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NAME         top - Network device naming schemes

DESCRIPTION         top

       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=,

       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

       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         top

       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              │
       │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:

           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

           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

           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.

           Table 2. Slot naming schemes
           │Format                                                      Description              │
           │prefix [Pdomain] sslot [ffunction] [nport_name | ddev_port] │ PCI slot number          │
           │prefix vslot                                                │ VIO slot number (IBM     │
           │                                                            │ PowerVM)                 │
           │... 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.

           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 iaddress nport_name                                            │ Netdevsim (simulated      │
           │                                                                      │ networking device) device │
           │                                                                      │ number and port name      │
           │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         top

       The following "naming schemes" have been defined:

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

           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

           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.

           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 for a description of

           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

           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.

           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).

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

EXAMPLES         top

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

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

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

           ID_NET_NAME_ONBOARD_LABEL=Ethernet Port 1

       Example 3. PCI Ethernet card in hotplug slot with firmware index

           # /sys/devices/pci0000:00/0000:00:1c.3/0000:05:00.0/net/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

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

       Example 5. PCI WLAN card

           # /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlp3s0

       Example 6. PCI IB host adapter with 2 ports

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

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

       Example 7. 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

       Example 8. USB Android phone

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

       Example 9. s390 grouped CCW interface

           # /sys/devices/css0/0.0.0007/0.0.f5f0/group_device/net/encf5f0

SEE ALSO         top

       udev(7), udevadm(8), Predictable Network Interface Names[1],

NOTES         top

        1. Predictable Network Interface Names

COLOPHON         top

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systemd 246                                     SYSTEMD.NET-NAMING-SCHEME(7)

Pages that refer to this page: systemd-nspawn(1)