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2012-02-07 20:35:30
BackboneFast是与UplinkFast互补的一项技术。尽管UplinkFast设计的目的是用来加速对直接连接到节点交换机的链路失效做出响应，但它不能对非直接连接的骨干区域中的交换机失效做出快速响应。BackboneFast是基于最大生成时间设置进行优化的。它允许把非直接连接的交换机的转发延时从50秒降到30秒。但它永远不可能完全消除转发延时。另外，要注意，要为网络中的每台交换机启用 BackboneFast功能。BackboneFast不支持令牌环VLAN，但在一些第三方的交换机上也支持。
要在IOS系统交换机上全局启用BackboneFast功能，可以按照表12-33所示的步骤进行。
表12-33 在IOS系统交换机上全局启用BackboneFast功能的步骤
|
步骤 |
命令 |
用途说明 |
|
1 |
Switch(config)# [no] spanning-tree backbonefast |
启用BackboneFast功能。可以使用no关键字禁止BackboneFast功能 |
|
2 |
Switch(config)# end |
退出配置模式 |
|
3 |
Switch# show spanning-tree backbonefast |
校验BackboneFast功能是否启用 |
【示例1】在交换机上启用BackboneFast功能。
Switch(config)# spanning-tree backbonefast
Switch(config)# end
Switch#
【示例2】校验交换机是否启用了BackboneFast功能（注意输出信息中的粗体字部分）。
Switch# show spanning-tree backbonefast
BackboneFast is enabled
BackboneFast statistics
-----------------------
Number of transition via backboneFast (all VLANs) : 0
Number of inferior BPDUs received (all VLANs) : 0
Number of RLQ request PDUs received (all VLANs) : 0
Number of RLQ response PDUs received (all VLANs) : 0
Number of RLQ request PDUs sent (all VLANs) : 0
Number of RLQ response PDUs sent (all VLANs) : 0
Switch#
【示例3】显示交换机的端口状态汇总（注意输出信息中的粗体字部分）。
Switch#show spanning-tree summary
Root bridge for:VLAN0001, VLAN1002-VLAN1005
Extended system ID is disabled
Portfast is enabled by default
PortFast BPDU Guard is disabled by default
Portfast BPDU Filter is enabled by default
Loopguard is disabled by default
EtherChannel misconfiguration guard is enabled
UplinkFast is enabled
BackboneFast is enabled
Pathcost method used is short
Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001 0 0 0 3 3
VLAN1002 0 0 0 2 2
VLAN1003 0 0 0 2 2
VLAN1004 0 0 0 2 2
VLAN1005 0 0 0 2 2
---------------------- -------- --------- -------- ---------- ----------
5 vlans 0 0 0 11 11
BackboneFast statistics
-----------------------
Number of transition via backboneFast (all VLANs) :0
Number of inferior BPDUs received (all VLANs) :0
Number of RLQ request PDUs received (all VLANs) :0
Number of RLQ response PDUs received (all VLANs) :0
Number of RLQ request PDUs sent (all VLANs) :0
Number of RLQ response PDUs sent (all VLANs) :0
Switch#
