| SYSTEMD.NET-NAMING-SCHEME(7) | systemd.net-naming-scheme | SYSTEMD.NET-NAMING-SCHEME(7) |
.SH "NAME" systemd.net-naming-scheme - Network device naming
schemes
.SH "DESCRIPTION"
.PP 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(7) properties (ID_NET_NAME_ONBOARD=,
ID_NET_LABEL_ONBOARD=, ID_NET_NAME_PATH=,
ID_NET_NAME_SLOT=).
.PP Names and MAC addresses are derived from various stable device metadata
attributes. Newer versions of systemd-udevd 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.
.PP 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).
.PP 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.
.SH "POLICIES"
.PP All names start with a two-character prefix that signifies the interface
type.
.sp
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) |
| mc | Management Component Transport Protocol (MCTP) |
.PP The udev(7) net_id builtin exports the following device
properties:
.PP 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.
.sp
Table 2. On-board naming schemes
| Format | Description |
| prefixonumber | PCI on-board index |
| prefixdnumber | DeviceTree alias index |
Added in version 243.
.RE
.PP ID_NET_LABEL_ONBOARD=label
This property is set based on textual label given by the firmware for
on-board devices. This is only available for PCI devices.
Added in version 243.
.RE
.PP 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.
.RE
.PP
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,
ID_NET_NAME_SLOT=prefix[Pdomain]sslot[ffunction][nport_name|ddev_port]Ssfnum
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.
.sp
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 |
| ... Ssfnum | Auxiliary sub-function (SF) 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.
Auxiliary sub-function (SF) network devices, where the network device's
parent is an auxiliary device exposing a sfnum sysfs attribute
(currently mlx5_core SFs), are named based on the underlying PCI function
(the PF, or for VF-SF the PF behind the VF), with a suffix of S and
the user-defined sub-function number from sfnum. This is analogous to
how SR-IOV virtual function devices are named with a v suffix.
If the SF's parent PCI function is itself an SR-IOV virtual function (VF-SF),
the name is rooted at the PF and both suffixes are chained, with the
v suffix preceding the S suffix (e.g. enp193s0f0v0S88). The
PF, the VF, and the SF therefore form a stable, hierarchical sequence
regardless of the VF's underlying PCI bus/device/function numbering.
In some configurations a parent PCI bridge of a given network controller may
be associated with a slot. In such case we do not generate this device
property to avoid possible naming conflicts.
Added in version 243.
.RE
.PP 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],
ID_NET_NAME_PATH=prefix[Pdomain]pbussslot[ffunction][nphys_port_name|ddev_port]Ssfnum
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.
.sp
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 |
| ... Ssfnum | Auxiliary sub-function (SF) number |
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.
.RE
.SH "HISTORY"
.PP 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):
.PP v238
This is the naming scheme that was implemented in systemd 238.
Added in version 243.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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 do not produce the ID_NET_NAME_SLOT property.
Added in version 247.
.RE
.PP 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(7) rule NAME= replaces :, /, and % with an underscore
(_), and refuses strings which contain only digits.
Added in version 249.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP v252
Added naming scheme for platform devices with devicetree aliases.
Added in version 252.
.RE
.PP v253
Set ID_NET_NAME_PATH for usb devices not connected via a PCI bus.
Added in version 253.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP v257
PCI slot number is now read from firmware_node/sun sysfs file.
The naming scheme based on devicetree aliases was extended to support aliases
for individual interfaces of controllers with multiple ports.
Added in version 257.
.RE
.PP v258
When no renaming is requested, ID_NET_NAME property is now equivalent
to INTERFACE property.
Added in version 258.
.RE
.PP v259
The naming scheme based on devicetree aliases was extended to support WLAN
devices.
Added in version 259.
.RE
.PP v260
MCTP interfaces are now assigned persistent names, using a mc
prefix.
Added in version 260.
.RE
.PP v261
Stable names are now generated for auxiliary sub-function (SF) network
devices (such as mlx5_core SFs). The name is built from the parent PCI
Physical Function's path with an Ssfnum suffix, where sfnum is
the user-defined SF number (the value passed to devlink port add ...
sfnum N, exposed by the kernel as the sfnum sysfs
attribute on the auxiliary device). This is analogous to the vN
suffix used for SR-IOV virtual functions; for SFs hosted on SR-IOV VFs
(VF-SF), the two suffixes are chained on top of the PF's base name.
Added in version 261.
.RE
.PP Note that latest may be used to denote the latest scheme known (to
this particular version of systemd).
.SH "LIMITING THE USE OF SPECIFIC SYSFS ATTRIBUTES"
.PP 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(7) 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.
.PP 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.
.RE
.PP
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.
.RE
.PP 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.
.SH "EXAMPLES"
.PP 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 ...
.PP Example 2. PCI Ethernet card with firmware index
"1"
ID_NET_NAME_ONBOARD=eno1 ID_NET_NAME_ONBOARD_LABEL=Ethernet Port 1
.PP Example 3. PCI Ethernet card in 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
.PP 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
.PP 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
.PP 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
.PP 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
.PP 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
.PP 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
.PP 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
.PP 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
.SH "SEE ALSO"
.PP udev(7), udevadm(8), systemd-udevd.service(8),
Predictable Network Interface Names[1], systemd-nspawn(1)
NOTES
- 1.
- Predictable Network Interface Names
| systemd 262.2 |