systemd-networkd.service, systemd-networkd — Network manager
systemd-networkd.service
/usr/lib/systemd/systemd-networkd
systemd-networkd is a system service that manages networks. It detects and configures network devices as they appear, as well as creating virtual network devices.
To configure low-level link settings independently of networks, see systemd.link(5).
systemd-networkd will create network devices based on the configuration in systemd.netdev(5) files, respecting the [Match] sections in those files.
systemd-networkd will manage network addresses and
    routes for any link for which it finds a .network file
    with an appropriate [Match] section, see
    systemd.network(5).
    For those links, it will flush existing network addresses and routes when
    bringing up the device. Any links not matched by one of the
    .network files will be ignored. It is also possible to
    explicitly tell systemd-networkd to ignore a link by
    using Unmanaged=yes option, see
    systemd.network(5).
    
When systemd-networkd exits, it generally leaves existing network devices and
    configuration intact. This makes it possible to transition from the initrd and to restart the service
    without breaking connectivity. This also means that when configuration is updated and
    systemd-networkd is restarted, netdev interfaces for which configuration was removed
    will not be dropped, and may need to be cleaned up manually.
systemd-networkd may be introspected and controlled at runtime using networkctl(1).
See org.freedesktop.network1(5) and org.freedesktop.LogControl1(5) for a description of the D-Bus API.
The configuration files are read from the files located in the
    system network directory /usr/lib/systemd/network,
    the volatile runtime network directory
    /run/systemd/network and the local administration
    network directory /etc/systemd/network.
Networks are configured in .network
    files, see
    systemd.network(5),
    and virtual network devices are configured in
    .netdev files, see
    systemd.netdev(5).