Move MAC address parts into its own document, signal that modifying it

is optional and in addition tell users how to do so in their operating system.

1 files changed, 99 insertions, 0 deletions

diff --git a/docs/hardware/mac_address.md b/docs/hardware/mac_address.md
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+---
+title: Changing the MAC address
+...
+
+Introduction (GM45)
+===================
+
+On all laptops with the GM45 chipset (T400,R400,T500,X200,X200S,X200T),
+the [MAC address](https://en.wikipedia.org/wiki/MAC_address)
+for the built-in gigabit ethernet controller is stored inside the flash chip,
+along with Libreboot and other configuration data.
+
+Prebuilt Libreboot for these laptops 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` 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).
+
+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
+==================================
+
+The existing MAC address may be obtained by the following methods:
+
+1.  Read the white label on the bottom of the case. Note that this will only
+    produce the correct address, if your motherboard has never been replaced.
+    Examples:
+
+    ![](../install/images/t400/macaddress0.jpg)
+    ![](../install/images/t400/macaddress1.jpg)
+    ![](../install/images/x200/disassembly/0002.jpg)
+    ![](../install/images/x200/disassembly/0001.jpg)
+
+2.  Run `ip link` or `ifconfig` in a terminal/console/shell;
+    look for your ethernet device (e.g., **enpXXX** in Arch-based distributions,
+    or **eth0** in Debian-based distributions),
+    and look for a set of colon-delimited hexadecimal (base 16) digits:
+    0,1,2,3,4,5,6,7,8,9,aA,bB,cC,dD,eE,fF. For example: `00:f3:f0:45:91:fe`.
+
+    * `$ ip link`
+
+         `... link/ether ??:??:??:??:??:?? brd ...`
+
+    * Alternatively:
+
+        `$ ifconfig`
+
+        `... ether ??:??:??:??:??:?? txqueuelen ...`
+
+
+Changing the MAC address in the operating system
+================================================
+
+There are three portable ways of doing so:
+
+1.  Using the new iproute2 package:
+
+    `# ip link set <interface> down`
+
+    `# ip link set dev <interface> address 00:4c:69:62:72:65`
+
+    `# ip link set <interface> up`
+
+
+2.  Using the old `ifconfig` command:
+
+    `# ifconfig <interface> 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 in Libreboot
+=====================================
+
+See [here](../gnulinux/grub_cbfs.md#changeMAC).
+
+
+
+Copyright © 2017 Fedja Beader <fedja@protonmail.ch>
+
+Copyright © 2014, 2015 Leah Rowe <info@minifree.org>
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License Version 1.3 or any later
+version published by the Free Software Foundation
+with no Invariant Sections, no Front Cover Texts, and no Back Cover Texts.
+A copy of this license is found in [../fdl-1.3.md](../fdl-1.3.md)