拓扑：
SW1配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 1
instance 1 vlan 10-19
instance 2 vlan 20-29
!
spanning-tree mst 1-2 priority 24576
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW2配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 1
instance 1 vlan 10-19
instance 2 vlan 20-29
!
spanning-tree mst 1-2 priority 28672
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
duplex auto
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW3配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 2
instance 1 vlan 10-19
instance 2 vlan 20-29
!
spanning-tree mst 1-2 priority 24576
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
duplex auto
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW4配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 2
instance 1 vlan 10-19
instance 2 vlan 20-29
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW5配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 2
instance 1 vlan 10-19
instance 2 vlan 20-29
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW6配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 3
instance 1 vlan 10-19
instance 2 vlan 20-29
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
interface Ethernet0/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW7配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 3
instance 1 vlan 10-19
instance 2 vlan 20-29
!
spanning-tree mst 1-2 priority 24576
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW8配置：
spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mst
revision 3
instance 1 vlan 10-19
instance 2 vlan 20-29
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
!
interface Ethernet0/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree mst 0-2 cost 10
SW9配置：
spanning-tree mode rapid-pvst
spanning-tree extend system-id
!
interface Ethernet0/0
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type point-to-point
分析：
区域A
由于SW1的优先级（24577）小于SW2的优先级（28637）所以对于区域A来说SW1是跟桥。
由于SW3的优先级大于SW4 SW5的优先级，所以在区域B中被选位跟桥。
由于SW7的优先级大于SW6 SW8的优先级，所以在区域C中被选位跟桥。
从上面分析可以看出在区域内的行为和RSTP类似。从这个交换机网络来说不管是MST区域还是非MST区域（SW9）选举跟桥（总根）的行为是一样的既最小的桥ID。
从上图看出如果把区域看做是一个虚拟的交换机，那个在整个区域的行为和RSTP类似。
