What factors cause OSPF adjacencies to fail during neighbor establishment?

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What factors cause OSPF adjacencies to fail during neighbor establishment?

Asked on Oct 16, 2025

Answer

OSPF adjacencies can fail during neighbor establishment due to several factors, including mismatched configurations, network issues, or protocol-specific settings. Understanding these factors is crucial for ensuring stable OSPF operations in your network.

Example Concept: OSPF adjacency failures often arise from mismatched OSPF parameters such as area ID, authentication settings, hello and dead intervals, or MTU size. Additionally, network issues like incorrect IP addressing, subnet mismatches, or interface problems can prevent successful neighbor relationships. Ensuring consistent configuration across all OSPF routers and verifying network connectivity are key steps in troubleshooting these failures.

Additional Comment:

Verify that OSPF area IDs are consistent between neighbors.
Ensure that authentication types and passwords match on both sides.
Check that hello and dead intervals are the same on all interfaces.
Confirm that the MTU size is consistent to avoid fragmentation issues.
Use network troubleshooting tools to verify IP connectivity and correct subnetting.
Ensure that interfaces are up and properly configured for OSPF.

✅ Answered with Networking best practices.

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