Why Ospf Neighbors Stuck In Init State or 2-way or Exchange

 Why Are Ospf Neighbors Stuck In Init State---

1- INIT State

OSPF can be stuck in INIT due to the mismatch in hello packet parameters such as .

-->>  Hello/dead intervals. 
-->> Authentication. 
-->>  Stubflag. 
-->> Interface subnet mask. 
-->> Area ID .

MTU will come into the picture when the exstart state gets active (if there is an MTU mismatch it will not get into EXSTART)

2 - TWO-Way State --

If you are seeing neighborship stuck in 2-Way state, there could be possibilities--

-->> In network segments with multiple OSPF routers, two routers are chosen as DR and BDR respectively based on their priority or Router ID. All other OSPF routers are supposed to form adjacency with DR and BDRs.

Note - This is normal behavior for OSPF. Whenever a router sees itself in a neighbor hello packet, it confirms bidirectional communication and transitions the neighbor state to two-way. At this point, the routers perform DR and BDR election

2- Exstart or exchange State --

Neighbor in exstart or exchange State. OSPF neighbors that are in exstart or exchange state are trying to exchange DBD packets. The router and its neighbor form a master and slave relationship. The adjacency should continue past this state

OSPF Stuck in Exstart or Exchange state because of The problem occurs most frequently when you attempt to run OSPF between a Cisco router and another vendor router. The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces do not match