Comment 2 for bug 578108

It looks like /etc/init/network-interface.conf from ifupdown should probably exclude ppp interfaces. It appears to be intended for hotplug, and ppp interfaces look like they're hotplugged, but in fact they're typically created as a result of an ifup invoking pppd. They need a way to be protected from automatic ifdown if they're persistent.

Adding ifupdown to the bug.