How does a client locate a WLAN during passive scanning?

• A. The client actively searches by sending probe requests on all channels.
• B. The client listens for beacons until it hears a beacon listing the SSID of the network it expects to join.
• C. The client connects to any available network without filtering.
• D. The client relies on DNS to identify the WLAN.

Answer: (B)

During passive scanning, the client does not transmit anything. It simply listens on each wireless channel for beacon frames that access points periodically broadcast. Those beacons advertise the network’s SSID (along with other details like the AP's BSSID, channel, and supported data rates). When the client hears a beacon that includes the SSID it’s looking for, it recognizes that WLAN is present and can decide to join it. This contrasts with active scanning, where the client sends probe requests to provoke responses and discover networks. DNS has nothing to do with discovering WLANs, since DNS resolves domain names rather than wireless network names. Note that if an SSID isn’t broadcast (hidden), passive listening may not reveal it, which is a nuance of passive discovery.