The corrective actions are to remove the passive-interface configuration from GigabitEthernet0/0, Serial0/0/0, and Serial0/0/1, and adjust the hello timer on Serial0/0/0 to 30 seconds. This is correct because a passive interface suppresses OSPF hello packets entirely, preventing any adjacency from forming, while a hello timer mismatch—here the default 10 seconds on R1 versus the required 30 seconds on the neighbor—causes the routers to reject each other’s hellos and never reach the 2-Way state. On the CCNA 200-301 v2 exam, this scenario tests your ability to diagnose two simultaneous OSPF adjacency blockers: a common misconfiguration where an engineer applies passive-interface default to all interfaces instead of only loopbacks, combined with a timer mismatch often seen on slower serial links. The trap is assuming only one issue exists; always verify both hello/dead timers and passive-interface status when adjacencies fail. Memory tip: “Passive stops the talk, timer mismatch stops the walk”—check both before troubleshooting further.
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.
Network Topology
You are connected to R1. R1, R2, and R3 are connected via serial links as shown. Configure single-area OSPFv2 on all three routers so that all interfaces in the 10.0.0.0/8 range participate in OSPF area 0, except the loopback interfaces. Currently R1 cannot form OSPF adjacencies with R2 and R3. Examine the running-config of R1 below and determine the corrective actions needed.
R1# show running-config | section router ospf
router ospf 1
router-id 1.1.1.1
network 10.0.0.0 0.255.255.255 area 0
passive-interface GigabitEthernet0/0
passive-interface Serial0/0/0
passive-interface Serial0/0/1
!
R1# show ip ospf interface brief
Interface PID Area IP Address/Mask Cost State Nbrs F/C
Gi0/0 1 0 10.0.0.1/24 1 DR 0/0
Se0/0/0 1 0 10.0.1.1/30 64 P2P 0/0
Se0/0/1 1 0 10.0.2.1/30 64 P2P 0/0
Lo0 1 0 10.0.255.1/24 1 LOOP 0/0
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/ - 00:00:32 10.0.1.2 Serial0/0/0
3.3.3.3 0 FULL/ - 00:00:39 10.0.2.2 Serial0/0/1
A
Remove the passive-interface configuration from GigabitEthernet0/0, Serial0/0/0, and Serial0/0/1, and adjust the hello timer on Serial0/0/0 to 30 seconds.
This fix deactivates passive behavior on the required interfaces so that OSPF hello packets can be sent, while the global passive-interface default still prevents loopbacks from participating. Setting the hello timer to match the neighbor’s 30-second interval resolves the timer mismatch.
B
Change the OSPF network type on all interfaces to point-to-point and increase the dead timer to 120 seconds.
Why wrong: This is incorrect because the problem is not about network type; the default network type on serial interfaces is point-to-point, which is fine. Increasing the dead timer does not address the passive-interface issue or the hello timer mismatch.
C
Add the network 10.0.0.0 0.255.255.255 area 0 command under router ospf and enable OSPF on all interfaces.
Why wrong: This is incorrect because the network command is already present in the configuration (as shown in the exhibit). The issue is not about missing network statements; it's about passive interfaces and timer mismatch.
D
Configure the loopback interfaces with the ip ospf network point-to-point command to ensure they participate in OSPF.
Why wrong: This is incorrect because the question explicitly states that loopback interfaces should not participate in OSPF. Configuring them would violate the requirement and does not address the adjacency issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the passive-interface configuration from GigabitEthernet0/0, Serial0/0/0, and Serial0/0/1, and adjust the hello timer on Serial0/0/0 to 30 seconds.
R1 has passive-interface configured on all active interfaces (G0/0, Se0/0/0, Se0/0/1), which prevents OSPF hello packets from being sent and stops adjacencies from forming. Additionally, the hello timer on Serial0/0/0 is mismatched (default 10 vs. required 30). To resolve the adjacency issues while keeping loopback interfaces inactive, the passive-interface command must be removed from only the necessary interfaces and the hello timer on Se0/0/0 must be set to 30 seconds.
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.
✓
Remove the passive-interface configuration from GigabitEthernet0/0, Serial0/0/0, and Serial0/0/1, and adjust the hello timer on Serial0/0/0 to 30 seconds.
Why this is correct
This fix deactivates passive behavior on the required interfaces so that OSPF hello packets can be sent, while the global passive-interface default still prevents loopbacks from participating. Setting the hello timer to match the neighbor’s 30-second interval resolves the timer mismatch.
Change the OSPF network type on all interfaces to point-to-point and increase the dead timer to 120 seconds.
Why it's wrong here
This is incorrect because the problem is not about network type; the default network type on serial interfaces is point-to-point, which is fine. Increasing the dead timer does not address the passive-interface issue or the hello timer mismatch.
✗
Add the network 10.0.0.0 0.255.255.255 area 0 command under router ospf and enable OSPF on all interfaces.
Why it's wrong here
This is incorrect because the network command is already present in the configuration (as shown in the exhibit). The issue is not about missing network statements; it's about passive interfaces and timer mismatch.
✗
Configure the loopback interfaces with the ip ospf network point-to-point command to ensure they participate in OSPF.
Why it's wrong here
This is incorrect because the question explicitly states that loopback interfaces should not participate in OSPF. Configuring them would violate the requirement and does not address the adjacency issue.
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.
✓Remove the passive-interface configuration from GigabitEthernet0/0, Serial0/0/0, and Serial0/0/1, and adjust the hello timer on Serial0/0/0 to 30 seconds.Correct answer▾
Why this is correct
This fix deactivates passive behavior on the required interfaces so that OSPF hello packets can be sent, while the global passive-interface default still prevents loopbacks from participating. Setting the hello timer to match the neighbor’s 30-second interval resolves the timer mismatch.
✗Change the OSPF network type on all interfaces to point-to-point and increase the dead timer to 120 seconds.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that changing network type is unnecessary and does not fix the passive-interface or timer mismatch problems.
Why candidates choose this
Candidates might think that changing network type or adjusting timers is a common fix for OSPF adjacency issues, but here the root cause is passive interfaces and hello timer mismatch.
✗Add the network 10.0.0.0 0.255.255.255 area 0 command under router ospf and enable OSPF on all interfaces.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the network command is already configured, so adding it again does not solve the adjacency problem.
Why candidates choose this
Candidates often assume that OSPF adjacency issues are due to missing network statements, but here the configuration already includes the correct network command.
✗Configure the loopback interfaces with the ip ospf network point-to-point command to ensure they participate in OSPF.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that loopback interfaces are intentionally excluded from OSPF, and forcing them to participate is not required and would be incorrect.
Why candidates choose this
Candidates might think that loopback interfaces need special configuration to work with OSPF, but the requirement is to exclude them, not include them.
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
This is incorrect because the network command is already present in the configuration (as shown in the exhibit). The issue is not about missing network statements; it's about passive interfaces and timer 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 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 200-301 OSPF questions on adjacency and route selection.
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: Remove the passive-interface configuration from GigabitEthernet0/0, Serial0/0/0, and Serial0/0/1, and adjust the hello timer on Serial0/0/0 to 30 seconds. — R1 has passive-interface configured on all active interfaces (G0/0, Se0/0/0, Se0/0/1), which prevents OSPF hello packets from being sent and stops adjacencies from forming. Additionally, the hello timer on Serial0/0/0 is mismatched (default 10 vs. required 30). To resolve the adjacency issues while keeping loopback interfaces inactive, the passive-interface command must be removed from only the necessary interfaces and the hello timer on Se0/0/0 must be set to 30 seconds.
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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