10.BFD
BFD
BFD（Bidirectional Forwarding Detection）：双向转发检查，是一种快速检测网络链路故障的协议，会定期发送控制报文来检测链路的可用性，一旦检测到链路故障，会立即通知相关设备进行故障切换，从而实现更快的故障检测和链路切换时间。
作用：可以做到毫秒级故障检查，通常结合三层协议（如静态路由、vrrp、ospf、BGP等）实现链路故障快速检查。
静态路由调用BFD
使用静态路由配置两条冗余备份的路由
配置接口IP
[R1]inter gi 0/0/0
[R1-GigabitEthernet0/0/0]ip add 21.1.1.1 30
[R1-GigabitEthernet0/0/0]inter gi 0/0/1
[R1-GigabitEthernet0/0/1]ip add 22.1.1.1 30
[R1-GigabitEthernet0/0/1]inter loop 0
[R1-LoopBack0]ip add 1.1.1.1 32
[R1-LoopBack0]
[R2]inter gi 0/0/0
[R2-GigabitEthernet0/0/0]ip add 21.1.1.2 30
[R2-GigabitEthernet0/0/0]inter gi 0/0/1
[R2-GigabitEthernet0/0/1]ip add 22.1.1.2 30
[R2-GigabitEthernet0/0/1]inter loop 0
[R2-LoopBack0]ip add 2.2.2.2 32
[R2-LoopBack0]
配置静态路由
[R1]ip route-static 2.2.2.2 255.255.255.255 22.1.1.2 pre
[R1]ip route-static 2.2.2.2 255.255.255.255 22.1.1.2 preference 70
[R2]ip route-static 1.1.1.1 32 22.1.1.1 pre
[R2]ip route-static 1.1.1.1 32 22.1.1.1 preference 70
由于不是接口直接相连，若其中一台的接口Down，另一台不会感知到，不会使静态路由失效，如果此时使用BFD进行检测，非直连接口down时，也会使静态路由失效，从而使用备份静态路由进行数据转发。
配置BFD会话的参数和属性
<R1>sys
Enter system view, return user view with Ctrl+Z.
[R1]bfd
[R1-bfd]q
[R1]bfd 1 bind peer-ip 21.1.1.2 source-ip 21.1.1.1 auto
[R1-bfd-session-1]commit
[R1-bfd-session-1]q
[R1]bfd 2 bind peer-ip 22.1.1.2 source-ip 22.1.1.1 auto
[R1-bfd-session-2]commit
[R1-bfd-session-2]q
[R1]
手动设置设备的辨识符
discriminator local 1
discriminator remote 1
[R2]bfd
[R2-bfd]q
[R2]bfd 1 bind peer-ip 21.1.1.1 source-ip 21.1.1.2 auto
[R2-bfd-session-1]commit
[R2-bfd-session-1]q
[R2]bfd 2 bind peer-ip 22.1.1.1 source-ip 22.1.1.2 auto
[R2-bfd-session-2]commit
[R2-bfd-session-2]q
[R2]
使BFD会话与静态路由关联起来
[R1]ip route-static 2.2.2.2 255.255.255.255 21.1.1.2 track bfd-session 1
Info: Succeeded in modifying route.
[R1]ip route-static 2.2.2.2 255.255.255.255 22.1.1.2 preference 70 track bfd-session 2
Info: Succeeded in modifying route.
[R1]
[R2]ip route-static 1.1.1.1 255.255.255.255 21.1.1.1 track bfd-session 1
Info: Succeeded in modifying route.
[R2]ip route-static 1.1.1.1 255.255.255.255 22.1.1.1 preference 70 track bfd-session 2
Info: Succeeded in modifying route.
[R2]
当BFD会话1检测到链路故障时，该静态路由将被自动失效，从而实现快速的故障切换。
查看BFD状态
<R1>dis bfd se all
--------------------------------------------------------------------------------
Local Remote PeerIpAddr State Type InterfaceName
--------------------------------------------------------------------------------
8192 8192 21.1.1.2 Up S_AUTO_PEER -
8193 8193 22.1.1.2 Up S_AUTO_PEER -
--------------------------------------------------------------------------------
Total UP/DOWN Session Number : 2/0
<R1>dis bfd se all verbose
--------------------------------------------------------------------------------
Session MIndex : 258 (Multi Hop) State : Up Name : 1
--------------------------------------------------------------------------------
Local Discriminator : 8192 Remote Discriminator : 8192
Session Detect Mode : Asynchronous Mode Without Echo Function
BFD Bind Type : Peer IP Address
Bind Session Type : Static_Auto
Bind Peer IP Address : 21.1.1.2
Bind Interface : -
Bind Source IP Address : 21.1.1.1
FSM Board Id : 0 TOS-EXP : 7
Min Tx Interval (ms) : 1000 Min Rx Interval (ms) : 1000
Actual Tx Interval (ms): 1000 Actual Rx Interval (ms): 1000
Local Detect Multi : 3 Detect Interval (ms) : 3000
Echo Passive : Disable Acl Number : -
Destination Port : 3784 TTL : 253
Proc Interface Status : Disable Process PST : Disable
WTR Interval (ms) : -
Active Multi : 3
Last Local Diagnostic : No Diagnostic
Bind Application : AUTO
Session TX TmrID : - Session Detect TmrID : -
Session Init TmrID : - Session WTR TmrID : -
Session Echo Tx TmrID : -
PDT Index : FSM-0 | RCV-0 | IF-0 | TOKEN-0
Session Description : -
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Session MIndex : 259 (Multi Hop) State : Up Name : 2
--------------------------------------------------------------------------------
Local Discriminator : 8193 Remote Discriminator : 8193
Session Detect Mode : Asynchronous Mode Without Echo Function
BFD Bind Type : Peer IP Address
Bind Session Type : Static_Auto
Bind Peer IP Address : 22.1.1.2
Bind Interface : -
Bind Source IP Address : 22.1.1.1
FSM Board Id : 0 TOS-EXP : 7
Min Tx Interval (ms) : 1000 Min Rx Interval (ms) : 1000
Actual Tx Interval (ms): 1000 Actual Rx Interval (ms): 1000
Local Detect Multi : 3 Detect Interval (ms) : 3000
Echo Passive : Disable Acl Number : -
Destination Port : 3784 TTL : 253
Proc Interface Status : Disable Process PST : Disable
WTR Interval (ms) : -
Active Multi : 3
Last Local Diagnostic : No Diagnostic
Bind Application : AUTO
Session TX TmrID : - Session Detect TmrID : -
Session Init TmrID : - Session WTR TmrID : -
Session Echo Tx TmrID : -
PDT Index : FSM-1 | RCV-0 | IF-0 | TOKEN-0
Session Description : -
--------------------------------------------------------------------------------
Total UP/DOWN Session Number : 2/0
<R1>
<R2>dis bfd se all
--------------------------------------------------------------------------------
Local Remote PeerIpAddr State Type InterfaceName
--------------------------------------------------------------------------------
8192 8192 21.1.1.1 Up S_AUTO_PEER -
8193 8193 22.1.1.1 Up S_AUTO_PEER -
--------------------------------------------------------------------------------
Total UP/DOWN Session Number : 2/0
<R2>
查看路由
[R1]dis ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 12 Routes : 12
Destination/Mask Proto Pre Cost Flags NextHop Interface
1.1.1.1/32 Direct 0 0 D 127.0.0.1 LoopBack0
2.2.2.2/32 Static 60 0 RD 21.1.1.2 GigabitEthernet
0/0/0
21.1.1.0/30 Direct 0 0 D 21.1.1.1 GigabitEthernet
0/0/0
21.1.1.1/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
21.1.1.3/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
22.1.1.0/30 Direct 0 0 D 22.1.1.1 GigabitEthernet
0/0/1
22.1.1.1/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
22.1.1.3/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
[R1]dis ip routing-table 2.2.2.2 255.255.255.255 verbose
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 2
Destination: 2.2.2.2/32
Protocol: Static Process ID: 0
Preference: 60 Cost: 0
NextHop: 21.1.1.2 Neighbour: 0.0.0.0
State: Active Adv Relied Age: 00h04m05s
Tag: 0 Priority: medium
Label: NULL QoSInfo: 0x0
IndirectID: 0x80000001
RelayNextHop: 0.0.0.0 Interface: GigabitEthernet0/0/0
TunnelID: 0x0 Flags: RD
Destination: 2.2.2.2/32
Protocol: Static Process ID: 0
Preference: 70 Cost: 0
NextHop: 22.1.1.2 Neighbour: 0.0.0.0
State: Inactive Adv Relied Age: 00h04m05s
Tag: 0 Priority: medium
Label: NULL QoSInfo: 0x0
IndirectID: 0x80000002
RelayNextHop: 0.0.0.0 Interface: GigabitEthernet0/0/1
TunnelID: 0x0 Flags: R
[R1]
OSPF 调用BFD加快收敛
撤销静态路由配置，配置OSPF
R1
ospf 1 router-id 1.1.1.1
area 0.0.0.0
network 1.1.1.1 0.0.0.0
network 21.1.1.0 0.0.0.7
network 22.1.1.0 0.0.0.7
R2
ospf 1 router-id 2.2.2.2
area 0.0.0.0
network 2.2.2.2 0.0.0.0
network 21.1.1.0 0.0.0.7
network 22.1.1.0 0.0.0.7
查看OSPF状态
[R2]display ospf interface
OSPF Process 1 with Router ID 2.2.2.2
Interfaces
Area: 0.0.0.0 (MPLS TE not enabled)
IP Address Type State Cost Pri DR BDR
21.1.1.2 Broadcast DR 1 1 21.1.1.2 21.1.1.1
22.1.1.2 Broadcast DR 1 1 22.1.1.2 22.1.1.1
2.2.2.2 P2P P-2-P 0 1 0.0.0.0 0.0.0.0
[R2]dis ospf peer brief
OSPF Process 1 with Router ID 2.2.2.2
Peer Statistic Information
----------------------------------------------------------------------------
Area Id Interface Neighbor id State
0.0.0.0 GigabitEthernet0/0/0 1.1.1.1 Full
0.0.0.0 GigabitEthernet0/0/1 1.1.1.1 Full
----------------------------------------------------------------------------
[R2]
不配置的情况下，OSPF收敛速度很慢
两台路由器R1和R2经过S1彼此互连，并将各自的接口运行于OSPF区域0，由于不是接口直接相连，若其中一台的接口Down，另一台不会立即感知，需要等待4倍的Hello时间来删除邻居，在这段时间内，对应路由不会失效，数据转发都会处于非正常状态。
手动down掉SW1的gi 0/0/2的接口，AR1的路由和OSPF邻居收敛速度很慢
配置OSPF启用BFD
[R1]ospf 1
[R1-ospf-1]bfd all-interfaces enable
[R1-ospf-1]q
[R1]
[R2]ospf 1
[R2-ospf-1]bfd all-interfaces enable
[R2-ospf-1]q
dis bfd session all
display ospf bfd session all
down掉SW1的gi 0/0/1口，重新查看ospf的BFD状态
如果开启了debug功能，观察debug日志，会出现如下内容：
BFD 与 VRRP 联动配置实验
配置接口IP和VRRP
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sys R1
[R1]inter gi 0/0/0
[R1-GigabitEthernet0/0/0]ip add 192.168.10.2 29
[R1-GigabitEthernet0/0/0]vrrp vrid 1 virtual-ip 192.168.10.1
[R1-GigabitEthernet0/0/0]
[R1-GigabitEthernet0/0/0]vrrp vrid 1 priority 105
[R1-GigabitEthernet0/0/0]dis vrrp br
Total:1 Master:1 Backup:0 Non-active:0
VRID State Interface Type Virtual IP
----------------------------------------------------------------
1 Master GE0/0/0 Normal 192.168.10.1
[R1-GigabitEthernet0/0/0]
[Huawei]sy R2
[R2]inter gi 0/0/0
[R2-GigabitEthernet0/0/0]ip add 192.168.10.4 29
[R2-GigabitEthernet0/0/0]ip add 192.168.10.3 29
[R2-GigabitEthernet0/0/0]vrrp vrid 1 virtual-ip 192.168.10.1
[R2-GigabitEthernet0/0/0]
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sys SW3
[SW3]inter vlanif 1
[SW3-Vlanif1]ip add 192.168.10.4 29
[SW3-Vlanif1]
配置BFD会话
[R1]bfd
[R1-bfd]q
[R1]bfd 1 bind peer-ip 192.168.10.4 source-ip 192.168.10.2 auto
[R1-bfd-session-1]commit
[R1-bfd-session-1]q
[R1]
[R2]bfd
[R2-bfd]q
[R2]bfd 2 bind peer-ip 192.168.10.4 source-ip 192.168.10.3 auto
[R2-bfd-session-2]commit
[R2-bfd-session-2]q
[R2]
SW3上配置BFD会话信息
[SW3]bfd 1 bind peer-ip 192.168.10.2 source-ip 192.168.10.4 auto
[SW3-bfd-session-1]commit
[SW3-bfd-session-1]q
[SW3]bfd 2 bind peer-ip 192.168.10.3 source-ip 192.168.10.4 auto
[SW3-bfd-session-2]commit
[SW3-bfd-session-2]q
[SW3]
查看bfd会话状态
[R1]dis bfd session all
--------------------------------------------------------------------------------
Local Remote PeerIpAddr State Type InterfaceName
--------------------------------------------------------------------------------
8192 8192 192.168.10.4 Up S_AUTO_PEER -
--------------------------------------------------------------------------------
Total UP/DOWN Session Number : 1/0
[R1]dis bfd session all verbose
--------------------------------------------------------------------------------
Session MIndex : 256 (Multi Hop) State : Up Name : 1
--------------------------------------------------------------------------------
Local Discriminator : 8192 Remote Discriminator : 8192
Session Detect Mode : Asynchronous Mode Without Echo Function
BFD Bind Type : Peer IP Address
Bind Session Type : Static_Auto
Bind Peer IP Address : 192.168.10.4
Bind Interface : -
Bind Source IP Address : 192.168.10.2
FSM Board Id : 0 TOS-EXP : 7
Min Tx Interval (ms) : 1000 Min Rx Interval (ms) : 1000
Actual Tx Interval (ms): 1000 Actual Rx Interval (ms): 1000
Local Detect Multi : 3 Detect Interval (ms) : 3000
Echo Passive : Disable Acl Number : -
Destination Port : 3784 TTL : 253
Proc Interface Status : Disable Process PST : Disable
WTR Interval (ms) : -
Active Multi : 3
Last Local Diagnostic : No Diagnostic
Bind Application : AUTO
Session TX TmrID : - Session Detect TmrID : -
Session Init TmrID : - Session WTR TmrID : -
Session Echo Tx TmrID : -
PDT Index : FSM-0 | RCV-0 | IF-0 | TOKEN-0
Session Description : -
--------------------------------------------------------------------------------
Total UP/DOWN Session Number : 1/0
[R1]
vrrp绑定BFD会话(配置跟踪BFD会话链路状态)
[R1]inter gi 0/0/0
[R1-GigabitEthernet0/0/0]vrrp vrid 1 track bfd-session session-name 1 reduced 10
[R1-GigabitEthernet0/0/0]q
[R1]
[R2]inter gi 0/0/0
[R2-GigabitEthernet0/0/0]vrrp vrid 1 track bfd-session session-name 2 reduced 10
[R2-GigabitEthernet0/0/0]q
检查联动配置
测试配置是否成功
LSW1的gi 0/0/2接口down掉，R1上查看BFD会话状态，R2上查看VRRP状态
