CCNA IP Routing Practice Question
Exhibit
R1# interface GigabitEthernet0/0 ip address 10.10.12.1 255.255.255.0 ip ospf hello-interval 10 ip ospf dead-interval 40 ! router ospf 1 network 10.10.12.0 0.0.0.255 area 0 R2# interface GigabitEthernet0/0 ip address 10.10.12.2 255.255.255.0 ip ospf hello-interval 5 ip ospf dead-interval 20 ! router ospf 1 network 10.10.12.0 0.0.0.255 area 0
A network engineer configures OSPF between R1 and R2, but the routers never become neighbors on GigabitEthernet0/0. Based on the exhibit, what is the most likely cause?
⚠ Common exam trap
A frequent exam trap is assuming that OSPF adjacency forms as long as routers are in the same area and can ping each other. Candidates often overlook the necessity for matching hello and dead intervals, which are critical for neighbor discovery and maintenance. Because routers can still exchange ICMP packets, it may appear that the link is fully operational, leading to the mistaken belief that OSPF should work. This misunderstanding causes candidates to select incorrect answers related to area mismatches or subnet masks, ignoring the timer mismatch that actually prevents adjacency.
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
✓
The OSPF interface timers do not match.
The most likely cause is a hello/dead timer mismatch. In practical terms, both routers are on the same subnet and both are trying to run OSPF in area 0, so the obvious items look correct. But OSPF does not form adjacency based on IP reachability alone. It also checks whether key interface parameters agree. Hello and dead intervals are among those required parameters. On R1, the hello interval is 10 seconds and the dead interval is 40 seconds. On R2, the hello interval is 5 seconds and the dead interval is 20 seconds. That mismatch is enough to prevent the neighbor relationship from forming. This is a common CCNA troubleshooting pattern because the interfaces can still ping each other, which makes the failure look less obvious at first glance.
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 routers are using different OSPF areas.
Why it's wrong here
For two OSPF routers to become neighbors on a shared segment, their interfaces must be configured in the same OSPF area. In this scenario, the engineer placed the connecting subnet into area 0 on both routers, so the area identity is consistent. Since the area IDs match, the adjacency failure is clearly not caused by an area mismatch.
When this WOULD be correct
In a different scenario, if the question specified that both routers must be in the same OSPF area for neighbor adjacency and the configurations showed different area IDs, then this option would be correct. For example, if R1 is in area 0 and R2 is in area 1, they would not become neighbors.
- ✓
The OSPF interface timers do not match.
Why this is correct
OSPF requires that neighbor routers on the same link agree on both the hello interval and the dead interval. If R1 uses the default 10-second hello and 40-second dead timers while R2 has modified those timers, the routers will not recognize each other as valid neighbors and will not exchange OSPF packets. This timer mismatch prevents adjacency formation, regardless of any other matching parameters.
- ✗
The routers must use the same hostname to become neighbors.
Why it's wrong here
Router hostnames are local administrative labels and are never included in OSPF hello or database packets. OSPF neighbor formation relies on matching router IDs, interface addresses, area IDs, and timer values, but the device hostname has no protocol meaning or influence. Therefore, having different hostnames on R1 and R2 cannot be the reason the OSPF adjacency fails.
When this WOULD be correct
In a different exam scenario, if the question specified that OSPF neighbor relationships depend on hostname resolution via DNS and that both routers are configured to use hostnames instead of IP addresses, then this option would be correct.
- ✗
The subnet mask prevents multicast OSPF traffic.
Why it's wrong here
The subnet mask assigned to the interfaces does not affect OSPF multicast hello transmission. OSPF routers send hello packets to multicast addresses 224.0.0.5 or 224.0.0.6, which are forwarded normally on the local broadcast segment regardless of the netmask length. A /24 mask correctly contains the interface IPs and does not block these multicast messages, so the mask is not the source of the neighbor problem.
When this WOULD be correct
In a different scenario where the question specifies that the routers are configured with different subnet masks that create separate broadcast domains, this option would be correct. For example, if R1 is configured with a /24 mask and R2 with a /30 mask, OSPF would fail to establish neighbors due to the inability to reach each other.
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.
✓The OSPF interface timers do not match.Correct answer▾
Why this is correct
OSPF requires that neighbor routers on the same link agree on both the hello interval and the dead interval. If R1 uses the default 10-second hello and 40-second dead timers while R2 has modified those timers, the routers will not recognize each other as valid neighbors and will not exchange OSPF packets. This timer mismatch prevents adjacency formation, regardless of any other matching parameters.
✗The routers are using different OSPF areas.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPF routers can still form neighbor relationships even if they are in different areas, as long as they are configured to communicate across area boundaries. The issue in the question is likely related to OSPF timers or other configuration mismatches.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that both routers must be in the same OSPF area for neighbor adjacency and the configurations showed different area IDs, then this option would be correct. For example, if R1 is in area 0 and R2 is in area 1, they would not become neighbors.
Why candidates choose this
Candidates may mistakenly believe that OSPF requires routers to be in the same area to establish neighbor relationships, leading them to choose this option due to a misunderstanding of OSPF area functionality.
✗The routers must use the same hostname to become neighbors.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because OSPF does not require routers to have the same hostname to establish neighbor relationships; it relies on IP addresses and OSPF configurations instead.
★ When this WOULD be the correct answer
In a different exam scenario, if the question specified that OSPF neighbor relationships depend on hostname resolution via DNS and that both routers are configured to use hostnames instead of IP addresses, then this option would be correct.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of OSPF requirements, mistakenly believing that hostname consistency is necessary for neighbor formation, especially if they confuse OSPF with other protocols that may have such requirements.
✗The subnet mask prevents multicast OSPF traffic.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPF can still form neighbors even if the subnet mask is not the same, as long as the interfaces are in the same broadcast domain and can reach each other. The issue in this scenario is related to OSPF timers, not the subnet mask.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that the routers are configured with different subnet masks that create separate broadcast domains, this option would be correct. For example, if R1 is configured with a /24 mask and R2 with a /30 mask, OSPF would fail to establish neighbors due to the inability to reach each other.
Why candidates choose this
Candidates might choose this option due to a common misconception that OSPF requires identical subnet masks for neighbor relationships, leading them to overlook the actual cause of the issue in the given context.
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
Area 0
Area 0 is the backbone area in OSPF routing that connects all other OSPF areas to ensure a loop-free and efficient network routing topology.
Key term
Dead timer
The Dead timer is the period an OSPF router waits to hear from a neighbor before declaring that neighbor as unreachable and removing it from the routing table.
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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.