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