Re: [gentoo-user] systemd DNS does not resolve 'local' addresses

[Alexander Puchmayr]

Thanks for the hint with mDNS, I wasn't aware of that. I'm using the '.local' 
domain for all my machines for more than 15 years now, longer than mDNS 
exists, but finally, after some research I found the problem, and actually it 
wasn't systemd per se, it was an update of /etc/nsswitch.conf. The old version 
had 

Hosts:          mymachines files myhostname dns

while the new version contains

Hosts:          mymachines resolve [!UNAVAIL=return] files myhostname dns

The extra "resolve [!UNAVAIL=return]" makes the difference. It loads the 
glibc's plugin nss-resolve [1], which then calls systemd-resolved [2], which 
interprets '.local' as mDNS address. The mDNS is not activated on purpose, it 
seems to be some default setting of the router which does not appear in the 
configuration pages (or I didn't find it).

Anyway, there are some ways to solve this:
1) create an entry in /etc/hosts on every machine. Contradicts the idea of 
DNS, but works
2) keep the old setting in nsswich.conf (without "resolve ...")
3) change my "own" TLD from .local to something else, like .home, as suggested 
in [3]

I think as long term strategy option 3 would be the best.

Regards
    Alex

[1] https://www.freedesktop.org/software/systemd/man/nss-resolve.html
[2] https://www.freedesktop.org/software/systemd/man/systemd-resolved.html#
[3] https://www.rfc-editor.org/rfc/rfc6762#appendix-G



Am Samstag, 2. April 2022, 23:48:06 CEST schrieb Rich Freeman:
> On Sat, Apr 2, 2022 at 5:22 PM Alexander Puchmayr
>
> <alexander.puchmayr@×××××××.at> wrote:
> > ## portage.local maps to 192.168.1.6
> > ## DNS-Server provided via DHCP is 192.168.1.1 (openwrt-router)
> >
> > buildhost-desktop ~ # ping portage.local
> > ping: portage.local: Temporary failure in name resolution
> >
> >            Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
>
> So, I haven't really used resolved much, but I see you have mDNS
> enabled.  Does the portage.local host broadcast itself using mDNS?  If
> it is running Gentoo then the answer is no unless you have it running
> avahi, which is usually not installed by default.  Many
> desktop-oriented linux distros provide avahi by default.
>
> A resolver that supports mDNS will not use DNS to resolve the .local
> TLD, in accordance with RFC 6762.
>
> If you intend to use .local for DNS and not mDNS then you probably do
> not want mDNS enabled.  You can either disable it for resolved
> globally by setting MulticastDNS=no in the [Resolve] section of
> /etc/systemd/resolved.conf, or by disabling it for a specific network
> in your network manager (the setting has the same name for
> systemd-networkd).
>
> This is one of those reasons why it is best to not use the .local TLD
> for DNS on your home network.  You can disable it on systemd-resolved,
> but some IoT device in your home might have it permanently enabled.
> It allows a form of name resolution to work without any DNS server as
> devices discover and broadcast on their own.