The answer is that the routers cannot exchange Hellos bidirectionally on the segment. In OSPF, the INIT state indicates a router has received a Hello packet from a neighbor but does not see its own Router ID in the Hello’s neighbor field, meaning the neighbor has not yet received a Hello back—this is one-way communication. On an Ethernet link, this often stems from a Layer 2 issue, such as a misconfigured access port blocking multicast, a mismatched subnet mask, or a firewall filtering OSPF multicast traffic (224.0.0.5). For the CCNA 200-301 v2 exam, this question tests your understanding of the OSPF neighbor state machine and the critical requirement of bidirectional Hello exchange before reaching 2WAY. A common trap is assuming a mismatched OSPF area or authentication causes INIT, but those typically prevent adjacency entirely or cause EXSTART problems. Memory tip: INIT means “I see you, but you don’t see me”—so check Layer 2 connectivity and multicast delivery first.
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 exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state.. 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 OSPF routers connected on an Ethernet link remain in the INIT state. Which issue 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 routers cannot exchange Hellos bidirectionally on the segment
INIT means a router is seeing Hellos from its neighbor but does not see its own router ID in the neighbor field of received Hellos. A common cause is one-way communication or a mismatched multicast/adjacency problem, often at Layer 2.
Key principle: OSPF routers must exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state.
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 routers have identical router IDs
Why it's wrong here
Duplicate router IDs cause problems, but INIT more commonly points to one-way communication.
When this WOULD be correct
In a different scenario, if the question asked about OSPF routers failing to establish adjacency due to configuration errors, such as a misconfigured network segment where router IDs are incorrectly set to the same value, this option could be correct. For example, if the routers were on a point-to-point link and the question specified that they could not form a neighbor relationship due to identical router IDs, then this would be valid.
✓
The routers cannot exchange Hellos bidirectionally on the segment
Why this is correct
Correct. INIT often indicates one-way Hello communication.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF routers must exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state.
✗
The routers have already reached FULL and are waiting to install routes
Why it's wrong here
FULL is a later state.
When this WOULD be correct
In a different scenario where the question states that two OSPF routers are already in the FULL state and are experiencing issues with route installation, this option would be correct, indicating that they are waiting for route updates or processing.
✗
The routers are using the same OSPF process ID
Why it's wrong here
The process ID is locally significant and not exchanged.
When this WOULD be correct
In a scenario where the question specifies that two OSPF routers are on different networks but have been configured with the same OSPF process ID, the option would be correct if the question asks about potential issues in establishing OSPF adjacency. In this case, the process ID conflict would prevent proper neighbor formation.
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 routers cannot exchange Hellos bidirectionally on the segmentCorrect answer▾
Why this is correct
Correct. INIT often indicates one-way Hello communication.
✗The routers have identical router IDsWrong answer — click to see why▾
Why this is wrong here
Duplicate router IDs can cause adjacency issues, but the INIT state specifically indicates that a router has received a Hello from a neighbor but the neighbor has not received a Hello back. Duplicate IDs typically lead to neighbor state flapping or failure to progress beyond EXSTART, not INIT.
★ When this WOULD be the correct answer
In a different scenario, if the question asked about OSPF routers failing to establish adjacency due to configuration errors, such as a misconfigured network segment where router IDs are incorrectly set to the same value, this option could be correct. For example, if the routers were on a point-to-point link and the question specified that they could not form a neighbor relationship due to identical router IDs, then this would be valid.
Why candidates choose this
Students may confuse the symptoms of duplicate router IDs with one-way communication, as both can prevent full adjacency. However, duplicate IDs are detected during the exchange of Database Description packets, not during the Hello phase.
✗The routers have already reached FULL and are waiting to install routesWrong answer — click to see why▾
Why this is wrong here
The FULL state is the final OSPF neighbor state, indicating that the routers have completed the adjacency process and have identical LSDBs. Routers in FULL do not wait to install routes; they already have the full topology. INIT is an early state, far before FULL.
★ When this WOULD be the correct answer
In a different scenario where the question states that two OSPF routers are already in the FULL state and are experiencing issues with route installation, this option would be correct, indicating that they are waiting for route updates or processing.
Why candidates choose this
Students might think that after reaching FULL, routers wait for a timer to install routes, confusing OSPF with other protocols like EIGRP. However, OSPF installs routes immediately upon reaching FULL.
✗The routers are using the same OSPF process IDWrong answer — click to see why▾
Why this is wrong here
The OSPF process ID is locally significant and is not exchanged in Hello packets. Two routers can have different process IDs and still form an adjacency. Therefore, identical process IDs are not required and do not cause the INIT state.
★ When this WOULD be the correct answer
In a scenario where the question specifies that two OSPF routers are on different networks but have been configured with the same OSPF process ID, the option would be correct if the question asks about potential issues in establishing OSPF adjacency. In this case, the process ID conflict would prevent proper neighbor formation.
Why candidates choose this
Students often confuse the OSPF process ID with the area ID or autonomous system number, thinking they must match for adjacency. However, only area ID, subnet mask, Hello/dead intervals, and authentication must match.
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 to assume that duplicate router IDs cause routers to remain stuck in the INIT state. While duplicate router IDs do cause adjacency issues, they typically result in different neighbor states or error messages, not the INIT state specifically. Another trap is to think that using the same OSPF process ID on both routers causes adjacency failure; however, the process ID is locally significant and does not affect neighbor formation. Misinterpreting the INIT state as a sign of routers already being fully adjacent or waiting to install routes is also incorrect, as FULL is a later state. The key is to recognize that INIT indicates one-way Hello communication, often due to Layer 2 or multicast issues.
Detailed technical explanation
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that establishes neighbor relationships by exchanging Hello packets on a common network segment. When two OSPF routers connect on an Ethernet link, they must successfully exchange Hello packets bidirectionally to progress through the neighbor states from Down to Init, then to 2-Way, and eventually to Full adjacency. The INIT state indicates that a router has received a Hello packet from its neighbor but has not yet seen its own router ID listed in the neighbor's Hello packet, meaning the communication is only one-way.
The OSPF neighbor state machine requires that routers see their own router ID in the neighbor field of received Hello packets to confirm bidirectional communication. If routers remain stuck in the INIT state, it usually means that one router can hear the other, but the reverse is not true. This can be caused by Layer 2 issues such as VLAN mismatches, incorrect interface configurations, or multicast filtering that blocks OSPF Hello packets. The OSPF process ID is locally significant and does not affect neighbor formation, so it is not a cause of this problem.
A common exam trap is to confuse the INIT state with other OSPF states or causes such as duplicate router IDs or process ID mismatches. Duplicate router IDs cause adjacency failures but typically result in different neighbor states or log messages. The INIT state specifically points to one-way Hello communication. In practical networks, verifying Layer 2 connectivity, multicast forwarding, and interface settings is critical to resolving INIT state issues and establishing full OSPF adjacency.
KKey Concepts to Remember
OSPF routers must exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state.
The INIT state means a router sees Hellos from its neighbor but does not see its own router ID in the neighbor field of received Hellos.
One-way communication or Layer 2 issues such as VLAN mismatches or multicast filtering commonly cause OSPF routers to remain in the INIT state.
OSPF process IDs are locally significant and do not affect neighbor adjacency or cause routers to remain in the INIT state.
Duplicate router IDs cause adjacency problems but typically do not cause routers to remain stuck in the INIT state.
OSPF adjacency states progress from Down to Init, then 2-Way, and finally Full, requiring bidirectional Hello packet exchange at each step.
Multicast filtering or interface misconfigurations can block OSPF Hello packets, preventing routers from seeing each other's router IDs.
Successful OSPF adjacency formation requires both Layer 2 connectivity and correct OSPF Hello packet exchange on the segment.
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 exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state.
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 exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — OSPF routers must exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state..
What is the correct answer to this question?
The correct answer is: The routers cannot exchange Hellos bidirectionally on the segment — INIT means a router is seeing Hellos from its neighbor but does not see its own router ID in the neighbor field of received Hellos. A common cause is one-way communication or a mismatched multicast/adjacency problem, often at Layer 2.
What should I do if I get this 200-301 question wrong?
Review oSPF routers must exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state., 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 exchange Hello packets bidirectionally on a common network segment to progress beyond the INIT neighbor state.
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