CCNA IP Routing Practice Question
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?
⚠ Common exam trap
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.
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 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.
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 OSPF `network` command on R1 uses the correct wildcard mask for the GigabitEthernet0/0 /30 link. The wildcard mask `0.0.0.3` is the inverse of the subnet mask `255.255.255.252`, so it matches only the 10.1.1.0/30 addresses. This command places the interface into OSPF area 0, so the lack of adjacency is not caused by an incorrect subnet mask.
- ✓
R1's passive-interface default prevents OSPF hello packets from being sent on GigabitEthernet0/0.
Why this is correct
R1's configuration includes `passive-interface default`, which makes all OSPF-enabled interfaces passive by default. A passive interface does not send or process OSPF hello packets, so R1 never establishes a neighbor relationship on GigabitEthernet0/0. Unless a `no passive-interface GigabitEthernet0/0` statement is present, hellos are suppressed even though the interface is up and the network statement matches.
- ✗
The GigabitEthernet0/0 interface on R2 is administratively down.
Why it's wrong here
The running configuration for R2's GigabitEthernet0/0 explicitly contains `no shutdown`, indicating the interface is administratively up. If it were shut down, the line protocol would remain down and OSPF could not send hellos, but that is not the case here. Interface status is not the cause of the neighbor adjacency failure.
- ✗
The routers are configured with different OSPF area IDs.
Why it's wrong here
Both R1 and R2 configure their OSPF network statements with the same area 0, so they do not mismatch on area ID. OSPF neighbors must be in the same area on the connecting link; since both are configured for area 0, area mismatch is not the reason no adjacency forms. Other parameters like hello/dead timers are also relevant, but area ID is clearly consistent.
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
R1's configuration includes `passive-interface default`, which makes all OSPF-enabled interfaces passive by default. A passive interface does not send or process OSPF hello packets, so R1 never establishes a neighbor relationship on GigabitEthernet0/0. Unless a `no passive-interface GigabitEthernet0/0` statement is present, hellos are suppressed even though the interface is up and the network statement matches.
✗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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
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Key term
OSPF
OSPF is a link-state routing protocol used to find the best path for data packets to travel across IP networks, like a smart GPS that recalculates routes when traffic changes.
Key term
OSPF
OSPF is a link-state routing protocol that uses the SPF algorithm to compute the shortest path to each destination within a single autonomous system.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.