12bab91d3b
For reliably identifying network interfaces, `PermanentMACAddress` is likely to be preferable to `MACAddress`. NetworkManager in particular commonly changes the MAC address of wireless interfaces. Reference: - https://www.freedesktop.org/software/systemd/man/systemd.link.html#PermanentMACAddress=
52 lines
1.8 KiB
Markdown
52 lines
1.8 KiB
Markdown
# Renaming network interfaces {#sec-rename-ifs}
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NixOS uses the udev [predictable naming
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scheme](https://systemd.io/PREDICTABLE_INTERFACE_NAMES/) to assign names
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to network interfaces. This means that by default cards are not given
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the traditional names like `eth0` or `eth1`, whose order can change
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unpredictably across reboots. Instead, relying on physical locations and
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firmware information, the scheme produces names like `ens1`, `enp2s0`,
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etc.
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These names are predictable but less memorable and not necessarily
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stable: for example installing new hardware or changing firmware
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settings can result in a [name
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change](https://github.com/systemd/systemd/issues/3715#issue-165347602).
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If this is undesirable, for example if you have a single ethernet card,
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you can revert to the traditional scheme by setting
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[](#opt-networking.usePredictableInterfaceNames)
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to `false`.
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## Assigning custom names {#sec-custom-ifnames}
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In case there are multiple interfaces of the same type, it's better to
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assign custom names based on the device hardware address. For example,
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we assign the name `wan` to the interface with MAC address
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`52:54:00:12:01:01` using a netword link unit:
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```nix
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systemd.network.links."10-wan" = {
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matchConfig.PermanentMACAddress = "52:54:00:12:01:01";
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linkConfig.Name = "wan";
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};
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```
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Note that links are directly read by udev, *not networkd*, and will work
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even if networkd is disabled.
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Alternatively, we can use a plain old udev rule:
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```nix
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services.udev.initrdRules = ''
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SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", \
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ATTR{address}=="52:54:00:12:01:01", KERNEL=="eth*", NAME="wan"
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'';
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```
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::: {.warning}
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The rule must be installed in the initrd using
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`services.udev.initrdRules`, not the usual `services.udev.extraRules`
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option. This is to avoid race conditions with other programs controlling
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the interface.
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:::
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