R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0
A router shows this output:
R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0
Which statement is correct?
Answer choices
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
R1 has failed to form adjacency with 10.1.1.3
A 2-Way state here is not automatically a failure.
This can be normal on a broadcast segment where DROTHER routers remain in 2-Way
Correct. This is normal DR/DROTHER behavior on many multiaccess networks.
R1 has a duplicate router ID with 10.1.1.3
The output does not indicate a duplicate router ID.
The interface is passive
A passive interface would not form neighbors at all.
Common exam trap
A common exam trap is assuming that any neighbor stuck in the 2-Way state indicates a failure to form adjacency. On broadcast networks, routers in the DROTHER role intentionally remain in the 2-Way state with each other and only form full adjacencies with the DR and BDR. Misreading this normal behavior as a problem can lead to incorrect conclusions about network issues. Another trap is confusing the 2-Way state with a passive interface, which actually prevents neighbor formation altogether. Candidates must carefully distinguish between these OSPF states and roles to avoid this pitfall.
Technical deep dive
OSPF (Open Shortest Path First) is a link-state routing protocol that uses a series of neighbor states to establish adjacencies between routers. On broadcast multiaccess networks such as Ethernet, OSPF elects a Designated Router (DR) and a Backup Designated Router (BDR) to reduce the number of adjacencies required. Routers that are neither DR nor BDR are called DROTHERs. These DROTHER routers form full adjacencies only with the DR and BDR, but remain in the 2-Way state with other DROTHER routers. The 2-Way state means that bidirectional communication has been established through the exchange of hello packets, and the routers recognize each other as neighbors. However, full adjacency, which involves database synchronization and exchange of link-state advertisements (LSAs), only occurs between DR/BDR and DROTHER routers. This behavior optimizes OSPF operation by limiting the number of full adjacencies on a broadcast segment. In the provided output, R1 shows a FULL/DR state with neighbor 10.1.1.2, indicating that R1 is the DR and has formed a full adjacency with that neighbor. The 2WAY/DROTHER state with 10.1.1.3 is normal and expected behavior for DROTHER routers on a broadcast network segment. This confirms that R1 has not failed to form adjacency with 10.1.1.3; rather, it is operating correctly according to OSPF design. Understanding these OSPF neighbor states and roles is essential for troubleshooting OSPF adjacency issues and ensuring efficient routing. Misinterpreting the 2-Way state as a failure can lead to unnecessary troubleshooting steps. Additionally, passive interfaces do not form neighbors at all, and duplicate router IDs cause different symptoms, such as adjacency flapping or failure to form neighbors entirely.
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practise DHCP scopes, relay, leases and troubleshooting.
Practise routing-table output, longest-prefix match, AD and route selection.
Practise trunk verification and VLAN forwarding across switches.
Practise WLAN security, authentication and wireless architecture concepts.
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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FAQ
OSPF forms full adjacencies only with the Designated Router (DR) and Backup Designated Router (BDR) on broadcast multiaccess networks.
The correct answer is: This can be normal on a broadcast segment where DROTHER routers remain in 2-Way — On broadcast OSPF networks, full adjacency is typically formed with the DR and BDR. DROTHER routers can remain in the 2-Way state with one another and still be operating normally.
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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