In the Eoan version of systemd, I can see in the logs these messages:
Oct 24 18:52:32.753746 ubuntu systemd-networkd[1167]: Setting '/proc/sys/net/ipv6/conf/interface1/proxy_ndp' to '0'
Oct 24 18:52:32.753848 ubuntu systemd-networkd[1167]: Setting '/proc/sys/net/ipv6/conf/interface1/use_tempaddr' to '0'
Oct 24 18:52:32.753884 ubuntu systemd-networkd[1167]: Setting '/proc/sys/net/ipv6/conf/interface1/accept_ra' to '0'
Oct 24 18:52:32.753962 ubuntu systemd-networkd[1167]: Setting '/proc/sys/net/ipv6/conf/interface1/mtu' to '5634'
These are not emitted in bionic or disco versions of systemd.
In the Eoan version of systemd, I can see in the logs these messages:
Oct 24 18:52:32.753746 ubuntu systemd- networkd[ 1167]: Setting '/proc/ sys/net/ ipv6/conf/ interface1/ proxy_ndp' to '0' networkd[ 1167]: Setting '/proc/ sys/net/ ipv6/conf/ interface1/ use_tempaddr' to '0' networkd[ 1167]: Setting '/proc/ sys/net/ ipv6/conf/ interface1/ accept_ ra' to '0' networkd[ 1167]: Setting '/proc/ sys/net/ ipv6/conf/ interface1/ mtu' to '5634'
Oct 24 18:52:32.753848 ubuntu systemd-
Oct 24 18:52:32.753884 ubuntu systemd-
Oct 24 18:52:32.753962 ubuntu systemd-
These are not emitted in bionic or disco versions of systemd.