This 200-301 practice question tests your understanding of ip routing. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: oSPF routers must be in the same OSPF area on a shared Ethernet segment to 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.
Which two statements about OSPF neighbor requirements on a shared Ethernet segment are correct? (Choose two.)
In a different question focused on OSPF configuration best practices, if the question asked about prerequisites for OSPF routing table synchronization or specific scenarios involving OSPF route selection, then having identical router IDs might be presented as a requirement to ensure consistent routing behavior.
✗
They must use the same process ID number on both routers.
Why it's wrong here
The process ID is locally significant only.
When this WOULD be correct
In a different exam scenario where the question asks about OSPF configuration requirements for routers that need to share routing information across multiple OSPF processes, having the same process ID would be necessary for them to exchange OSPF routing information effectively.
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.
✓They must be in the same OSPF area on that link.Correct answer▾
Why this is correct
Correct. Area mismatch prevents adjacency.
✗They must have identical router IDs.Wrong answer — click to see why▾
Why this is wrong here
Router IDs must be unique across the OSPF domain to avoid routing loops and confusion. Identical router IDs would cause OSPF to reject the neighbor relationship, as the router ID is used to identify each router uniquely in the LSDB.
★ When this WOULD be the correct answer
In a different question focused on OSPF configuration best practices, if the question asked about prerequisites for OSPF routing table synchronization or specific scenarios involving OSPF route selection, then having identical router IDs might be presented as a requirement to ensure consistent routing behavior.
Why candidates choose this
Students might confuse router ID with other parameters that need to match, such as area ID or subnet. They may think that identical router IDs are required for consistency, but in reality, uniqueness is critical.
✗They must use the same process ID number on both routers.Wrong answer — click to see why▾
Why this is wrong here
The OSPF process ID is locally significant and only used to identify the OSPF process on the local router. Neighbors can have different process IDs and still form an adjacency, as the process ID is not exchanged in OSPF packets.
★ When this WOULD be the correct answer
In a different exam scenario where the question asks about OSPF configuration requirements for routers that need to share routing information across multiple OSPF processes, having the same process ID would be necessary for them to exchange OSPF routing information effectively.
Why candidates choose this
Many students mistakenly believe that the process ID must match between neighbors, similar to how EIGRP requires the same autonomous system number. This is a common point of confusion between OSPF and other routing protocols.
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 confusing the OSPF process ID with the area ID or router ID requirements. Candidates often think the process ID must match between neighbors, but it is locally significant and does not affect adjacency. Another common mistake is assuming router IDs must be identical; in fact, router IDs must be unique within the OSPF domain to prevent routing conflicts. Misunderstanding these distinctions can lead to selecting incorrect answers about neighbor requirements. The key is to focus on area ID and subnet matching for adjacency on shared Ethernet segments, not process ID or identical router IDs.
Detailed technical explanation
How to think about this question
Open Shortest Path First (OSPF) is a link-state routing protocol that forms neighbor adjacencies to exchange routing information. On a shared Ethernet segment, OSPF routers send multicast Hello packets to discover neighbors and establish adjacencies. These Hello packets contain critical information such as the router's OSPF area ID, subnet, Hello and Dead intervals, and router ID. For two routers to become OSPF neighbors on a shared Ethernet link, they must be in the same OSPF area and use the same subnet on their connected interfaces. This ensures that the routers are logically connected within the same routing domain and can communicate directly at Layer 3.
The requirement for matching OSPF area IDs on a shared segment is fundamental because OSPF organizes routers into areas to optimize routing and reduce overhead. Routers in different areas do not form neighbor relationships on the same link. Similarly, the subnet on the connected interfaces must be identical so that the routers can reach each other directly via IP. Without the same subnet, Hello packets will not be received or acknowledged, preventing adjacency formation. The OSPF process ID, however, is locally significant and does not need to match between neighbors, while router IDs must be unique to avoid routing conflicts.
A common exam trap is confusing the OSPF process ID and router ID requirements. Many candidates mistakenly believe that the process ID must match between neighbors, but it only identifies the OSPF instance locally on a router. Another trap is assuming router IDs must be identical; in reality, they must be unique. Understanding these distinctions helps avoid incorrect answers. In practical networks, ensuring area and subnet consistency on shared Ethernet segments is critical for OSPF neighbor relationships and stable routing operation.
KKey Concepts to Remember
OSPF routers must be in the same OSPF area on a shared Ethernet segment to form neighbor adjacencies and exchange routing information.
OSPF neighbors on a shared Ethernet link must use the same subnet on their connected interfaces to ensure Layer 3 reachability and successful Hello packet exchange.
OSPF router IDs must be unique within the OSPF domain to prevent routing conflicts but do not need to be identical between neighbors.
The OSPF process ID is locally significant to each router and does not affect neighbor relationships or adjacency formation.
OSPF Hello packets include the area ID and subnet information, which neighbors use to verify compatibility before forming adjacencies.
Mismatch in OSPF area ID or subnet between routers on the same Ethernet segment prevents neighbor adjacency and routing updates.
OSPF uses multicast Hello packets on shared Ethernet segments to discover neighbors and establish adjacencies based on matching parameters.
OSPF adjacency formation on shared media requires agreement on key parameters such as area ID, subnet, Hello and Dead intervals.
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 be in the same OSPF area on a shared Ethernet segment to 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 routers must be in the same OSPF area on a shared Ethernet segment to 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 routers must be in the same OSPF area on a shared Ethernet segment to form neighbor adjacencies and exchange routing information..
What is the correct answer to this question?
The correct answer is: They must be in the same OSPF area on that link. — Neighbors must agree on key parameters such as area ID and subnet, and they exchange Hello packets on the segment.
What should I do if I get this 200-301 question wrong?
Review oSPF routers must be in the same OSPF area on a shared Ethernet segment to form neighbor adjacencies and exchange routing information., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
OSPF routers must be in the same OSPF area on a shared Ethernet segment to form neighbor adjacencies and exchange routing information.
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