioned, duplicate router-IDs are not indicated, and no timer modification is described.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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