说明：  某学校网络拓扑模拟图，接入层设备采用S2126G交换机，在接入交换机上划分了办公网VLAN20和学生网VLAN30。为了保证网络的稳定性，接入层和汇聚层通过两条链路相连，
(Simulation of a school network topology map, access layer switches S2126G equipment used in the access switch on the office network division VLAN20 and students Network VLAN30. In order to ensure the stability of the network, access layer and aggregation layers connected through two links,)