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, 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 |
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=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.
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.
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.
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
"v", where portport 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).
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.
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.
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).
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.
v252¶Added naming scheme for platform devices with devicetree aliases.
v253¶Set ID_NET_NAME_PATH for usb devices not connected via a PCI bus.
v254¶Naming was changed for SR-IOV virtual device representors, optionally settable at
compilation time. The "r" 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.slot
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.
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.
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.
ID_NET_NAME_ALLOW_sysfsattr=BOOL¶This udev property explicitly states if udev shall use the specified
sysfsattr, when composing the device name.
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_
options. In case of a denylist, the user needs to provide the list of denied attributes with
the sysfsattr=1ID_NET_NAME_ALLOW_ options.sysfsattr=0
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=1Example 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