CCNA IP Routing Practice Question
Exhibit
R1# show ip ospf interface g0/0 GigabitEthernet0/0 is up, line protocol is up Internet Address 10.12.12.1/30, Area 0 Network Type POINT_TO_POINT R2# show ip ospf interface g0/0 GigabitEthernet0/0 is up, line protocol is up Internet Address 10.12.12.2/30, Area 0 Network Type BROADCAST
R1 and R2 are directly connected and both configured for OSPF area 0. The IP addresses are correct, but the routers do not become neighbors. What is the most likely cause?
⚠ Common exam trap
A frequent exam trap is to overlook the importance of matching OSPF network types on connected interfaces. Candidates might assume that correct IP addressing and area numbers are sufficient for adjacency. However, if one router uses a broadcast network type and the other uses point-to-point, they will not become neighbors despite appearing correctly configured. This subtle mismatch is often missed because it does not generate explicit errors, leading to confusion and incorrect troubleshooting steps.
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 network types on the interfaces do not match.
The most likely cause is an OSPF network type mismatch. In practical terms, both routers are on the same IP segment and both are trying to use OSPF in the same area, but they do not agree on the type of OSPF network the interface represents. That matters because OSPF behavior changes depending on the network type, including how neighbors are discovered and how adjacencies are formed. This is a classic exam-style troubleshooting case because the obvious items look correct: IP addressing works and the area matches. But a mismatch between point-to-point and broadcast expectations can still stop the relationship from forming cleanly. That makes network type mismatch the strongest answer here.
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 OSPF network types on the interfaces do not match.
Why this is correct
This is correct because OSPF network type controls fundamental adjacency behaviors such as Hello/Dead timer intervals and DR/BDR election. A point-to-point interface expects to form an adjacency without a DR, while a broadcast interface will wait for a DR/BDR process, and their timer values typically differ. Even if both routers have matching subnet masks and are directly connected, a mismatch in network type causes the routers to discard each other's Hello packets or fail to reach Full state, preventing any LSA exchange.
- ✗
The routers need matching hostnames to exchange LSAs.
Why it's wrong here
This is wrong because OSPF adjacency relies solely on the Router ID (derived from a loopback address, a physical interface address, or an explicitly configured Router ID) and not on hostnames. Hostnames are only used for administrative convenience in CLI output and do not affect the operation of the OSPF protocol. Even if two routers have completely different hostnames, they will still exchange Hello packets and build a full adjacency as long as all other OSPF parameters match.
When this WOULD be correct
In a different scenario, if the question specified that the routers were configured to use OSPF with a custom authentication method that required matching hostnames for verification, then this option could be correct. For example, if the routers were part of a security policy that mandates hostname verification for OSPF neighbor relationships.
- ✗
The /30 subnet is too small for OSPF to operate.
Why it's wrong here
This is wrong because OSPF does not impose any minimum prefix length; it operates on any interface that has a valid IP address. A /30 mask is standard for point-to-point links and is fully supported by OSPF, as it provides two usable host addresses. The real problem on a directly connected link with a /30 would be something like an MTU mismatch or a network type mismatch, not the subnet size.
When this WOULD be correct
In a different scenario, if the question stated that OSPF requires a minimum of a /29 subnet for its operation due to specific network design constraints or if it involved a multi-access network setup, then this option could be correct.
- ✗
The interfaces must be converted into switch trunks.
Why it's wrong here
This is wrong because OSPF is a Layer 3 protocol that runs over IP interfaces, not Layer 2 switch ports. Trunk ports are used to carry multiple VLANs over a single link, but routers typically connect using routed ports with IP addresses assigned directly to the interface. Converting interfaces to switch trunks would not help OSPF form an adjacency and would actually remove the necessary Layer 3 capability.
When this WOULD be correct
In a different scenario where the question involves OSPF running on a switch with multiple VLANs, and the interfaces are configured as access ports instead of trunk ports, this option could be correct. If the routers were connected through a switch that required trunking for OSPF to function, then this would be a valid cause for neighbor issues.
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 network types on the interfaces do not match.Correct answer▾
Why this is correct
This is correct because OSPF network type controls fundamental adjacency behaviors such as Hello/Dead timer intervals and DR/BDR election. A point-to-point interface expects to form an adjacency without a DR, while a broadcast interface will wait for a DR/BDR process, and their timer values typically differ. Even if both routers have matching subnet masks and are directly connected, a mismatch in network type causes the routers to discard each other's Hello packets or fail to reach Full state, preventing any LSA exchange.
✗The routers need matching hostnames to exchange LSAs.Wrong answer — click to see why▾
Why this is wrong here
OSPF neighbor relationships are established based on router IDs, IP addresses, and area configuration, not hostnames. Hostnames are only used for local identification and do not affect LSA exchange or adjacency formation.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that the routers were configured to use OSPF with a custom authentication method that required matching hostnames for verification, then this option could be correct. For example, if the routers were part of a security policy that mandates hostname verification for OSPF neighbor relationships.
Why candidates choose this
Students may confuse the requirement for matching hostnames in other protocols (like EIGRP) or think that OSPF uses hostnames for neighbor authentication, but OSPF does not require hostname matching.
✗The /30 subnet is too small for OSPF to operate.Wrong answer — click to see why▾
Why this is wrong here
OSPF operates correctly over any subnet size, including /30 point-to-point links. The /30 subnet provides two usable IP addresses, which is sufficient for a direct link between two routers.
★ When this WOULD be the correct answer
In a different scenario, if the question stated that OSPF requires a minimum of a /29 subnet for its operation due to specific network design constraints or if it involved a multi-access network setup, then this option could be correct.
Why candidates choose this
Some might think that OSPF requires a larger subnet (like /24) because they associate OSPF with broadcast networks, but OSPF works fine with /30 on point-to-point links.
✗The interfaces must be converted into switch trunks.Wrong answer — click to see why▾
Why this is wrong here
OSPF runs on routed interfaces (Layer 3), not on switch trunks (Layer 2). Trunk ports are used for VLAN tagging and are not relevant to OSPF adjacency, which requires Layer 3 connectivity.
★ When this WOULD be the correct answer
In a different scenario where the question involves OSPF running on a switch with multiple VLANs, and the interfaces are configured as access ports instead of trunk ports, this option could be correct. If the routers were connected through a switch that required trunking for OSPF to function, then this would be a valid cause for neighbor issues.
Why candidates choose this
Students may confuse OSPF with VLAN routing or think that trunking is needed for OSPF to carry multiple VLANs, but OSPF operates at Layer 3 and does not require trunk ports.
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
CAN
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Key term
OSPF area
An OSPF area is a logical grouping of routers and networks within an OSPF routing domain, used to control routing traffic and improve scalability.
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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.