Every network interface — wired or Wi-Fi — has a [[!wikipedia MAC address]], which is a serial number assigned to each interface at the factory by the vendor. MAC addresses are used on the local network to identify the communications of each network interface.
While your IP address identifies where you are on the Internet, your MAC address identifies which device you are using on the local network. MAC addresses are only useful on the local network and are not sent over the Internet.
1. If you use your laptop to connect to several Wi-Fi networks, the same MAC address of your Wi-Fi interface is used on all those local networks. Someone observing those networks can recognize your MAC address and **track your geographical location**.
1. Unless you choose to [[hide that you are connecting to the Tor network|anonymous_internet/tor]], someone who monitors your Internet connection can know that. In this case, your MAC address can **reveal that you are a Tor user**.
When MAC address anonymization is enabled, Tails temporarily changes the MAC addresses of your network interfaces to random values for the time of your Tails session.MAC address anonymization hides the serial number of your network interface, and so, to some extent, who you are, from the local network.
MAC address anonymization is enabled by default in Tails because it is usually beneficial. But in some situations it might also lead to connectivity problems or make your network activity look suspicious. This documentation explains whether to use MAC address anonymization or not, depending on your situation.
<p>To learn how Tails implements MAC address anonymization, see our [[design documentation about MAC address anonymization|contribute/design/MAC_address]].</p>
**MAC address anonymization is enabled by default for all network interfaces.** This is usually beneficial, even if you don't want to hide your geographical location.
**Using your own computer on an public network without registration**, for example a free Wi-Fi service in a restaurant where you don't need to register with your identity. In this case, MAC address anonymization hides the fact that your computer is connected to this network.
**Using your own computer on a network that you use frequently**, for example at a friend's place, at work, at university, etc. You already have a strong relationship with this place but MAC address anonymization hides the fact that your computer is connected to this network *at a particular time*. It also hides the fact that *you* are connecting to the Tor network on this network.
