wanderings/content/posts/local-name-resolution.md

+++ title = "Local Name Resolution in Arch" date = 2020-09-26 tags = ["admin"] +++ It's quite handy to be able to access clients connected at the same Access Point as you using their hostname. There are a few technologies to do that : mostly, Apple's Bonjour translates as mDNS in the Linux world, then there is Microsoft's NetBIOS protocol, that is provided by samba under Linux but not running as a default. And Microsoft also created the LLMNR resolution protocol, that ships with Windows starting at Vista (and with 7, 8 and 10).

To have local name resolution, your best option is probably systemd-resolved, since it does both mDNS and LLMNR. On the other side, avahi does mDNS and lets you advertise specific services on the network. If you're interested in this you might want to go for it ; check Archwiki's page on network configuration. Here we will deal with systemd-resolved.

The first thing to do is to disable avahi services, since they interfere with systemd-networkd. Go on and

# systemctl disable avahi-daemon

Now we need to check how you do domain resolution on your computer. Under Linux this is dependent on who manages /etc/resolv.conf. If it's a symlink to some NetworkManager folder, it's NetworkManager. If it's linked to some Systemd folder, then it's systemd-resolved. If it is NetworkManager and you want to switch to systemd-resolved and keep NetworkManager to manage connections, just do :

# ln -sf /run/systemd/resolve/stub-resolve.conf /etc/resolv.conf

It may also be a real file, meaning your computer uses static IP addresses for DNS servers. In this case you can do the same (back it up if you will).

Edit /etc/systemd/resolved.conf so that inside of the [Resolve] section, you have MulticastDNS=yes and LLMNR=yes. After that, you will have to

# systemctl enable systemd-resolved 

And reboot.

Now run resolvectl to see how it goes. If your network interface doesn't specifically allow MulticastDNS, you will have to tell the network manager to do it. If it's systemd-networkd, you will need to add the very same option in the relevant .network files in /etc/systemd/network/. If it's NetworkManager, no luck, you will have to update each and every connection by adding mdns=2 to the [connection] section of the connection definition in /etc/NetworkManager/system-connections.

If you changed anything, you might want to reboot again. Then try

$ resolvectl query SOMEHOSTNAME.local

SOMEHOSTNAME being the name of a device you know is connected. It should answer through mDNS. You may also try resolvectl query SOMEHOSTNAME, skipping the .local extension ; it should answer with LLMNR. Do note that Android devices don't seem to show up on the local network. But they do see declared neighbours ; I suspect they ship with LLMNR since they're only able to ping names without the .local extension.