SYSTEMD.NET-NAMING-SCHEME(7)

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

DESCRIPTION

Network interfaces may be renamed to give them predictable names when there's enough information to generate appropriate names and the use of certain types of names is configured. This page describes the first part, 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 are derived from various device metadata attributes. Newer versions of udev take more of these attributes into account, improving (and thus possibly changing) the names used for the same devices. Differents version of the naming 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 overriden using the net.naming-scheme= kernel command line switch, see systemd-udevd.service(8). Available naming schemes are described below.

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

NAMING

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

Table 1. Two character prefixes based on the type of interface
Prefix | Description
en | Ethernet
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=prefixonumber
    This name is set based on the 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 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=prefixxAABBCCDDEEFF
    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[Pdomain]sslot[ffunction][nport_name|ddev_port], ID_NET_NAME_SLOT=prefix[Pdomain]sslot[ffunction][nport_name|ddev_port]bnumber, ID_NET_NAME_SLOT=prefix[Pdomain]sslot[ffunction][nport_name|ddev_port]uport...[cconfig][iinterface], ID_NET_NAME_SLOT=prefix[Pdomain]sslot[ffunction][nport_name|ddev_port]vslot
    This property describes the slot position. Different schemes are used depending on the bus type, as described in the table below. In all cases, PCI slot information must be known. 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.

    Table 2. Slot naming schemes
    Format | Description
    prefix [Pdomain] sslot [ffunction] [nport_name | ddev_port] | PCI slot number
    ... bnumber | Broadcom bus (BCMA) core number
    ... uport... [cconfig] [iinterface] | USB port number chain
    ... vslot | 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 ddev_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=prefixcbus_id, ID_NET_NAME_PATH=prefixavendormodeliinstance, ID_NET_NAME_PATH=prefixiaddressnport_name, ID_NET_NAME_PATH=prefix[Pdomain]pbussslot[ffunction][nphys_port_name|ddev_port], ID_NET_NAME_PATH=prefix[Pdomain]pbussslot[ffunction][nphys_port_name|ddev_port]bnumber, ID_NET_NAME_PATH=prefix[Pdomain]pbussslot[ffunction][nphys_port_name|ddev_port]uport...[cconfig][iinterface]
    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.

    Table 3. Path naming schemes
    Format | Description
    prefix cbus_id | CCW or grouped CCW device identifier
    prefix avendor model iinstance | ACPI path names for ARM64 platform devices
    prefix [Pdomain] pbus sslot [ffunction] [nphys_port_name | ddev_port] | PCI geographical location
    ... bnumber | Broadcom bus (BCMA) core number
    ... uport... [cconfig] [iinterface] | 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:

rhel-8.0
    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.

rhel-8.1

    Same as naming scheme rhel-8.0.

rhel-8.2

    Same as naming scheme rhel-8.0.

rhel-8.3

    Same as naming scheme rhel-8.0.

rhel-8.4
    If the PCI slot is assocated with PCI bridge and that has multiple child network controllers then all of them might derive the same value of ID_NET_NAME_SLOT property. That could cause naming conflict if the property is selected as a device name. Now, we detect the situation, slot - bridge relation, and we don't produce the ID_NET_NAME_SLOT property to avoid possible naming conflict.

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

EXAMPLES

Example 1. Using udevadm test-builtin to display device properties

    $ udevadm test-builtin net_id /sys/class/net/enp0s31f6
    ...
    Using default interface naming scheme 'rhel-8.3'.
    ID_NET_NAMING_SCHEME=rhel-8.3
    ID_NET_NAME_MAC=enx54ee75cb1dc0
    ID_OUI_FROM_DATABASE=Wistron InfoComm(Kunshan)Co.,Ltd.
    ID_NET_NAME_PATH=enp0s31f6
    ...

Example 2. PCI Ethernet card with firmware index "1"

    ID_NET_NAME_ONBOARD=eno1
    ID_NET_NAME_ONBOARD_LABEL=enEthernet Port 1

Example 3. 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

Example 4. 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

Example 5. 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

Example 6. 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

Example 7. 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

Example 8. 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), the original page describing stable interface names[1]

NOTES

1.  the original page describing stable interface names
    https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames