Final answer:
The OSPF nonbroadcast network type is enabled by default on Frame Relay interfaces. This setting is used because Frame Relay does not natively support multicast traffic, which OSPF uses for some communications.
Step-by-step explanation:
The OSPF nonbroadcast network type is enabled by default on a Frame Relay interface. OSPF (Open Shortest Path First) is a routing protocol that's used to find the best path for packet transmission within an IP network. The nonbroadcast network type specifies that OSPF should not assume that multicast is supported on the network segment, common in networks like Frame Relay where multicast traffic is not natively supported. In contrast, network types such as PPP, X.25, FDDI, HDLC, and Ethernet do not have nonbroadcast as their default network type for OSPF.