Comment 15 for bug 78043

Stéphane, the following is an extract from my /etc/network/interfaces:

auto eth0
iface eth0 inet static
        address 10.0.0.251
        netmask 255.255.255.0
        ...

auto ppp0
iface ppp0 inet ppp
        pre-up /sbin/ifconfig eth0 up # line maintained by pppoeconf
        provider internode

as you can see, I do have it named "ppp0".

Is the reason why the problem doesn't occur with other names that the $INTERFACES argument passed to /etc/init/network-interface.conf will always be "ppp0" and so if you have a name other than ppp0 in interfaces then it will ignore the unknown interface?

In my opinion, it is more consistent to configure ppp (especially pppoe) interfaces to always use the same pppX interface and also be configured as such in /etc/network/interfaces. That way if you "ifup ppp0" you know you're bringing up "ppp0". Running "ifup myprovider" or such and having the next available pppX interface come up isn't ideal for several reasons, the first being that it makes firewall configuration difficult if there is a chance that an interface will come up differently each time (imagine the case where you have to ppp interfaces and you want to firewall them differently).

Also, in your suggestion, you don't include "auto ppp0" which as far as I know is required to bring the interface up on boot and is how pppoe-conf will set up the interface if you request it to automatically come up on boot.
An alternative would be to have a post-up command as Teemu proposes, however this is not how pppoe-conf sets up the interface.

If the solution is to set up ppp interfaces as proposed by Teemu then I would suggest pppoe-conf needs to be changed to configure interfaces in the same way.