单项选择题 Which term describes a spanning-tree network that has all switch ports in either the blocking or forwarding state?（）

单项选择题 Which PPP subprotocol negotiates authentication options?（）

单项选择题 You are working in a data center environment and are assigned the address range 10.188.31.0/23.You are asked to develop an IP addressing plan to allow the maximum number of subnets with as many as 30 hosts each.Which IP address range meets these requirements?（）