Core Issue
The Open Shortest Path First (OSPF) neighbors are established by exchanging hello packets at multicast address 224.0.0.5. If these packets fail with any Layer 2 (L2) issue, OSPF neighbors flap. This results in the error message.
Resolution
To resolve this issue, ensure that the underlying L2 between OSPF neighbors is working properly by issuing the ping command. This ensures reachability to the neighbor address.
If neighbors are on a multi-access segment, issue the ping command to address 224.0.0.5. This ensures reachability to all OSPF neighbors.
For more information, refer to the Troubleshooting OSPF Neighbor States section of Troubleshooting OSPF.
