组网需求

如图1所示，DeviceA通过SwithC和DeviceB相连。在DeviceA上配置静态缺省路由可以与外部进行正常通信。同时，在DeviceA和DeviceB之间配置BFD会话来快速检测链路故障。

图1 配置静态BFD for IPv4静态路由组网图

配置思路

1. 在DeviceA和DeviceB上配置BFD会话，检测DeviceA和DeviceB之间的链路。
2. 配置DeviceA到外部的缺省路由并绑定BFD会话。

操作步骤

1.配置各接口IP地址（略）

2.配置DeviceA和DeviceB之间的BFD会话

# 在DeviceA上配置与DeviceB之间的BFD Session。

<DeviceA> system-view
[~DeviceA] bfd
[*DeviceA-bfd] quit
[*DeviceA] bfd aa bind peer-ip 1.1.1.2
[*DeviceA-bfd-session-aa] discriminator local 10
[*DeviceA-bfd-session-aa] discriminator remote 20
[*DeviceA-bfd-session-aa] commit
[~DeviceA-bfd-session-aa] quit

# 在DeviceB上配置与DeviceA之间的BFD Session。

<DeviceB> system-view
[~DeviceB] bfd
[*DeviceB-bfd] quit
[*DeviceB] bfd bb bind peer-ip 1.1.1.1
[*DeviceB-bfd-session-bb] discriminator local 20
[*DeviceB-bfd-session-bb] discriminator remote 10
[*DeviceB-bfd-session-bb] commit
[~DeviceB-bfd-session-bb] quit

3.配置静态缺省路由并绑定BFD会话

# 在DeviceA上配置到外部网络的静态缺省路由，并绑定BFD会话aa。

[~DeviceA] ip route-static 0.0.0.0 0 1.1.1.2 track bfd-session aa

4.验证配置结果

# 配置完成后，在DeviceA和DeviceB上执行display bfd session all命令，可以看到BFD会话已经建立，且状态为Up。在系统视图下执行display current-configuration | include bfd命令，可以看到静态路由已经绑定BFD会话。

以DeviceA上的显示为例。

[~DeviceA] display bfd session all
--------------------------------------------------------------------------------
Local  Remote PeerIpAddr      State     Type        InterfaceName
--------------------------------------------------------------------------------
10     20     1.1.1.2         Up       S_IP_PEER   -
--------------------------------------------------------------------------------
     Total UP/DOWN Session Number : 1/0

S: Static session
D: Dynamic session
IP: IP session
IF: Single-hop session
PEER: Multi-hop session
AUTO: Automatically negotiated session
--------------------------------------------------------------------------------
Local  Remote PeerIpAddr      State     Type        InterfaceName
--------------------------------------------------------------------------------
10     20     1.1.1.2         Up       S_IP_PEER   -
--------------------------------------------------------------------------------
Total UP/DOWN Session Number : 1/0
[~DeviceA] display current-configuration | include bfd
 bfd
 bfd aa bind peer-ip 1.1.1.2
 ip route-static 0.0.0.0 0.0.0.0 1.1.1.2 track bfd-session aa

# 在DeviceA上查看IP路由表，静态路由存在于路由表中。

[~DeviceA] display ip routing-table
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table: Public
         Destinations : 5        Routes : 5
Destination/Mask    Proto  Pre  Cost     Flags NextHop         Interface

        0.0.0.0/0   Static 60   0          RD  1.1.1.2         GigabitEthernet1/0/0
        1.1.1.0/24  Direct 0    0           D  1.1.1.1         GigabitEthernet1/0/0
        1.1.1.1/32  Direct 0    0           D  127.0.0.1       GigabitEthernet1/0/0
      1.1.1.255/32  Direct 0    0           D  127.0.0.1       GigabitEthernet1/0/0
255.255.255.255/32  Direct 0    0           D  127.0.0.1       InLoopBack0

# 对DeviceB的接口GE1/0/0执行shutdown命令模拟链路故障。

[~DeviceB] interface GigabitEthernet 1/0/0
[~DeviceB-GigabitEthernet1/0/0] shutdown

# 查看DeviceA的路由表，发现静态缺省路由0.0.0.0/0也不存在了。因为静态缺省路由绑定了BFD会话，当BFD检测到故障后，就会迅速通知所绑定的静态路由不可用。

[~DeviceA] display ip routing-table
Route Flags: R - relay, D - download to fib, T - to vpn-instance, B - black hole route
------------------------------------------------------------------------------
Routing Table: Public
         Destinations : 4        Routes : 4
Destination/Mask    Proto  Pre  Cost     Flags NextHop         Interface
        1.1.1.0/24  Direct 0    0           D  1.1.1.1         GigabitEthernet1/0/0
        1.1.1.1/32  Direct 0    0           D  127.0.0.1       GigabitEthernet1/0/0
      1.1.1.255/32  Direct 0    0           D  127.0.0.1       GigabitEthernet1/0/0
255.255.255.255/32  Direct 0    0           D  127.0.0.1       InLoopBack0