I had a huge puzzle in Sid, why is lightdm coming online faster than my network. I was going to tty1 after logging in and systemd was still chugging along
From the debian changelog of ifupdown
http://metadata.ftp-master.debian.org/changelogs/main/i/ifupdown/ifupdown_0.8.10_changelog
Quoteifupdown (0.8.9) unstable; urgency=medium
* It's network-online.target, not .service.
* Do not run "ip link set down" on manual interfaces during "ifdown -a".
Closes: #809166
* Add the keywords "no-auto-down" and "no-scripts". Closes: #615130
search engines are not great for non-existing services, ha ha.
Also adding to the mix was the change in 8.7
Impose a 5 minute timeout for starting network services.
Closes: #318577, #810656
So, if it is taking forever ("systemd-analyze blame" is your friend here to identify) - well it is mostly harmless and will be upgraded soon.
Lot of juggling going on with ifupdown taking some things away from systemd in Debian (and probably ubuntu also)