Based on this interface configuration, what is the expected state of OSPF adjacency?

Question

Exhibits

Options

• AFull on both routers
• Bnot established
• C2WAY/DROTHER on both routers
• DFULL/BDR on R1 and FULL/BDR on R2

• A
  6% (3)
• B
  81% (38)
• C
  2% (1)
• D
  11% (5)

Explanation

OSPF Adjacency Explanation

Option B is correct because OSPF adjacency cannot be established when there is a mismatch in a fundamental parameter - most commonly a subnet mismatch, mismatched OSPF area IDs, mismatched Hello/Dead timers, or authentication settings between the two interfaces. Without seeing the exact configuration, the key indicator is that at least one critical OSPF parameter differs between the routers, preventing neighbor formation entirely.

Why the distractors are wrong:

• A (Full on both) is incorrect because "Full" state requires successful parameter matching and successful LSA exchange - conditions not met here.
• C (2WAY/DROTHER) is incorrect because 2WAY state still requires basic Hello packet exchange to succeed, which cannot happen with a fundamental mismatch.
• D (FULL/BDR on both) is incorrect because two routers cannot both be BDR simultaneously, and again, Full state cannot be reached with mismatched parameters.

Memory Tip: Think of OSPF adjacency requirements as a checklist handshake - Area ID, subnet/mask, Hello/Dead timers, MTU, and authentication must all match. If even one item fails, the routers stay strangers (adjacency = "not established"). Remember the acronym ASHMA: Area, Subnet, Hello timers, MTU, Auth.

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