单项选择题
A. A virtual link to area 0.
B. OSPF summarization command.
C. default - cost extension to the area command.
D. no - summary extension to the area stub comm and.
E. None of the other alternatives apply
多项选择题 An etwork 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?（）
单项选择题 According to RFC 2328, what is the stateful order in which an OSPF router transitions to a full adjacency with a neighbor router？（）
单项选择题 Refer to the exhibit. OSPF has been configured on all routers in the network and Area 1 has been configured as a NSSA. Which statement is true about the NSSA Area 1？（）