Bidirectional Forwarding Detection (BFD) 顧名思義爲雙向偵測協議，只檢測與下一跳設備設備連接狀態。目前只在7200以上系列路由器千兆以太接口以上支持，並支持OSPF、ERGRP、ISIS、BGP協議。當客戶端協議建立後，將告訴BFD協議去檢測鄰接連接狀態。BFD檢測包在CEF中具有高的優先級，並且通過unicast形式相互傳播。
FIGURE 1 When OSPF discovers a neighbor (step 1) it sends a request to the local BFD process to initiate a BFD neighbor session with the OSPF neighbor router (step 2). The BFD neighbor session with the OSPF neighbor router is established (step 3).
FIGURE 2 When a failure occurs in the network (step 1), the BFD neighbor session with the OSPF neighbor router is torn down (step 2). BFD notifies the local OSPF process that the BFD neighbor is no longer reachable (step 3). The local OSPF process tears down the OSPF neighbor relationship (step 4)
配置
可以應用到所有接口上
router ospf 1
[no] bfd all-interfaces
也可以應用在單個接口上
[no] ip ospf bfd [disable]
例子
Configuration for Router A
interface Ethernet2/0
ip address 172.16.10.1 255.255.0.0
bfd interval 50 min_rx 50 multiplier 3
!
router ospf 1
log-adjacency-changes detail
network 172.16.0.0 0.0.255.255 area 0
bfd all-interfaces
Configuration for Router B
interface Ethernet1/0
ip address 172.16.10.2 255.255.0.0
bfd interval 50 min_rx 50 multiplier 3
!
router ospf 1
log-adjacency-changes detail
network 172.16.0.0 0.0.255.255 area 0
bfd all-interfaces
顯示本地狀態
RouterA#sh ip ospf int e2/0
Ethernet2/0 is up, line protocol is up
Internet Address 172.16.10.1/16, Area 0
Process ID 1, Router ID 172.16.10.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1,BFD enabled
Designated Router (ID) 172.16.10.2, Interface address 172.16.10.2
Backup Designated router (ID) 172.16.10.1,Interface address 172.16.10.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
查看鄰居狀態 show ip ospf neighbor
RouterA#sh ip ospf nei 172.16.10.2 det
Neighbor 172.16.10.2, interface address 172.16.10.2
In the area 0 via interface Ethernet2/0, BFD enabled
Neighbor priority is 1, State is FULL, 6 state changes
FIGURE 1 When OSPF discovers a neighbor (step 1) it sends a request to the local BFD process to initiate a BFD neighbor session with the OSPF neighbor router (step 2). The BFD neighbor session with the OSPF neighbor router is established (step 3).
FIGURE 2 When a failure occurs in the network (step 1), the BFD neighbor session with the OSPF neighbor router is torn down (step 2). BFD notifies the local OSPF process that the BFD neighbor is no longer reachable (step 3). The local OSPF process tears down the OSPF neighbor relationship (step 4)
配置
可以應用到所有接口上
router ospf 1
[no] bfd all-interfaces
也可以應用在單個接口上
[no] ip ospf bfd [disable]
例子
Configuration for Router A
interface Ethernet2/0
ip address 172.16.10.1 255.255.0.0
bfd interval 50 min_rx 50 multiplier 3
!
router ospf 1
log-adjacency-changes detail
network 172.16.0.0 0.0.255.255 area 0
bfd all-interfaces
Configuration for Router B
interface Ethernet1/0
ip address 172.16.10.2 255.255.0.0
bfd interval 50 min_rx 50 multiplier 3
!
router ospf 1
log-adjacency-changes detail
network 172.16.0.0 0.0.255.255 area 0
bfd all-interfaces
顯示本地狀態
RouterA#sh ip ospf int e2/0
Ethernet2/0 is up, line protocol is up
Internet Address 172.16.10.1/16, Area 0
Process ID 1, Router ID 172.16.10.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1,BFD enabled
Designated Router (ID) 172.16.10.2, Interface address 172.16.10.2
Backup Designated router (ID) 172.16.10.1,Interface address 172.16.10.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
查看鄰居狀態 show ip ospf neighbor
RouterA#sh ip ospf nei 172.16.10.2 det
Neighbor 172.16.10.2, interface address 172.16.10.2
In the area 0 via interface Ethernet2/0, BFD enabled
Neighbor priority is 1, State is FULL, 6 state changes
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