CCNA IP Routing Practice Question
A technician configures OSPF on R1 using the command network 10.0.0.0 0.0.0.255 area 0. R1's GigabitEthernet0/0 interface has IP address 10.0.0.1/30 and is included in the OSPF process. The technician confirms the interface is not passive using the show ip ospf interface GigabitEthernet0/0 command. However, R2 is not forming an OSPF adjacency with R1. What should the technician do next?
⚠ Common exam trap
Cisco often tests the misconception that the OSPF network command's wildcard mask determines the subnet for adjacency, when in fact the interface's configured subnet mask is what OSPF uses to verify the neighbor is on the same link.
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
✓
Verify the subnet mask configured on R2's connecting interface.
The OSPF network command 10.0.0.0 0.0.0.255 area 0 uses a wildcard mask that matches only the first 24 bits. The interface on R1 has a /30 mask (255.255.255.252), so its IP 10.0.0.1 falls within the 10.0.0.0/24 range. However, if R2's connecting interface has a different subnet mask (e.g., /24 or /28), the two interfaces will be in different subnets, preventing OSPF adjacency from forming. OSPF requires that interfaces on the same link share the same subnet prefix length to establish a neighbor relationship.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Check the OSPF hello and dead intervals on R1 and R2.
Why it's wrong here
Checking hello and dead intervals fails here because the interface timers were not altered from defaults, so mismatch is unlikely; the real cause is probably a subnet mismatch—R1's /30 link requires R2's interface to be in the same /30, but the network command uses a wider /24 wildcard, which does not enforce this. It is tempting because differing hello/dead intervals are a common adjacency blocker, and verifying them is standard practice when timers have been manually changed on either router.
- ✗
Verify the OSPF area ID configured on R2's interface.
Why it's wrong here
Area mismatches are a common cause of adjacency failure, but the technician has already confirmed that R1's interface is in area 0. Checking R2's area is a valid step, but it does not address the possibility that R2's interface may have a wrong IP subnet mask, which would also prevent adjacency.
- ✗
Check whether R2's interface is configured as a passive interface.
Why it's wrong here
The technician verified that R1's interface is not passive, but R2 could be passive. However, a passive interface on R2 would suppress OSPF hello packets and prevent adjacency. While this is a plausible next step, the scenario provides no indication of a passive configuration on R2, and the subnet mask mismatch is a more common misconfiguration to rule out first.
- ✓
Verify the subnet mask configured on R2's connecting interface.
Why this is correct
OSPF on a broadcast network requires an exact subnet mask match; a mismatch will prevent neighbor relationships. Given that R1's interface is properly added to OSPF, is not passive, and is in the correct area, the most likely cause is a misconfigured subnet mask on R2. Checking this resolves a basic Layer 3 requirement before investigating any OSPF-specific parameters.
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.
✓Verify the subnet mask configured on R2's connecting interface.Correct answer▾
Why this is correct
OSPF on a broadcast network requires an exact subnet mask match; a mismatch will prevent neighbor relationships. Given that R1's interface is properly added to OSPF, is not passive, and is in the correct area, the most likely cause is a misconfigured subnet mask on R2. Checking this resolves a basic Layer 3 requirement before investigating any OSPF-specific parameters.
✗Check the OSPF hello and dead intervals on R1 and R2.Wrong answer — click to see why▾
Why this is wrong here
Skips the more likely and fundamental subnet mask check, which would render timer issues irrelevant until resolved.
✗Verify the OSPF area ID configured on R2's interface.Wrong answer — click to see why▾
Why this is wrong here
Ignores the more foundational IP addressing check that could also cause the issue, and area troubleshooting would be misleading if the subnet mask is incorrect.
✗Check whether R2's interface is configured as a passive interface.Wrong answer — click to see why▾
Why this is wrong here
Jumps to an OSPF-specific command without first verifying the fundamental IP subnet configuration, which is a more direct cause of failed adjacencies on broadcast links.
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
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
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.
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.
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JA
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.