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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

       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

           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.

           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.

           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

           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

           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

           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 (which may be
       chosen at system boot-up time via the net.naming-scheme= kernel
       command line switch, see above):

           This is the naming scheme that was implemented in systemd

           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.

           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 NamePolicy=.

           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.

           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).

           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.

           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
           unreasonable high numbers for the onboard index. To prevent
           the generation of bogus onbard interface names, index numbers
           greater than 16381 (2^14-1) were ignored. For s390 PCI
           devices index values up to 65535 (2^16-1) are valid. To
           account for that, the limit is increased to now 65535.

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

       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

           $ 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

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
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       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
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systemd 249                                 SYSTEMD.NET-NAMING-SCHEME(7)

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