OSPF adjacency is stuck in EXSTART/EXCHANGE. Which parameter mismatch should be corrected to resolve this?

OSPF adjacency getting stuck in EXSTART/EXCHANGE is a classic symptom of an MTU mismatch. During the EXSTART state, OSPF routers negotiate the Master/Slave relationship and exchange initial Database Description (DBD) packets. If the MTU on the interface of one router is larger than the MTU on the interface of its neighbor, the larger DBD packets sent by the router with the higher MTU will be dropped by the neighbor, preventing the adjacency from progressing. Matching the MTUs ensures DBD packets are exchanged successfully. Password mismatches prevent adjacency formation entirely (INIT state), hello timer mismatches cause adjacency flapping or prevent formation (INIT state), and network type mismatches can cause issues with DR/BDR election or neighbor discovery, but typically don't halt the process specifically in EXSTART/EXCHANGE.