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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.

POLICIES         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. Different schemes
           are used depending on the firmware type, as described in the
           table below.

           Table 2. On-board naming schemes
           │ Format        Description            │
           │ prefixonumber │ PCI on-board index     │
           │ prefixdnumber │ Devicetree alias index │

           Added in version 243.

       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.

           Added in version 243.

           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.

           Added in version 243.

       ID_NET_NAME_SLOT=prefixvslot, ID_NET_NAME_SLOT=prefixxslot,
           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 3. Slot naming schemes
           │ Format                                                      Description              │
           │ prefix [Pdomain] sslot [ffunction] [nport_name | ddev_port] │ PCI slot number          │
           │ prefix vslot                                                │ VIO slot number (IBM     │
           │                                                             │ PowerVM)                 │
           │ prefix Xnumber                                              │ VIF interface number     │
           │                                                             │ (Xen)                    │
           │ ... bnumber                                                 │ Broadcom bus (BCMA) core │
           │                                                             │ number                   │
           │ ... uport... [cconfig] [iinterface]                         │ USB port number chain    │
           │ ... vslot                                                   │ SR-VIO slot number       │
           │ ... rslot                                                   │ SR-IOV 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

           SR-IOV virtual device representors are named based on the
           name of the physical device interface, with a suffix of r and
           the number of the virtual device that is linked to the
           particular representor, with any leading zeros removed. The
           physical port name and the bus number are 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

           Added in version 243.

           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 4. 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.

           Added in version 243.

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

           Added in version 243.

           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.

           Added in version 243.

           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=.

           Added in version 243.

           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.

           Added in version 243.

           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.

           Added in version 243.

           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).

           Added in version 245.

           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.

           Added in version 247.

           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 on-board index. To prevent
           the generation of bogus on-board 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

           Added in version 249.

           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).

           Added in version 250.

           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.

           Added in version 251.

           Added naming scheme for platform devices with devicetree

           Added in version 252.

           Set ID_NET_NAME_PATH for usb devices not connected via a PCI

           Added in version 253.

           Naming was changed for SR-IOV virtual device representors,
           optionally settable at compilation time. The "rslot" suffix
           was added to differentiate SR-IOV virtual device representors
           attached to a single physical device interface. Because of a
           mistake, this scheme was not the the default scheme for
           systemd version 254.

           Added in version 255.

           Naming was changed for SR-IOV virtual device representors to
           enable the change introduced in v254 by default.

           Added in version 255.

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


       When creating names for network cards, some naming schemes use
       data from sysfs populated by the kernel. This means that although
       a specific naming scheme in udev is picked, the network card's
       name can still change when a new kernel version adds a new sysfs
       attribute. For example if kernel starts setting the
       phys_port_name, udev will append the "nphys_port_name" suffix to
       the device name.

           This udev property sets a fallback policy for reading a sysfs
           attribute. If set to 0 udev will not read any sysfs attribute
           by default, unless it is explicitly allowlisted, see below.
           If set to 1 udev can use any sysfs attribute unless it is
           explicitly forbidden. The default value is 1.

           Added in version 256.

           This udev property explicitly states if udev shall use the
           specified sysfsattr, when composing the device name.

           Added in version 256.

       With these options, users can set an allowlist or denylist for
       sysfs attributes. To create an allowlist, the user needs to set
       ID_NET_NAME_ALLOW=0 for the device and then list the allowed
       attributes with the ID_NET_NAME_ALLOW_sysfsattr=1 options. In
       case of a denylist, the user needs to provide the list of denied
       attributes with the ID_NET_NAME_ALLOW_sysfsattr=0 options.

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

       Example 10. Set an allowlist for reading sysfs attributes for
       network card naming


       Example 11. Set a denylist so that specified sysfs attribute are


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 255                                      SYSTEMD....NG-SCHEME(7)

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