Since 17fd304e60 ("resolve: Don't install individual servers via
resolvconf"), DNS servers were sorted if getting installed via resolvconf.
In some setups the order might be important (even though relying on it
isn't a good idea in general as stub resolvers are free to use all of
the servers as they please).
The resolvconf implementation provided by systemd via resolvectl strips
everything after the interface name, so each additional server that's
installed replaces the previous one. And even for other resolvconf
implementations installing them individually doesn't seem necessary as
we track and refcount them anyway.
Closesstrongswan/strongswan#1353
Newer releases of systemd contain a change that removes not the part
after the first dot but the part after the last when determining the
interface name (apparently some interface names actually contain a dot).
This changes the default prefix to only contain one dot and avoids the
dots added by IPv4 addresses to create a unique interface/protocol for
each DNS server (it also replaces the `:` in IPv6 addresses with
something that might cause less conflicts).
References strongswan/strongswan#1353
This fixes DNS server installation if make-before-break reauthentication
is used as there the new SA and DNS server is installed before it then
is removed again when the old IKE_SA is torn down.
If running resolvconf fails handle() fails release() is not called, which
might leave an interface file on the system (or depending on which script
called by resolvconf actually failed even the installed DNS server).
Tobias Brunner