mstp實例分析

拓撲：

 

 

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：

區域A

 因爲SW1的優先級（24577）小於SW2的優先級（28637）因此對於區域A來講SW1是跟橋。

因爲SW3的優先級大於SW4 SW5的優先級，因此在區域B中被選位跟橋。

因爲SW7的優先級大於SW6 SW8的優先級，因此在區域C中被選位跟橋。

從上面分析能夠看出在區域內的行爲和RSTP相似。從這個交換機網絡來講無論是MST區域仍是非MST區域（SW9）選舉跟橋（總根）的行爲是同樣的既最小的橋ID。

 

 

從上圖看出若是把區域看作是一個虛擬的交換機，那個在整個區域的行爲和RSTP相似。