The Open Shortest Path First (OSPF) neighbors are established by exchanging hello packets at multicast address 126.96.36.199. If these packets fail due to any Layer 2 (L2) issue, OSPF neighbors flap. This results in the error message ‘OSPF-5-ADJCHG’
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.