单项选择题
A. to aggregate routes learned from the ABR
B. to lower the cost of routes advertised by the ABR
C. to connect a non-contiguous area to the backbone
D. to decrease the size of the link-state database in that 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?（）
多项选择题 A firewall filter is applied as an input filter on a transit interface. What three types of traffic will this affect? （）