Greetings! I'm having some trouble with name resolution in my home network and would love some help .
I'm a software engineer, so not completly computer-illiterate, but not a good network engineer, as it turns out.
Dramatis Personae:
- A Router "R"
- Some windows machines "W1","W2", ...
- A windows server "WS"
- An ubuntu VM "U" running on WS (Hyper-V), bridged into the same network everyone else is in
- No machine is set up as an dns server

My Problem:
IP V6 name resolution does not work as expected:
- All windows machines can ping -6 each other by name
- All windows machines can ping -4 the ubuntu vm by name
- No windows machine can ping -6 the ubuntu vm by name
- All windows machines can ping -6 the ubuntu vm by ip
- The ubuntu machine can ping (-4 and -6) most windows machines by name

TBH I'm not even sure how it is meant to work; from what I gathered, Netbios doesn't work for v6, so I don't even know why the windows machines can resolve each other.
Could any kind soul shed some light into my darkness ?

Assuming everything is on the same network, the Windows machines probably use mDNS. I figured this out recently when my Windows PC stubbornly ignored names of several Linux computers in the network. It turned out that the Linux boxes didn't respond to mDNS broadcasts.

The tool to find out is wireshark or its command line cousin tcpdump. Filter for port 5353, the mDNS port.

Thanks for the input. That may very well be:
systemd-resolve --status says MulticastDNS setting: no for the network adapter.

Now I'm struggling to get that to work; the vm uses netplan, and there doesn't seem to be a way to enable mDNS via netplan (at least not that I'd found one). How did you enable mDNS on your machine?

I DISabled it on Windows to force the PC to use my DNS server.

I did notice that Debian puts mdns4_minimal in /etc/nsswitch.conf. Perhaps there is an mdns6_minimal?

I got it to work by uninstalling netplan and switching to ifupdown.