Loop(BPL) Network consist of AR-28---->AR-46----->NE40E.
The BSC port is used to connect to AR-28 router ethernet port.
After problem happen I did following tests:
1) Checked all connectivity it was ok.
2) Checked MTU on both sides which was same as MTU:1500 bytes
3) Then checked debug OSPF packet where it was seen that the DD packets were not exchanged between two.
4) In debug OSPF DD packet also nothing was found.
5) Then I checked Ethernet interfaces where I found that “ip address dhcp-alloc” command was there so after removal of this command the OSPF state came to Full state.
So that problem got resoved.
The OSPF State between two AR28 routers hanged to Exstart state due to use of comman "ip address dhcp-alloc" on the interface which is used to connect two AR-28 routers.
the reason of this is as follows:
when a interface is added into bridge 1,it will be a Layer2 interface to use,So the interface self don't need ip address to do Layer3 forwarding.
So using of "ip address dhcp-alloc" command will cause router to behave abnormally so that the OSPF will also work abnormally.
Always undo unwanted configuration on any device before any connectivity.