Comment 66 for bug 881079

On Sat, Jun 02, 2012 at 09:58:18AM -0000, Roberto Gordo Saez wrote:
> Please note there is a problem with removable network devices (usually
> usb). The file /etc/init/network-interface.conf "causes network devices
> to be brought up or down as a result of hardware being added or
> removed", as its own comment says, but they must be configured as "auto"
> in /etc/network/interfaces

If you have network devices that are not always present, which you want to
be autoconfigured when they are, it may be better to configure them with
NetworkManager instead of with ifupdown.

> For removable network devices, there should be a method of bringing them
> up and down correctly without requiring them to be plugged at boot. It
> was working on previous releases of Ubuntu, probably because there was
> no delay at boot for missing devices.

It still works, it just introduces a delay. You can certainly edit the
upstart job to remove / reduce the delay, if that works better for your
environment.

A more complete fix for the problem of ifupdown starting of
sometimes-available network interfaces is unlikely to happen any time soon,
I'm afraid.