The answer is an OSPF area mismatch on the shared link. This is the most likely cause because OSPF requires that both routers agree on the area ID for the directly connected interface before they can form an adjacency; even if IP addressing and hello timers match perfectly, a mismatch in area assignment prevents the routers from viewing the segment in the same OSPF context, causing the neighbor relationship to fail. On the CCNA 200-301 v2 exam, this scenario tests your understanding that OSPF adjacency verification goes beyond Layer 3 connectivity—it demands consistency in critical parameters like area ID, network type, and authentication. A common trap is assuming matching IPs and timers guarantee neighbor formation, but the area field in the Hello packet must match exactly. Memory tip: think of OSPF areas as different neighborhoods—two houses on the same street but in different towns cannot share a mailbox.
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 requires that all routers on a shared link must be configured with the same area ID to 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.
Two routers are directly connected and running OSPF. Their IP addresses and hello timers match, but they still do not become neighbors. One side is configured for area 0 and the other for area 1 on the shared link. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interfaces are in different OSPF areas on the shared link.
An OSPF area mismatch is the most likely cause. In plain language, the routers may be physically connected and able to exchange packets, but OSPF still requires that both sides agree on the area associated with the shared segment. If one interface belongs to area 0 and the other belongs to area 1, the routers do not view the segment in the same OSPF context and the adjacency fails.
This is a classic CCNA troubleshooting case because the addressing can look perfect while the protocol still refuses to form a neighbor relationship. OSPF is strict about several interface-level values, and the area assignment is one of the most important.
Key principle: OSPF requires that all routers on a shared link must be configured with the same area ID to 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 interfaces are in different OSPF areas on the shared link.
Why this is correct
This is correct because OSPF neighbors on the same segment must agree on the area.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF requires that all routers on a shared link must be configured with the same area ID to form neighbor adjacencies.
✗
The routers need identical hostnames.
Why it's wrong here
This is wrong because hostnames do not determine OSPF adjacency.
When this WOULD be correct
In a different scenario, if the question asked about OSPF neighbor formation issues and specifically mentioned that hostname mismatches can affect certain OSPF features like authentication or logging, then this option could be correct.
✗
The link must be converted to a trunk.
Why it's wrong here
This is wrong because OSPF adjacency on routed interfaces does not require trunking.
When this WOULD be correct
In a different scenario where the question specifies that OSPF is being used over a network that requires VLAN segmentation, and the routers are configured on different VLANs, converting the link to a trunk would be necessary for OSPF to function properly across those VLANs.
✗
The routers must use static routes first.
Why it's wrong here
This is wrong because static routes are not required for OSPF adjacency formation.
When this WOULD be correct
In a different question, if the scenario described routers that were configured to use static routes exclusively and were not establishing OSPF neighbors due to misconfiguration, then the requirement for static routes could be the correct answer. For example, if the question stated that both routers were configured for static routing only and OSPF was not enabled, this option would be valid.
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 interfaces are in different OSPF areas on the shared link.Correct answer▾
Why this is correct
This is correct because OSPF neighbors on the same segment must agree on the area.
✗The routers need identical hostnames.Wrong answer — click to see why▾
Why this is wrong here
OSPF neighbor formation does not require identical hostnames; hostnames are only used for identification and do not affect OSPF operation. The routers can have any hostname and still form an adjacency as long as other OSPF parameters match.
★ When this WOULD be the correct answer
In a different scenario, if the question asked about OSPF neighbor formation issues and specifically mentioned that hostname mismatches can affect certain OSPF features like authentication or logging, then this option could be correct.
Why candidates choose this
Students might think that hostnames must match because they confuse OSPF with other protocols like EIGRP, which uses a router ID that can be derived from the hostname, or because they assume consistency in naming is required for network devices to communicate.
✗The link must be converted to a trunk.Wrong answer — click to see why▾
Why this is wrong here
OSPF operates on routed interfaces, which are Layer 3 interfaces, and does not require trunking. Trunking is a Layer 2 concept used to carry multiple VLANs over a single link, and it is not relevant to OSPF adjacency formation.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that OSPF is being used over a network that requires VLAN segmentation, and the routers are configured on different VLANs, converting the link to a trunk would be necessary for OSPF to function properly across those VLANs.
Why candidates choose this
Test-takers might confuse OSPF with VLAN trunking or think that because OSPF can run over VLANs, the link must be a trunk. However, OSPF can run on access ports or routed ports without any trunk configuration.
✗The routers must use static routes first.Wrong answer — click to see why▾
Why this is wrong here
OSPF is a dynamic routing protocol that can form adjacencies and exchange routes without any static routes. Static routes are not a prerequisite for OSPF neighbor formation; OSPF uses its own hello protocol to discover neighbors.
★ When this WOULD be the correct answer
In a different question, if the scenario described routers that were configured to use static routes exclusively and were not establishing OSPF neighbors due to misconfiguration, then the requirement for static routes could be the correct answer. For example, if the question stated that both routers were configured for static routing only and OSPF was not enabled, this option would be valid.
Why candidates choose this
Some students believe that a router must have a route to the neighbor's network before forming an adjacency, but OSPF uses multicast hello packets to discover neighbors directly connected on the same link, regardless of existing routing table entries.
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 assuming that matching IP addresses and hello timers alone guarantee OSPF adjacency. Candidates often overlook the OSPF area configuration, which must be identical on both sides of a shared link. This mistake leads to confusion because the routers appear connected and can exchange packets, but OSPF adjacency never forms. The trap is focusing on interface parameters like timers or IP addressing while ignoring the fundamental requirement that both interfaces must belong to the same OSPF area to establish neighbor relationships.
Detailed technical explanation
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that organizes routers into areas to optimize routing and reduce overhead. Each OSPF interface must be assigned to a specific area, and routers form neighbor adjacencies only if they share the same area on the connected segment. This area concept segments the network logically, allowing routers to exchange link-state advertisements (LSAs) only within their area, which improves scalability and stability.
When two routers are directly connected and running OSPF, they exchange hello packets to establish adjacency. For adjacency to form successfully, several parameters must match, including hello and dead intervals, subnet mask, authentication, and crucially, the OSPF area ID on the interface. If one router’s interface is configured in area 0 and the other in area 1 on the same link, they will not recognize each other as neighbors because they belong to different OSPF areas. This mismatch prevents the exchange of LSAs and the formation of a neighbor relationship.
A common exam trap is to overlook the importance of area consistency on shared links and focus only on IP addressing or timers. Physically connected routers with matching hello timers but mismatched areas will fail to form adjacency, leading to routing issues. In practical networks, ensuring area consistency on all interfaces participating in OSPF is critical to maintain proper routing topology and avoid silent failures in neighbor formation.
KKey Concepts to Remember
OSPF requires that all routers on a shared link must be configured with the same area ID to form neighbor adjacencies.
OSPF adjacency formation depends on matching hello and dead intervals, subnet masks, authentication, and area IDs on connected interfaces.
Routers in different OSPF areas do not establish neighbor relationships even if IP addresses and timers match.
OSPF areas segment the network logically to reduce routing overhead and control the scope of link-state advertisements.
OSPF interfaces assigned to different areas on the same physical link cause adjacency failure and prevent routing updates.
OSPF adjacency failure due to area mismatch can appear as a connectivity issue despite correct IP addressing and timer settings.
The 'show ip ospf interface' command helps verify area configuration and troubleshoot adjacency problems effectively.
OSPF adjacency rules enforce strict parameter matching to ensure consistent and reliable routing topology formation.
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 requires that all routers on a shared link must be configured with the same area ID to 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 requires that all routers on a shared link must be configured with the same area ID to 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 requires that all routers on a shared link must be configured with the same area ID to form neighbor adjacencies..
What is the correct answer to this question?
The correct answer is: The interfaces are in different OSPF areas on the shared link. — An OSPF area mismatch is the most likely cause. In plain language, the routers may be physically connected and able to exchange packets, but OSPF still requires that both sides agree on the area associated with the shared segment. If one interface belongs to area 0 and the other belongs to area 1, the routers do not view the segment in the same OSPF context and the adjacency fails.
This is a classic CCNA troubleshooting case because the addressing can look perfect while the protocol still refuses to form a neighbor relationship. OSPF is strict about several interface-level values, and the area assignment is one of the most important.
What should I do if I get this 200-301 question wrong?
Review oSPF requires that all routers on a shared link must be configured with the same area ID to 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 requires that all routers on a shared link must be configured with the same area ID to form neighbor adjacencies.
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