I have configured three router and it is OSPF broadcast network. I wonder why there are TWO BDR states as below when i do sh ip ospf nei
Router#sh ip ospf nei
Neighbor ID Pri State Dead Time Address Interface
188.8.131.52 1 FULL/BDR 00:00:36 10.10.10.6 FastEthernet1/1
184.108.40.206 1 FULL/BDR 00:00:38 10.10.10.1 FastEthernet1/0
Any reason?? Cause usually there will be only 1 DR and 1 BDR
This will not be the answer you are looking for but two states exist because they have been configured to exist. As for what caused those states to be configured to exist that information isn't provided here.
Backup designated router
A backup designated router (BDR) is a router that becomes the designated router if the current designated router has a problem or fails. The BDR is the OSPF router with second highest priority at the time of the last election.
Are those FastEthernet1/0 and FastEthernet1/1 connected to the same segment (LAN) or different ones? My guess is that they are on different LANs (depending the subnet mask used). If I'm correct, then it's normal to have multiple DRs and BDRs, because you have multiple segments. Each segment (broadcast domain) can have 1 DR and 1 BDR.