Comment 11 for bug 1664844

Well, to clarify, I guess I'm not 100% happy with that. ;-)

What you describe will work for the majority of server and cloud use cases. But installing Ubuntu on a router (or L3 switch) will be problematic if nothing happens when links go up or down. Actions need to be taken, such as adding or removing routes, so that the kernel doesn't attempt to route traffic to link-down interfaces.

That is, with a standard ifupdown configuration, I observe that when an interface becomes link-down (assuming it is administratively up per ifupdown) the IP addresses remain configured, the local routes remain in place, and any routes via the interface remain in the kernel. Arguably this is incorrect behavior, and I don't know if networkd handles this in some different way. (If I remember correctly, it behaved similarly to ifupdown, but correct me if I'm wrong.)