生成树协议是一种二层管理协议，它通过有选择性地阻塞网络冗余链路来达到消除网络二层环路的目的，同时具备链路的备份功能。
每个VLAN都生成一棵树是一种比较直接，而且最简单的解决方法。它能够保证每一个VLAN都不存在环路。但是由于种种原因，以这种方式工作的生成树协议并没有形成标准，而是各个厂商各有一套，尤其是以Cisco的VLAN生成树PVST(Per VLAN Spanning Tree)为代表。
SW1，SW2，SW3同一的配置。 SW1为例
Switch>en
Switch#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#hostname SW1 SW1(config)#interface range fastEthernet /- SW1(config-if-range)#switchport mode trunk SW1(config-if-range)#end SW1#show interfaces trunk
Port Mode Encapsulation Status Native vlan
Fa0/ on .1q trunking
Fa0/ on .1q trunking Port Vlans allowed on trunk
Fa0/ -
Fa0/ - Port Vlans allowed and active in management domain
Fa0/
Fa0/ Port Vlans in spanning tree forwarding state and not pruned
Fa0/ none
Fa0/ none SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z. SW1(config)#vlan
SW1(config-vlan)#name caiwu
SW1(config-vlan)#vlan
SW1(config-vlan)#name it SW1(config)#end SW1#show vlan brief VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
default active Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Gig0/, Gig0/
caiwu active
it active
fddi-default active
token-ring-default active
fddinet-default active
trnet-default
SW3 划分VLAN 配置
SW3#conf t
Enter configuration commands, one per line. End with CNTL/Z. SW3(config)#interface range fastEthernet /- SW3(config-if-range)#switchport mode access SW3(config-if-range)#switchport access vlan SW3(config-if-range)#interface range fastEthernet /- SW3(config-if-range)#switchport mode access SW3(config-if-range)#switchport access vlan
SW3(config-if-range)#end SW3#show vlan brief VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
default active Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Fa0/, Fa0/
Fa0/, Fa0/, Gig0/, Gig0/
caiwu active Fa0/, Fa0/
it active Fa0/, Fa0/
fddi-default active
token-ring-default active
fddinet-default active
trnet-default active
SW3#
查看
BID：优先级+MAC （MAC地址数字越小，为根桥）
SW1 SW1#show version 63488K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : 0001.9766.27A9
Motherboard assembly number : --
Power supply part number : --
Motherboard serial number : FOC103248MJ
Power supply serial number : DCA102133JA
Model revision number : B0
Motherboard revision number : C0
Model number : WS-C2960-24TT
System serial number : FOC1033Z1EY SW2 SW2#show version 63488K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : .E44D.7A96
Motherboard assembly number : --
Power supply part number : --
Motherboard serial number : FOC103248MJ
Power supply serial number : DCA102133JA
Model revision number : B0
Motherboard revision number : C0
Model number : WS-C2960-24TT
System serial number : FOC1033Z1EY SW3 SW3#show version
63488K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : 00D0.97CD.098A
Motherboard assembly number : --
Power supply part number : --
Motherboard serial number : FOC103248MJ
Power supply serial number : DCA102133JA
Model revision number : B0
Motherboard revision number : C0
Model number : WS-C2960-24TT
System serial number : FOC1033Z1EY
SW1
SW1#show spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority
Address 0001.9766.27A9
This bridge is the root
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address 0001.9766.27A9
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Desg FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p VLAN0002
Spanning tree enabled protocol ieee
Root ID Priority
Address 0001.9766.27A9
This bridge is the root
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address 0001.9766.27A9
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Desg FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p VLAN0003
Spanning tree enabled protocol ieee
Root ID Priority
Address 0001.9766.27A9
This bridge is the root
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address 0001.9766.27A9
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Desg FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p
SW1 SW2 SW3 配置快速STP
SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#sp
SW1(config)#spanning-tree mode ?
pvst Per-Vlan spanning tree mode
rapid-pvst Per-Vlan rapid spanning tree mode SW1(config)#spanning-tree mode rapid-pvst
根 负载均衡 配置。 默认（4096）倍数 primary -4096-4096 ... secondary -4096
SW1成为VLAN2的根，VLAN3的备份根
SW2成为VLAN3的根, VLAB2的备份根
SW1
SW1(config)#spanning-tree vlan priority ?
<-> bridge priority in increments of #可以使用思科的宏命令
SW1(config)#spanning-tree vlan root primary SW1(config)#spanning-tree vlan root secondary SW1#show running-config
Building configuration... Current configuration : bytes
!
version 12.2
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname SW1
!
!
!
!
!
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 2 priority 24576
spanning-tree vlan 3 priority 28672
!
interface FastEthernet0/
!
SW2
SW2>en
SW2#conf t
Enter configuration commands, one per line. End with CNTL/Z. SW2(config)#spanning-tree vlan root ?
primary Configure this switch as primary root for this spanning tree #相反
SW2(config)#spanning-tree vlan root primary SW2(config)#spanning-tree vlan root secondary SW2#show running-config
Building configuration... Current configuration : bytes
!
version 12.2
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname SW2
!
!
!
!
!
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 3 priority 24576
spanning-tree vlan 2 priority 28672
查看是否配置正确
SW1
SW1# show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority
Address 0001.9766.27A9
This bridge is the root
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address 0001.9766.27A9
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Desg FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority
Address 0001.9766.27A9
This bridge is the root
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address 0001.9766.27A9
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Desg FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p VLAN0003
Spanning tree enabled protocol rstp
Root ID Priority
Address .E44D.7A96
Cost
Port (FastEthernet0/)
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address 0001.9766.27A9
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Root FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p
SW2
SW2# show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority
Address 0001.9766.27A9
Cost
Port (FastEthernet0/)
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address .E44D.7A96
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Root FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority
Address 0001.9766.27A9
Cost
Port (FastEthernet0/)
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address .E44D.7A96
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Root FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p VLAN0003
Spanning tree enabled protocol rstp
Root ID Priority
Address .E44D.7A96
This bridge is the root
Hello Time sec Max Age sec Forward Delay sec Bridge ID Priority (priority sys-id-ext )
Address .E44D.7A96
Hello Time sec Max Age sec Forward Delay sec
Aging Time Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/ Desg FWD 128.23 P2p
Fa0/ Desg FWD 128.24 P2p