GNU Boot – Changing the MAC address

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# Introduction (GM45+e1000)

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This section is applicable to all Libreboot-supported laptops with the mobile 4 series chipset (as shown in `$ lspci`) that use the e1000 ethernet controller (e.g. T400, X200). The R500 is an exception to this as it does not use the built-in e1000.

On all these laptops, the MAC address for the built-in gigabit ethernet controller is stored inside the flash chip, along with Libreboot and other configuration data. Therefore, installing Libreboot will overwrite it.

Thus, for these laptops, prebuilt Libreboot already contains a generic MAC address in the configuration section. This address is `00:f5:f0:40:71:fe in builds before 2018-01-16 and`00:4c:69:62:72:65` (see the ascii character set) afterwards. Unless you change it, your computer will boot and use it. This can lead to network problems if you have more than one Libreboot computer on the same layer2 network (e.g. on the same network switch). The switch (postman) will simply not know who to deliver to as the MAC (house) addresses will be the same.

To prevent these address clashes, you can either modify prebuilt Libreboot to use an address of your own choosing or you can change the address in your operating system’s boot scripts.

In either case, it is a good idea to write down the address that your computer originally had.

# Obtaining the existing MAC address

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The existing MAC address may be obtained by the following methods:

1. Run `ip link` or `ifconfig` in a terminal/console/shell; find your ethernet device (e.g., enpXXX or ethXXX), and look for a set of 12 colon-delimited hexadecimal digits. For example: `00:f3:f0:45:91:fe`.

   - `$ ip link

     … link/ether ??:??:??:??:??:?? brd …

   - Alternatively:

     ifconfig

     … ether ??:??:??:??:??:?? txqueuelen …

2. Otherwise you can read the white label that is often found on the motherboard under the memory sticks:

3. The MAC address is usually listed on the laptop chassis as well. This one will be incorrect if the motherboard was changed and the stickers were not updated.

# Changing the MAC address in the operating system

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There are three portable ways of doing so:

1. Using the new iproute2 package:

   ip link set down

   ip link set dev address 00:4c:69:62:72:65

   ip link set up

2. Using the old `ifconfig` command:

   ifconfig hw ether 00:4c:69:62:72:65

3. Using the macchanger package.

You can use use of these three methods in your operating system’s init scripts or you can use your operating system’s own networking configuration. Refer to your operating system’s documentation for how to do this.

# Changing the MAC address on X200/T400/T500/W500

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On GM45 laptops with ICH9M southbridge and Intel PHY module, the MAC address is hardcoded in boot flash, which means it can be changed if you re-flash.

See ich9utils documentation

Markdown file for this page: https://gnu.org/software/gnuboot/web/docs/hardware/mac_address.md