Which of the following are characteristics of OSPF areas?()
A、Hierarchical OSPF networks need to be in one area
B、Multiple OSPF areas must connect to area 0
C、Single area OSPF networks must be configured in area 1
D、Areas can be assigned any number from 0 to 63535
E、Area 0 is called the backbone area
F、Each OSPF area need to be configured with a loopback interface