组网及说明
如下图拓扑所示：
SW1 与 SW2 交换机采用静态链路聚合模式部署。
为避免由于链路感知延迟（如长距离链路，或链路中存在有源传输设备），导致可能出现的“黑洞”现象（一端链路接口UP，另一端链路接口Down），增加BFD功能。实现链路聚合快速毫秒级感知链路状态。
配置步骤
<SW1>
#
interface Bridge-Aggregation1
link-aggregation bfd ipv4 source 1.1.1.1 destination 2.2.2.2
bfd authentication-mode simple 1 plain 123 //可选，配置密钥123
#
interface Ten-GigabitEthernet1/0/1
port link-mode bridge
link-aggregation port-priority 4096
port link-aggregation group 1
#
interface Ten-GigabitEthernet1/0/3
port link-mode bridge
port link-aggregation group 1
#
<SW2>
#
interface Bridge-Aggregation1
link-aggregation bfd ipv4 source 2.2.2.2 destination 1.1.1.1
bfd authentication-mode simple 1 plain 123 //可选，配置密钥123
#
interface Ten-GigabitEthernet1/0/1
port link-mode bridge
port link-aggregation group 1
#
interface Ten-GigabitEthernet1/0/3
port link-mode bridge
port link-aggregation group 1
#
配置关键点
当链路正常情况下：
<SW1> display link-aggregation verbose
……
Aggregate Interface: Bridge-Aggregation1
Aggregation Mode: Static
Loadsharing Type: Shar
Management VLANs: None
Port Status Priority Oper-Key
XGE1/0/1(R) S 4096 1
XGE1/0/3 S 32768 1
<SW1> display bfd session
Total Session Num: 2 Up Session Num: 2 Init Mode: Active
IPv4 session working in control packet mode:
LD/RD SourceAddr DestAddr State Holdtime Interface
257/257 1.1.1.1 2.2.2.2 Up 1983ms XGE1/0/1
258/258
1.1.1.1 2.2.2.2 Up 1703ms XGE1/0/3
<SW2>display link-aggregation verbose
……
Aggregate Interface: Bridge-Aggregation1
Aggregation Mode: Static
Loadsharing Type: Shar
Management VLANs: None
Port Status Priority Oper-Key
XGE1/0/1(R) S 32768 1
XGE1/0/3 S 32768 1
<SW2>display bfd session
Total Session Num: 2 Up Session Num: 2 Init Mode: Active
IPv4 session working in control packet mode:
LD/RD SourceAddr DestAddr State Holdtime Interface
257/257 2.2.2.2 1.1.1.1 Up 2000ms XGE1/0/1
258/258 2.2.2.2 1.1.1.1 Up 1966ms XGE1/0/3
若SW2本地XG1/0/1接口down后，及链路故障时：
<SW1>
%Jan 28 03:34:10:784 1980 sw1 BFD/5/BFD_CHANGE_FSM: Sess[1.1.1.1/2.2.2.2, LD/RD:259/259, Interface:XGE1/0/1, SessType:Ctrl, LinkType:INET], Ver:1, Sta: UP->DOWN, Diag: 1 (Control Detection Time Expired) //SW1的bfd会话快速感知到会话down
*Jan 28 03:34:10:785 1980 sw1 LAGG/7/Event: Group 1 updated because of member port BFD session up/down.
*Jan 28 03:34:10:830 1980 sw1 LAGG/7/Event: Group 1 updated because of other reason.
%Jan 28 03:34:10:838 1980 sw1 LAGG/6/LAGG_INACTIVE_BFD: Member port XGE1/0/1 of aggregation group BAGG1 changed to the inactive state, because the BFD session state of the port is down. //BFD模块通知链路聚合模块相关接口出现“异常”，需要将SW1本地对应链路接口置为Unselected状态。
%Jan 28 03:34:10:843 1980 sw1 IFNET/5/LINK_UPDOWN: Line protocol state on the interface Ten-GigabitEthernet1/0/1 changed to down. //SW1本地XG1/0/1接口逻辑链路层快速被down掉。
<SW1>display link-aggregation verbose
……
Aggregate Interface: Bridge-Aggregation1
Aggregation Mode: Static
Loadsharing Type: Shar
Management VLANs: None
Port Status Priority Oper-Key
XGE1/0/1 U 4096 1
XGE1/0/3(R) S 32768 1
<sw1>display bfd session
Total Session Num: 1 Up Session Num: 1 Init Mode: Active
IPv4 session working in control packet mode:
LD/RD SourceAddr DestAddr State Holdtime Interface
258/258 1.1.1.1 2.2.2.2 Up 1737ms XGE1/0/3
<SW2>display link-aggregation verbose
……
Aggregate Interface: Bridge-Aggregation1
Aggregation Mode: Static
Loadsharing Type: Shar
Management VLANs: None
Port Status Priority Oper-Key
XGE1/0/3(R) S 32768 1
<SW2>display bfd sesion
Total Session Num: 1 Up Session Num: 1 Init Mode: Active
IPv4 session working in control packet mode:
LD/RD SourceAddr DestAddr State Holdtime Interface
258/258 2.2.2.2 1.1.1.1 Up 1899ms XGE1/0/3