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 (71) algorithm. Routingprotocols in internetworks differ slightly from the idealized graph model. In an internetwork, the goal ofthe routers to forward (72) to various networks.
Routers running RIP send their advertisement abOLit cost every (73) seconds. A router also sends an up date message whenever an update from another router causes it to change its routing table.
Routing protocols use different techniques for assigning (74) to individual networks. Further, each routing protocol forms a metric aggregation in a different way. RIP takes the simplestapproach, with all link costs being equal (75) . Thus it always tries to find the minimum hop route. Valid distances are 1 through 15. This also limits RIP to running on fairly small networks.
A．1
B．15
C．16
D．length of the link
参考答案：A
解析： 路由信息协议(RIP)是IP网络中使用广泛的路由协议之一。RIP是一个基于距离向量(distance vector)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网络(networks)。
运行RIP协议的路由器每隔30秒广播一次它们的路由信息。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。
各种路由协议使用不同的技术来为网络赋予度量值(metrics)。并且，每一种路由协议都形成了不同的度量汇聚模式。RIP采取了一种简单的方法，将所有的链路费用都公平地赋予1。因此，它总是试图寻找出跳数最少的路径。RIP有效的距离范围是1～15。这也限制了它只能运行在相当小规模的网络中。