单选题 Routing protocols use different techniques for assigning ______ to individual networks. Further, each routing protocol forms a metric aggregation in a different way. Most routing protocols can use multiple paths if the paths have an equal ______ . Some routing protocols can even use multiple paths when paths have an unequal cost. In either case, load ______ can improve overall allocation of network bandwidth. When multiple paths are used, there are several ways to distribute the packets. The two most common mechanisms are per-packet load balancing and per-destination load balancing. Per-packet load balancing distributes the ______ across the possible routes in a manner proportional to the route metrics. Per-destination load balancing distributes packets across the possible routes based on ______.

【正确答案】 C

【答案解析】[解析] 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。当每条路径的费用(cost)都相同时，大多数路由协议则可以使用多条通路。某些路由协议甚至在各条路径的费用不相等时也可以使用多条通路。在上述任何一种情况下，负载均衡(balancing)都可以改进网络带宽的全局分配。当使用多条通路时，可以使用多种方法来分配分组。按分组进行负载均衡和按目标进行负载均衡是其两种最通常的机制。按分组进行负载均衡是指按照路由度量的比例向各个可能的路由上分配分组(packets)。按目标进行负载均衡是指根据目的地(destinations)向各个可能的路由上分配分组。