SYSTEMD.NET-NAMING-SCHEME(7systemd.net-naming-scheSYSTEMD.NET-NAMING-SCHEME(7)
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.
NAMING
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.
HISTORY
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.
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
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
systemd 245 SYSTEMD.NET-NAMING-SCHEME(7)