Dear Maintainer,

        With the release of Debian 13 "Trixie," mDNS resolution has been
disabled in systemd-resolved at a global level, apparently per bug
1098914. This can cause mDNS resolution to unexpectedly break in existing
setups. The changelog for the systemd-resolved package has documentation for
how to mask the new drop-in configuration file that causes this, but this
information was not included in the Debian 13 release notes.

As this is a breaking change that can cause local name resolution to fail
completely for users who are not using Avahi, I believe that this should be
included in the release notes, most likely in the "Issues to be aware of for
trixie" section.

Thank you,
Colin J Crawford

I agree, please send an MR / patch / text draft.

Best,
Chris

 Hi Chris,

Thanks for the quick reply. I'm not a developer, so I'm afraid I don't know
what an MR is or how to submit a patch. However, I've taken the text of the
relevant NEWS item from the systemd-resolved package as a starting point
for the text below. Please let me know if this draft is useful:

For trixie, mDNS support is now globally disabled by default in
systemd-resolved.
Users relying on mDNS who are not already using Avahi must mask the
associated drop-in configuration file before upgrading, or the machine may
become unreachable upon package upgrade. To mask the drop-in, do the
following as root:

      mkdir -p /etc/systemd/resolved.conf.d/
      touch /etc/systemd/resolved.conf.d/00-disable-mdns.conf

Best,
Colin

can we explain what mDNS is - or link to somewhere that does. i have
tried and failed to understand what it's purpose is before, without
success.

this bit is a bit confusing as it starts talking about one package and
then mentions avahi which is a different package. I suggest:


In trixie, systemd-resolved no longer enables mDNS support by default
to prevent conflicts with the avahi. mDNS is [xxxx]

To continue using systemd-resolved's mDNS support you can run the
following as root:

       mkdir -p /etc/systemd/resolved.conf.d/
       touch /etc/systemd/resolved.conf.d/00-disable-mdns.conf

It is recommended to do this before upgrading to ensure your system
remains reachable.

that link can just be https://en.wikipedia.org/wiki/Multicast_DNS

Chris

Hi all,

Thanks for the feedback. The point re: bringing up a second package is
well-taken. I originally added that because the root cause for why mDNS
support was disabled was to prefer Avahi, but I see how it can be confusing
here. I also understand the confusion about mDNS, so I tried adding a line
to illustrate the use cases where Debian admins may be affected. Hopefully
it's helpful without being overly complex.

How does the following look:

For trixie, support for [mDNS](https://en.wikipedia.org/wiki/Multicast_DNS)
in systemd-resolved has been disabled by default. This has been done to
prevent conflicts for users who have both systemd-resolved and avahi-daemon
installed.

If you rely on systemd-resolved for mDNS resolution of *.local DNS names,
or for answering mDNS queries from other hosts, you can mask the new
drop-in config file so that mDNS support in systemd-resolved remains
enabled. To do so, execute the following commands as root prior to
upgrading systemd-resolved:

       mkdir -p /etc/systemd/resolved.conf.d/
       touch /etc/systemd/resolved.conf.d/00-disable-mdns.conf

Best,
Colin