单项选择题
A. describes a change to the OSPF hello timer
B. carries one or more link-state advertisements
C. establishes and maintains neighbor relationships
D. describes the contents of the entire link-state database
单项选择题 Why would you make a non-backbone area a stub or not-so-stubby area?（）
单项选择题 During OSPF adjacency formation, in what state is a router when it is negotiating to be in charge of the database synchronization process?（）
单项选择题 By default, which command can be used to display information about packets that have been logged with the syslog firewall filter action?（）