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Question 1,270 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: An engineer is troubleshooting OSPF adjacency…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
Exhibit
RouterA# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.1.1.2 1 FULL/DR 00:00:35 10.1.1.2 GigabitEthernet0/0
RouterA# show ip ospf interface gigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 10.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 10.1.1.2, Interface address 10.1.1.2
Backup Designated Router (ID) 10.1.1.1, Interface address 10.1.1.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:01
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1/1, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.1.1.2 (Designated Router)
Suppress hello for 0 neighbor(s)An engineer is troubleshooting OSPF adjacency between Router A (GigabitEthernet0/0, 10.1.1.1/30) and Router B (GigabitEthernet0/1, 10.1.1.2/30). Hosts on both sides cannot ping each other. The engineer checks OSPF neighbor status on Router A and sees the following output. What is the most likely cause of the problem?
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
✓
Configure a network statement under OSPF process 1 on Router A for the LAN subnet.
The OSPF neighbor state is FULL/DR, indicating adjacency is fully established. However, the problem is that Router A's router ID is 10.1.1.1, which is the same as the IP address on its GigabitEthernet0/0 interface. This is a common misconfiguration where the router ID is not set manually and defaults to the highest loopback or interface IP. In this case, the router ID matches the interface IP, causing potential routing issues. But the real clue is that the 'show ip ospf interface' output shows Router A as BDR and Router B as DR, which is normal. The issue is that the router ID should be unique and not an interface IP that could cause confusion. However, the most likely cause of hosts not being able to ping is that the OSPF process is not advertising the correct networks. Looking at the running-config would reveal that the network statement under OSPF is missing or incorrect. But based on the given output, the adjacency is fine, so the problem is elsewhere. Actually, the correct answer is that the router ID is not set, but the adjacency is up, so the problem is that the OSPF process is not enabled on the correct interfaces or the network statement is missing. Wait, the scenario says hosts cannot ping, but OSPF adjacency is up. This suggests a routing issue. The most common cause is that the OSPF network statement does not include the subnet of the interface, or the interface is passive. However, the exhibit does not show passive-interface. Given the output, the router ID is the same as the interface IP, which is not recommended but does not break adjacency. The real issue is that the OSPF process is not advertising the LAN networks. But without that config, we must infer. In many CCNA scenarios, if the router ID is not set manually, it can cause issues if the interface IP changes. However, the correct answer here is that the OSPF network statement is missing for the LAN interfaces. But since the exhibit does not show that, I'll choose the option that says 'The OSPF process is not configured with a network statement for the LAN subnet.' That is the most plausible. But let's stick to the given output. The output shows only the point-to-point link. The hosts are on other interfaces. So the problem is that OSPF is not advertising those subnets. Option B is correct: 'Configure a network statement on Router A for the LAN subnet.' The distractors: A) Changing router ID won't fix; C) interface is not passive; D) network type is broadcast, which is fine. So explanation: The adjacency is up, but routes to LAN subnets are missing because OSPF is not advertising them. Adding the correct network statement will propagate the routes.
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.
- ✗
Change the router ID on Router A to a loopback interface IP.
Why it's wrong here
The router ID is already set to 10.1.1.1, which is the interface IP. Changing it to a loopback would not affect the adjacency or routing of LAN subnets.
- ✓
Configure a network statement under OSPF process 1 on Router A for the LAN subnet.
Why this is correct
The OSPF adjacency is established on the point-to-point link, but the LAN subnets are not advertised. Adding the correct network statement (e.g., network 192.168.1.0 0.0.0.255 area 0) will allow OSPF to advertise those routes, enabling end-to-end connectivity.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Remove the passive-interface command from GigabitEthernet0/0.
Why it's wrong here
The output shows that the interface is not passive; hellos are being sent and received. The adjacency is up, so passive-interface is not the issue.
- ✗
Change the OSPF network type to point-to-point on both interfaces.
Why it's wrong here
The current network type is BROADCAST, which is working fine as evidenced by the FULL adjacency. Changing to point-to-point would not resolve missing route advertisements.
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.
✓Configure a network statement under OSPF process 1 on Router A for the LAN subnet.Correct answer▾
Why this is correct
The OSPF adjacency is established on the point-to-point link, but the LAN subnets are not advertised. Adding the correct network statement (e.g., network 192.168.1.0 0.0.0.255 area 0) will allow OSPF to advertise those routes, enabling end-to-end connectivity.
✗Change the router ID on Router A to a loopback interface IP.Wrong answer — click to see why▾
Why this is wrong here
The adjacency is already FULL; the issue is missing route advertisements, not router ID conflict.
✗Remove the passive-interface command from GigabitEthernet0/0.Wrong answer — click to see why▾
Why this is wrong here
Passive-interface would prevent adjacency formation, but adjacency is FULL.
✗Change the OSPF network type to point-to-point on both interfaces.Wrong answer — click to see why▾
Why this is wrong here
The network type is not causing the problem; the issue is missing network statements.
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
The output shows that the interface is not passive; hellos are being sent and received. The adjacency is up, so passive-interface is not the issue.
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?
OSPF neighbours must agree on key parameters.
What is the correct answer to this question?
The correct answer is: Configure a network statement under OSPF process 1 on Router A for the LAN subnet. — The OSPF neighbor state is FULL/DR, indicating adjacency is fully established. However, the problem is that Router A's router ID is 10.1.1.1, which is the same as the IP address on its GigabitEthernet0/0 interface. This is a common misconfiguration where the router ID is not set manually and defaults to the highest loopback or interface IP. In this case, the router ID matches the interface IP, causing potential routing issues. But the real clue is that the 'show ip ospf interface' output shows Router A as BDR and Router B as DR, which is normal. The issue is that the router ID should be unique and not an interface IP that could cause confusion. However, the most likely cause of hosts not being able to ping is that the OSPF process is not advertising the correct networks. Looking at the running-config would reveal that the network statement under OSPF is missing or incorrect. But based on the given output, the adjacency is fine, so the problem is elsewhere. Actually, the correct answer is that the router ID is not set, but the adjacency is up, so the problem is that the OSPF process is not enabled on the correct interfaces or the network statement is missing. Wait, the scenario says hosts cannot ping, but OSPF adjacency is up. This suggests a routing issue. The most common cause is that the OSPF network statement does not include the subnet of the interface, or the interface is passive. However, the exhibit does not show passive-interface. Given the output, the router ID is the same as the interface IP, which is not recommended but does not break adjacency. The real issue is that the OSPF process is not advertising the LAN networks. But without that config, we must infer. In many CCNA scenarios, if the router ID is not set manually, it can cause issues if the interface IP changes. However, the correct answer here is that the OSPF network statement is missing for the LAN interfaces. But since the exhibit does not show that, I'll choose the option that says 'The OSPF process is not configured with a network statement for the LAN subnet.' That is the most plausible. But let's stick to the given output. The output shows only the point-to-point link. The hosts are on other interfaces. So the problem is that OSPF is not advertising those subnets. Option B is correct: 'Configure a network statement on Router A for the LAN subnet.' The distractors: A) Changing router ID won't fix; C) interface is not passive; D) network type is broadcast, which is fine. So explanation: The adjacency is up, but routes to LAN subnets are missing because OSPF is not advertising them. Adding the correct network statement will propagate the routes.
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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