Passive Scan Technique

A.

The passive scan technique used by wireless clients to discover available wireless networks is based on listening for access point (AP) beacons that contain available wireless networks.

Access points periodically broadcast beacons that contain information about the wireless network, such as the network name (SSID), supported data rates, and security settings. When a wireless client is looking for available wireless networks, it listens for these beacons on all available channels. This allows the client to detect and display a list of available wireless networks to the user.

The other options listed in the question, such as sending null probe or association requests, are not used for passive scanning. Instead, these techniques are used for active scanning, where the client actively probes for available networks by sending requests to the APs.

Sending a null probe request involves sending a request for information from a specific access point. The access point will respond with information about its network, such as the SSID and supported data rates. This technique is often used to gather more detailed information about a specific network.

Sending a null association request involves sending a request to join a specific network. The access point will respond with information about the network, including whether the client is authorized to join the network. This technique is used after a client has selected a network to join.

Finally, listening for access point probe response frames is another active scanning technique that involves sending a probe request and waiting for a response from the access point. The response contains information about the network, which the client can use to determine if it wants to join the network.

In summary, the passive scan technique used by wireless clients to discover available wireless networks involves listening for access point beacons that contain information about available networks.