单选题 One of the most widely used routing protocols in IP networks is the Routing Information Protocol (RIP). RIP is the canonical example of a routing protocol built on the ______ algorithm. Routing protocols in intemetworks differ slightly from the idealized graph model. In an internetwork, the goal of the routers to forward packets to various ______.
Routers running RIP send their advertisement about cost every ______ seconds. A router also sends an update message whenever an update from another router causes it to change its routing table.
It is possible to use a range of different metrics or costs for the links in a routing protocol. RIP takes the simplest approach, with all link costs being equal ______. Thus it always tries to fend the minimum hop route. Valid distances are 1 through ______. This also limits RIP to running on fairly small networks.

【正确答案】 A

【答案解析】IP网络中广泛使用的路由协议之一是路由信息协议(RIP)。RIP是基于______路由算法的路由协议。网络中的路由协议与理想的图算法存在少量的差异。在互联网中，路由器的目的是将数据包转发给不同的______。
运行RIP协议的路由器每______秒广播一次路由信息，另外，每当路由器收到其他路由器的更新消息而导致其路由表变化时，就会发送更新消息。
路由协议在链路上使用不同的度量或成本是可能的。RIP采用了最简单的方法，所有链路的成本都等于______。这样，它总是试图寻找跳数最少的路径。有效的距离范围是从1到______。这也限制了RIP只能在相当小规模的网络上运行。