The answer is that R1's passive-interface default prevents OSPF adjacency by blocking hello packets on GigabitEthernet0/0. This command configures all interfaces as passive by default, meaning OSPF hello packets are suppressed on every interface unless explicitly overridden with a no passive-interface statement. Without those hello packets, R1 cannot discover R2 or form a neighbor relationship, even though the network command correctly enables OSPF on that interface. On the CCNA 200-301 v2 exam, this is a classic trap: candidates often assume a network statement alone guarantees adjacency, but the passive-interface default silently kills neighbor formation. A common memory tip is to think of passive as "silent" — the router listens but never speaks, so no hello, no adjacency. Remember the mnemonic "No Hello, No Neighbor" to catch this pitfall during troubleshooting.
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.
Exhibit
R1# show running-config | section router ospf
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
passive-interface default
R1# show running-config interface GigabitEthernet0/0
interface GigabitEthernet0/0
ip address 10.1.1.1 255.255.255.252
no shutdown
R2# show running-config | section router ospf
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
R2# show running-config interface GigabitEthernet0/0
interface GigabitEthernet0/0
ip address 10.1.1.2 255.255.255.252
no shutdown
Two directly connected routers, R1 and R2, are configured with single-area OSPF in Area 0. The administrator notices that they are not forming a full OSPF neighbor adjacency. The exhibit displays relevant portions of the running configurations. 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.
R1# show running-config | section router ospf
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
passive-interface default
R1# show running-config interface GigabitEthernet0/0
interface GigabitEthernet0/0
ip address 10.1.1.1 255.255.255.252
no shutdown
R2# show running-config | section router ospf
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
R2# show running-config interface GigabitEthernet0/0
interface GigabitEthernet0/0
ip address 10.1.1.2 255.255.255.252
no shutdown
A
The network command on R1 does not include the correct subnet mask.
Why wrong: The network command uses a wildcard mask of 0.0.0.3, which correctly matches the 10.1.1.0/30 subnet on GigabitEthernet0/0.
B
R1's passive-interface default prevents OSPF hello packets from being sent on GigabitEthernet0/0.
The passive-interface default command makes all interfaces passive, disabling hello transmission, which is necessary for neighbor adjacency. Without hellos, no adjacency forms.
C
The GigabitEthernet0/0 interface on R2 is administratively down.
Why wrong: The running configuration for R2's interface explicitly includes 'no shutdown', so the interface is administratively up.
D
The routers are configured with different OSPF area IDs.
Why wrong: Both routers have the network statement specifying area 0, as shown in the exhibit.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
R1's passive-interface default prevents OSPF hello packets from being sent on GigabitEthernet0/0.
The passive-interface default command on R1 sets all interfaces to passive by default, which prevents OSPF hello packets from being sent out GigabitEthernet0/0. Without hello packets, R1 cannot discover R2 or form a neighbor adjacency, even though the network command is correctly configured. This is the most likely cause because the exhibit shows R1's configuration includes passive-interface default without a corresponding no passive-interface GigabitEthernet0/0 statement.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 network command on R1 does not include the correct subnet mask.
Why it's wrong here
The network command uses a wildcard mask of 0.0.0.3, which correctly matches the 10.1.1.0/30 subnet on GigabitEthernet0/0.
✓
R1's passive-interface default prevents OSPF hello packets from being sent on GigabitEthernet0/0.
Why this is correct
The passive-interface default command makes all interfaces passive, disabling hello transmission, which is necessary for neighbor adjacency. Without hellos, no adjacency forms.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The GigabitEthernet0/0 interface on R2 is administratively down.
Why it's wrong here
The running configuration for R2's interface explicitly includes 'no shutdown', so the interface is administratively up.
✗
The routers are configured with different OSPF area IDs.
Why it's wrong here
Both routers have the network statement specifying area 0, as shown in the exhibit.
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 passive-interface default prevents OSPF hello packets from being sent on GigabitEthernet0/0.Correct answer▾
Why this is correct
The passive-interface default command makes all interfaces passive, disabling hello transmission, which is necessary for neighbor adjacency. Without hellos, no adjacency forms.
✗The network command on R1 does not include the correct subnet mask.Wrong answer — click to see why▾
Why this is wrong here
The network statement is syntactically correct and covers the interface IP address, so it does enable OSPF process on that interface (subject to the passive-interface setting).
✗The GigabitEthernet0/0 interface on R2 is administratively down.Wrong answer — click to see why▾
Why this is wrong here
The configuration shows 'no shutdown', indicating the interface is enabled. Administrative down would require the 'shutdown' command or lack of 'no shutdown'.
✗The routers are configured with different OSPF area IDs.Wrong answer — click to see why▾
Why this is wrong here
The output clearly shows 'area 0' in both routers' OSPF configurations, so area mismatch is not the cause.
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: answer the scenario, not the keyword
Cisco often tests the passive-interface default command as a trap, because candidates may overlook that it applies to all interfaces unless explicitly overridden, leading them to incorrectly focus on network command mismatches or area ID issues.
Trap categories for this question
Command / output trap
The network command uses a wildcard mask of 0.0.0.3, which correctly matches the 10.1.1.0/30 subnet on GigabitEthernet0/0.
Detailed technical explanation
How to think about this question
OSPF uses hello packets sent every 10 seconds (by default on broadcast and point-to-point networks) to discover neighbors and maintain adjacencies. The passive-interface command suppresses hello packets on the specified interface, effectively making the router a 'silent host' that can still learn routes via LSAs but cannot form neighbor relationships. In real-world scenarios, passive-interface default is often used on WAN links or loopbacks to prevent unnecessary OSPF overhead, but it must be explicitly overridden with no passive-interface on interfaces that should form adjacencies.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 200-301 question in full detail.
IP Routing — This question tests IP Routing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: R1's passive-interface default prevents OSPF hello packets from being sent on GigabitEthernet0/0. — The passive-interface default command on R1 sets all interfaces to passive by default, which prevents OSPF hello packets from being sent out GigabitEthernet0/0. Without hello packets, R1 cannot discover R2 or form a neighbor adjacency, even though the network command is correctly configured. This is the most likely cause because the exhibit shows R1's configuration includes passive-interface default without a corresponding no passive-interface GigabitEthernet0/0 statement.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to R1 via the console. Configure single-area OSPFv2 on R1 and R2 so that they form a full adjacency. The link between R1 and R2 uses 203.0.113.0/30. R1 has G0/0 203.0.113.1/30 and R2 has G0/0 203.0.113.2/30. R1's router-id must be 1.1.1.1, and R2's router-id must be 2.2.2.2. R1's GigabitEthernet0/0 interface is configured as a passive interface under OSPF, preventing OSPF hello messages from being sent out of that interface. Ensure that R1 does not send OSPF hellos out of its loopback0 interface (203.0.113.129/32). After configuration, verify the adjacency is established and OSPF routes are exchanged.
hard
✓ A.The adjacency fails because R1's GigabitEthernet0/0 interface is configured as passive-interface. Remove the passive-interface command for G0/0.
B.The adjacency fails because the router-id 1.1.1.1 is not reachable from R2. Configure a static route for 1.1.1.1/32 on R2.
C.The adjacency fails because the subnet mask on the link is /30 but OSPF expects a /24. Change the mask to /24 on both interfaces.
D.The adjacency fails because OSPF is not enabled on R2's GigabitEthernet0/0 interface. Configure 'ip ospf 1 area 0' on R2's G0/0.
Why A: The adjacency fails because R1's GigabitEthernet0/0 interface is configured as passive-interface (the 'No Hellos' line in show ip ospf interface). This prevents R1 from sending OSPF hellos to R2. To fix, remove the passive-interface command for G0/0. The loopback0 interface should remain passive. After removal, verify with 'show ip ospf neighbor' to see the neighbor state change to FULL and 'show ip route ospf' to see routes.
Last reviewed: Jun 25, 2026
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