During testing, we observed that if the OSPF test tool send the LSU with the mismatch LS Seq (the LS Seq number of the LSA in the message is less recent than the peer Cisco router LSA database copy, the Cisco router is change the neighbor state(OSPF test tool) from FULL to EXSTART and send the init DD to OSPF test tool to put the its neighbor (Cisco router) state to EXSTART to re-sync LSA DB again. Could some one verify this behavior of Cisco router ?
Thanks, Regards, Nick V.