Installing the os-vnstat plugin tells you to put your default interface into it's configuration file before starting the service. So I looked at what 'vnstat --iflist' said and put pppoe0 as interface.
Then when I looked at the GUI to start the service, I could pick the interfaces, so I picked the WAN interface. There is no pppoe0 interface in that list. Now the configuration has a bunch of entries and still starts with 'Interface pppoe0'. I didn't find any other 'interface' lines in the file.
Is it supposed to be like this or is this now a misconfiguration?
Look at Interfaces > Assignments. Probably WAN is assigned to pppoe0. So they are one and the same. It's a bit unfortunate different subsystems and/or plugins use different identifiers. Since OPNsense introduced that WAN, LAN, ... abstraction layer above the device names IMHO all fuctions should explicitly use these only.
Well, it says Identifier wan for the WAN interface, and Device is pppoe0. That's already three different designations. It's not any better at other places but even worse because I have an interface titled Interfaces: [FORPPPOE] which turns into forPPPoE when I copy and paste the title --- while the interface is actually named forPPPoE. But that interface has an identifier of opt5 (what is that for??), and at the same time, the device is bce0. Why the hell does that have to be made so confusing?
And I'm just noticing that that interface is not enabled, which is probably bad because IIUC, it means that the interface settings are not being applied. But I don't remember why I didn't enable it and what exactly it is for. There must have been some reason that I didn't enable the interface when I set things up.
So pppoe0 is bce0. Should that interface be enabled or not? How is it even possible to use an interface that is disabled?
And how do I tell if vnstat is configured right?