systemd.net-naming-scheme

systemd
systemd.net-naming-scheme 7
systemd.net-naming-scheme Network device naming schemes

## Description

Network interfaces names and MAC addresses may be generated based on certain stable interface attributes. This is possible when there is enough information about the device to generate those attributes and the use of this information is configured. This page describes interface naming, i.e. what possible names may be generated. Those names are generated by the systemd-udevd.service 8 builtin `net_id` and exported as udev properties (`ID_NET_NAME_ONBOARD=`, `ID_NET_LABEL_ONBOARD=`, `ID_NET_NAME_PATH=`, `ID_NET_NAME_SLOT=`).

Names and MAC addresses are derived from various stable device metadata attributes. Newer versions of udev take more of these attributes into account, improving (and thus possibly changing) the names and addresses used for the same devices. Different versions of those generation rules are called "naming schemes". The default naming scheme is chosen at compilation time. Usually this will be the latest implemented version, but it is also possible to set one of the older versions to preserve compatibility. This may be useful for example for distributions, which may introduce new versions of systemd in stable releases without changing the naming scheme. The naming scheme may also be overridden using the `net.naming-scheme=` kernel command line switch, see systemd-udevd.service 8. Available naming schemes are described below.

After the udev properties have been generated, appropriate udev rules may be used to actually rename devices based on those properties. See the description of `NamePolicy=` and `MACAddressPolicy=` in systemd.link 5.

Note that while the concept of network interface naming schemes is primarily relevant in the context of `systemd-udevd.service`, the systemd-nspawn 1 container manager also takes it into account when naming network interfaces, see below.

## Naming

All names start with a two-character prefix that signifies the interface type.

Two character prefixes based on the type of interface

Prefix | Description
--- | ---
`en` | Ethernet
`ib` | InfiniBand
`sl` | Serial line IP (slip)
`wl` | Wireless local area network (WLAN)
`ww` | Wireless wide area network (WWAN)

The udev `net_id` builtin exports the following udev device properties:

`ID_NET_NAME_ONBOARD=prefix`o`number`

  This name is set based on the numeric ordering information given by the firmware for on-board devices. The name consists of the prefix, letter `o`, and a number specified by the firmware. This is only available for PCI devices.

`ID_NET_LABEL_ONBOARD=prefix label`

  This property is set based on textual label given by the firmware for on-board devices. The name consists of the prefix concatenated with the label. This is only available for PCI devices.

`ID_NET_NAME_MAC=prefix`x`AABBCCDDEEFF`

  This name consists of the prefix, letter `x`, and 12 hexadecimal digits of the MAC address. It is available if the device has a fixed MAC address. Because this name is based on an attribute of the card itself, it remains "stable" when the device is moved (even between machines), but will change when the hardware is replaced.

`ID_NET_NAME_SLOT=prefix[`P`domain]`s`slot[`f`function][`n`port_name|`d`dev_port]`
`ID_NET_NAME_SLOT=prefix`v`slot`
`ID_NET_NAME_SLOT=prefix`x`slot`
`ID_NET_NAME_SLOT=prefix[`P`domain]`s`slot[`f`function][`n`port_name|`d`dev_port]`b`number`
`ID_NET_NAME_SLOT=prefix[`P`domain]`s`slot[`f`function][`n`port_name|`d`dev_port]`u`port…[`c`config][`i`interface]`
`ID_NET_NAME_SLOT=prefix[`P`domain]`s`slot[`f`function][`n`port_name|`d`dev_port]`v`slot`

  This property describes the slot position. Different schemes are used depending on the bus type, as described in the table below. In case of USB, BCMA, and SR-VIO devices, the full name consists of the prefix, PCI slot identifier, and USB or BCMA or SR-VIO slot identifier. The first two parts are denoted as "…" in the table below.

  Slot naming schemes

  Format | Description
  --- | ---
  prefix [`P` domain] `s` slot [`f` function] [`n` port_name | `d` dev_port] | PCI slot number
  prefix `v` slot | VIO slot number (IBM PowerVM)
  prefix `X` number | VIF interface number (Xen)
  … `b` number | Broadcom bus (BCMA) core number
  … `u` port… [`c` config] [`i` interface] | USB port number chain
  … `v` slot | SR-VIO slot number

  The PCI domain is only prepended when it is not 0. All multi-function PCI devices will carry the `ffunction` number in the device name, including the function 0 device. For non-multi-function devices, the number is suppressed if 0. The port name port_name is used, or the port number `d` dev_port if the name is not known.

  For BCMA devices, the core number is suppressed when 0.

  For USB devices the full chain of port numbers of hubs is composed. If the name gets longer than the maximum number of 15 characters, the name is not exported. The usual USB configuration number 1 and interface number 0 values are suppressed.

  SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of `v` and the virtual device number, with any leading zeros removed. The bus number is ignored.

  In some configurations a parent PCI bridge of a given network controller may be associated with a slot. In such case we don't generate this device property to avoid possible naming conflicts.

`ID_NET_NAME_PATH=prefix`c`bus_id`
`ID_NET_NAME_PATH=prefix`a`vendormodel`i`instance`
`ID_NET_NAME_PATH=prefix`i`address`n`port_name`
`ID_NET_NAME_PATH=prefix[`P`domain]`p`bus`s`slot[`f`function][`n`phys_port_name|`d`dev_port]`
`ID_NET_NAME_PATH=prefix[`P`domain]`p`bus`s`slot[`f`function][`n`phys_port_name|`d`dev_port]`b`number`
`ID_NET_NAME_PATH=prefix[`P`domain]`p`bus`s`slot[`f`function][`n`phys_port_name|`d`dev_port]`u`port…[`c`config][`i`interface]`

  This property describes the device installation location. Different schemes are used depending on the bus type, as described in the table below. For BCMA and USB devices, PCI path information must known, and the full name consists of the prefix, PCI slot identifier, and USB or BCMA location. The first two parts are denoted as "…" in the table below.

  Path naming schemes

  Format | Description
  --- | ---
  prefix `c` bus_id | CCW or grouped CCW device identifier
  prefix `a` vendor model `i` instance | ACPI path names for ARM64 platform devices
  prefix `i` address `n` port_name | Netdevsim (simulated networking device) device number and port name
  prefix [`P` domain] `p` bus `s` slot [`f` function] [`n` phys_port_name | `d` dev_port] | PCI geographical location
  … `b` number | Broadcom bus (BCMA) core number
  … `u` port… [`c` config] [`i` interface] | USB port number chain

  CCW and grouped CCW devices are found in IBM System Z mainframes. Any leading zeros and dots are suppressed.

  For PCI, BCMA, and USB devices, the same rules as described above for slot naming are used.

## History

The following "naming schemes" have been defined (which may be chosen at system boot-up time via the `net.naming-scheme=` kernel command line switch, see above):

`v238`

  This is the naming scheme that was implemented in systemd 238.

`v239`

  Naming was changed for virtual network interfaces created with SR-IOV and NPAR and for devices where the PCI network controller device does not have a slot number associated.

  SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of `vport`, where port is the virtual device number. Previously those virtual devices were named as if completely independent.

  The ninth and later NPAR virtual devices are named following the scheme used for the first eight NPAR partitions. Previously those devices were not renamed and the kernel default ("ethN") was used.

  Names are also generated for PCI devices where the PCI network controller device does not have an associated slot number itself, but one of its parents does. Previously those devices were not renamed and the kernel default was used.

`v240`

  The `ib` prefix and stable names for infiniband devices are introduced. Previously those devices were not renamed.

  The ACPI index field (used in `ID_NET_NAME_ONBOARD=`) is now also used when 0.

  A new naming policy `NamePolicy=keep` was introduced. With this policy, if the network device name was already set by userspace, the device will not be renamed again. Previously, this naming policy applied implicitly, and now it must be explicitly requested. Effectively, this means that network devices will be renamed according to the configuration, even if they have been renamed already, if `keep` is not specified as the naming policy in the `.link` file. See systemd.link 5 for a description of `NamePolicy=`.

`v241`

  `MACAddressPolicy=persistent` was extended to set MAC addresses based on the device name. Previously addresses were only based on the `ID_NET_NAME_*` attributes, which meant that interface names would never be generated for virtual devices. Now a persistent address will be generated for most devices, including in particular bridges.

  Note: when userspace does not set a MAC address for a bridge device, the kernel will initially assign a random address, and then change it when the first device is enslaved to the bridge. With this naming policy change, bridges get a persistent MAC address based on the bridge name instead of the first enslaved device.

`v243`

  Support for renaming netdevsim (simulated networking) devices was added. Previously those devices were not renamed.

  Previously two-letter interface type prefix was prepended to `ID_NET_LABEL_ONBOARD=`. This is not done anymore.

`v245`

  When systemd-nspawn 1 derives the name for the host side of the network interface created with `--network-veth` from the container name it previously simply truncated the result at 15 characters if longer (since that's the maximum length for network interface names). From now on, for any interface name that would be longer than 15 characters the last 4 characters are set to a 24bit hash value of the full interface name. This way network interface name collisions between multiple similarly named containers (who only differ in container name suffix) should be less likely (but still possible, since the 24bit hash value is very small).

`v247`

  When a PCI slot is associated with a PCI bridge that has multiple child network controllers, the same value of the `ID_NET_NAME_SLOT` property might be derived for those controllers. This would cause a naming conflict if the property is selected as the device name. Now, we detect this situation and don't produce the `ID_NET_NAME_SLOT` property.

`v249`

  PCI hotplug slot names for the s390 PCI driver are a hexadecimal representation of the `function_id` device attribute. This attribute is now used to build the `ID_NET_NAME_SLOT`. Before that, all slot names were parsed as decimal numbers, which could either result in an incorrect value of the `ID_NET_NAME_SLOT` property or none at all.

  Some firmware and hypervisor implementations report unreasonably high numbers for the onboard index. To prevent the generation of bogus onbard interface names, index numbers greater than 16381 (2¹⁴-1) were ignored. For s390 PCI devices index values up to 65535 (2¹⁶-1) are valid. To account for that, the limit was increased to 65535.

  The udev rule `NAME=` replaces `:`, `/`, and `%` with an underscore (`_`), and refuses strings which contain only numerics.

`v250`

  Added naming scheme for Xen netfront "vif" interfaces based on the guest side VIF number set from the Xen config (or the interface index in AWS EC2).

`v251`

  Since version `v247` we no longer set `ID_NET_NAME_SLOT` if we detect that a PCI device associated with a slot is a PCI bridge as that would create naming conflict when there are more child devices on that bridge. Now, this is relaxed and we will use slot information to generate the name based on it but only if the PCI device has multiple functions. This is safe because distinct function number is a part of the device name for multifunction devices.

Note that `latest` may be used to denote the latest scheme known (to this particular version of systemd).

## Examples

Using `udevadm test-builtin` to display device properties

    $ udevadm test-builtin net_id /sys/class/net/enp0s31f6
    ...
    Using default interface naming scheme 'v243'.
    ID_NET_NAMING_SCHEME=v243
    ID_NET_NAME_MAC=enx54ee75cb1dc0
    ID_OUI_FROM_DATABASE=Wistron InfoComm(Kunshan)Co.,Ltd.
    ID_NET_NAME_PATH=enp0s31f6
    ...

PCI Ethernet card with firmware index "1"

    ID_NET_NAME_ONBOARD=eno1
    ID_NET_NAME_ONBOARD_LABEL=Ethernet Port 1

PCI Ethernet card in hotplug slot with firmware index number

    # /sys/devices/pci0000:00/0000:00:1c.3/0000:05:00.0/net/ens1
    ID_NET_NAME_MAC=enx000000000466
    ID_NET_NAME_PATH=enp5s0
    ID_NET_NAME_SLOT=ens1

PCI Ethernet multi-function card with 2 ports

    # /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.0/net/enp2s0f0
    ID_NET_NAME_MAC=enx78e7d1ea46da
    ID_NET_NAME_PATH=enp2s0f0

    # /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.1/net/enp2s0f1
    ID_NET_NAME_MAC=enx78e7d1ea46dc
    ID_NET_NAME_PATH=enp2s0f1

PCI WLAN card

    # /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlp3s0
    ID_NET_NAME_MAC=wlx0024d7e31130
    ID_NET_NAME_PATH=wlp3s0

PCI IB host adapter with 2 ports

    # /sys/devices/pci0000:00/0000:00:03.0/0000:15:00.0/net/ibp21s0f0
    ID_NET_NAME_PATH=ibp21s0f0

    # /sys/devices/pci0000:00/0000:00:03.0/0000:15:00.1/net/ibp21s0f1
    ID_NET_NAME_PATH=ibp21s0f1

USB built-in 3G modem

    # /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.4/2-1.4:1.6/net/wwp0s29u1u4i6
    ID_NET_NAME_MAC=wwx028037ec0200
    ID_NET_NAME_PATH=wwp0s29u1u4i6

USB Android phone

    # /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2/2-1.2:1.0/net/enp0s29u1u2
    ID_NET_NAME_MAC=enxd626b3450fb5
    ID_NET_NAME_PATH=enp0s29u1u2

s390 grouped CCW interface

    # /sys/devices/css0/0.0.0007/0.0.f5f0/group_device/net/encf5f0
    ID_NET_NAME_MAC=enx026d3c00000a
    ID_NET_NAME_PATH=encf5f0

## See Also

udev 7, udevadm 8, Predictable Network Interface Names, systemd-nspawn 1