which two statements are true?

A network administrator has enabled OSPF across an NBMA network and has issued the
command ip ospf network nonbroadcast. Given those facts, which two statements are true?
(Choose two.)

A.
DR and BDR elections will occur.

B.
DR and BDR elections will not occur.

C.
All routers must be configured in a fully meshed topology with all other routers.

D.
The neighbor command is required to build adjacencies.

E.
Interfaces will automatically detect and build adjacencies with neighbor routers.

Explanation:
Even if there is only one router, broadcast multiaccess networks elect a DR and a BDR to serve as
focal points for routing information. In contrast, point-to-point OSPF networks do not elect a DR
because they can never include more than two nodes.
Another type of OSPF network, Nonbroadcast Multiaccess (NBMA), can include more than two
nodes. Therefore, NBMA will try to elect a DR and a BDR. Common NBMA implementations
include Frame Relay, X.25, and SMDS. NBMA networks follow rules at Layer 2 that prevent the
delivery of broadcasts and multicasts.
A non-broadcast environment requires that all OSPF neighbors be manually configured. This is
the default setting for physical interfaces with Frame Relay encapsulation, as well as for their
point-to-multipoint subinterfaces. By manually configuring each neighbor, OSPF knows exactly
which neighbors need to participate and which neighbor is identified as the DR. Also,
communication between neighbors is done via unicast instead of multicast. This configuration also
requires a full mesh and has the same weakness as the broadcast environment.
For non-broadcast networks the default Hello interval is 30 seconds and the Dead interval is four

times the Hello interval, 120 seconds. Non-broadcast multi-access networks do elect a DR and
BDR, due to their multi-access nature. In order to set which router you want as the DR, you must
set the priority in the neighbor statement to elect the neighbor as the DR. In order to manually
configure who your neighbors are, the following command must be entered in router configuration
mode for the selected OSPF process:
neighbor ip_address
ip_address= the ip address of the neighbor.
If you would like to set the priority of this router to become the DR, you will need to append the
priority of the neighbor:
neighbor ip_address priority value