OSPF Over IPSEC

First, it has to be interface mode IPsec (current default) otherwise you can't configure interface IPs for both ends. Then you need to specify it as "point-to-point". In CLI, configured like below:
config router ospf
  config ospf-interface
    edit "ipsec_name"
      set interface "ipsec_name"
      set network-type point-to-point
    next
  end
end

For the network types, it's explained in any OSPF document/articles like below:
https://study-ccna.com/ospf-network-types/

Toshi

Hi @Toshi_Esumi 

Thanks for the valuable comment.

I understand point to point link can form a neighbourship over unicast communication.

On ipsec tunnel interface we will configure private IP's then how to private ip's will communicate with each other over ipsec tunnel to form neighborship.

as per my knowledge tunnel interface ip will not be configured under phase 2 interesting traffic.

kindly share any links or document which explains how ipsec will handel tunnel interface communication.

There are multiple examples you can find, which how I found this, just Googling it. But this is one of them containing all parts of OSPF config over IPsec.
https://docs.fortinet.com/document/fortigate/6.2.16/cookbook/632796/ospf-with-ipsec-vpn-for-network-redundancy

Toshi

Thanks for sharing the links.

Iam not looking for any config examples i am trying to understand how traffic will be handelled for tunnel interface IP to form neighborship.

tunnel interface ip will not be configured in phase2  then how it will be transfered over wan link to reach other side of the tunnel.

As in the config example, the tunnel interface IP is configured on the "interface"(same as the phase1-name because it's automatically generated when you configure the phase1-interface) under config system interface. It's quite similar to Cisco's, and others', Tunnel Interface config.
In the interface config, you have to configure "remote-ip" as in the example. Those /32 IPs would be injected into the routing table as connected routes. That's why you can simply ping the other end even before configuring any routing protocol. We use this for BGP, which uses unicast.

If you configure on your FGT (I'm assuming you have one already) with an IPsec, you can see how it's working. The other end can be any device as long as it supports point-to-point network type. 

Toshi