路由器工作原理

路由器工作原理路由器的工作原理路由功能： 学习和维护网络拓扑结构知识的机制，产生和维护路由表交换/转发功能：

数据在路由器内部移动与处理的过程（从路由器一个接口输入，然后选择合适接口输出、做帧的解封装与封装，并对包做相应处理）

路由功能

学习和维持网络拓扑结构知识的机制被认为是路由功能。完成路由功能需要的几个基本信息：路由的是什么协议？目的地址是否已存在?从哪个端口发送出去？下一跳地址是什么？＝帧校验并缓存数据包进入接口将目的地逻辑地址与下一跳逻辑设备和外出接口相关联路由表将下一跳逻辑设备与物理地址相关联以生成帧头ARP缓存（局域网）封装数据包并转发帧外出接口＝＝＝由路由协议维护由ARP或逆向ARP进程所维护映射列表（广域网）交换/转发功能RoutingprocessRoutingprocessRoutingprocessRoutingprocessRoutingtableForwardingprocess基于目的地址查找路由条目遵循最长匹配原则基于路由优先级向路由表加入路由路由协议学习所有可能的路由，基于metric值选择最佳路由路由器工作过程总结同网段内的通信—ARP请求过程IP地址： 192.168.1.3MAC地址：00:20:AF:00:00:03IP：192.168.1.1MAC：00:20:AF:00:00:01IP：192.168.1.2MAC：00:20:AF:00:00:02ABCFei_1/1Fei_1/2Fei_1/3Switch假设A要与B通信目的MAC:ff:ff:ff:ff:ff:ff源MAC:00:20:af:00:00:01目的IP:192.168.1.2源IP:192.168.1.1ARP请求

MACPort00:20:af:00:00:01fei_1/1A判断与B属于同一网段A在ARP表中查找B的MAC地址A发送ARP请求报文查找B的MAC同网段内的通信—ARP响应IP地址： 192.168.1.3MAC地址：00:20:AF:00:00:03IP：192.168.1.1MAC：00:20:AF:00:00:01IP：192.168.1.2MAC：00:20:AF:00:00:02ABCFei_1/1Fei_1/2Fei_1/3Switch目的MAC:00:20:af:00:00:01源MAC:00:20:af:00:00:02目的IP:192.168.1.1源IP:192.168.1.2ARP响应

MACPort00:20:af:00:00:01fei_1/100:20:af:00:00:02fei_1/2同网段内的通信—报文转发IP地址： 192.168.1.3MAC地址：00:20:AF:00:00:03IP：192.168.1.1MAC：00:20:AF:00:00:01IP：192.168.1.2MAC：00:20:AF:00:00:02ABCFei_1/1Fei_1/2Fei_1/3Switch目的MAC:00:20:af:00:00:02源MAC:00:20:af:00:00:01目的IP:192.168.1.2源IP:192.168.1.1

MACPort00:20:af:00:00:01fei_1/100:20:af:00:00:02fei_1/2不同网段间的通信IP:10.1.1.9G:10.1.1.10MAC:00:20:AF:00:00:03IP:10.1.1.5/30G:10.1.1.6MAC:00:20:AF:00:00:02ABCRouterIP:10.1.1.1/30G:10.1.1.2MAC:00:20:AF:00:00:01假设A要与B通信A判断与B处于不同网段A查找网关的MAC地址fei_1/1:10.1.1.2/30MAC:00:20:AF:00:00:04fei_1/2:10.1.1.6/30MAC:00:20:AF:00:00:05fei_1/3:10.1.1.10/30MAC:00:20:AF:00:00:05目的MAC:00:20:af:00:00:04源MAC:00:20:af:00:00:01目的IP:10.1.1.5源IP:10.1.1.1A发送报文给B，目的MAC是网关

Destnetworkinterface10.1.1.0255.255.255.252fei_1/110.1.1.4255.255.255.252fei_1/210.1.1.8255.255.255.252fei_1/3不同网段间的通信—路由器转发IP:10.1.1.9G:10.1.1.10MAC:00:20:AF:00:00:03IP:10.1.1.5/30G:10.1.1.6MAC:00:20:AF:00:00:02ABCRouterIP:10.1.1.1/30G:10.1.1.2MAC:00:20:AF:00:00:01fei_1/1:10.1.1.2/30MAC:00:20:AF:00:00:04fei_1/2:10.1.1.6/30MAC:00:20:AF:00:00:05fei_1/3:10.1.1.10/30MAC:00:20:AF:00:00:05

Destnetworkinterface10.1.1.0255.255.255.252fei_1/110.1.1.4255.255.255.252fei_1/210.1.1.8255.255.255.252fei_1/3目的MAC:00:20:af:00:00:02源MAC:00:20:af:00:00:05目的IP:10.1.1.5源IP:10.1.1.1判断与对端是否处于同一网段检查ARP表是否有对端的MAC地址做数据链路层封装（目的MAC为对端MAC地址）通过物理层发送数据通过ARP获得对端MAC地址YESNOYESNO是否配置了缺省网关？YES检查路由表是否有目的网络地址做数据链路层封装（目的MAC为网关MAC地址）丢弃NO发送错误信息YESNOEnd

获取对端IP地址通信流程IP通信流程基本概念IP通信流程基本概念IP通讯是基于hopbyhop的方式从源到目的之间源IP和目的IP地址保持不变每经过一个数据链路层，数据链路层封装都要做相应的重新封装返回的数据选路与到达的数据选路无关路由过程示例192.168.6.0/24192.168.2.0/24e1_1e1_1fei_1/1192.168.2.3192.168.1.0/24192.168.3.0/24192.168.3.3192.168.4.1/24R1R2R3R1路由表192.168.4.0255.255.255.0192.168.4.1e1_1direct00192.168.2.0255.255.255.0192.168.2.1fei_1/1direct00192.168.1.0255.255.255.0192.168.4.2e1_1rip1201192.168.6.0255.255.255.0192.168.4.2e1_1rip1201192.168.3.0255.255.255.0192.168.4.2e1_1rip1202e1_2e1_1fei_1/1fei_1/1目的地址为:192.168.3.3AB192.168.4.2/241.目的地址为:192.168.3.3192.168.6.2/24192.168.2.0/24192.168.2.3192.168.1.0/24192.168.3.0/24192.168.3.3192.168.4.0/24R1R2R3R2路由表192.168.4.0255.255.255.0192.168.4.2e1_1direct00192.168.6.0255.255.255.0192.168.6.1e1_2direct00192.168.1.0255.255.255.0192.168.1.1fei_1/1direct00192.168.2.0255.255.255.0192.168.4.1e1_1rip1201192.168.3.0255.255.255.0192.168.6.2e1_2rip1201e1_1e1_1fei_1/1e1_2e1_1fei_1/1fei_1/1目的地址为:192.168.3.3路由过程示例（续）192.168.6.1/24路由过程示例（续）192.168.6.0/24192.168.2.0/24192.168.2.3192.168.1.0/24192.168.3.0/24192.168.3.3192.168.4.0/24R1R2R3R3路由表192.168.3.0255.255.255.0192.168.3.1fei_1/1direct00

192.168.6.0255.255.255.0192.168.6.2e1_1direct00192.168.1.0255.255.255.0192.168.6.1e1_1rip1201192.168.4.0255.255.255.0192.168.6.1e1_1rip1201192.168.2.0255.255.255.0192.168.6.1e1_1rip1202反方向数据包的转发流程？e1_1e1_1fei_1/1e1_2e1_1fei_1/1fei_1/1目的地址为:192.168.3.3VLANoneVLANtwoVLANthree方式一普通路由方式二单臂路由方式三三层/多层交换机VLANoneVLANtwoVLANthreefei_1/1fei_1/3fei_1/2VLANoneVLANtwoVLANthree802.1Qtrunkencapsulationfei_1/1.1fei_1/1.2fei_1/1.3VLAN间路由VLANoneVLANtwoVLANthreefei_1/1fei_1/3配置：路由器上在多个物理接口配置不同

VLAN缺省网关IP地址，交换机上的端口设置为ACCESSPORT，分别属于不同的VLAN特点：需要多个路由器物理接口，成本高灵活性与可扩展性差fei_1/2方式一：普通路由VLANoneVLANtwoVLANthree802.1Qtrunkencapsulationfei_1/1.1fei_1/1.2fei_1/1.3ZXR10(config)#interfacefei_1/1.1ZXR10(config-subif)#encapsulationdot1Q1ZXR10(config-subif)#ipadd1.1.1.1255.0.0.0ZXR10(config)#interfacefei_1/1.2ZXR10(config-subif)#encapsulationdot1Q2ZXR10(config-subif)#ipadd2.1.1.1255.0.0.0ZXR10(config)#interfacefei_1/1.