Network infrastructure needs to be managed in response to frequent revisions of organization. VLAN (Virtual LAN) is a key technology for flexibly configuring the network. It enables to reconfigure the network without changing physical cabling for accommodating it to the current organizational structure. Accurately configuring VLAN structure, however, is a complicated task and highly-skilled administrators can only perform the task. In this paper, we propose a mobile assistant for visually administering VLAN configuration using AR (Augmented Reality). When an administrator simply looks at a specific switch device, the proposed system acquires the latest configuration information about the device and graphically superimposes the result. The administrator can also invoke some commands to validate the configuration result without typing them by using the system. It can assist even less-experienced administrators to easily grasp the VLAN configuration and perform some basic management tasks.