systemd.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(7) 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 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.

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

The udev(7) net_id builtin exports the following device properties:

ID_NET_NAME_ONBOARD=prefixonumber, ID_NET_NAME_ONBOARD=prefixdnumber

Table 2. On-board naming schemes

Added in version 243.

ID_NET_LABEL_ONBOARD=label

Added in version 243.

ID_NET_NAME_MAC=prefixxAABBCCDDEEFF

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

Table 3. Slot naming schemes

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 do not 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]

Table 4. Path naming schemes

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

Added in version 243.

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.

Added in version 243.

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=.

Added in version 243.

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.

Added in version 243.

v243

Previously two-letter interface type prefix was prepended to ID_NET_LABEL_ONBOARD=. This is not done anymore.

Added in version 243.

v245

Added in version 245.

v247

Added in version 247.

v249

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.

v250

Added in version 250.

v251

Added in version 251.

v252

Added in version 252.

v253

Added in version 253.

v254

Added in version 255.

v255

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.

v257

The naming scheme based on devicetree aliases was extended to support aliases for individual interfaces of controllers with multiple ports.

Added in version 257.

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(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.

ID_NET_NAME_ALLOW=BOOL

Added in version 256.

ID_NET_NAME_ALLOW_sysfsattr=BOOL

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 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:*
\n
  ID_NET_NAME_ALLOW=0
\n
  ID_NET_NAME_ALLOW_ACPI_INDEX=1
\n
  ID_NET_NAME_ALLOW_ADDR_ASSIGN_TYPE=1
\n
  ID_NET_NAME_ALLOW_ADDRESS=1
\n
  ID_NET_NAME_ALLOW_ARI_ENABLED=1
\n
  ID_NET_NAME_ALLOW_DEV_PORT=1
\n
  ID_NET_NAME_ALLOW_FUNCTION_ID=1
\n
  ID_NET_NAME_ALLOW_IFLINK=1
\n
  ID_NET_NAME_ALLOW_INDEX=1
\n
  ID_NET_NAME_ALLOW_LABEL=1
\n
  ID_NET_NAME_ALLOW_PHYS_PORT_NAME=1
\n
  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:*
\n
  ID_NET_NAME_ALLOW=1
\n
  ID_NET_NAME_ALLOW_DEV_PORT=0
\n
  ID_NET_NAME_ALLOW_PHYS_PORT_NAME=0

SEE ALSO#

udev(7), udevadm(8), systemd-udevd.service(8), Predictable Network Interface Names[1], systemd-nspawn(1)

NOTES#

1.

Predictable Network Interface Names