Comment 22 for bug 1721223

root@systemd-sru-xenial:~# dpkg-query -W systemd
systemd 229-4ubuntu21.1

Installed netplan, executed ifupdown-upgrade, rebooted:

root@systemd-sru-xenial:~# grep -e 0 -e 1 /proc/sys/net/ipv4/conf/*/promote_secondaries
/proc/sys/net/ipv4/conf/all/promote_secondaries:0
/proc/sys/net/ipv4/conf/default/promote_secondaries:0
/proc/sys/net/ipv4/conf/eth0/promote_secondaries:0
/proc/sys/net/ipv4/conf/lo/promote_secondaries:0

Upgraded systemd to the one in proposed:

# dpkg-query -W systemd
systemd 229-4ubuntu21.2

# grep -e 0 -e 1 /proc/sys/net/ipv4/conf/*/promote_secondaries
/proc/sys/net/ipv4/conf/all/promote_secondaries:0
/proc/sys/net/ipv4/conf/default/promote_secondaries:0
/proc/sys/net/ipv4/conf/eth0/promote_secondaries:1
/proc/sys/net/ipv4/conf/lo/promote_secondaries:0

Observed change in promote_secondaries for eth0 device.

Note, when not migrating to netplan, promote_secondaries remains as 0, preserving the current xenial behaviour under ifupdown.