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.
Answer: A D
Explanation
When using the command “ip ospf network nonbroadcast”, we turn the network into a nonbroadcast network so routers can not send broadcast or multicast. But OSPF uses multicast address 224.0.0.5 to send Hello packet periodically. Therefore we have to manually define the neighbor (via the neighbor command) to make OSPF send Hello packets to its adjacent routers -> D is correct.
For Multi-access network (for example Ethernet or Frame Relay), a designated router (DR) and a backup designated router (BDR) are elected ->A is correct.
Note: By default, Frame Relay environment is nonbroadcast so it is actually not necessary to use the command “ip ospf network nonbroadcast” on Frame Relay network.