使用SLA检测链路状态，实现自动路由切换

测试环境

**GNS3：**2.2.16 + GNS3 KVM 2.2.16

**设备：**Cisco 7200 124-24.T5
CHECKSUM：6b89d0d804e1f2bb5b8bda66b5692047

拓扑：

线路连接：
R4 F0/0 ---> R2 F0/0
R4 F0/1 ---> R3 F0/0

测试过程

1. 配置对端

   • R2 Config

     interface Loopback8
       ip address 8.8.8.8 255.255.255.255
     !
     interface FastEthernet0/0
       ip address 10.0.0.1 255.255.255.248
       no shutdown
     !
     

   • R3 Config

     interface Loopback8
       ip address 8.8.8.8 255.255.255.255
     !
     interface FastEthernet0/0
       ip address 10.0.0.9 255.255.255.248
       no shutdown
     !
     

2. 配置本地端
   R4 config

   interface FastEthernet0/0
     ip address 10.0.0.2 255.255.255.248
     no shutdown
   !
   interface FastEthernet0/1
     ip address 10.0.0.10 255.255.255.248
   no shutdown
   !
   ip route 8.8.8.8 255.255.255.255 10.0.0.1 100
   ip route 8.8.8.8 255.255.255.255 10.0.0.9 101
   

3. 检查路由
   R4 show ip route

        8.0.0.0/32 is subnetted, 1 subnets
   S       8.8.8.8 [100/0] via 10.0.0.1
   S       8.8.8.8 [101/0] via 10.0.0.9
   

4. 检查Ping
   R4 ping 8.8.8.8

   Type escape sequence to abort.
   Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:
   !!!!!
   Success rate is 100 percent (5/5), round-trip min/avg/max = 8/16/36 ms
   

5. 断开R2
   R2 config

   R2#conf t
   R2(config)#int f0/0
   R2(config-if)#shu
   *Mar 1 00:07:46.003: %LINK-5-CHANGED: Interface FastEthernet0/0, changed state to administratively down
   *Mar 1 00:07:47.003: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to down
   

6. 检查Ping
   R4 ping 8.8.8.8

   Type escape sequence to abort.
   Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:
   .....
   Success rate is 0 percent (0/5)
   

7. 配置SLA
   R4 config

   R4(config)#ip sla 1
   R4(config-ip-sla)#icmp-echo 10.0.0.1
   R4(config-ip-sla-echo)#timeout 5000
   R4(config-ip-sla-echo)#frequency 5
   R4(config-ip-sla-echo)#exit
   R4(config)#ip sla schedule 1 start-time now life forever
   R4(config)#track 1 ip sla 1 reachability
   R4(config)#
   R4(config)#ip sla 2
   R4(config-ip-sla)#icmp-echo 10.0.0.9
   R4(config-ip-sla-echo)#timeout 5000
   R4(config-ip-sla-echo)#frequency 5
   R4(config-ip-sla-echo)#exit
   R4(config)#ip sla schedule 2 start-time now life forever
   R4(config)#track 2 ip sla 2 reachability
   R4(config)#
   R4(config)#no ip route 8.8.8.8 255.255.255.255
   R4(config)#ip route 8.8.8.8 255.255.255.255 10.0.0.1 track 1 100
   R4(config)#ip route 8.8.8.8 255.255.255.255 10.0.0.9 track 2 101
   

8. 检查路由
   R4 show ip route

        8.0.0.0/32 is subnetted, 1 subnets
   S       8.8.8.8 [101/0] via 10.0.0.9
   

9. 检查Ping
   R4 show ip sla statistics

   IPSLAs Latest Operation Statistics
     
   IPSLA operation id: 1
   Type of operation: icmp-echo
   Latest RTT: NoConnection/Busy/Timeout
   Latest operation start time: *08:22:36.291 UTC Fri Nov 27 2020
   Latest operation return code: Timeout
   Number of successes: 0
   Number of failures: 8
   Operation time to live: Forever
   
   IPSLA operation id: 2
   Type of operation: icmp-echo
   Latest RTT: 28 milliseconds
   Latest operation start time: *08:22:41.711 UTC Fri Nov 27 2020
   Latest operation return code: OK
   Number of successes: 4
   Number of failures: 0
   Operation time to live: Forever
   

10. 连接R2
    R2 config

```
R2#conf t
R2(config)#int f0/0
R2(config-if)#no sh
*Mar 1 00:36:37.707: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Mar 1 00:36:38.707: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
```

1. 获取日志
   R4 Logs

```
*Nov 27 08:26:21.059: %TRACKING-5-STATE: 1 ip sla 1 reachability Down->Up
```

1. 检查路由
   R4 show ip route

       8.0.0.0/32 is subnetted, 1 subnets
   S       8.8.8.8 [100/0] via 10.0.0.1
   

2. 检查Ping
   R4 show ip sla statistics

   IPSLAs Latest Operation Statistics
   
   IPSLA operation id: 1
   Type of operation: icmp-echo
   Latest RTT: 8 milliseconds
   Latest operation start time: *08:58:01.303 UTC Fri Nov 27 2020
   Latest operation return code: OK
   Number of successes: 382
   Number of failures: 29
   Operation time to live: Forever
   
   IPSLA operation id: 2
   Type of operation: icmp-echo
   Latest RTT: 16 milliseconds
   Latest operation start time: *08:58:01.711 UTC Fri Nov 27 2020
   Latest operation return code: OK
   Number of successes: 428
   Number of failures: 0
   Operation time to live: Forever