netplan is now the default network configurator on 18.04
- But on a freshly installed 18.04 system, I am still finding
/etc/networkstuff withinterfacesfile and other directories. - the ifup/ifdown utilities are still installed
Why ? It seems the ifupdown package is a dependance of pppoeconf (?). There is even a systemd service called networking that calls ifquery/ifup/ifdown ???
ifupdown is still being pulled in by pppoeconf; which may get installed on desktops (on servers, there should be no trace of ifupdown).
There is no use for ifupdown if you don't use pppoeconf, both can be safely removed. They were still installed automatically because some users may need pppoeconf to successfully get online and get additional packages.
If you upgrade from 16.04 or from 17.10, you will also have ifupdown remain on the system, since we can't safely migrate all configurations. It's better to leave ~400k around on the system (ifupdown + pppoeconf + any config they have) than to remove them and risk breaking things on upgrade.
/etc/network/interfaces is also left behind so we can point users to netplan, given the large number of docs that will be left around mentioning ifupdown here and there on the Internet.