Systemd-networkd

 Aug 16 14:49:00 SERVER systemd-networkd[1736]: macvtap32: Gained IPv6LL

Aug 16 14:52:13 SERVER systemd-networkd[1736]: macvtap32: Lost carrier

Dec 09 08:21:59 SERVER systemd-networkd[1617]: enx0t5b8f279a99: Link DOWN
Dec 09 08:21:59 SERVER systemd-networkd[1617]: enx0t5b8f279a99: Lost carrier

Dec 09 08:21:59 SERVER systemd-networkd[1617]: enx0t5b8f279a99: DHCP lease lost
Dec 09 08:21:59 SERVER systemd-networkd[1617]: enx0t5b8f279a99: DHCPv6 lease lost

Dec 09 08:22:25 SERVER systemd-networkd[1617]: enx0t5b8f279a99: Link UP
Dec 09 08:22:25 SERVER systemd-networkd[1617]: enx0t5b8f279a99: Gained carrier
Dec 09 08:22:25 SERVER systemd-networkd[1617]: enx0t5b8f279a99: DHCPv4 address xx.xx.xx.xx/24 via xx.xx.x.x

See also

• Netplan: netplan try, netplan apply, examples, networkd
• Systemd: systemctl, systemd-journald, journalctl systemd-cat, systemd-logind, systemd-networkd:networkctl, systemd-timesyncd, systemd-resolved, systemd-udevd , Systemd-logind: loginctl, hostnamectl, udevadm, systemd-run, portablectl, systemd-nspawn, systemd resource management, Timer (systemd), systemd logs, /etc/systemd/, systemd services, systemd-mount, /run/systemd/, .service, /usr/lib/systemd/, /usr/lib/systemd/system/, /usr/lib/systemd/system/systemd-resolved.service, /lib/systemd/, machinectl, systemd-oomd, systemd-analyze

https://wiki.ubuntu.com/DebuggingSystemd