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Say you have a wifi device (D) and a wifi router (R) that have never shared radio waves before, and are within range. How does D discover that R exists? Does R constantly broadcast a message with its MAC, SSID, etc that D will eventually passively pick up? The other way around? Some combination?

In general, what messages are sent between D and R that will ultimately produce that wonderful list of available networks to choose from (including details such as SSID [or lack thereof], encryption mechanism, etc)? Bonus: What, if any, is the difference between this and ARP?

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closed as off topic by Sven, Chopper3, David Schwartz, Ward, Greg Askew Jul 14 '12 at 17:16

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2 Answers 2

up vote 3 down vote accepted

It's called a 802.11 beacon and it broadcasts a lot more information than just the SSID/MAC address.

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The access point broadcasts its SSID periodically (unless configured not to). The client scans the channels looking for SSID broadcasts.

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Really= Is there a way for a device to ASK for a broadcast? How often do they happen? I mean, I can see networks immediately, it does not look like I have to wait for the next braodcast OR the broadcastas are quite frequent. –  TomTom Jul 14 '12 at 7:44
    
There is no way for a device to ask for a broadcast. Typically, an access point broadcasts its SSID ten times per second. –  David Schwartz Jul 14 '12 at 7:46
    
Ok, that explins why I see them "immediately": 10 times per second is quite often. Thanks. –  TomTom Jul 14 '12 at 9:09

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