2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
6 <refentry id=
"systemd.net-naming-scheme">
8 <title>systemd.net-naming-scheme
</title>
9 <productname>systemd
</productname>
13 <refentrytitle>systemd.net-naming-scheme
</refentrytitle>
14 <manvolnum>7</manvolnum>
18 <refname>systemd.net-naming-scheme
</refname>
19 <refpurpose>Network device naming schemes
</refpurpose>
23 <title>Description
</title>
25 <para>Network interfaces names and MAC addresses may be generated based on certain stable interface
26 attributes. This is possible when there is enough information about the device to generate those
27 attributes and the use of this information is configured. This page describes interface naming, i.e. what
28 possible names may be generated. Those names are generated by the
29 <citerefentry><refentrytitle>systemd-udevd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
30 builtin
<command>net_id
</command> and exported as udev properties
31 (
<varname>ID_NET_NAME_ONBOARD=
</varname>,
<varname>ID_NET_LABEL_ONBOARD=
</varname>,
32 <varname>ID_NET_NAME_PATH=
</varname>,
<varname>ID_NET_NAME_SLOT=
</varname>).
</para>
34 <para>Names and MAC addresses are derived from various stable device metadata attributes. Newer versions
35 of udev take more of these attributes into account, improving (and thus possibly changing) the names and
36 addresses used for the same devices. Different versions of those generation rules are called
"naming
37 schemes". The default naming scheme is chosen at compilation time. Usually this will be the latest
38 implemented version, but it is also possible to set one of the older versions to preserve
39 compatibility. This may be useful for example for distributions, which may introduce new versions of
40 systemd in stable releases without changing the naming scheme. The naming scheme may also be overridden
41 using the
<varname>net.naming-scheme=
</varname> kernel command line switch, see
42 <citerefentry><refentrytitle>systemd-udevd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
43 Available naming schemes are described below.
</para>
45 <para>After the udev properties have been generated, appropriate udev rules may be used to actually rename
46 devices based on those properties. See the description of
<varname>NamePolicy=
</varname> and
47 <varname>MACAddressPolicy=
</varname> in
48 <citerefentry><refentrytitle>systemd.link
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
50 <para>Note that while the concept of network interface naming schemes is primarily relevant in the
51 context of
<filename>systemd-udevd.service
</filename>, the
52 <citerefentry><refentrytitle>systemd-nspawn
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
53 container manager also takes it into account when naming network interfaces, see below.
</para>
59 <para>All names start with a two-character prefix that signifies the interface type.
</para>
62 <title>Two character prefixes based on the type of interface
</title>
68 <entry>Description
</entry>
73 <entry><constant>en
</constant></entry>
74 <entry>Ethernet
</entry>
77 <entry><constant>ib
</constant></entry>
78 <entry>InfiniBand
</entry>
81 <entry><constant>sl
</constant></entry>
82 <entry>Serial line IP (slip)
</entry>
85 <entry><constant>wl
</constant></entry>
86 <entry>Wireless local area network (WLAN)
</entry>
89 <entry><constant>ww
</constant></entry>
90 <entry>Wireless wide area network (WWAN)
</entry>
96 <para>The udev
<command>net_id
</command> builtin exports the following udev device properties:
</para>
100 <term><varname>ID_NET_NAME_ONBOARD=
<replaceable>prefix
</replaceable><constant>o
</constant><replaceable>number
</replaceable></varname></term>
102 <listitem><para>This name is set based on the numeric ordering information given by the firmware
103 for on-board devices. The name consists of the prefix, letter
<constant>o
</constant>, and a number
104 specified by the firmware. This is only available for PCI devices.
</para>
109 <term><varname>ID_NET_LABEL_ONBOARD=
<replaceable>prefix
</replaceable> <replaceable>label
</replaceable></varname></term>
111 <listitem><para>This property is set based on textual label given by the firmware for on-board
112 devices. The name consists of the prefix concatenated with the label. This is only available for
119 <term><varname>ID_NET_NAME_MAC=
<replaceable>prefix
</replaceable><constant>x
</constant><replaceable>AABBCCDDEEFF
</replaceable></varname></term>
121 <listitem><para>This name consists of the prefix, letter
<constant>x
</constant>, and
12 hexadecimal
122 digits of the MAC address. It is available if the device has a fixed MAC address. Because this name
123 is based on an attribute of the card itself, it remains
"stable" when the device is moved (even
124 between machines), but will change when the hardware is replaced.
</para>
129 <term><varname>ID_NET_NAME_SLOT=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
</varname></term>
130 <term><varname>ID_NET_NAME_SLOT=
<replaceable>prefix
</replaceable><constant>v
</constant><replaceable>slot
</replaceable></varname></term>
131 <term><varname>ID_NET_NAME_SLOT=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
<constant>b
</constant><replaceable>number
</replaceable></varname></term>
132 <term><varname>ID_NET_NAME_SLOT=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
<constant>u
</constant><replaceable>port
</replaceable>…[
<constant>c
</constant><replaceable>config
</replaceable>][
<constant>i
</constant><replaceable>interface
</replaceable>]
</varname></term>
133 <term><varname>ID_NET_NAME_SLOT=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
<constant>v
</constant><replaceable>slot
</replaceable></varname></term>
135 <listitem><para>This property describes the slot position. Different schemes are used depending on
136 the bus type, as described in the table below. In case of USB, BCMA, and SR-VIO devices, the full
137 name consists of the prefix, PCI slot identifier, and USB or BCMA or SR-VIO slot identifier. The
138 first two parts are denoted as
"…" in the table below.
</para>
141 <title>Slot naming schemes
</title>
146 <entry>Format
</entry>
147 <entry>Description
</entry>
153 <entry><replaceable>prefix
</replaceable> [
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>s
</constant><replaceable>slot
</replaceable> [
<constant>f
</constant><replaceable>function
</replaceable>] [
<constant>n
</constant><replaceable>port_name
</replaceable> |
<constant>d
</constant><replaceable>dev_port
</replaceable>]
</entry>
154 <entry>PCI slot number
</entry>
158 <entry><replaceable>prefix
</replaceable> <constant>v
</constant><replaceable>slot
</replaceable></entry>
159 <entry>VIO slot number (IBM PowerVM)
</entry>
163 <entry>…
<constant>b
</constant><replaceable>number
</replaceable></entry>
164 <entry>Broadcom bus (BCMA) core number
</entry>
168 <entry>…
<constant>u
</constant><replaceable>port
</replaceable>… [
<constant>c
</constant><replaceable>config
</replaceable>] [
<constant>i
</constant><replaceable>interface
</replaceable>]
</entry>
169 <entry>USB port number chain
</entry>
173 <entry>…
<constant>v
</constant><replaceable>slot
</replaceable></entry>
174 <entry>SR-VIO slot number
</entry>
180 <para>The PCI domain is only prepended when it is not
0. All multi-function PCI devices will carry
181 the
<constant>f
<replaceable>function
</replaceable></constant> number in the device name, including
182 the function
0 device. For non-multi-function devices, the number is suppressed if
0. The port name
183 <replaceable>port_name
</replaceable> is used, or the port number
184 <constant>d
</constant><replaceable>dev_port
</replaceable> if the name is not known.
</para>
186 <para>For BCMA devices, the core number is suppressed when
0.
</para>
188 <para>For USB devices the full chain of port numbers of hubs is composed. If the name gets longer
189 than the maximum number of
15 characters, the name is not exported. The usual USB configuration
190 number
1 and interface number
0 values are suppressed.
</para>
192 <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
193 <constant>v
</constant> and the virtual device number, with any leading zeros removed. The bus
194 number is ignored.
</para>
196 <para>In some configurations a parent PCI bridge of a given network controller may be associated
197 with a slot. In such case we don't generate this device property to avoid possible naming conflicts.
</para>
202 <term><varname>ID_NET_NAME_PATH=
<replaceable>prefix
</replaceable><constant>c
</constant><replaceable>bus_id
</replaceable></varname></term>
203 <term><varname>ID_NET_NAME_PATH=
<replaceable>prefix
</replaceable><constant>a
</constant><replaceable>vendor
</replaceable><replaceable>model
</replaceable><constant>i
</constant><replaceable>instance
</replaceable></varname></term>
204 <term><varname>ID_NET_NAME_PATH=
<replaceable>prefix
</replaceable><constant>i
</constant><replaceable>address
</replaceable><constant>n
</constant><replaceable>port_name
</replaceable></varname></term>
205 <term><varname>ID_NET_NAME_PATH=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>p
</constant><replaceable>bus
</replaceable><constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>phys_port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
</varname></term>
206 <term><varname>ID_NET_NAME_PATH=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>p
</constant><replaceable>bus
</replaceable><constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>phys_port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
<constant>b
</constant><replaceable>number
</replaceable></varname></term>
207 <term><varname>ID_NET_NAME_PATH=
<replaceable>prefix
</replaceable>[
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>p
</constant><replaceable>bus
</replaceable><constant>s
</constant><replaceable>slot
</replaceable>[
<constant>f
</constant><replaceable>function
</replaceable>][
<constant>n
</constant><replaceable>phys_port_name
</replaceable>|
<constant>d
</constant><replaceable>dev_port
</replaceable>]
<constant>u
</constant><replaceable>port
</replaceable>…[
<constant>c
</constant><replaceable>config
</replaceable>][
<constant>i
</constant><replaceable>interface
</replaceable>]
</varname></term>
209 <listitem><para>This property describes the device installation location. Different schemes are
210 used depending on the bus type, as described in the table below. For BCMA and USB devices, PCI path
211 information must known, and the full name consists of the prefix, PCI slot identifier, and USB or
212 BCMA location. The first two parts are denoted as
"…" in the table below.
</para>
215 <title>Path naming schemes
</title>
220 <entry>Format
</entry>
221 <entry>Description
</entry>
227 <entry><replaceable>prefix
</replaceable> <constant>c
</constant><replaceable>bus_id
</replaceable></entry>
228 <entry>CCW or grouped CCW device identifier
</entry>
232 <entry><replaceable>prefix
</replaceable> <constant>a
</constant><replaceable>vendor
</replaceable> <replaceable>model
</replaceable> <constant>i
</constant><replaceable>instance
</replaceable></entry>
233 <entry>ACPI path names for ARM64 platform devices
</entry>
237 <entry><replaceable>prefix
</replaceable> <constant>i
</constant><replaceable>address
</replaceable> <constant>n
</constant><replaceable>port_name
</replaceable></entry>
238 <entry>Netdevsim (simulated networking device) device number and port name
</entry>
242 <entry><replaceable>prefix
</replaceable> [
<constant>P
</constant><replaceable>domain
</replaceable>]
<constant>p
</constant><replaceable>bus
</replaceable> <constant>s
</constant><replaceable>slot
</replaceable> [
<constant>f
</constant><replaceable>function
</replaceable>] [
<constant>n
</constant><replaceable>phys_port_name
</replaceable> |
<constant>d
</constant><replaceable>dev_port
</replaceable>]
</entry>
243 <entry>PCI geographical location
</entry>
247 <entry>…
<constant>b
</constant><replaceable>number
</replaceable></entry>
248 <entry>Broadcom bus (BCMA) core number
</entry>
252 <entry>…
<constant>u
</constant><replaceable>port
</replaceable>… [
<constant>c
</constant><replaceable>config
</replaceable>] [
<constant>i
</constant><replaceable>interface
</replaceable>]
</entry>
253 <entry>USB port number chain
</entry>
260 <para>CCW and grouped CCW devices are found in IBM System Z mainframes. Any leading zeros and
261 dots are suppressed.
</para>
263 <para>For PCI, BCMA, and USB devices, the same rules as described above for slot naming are
271 <title>History
</title>
273 <para>The following
"naming schemes" have been defined (which may be chosen at system boot-up time via
274 the
<varname>net.naming-scheme=
</varname> kernel command line switch, see above:
</para>
278 <term><constant>v238
</constant></term>
280 <listitem><para>This is the naming scheme that was implemented in systemd
238.
</para></listitem>
284 <term><constant>v239
</constant></term>
286 <listitem><para>Naming was changed for virtual network interfaces created with SR-IOV and NPAR and
287 for devices where the PCI network controller device does not have a slot number associated.
</para>
289 <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
290 <literal>v
<replaceable>port
</replaceable></literal>, where
<replaceable>port
</replaceable> is the
291 virtual device number. Previously those virtual devices were named as if completely independent.
294 <para>The ninth and later NPAR virtual devices are named following the scheme used for the first
295 eight NPAR partitions. Previously those devices were not renamed and the kernel default
296 (
"eth<replaceable>N</replaceable>") was used.
</para>
298 <para>Names are also generated for PCI devices where the PCI network controller device does not
299 have an associated slot number itself, but one of its parents does. Previously those devices were
300 not renamed and the kernel default was used.
</para>
305 <term><constant>v240
</constant></term>
307 <listitem><para>The
<literal>ib
</literal> prefix and stable names for infiniband devices are
308 introduced. Previously those devices were not renamed.
</para>
310 <para>The ACPI index field (used in
<varname>ID_NET_NAME_ONBOARD=
</varname>) is now also used when
313 <para>A new naming policy
<varname>NamePolicy=keep
</varname> was introduced. With this policy, if
314 the network device name was already set by userspace, the device will not be renamed
315 again. Previously, this naming policy applied implicitly, and now it must be explicitly
316 requested. Effectively, this means that network devices will be renamed according to the
317 configuration, even if they have been renamed already, if
<constant>keep
</constant> is not
318 specified as the naming policy in the
<filename index=
"false">.link
</filename> file. See
319 <citerefentry><refentrytitle>systemd.link
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
320 for a description of
<varname>NamePolicy=
</varname>.
</para></listitem>
324 <term><constant>v241
</constant></term>
326 <listitem><para><option>MACAddressPolicy=persistent
</option> was extended to set MAC addresses
327 based on the device name. Previously addresses were only based on the
328 <varname index=
"false">ID_NET_NAME_*
</varname> attributes, which meant that interface names would
329 never be generated for virtual devices. Now a persistent address will be generated for most
330 devices, including in particular bridges.
</para>
332 <para>Note: when userspace does not set a MAC address for a bridge device, the kernel will
333 initially assign a random address, and then change it when the first device is enslaved to the
334 bridge. With this naming policy change, bridges get a persistent MAC address based on the bridge
335 name instead of the first enslaved device.
</para></listitem>
339 <term><constant>v243
</constant></term>
341 <listitem><para>Support for renaming netdevsim (simulated networking) devices was added. Previously
342 those devices were not renamed.
</para>
344 <para>Previously two-letter interface type prefix was prepended to
345 <varname>ID_NET_LABEL_ONBOARD=
</varname>. This is not done anymore.
</para></listitem>
349 <term><constant>v245
</constant></term>
352 <citerefentry><refentrytitle>systemd-nspawn
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
353 derives the name for the host side of the network interface created with
354 <option>--network-veth
</option> from the container name it previously simply truncated the result
355 at
15 characters if longer (since that's the maximum length for network interface names). From now
356 on, for any interface name that would be longer than
15 characters the last
4 characters are set to
357 a
24bit hash value of the full interface name. This way network interface name collisions between
358 multiple similarly named containers (who only differ in container name suffix) should be less
359 likely (but still possible, since the
24bit hash value is very small).
</para></listitem>
363 <term><constant>v247
</constant></term>
365 <listitem><para>If the PCI slot is associated with PCI bridge and that has multiple child network
366 controllers then all of them might derive the same value of
<varname>ID_NET_NAME_SLOT
</varname>
367 property. That could cause naming conflict if the property is selected as a device name. Now, we detect the
368 situation, slot - bridge relation, and we don't produce the
<varname>ID_NET_NAME_SLOT
</varname> property to
369 avoid possible naming conflict.
</para></listitem>
374 <para>Note that
<constant>latest
</constant> may be used to denote the latest scheme known (to this
375 particular version of systemd).
</para>
379 <title>Examples
</title>
382 <title>Using
<command>udevadm test-builtin
</command> to display device properties
</title>
384 <programlisting>$ udevadm test-builtin net_id /sys/class/net/enp0s31f6
386 Using default interface naming scheme 'v243'.
387 ID_NET_NAMING_SCHEME=v243
388 ID_NET_NAME_MAC=enx54ee75cb1dc0
389 ID_OUI_FROM_DATABASE=Wistron InfoComm(Kunshan)Co.,Ltd.
390 ID_NET_NAME_PATH=enp0s31f6
395 <title>PCI Ethernet card with firmware index
"1"</title>
397 <programlisting>ID_NET_NAME_ONBOARD=eno1
398 ID_NET_NAME_ONBOARD_LABEL=Ethernet Port
1
403 <title>PCI Ethernet card in hotplug slot with firmware index number
</title>
405 <programlisting># /sys/devices/pci0000:
00/
0000:
00:
1c
.3/
0000:
05:
00.0/net/ens1
406 ID_NET_NAME_MAC=enx000000000466
407 ID_NET_NAME_PATH=enp5s0
408 ID_NET_NAME_SLOT=ens1
</programlisting>
412 <title>PCI Ethernet multi-function card with
2 ports
</title>
414 <programlisting># /sys/devices/pci0000:
00/
0000:
00:
1c
.0/
0000:
02:
00.0/net/enp2s0f0
415 ID_NET_NAME_MAC=enx78e7d1ea46da
416 ID_NET_NAME_PATH=enp2s0f0
418 # /sys/devices/pci0000:
00/
0000:
00:
1c
.0/
0000:
02:
00.1/net/enp2s0f1
419 ID_NET_NAME_MAC=enx78e7d1ea46dc
420 ID_NET_NAME_PATH=enp2s0f1
</programlisting>
424 <title>PCI WLAN card
</title>
426 <programlisting># /sys/devices/pci0000:
00/
0000:
00:
1c
.1/
0000:
03:
00.0/net/wlp3s0
427 ID_NET_NAME_MAC=wlx0024d7e31130
428 ID_NET_NAME_PATH=wlp3s0
</programlisting>
432 <title>PCI IB host adapter with
2 ports
</title>
434 <programlisting># /sys/devices/pci0000:
00/
0000:
00:
03.0/
0000:
15:
00.0/net/ibp21s0f0
435 ID_NET_NAME_PATH=ibp21s0f0
437 # /sys/devices/pci0000:
00/
0000:
00:
03.0/
0000:
15:
00.1/net/ibp21s0f1
438 ID_NET_NAME_PATH=ibp21s0f1
</programlisting>
442 <title>USB built-in
3G modem
</title>
444 <programlisting># /sys/devices/pci0000:
00/
0000:
00:
1d
.0/usb2/
2-
1/
2-
1.4/
2-
1.4:
1.6/net/wwp0s29u1u4i6
445 ID_NET_NAME_MAC=wwx028037ec0200
446 ID_NET_NAME_PATH=wwp0s29u1u4i6
</programlisting>
450 <title>USB Android phone
</title>
452 <programlisting># /sys/devices/pci0000:
00/
0000:
00:
1d
.0/usb2/
2-
1/
2-
1.2/
2-
1.2:
1.0/net/enp0s29u1u2
453 ID_NET_NAME_MAC=enxd626b3450fb5
454 ID_NET_NAME_PATH=enp0s29u1u2
</programlisting>
458 <title>s390 grouped CCW interface
</title>
460 <programlisting># /sys/devices/css0/
0.0.0007/
0.0.f5f0/group_device/net/encf5f0
461 ID_NET_NAME_MAC=enx026d3c00000a
462 ID_NET_NAME_PATH=encf5f0
</programlisting>
467 <title>See Also
</title>
469 <citerefentry><refentrytitle>udev
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
470 <citerefentry><refentrytitle>udevadm
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
471 <ulink url=
"https://systemd.io/PREDICTABLE_INTERFACE_NAMES">Predictable Network Interface Names
</ulink>,
472 <citerefentry><refentrytitle>systemd-nspawn
</refentrytitle><manvolnum>1</manvolnum></citerefentry>