The answer is an OSPF network type mismatch. When two directly connected routers have correct IP addresses and are both in OSPF area 0 but fail to form an adjacency, the most likely cause is that their interfaces are configured for different OSPF network types—for example, one set to broadcast and the other to point-to-point. This matters because OSPF network types dictate neighbor discovery: broadcast types use DR/BDR elections and multicast Hello packets, while point-to-point types skip elections and use unicast, so mismatched expectations prevent the routers from ever reaching the 2-Way or Full state. On the CCNA 200-301 v2 exam, this scenario tests your ability to look beyond obvious Layer 3 connectivity and recognize that OSPF’s operational behavior depends on the network type configured under the interface. A common trap is assuming that matching areas and IPs guarantee adjacency, but a mismatch silently blocks neighbor formation. Memory tip: “If the Hello stops, check the type—broadcast vs. point-to-point is the fight.”
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. A key principle to apply: oSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.. 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.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
A
The OSPF network types on the interfaces do not match.
This is correct because OSPF network type mismatch can prevent normal adjacency formation.
B
The routers need matching hostnames to exchange LSAs.
Why wrong: This is wrong because hostnames do not determine OSPF neighbor relationships.
C
The /30 subnet is too small for OSPF to operate.
Why wrong: This is wrong because OSPF works normally over /30 point-to-point links.
D
The interfaces must be converted into switch trunks.
Why wrong: This is wrong because OSPF commonly runs over routed interfaces, not trunk ports.
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.
Key principle: OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
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 mismatch can prevent normal adjacency formation.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
✗
The routers need matching hostnames to exchange LSAs.
Why it's wrong here
This is wrong because hostnames do not determine OSPF neighbor relationships.
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 works normally over /30 point-to-point links.
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 commonly runs over routed interfaces, not trunk ports.
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 mismatch can prevent normal adjacency formation.
✗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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that forms neighbor adjacencies between routers on shared networks. One critical factor in adjacency formation is the OSPF network type configured on each interface. Common OSPF network types include broadcast, point-to-point, point-to-multipoint, and non-broadcast multi-access (NBMA). These types influence how routers discover neighbors, elect designated routers (DR/BDR), and exchange link-state advertisements (LSAs).
When two routers are directly connected and configured in the same OSPF area, their interfaces must have matching OSPF network types to form a neighbor relationship. For example, if one router’s interface is set to broadcast and the other to point-to-point, the routers will not recognize each other as neighbors because their OSPF hello packets and neighbor discovery mechanisms differ. This mismatch prevents the adjacency from progressing beyond the initial state.
A common exam trap is assuming that correct IP addressing and area configuration guarantee OSPF adjacency. However, the network type mismatch silently blocks adjacency formation, causing confusion. In practical networks, verifying and aligning OSPF network types on both ends of a link is essential. Cisco IOS allows explicit configuration of the OSPF network type per interface, and understanding this behavior helps troubleshoot adjacency failures effectively.
KKey Concepts to Remember
OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
OSPF network types determine how routers discover neighbors and exchange routing information, affecting adjacency formation.
A mismatch between broadcast and point-to-point OSPF network types prevents routers from establishing full OSPF adjacency.
OSPF adjacency formation requires consistent area configuration and compatible interface network types on both routers.
IP addressing correctness alone does not guarantee OSPF neighbor relationships if network types differ on interfaces.
OSPF does not require matching hostnames for neighbor relationships; adjacency depends on interface and protocol parameters.
OSPF operates normally over /30 subnets on point-to-point links, so subnet size is not a limiting factor for adjacency.
OSPF runs over routed interfaces and does not require interfaces to be configured as switch trunks for adjacency.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
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 routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 200-301 question wrong?
Review oSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies., then practise related 200-301 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
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