man/systemd.net-naming-scheme.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="systemd.net-naming-scheme">
   7   <refentryinfo>
   8     <title>systemd.net-naming-scheme</title>
   9     <productname>systemd</productname>
  10   </refentryinfo>
  11
  12   <refmeta>
  13     <refentrytitle>systemd.net-naming-scheme</refentrytitle>
  14     <manvolnum>7</manvolnum>
  15   </refmeta>
  16
  17   <refnamediv>
  18     <refname>systemd.net-naming-scheme</refname>
  19     <refpurpose>Network device naming schemes</refpurpose>
  20   </refnamediv>
  21
  22   <refsect1>
  23     <title>Description</title>
  24
  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>
  33
  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>
  44
  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>
  49
  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>
  54   </refsect1>
  55
  56   <refsect1>
  57     <title>Naming</title>
  58
  59     <para>All names start with a two-character prefix that signifies the interface type.</para>
  60
  61     <table>
  62       <title>Two character prefixes based on the type of interface</title>
  63
  64       <tgroup cols='2'>
  65         <thead>
  66           <row>
  67             <entry>Prefix</entry>
  68             <entry>Description</entry>
  69           </row>
  70         </thead>
  71         <tbody>
  72           <row>
  73             <entry><constant>en</constant></entry>
  74             <entry>Ethernet</entry>
  75           </row>
  76           <row>
  77             <entry><constant>ib</constant></entry>
  78             <entry>InfiniBand</entry>
  79           </row>
  80           <row>
  81             <entry><constant>sl</constant></entry>
  82             <entry>Serial line IP (slip)</entry>
  83           </row>
  84           <row>
  85             <entry><constant>wl</constant></entry>
  86             <entry>Wireless local area network (WLAN)</entry>
  87           </row>
  88           <row>
  89             <entry><constant>ww</constant></entry>
  90             <entry>Wireless wide area network (WWAN)</entry>
  91           </row>
  92         </tbody>
  93       </tgroup>
  94     </table>
  95
  96     <para>The udev <command>net_id</command> builtin exports the following udev device properties:</para>
  97
  98     <variablelist>
  99         <varlistentry>
 100           <term><varname>ID_NET_NAME_ONBOARD=<replaceable>prefix</replaceable><constant>o</constant><replaceable>number</replaceable></varname></term>
 101           <term><varname>ID_NET_NAME_ONBOARD=<replaceable>prefix</replaceable><constant>d</constant><replaceable>number</replaceable></varname></term>
 102
 103           <listitem><para>This name is set based on the numeric ordering information given by the firmware
 104           for on-board devices. Different schemes are used depending on the firmware type, as described in
 105           the table below.</para>
 106
 107             <table>
 108               <title>On-board naming schemes</title>
 109
 110               <tgroup cols='2'>
 111                 <thead>
 112                   <row>
 113                     <entry>Format</entry>
 114                     <entry>Description</entry>
 115                   </row>
 116                 </thead>
 117
 118                 <tbody>
 119                   <row>
 120                     <entry><replaceable>prefix</replaceable><constant>o</constant><replaceable>number</replaceable></entry>
 121                     <entry>PCI on-board index</entry>
 122                   </row>
 123
 124                   <row>
 125                     <entry><replaceable>prefix</replaceable><constant>d</constant><replaceable>number</replaceable></entry>
 126                     <entry>Devicetree alias index</entry>
 127                   </row>
 128
 129                 </tbody>
 130               </tgroup>
 131             </table>
 132           </listitem>
 133         </varlistentry>
 134
 135         <varlistentry>
 136           <term><varname>ID_NET_LABEL_ONBOARD=<replaceable>prefix</replaceable> <replaceable>label</replaceable></varname></term>
 137
 138           <listitem><para>This property is set based on textual label given by the firmware for on-board
 139           devices. The name consists of the prefix concatenated with the label. This is only available for
 140           PCI devices.
 141           </para>
 142           </listitem>
 143         </varlistentry>
 144
 145         <varlistentry>
 146           <term><varname>ID_NET_NAME_MAC=<replaceable>prefix</replaceable><constant>x</constant><replaceable>AABBCCDDEEFF</replaceable></varname></term>
 147
 148           <listitem><para>This name consists of the prefix, letter <constant>x</constant>, and 12 hexadecimal
 149           digits of the MAC address. It is available if the device has a fixed MAC address. Because this name
 150           is based on an attribute of the card itself, it remains "stable" when the device is moved (even
 151           between machines), but will change when the hardware is replaced.</para>
 152           </listitem>
 153         </varlistentry>
 154
 155         <varlistentry>
 156           <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>
 157           <term><varname>ID_NET_NAME_SLOT=<replaceable>prefix</replaceable><constant>v</constant><replaceable>slot</replaceable></varname></term>
 158           <term><varname>ID_NET_NAME_SLOT=<replaceable>prefix</replaceable><constant>x</constant><replaceable>slot</replaceable></varname></term>
 159           <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>
 160           <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>
 161           <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>
 162
 163           <listitem><para>This property describes the slot position. Different schemes are used depending on
 164           the bus type, as described in the table below. In case of USB, BCMA, and SR-VIO devices, the full
 165           name consists of the prefix, PCI slot identifier, and USB or BCMA or SR-VIO slot identifier. The
 166           first two parts are denoted as "…" in the table below.</para>
 167
 168           <table>
 169             <title>Slot naming schemes</title>
 170
 171             <tgroup cols='2'>
 172               <thead>
 173                 <row>
 174                   <entry>Format</entry>
 175                   <entry>Description</entry>
 176                 </row>
 177               </thead>
 178
 179               <tbody>
 180                 <row>
 181                   <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>
 182                   <entry>PCI slot number</entry>
 183                 </row>
 184
 185                 <row>
 186                   <entry><replaceable>prefix</replaceable> <constant>v</constant><replaceable>slot</replaceable></entry>
 187                   <entry>VIO slot number (IBM PowerVM)</entry>
 188                 </row>
 189
 190                 <row>
 191                   <entry><replaceable>prefix</replaceable> <constant>X</constant><replaceable>number</replaceable></entry>
 192                   <entry>VIF interface number (Xen)</entry>
 193                 </row>
 194
 195                 <row>
 196                   <entry>… <constant>b</constant><replaceable>number</replaceable></entry>
 197                   <entry>Broadcom bus (BCMA) core number</entry>
 198                 </row>
 199
 200                 <row>
 201                   <entry>… <constant>u</constant><replaceable>port</replaceable>… [<constant>c</constant><replaceable>config</replaceable>] [<constant>i</constant><replaceable>interface</replaceable>]</entry>
 202                   <entry>USB port number chain</entry>
 203                 </row>
 204
 205                 <row>
 206                   <entry>… <constant>v</constant><replaceable>slot</replaceable></entry>
 207                   <entry>SR-VIO slot number</entry>
 208                 </row>
 209               </tbody>
 210             </tgroup>
 211           </table>
 212
 213           <para>The PCI domain is only prepended when it is not 0. All multi-function PCI devices will carry
 214           the <constant>f<replaceable>function</replaceable></constant> number in the device name, including
 215           the function 0 device. For non-multi-function devices, the number is suppressed if 0. The port name
 216           <replaceable>port_name</replaceable> is used, or the port number
 217           <constant>d</constant><replaceable>dev_port</replaceable> if the name is not known.</para>
 218
 219           <para>For BCMA devices, the core number is suppressed when 0.</para>
 220
 221           <para>For USB devices the full chain of port numbers of hubs is composed. If the name gets longer
 222           than the maximum number of 15 characters, the name is not exported. The usual USB configuration
 223           number 1 and interface number 0 values are suppressed.</para>
 224
 225           <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
 226           <constant>v</constant> and the virtual device number, with any leading zeros removed. The bus
 227           number is ignored.</para>
 228
 229           <para>In some configurations a parent PCI bridge of a given network controller may be associated
 230           with a slot. In such case we don't generate this device property to avoid possible naming conflicts.</para>
 231           </listitem>
 232         </varlistentry>
 233
 234         <varlistentry>
 235           <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>c</constant><replaceable>bus_id</replaceable></varname></term>
 236           <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>
 237           <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>i</constant><replaceable>address</replaceable><constant>n</constant><replaceable>port_name</replaceable></varname></term>
 238           <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>u</constant><replaceable>port</replaceable>…</varname></term>
 239           <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>
 240           <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>
 241           <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>
 242
 243           <listitem><para>This property describes the device installation location. Different schemes are
 244           used depending on the bus type, as described in the table below. For BCMA and USB devices, PCI path
 245           information must known, and the full name consists of the prefix, PCI slot identifier, and USB or
 246           BCMA location. The first two parts are denoted as "…" in the table below.</para>
 247
 248           <table>
 249             <title>Path naming schemes</title>
 250
 251             <tgroup cols='2'>
 252               <thead>
 253                 <row>
 254                   <entry>Format</entry>
 255                   <entry>Description</entry>
 256                 </row>
 257               </thead>
 258
 259               <tbody>
 260                 <row>
 261                   <entry><replaceable>prefix</replaceable> <constant>c</constant><replaceable>bus_id</replaceable></entry>
 262                   <entry>CCW or grouped CCW device identifier</entry>
 263                 </row>
 264
 265                 <row>
 266                   <entry><replaceable>prefix</replaceable> <constant>a</constant><replaceable>vendor</replaceable> <replaceable>model</replaceable> <constant>i</constant><replaceable>instance</replaceable></entry>
 267                   <entry>ACPI path names for ARM64 platform devices</entry>
 268                 </row>
 269
 270                 <row>
 271                   <entry><replaceable>prefix</replaceable> <constant>i</constant><replaceable>address</replaceable> <constant>n</constant><replaceable>port_name</replaceable></entry>
 272                   <entry>Netdevsim (simulated networking device) device number and port name</entry>
 273                 </row>
 274
 275                 <row>
 276                   <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>
 277                   <entry>PCI geographical location</entry>
 278                 </row>
 279
 280                 <row>
 281                   <entry>… <constant>b</constant><replaceable>number</replaceable></entry>
 282                   <entry>Broadcom bus (BCMA) core number</entry>
 283                 </row>
 284
 285                 <row>
 286                   <entry>… <constant>u</constant><replaceable>port</replaceable>… [<constant>c</constant><replaceable>config</replaceable>] [<constant>i</constant><replaceable>interface</replaceable>]</entry>
 287                   <entry>USB port number chain</entry>
 288                 </row>
 289
 290               </tbody>
 291             </tgroup>
 292           </table>
 293
 294           <para>CCW and grouped CCW devices are found in IBM System Z mainframes. Any leading zeros and
 295           dots are suppressed.</para>
 296
 297           <para>For PCI, BCMA, and USB devices, the same rules as described above for slot naming are
 298           used.</para>
 299           </listitem>
 300         </varlistentry>
 301     </variablelist>
 302   </refsect1>
 303
 304   <refsect1>
 305     <title>History</title>
 306
 307     <para>The following "naming schemes" have been defined (which may be chosen at system boot-up time via
 308     the <varname>net.naming-scheme=</varname> kernel command line switch, see above):</para>
 309
 310     <variablelist>
 311         <varlistentry>
 312           <term><constant>v238</constant></term>
 313
 314           <listitem><para>This is the naming scheme that was implemented in systemd 238.</para></listitem>
 315         </varlistentry>
 316
 317         <varlistentry>
 318           <term><constant>v239</constant></term>
 319
 320           <listitem><para>Naming was changed for virtual network interfaces created with SR-IOV and NPAR and
 321           for devices where the PCI network controller device does not have a slot number associated.</para>
 322
 323           <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
 324           <literal>v<replaceable>port</replaceable></literal>, where <replaceable>port</replaceable> is the
 325           virtual device number. Previously those virtual devices were named as if completely independent.
 326           </para>
 327
 328           <para>The ninth and later NPAR virtual devices are named following the scheme used for the first
 329           eight NPAR partitions. Previously those devices were not renamed and the kernel default
 330           ("eth<replaceable>N</replaceable>") was used.</para>
 331
 332           <para>Names are also generated for PCI devices where the PCI network controller device does not
 333           have an associated slot number itself, but one of its parents does. Previously those devices were
 334           not renamed and the kernel default was used.</para>
 335           </listitem>
 336         </varlistentry>
 337
 338         <varlistentry>
 339           <term><constant>v240</constant></term>
 340
 341           <listitem><para>The <literal>ib</literal> prefix and stable names for infiniband devices are
 342           introduced. Previously those devices were not renamed.</para>
 343
 344           <para>The ACPI index field (used in <varname>ID_NET_NAME_ONBOARD=</varname>) is now also used when
 345           0.</para>
 346
 347           <para>A new naming policy <varname>NamePolicy=keep</varname> was introduced. With this policy, if
 348           the network device name was already set by userspace, the device will not be renamed
 349           again. Previously, this naming policy applied implicitly, and now it must be explicitly
 350           requested. Effectively, this means that network devices will be renamed according to the
 351           configuration, even if they have been renamed already, if <constant>keep</constant> is not
 352           specified as the naming policy in the <filename index="false">.link</filename> file. See
 353           <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 354           for a description of <varname>NamePolicy=</varname>.</para></listitem>
 355         </varlistentry>
 356
 357         <varlistentry>
 358           <term><constant>v241</constant></term>
 359
 360           <listitem><para><option>MACAddressPolicy=persistent</option> was extended to set MAC addresses
 361           based on the device name. Previously addresses were only based on the
 362           <varname index="false">ID_NET_NAME_*</varname> attributes, which meant that interface names would
 363           never be generated for virtual devices. Now a persistent address will be generated for most
 364           devices, including in particular bridges.</para>
 365
 366           <para>Note: when userspace does not set a MAC address for a bridge device, the kernel will
 367           initially assign a random address, and then change it when the first device is enslaved to the
 368           bridge. With this naming policy change, bridges get a persistent MAC address based on the bridge
 369           name instead of the first enslaved device.</para></listitem>
 370         </varlistentry>
 371
 372         <varlistentry>
 373           <term><constant>v243</constant></term>
 374
 375           <listitem><para>Support for renaming netdevsim (simulated networking) devices was added. Previously
 376           those devices were not renamed.</para>
 377
 378           <para>Previously two-letter interface type prefix was prepended to
 379           <varname>ID_NET_LABEL_ONBOARD=</varname>. This is not done anymore.</para></listitem>
 380         </varlistentry>
 381
 382         <varlistentry>
 383           <term><constant>v245</constant></term>
 384
 385           <listitem><para>When
 386           <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 387           derives the name for the host side of the network interface created with
 388           <option>--network-veth</option> from the container name it previously simply truncated the result
 389           at 15 characters if longer (since that's the maximum length for network interface names). From now
 390           on, for any interface name that would be longer than 15 characters the last 4 characters are set to
 391           a 24bit hash value of the full interface name. This way network interface name collisions between
 392           multiple similarly named containers (who only differ in container name suffix) should be less
 393           likely (but still possible, since the 24bit hash value is very small).</para></listitem>
 394         </varlistentry>
 395
 396         <varlistentry>
 397           <term><constant>v247</constant></term>
 398
 399           <listitem><para>When a PCI slot is associated with a PCI bridge that has multiple child network
 400           controllers, the same value of the <varname>ID_NET_NAME_SLOT</varname> property might be derived
 401           for those controllers. This would cause a naming conflict if the property is selected as the device
 402           name. Now, we detect this situation and don't produce the <varname>ID_NET_NAME_SLOT</varname>
 403           property.</para></listitem>
 404         </varlistentry>
 405
 406         <varlistentry>
 407           <term><constant>v249</constant></term>
 408
 409           <listitem><para>PCI hotplug slot names for the s390 PCI driver are a hexadecimal representation
 410           of the <filename>function_id</filename> device attribute. This attribute is now used to build the
 411           <varname>ID_NET_NAME_SLOT</varname>. Before that, all slot names were parsed as decimal
 412           numbers, which could either result in an incorrect value of the <varname>ID_NET_NAME_SLOT</varname>
 413           property or none at all.</para>
 414
 415           <para>Some firmware and hypervisor implementations report unreasonably high numbers for the
 416           on-board index. To prevent the generation of bogus onbard interface names, index numbers greater
 417           than 16381 (2¹⁴-1) were ignored. For s390 PCI devices index values up to 65535 (2¹⁶-1) are valid.
 418           To account for that, the limit was increased to 65535.</para>
 419
 420           <para>The udev rule <varname>NAME=</varname> replaces <literal>:</literal>,
 421           <literal>/</literal>, and <literal>%</literal> with an underscore (<literal>_</literal>), and
 422           refuses strings which contain only numerics.</para>
 423           </listitem>
 424         </varlistentry>
 425
 426         <varlistentry>
 427           <term><constant>v250</constant></term>
 428
 429           <listitem><para>Added naming scheme for Xen netfront "vif" interfaces based on the guest side
 430           VIF number set from the Xen config (or the interface index in AWS EC2).</para>
 431           </listitem>
 432         </varlistentry>
 433
 434         <varlistentry>
 435           <term><constant>v251</constant></term>
 436
 437           <listitem><para>Since version <constant>v247</constant> we no longer set
 438           <varname>ID_NET_NAME_SLOT</varname> if we detect that a PCI device associated with a slot is a PCI
 439           bridge as that would create naming conflict when there are more child devices on that bridge. Now,
 440           this is relaxed and we will use slot information to generate the name based on it but only if
 441           the PCI device has multiple functions. This is safe because distinct function number is a part of
 442           the device name for multifunction devices.</para>
 443           </listitem>
 444         </varlistentry>
 445
 446         <varlistentry>
 447           <term><constant>v252</constant></term>
 448
 449           <listitem><para>Added naming scheme for platform devices with devicetree aliases.</para>
 450           </listitem>
 451         </varlistentry>
 452
 453         <varlistentry>
 454           <term><constant>v253</constant></term>
 455
 456           <listitem><para>Set <varname>ID_NET_NAME_PATH</varname> for usb devices not connected via a PCI bus.</para>
 457           </listitem>
 458         </varlistentry>
 459
 460       </variablelist>
 461
 462     <para>Note that <constant>latest</constant> may be used to denote the latest scheme known (to this
 463     particular version of systemd).</para>
 464   </refsect1>
 465
 466   <refsect1>
 467     <title>Examples</title>
 468
 469     <example>
 470       <title>Using <command>udevadm test-builtin</command> to display device properties</title>
 471
 472       <programlisting>$ udevadm test-builtin net_id /sys/class/net/enp0s31f6
 473 ...
 474 Using default interface naming scheme 'v243'.
 475 ID_NET_NAMING_SCHEME=v243
 476 ID_NET_NAME_MAC=enx54ee75cb1dc0
 477 ID_OUI_FROM_DATABASE=Wistron InfoComm(Kunshan)Co.,Ltd.
 478 ID_NET_NAME_PATH=enp0s31f6
 479 ...</programlisting>
 480     </example>
 481
 482     <example>
 483       <title>PCI Ethernet card with firmware index "1"</title>
 484
 485       <programlisting>ID_NET_NAME_ONBOARD=eno1
 486 ID_NET_NAME_ONBOARD_LABEL=Ethernet Port 1
 487       </programlisting>
 488     </example>
 489
 490     <example>
 491       <title>PCI Ethernet card in hotplug slot with firmware index number</title>
 492
 493       <programlisting># /sys/devices/pci0000:00/0000:00:1c.3/0000:05:00.0/net/ens1
 494 ID_NET_NAME_MAC=enx000000000466
 495 ID_NET_NAME_PATH=enp5s0
 496 ID_NET_NAME_SLOT=ens1</programlisting>
 497     </example>
 498
 499     <example>
 500       <title>PCI Ethernet multi-function card with 2 ports</title>
 501
 502       <programlisting># /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.0/net/enp2s0f0
 503 ID_NET_NAME_MAC=enx78e7d1ea46da
 504 ID_NET_NAME_PATH=enp2s0f0
 505
 506 # /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.1/net/enp2s0f1
 507 ID_NET_NAME_MAC=enx78e7d1ea46dc
 508 ID_NET_NAME_PATH=enp2s0f1</programlisting>
 509     </example>
 510
 511     <example>
 512       <title>PCI WLAN card</title>
 513
 514       <programlisting># /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlp3s0
 515 ID_NET_NAME_MAC=wlx0024d7e31130
 516 ID_NET_NAME_PATH=wlp3s0</programlisting>
 517     </example>
 518
 519     <example>
 520       <title>PCI IB host adapter with 2 ports</title>
 521
 522       <programlisting># /sys/devices/pci0000:00/0000:00:03.0/0000:15:00.0/net/ibp21s0f0
 523 ID_NET_NAME_PATH=ibp21s0f0
 524
 525 # /sys/devices/pci0000:00/0000:00:03.0/0000:15:00.1/net/ibp21s0f1
 526 ID_NET_NAME_PATH=ibp21s0f1</programlisting>
 527     </example>
 528
 529     <example>
 530       <title>USB built-in 3G modem</title>
 531
 532       <programlisting># /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.4/2-1.4:1.6/net/wwp0s29u1u4i6
 533 ID_NET_NAME_MAC=wwx028037ec0200
 534 ID_NET_NAME_PATH=wwp0s29u1u4i6</programlisting>
 535     </example>
 536
 537     <example>
 538       <title>USB Android phone</title>
 539
 540       <programlisting># /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2/2-1.2:1.0/net/enp0s29u1u2
 541 ID_NET_NAME_MAC=enxd626b3450fb5
 542 ID_NET_NAME_PATH=enp0s29u1u2</programlisting>
 543     </example>
 544
 545     <example>
 546       <title>s390 grouped CCW interface</title>
 547
 548       <programlisting># /sys/devices/css0/0.0.0007/0.0.f5f0/group_device/net/encf5f0
 549 ID_NET_NAME_MAC=enx026d3c00000a
 550 ID_NET_NAME_PATH=encf5f0</programlisting>
 551     </example>
 552   </refsect1>
 553
 554   <refsect1>
 555     <title>See Also</title>
 556     <para>
 557       <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 558       <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 559       <ulink url="https://systemd.io/PREDICTABLE_INTERFACE_NAMES">Predictable Network Interface Names</ulink>,
 560       <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 561     </para>
 562   </refsect1>
 563
 564 </refentry>