PVST+(每个VLAN 的生成树PVST 加)

PVST+(每个VLAN 的生成树PVST 加)

实验拓扑：

分别在 SW1 和SW2 上show spanning-tree 查看结果：

SW1#show spanning-tree

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0008.20ff.6400

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 0008.20ff.6400

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 15

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Desg FWD 19 128.23 P2p

Fa0/24 Desg FWD 19 128.24 P2p

SW2#show spanning-tree

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0008.20ff.6400

Cost 19

Port 23 (FastEthernet0/23)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

注：以上拓扑中经过选举最终SW1 为根网桥，SW2 的F0/24 为blocking 端口，也是就线路2 成为了备

份链路。

分别在 SW1 和SW2 上创建VLAN2，VLAN3，VLAN4，按如下拓扑要求完成本实验：

在 SW1 上创建VLAN2，VLAN3，VLAN4 并查看：

SW1(config)#vlan 2-4

SW1#show vlan

VLAN Name Status Ports

---- -------------------------------- --------- -------------------------------

1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4

Fa0/5, Fa0/6, Fa0/7, Fa0/8

Fa0/9, Fa0/10, Fa0/11, Fa0/12

Fa0/13, Fa0/14, Fa0/15, Fa0/16

Fa0/17, Fa0/18, Fa0/19, Fa0/20

Fa0/21, Fa0/22

2 VLAN0002 active

3 VLAN0003 active

4 VLAN0004 active

在 SW2 上创建VLAN2，VLAN3，VLAN4 并查看:

SW2(config)#vlan 2-4

SW2#show vlan

VLAN Name Status Ports

---- -------------------------------- --------- -------------------------------

1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4

Fa0/5, Fa0/6, Fa0/7, Fa0/8

Fa0/9, Fa0/10, Fa0/11, Fa0/12

Fa0/13, Fa0/14, Fa0/15, Fa0/16

Fa0/17, Fa0/18, Fa0/19, Fa0/20

Fa0/21, Fa0/22

2 VLAN0002 active

3 VLAN0003 active

4 VLAN0004 active

按如下拓扑要求完成本实验：

要求：SW2 的VLAN1 和VLAN2 流量通过线路1 到达SW1 , SW2 的VLAN3 和VLAN4 的流量

经过线路2 到达SW1,当其中一条链路有问题走同一链路.

分别在 SW1 和SW2 上创建了VLAN2-4 后查看目前的生成树状态.

在SW1 上查看:

命令:show spanning-tree vlan 1

show spanning-tree vlan 2

show spanning-tree vlan 3

show spanning-tree vlan 4

SW1#show spanning-tree vlan 1

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0008.20ff.6400

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 0008.20ff.6400

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Desg FWD 19 128.23 P2p

Fa0/24 Desg FWD 19 128.24 P2p

SW1#show spanning-tree vlan 2

VLAN0002

Spanning tree enabled protocol ieee

Root ID Priority 32770

Address 0008.20ff.6400

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32770 (priority 32768 sys-id-ext 2)

Address 0008.20ff.6400

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Desg FWD 19 128.23 P2p

Fa0/24 Desg FWD 19 128.24 P2p

SW1#show spanning-tree vlan 3

VLAN0003

Spanning tree enabled protocol ieee

Root ID Priority 32771

Address 0008.20ff.6400

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32771 (priority 32768 sys-id-ext 3)

Address 0008.20ff.6400

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Desg FWD 19 128.23 P2p

Fa0/24 Desg FWD 19 128.24 P2p

SW1#show spanning-tree vlan 4

VLAN0004

Spanning tree enabled protocol ieee

Root ID Priority 32772

Address 0008.20ff.6400

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32772 (priority 32768 sys-id-ext 4)

Address 0008.20ff.6400

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Desg FWD 19 128.23 P2p

Fa0/24 Desg FWD 19 128.24 P2p

结果:查看生成树状态后发现针对VLAN1,VLAN2,VLAN3,VLAN3,SW1 都是扮演根网桥角

色.SW1 连接SW2 的两个端口F0/23,F0/24 都是指定端口.

在SW2 上查看:

命令:show spanning-tree vlan 1

show spanning-tree vlan 2

show spanning-tree vlan 3

show spanning-tree vlan 4

SW2#show spanning-tree vlan 1

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0008.20ff.6400

Cost 19

Port 23 (FastEthernet0/23)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

SW2#show spanning-tree vlan 2

VLAN0002

Spanning tree enabled protocol ieee

Root ID Priority 32770

Address 0008.20ff.6400

Cost 19

Port 23 (FastEthernet0/23)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32770 (priority 32768 sys-id-ext 2)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

SW2#show spanning-tree vlan 3

VLAN0003

Spanning tree enabled protocol ieee

Root ID Priority 32771

Address 0008.20ff.6400

Cost 19

Port 23 (FastEthernet0/23)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32771 (priority 32768 sys-id-ext 3)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

SW2#show spanning-tree vlan 4

VLAN0004

Spanning tree enabled protocol ieee

Root ID Priority 32772

Address 0008.20ff.6400

Cost 19

Port 23 (FastEthernet0/23)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32772 (priority 32768 sys-id-ext 4)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

结果:查看生成树状态后发现针对VLAN1,VLAN2,VLAN3,VLAN3,SW2 都是扮演非根网桥角色,

SW2 的端口F0/24 都处在blocking 状态.

问题所在：通过在SW1 和SW2 查看得到的结果我们来分析一下,现在SW1 的VLAN1 和VLAN2

是通过线路1 到达SW1 的,这符合本实验的要求,但VLAN3,VLAN4 到SW1 走线路1 不符合本实验的要

求,VLAN3,VLAN4 到SW1 要求走线路2.

分析:SW2 的VLAN3,VLAN4 到SW1 为什么走线路1 呢?因为SW2 相对于VLAN3,VLAN4 来说到

达SW1 F0/24 都是blocking 状态,F0/23 为转发状态,导致VLNA3,VLAN3 通过F0/23 走线路1 到达SW1.

解决方法:在SW2 上VLAN2,VLAN3 要到达SW1 只要SW2 的F0/23 为blocking 状态,F0/24 为转发

状态,就达到本实验的要求(SW2 的VLAN3,VLAN4 到SW1 走线路2)

之所以SW2 的F0/24 为blocking 状态,是因为相对于VLAN3,VLAN4 来说在通过生成树决策的第4

步时,F0/23 端口号小于F0/23,小的优先，Lowest sender port ID 当两台交换机之间有两条线路直连

时会用到这一项，<本实验就是这样>。通过以上分析,在SW2 上相对于VLAN3,VLAN4 来说,我们可以

更改参数,也就是在生成树决策的第2 步就可以做出决策，即使用Lowest path cost to root bridge

（到达根的最小路径开销）。

在SW2 上相对于VLAN3,VLAN4 更F0/24 到根(SW1)的花费,目前为19,F0/23 到根也为19,我们更

改F0/24 端口到达SW1 的花费为18 就可以满足本实验的要求.

在SW2 上配置以下命令:

SW2(config)#interface fastEthernet 0/24

SW2(config-if)#spanning-tree vlan 3-4 cost 18

查看更改的配置:

SW2#show run int f0/24

interface FastEthernet0/24

spanning-tree vlan 3-4 cost 18

end

做上以上配置后在SW2 上查看当前的VLAN3,VLAN4 的生成树状态:

SW2#show spanning-tree vlan 3

VLAN0003

Spanning tree enabled protocol ieee

Root ID Priority 32771

Address 0008.20ff.6400

Cost 18

Port 24 (FastEthernet0/24)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32771 (priority 32768 sys-id-ext 3)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Altn BLK 19 128.23 P2p

Fa0/24 Root FWD 18 128.24 P2p

SW2#show spanning-tree vlan 4

VLAN0004

Spanning tree enabled protocol ieee

Root ID Priority 32772

Address 0008.20ff.6400

Cost 18

Port 24 (FastEthernet0/24)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32772 (priority 32768 sys-id-ext 4)

Address 000d.bce7.5940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/23 Altn BLK 19 128.23 P2p

Fa0/24 Root FWD 18 128.24 P2p

通过命令show spanning-tree vlan 3 , show spanning-tree vlan 4 查看,我们发现F0/23 为blocking 状

态,SW2 的VLAN3,VLAN4 到达SW1 的通过F0/24 到达,也就是走线路2,实现在本实验的要求。最终线

路1,线路2 流量走势图: