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: