2.6 实训二 生成树协议STP配置
1.实验目的
掌握启用和关闭STP的方法；了解不同STP模式的差异；掌握修改网桥优先级影响根网桥选举的方法；掌握修改端口优先级影响根端口与指定端口选举的方法；掌握配置边缘端口的方法。
2.实验拓扑
生成树拓扑如图2-37所示。
图2-37 生成树拓扑
3.配置步骤
step1:STP配置。
实验之前，关闭S3的接口E0/0/1，以避免对实验的影响。请保证设备以空配置启动，如果设备默认生成树没有开启，使用stp enable命令开启。本次实验使用传统生成树。
<Quidway>system-view
Enter system view,return user view with Ctrl+Z.
[Quidway]sysname S1
[S1]stp mode stp
[S1]stp root secondary
===========================================
<Quidway>system-view
Enter system view,return user view with Ctrl+Z.
[Quidway]sysname S2
[S2]stp mode stp
[S2]stp root primary
===========================================
<Quidway>system-view
Enter system view,return user view with Ctrl+Z.
[Quidway]sysname S3
[S3]stp mode stp
===========================================
<Quidway>system-view
Enter system view,return user view with Ctrl+Z.
[Quidway]sysname S4
[S4]stp mode stp
使用display stp brief命令查看各接口简要STP状态。
[S1]display stp brief
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/9 ROOT FORWARDING NONE
0 GigabitEthernet0/0/10 ALTE DISCARDING NONE
0 GigabitEthernet0/0/13 DESI FORWARDING NONE
0 GigabitEthernet0/0/14 DESI FORWARDING NONE
[S2]display stp brief
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/9 DESI FORWARDING NONE
0 GigabitEthernet0/0/10 DESI FORWARDING NONE
0 GigabitEthernet0/0/23 DESI FORWARDING NONE
0 GigabitEthernet0/0/24 DESI FORWARDING NONE
[S3]display stp brief
MSTID Port Role STP State Protection
0 Ethernet0/0/13 ALTE DISCARDING NONE
0 Ethernet0/0/23 ROOT FORWARDING NONE
[S4]display stp brief
MSTID Port Role STP State Protection
0 Ethernet0/0/14 ALTE DISCARDING NONE
0 Ethernet0/0/24 ROOT FORWARDING NONE
使用display stp interface命令查看某接口详细STP状态。
[S1]display stp interface GigabitEthernet 0/0/10
----[CIST][Port10（GigabitEthernet0/0/10）][DISCARDING]---
Port Protocol :enabled
Port Role :Alternate Port
Port Priority :128
Port Cost（Dot1T ） :Config=auto / Active=20000
Desg.Bridge/Port :0.0018-82e1-aea6 / 128.10
Port Edged :Config=default / Active=disabled
Point-to-point :Config=auto / Active=true
Transit Limit :147 packets/hello-time
Protection Type :None
Port Stp Mode :STP
Port Protocol Type :Config=auto / Active=dot1s
PortTimes :Hello 2s MaxAge 20s FwDly 15s RemHop 0
TC or TCN send :2
TC or TCN received :64
BPDU Sent :24
TCN:0,Config:0,RST:24,MST:0
BPDU Received :350601
TCN:0,Config:0,RST:350601,MST:0
step2：根网桥选举控制。
使用display stp命令查看当前根网桥消息。
[S2]display stp
-------[CIST Global Info][Mode STP]------
CIST Bridge :0 .0018-82e1-aea6
Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC :0 .0018-82e1-aea6 / 0
CIST RegRoot/IRPC :0 .0018-82e1-aea6 / 0
CIST RootPortId :0.0
BPDU-Protection :disabled
CIST Root Type :PRIMARY root
TC or TCN received :41
TC count per hello :0
STP Converge Mode :Nomal
Time since last TC :0 days 0h:1m:6s
······output omit······
实验中特别定义了S2为主根网桥，S1为备份根网桥。如上输出“CIST Bridge”“CIST Root/ERPC”字段值相同的即为根网桥。
桥优先级数值越小的优先级越高，因此将S1的桥优先级修改为4096，将S2的桥优先级修改为8192,S1的优先级高于S2,S1将选举为根网桥。
[S1]undo stp root
[S1]stp priority 4096
[S2]undo stp root
[S2]stp priority 8192
使用display stp命令查看新的根网桥信息。
[S1]display stp
-------[CIST Global Info][Mode STP]------
CIST Bridge :4096 .0018-82e1-aea6
Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC :4096 .0018-82e1-aea6 / 0
CIST RegRoot/IRPC :4096 .0018-82e1-aea6 / 0
CIST RootPortId :0.0
BPDU-Protection :disabled
TC or TCN received :62
TC count per hello :0
STP Converge Mode :Nomal
Time since last TC :0 days 0h:0m:3s
······output omit······
[S2]display stp
-------[CIST Global Info][Mode STP]------
CIST Bridge :8192 .0018-82e1-ae82
Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC :4096 .0018-82e1-aea6 / 20000
CIST RegRoot/IRPC :8192 .0018-82e1-ae82 / 0
CIST RootPortId :128.9
BPDU-Protection :disabled
TC or TCN received :174
TC count per hello :2
STP Converge Mode :Nomal
Time since last TC :0 days 0h:0m:1s
······output omit······
由以上输出可以看出，S1成为了新的根网桥。关闭S1上的G0/0/9、G0/0/10、G0/0/13、G0/0/14四个接口达到隔离S1的目的。
[S1]interface GigabitEthernet 0/0/9
[S1-GigabitEthernet0/0/9]shutdown
[S1-GigabitEthernet0/0/9]interface GigabitEthernet 0/0/10
[S1-GigabitEthernet0/0/10]shutdown
[S1-GigabitEthernet0/0/10]interface GigabitEthernet 0/0/13
[S1-GigabitEthernet0/0/13]shutdown
[S1-GigabitEthernet0/0/13]interface GigabitEthernet 0/0/14
[S1-GigabitEthernet0/0/14]shutdown
[S2]display stp
-------[CIST Global Info][Mode STP]------
CIST Bridge :8192 .0018-82e1-ae82
Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC :8192 .0018-82e1-ae82 / 0
CIST RegRoot/IRPC :8192 .0018-82e1-ae82 / 0
CIST RootPortId :0.0
BPDU-Protection :disabled
TC or TCN received :197
TC count per hello :0
STP Converge Mode :Nomal
Time since last TC :0 days 0h:0m:3s
······output omit······
由以上粗体字部分可以看出，在S1失效的情况下，S2由备份根网桥成为了根网桥。
开启S1之前关闭的接口。
[S1]interface GigabitEthernet 0/0/9
[S1-GigabitEthernet0/0/9]undo shutdown
[S1-GigabitEthernet0/0/9]interface GigabitEthernet 0/0/10
[S1-GigabitEthernet0/0/10]undo shutdown
[S1-GigabitEthernet0/0/10]interface GigabitEthernet 0/0/13
[S1-GigabitEthernet0/0/13]undo shutdown
[S1-GigabitEthernet0/0/13]interface GigabitEthernet 0/0/14
[S1-GigabitEthernet0/0/14]undo shutdown
[S1]display stp
-------[CIST Global Info][Mode STP]------
CIST Bridge :4096 .0018-82e1-aea6
Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC :4096 .0018-82e1-aea6 / 0
CIST RegRoot/IRPC :4096 .0018-82e1-aea6 / 0
CIST RootPortId :0.0
BPDU-Protection :disabled
TC or TCN received :63
TC count per hello :0
STP Converge Mode :Nomal
Time since last TC :0 days 0h:1m:6s
······output omit······
[S2]display stp
-------[CIST Global Info][Mode STP]------
CIST Bridge :8192 .0018-82e1-ae82
Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
CIST Root/ERPC :4096 .0018-82e1-aea6 / 20000
CIST RegRoot/IRPC :8192 .0018-82e1-ae82 / 0
CIST RootPortId :128.9
BPDU-Protection :disabled
TC or TCN received :251
TC count per hello :0
STP Converge Mode :Nomal
Time since last TC :0 days 0h:0m:1s
······output omit······
由以上输出可以看出，当S1恢复后重新被选举成为根网桥。
step3：根端口选举控制。
在S2上使用display stp brief查看当前接口的角色信息。
[S2]display stp brief
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/9 ROOT FORWARDING NONE
0 GigabitEthernet0/0/10 ALTE DISCARDING NONE
0 GigabitEthernet0/0/23 DESI FORWARDING NONE
0 GigabitEthernet0/0/24 DESI FORWARDING NONE
此时，G0/0/9为根端口，G0/0/10为替代端口，将在下面通过修改S1端口优先级的方式实现S2端口G0/0/10成为根端口，G0/0/9成为替代端口。
修改S1接口G0/0/9和G0/0/10的端口优先级。端口优先级默认值为128，数值越大优先级越小，因此在下面实验中将S1的接口G0/0/9端口优先级设置为32,G0/0/10端口优先级设置为16，这样S1的接口G0/0/10优先级高于G0/0/9,S2的接口G0/0/10将选举成为新的根端口。
[S1]interface GigabitEthernet 0/0/9
[S1-GigabitEthernet0/0/9]stp port priority 32
[S1-GigabitEthernet0/0/9]interface GigabitEthernet 0/0/10
[S1-GigabitEthernet0/0/10]stp port priority 16
提示：此处是修改S1的端口优先级，而不是修改S2的端口优先级。
[S1]display stp interface GigabitEthernet 0/0/9
----[CIST][Port9（GigabitEthernet0/0/9）][FORWARDING]---
Port Protocol :enabled
Port Role :Designated Port
Port Priority :32
Port Cost（Dot1T ） :Config=auto / Active=20000
Desg.Bridge/Port :4096.0018-82e1-aea6 / 32.9
Port Edged :Config=default / Active=disabled
Point-to-point :Config=auto / Active=true
Transit Limit :147 packets/hello-time
Protection Type :None
Port Stp Mode :STP
Port Protocol Type :Config=auto / Active=dot1s
PortTimes :Hello 2s MaxAge 20s FwDly 15s RemHop 20
TC or TCN send :0
TC or TCN received :0
BPDU Sent :229
TCN:0,Config:229,RST:0,MST:0
BPDU Received :3
TCN:1,Config:2,RST:0,MST:0
[S1]display stp interface GigabitEthernet 0/0/10
----[CIST][Port10（GigabitEthernet0/0/10）][FORWARDING]---
Port Protocol :enabled
Port Role :Designated Port
Port Priority :16
Port Cost（Dot1T ） :Config=auto / Active=20000
Desg.Bridge/Port :4096.0018-82e1-aea6 / 16.10
Port Edged :Config=default / Active=disabled
Point-to-point :Config=auto / Active=true
Transit Limit :147 packets/hello-time
Protection Type :None
Port Stp Mode :STP
Port Protocol Type :Config=auto / Active=dot1s
PortTimes :Hello 2s MaxAge 20s FwDly 15s RemHop 20
TC or TCN send :0
TC or TCN received :0
BPDU Sent :210
TCN:0,Config:210,RST:0,MST:0
BPDU Received :3
TCN:1,Config:2,RST:0,MST:0
在S2上使用display stp brief查看当前接口的角色信息。
[S2]display stp brief
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/9 ALTE DISCARDING NONE
0 GigabitEthernet0/0/10 ROOT FORWARDING NONE
0 GigabitEthernet0/0/23 DESI FORWARDING NONE
0 GigabitEthernet0/0/24 DESI FORWARDING NONE
由上输出可以看出，S2的接口G0/0/10被选举成了新的根端口，G0/0/9成了替代端口。关闭S2上的根端口G0/0/10，观察替代端口选举为新的根端口情况。
[S2]interface GigabitEthernet 0/0/10
[S2-GigabitEthernet0/0/10]shutdown
<S2>display stp brief
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/9 ROOT FORWARDING NONE
0 GigabitEthernet0/0/23 DESI FORWARDING NONE
0 GigabitEthernet0/0/24 DESI FORWARDING NONE
此时G0/0/9被选举成为了新的根端口。
step4：边缘端口配置。
将连接用户终端设备如计算机的端口配置成边缘端口，可以使该端口无须经历STP计算过程快速进入转发状态。本任务中，仅示例将S3接口E0/0/3、E0/0/4配置成边缘端口，实际网络中可以根据需要配置。
[S3]interface Ethernet0/0/3
[S3-Ethernet0/0/3]stp edged-port enable
[S3-Ethernet0/0/3]interface Ethernet0/0/4
[S3-Ethernet0/0/4]stp edged-port enable
配置完成后可以将计算机网线接入到S3的E0/0/3，在S3上使用display stp brief命令查看端口状态。由于E0/0/2是边缘端口，发现端口立刻就转变到“Forwarding”状态了。
而连接到其他没有配置边缘端口的如E0/0/5接口，则在链路UP之后要等待约30s才能达到“Forwarding”状态。