第六章路由协议.ppt

Summary 直接交付 VS 间接交付 分组的交付者（主机或路由器）与终点都连接在同一个网络上 分组的交付者（主机或路由器）与终点不是连接在同一个网络上 Summary 在使用下一跳方法时，不需要将分组所经过的每一站都完整地写在路由表中，只需要将下一跳写在路由表中 在使用特定网络方法时，在一个网络上的所有主机共享路由表中的一个项目 特定主机方法时，路由表给出主机的完整地址。 在使用默认方法时，有一个路由器被指派接收所有在路由表中的无匹配的分组。 应用 根据网络拓扑或分组的源、目的IP地址 判断直接交付和间接交付 根据路由表 查找到达给定目的的路径 Summary 分类编址的路由表可以有3列 无分类编址的路由表至少4列 路由表中的列数与厂商有关 在无分类编址中，地址聚合简化了转发过程 无分类编址需要使用最长前缀匹配 无分类编址需要使用层次路由选择和地区路由选择以防止出现过于庞大的路由表 Forwarding with classful addressing Forwarding without subnetting A typical forwarding module of classing address can be designed using three tables, one for each unicast class(A,B,C). Next-hop address Network address Interface number Each routing table has a minimum of three columns: The network address of the destination network tells us where the destination host is located. The next-hop address tells us to which router the packet must be delivered for an indirect delivery. The interface number defines the outgoing port from which the packet is sent out. The forwarding module The destination address of the packet is extracted. A copy of the destination address is used to find the class of the address. The result of step 2 for class A,B or C and the destination address are used to extract the network address. The class of the address and the network address are used to find next-hop information. The class determines the table to be searched. The ARP module used the next-hop address and the interface number to find the physical address of the next router. Forwarding with subnetting In classful addressing, subnetting happens inside the organization. The routers that handle subnetting are either at the border of the organization site or inside the site boundary. If the organization is using variable-length subnetting, we need several tables; otherwise, we need only one table. Solution 因特网的其余部分 130.4.8.0/24 202.14.17.224/27 m1 145.23.193.0/18 m2 145.23.192.0/18 m0 R1 193.1 192.1 * 转发：从一个接口进来，从另一个接口出去 物理上的转发：数据传输的物理方向 分组的交付由IP层处理 Routed protocol转发协议 Routing protocol路由协议 * 类似