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When cell phone try to connect AP, it sends probe request and it include all past SSID history in it. Strangely enough, when I run a MAC-built-in data packet sniffing program, called Wifi-Diagnostic, it show only two ssid which I had connected 6 monthes ago. I want to know why. Thanks^^

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This is generally the case because they want to simplify the UI, specifically avoiding options that many users don't really understand or can cause them problems. The 802.11 feature that leads to the SSID being part of the probe request is the ability to provide a non-broadcast SSID (i.e. hidden SSID).

For a client to connect to an SSID that is non-broadcast, it has to specifically know the SSID name. Many people use this believing it to be some sort of security feature, but anyone who wants to figure out the SSID can do so with almost no effort.

Generally speaking probe requests, while always broadcast, function in one of two ways. They can send out a generic request ("Hey, is anybody out there?") or a more specific request ("Hey, is Bob out there?").

In some operating systems, you can specify that the probe request should include the latter by selecting some sort of "Connect even if the network is not broadcasting its name (SSID)" (Windows 7 example) so that it can connect to a non-broadcast SSID.

However in some operating systems and many mobile devices, they streamline the UI for connecting to an 802.11 network. The reasoning goes like so:

  • A client device can connect to a broadcast SSID with either type of probe.
  • A client device requires the more specific probe to connect to a non-broadcast SSID.
  • By using the more specific probe, the device will be able to connect to either type of network.

End result is that is what they have the device do by default, leaving one less option that may confuse or cause problems for a user.

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