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路由器的工作原理

1.路由表

路由器中维护路由条目的集合，路由器转发过程中根据路由表进行路径选择，路由表可以通过直连网段获取也可以通过静态动态路由获取。

2.路由器转发数据包的封装过程

目前已知：PC1知道PC2的ip地址但不知道PC2的MAC地址。R1知道PC2的IP和MAC地址，R2知道PC1的IP地址和MAC地址。

PC第一次发信息给PC2，由于不知道PC2的MAC地址所以进行广播。广播被R1接收解封后开始查找路由表发现目标IP和对应的MAC地址封装自己的MAC地址开始传输，传输到R2后，R2解封开始查找路由表发现PC2就在自己直连的网段，封装上自己的MAC地址然后把信息传给PC2，PC2收到PC1的信息在ARP表记录下PC1的IP地址和MAC地址后进行回应通过R2-R1的线路传给PC1，PC1收到回应信息后在ARP表记录下PC2的IP地址和MAC地址，之后就可以直连通信了。

静态路由和默认路由

静态路由的配置：

   
    sysEnter system view, return user view with Ctrl+Z.[Huawei]sysname r1[r1]ip route-static “目标ip所在的网段” “目标ip的子网掩码” “下一跳的ip地址”
   

默认路由的配置：

   
    sysEnter system view, return user view with Ctrl+Z.[Huawei]sysname r1[r1]ip route-static 0.0.0.0 0 “下一跳的ip地址”
   

实验

实验一

先给PC和服务器配好ip，子网掩码和网关，然后给3个路由器的每个接口设置ip和子网掩码。 AR9的设置

   
    sysEnter system view, return user view with Ctrl+Z.[Huawei]sysname ar9[AR9]interface g0/0/1[AR9-GigabitEthernet0/0/1]ip address 192.168.1.1 24[AR9]interface g0/0/2[AR9-GigabitEthernet0/0/2]ip address 192.168.2.1 24[AR9]interface g0/0/0[AR9-GigabitEthernet0/0/0]ip address 192.168.10.1 24
   

AR6的设置

   
    sysEnter system view, return user view with Ctrl+Z.[Huawei]sysname ar6[AR6]interface g0/0/1[AR6-GigabitEthernet0/0/1]ip address 192.168.20.1 24[AR6]interface g0/0/0[AR6-GigabitEthernet0/0/0]ip address 192.168.10.2 24
   

AR7的设置

   
    sysEnter system view, return user view with Ctrl+Z.[Huawei]sysname ar7[AR7]interface g0/0/1[AR7-GigabitEthernet0/0/1]ip address 192.168.30.1 24[AR7]interface g0/0/0[AR7-GigabitEthernet0/0/0]ip address 192.168.20.2 24
   

设置好后给AR9设置默认路由，给AR6，AR7设置静态路由，使得PC2PC3能访问服务器

AR9的默认路设置

   
    sysEnter system view, return user view with Ctrl+Z.[AR9]ip route-static 0.0.0.0 0 192.168.10.2
   

AR6的静态路由设置

   
    sysEnter system view, return user view with Ctrl+Z.[AR6]ip route-static 192.168.1.0 24 192.168.10.1[AR6]ip route-static 192.168.2.0 24 192.168.10.1[AR6]ip route-static 192.168.30.0 24 192.168.20.2
   

AR7的静态路由设置

   
    sysEnter system view, return user view with Ctrl+Z.[AR7]ip route-static 192.168.1.0 24 192.168.20.1[AR7]ip route-static 192.168.2.0 24 192.168.20.1
   

设置好后ping一下

实验2

先给PC1PC2配上ip子网掩码和网关。R1,R2,R3每个接口配上ip和子网掩码。

R1配置

   
    sysEnter system view, return user view with Ctrl+Z.[R1]interface g0/0/0[R1-GigabitEthernet0/0/0]ip address 192.168.10.254 24[R1]interface g0/0/1[R1-GigabitEthernet0/0/1]ip address 192.168.3.1 24[R1]interface g0/0/2[R1-GigabitEthernet0/0/2]ip address 192.168.1.1 24
   

R2配置

   
    sysEnter system view, return user view with Ctrl+Z.[R2]interface g0/0/0[R2-GigabitEthernet0/0/0]ip address 192.168.2.2 24[R2]interface g0/0/1[R2-GigabitEthernet0/0/1]ip address 192.168.1.2 24[R2]interface g0/0/2[R2-GigabitEthernet0/0/2]ip address 192.168.20.254 24
   

R3配置

   
    sysEnter system view, return user view with Ctrl+Z.[R3]interface g0/0/0[R3-GigabitEthernet0/0/0]ip address 192.168.3.2 24[R3]interface g0/0/1[R3-GigabitEthernet0/0/1]ip address 192.168.2.1 24
   

给R1设置静态路由和优先级

[R1]ip route-static 192.168.20.0 24 192.168.1.2[R1]ip route-static 192.168.20.0 24 192.168.3.2 preference 75

给R2设置静态路由和优先级

[R2]ip route-static 192.168.10.0 24 192.168.1.1[R2]ip route-static 192.168.10.0 24 192.168.2.1 preference 75

此时，PC1pingPC2

PC>ping 192.168.20.1Ping 192.168.20.1: 32 data bytes, Press Ctrl_C to breakFrom 192.168.20.1: bytes=32 seq=1 ttl=126 time=16 msFrom 192.168.20.1: bytes=32 seq=2 ttl=126 time=16 msFrom 192.168.20.1: bytes=32 seq=3 ttl=126 time=16 msFrom 192.168.20.1: bytes=32 seq=4 ttl=126 time=15 msFrom 192.168.20.1: bytes=32 seq=5 ttl=126 time=16 ms--- 192.168.20.1 ping statistics ---  5 packet(s) transmitted  5 packet(s) received  0.00% packet loss  round-trip min/avg/max = 15/15/16 ms

给R3设置静态路由

[R3]ip route-static 192.168.10.0 24 192.168.3.1[R3]ip route-static 192.168.20.0 24 192.168.2.2

关闭R2的0/0/0接口

[R2]interface g0/0/0[R2-GigabitEthernet0/0/0]shutdownApr  5 2021 16:40:28-08:00 R2 %%01IFPDT/4/IF_STATE(l)[0]:Interface GigabitEthernet0/0/0 has turned into DOWN state.[R2-GigabitEthernet0/0/0][R2-GigabitEthernet0/0/0]Apr  5 2021 16:40:28-08:00 R2 %%01IFNET/4/LINK_STATE(l)[1]:The line protocol IP on the interface GigabitEthernet0/0/0 has entered the DOWN state.

PC1pingPC2

PC>ping 192.168.20.1Ping 192.168.20.1: 32 data bytes, Press Ctrl_C to breakRequest timeout!From 192.168.20.1: bytes=32 seq=2 ttl=126 time=16 msFrom 192.168.20.1: bytes=32 seq=3 ttl=126 time=16 msFrom 192.168.20.1: bytes=32 seq=4 ttl=126 time=15 msFrom 192.168.20.1: bytes=32 seq=5 ttl=126 time=16 ms--- 192.168.20.1 ping statistics ---  5 packet(s) transmitted  4 packet(s) received  20.00% packet loss  round-trip min/avg/max = 0/15/16 ms

仍然能ping通，路由表的查询命令是

[R2]dis ip routing-table

实验三

依旧是给各个设备主机配好ip，子网掩码，网关 R1设置

   
    sysEnter system view, return user view with Ctrl+Z.[R1]interface g0/0/0[R1-GigabitEthernet0/0/0]ip address 192.168.10.254[R1]interface g0/0/1[R1-GigabitEthernet0/0/1]ip address 192.168.1.1
   

R2设置

   
    sysEnter system view, return user view with Ctrl+Z.[R2]interface g0/0/0[R2-GigabitEthernet0/0/0]ip address 192.168.20.254[R2]interface g0/0/1[R2-GigabitEthernet0/0/1]ip address 192.168.2.1
   

R3设置

   
    sysEnter system view, return user view with Ctrl+Z.[R3]interface g0/0/0[R3-GigabitEthernet0/0/0]ip address 192.168.30.254[R3]interface g0/0/1[R3-GigabitEthernet0/0/1]ip address 192.168.1.2[R3]interface g0/0/2[R3-GigabitEthernet0/0/2]ip address 192.168.2.2
   

给R1，R2配默认路由

[R1]ip route-static 0.0.0.0 0 192.168.1.2

[R2]ip route-static 0.0.0.0 0 192.168.2.2

给R3配置静态路由

```javascript[R3]ip route-static 192.168.10.1 24 192.168.1.1[R3]ip route-static 192.168.20.1 192.168.2.1

之后再ping就能互相ping通了

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