Provided by: systemd_256.5-2ubuntu4_amd64 
NAME
systemd.net-naming-scheme - Network device naming schemes
DESCRIPTION
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.
POLICIES
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_NAME_ONBOARD=prefixdnumber
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.
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.
Added in version 243.
ID_NET_NAME_SLOT=prefix[Pdomain]sslot[ffunction][nport_name|ddev_port],
ID_NET_NAME_SLOT=prefixvslot, ID_NET_NAME_SLOT=prefixxslot,
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,
ID_NET_NAME_SLOT=prefix[Pdomain]sslot[ffunction][nport_name|ddev_port]rslot
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 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.
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 conflicts.
Added in version 243.
ID_NET_NAME_PATH=prefixcbus_id, ID_NET_NAME_PATH=prefixavendormodeliinstance,
ID_NET_NAME_PATH=prefixiaddressnport_name, ID_NET_NAME_PATH=prefixuport...,
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 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
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
This is the naming scheme that was implemented in systemd 238.
Added in version 243.
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.
Added in version 243.
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=.
Added in version 243.
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.
Added in version 243.
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.
Added in version 243.
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).
Added in version 245.
v247
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.
v249
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 numerics.
Added in version 249.
v250
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.
v251
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. Note, this is reverted in v255. See below.
Added in version 251.
v252
Added naming scheme for platform devices with devicetree aliases.
Added in version 252.
v253
Set ID_NET_NAME_PATH for usb devices not connected via a PCI bus.
Added in version 253.
v254
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 default scheme for systemd version 254.
Added in version 255.
v255
Naming was changed for SR-IOV virtual device representors to enable the change
introduced in v254 by default.
If we detect that a PCI device associated with a slot is a PCI bridge, we no longer
set ID_NET_NAME_SLOT, reverting a change that was introduced in v251.
Added in version 255.
Note that latest may be used to denote the latest scheme known (to this particular version
of systemd).
LIMITING THE USE OF SPECIFIC SYSFS ATTRIBUTES
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.
ID_NET_NAME_ALLOW=BOOL
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.
ID_NET_NAME_ALLOW_sysfsattr=BOOL
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
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
Example 10. Set an allowlist for reading sysfs attributes for network card naming
/etc/udev/hwdb.d/50-net-naming-allowlist.hwdb
net:naming:drvirtio_net:*
ID_NET_NAME_ALLOW=0
ID_NET_NAME_ALLOW_ACPI_INDEX=1
ID_NET_NAME_ALLOW_ADDR_ASSIGN_TYPE=1
ID_NET_NAME_ALLOW_ADDRESS=1
ID_NET_NAME_ALLOW_ARI_ENABLED=1
ID_NET_NAME_ALLOW_DEV_PORT=1
ID_NET_NAME_ALLOW_FUNCTION_ID=1
ID_NET_NAME_ALLOW_IFLINK=1
ID_NET_NAME_ALLOW_INDEX=1
ID_NET_NAME_ALLOW_LABEL=1
ID_NET_NAME_ALLOW_PHYS_PORT_NAME=1
ID_NET_NAME_ALLOW_TYPE=1
Example 11. Set a denylist so that specified sysfs attribute are ignored
/etc/udev/hwdb.d/50-net-naming-denylist.hwdb
net:naming:drvirtio_net:*
ID_NET_NAME_ALLOW=1
ID_NET_NAME_ALLOW_DEV_PORT=0
ID_NET_NAME_ALLOW_PHYS_PORT_NAME=0
SEE ALSO
udev(7), udevadm(8), Predictable Network Interface Names[1], systemd-nspawn(1)
NOTES
1. Predictable Network Interface Names
https://systemd.io/PREDICTABLE_INTERFACE_NAMES