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NAME | DESCRIPTION | NAMING | HISTORY | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
SYSTEMD.NET-NAMING-SCHEME(7)stemd.net-naming-schemeTEMD.NET-NAMING-SCHEME(7)
systemd.net-naming-scheme - Network device naming schemes
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.
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:
ID_NET_NAME_ONBOARD=prefixonumber
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=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=prefixvslot,
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 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.
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 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.
The following "naming schemes" have been defined:
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).
Note that latest may be used to denote the latest scheme known (to
this particular version of systemd).
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_NET_NAMING_SCHEME=v243
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=Ethernet 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. 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
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
ID_NET_NAME_MAC=wwx028037ec0200
ID_NET_NAME_PATH=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
ID_NET_NAME_MAC=enxd626b3450fb5
ID_NET_NAME_PATH=enp0s29u1u2
Example 9. 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
udev(7), udevadm(8), Predictable Network Interface Names[1],
systemd-nspawn(1)
1. Predictable Network Interface Names
https://systemd.io/PREDICTABLE_INTERFACE_NAMES
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project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
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systemd 246 SYSTEMD.NET-NAMING-SCHEME(7)
Pages that refer to this page: systemd-nspawn(1) , systemd.link(5) , 30-systemd-environment-d-generator(7) , systemd.directives(7) , systemd.index(7) , systemd-udevd(8) , systemd-udevd-control.socket(8) , systemd-udevd-kernel.socket(8) , systemd-udevd.service(8)