SW1：
<HW-SW1>sys //进入系统视图
[HW-SW1]stp mode stp //生成树为STP
[HW-SW1]stp priority 0 //STP生成树优先级为零

SW2：
<HW-SW2>sys //进入系统视图
[HW-SW2]stp mode stp //生成树为STP
[HW-SW2]stp priority 4096 //STP生成树优先级为4096

SW3更改前：
<HW-SW3>dis stp brief //查看生成树概述
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/1 ROOT FORWARDING NONE
0 GigabitEthernet0/0/3 ALTE DISCARDING NONE
0 GigabitEthernet0/0/10 DESI FORWARDING NONE
0 GigabitEthernet0/0/11 DESI FORWARDING NONE
0 GigabitEthernet0/0/12 DESI FORWARDING NONE
SW3更改后：
<HW-SW3>dis stp brief //查看生成树概述
MSTID Port Role STP State Protection
0 GigabitEthernet0/0/1 ALTE DISCARDING NONE
0 GigabitEthernet0/0/3 ROOT FORWARDING NONE
0 GigabitEthernet0/0/10 DESI LEARNING NONE
0 GigabitEthernet0/0/11 DESI LEARNING NONE
0 GigabitEthernet0/0/12 DESI LEARNING NONE
<HW-SW3>