OSPF is a link-state routing protocol。It is designed to be runinternal to a single （  ）system。Each OSPF router maintains an identical （  ）describing the autonomous system’s topology。From this database，a routing table is calculated by constructing a shortest-path （  ）。OSPF recalculates routes quickly in the face of topological changes，utilizing a minimum of routing （  ） traffic。OSPF provides support for equal-cost multipath。An area routing capability is provided，enabling an additional level of routing protection and a reduction in routing protocol（  ）。