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00.基础阶段/01.网络基础/04.静态路由.md
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00.基础阶段/01.网络基础/04.静态路由.md
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# 04.静态路由
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## 1. 静态路由
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- 在少量网段并且相对固定的时候可以使用静态路由
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- 临时测试的时候
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## 2. 实验
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### 2.1 配置IP地址
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```
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R1
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en
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conf t
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int e0/0
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ip add 192.168.12.1 255.255.255.0
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no sh
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end
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============================
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R2
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en
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conf t
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int e0/0
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ip add 192.168.12.2 255.255.255.0
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no sh
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int e0/1
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ip add 192.168.23.2 255.255.255.0
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no sh
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end
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=============================
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R3
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en
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conf t
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int e0/0
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ip add 192.168.23.3 255.255.255.0
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no sh
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end
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```
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在R2上可以检查到R1或者R3的连通性，确保IP地址配置正确
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```
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R2#ping 192.168.12.1
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Type escape sequence to abort.
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Sending 5, 100-byte ICMP Echos to 192.168.12.1, timeout is 2 seconds:
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.!!!!
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Success rate is 80 percent (4/5), round-trip min/avg/max = 1/3/5 ms
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R2#ping 192.168.23.3
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Type escape sequence to abort.
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Sending 5, 100-byte ICMP Echos to 192.168.23.3, timeout is 2 seconds:
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.!!!!
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Success rate is 80 percent (4/5), round-trip min/avg/max = 1/1/2 ms
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```
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如果IP地址配置不正确，出现了问题，可以再每台设备上使用如下命令检查
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```
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R2#show ip int br
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Interface IP-Address OK? Method Status Protocol
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Ethernet0/0 192.168.12.2 YES manual up up
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Ethernet0/1 192.168.23.2 YES manual up up
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Ethernet0/2 unassigned YES unset administratively down down
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Ethernet0/3 unassigned YES unset administratively down down
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```
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### 2.2 检查R1和R3的联通性
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```
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R1#ping 192.168.23.3
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Type escape sequence to abort.
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Sending 5, 100-byte ICMP Echos to 192.168.23.3, timeout is 2 seconds:
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.....
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Success rate is 0 percent (0/5)
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```
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检查R1的路由表
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```
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R1#show ip route
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192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks
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C 192.168.12.0/24 is directly connected, Ethernet0/0
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L 192.168.12.1/32 is directly connected, Ethernet0/0
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```
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发现`192.168.23.3`没有匹配条目
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在R1上加上静态路由，告知R1如果想去往`192.168.23.0/24`需要从e0/0接口发出
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```
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R1(config)#ip route 192.168.23.0 255.255.255.0 e0/0
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```
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然而还是不通，因为R3并没有返回`192.168.12.0/24`的路由，导致R3只能收到R1的消息，但是不能回复
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```
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R3(config)#ip route 192.168.12.0 255.255.255.0 e0/0
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```
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现在三台路由器都知道了`192.168.12.0/24`和`192.168.23.0/24`两个网段的去法
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```
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R1#ping 192.168.23.3
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Type escape sequence to abort.
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Sending 5, 100-byte ICMP Echos to 192.168.23.3, timeout is 2 seconds:
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..!!!
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Success rate is 60 percent (3/5), round-trip min/avg/max = 1/1/1 ms
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```
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### 2.3 ARP在这个过程中
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通过检查R1的arp表，我们可以发现`192.168.23.3`的arp结果和`192.168.12.2`的一样
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```
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R1#show arp
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Protocol Address Age (min) Hardware Addr Type Interface
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Internet 192.168.12.1 - aabb.cc00.1000 ARPA Ethernet0/0
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Internet 192.168.12.2 5 aabb.cc00.2000 ARPA Ethernet0/0
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Internet 192.168.23.3 0 aabb.cc00.2000 ARPA Ethernet0/0
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```
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上面这种情况是代理ARP产生的，如果R1并不是去往R3，而是作为局域网连接外网网关，那么访问的目的地址可能无数个。这种情况下，会导致ARP结果越来越多，影响效率。
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```
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R1(config)#ip route 0.0.0.0 0.0.0.0 e0/0 # 在R1配置默认路由，模拟R1的e0/0接口是外网
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R1#ping 192.168.23.4
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Type escape sequence to abort.
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Sending 5, 100-byte ICMP Echos to 192.168.23.4, timeout is 2 seconds:
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..
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Success rate is 0 percent (0/2)
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R1#show arp
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Protocol Address Age (min) Hardware Addr Type Interface
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Internet 123.123.123.123 0 aabb.cc00.2000 ARPA Ethernet0/0
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Internet 192.168.12.1 - aabb.cc00.1000 ARPA Ethernet0/0
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Internet 192.168.12.2 9 aabb.cc00.2000 ARPA Ethernet0/0
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Internet 192.168.23.3 4 aabb.cc00.2000 ARPA Ethernet0/0
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Internet 192.168.23.4 0 aabb.cc00.2000 ARPA Ethernet0/0
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```
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发现不管去往什么地址，都会导致ARP表多出一条。
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检查路由表
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```
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R1#show ip route
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S* 0.0.0.0/0 is directly connected, Ethernet0/0 # 发现默认路由条目一次查找，就知道出口了
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192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks
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C 192.168.12.0/24 is directly connected, Ethernet0/0
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L 192.168.12.1/32 is directly connected, Ethernet0/0
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S 192.168.23.0/24 is directly connected, Ethernet0/0
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```
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如果数据目的IP地址在路由表中直接能找到出接口，就回直接封装然后转发，如果没有MAC地址的记录，就会触发ARP。
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如果静态路由尝试用下一跳IP地址作为出站线索，触发路由表递归查询
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```
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R1(config)#ip route 192.168.23.0 255.255.255.0 192.168.12.2
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R1#sh ip route
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192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks
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C 192.168.12.0/24 is directly connected, Ethernet0/0
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L 192.168.12.1/32 is directly connected, Ethernet0/0
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S 192.168.23.0/24 [1/0] via 192.168.12.2
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R1#ping 192.168.23.3
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Type escape sequence to abort.
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Sending 5, 100-byte ICMP Echos to 192.168.23.3, timeout is 2 seconds:
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!!!!!
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Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
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R1#sh arp
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Protocol Address Age (min) Hardware Addr Type Interface
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Internet 192.168.12.1 - aabb.cc00.1000 ARPA Ethernet0/0
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Internet 192.168.12.2 0 aabb.cc00.2000 ARPA Ethernet0/0
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```
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如果静态路由配置下一跳的IP地址作为出站线索，那么就会触发路由表递归查找，而最终不仅仅是找到了出口信息，同时还找到了下一跳IP地址的MAC地址，直接会被拿来作为数据链路层的目的MAC地址。
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### 2.4 结论
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在配置静态路由的时候，尽量配置下一跳IP地址作为出口，这样可以避免ARP表的增大。
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## 3. 路由汇总
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为了测试，在R1上配置多个loopback接口，用于模拟多个网段
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```
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R1#sh ip int br
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Interface IP-Address OK? Method Status Protocol
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Ethernet0/0 192.168.12.1 YES manual up up
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Ethernet0/1 unassigned YES unset administratively down down
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Ethernet0/2 unassigned YES unset administratively down down
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Ethernet0/3 unassigned YES unset administratively down down
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Loopback1 172.16.1.1 YES manual up up
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Loopback2 172.16.2.1 YES manual up up
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Loopback3 172.16.3.1 YES manual up up
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```
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这些地址配置的都是/24,但是我们发现前16位都是一样的，那么R2上可以写如下的汇总静态路由
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```
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R2(config)#ip route 172.16.0.0 255.255.0.0 192.168.12.1
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```
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汇总路由可以精简路由条目，加快了查找效率
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但是汇总路由也会导致明细的丢失，造成不必要的路由转发
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## 4. 路由器的配置保存与查看
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当上面的实验做完了，检查网络状态都可以，就可以保存配置了
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```
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R1#copy running-config startup-config # 把内存中的配置文件，保存到开机启动配置文件中
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R1#write
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```
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在配置的时候，可以查看当前的配置文件
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```
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R1#show running-config # 然后按空格翻页，按q退出
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R1#show run int e0/0 # 查看接口e0/0下的配置
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R1#show running-config | section ip route # 查看有ip route的那一行配置
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```
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正常情况下，`ping`,`show`,`write`等命令只能在特权模式下(#)或者用户模式下(>)使用，如果想在各种配置模式中使用这些命令，可以在命令前面加个`do`来调用
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```
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R1(config)#show ip route
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^
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% Invalid input detected at '^' marker.
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R1(config)#do show ip route # 前面加do可以调用非配置模式下的命令
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```
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## 5. 管理距离
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当路由器从不同的方式学到了同一条路由条目，由于路由器只能将最佳路由放在路由表中。所以会从多个可用条目中将最佳结果放入路由表。
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路由器使用管理距离去评判路由获得方式优劣。
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注意！上表是cisco设备的管理距离，每个品牌都会有些不一样，用的时候需要去查一下。
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这个管理距离只是设备自己这么认为，无法影响其他设备，所以必要的时候，我们可以去修改，而不用担心全网的影响。越小越优。不优的不会出现在路由表中。
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```
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S 192.168.23.0/24 [1/0] via 192.168.12.2
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# 这个条目中[1/0]里面1是管理距离，是用来判断同一个路由的不同来源的优先级
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R1#show ip route 192.168.23.0
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Routing entry for 192.168.23.0/24
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Known via "static", distance 1, metric 0 # 管理距离是1，度量值是0
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Routing Descriptor Blocks:
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* 192.168.12.2
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Route metric is 0, traffic share count is 1
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```
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## 6. 浮动静态路由
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浮动静态路由是通过修改管理距离的方式，让静态路由可以做到控制路径，在发生故障的时候，也能切换。
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两个路线都正常的情况下
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当下面的路线断开之后
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先配置IP地址
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```
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R1
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int e0/0
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ip add 192.168.12.1 255.255.255.0
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no sh
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==========================
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R2
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int e0/0
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ip add 192.168.12.2 255.255.255.0
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no sh
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int e0/2
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ip add 192.168.23.2 255.255.255.0
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no sh
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int e0/1
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ip add 192.168.32.2 255.255.255.0
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no sh
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===========================
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R3
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int e0/0
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ip add 192.168.34.3 255.255.255.0
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no sh
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int e0/2
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ip add 192.168.23.3 255.255.255.0
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no sh
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int e0/1
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ip add 192.168.32.3 255.255.255.0
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no sh
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==========================
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R4
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int e0/0
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ip add 192.168.34.4 255.255.255.0
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no sh
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```
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配置静态路由
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```
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R1(config)#ip route 0.0.0.0 0.0.0.0 192.168.12.2
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==================================
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R2(config)#ip route 192.168.34.0 255.255.255.0 192.168.23.3
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R2(config)#ip route 192.168.34.0 255.255.255.0 192.168.32.3 2
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===================================
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R3(config)#ip route 192.168.12.0 255.255.255.0 192.168.23.2 2
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R3(config)#ip route 192.168.12.0 255.255.255.0 192.168.32.2
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==================================
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R4(config)#ip route 0.0.0.0 0.0.0.0 192.168.34.3
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```
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检查在线路正常的时候访问的路径
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```
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R1#traceroute 192.168.34.4
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Type escape sequence to abort.
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Tracing the route to 192.168.34.4
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VRF info: (vrf in name/id, vrf out name/id)
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1 192.168.12.2 1 msec 0 msec 1 msec
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2 192.168.23.3 1 msec 1 msec 0 msec
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3 192.168.34.4 1 msec * 1 msec
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==========================
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R4#traceroute 192.168.12.1
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Type escape sequence to abort.
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Tracing the route to 192.168.12.1
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VRF info: (vrf in name/id, vrf out name/id)
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1 192.168.34.3 0 msec 1 msec 1 msec
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2 192.168.32.2 0 msec 1 msec 1 msec
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3 192.168.12.1 0 msec * 3 msec
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```
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下面关闭R2的e0/2口，来模拟线路有一个损坏，再次检查线路是否切换
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```
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R1#traceroute 192.168.34.4
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Type escape sequence to abort.
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Tracing the route to 192.168.34.4
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VRF info: (vrf in name/id, vrf out name/id)
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1 192.168.12.2 5 msec 5 msec 5 msec
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2 192.168.32.3 1 msec 5 msec 5 msec
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3 192.168.34.4 1 msec * 1 msec
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```
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## 7. 负载均衡
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当去往同一个路由条目有多个出口的时候，并且管理距离和度量值都是一样的，也就是说路由器分辨不出来哪个路径好坏。路由器会将这些路线全部加到路由表中，进行等价负载均衡。
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```
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R2(config)#ip route 100.0.0.0 255.0.0.0 192.168.12.1
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R2(config)#ip route 100.0.0.0 255.0.0.0 192.168.23.3
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R2(config)#do sh ip route
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.........
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S 100.0.0.0/8 [1/0] via 192.168.23.3
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[1/0] via 192.168.12.1
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........
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```
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比如：100.0.0.0/8就有两个下一跳IP地址，并且都是`[1/0]`，所以全部加入了路由表，在发数据的时候，会将数据包一个IP地址发一个。可以通过如下命令查看下次往哪里走。
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```
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R2(config)#do sh ip route 100.0.0.0
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Routing entry for 100.0.0.0/8
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Known via "static", distance 1, metric 0
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Routing Descriptor Blocks:
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192.168.23.3
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Route metric is 0, traffic share count is 1
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* 192.168.12.1 # 前面的*表示下一个IP包将发到这个地址
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Route metric is 0, traffic share count is 1
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R2#ping 100.1.1.1 repeat 1
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Type escape sequence to abort.
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Sending 1, 100-byte ICMP Echos to 100.1.1.1, timeout is 2 seconds:
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! # 100.1.1.1只有R1有，所以这次通了
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Success rate is 100 percent (1/1), round-trip min/avg/max = 2/2/2 ms
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R2#show ip route 100.0.0.0
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Routing entry for 100.0.0.0/8
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Known via "static", distance 1, metric 0
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Routing Descriptor Blocks:
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* 192.168.23.3 # 由于192.168.12.1上次才发过数据包，所以下次走192.168.23.3
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Route metric is 0, traffic share count is 1 # 这个是线路共享比例，等价负载均衡是1:1
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192.168.12.1
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Route metric is 0, traffic share count is 1
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R2#ping 100.1.1.1 repeat 1
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Type escape sequence to abort.
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||||
Sending 1, 100-byte ICMP Echos to 100.1.1.1, timeout is 2 seconds:
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U # 100.1.1.1只有R1有，所以这次不通
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Success rate is 0 percent (0/1)
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```
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负载均衡在企业的应用中非常的广泛，可以用于提升链路的可靠性，提升链路的速率。
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Reference in New Issue
Block a user