path: root/man/systemd.net-naming-scheme.xml

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<refentry id="systemd.net-naming-scheme">
  <refentryinfo>
    <title>systemd.net-naming-scheme</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.net-naming-scheme</refentrytitle>
    <manvolnum>7</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.net-naming-scheme</refname>
    <refpurpose>Network device naming schemes</refpurpose>
  </refnamediv>

  <refsect1>
    <title>Description</title>

    <para>Network interfaces may be renamed to give them predictable names when there's enough information to
    generate appropriate names and the use of certain types of names is configured. This page describes the
    first part, i.e. what possible names may be generated. Those names are generated by the
    <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    builtin <command>net_id</command> and exported as udev properties
    (<varname>ID_NET_NAME_ONBOARD=</varname>, <varname>ID_NET_LABEL_ONBOARD=</varname>,
    <varname>ID_NET_NAME_PATH=</varname>, <varname>ID_NET_NAME_SLOT=</varname>).</para>

    <para>Names are derived from various device metadata attributes. Newer versions of udev take more of
    these attributes into account, improving (and thus possibly changing) the names used for the same
    devices. Differents version of the naming 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 overriden using the <varname>net.naming-scheme=</varname> kernel
    command line switch, see
    <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    Available naming schemes are described below.</para>

    <para>After the udev proprties have been generated, appropriate udev rules may be used to actually rename
    devices based on those properties. See the description of <varname>NamePolicy=</varname> in
    <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    </para>
  </refsect1>

  <refsect1>
    <title>Naming</title>

    <para>All names start with a two-character prefix that signifies the interface type.</para>

    <table>
      <title>Two character prefixes based on the type of interface</title>

      <tgroup cols='2'>
        <thead>
          <row>
            <entry>Prefix</entry>
            <entry>Description</entry>
          </row>
        </thead>
        <tbody>
          <row>
            <entry><constant>en</constant></entry>
            <entry>Ethernet</entry>
          </row>
          <row>
            <entry><constant>ib</constant></entry>
            <entry>InfiniBand</entry>
          </row>
          <row>
            <entry><constant>sl</constant></entry>
            <entry>serial line IP (slip)</entry>
          </row>
          <row>
            <entry><constant>wl</constant></entry>
            <entry>Wireless local area network (WLAN)</entry>
          </row>
          <row>
            <entry><constant>ww</constant></entry>
            <entry>Wireless wide area network (WWAN)</entry>
          </row>
        </tbody>
      </tgroup>
    </table>

    <para>The udev <command>net_id</command> builtin exports the following udev device properties:</para>

    <variablelist>
        <varlistentry>
          <term><varname>ID_NET_NAME_ONBOARD=<replaceable>prefix</replaceable><constant>o</constant><replaceable>number</replaceable></varname></term>

          <listitem><para>This name is set based on the ordering information given by the firmware for
          on-board devices. The name consists of the prefix, letter <constant>o</constant>, and a number
          specified by the firmware. This is only available for PCI devices.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>ID_NET_LABEL_ONBOARD=<replaceable>prefix</replaceable> <replaceable>label</replaceable></varname></term>

          <listitem><para>This property is set based on 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.
          </para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>ID_NET_NAME_MAC=<replaceable>prefix</replaceable><constant>x</constant><replaceable>AABBCCDDEEFF</replaceable></varname></term>

          <listitem><para>This name consists of the prefix, letter <constant>x</constant>, 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.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <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>
          <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>
          <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>
          <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>

          <listitem><para>This property describes the slot position. Different schemes are used depending on
          the bus type, as described in the table below. In all cases, PCI slot information must be known. 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.</para>

          <table>
            <title>Slot naming schemes</title>

            <tgroup cols='2'>
              <thead>
                <row>
                  <entry>Format</entry>
                  <entry>Description</entry>
                </row>
              </thead>

              <tbody>
                <row>
                  <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>
                  <entry>PCI slot number</entry>
                </row>

                <row>
                  <entry>… <constant>b</constant><replaceable>number</replaceable></entry>
                  <entry>Broadcom bus (BCMA) core number</entry>
                </row>

                <row>
                  <entry>… <constant>u</constant><replaceable>port</replaceable>… [<constant>c</constant><replaceable>config</replaceable>] [<constant>i</constant><replaceable>interface</replaceable>]</entry>
                  <entry>USB port number chain</entry>
                </row>

                <row>
                  <entry>… <constant>v</constant><replaceable>slot</replaceable></entry>
                  <entry>SR-VIO slot number</entry>
                </row>
              </tbody>
            </tgroup>
          </table>

          <para>The PCI domain is only prepended when it is not 0. All multi-function PCI devices will carry
          the <constant>f<replaceable>function</replaceable></constant> number in the device name, including
          the function 0 device. For non-multi-function devices, the number is suppressed if 0. The port name
          <replaceable>port_name</replaceable> is used, or the port number
          <constant>d</constant><replaceable>dev_port</replaceable> if the name is not known.</para>

          <para>For BCMA devices, the core number is suppressed when 0.</para>

          <para>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.</para>
          </listitem>

          <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
          <constant>v</constant> and the virtual device number, with any leading zeros removed. The bus
          number is ignored. This device type is found in IBM PowerVMs.</para>
        </varlistentry>

        <varlistentry>
          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>c</constant><replaceable>bus_id</replaceable></varname></term>
          <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>
          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>i</constant><replaceable>address</replaceable><constant>n</constant><replaceable>port_name</replaceable></varname></term>
          <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>
          <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>
          <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>

          <listitem><para>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.</para>

          <table>
            <title>Path naming schemes</title>

            <tgroup cols='2'>
              <thead>
                <row>
                  <entry>Format</entry>
                  <entry>Description</entry>
                </row>
              </thead>

              <tbody>
                <row>
                  <entry><replaceable>prefix</replaceable> <constant>c</constant><replaceable>bus_id</replaceable></entry>
                  <entry>CCW or grouped CCW device identifier</entry>
                </row>

                <row>
                  <entry><replaceable>prefix</replaceable> <constant>a</constant><replaceable>vendor</replaceable> <replaceable>model</replaceable> <constant>i</constant><replaceable>instance</replaceable></entry>
                  <entry>ACPI path names for ARM64 platform devices</entry>
                </row>

                <row>
                  <entry><replaceable>prefix</replaceable> <constant>i</constant><replaceable>address</replaceable> <constant>n</constant><replaceable>port_name</replaceable></entry>
                  <entry>Netdevsim (simulated networking device) device number and port name</entry>
                </row>

                <row>
                  <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>
                  <entry>PCI geographical location</entry>
                </row>

                <row>
                  <entry>… <constant>b</constant><replaceable>number</replaceable></entry>
                  <entry>Broadcom bus (BCMA) core number</entry>
                </row>

                <row>
                  <entry>… <constant>u</constant><replaceable>port</replaceable>… [<constant>c</constant><replaceable>config</replaceable>] [<constant>i</constant><replaceable>interface</replaceable>]</entry>
                  <entry>USB port number chain</entry>
                </row>

              </tbody>
            </tgroup>
          </table>

          <para>CCW and grouped CCW devices are found in IBM System Z mainframes. Any leading zeros and
          dots are suppressed.</para>

          <para>For PCI, BCMA, and USB devices, the same rules as described above for slot naming are
          used.</para>
          </listitem>
        </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>History</title>

    <para>The following "naming schemes" have been defined:</para>

    <variablelist>
        <varlistentry>
          <term><constant>v238</constant></term>

          <listitem><para>This is the naming naming that was implemented in systemd 238.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>v239</constant></term>

          <listitem><para>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.</para>

          <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
          <literal>v<replaceable>port</replaceable></literal>, where <replaceable>port</replaceable> is the
          virtual device number. Previously those virtual devices were named as if completely independent.
          </para>

          <para>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
          ("eth<replaceable>N</replaceable>") was used.</para>

          <para>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.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>v240</constant></term>

          <para>The <literal>ib</literal> prefix and stable names for infiniband devices are
          introduced. Previously those devices were not renamed.</para>

          <para>The ACPI index field (used in <varname>ID_NET_NAME_ONBOARD=</varname>) is now also used when
          0.</para>

          <para>A new naming policy <varname>NamePolicy=keep</varname> 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 <constant>keep</constant> is not
          specified as the naming policy in the <filename noindex='true'>.link</filename> file. See
          <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for a description of <varname>NamePolicy=</varname>.</para>
        </varlistentry>

        <varlistentry>
          <term><constant>v243</constant></term>

          <para>Support for netdevsim (simulated networking devices) was added. Previously those devices were
          not renamed.</para>

          <para>Previously two-letter interface type prefix was prepended to
          <varname>ID_NET_LABEL_ONBOARD=</varname>. This is not done anymore.</para>
        </varlistentry>

        <para>Note that <constant>latest</constant> may be used to denote the latest scheme known (to this
        particular version of systemd.</para>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Using <command>udevadm test-builtin</command> to display device properties</title>

      <programlisting>$ 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
...</programlisting>
    </example>

    <example>
      <title>PCI Ethernet card with firmware index "1"</title>

      <programlisting>ID_NET_NAME_ONBOARD=eno1
ID_NET_NAME_ONBOARD_LABEL=Ethernet Port 1
      </programlisting>
    </example>

    <example>
      <title>PCI Ethernet card in hotplug slot with firmware index number</title>

      <programlisting># /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</programlisting>
    </example>

    <example>
      <title>PCI Ethernet multi-function card with 2 ports</title>

      <programlisting># /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</programlisting>
    </example>

    <example>
      <title>PCI WLAN card</title>

      <programlisting># /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlp3s0
ID_NET_NAME_MAC=wlx0024d7e31130
ID_NET_NAME_PATH=wlp3s0</programlisting>
    </example>

    <example>
      <title>PCI IB host adapter with 2 ports</title>

      <programlisting># /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</programlisting>
    </example>

    <example>
      <title>USB built-in 3G modem</title>

      <programlisting># /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</programlisting>
    </example>

    <example>
      <title>USB Android phone</title>

      <programlisting># /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</programlisting>
    </example>

    <example>
      <title>s390 grouped CCW interface</title>

      <programlisting># /sys/devices/css0/0.0.0007/0.0.f5f0/group_device/net/encf5f0
ID_NET_NAME_MAC=enx026d3c00000a
ID_NET_NAME_PATH=encf5f0</programlisting>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <ulink url="https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames">the
      original page describing stable interface names</ulink>
    </para>
  </refsect1>

</refentry>