组网需求
如图1所示，SwitchA、SwitchB和SwitchC之间运行OSPF，SwitchA和SwitchB之间的交换机仅作透传功能。现在需要SwitchA和SwitchB能快速感应它们之间的链路状态，当链路SwitchA-SwitchB发生故障时，业务能快速切换到备份链路SwitchA-SwitchC-SwitchB上
说明
请确保该场景下互联接口的STP处于未使能状态。因为在使能STP的环形网络中，如果用交换机的VLANIF接口构建三层网络，会导致某个端口被阻塞，从而导致三层业务不能正常运行
配置思路
采用如下思路配置OSPF与BFD联动：
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在各交换机上配置OSPF基本功能，实现整个OSPF网络的互通。
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在各交换机上配置OSPF与BFD联动功能，实现当SwitchA和SwitchB之间的链路出现故障时快速的切换到备份链路。
操作步骤
配置各接口所属的VLAN
# 配置SwitchA。SwitchB和SwitchC的配置与SwitchA类似。
[zhongwanzhi]vlan batch 10 30
[zhongwanzhi]interface GigabitEthernet 0/0/1
[zhongwanzhi-GigabitEthernet0/0/1]port link-type trunk
[zhongwanzhi-GigabitEthernet0/0/1]port trunk allow-pass vlan 10
[zhongwanzhi-GigabitEthernet0/0/1]quit
[zhongwanzhi]interface GigabitEthernet 0/0/2
[zhongwanzhi-GigabitEthernet0/0/2]port link-type tr
[zhongwanzhi-GigabitEthernet0/0/2]port link-type trunk
[zhongwanzhi-GigabitEthernet0/0/2]port trunk allow-pass vlan 30
[zhongwanzhi-GigabitEthernet0/0/2]quit配置各VLANIF接口的IP地址
# 配置SwitchA。SwitchB和SwitchC的配置与SwitchA类似
[zhongwanzhi]interface Vlanif 30
[zhongwanzhi-Vlanif30]ip address 10.3.3.1 24
[zhongwanzhi-Vlanif30]quit
[zhongwanzhi]interface Vlanif 10
[zhongwanzhi-Vlanif10]ip address 10.1.1.1 24
[zhongwanzhi-Vlanif10]quit配置OSPF基本功能
# 配置SwitchA、SwitchB和SwitchC的配置与SwitchA类似
[zhongwanzhi]ospf 1 router-id 10.10.10.1
[zhongwanzhi-ospf-1]area 0
[zhongwanzhi-ospf-1-area-0.0.0.0]network 10.1.1.0 0.0.0.255
[zhongwanzhi-ospf-1-area-0.0.0.0]network 10.3.3.0 0.0.0.255
[zhongwanzhi-ospf-1-area-0.0.0.0]quit
[zhongwanzhi-ospf-1]quit# 配置完成后，执行命令display ospf peer，可以看到SwitchA，SwitchB和SwitchC之间互相建立了邻接关系。以SwitchA的显示结果为例
[zhongwanzhi]display ospf peer
OSPF Process 1 with Router ID 10.10.10.1
Neighbors
Area 0.0.0.0 interface 10.1.1.1(Vlanif10)'s neighbors
Router ID: 10.10.10.3 Address: 10.1.1.2
State: Full Mode:Nbr is Master Priority: 1
DR: 10.1.1.1 BDR: 10.1.1.2 MTU: 0
Dead timer due in 34 sec
Retrans timer interval: 5
Neighbor is up for 00:00:20
Authentication Sequence: [ 0 ]
[zhongwanzhi]display ospf peer
OSPF Process 1 with Router ID 10.10.10.1
Neighbors
Area 0.0.0.0 interface 10.1.1.1(Vlanif10)'s neighbors
Router ID: 10.10.10.3 Address: 10.1.1.2
State: Full Mode:Nbr is Master Priority: 1
DR: 10.1.1.1 BDR: 10.1.1.2 MTU: 0
Dead timer due in 34 sec
Retrans timer interval: 5
Neighbor is up for 00:00:47
Authentication Sequence: [ 0 ] 配置OSPF与BFD联动
# 在SwitchA上配置OSPF与BFD联动功能。SwitchB和SwitchC的配置与SwitchA类似。
[zhongwanzhi]bfd
[zhongwanzhi-bfd]quit
[zhongwanzhi]ospf 1
[zhongwanzhi-ospf-1]bfd all-interfaces enable
[zhongwanzhi-ospf-1]quit# 配置完成后，在SwitchA或SwitchB、SwitchC上执行display ospf bfd session all命令，可以看到BFD会话的状态为Up。以SwitchA的显示为例。
[zhongwanzhi]display ospf bfd session all
OSPF Process 1 with Router ID 10.10.10.1
Area 0.0.0.0 interface 10.1.1.1(Vlanif10)'s BFD Sessions
NeighborId:10.10.10.3 AreaId:0.0.0.0 Interface:Vlanif10
BFDState:up rx :1000 tx :1000
Multiplier:3 BFD Local Dis:8192 LocalIpAdd:10.1.1.1
RemoteIpAdd:10.1.1.2 Diagnostic Info:No diagnostic information
