Every network interface — wired or Wi-Fi — has a MAC address which is a serial number defined for each interface from factory by its 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.
Having such a unique identifier used on the local network can harm your privacy. Here are two examples:
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.
As explained in our documentation on network fingerprint, someone observing the traffic coming out of your computer on the local network can probably see that you are using Tails. In that case, your MAC address can identify you as a Tails user.
Tails can temporarily change the MAC address of your network interfaces to random values for the time of a working session. This is what we call "MAC address spoofing". MAC address spoofing in Tails hides the serial number of your network interface, and so to some extend, who you are, to the local network.
MAC address spoofing 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 spoofing or not, depending on your situation.
MAC address spoofing is enabled by default for all network interfaces. This is usually beneficial, even if you don't want to hide your geographical location.
Here are a few examples:
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 spoofing 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 spoofing hides the fact that your computer is connected to this network at a particular time. It also hides the fact that you are running Tails on this network.
In some situations MAC address spoofing is not useful but can instead be problematic. In such cases, you might want to disable MAC address spoofing.
Note that even if MAC spoofing is disabled, your anonymity on the Internet is preserved:
- An adversary on the local network can only see encrypted connections to the Tor network.
- Your MAC address is not sent over the Internet to the websites that you are visiting.
However, disabling MAC address spoofing makes it possible again for the local network to track your geographical location. If this is problematic, consider using a different network device or moving to another network.
Here are a few examples:
Using a public computer, for example in an Internet café or a library. This computer is regularly used on this local network, and its MAC address is not associated with your identity. In this case, MAC address spoofing can make it impossible to connect. It can even look suspicious to the network administrators to see an unknown MAC address being used on that network.
On some network interfaces, MAC address spoofing is impossible due to limitations in the hardware or in Linux. Tails temporarily disables such network interfaces. You might disable MAC address spoofing to be able to use them.
Some networks only allow connections from a list of authorized MAC addresses. In this case, MAC address spoofing makes it impossible to connect to such networks. If you were granted access to such network in the past, then MAC address spoofing might prevent you from connecting.
Using your own computer at home. Your identity and the MAC address of your computer are already associated to this local network, so MAC address spoofing is probably useless. But if access to your local network is restricted based on MAC addresses it might be impossible to connect with a spoofed MAC address.
You can disable MAC address spoofing from Tails Greeter:
When Tails Greeter appears, in the Welcome to Tails window, click on the button. Then click on the button.
In the MAC address spoofing section, deselect the Spoof all MAC addresses option.
Other means of surveillance can reveal your geographical location: video surveillance, mobile phone activity, credit card transactions, social interactions, etc.
While using Wi-Fi, anybody within range of your Wi-Fi interface can see your MAC address, even without being connected to the same Wi-Fi access point.
When using mobile phone connectivity, such as 3G or GSM, the identifier of your SIM card (IMSI) and the serial number of your phone (IMEI) are always revealed to the mobile phone operator.
Some captive portals might send your MAC address over the Internet to their authentication servers. This should not affect your decision regarding MAC address spoofing. If you decide to disable MAC address spoofing your computer can already be identified by your ISP.