On which interfaces is the Non-broadcast network type enabled by default in OSPF?

In OSPF (Open Shortest Path First), the Non-broadcast network type is enabled by default on Frame Relay and X.25 interfaces. This is because these types of networks do not have a native broadcast capability; they require a manual configuration of neighbor relationships. Rather than discovering neighbors automatically through broadcasts, routers on these networks must be specifically configured to know about each other.

In contrast, Ethernet and FDDI (as mentioned in the first choice) typically allow for broadcast communication, meaning that OSPF uses a different network type for these interfaces. Similarly, PPP and HDLC, which are point-to-point protocols, do not fall under the non-broadcast category because they inherently support direct neighbor discovery and do not require intervention to establish OSPF adjacencies. The option stating LAN and WAN is too broad and does not specifically denote the behavior of OSPF in relation to non-broadcast types.

Thus, recognizing the nature of Frame Relay and X.25 networks allows for a better understanding of why Non-broadcast multi-access (NBMA) configurations are associated with these types in the context of OSPF.