When OSPF specifies that the connection type is P2P, it enables devices on both ends that are not in the same subnet to Ping each other

The two devices cannot use the subnet IP Address establishment P2P Type of OSPF, Neighbors can be established normally , But each other PING no , Because it was sent ARP When requesting to the peer device , When the peer device finds a request that is not sent from the same subnet , Will be discarded . You can use static ARP Appoint MAC Address , Or to switch to SERIAL configure HDLC or P2P.