路由器的工作原理，静态路由和默认路由

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：

<Huawei>sys
Enter 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：

<Huawei>sys
Enter 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

<Huawei>sys
Enter 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

<Huawei>sys
Enter 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

<Huawei>sys
Enter 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

<AR9>sys
Enter 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

<AR6>sys
Enter 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

<AR6>sys
Enter 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

<R1>sys
Enter 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

<R2>sys
Enter 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

<R3>sys
Enter 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 192.168.20.1

Ping 192.168.20.1: 32 data bytes, Press Ctrl_C to break
From 192.168.20.1: bytes=32 seq=1 ttl=126 time=16 ms
From 192.168.20.1: bytes=32 seq=2 ttl=126 time=16 ms
From 192.168.20.1: bytes=32 seq=3 ttl=126 time=16 ms
From 192.168.20.1: bytes=32 seq=4 ttl=126 time=15 ms
From 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]shutdown
Apr  5 2021 16:40:28-08:00 R2 %%01IFPDT/4/IF_STATE(l)[0]:Interface GigabitEthern
et0/0/0 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 192.168.20.1

Ping 192.168.20.1: 32 data bytes, Press Ctrl_C to break
Request timeout!
From 192.168.20.1: bytes=32 seq=2 ttl=126 time=16 ms
From 192.168.20.1: bytes=32 seq=3 ttl=126 time=16 ms
From 192.168.20.1: bytes=32 seq=4 ttl=126 time=15 ms
From 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

<R1>sys
Enter 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

<R2>sys
Enter 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

<R3>sys
Enter 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