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1<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-rename-ifs">
2 <title>Renaming network interfaces</title>
3 <para>
4 NixOS uses the udev
5 <link xlink:href="https://systemd.io/PREDICTABLE_INTERFACE_NAMES/">predictable
6 naming scheme</link> to assign names to network interfaces. This
7 means that by default cards are not given the traditional names like
8 <literal>eth0</literal> or <literal>eth1</literal>, whose order can
9 change unpredictably across reboots. Instead, relying on physical
10 locations and firmware information, the scheme produces names like
11 <literal>ens1</literal>, <literal>enp2s0</literal>, etc.
12 </para>
13 <para>
14 These names are predictable but less memorable and not necessarily
15 stable: for example installing new hardware or changing firmware
16 settings can result in a
17 <link xlink:href="https://github.com/systemd/systemd/issues/3715#issue-165347602">name
18 change</link>. If this is undesirable, for example if you have a
19 single ethernet card, you can revert to the traditional scheme by
20 setting
21 <xref linkend="opt-networking.usePredictableInterfaceNames" /> to
22 <literal>false</literal>.
23 </para>
24 <section xml:id="sec-custom-ifnames">
25 <title>Assigning custom names</title>
26 <para>
27 In case there are multiple interfaces of the same type, it’s
28 better to assign custom names based on the device hardware
29 address. For example, we assign the name <literal>wan</literal> to
30 the interface with MAC address
31 <literal>52:54:00:12:01:01</literal> using a netword link unit:
32 </para>
33 <programlisting language="bash">
34systemd.network.links."10-wan" = {
35 matchConfig.MACAddress = "52:54:00:12:01:01";
36 linkConfig.Name = "wan";
37};
38</programlisting>
39 <para>
40 Note that links are directly read by udev, <emphasis>not
41 networkd</emphasis>, and will work even if networkd is disabled.
42 </para>
43 <para>
44 Alternatively, we can use a plain old udev rule:
45 </para>
46 <programlisting language="bash">
47services.udev.initrdRules = ''
48 SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", \
49 ATTR{address}=="52:54:00:12:01:01", KERNEL=="eth*", NAME="wan"
50'';
51</programlisting>
52 <warning>
53 <para>
54 The rule must be installed in the initrd using
55 <literal>services.udev.initrdRules</literal>, not the usual
56 <literal>services.udev.extraRules</literal> option. This is to
57 avoid race conditions with other programs controlling the
58 interface.
59 </para>
60 </warning>
61 </section>
62</section>