- A
The neighbor on Gi0/1 is not forming a full adjacency because it is in 2WAY state.
Why wrong: Incorrect. The 2WAY state is normal for DROTHER routers on a broadcast multi-access network; it is not an issue.
- B
The neighbor on Gi0/0 is the DR, which is causing high CPU usage.
Why wrong: Incorrect. The neighbor on Gi0/0 being the DR is normal and not necessarily a cause of high CPU usage.
- C
The neighbor on Gi0/2 is the BDR, which is a problem because it should be the DR.
Why wrong: Incorrect. The neighbor on Gi0/2 being the BDR is normal; there is no requirement that it should be the DR.
- D
All neighbors are in FULL state, indicating no issues.
Correct. All neighbor states are appropriate for their roles, so there is no issue.
Question 356 of 2,152
OSPF Neighbor 2WAY State Interpretation
This 300-410 practice question tests your understanding of device access control. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: oSPF neighbor states. 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.
A network engineer runs the following command on Router R1:
R1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 192.168.1.2 1 FULL/DR 00:00:35 10.1.1.2 GigabitEthernet0/0 192.168.2.2 1 2WAY/DROTHER 00:00:32 10.2.2.2 GigabitEthernet0/1 192.168.3.2 1 FULL/BDR 00:00:38 10.3.3.2 GigabitEthernet0/2
Based on this output, what is a potential issue?
Quick Answer
The answer is the neighbor on GigabitEthernet0/1 stuck in the 2WAY/DROTHER state, which is the only adjacency not reaching FULL. In OSPF, the 2WAY state is a normal and stable condition for DROTHER routers on a broadcast multi-access network, indicating that two-way communication is established but the router is neither the Designated Router (DR) nor the Backup Designated Router (BDR). Because only DR and BDR routers form FULL adjacencies with all neighbors, DROTHER routers remain in 2WAY with each other, meaning they do not exchange Link State Advertisements directly. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of OSPF network types and neighbor state progression; a common trap is assuming 2WAY is always an error, when it is actually expected on multi-access segments unless the link is point-to-point. Remember the memory tip: “DR and BDR go FULL, DROTHERs stay 2WAY.”
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
All neighbors are in FULL state, indicating no issues.
The output shows normal OSPF neighbor states on a broadcast multi-access network. The neighbor on Gi0/1 is in the 2WAY/DROTHER state, which is expected for non-DR/BDR routers. The neighbors on Gi0/0 and Gi0/2 are in FULL state (DR and BDR respectively). All states are valid, so there is no issue.
Key principle: OSPF neighbor states
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 neighbor on Gi0/1 is not forming a full adjacency because it is in 2WAY state.
Why it's wrong here
Incorrect. The 2WAY state is normal for DROTHER routers on a broadcast multi-access network; it is not an issue.
- ✗
The neighbor on Gi0/0 is the DR, which is causing high CPU usage.
Why it's wrong here
Incorrect. The neighbor on Gi0/0 being the DR is normal and not necessarily a cause of high CPU usage.
- ✗
The neighbor on Gi0/2 is the BDR, which is a problem because it should be the DR.
Why it's wrong here
Incorrect. The neighbor on Gi0/2 being the BDR is normal; there is no requirement that it should be the DR.
- ✓
All neighbors are in FULL state, indicating no issues.
Why this is correct
Correct. All neighbor states are appropriate for their roles, so there is no issue.
Related concept
OSPF neighbor states
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often incorrectly assume that any state other than FULL indicates a problem. However, in OSPF broadcast multi-access networks, the 2WAY state between DROTHER routers is normal and does not indicate an issue.
Detailed technical explanation
How to think about this question
In OSPF broadcast multi-access networks, only the DR and BDR form FULL adjacencies with all other routers on the segment; DROTHER routers only exchange LSAs with the DR and BDR, resulting in a 2WAY state between DROTHER routers. This behavior is defined in RFC 2328, Section 9.3, and is designed to reduce the number of adjacencies and LSA flooding overhead. A common real-world scenario is when an engineer misconfigures an interface as broadcast on a point-to-point link, causing unexpected 2WAY states and incomplete routing information exchange.
KKey Concepts to Remember
- OSPF neighbor states
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 neighbor states
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.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
Got this wrong? Here's your next step.
Review oSPF neighbor states, then practise related 300-410 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Access Control — This question tests Device Access Control — OSPF neighbor states.
What is the correct answer to this question?
The correct answer is: All neighbors are in FULL state, indicating no issues. — The output shows normal OSPF neighbor states on a broadcast multi-access network. The neighbor on Gi0/1 is in the 2WAY/DROTHER state, which is expected for non-DR/BDR routers. The neighbors on Gi0/0 and Gi0/2 are in FULL state (DR and BDR respectively). All states are valid, so there is no issue.
What should I do if I get this 300-410 question wrong?
Review oSPF neighbor states, then practise related 300-410 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
OSPF neighbor states
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Last reviewed: Jun 24, 2026
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