Abstract: Aspects of the disclosure provide a network device that includes a test frame generator and an analyzer. The test frame generator is configured to generate a request frame that is compliant with a Layer 2 protocol and to transmit the request frame to a target network device that is a member of a virtual local area network (VLAN) of which the network device is also a member. The analyzer is configured to transmit a query to the target network device to detect whether a forwarding database associated with the target network device includes a first media access control (MAC) address of the network device, and to determine whether the target network device is connected to the network device based on the detection.