OSPF adjacencies without DR/BDR elections With which OSPF network type do routers form adjacencies but do not run a DR/BDR election process?

Introduction / Context:OSPF behavior varies with the underlying network type. DR/BDR elections occur on multiaccess networks to reduce adjacency overhead. On links that inherently have only two endpoints, there is no need for a DR/BDR, yet full adjacencies still form. Recognizing these differences aids design and troubleshooting.

Given Data / Assumptions:

• Network types considered: point-to-point, broadcast multi-access, NBMA.
• Adjacency formation is required in all OSPF network types.
• The question asks specifically where DR/BDR is not elected.

Concept / Approach:DR/BDR election is only needed when more than two routers share a segment, as on Ethernet (broadcast) or Frame Relay (NBMA). On point-to-point links (for example, serial PPP links or point-to-point subinterfaces), only two routers exist; therefore, OSPF forms a full adjacency without any DR/BDR roles.

Step-by-Step Solution:Classify network type: point-to-point means two routers only.Apply OSPF rule: DR/BDR elections occur only on multiaccess segments.Conclude: point-to-point links have no DR/BDR election but do form full adjacencies.

Verification / Alternative check:Command show ip ospf interface on a serial PPP link reports “Network Type POINT_TO_POINT, No designated router on this network,” confirming the behavior.

Why Other Options Are Wrong:

• B: Area 0 is a logical construct; DR/BDR depends on network type, not area number.
• C/D: Both are multiaccess and do run DR/BDR elections.
• E: Virtual links traverse areas but do not change the underlying network-type rules.

Common Pitfalls:Assuming all Ethernet links are point-to-point; Ethernet is broadcast multi-access in OSPF, and elections occur.

Final Answer:Point-to-point