拓朴如下：
主要配置如下：
[R1]
interface GigabitEthernet0/0/0ip address 10.1.1.1 255.255.255.0 vrrp vrid 1 virtual-ip 10.1.1.254vrrp vrid 1 priority 200vrrp vrid 1 preempt-mode timer delay 20
#
interface GigabitEthernet0/0/1ip address 13.1.1.1 255.255.255.0
#
ospf 1 router-id 1.1.1.1 area 0.0.0.0 network 0.0.0.0 255.255.255.255
#[R2]
interface GigabitEthernet0/0/0ip address 10.1.1.2 255.255.255.0 vrrp vrid 1 virtual-ip 10.1.1.111
#
interface GigabitEthernet0/0/1ip address 23.1.1.2 255.255.255.0
#
interface GigabitEthernet0/0/2
#
ospf 1 router-id 2.2.2.2 area 0.0.0.0 network 0.0.0.0 255.255.255.255
#[R3]
interface GigabitEthernet0/0/1ip address 13.1.1.3 255.255.255.0
#
interface GigabitEthernet0/0/2ip address 23.1.1.3 255.255.255.0
#
interface LoopBack0ip address 3.3.3.3 255.255.255.255
#
ospf 1 router-id 3.3.3.3 area 0.0.0.0 network 0.0.0.0 255.255.255.255
#
检测：
断开R1的G0/0/0口，发现丢了一个包后，仍能ping通R3的环回口3.3.3.3
