Question 926 of 1,389
CCNA IP Routing Practice Question
Exhibit
R1# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.1 1 FULL/DR 00:00:35 192.168.1.1 GigabitEthernet0/0 10.2.2.2 1 FULL/BDR 00:00:36 192.168.1.2 GigabitEthernet0/0 172.16.1.1 0 2WAY/DROTHER 00:00:38 192.168.1.3 GigabitEthernet0/0 Total number of neighbors: 3
Refer to the exhibit. A network administrator is troubleshooting why not all OSPF neighbors are fully adjacent on a multi-access broadcast segment. After issuing the show ip ospf neighbor command on R1, the output is displayed. What is the most likely cause of the 2WAY/DROTHER state for neighbor 172.16.1.1?
⚠ Common exam trap
Cisco often tests the misconception that any neighbor state other than FULL is a problem, but here the trap is that 2WAY/DROTHER is actually expected behavior for non-DR/BDR routers on a broadcast segment, and candidates may incorrectly assume a timer mismatch or reachability issue.
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
✓
The neighbor is a DROther and a full adjacency with another DROther is not required; adjacency is formed only with the DR and BDR.
In a multi-access broadcast OSPF network, only the Designated Router (DR) and Backup Designated Router (BDR) form full adjacencies with all other routers. DROthers (routers that are neither DR nor BDR) only form full adjacencies with the DR and BDR, and remain in the 2WAY state with other DROthers. The show ip ospf neighbor output on R1 shows neighbor 172.16.1.1 as 2WAY/DROTHER, which is normal behavior because both are DROthers and do not need to exchange LSAs directly.
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 is a DROther and a full adjacency with another DROther is not required; adjacency is formed only with the DR and BDR.
Why this is correct
The exhibit shows neighbor 172.16.1.1 in state 2WAY/DROTHER. In a broadcast multi-access OSPF network, DROthers exchange hellos and reach 2-Way state with each other but stop at that stage, establishing full adjacency only with the DR and BDR. This is standard OSPF behavior and the most likely reason for the state.
- ✗
The OSPF hello and dead timers are mismatched between R1 and neighbor 172.16.1.1.
Why it's wrong here
An OSPF hello/dead timer mismatch would prevent the neighbor relationship from ever reaching the 2WAY state. When a router receives a hello packet, it validates the hello and dead intervals contained in that packet against its own configured values; if they do not match, the hello is silently dropped and the sending router is not even listed as a neighbor. The neighbor state would remain Down or oscillate in Init, never progressing to 2WAY, which requires two-way communication with acknowledged and matching OSPF parameters. Since the exhibit clearly shows the neighbor in state 2WAY/DROTHER, the timers must be correctly matched, making this option incorrect.
- ✗
The network type is configured as point-to-point on one side and broadcast on the other, causing a DR/BDR election failure.
Why it's wrong here
The presence of DR and BDR roles in the output (FULL/DR, FULL/BDR) confirms that the network type is broadcast. A network type mismatch would cause the adjacency to fail in Exstart or Exchange, not result in a stable 2WAY/DROTHER state.
- ✗
The neighbor's router ID 172.16.1.1 is not reachable, preventing the completion of the adjacency process.
Why it's wrong here
OSPF neighbor adjacency does not depend on the router ID being reachable via the routing table. The 2WAY state shows that both routers see each other's hello packets and have agreed on parameters; a missing route to the router ID would not cause 2WAY.
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 neighbor is a DROther and a full adjacency with another DROther is not required; adjacency is formed only with the DR and BDR.Correct answer▾
Why this is correct
The exhibit shows neighbor 172.16.1.1 in state 2WAY/DROTHER. In a broadcast multi-access OSPF network, DROthers exchange hellos and reach 2-Way state with each other but stop at that stage, establishing full adjacency only with the DR and BDR. This is standard OSPF behavior and the most likely reason for the state.
✗The OSPF hello and dead timers are mismatched between R1 and neighbor 172.16.1.1.Wrong answer — click to see why▾
Why this is wrong here
Candidates mistakenly think any non-FULL state implies a timer mismatch, overlooking that timer issues prevent even reaching 2WAY.
✗The network type is configured as point-to-point on one side and broadcast on the other, causing a DR/BDR election failure.Wrong answer — click to see why▾
Why this is wrong here
Some candidates assume any DR/BDR-related issue indicates a network type mismatch, but the exhibit clearly shows successful DR/BDR formation, ruling out this option.
✗The neighbor's router ID 172.16.1.1 is not reachable, preventing the completion of the adjacency process.Wrong answer — click to see why▾
Why this is wrong here
Candidates may confuse LSA reachability with neighbor adjacency requirements. The 2WAY state proves basic connectivity is intact.
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?”
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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Last reviewed: Jul 4, 2026
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