Comment 21 for bug 216847

As Seth mentioned in comment #13 likely network-online.target should be the solution.
@Owlbsidian - could you test and confirm with that as a fix as well?

A related fun quote from the systemd page about it:
"... please just fix your program to be friendly to dynamically changing network configuration. That way you will make your users happy because things just start to work, and you will get fewer bug reports ..."

Without that support you can still run into issues if e.g. you have a manually added interface you depend on (no service target will help you there). But that in turn would be an upstream feature request more than anything else.

Anyway, as long as ssh doesn't support that we might want to finally tackle that issue to at least improve it. Now that systemd has more means to express "online".
Maybe even by directly fixing it in Debian.

Subscribing server to track and cjwatson for his opinion (actually I see he is auto-subscribed to the pkg so he will see).