交换机配置SW1,SW2,SW3启用MSTP，实现网络二层负载均衡和冗余备份，创建实例Instance10和Instance20,名称为SKILLS，修订版本为1,其中Instance10关联vlan 60和vlan 70,Instance20关联vlan 80和vlan 90。SW1为Instance0和Instance10的根交换机，为Instance20备份根交换机；SW2为Instance20根交换机，为Instance0和Instance10的备份根交换机；根交换机STP优先级为0,备份根交换机STP优先级为4096.关闭交换机之间三层互联接口的STP

配置SW1:

enable
configure terminal
spanning-tree mode mst
spanning-tree mst configuration
name SKILLS
revision 1
instance 10 vlan 60,70
exit
instance 20 vlan 80,90
exit
spanning-tree instance 0 priority 0
spanning-tree instance 10 priority 0
spanning-tree instance 20 priority 4096
interface <interface_name> (三层互联接口)
spanning-tree mst 0 port-priority 240 (关闭STP)
end
write memory

配置SW2:

enable
configure terminal
spanning-tree mode mst
spanning-tree mst configuration
name SKILLS
revision 1
instance 10 vlan 60,70
exit
instance 20 vlan 80,90
exit
spanning-tree instance 10 priority 4096
spanning-tree instance 20 priority 0
interface <interface_name> (三层互联接口)
spanning-tree mst 0 port-priority 240 (关闭STP)
end
write memory

配置SW3:

enable
configure terminal
spanning-tree mode mst
spanning-tree mst configuration
name SKILLS
revision 1
instance 10 vlan 60,70
exit
instance 20 vlan 80,90
exit
interface <interface_name> (三层互联接口)
spanning-tree mst 0 port-priority 240 (关闭STP)
end
write memory

这样配置可以实现MSTP下的二层负载均衡和冗余备份，并且关闭了交换机之间三层互联接口的STP。注意根交换机和备份根交换机的优先级设置。