resolved vs. DNS servers listening on Linux dummy interfaces

[Peter Mattern <pmattern@xxxxxxxx>]

Hello.

Apparently resolved is ignoring DNS servers which are listening on Linux 
dummy interfaces.

When directive "Domains" in section [Network] of the dummy interface's 
*.network unit is set as usual, "resolvectl status <dummy interface>" 
still shows "Current Scopes: none" and "resolvectl query <DNS NAME 
handled by the server>" fails.
Seen on up to date Arch Linux with the network setup handled completely 
by networkd/resolved. As DNS servers dnsmasq and Knot were tested, both 
were working as expected on that interface type according to drill 
queries pointing to the interface's IP.

Use case is a router on which I'd like to use Knot to serve a subdomain 
used in the LAN only while leaving the upstream interface to the ISP's 
DNS server and having resolved's stub resolver provide DNS to the LAN on 
the downstream interface.
Tbh. I'm not even sure whether Linux dummy interfaces are meant for a 
purpose like this. But given that both servers (as well as nginx, btw.) 
seem to work well on the interface I'd actually expect resolved to pick 
them.

So can anybody tell me what's the matter here, in particular whether 
this may be a problem of resolved or whether there's a way to get this 
working somehow?

Regards

Peter Mattern