判断题 RIP协议引入路由保持机制的作用是防止路由形成环路。

单项选择题 While troubleshooting a network connectivity problem, a technician observes steady link lights on both the workstation NIC and the switch port to which the workstation is connected. However, when the ping command is issued from the workstation, the output message "Request timed out." is displayed. At which layer of the OSI model does the problem most likely exist（）。

多项选择题 Which statements describe the routing protocol OSPF? （）