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).
Network configurations applied before networkd is started are not removed, and static configuration applied by networkd is not removed when networkd exits. Dynamic configuration applied by networkd may also optionally be left in place on shutdown. This ensures restarting networkd does not cut the network connection, and, in particular, that it is safe to transition between the initrd and the real root, and back.
The configuration files are read from the files located in the system network directory /lib/systemd/network, the volatile runtime network directory /run/systemd/network and the local administration network directory /etc/systemd/network.