mediumMultiple ChoiceObjective-mapped
OSPF Neighbor States: FULL, 2WAY, DROTHER
A network engineer runs the following command on Router R1:
R1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.0.0.2 1 FULL/DR 00:00:32 192.168.1.2 GigabitEthernet0/0 10.0.0.3 1 2WAY/DROTHER 00:00:35 192.168.1.3 GigabitEthernet0/0
Based on this output, what can be concluded?
Quick Answer
The answer is that R1 is a DROTHER on this broadcast multiaccess segment. This conclusion is drawn directly from the OSPF neighbor state output: R1 sees a neighbor in the 2WAY/DROTHER state, which means both routers are DROTHERs, as they have formed a two-way adjacency but have not progressed to a full database exchange with each other. The neighbor in the FULL/DR state is the Designated Router, and since R1 is neither the DR nor the BDR (no FULL/BDR entry), it must be a DROTHER. On the ENCOR 350-401 exam, this question tests your ability to interpret OSPF neighbor states in a broadcast multiaccess network, where the DR and BDR form FULL adjacencies with all routers, while DROTHERs remain in 2WAY with each other. A common trap is assuming a FULL state always indicates a router’s role; remember that FULL only confirms adjacency with the DR/BDR, not the router’s own status. Memory tip: “DROTHERs say ‘2WAY’ to each other, but go ‘FULL’ with the DR.”
⚠ Common exam trap
Cisco often tests the misconception that 2WAY state means a full adjacency, but in OSPF, 2WAY is a normal neighbor state on broadcast networks between DROTHERs, not a full adjacency (which requires FULL state).
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
✓
R1 is a DROTHER on this segment.
The output shows R1 has a neighbor with state 2WAY/DROTHER (10.0.0.3), which indicates that R1 is also a DROTHER on this broadcast multiaccess segment. The FULL/DR neighbor (10.0.0.2) is the Designated Router, and since R1 is not the BDR (no FULL/BDR state), it must be a DROTHER.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
R1 is the Backup Designated Router (BDR) on this segment.
Why it's wrong here
The state field does not show BDR; R1's own state is not displayed, but the neighbor states indicate R1 is a DROTHER.
- ✗
R1 has a full OSPF adjacency with the neighbor 10.0.0.3.
Why it's wrong here
The state for 10.0.0.3 is 2WAY, not FULL, so only a two-way relationship exists.
- ✓
R1 is a DROTHER on this segment.
Why this is correct
Since the DR is 10.0.0.2 and the BDR is not listed, and R1 has a full adjacency only with the DR, R1 must be a DROTHER.
- ✗
The OSPF network type is point-to-point.
Why it's wrong here
The presence of DR/BDR states indicates a broadcast or NBMA network type, not point-to-point.
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.
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Same concept, more angles
1 more way this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer runs the following command on Router R9: R9# show ip ospf interface brief Interface PID Area IP Address/Mask Cost State Nbrs F/C Gi0/0 1 0 192.168.1.9/24 10 DR 2/2 Gi0/1 1 1 10.0.0.9/24 20 BDR 1/1 Lo0 1 0 9.9.9.9/32 1 LOOP 0/0 Based on this output, what can be concluded?
medium- A.R9 is the Designated Router on the segment connected to Gi0/1.
- ✓ B.R9 has two fully adjacent neighbors on Gi0/0.
- C.The loopback interface Lo0 is advertised as a /24 network.
- D.R9 is an Area Border Router.
Why B: The output shows that on interface Gi0/0, R9 has a state of DR (Designated Router) and 2 fully adjacent neighbors (Nbrs F/C = 2/2). The '2/2' indicates 2 neighbors in a full state out of 2 total neighbors, meaning both neighbors have completed the OSPF adjacency process. Therefore, R9 has two fully adjacent neighbors on Gi0/0, making option B correct.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.