This 200-301 practice question tests your understanding of ip routing. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: oSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.. 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 10.1.12.1/30, Area 0
Network Type POINT_TO_POINT
R2# show ip ospf interface g0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.1.12.2/30, Area 0
Network Type BROADCAST
A router pair is directly connected, but they do not become OSPF neighbors. IP addressing and area assignment are correct. 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 10.1.12.1/30, Area 0
Network Type POINT_TO_POINT
R2# show ip ospf interface g0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.1.12.2/30, Area 0
Network Type BROADCAST
A
OSPF network type mismatch on the connected interfaces
This is correct because one side is using point-to-point and the other is using broadcast, which can prevent a stable adjacency.
B
Duplicate default routes on both routers
Why wrong: This is wrong because the issue described is neighbor formation, not route selection involving default routes.
C
Missing VLAN trunking on the link
Why wrong: This is wrong because the interfaces shown are routed OSPF interfaces, not switch trunks.
D
The OSPF process IDs are required to match
Why wrong: This is wrong because OSPF process IDs are locally significant.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
OSPF network type mismatch on the connected interfaces
OSPF network type mismatch is a frequent reason for adjacency failure when basic IP and area settings are correct. If one side is configured as broadcast and the other as point-to-point, the hello timers, neighbor discovery behavior, and designated router election rules diverge, preventing neighbor formation. Unlike process IDs (which are locally significant), a mismatch in network type directly affects how OSPF hellos are processed. This is a well-known L2/L3 misconfiguration that must be checked alongside router‑ID and authentication parameters.
Key principle: OSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
OSPF network type mismatch on the connected interfaces
Why this is correct
This is correct because one side is using point-to-point and the other is using broadcast, which can prevent a stable adjacency.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
✗
Duplicate default routes on both routers
Why it's wrong here
This is wrong because the issue described is neighbor formation, not route selection involving default routes.
When this WOULD be correct
In a different scenario where the question involves troubleshooting routing issues in a network with multiple routing protocols, and the presence of duplicate default routes is explicitly stated as causing routing conflicts, this option would be correct.
✗
Missing VLAN trunking on the link
Why it's wrong here
This is wrong because the interfaces shown are routed OSPF interfaces, not switch trunks.
When this WOULD be correct
In a scenario where the question specifies that OSPF is being used over a trunk link between two switches, and the interfaces are configured as access ports instead of trunk ports, this option would be correct. The lack of trunking would prevent OSPF from seeing the necessary subnets to form neighbors.
✗
The OSPF process IDs are required to match
Why it's wrong here
This is wrong because OSPF process IDs are locally significant.
When this WOULD be correct
In a different scenario where the question specifies that two routers are configured with different OSPF process IDs and are unable to establish adjacency, this option would be correct. For example, if the question indicates that both routers are configured with different OSPF process IDs but are intended to be in the same OSPF area, then this would be the cause of the issue.
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.
✓OSPF network type mismatch on the connected interfacesCorrect answer▾
Why this is correct
This is correct because one side is using point-to-point and the other is using broadcast, which can prevent a stable adjacency.
✗Duplicate default routes on both routersWrong answer — click to see why▾
Why this is wrong here
Duplicate default routes do not affect OSPF neighbor formation; they only impact routing table entries and potential routing loops. The issue here is about the adjacency process, which relies on Hello packets and matching parameters, not on route advertisements.
★ When this WOULD be the correct answer
In a different scenario where the question involves troubleshooting routing issues in a network with multiple routing protocols, and the presence of duplicate default routes is explicitly stated as causing routing conflicts, this option would be correct.
Why candidates choose this
Students might confuse routing issues with neighbor formation, thinking that duplicate routes could cause instability that prevents adjacency. However, OSPF neighbor formation is independent of the routes being advertised.
✗Missing VLAN trunking on the linkWrong answer — click to see why▾
Why this is wrong here
VLAN trunking is a Layer 2 concept used on switch-to-switch or switch-to-router links to carry multiple VLANs. The scenario describes a router pair directly connected via routed interfaces, which operate at Layer 3 and do not require trunking.
★ When this WOULD be the correct answer
In a scenario where the question specifies that OSPF is being used over a trunk link between two switches, and the interfaces are configured as access ports instead of trunk ports, this option would be correct. The lack of trunking would prevent OSPF from seeing the necessary subnets to form neighbors.
Why candidates choose this
Test-takers might assume that any link between routers needs trunking if they are familiar with switch configurations, but OSPF neighbor formation over routed interfaces does not involve VLANs.
✗The OSPF process IDs are required to matchWrong answer — click to see why▾
Why this is wrong here
OSPF process IDs are locally significant and do not need to match between routers. Neighbor formation only requires matching area IDs, network types, Hello/Dead intervals, and authentication if configured.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that two routers are configured with different OSPF process IDs and are unable to establish adjacency, this option would be correct. For example, if the question indicates that both routers are configured with different OSPF process IDs but are intended to be in the same OSPF area, then this would be the cause of the issue.
Why candidates choose this
Many students mistakenly believe that OSPF process IDs must match because they are used to configure OSPF, but they are only used to identify the OSPF process on the local router.
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 common exam trap is assuming that OSPF process IDs must match on both routers to form neighbors. Many candidates mistakenly believe process IDs are globally significant, but they are only locally important identifiers. Another tempting mistake is blaming IP addressing or area mismatches without checking the OSPF network type. Since network type controls how OSPF hellos are sent and received, a mismatch between broadcast and point-to-point types can silently block adjacency formation even when IP and area configurations appear correct. This subtlety often leads to confusion during troubleshooting and exam scenarios.
Trap categories for this question
Command / output trap
This is wrong because the interfaces shown are routed OSPF interfaces, not switch trunks.
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 directly connected networks. One critical parameter for adjacency formation is the OSPF network type configured on the interfaces. Network types define how OSPF treats the link, such as broadcast, point-to-point, point-to-multipoint, or non-broadcast multi-access (NBMA). These types influence the hello and dead intervals, DR/BDR election, and neighbor discovery mechanisms.
For two routers to become OSPF neighbors, their network types on the connected interfaces must match. If one router treats the link as broadcast (expecting DR/BDR elections and multicast hellos) and the other treats it as point-to-point (no DR/BDR, unicast hellos), the hello packets and neighbor expectations will not align, preventing adjacency formation. This mismatch causes the routers to see each other but never establish full neighbor states despite correct IP addressing and area assignments.
This scenario is a common CCNA exam trap because candidates often verify IP addressing and area IDs but overlook network type consistency. Practically, mismatched network types cause OSPF adjacency failures even when physical connectivity is perfect. Cisco IOS allows manual configuration of network types, so understanding this behavior helps troubleshoot adjacency issues in lab and production environments.
KKey Concepts to Remember
OSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
The OSPF network type determines hello packet behavior, DR/BDR election, and neighbor discovery mechanisms on a link.
A mismatch between broadcast and point-to-point network types prevents OSPF routers from establishing stable adjacencies despite correct IP and area settings.
OSPF process IDs are locally significant and do not need to match for neighbor relationships to form.
Duplicate default routes do not affect OSPF neighbor formation but influence routing decisions after adjacency is established.
VLAN trunking is irrelevant for routed OSPF interfaces because OSPF operates at Layer 3, not Layer 2 switching.
OSPF adjacency failures due to network type mismatches often show interfaces up and in the same subnet but no neighbor state progression.
→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 requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
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 requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — OSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information..
What is the correct answer to this question?
The correct answer is: OSPF network type mismatch on the connected interfaces — OSPF network type mismatch is a frequent reason for adjacency failure when basic IP and area settings are correct. If one side is configured as broadcast and the other as point-to-point, the hello timers, neighbor discovery behavior, and designated router election rules diverge, preventing neighbor formation. Unlike process IDs (which are locally significant), a mismatch in network type directly affects how OSPF hellos are processed. This is a well-known L2/L3 misconfiguration that must be checked alongside router‑ID and authentication parameters.
What should I do if I get this 200-301 question wrong?
Review oSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information., 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 requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
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