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
ID_NET_LABEL_ONBOARD=prefix label
ID_NET_NAME_MAC=prefixxAABBCCDDEEFF
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
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.
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]
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 (which may be chosen at system boot-up time via the net.naming-scheme= kernel command line switch, see above):
v238
v239
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 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
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
Previously two-letter interface type prefix was prepended to ID_NET_LABEL_ONBOARD=. This is not done anymore.
v245
v247
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), m[blue]Predictable Network Interface Namesm[][1], systemd-nspawn(1)