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Comment by keithpeter | Hacker News Reader

The small educational centre where I teach has recently provided free wifi to users of the building. It is a good connection. You have to give a mobile phone number once to use the system.

This morning, I went in with my old Thinkpad on which I have replaced Xubuntu with Slackware/MLED including a complete reformat and encryption of the SSD. The wifi recognised the machine and greeted me by name. I can only assume that the server is recording the MAC addresses of devices that use the system. That is just about the only thing left that it could be reading.

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> the server is recording the MAC addresses

I believe WiFi routers have options for white-listing devices by MAC address. Probably being done automatically in your building.

> You have to give a mobile phone number once to use the system.

I encountered this problem in Dublin airport a few years ago, before they switched to a different wifi provider.

The authentication code to join the wifi network would be sent by SMS. Which seems clever, until you realise that many people transiting Dublin won't have international roaming ( I didn't ) so can't receive the SMS.

That will probably be the new normal.

When toll-free phone number services started providing number identification to the service in the 1980s, American Express had their system look up the customer's record from the phone number, and their operators started greeting customers by name. Some customers saw this as "creepy", and American Express stopped such greetings, although the customer's record was still looked up.

Today, everybody has caller ID and name lookup.

Why do machines broadcast MAC addresses to networks? to identify themselves? Is it easy to randomize your MAC?

> Is it easy to randomize your MAC?

It would appear to be: http://www.zdziarski.com/blog/?p=2738

Yes, computers broadcast their MAC address when they first connect to a network so that they can, for example, obtain an IP address via DHCP. However the MAC address isn't forwarded beyond the LAN to which the computer is connected.

https://en.wikipedia.org/wiki/Address_Resolution_Protocol

MAC addresses are part of the link layer of an Ethernet network. The same link layer segment of a network must have unique MAC addresses so that packets can be unambiguously routed to the correct destination. MAC addresses actually consist of two parts, one part is assigned to the manufacturer, the other part is basically a serial number that the manufacturer generates. So from looking at a MAC address, you can look up who manufactured the device. The MAC addresses are not broadcast beyond the layer 2 network segment that you're connected to. However, that does mean that anyone in range can read the MAC address of your wifi card as it is sent 'in the clear' (not encrypted). Generally MAC addresses are also used for access control (though this is not particularly effective as MAC addresses can be spoofed) and for long-term IP address assignments (same IP can be assigned on subsequent connections).

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