For wifi networks that are operated by small businesses, they often ask the user to register a name and accept a TOS agreement before they can start browsing. And later those networks will remember this device and wont ask for information again. I'm wondering how they can tell it's the same device. Is it the mac address, or is there some kind of certificate stored on your device? I tried spoofing the mac on my wifi network the other day, but the network still remembered me. In other words, what are the ways the owner of a network can identify the devices connected to it?