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I have an application which has an mDNS server running on an ESP32 device. Its hostname is esp32-mdns.local. I can ping this hostname from Windows. However, it is not possible from my Ubuntu 22.04 system.

I have re-installed the avahi daemon and the utils again. When I do avahi-browse --all :

avahi-browse -all
+ wlp0s20f3 IPv6 192-168-178-1                                 Microsoft Windows Network local
+ wlp0s20f3 IPv6 fritz-box                                     Microsoft Windows Network local
+ wlp0s20f3 IPv4 192-168-178-1                                 Microsoft Windows Network local
+ wlp0s20f3 IPv4 fritz-box                                     Microsoft Windows Network local
+ wlp0s20f3 IPv6 ESP32-WebServer1                              Web Site             local
+ wlp0s20f3 IPv6 ESP32-WebServer                               Web Site             local
+ wlp0s20f3 IPv4 ESP32-WebServer1                              Web Site             local
+ wlp0s20f3 IPv4 ESP32-WebServer                               Web Site             local

Then avahi-resolve --name esp32-mdns.local :

avahi-resolve --name esp32-mdns.local
esp32-mdns.local    192.168.178.71

So, the name is getting resolved, but when I ping it :

ping esp32-mdns.local
ping: esp32-mdns.local: Name or service not known

I can ping the IP address directly, but not the hostname.

Here is my /etc/avahi/avahi-daemon.conf file. Am I missing something? Or what could be the issue? Thanks.

# avahi is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
# License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with avahi; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
# USA.

# See avahi-daemon.conf(5) for more information on this configuration
# file!

[server]
#host-name=foo
#domain-name=local
#browse-domains=0pointer.de, zeroconf.org
use-ipv4=yes
use-ipv6=yes
#allow-interfaces=eth0
#deny-interfaces=eth1
#check-response-ttl=no
#use-iff-running=no
#enable-dbus=yes
#disallow-other-stacks=no
#allow-point-to-point=no
#cache-entries-max=4096
#clients-max=4096
#objects-per-client-max=1024
#entries-per-entry-group-max=32
ratelimit-interval-usec=1000000
ratelimit-burst=1000

[wide-area]
enable-wide-area=yes

[publish]
#disable-publishing=no
#disable-user-service-publishing=no
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1 Answer 1

Reset to default
5

You need the libnss_mdns_minimal.so library installed (from the "libnss-mdns" package) and configured in /etc/nsswitch.conf so that the system would know to talk to Avahi-daemon for looking up hostnames.

Ubuntu's packaging will likely enable it automatically (or will enable the IPv4-only 'mdns4'; you can then edit nsswitch.conf to change to the dual-stack variant). If it is not automatically enabled, add

mdns_minimal [NOTFOUND=return]

to the hosts: line of /etc/nsswitch.conf, after the files module – but before dns or resolve. For example:

hosts: files mdns_minimal [NOTFOUND=return] dns

Many recent distributions instead have partial mDNS support as part of the resolve module from systemd-resolved; you can use that instead – although when I tried it the last time, it insisted on doing mDNS reverse queries for IPv6 causing every reverse lookup to take exceedingly long (not to mention it conflicting with avahi-daemon for inbound queries, so it is generally better to not mix the two).

(That is, if you have a program that relies on Avahi's DNS-SD service discovery API, then stick to Avahi. Whereas if you only need *.local hostname lookup and nothing else, then you can use either Avahi or systemd-resolved, but not both of them.)


In the case of systemd-resolved, the nsswitch.conf module is called resolve – the same module handles both DNS and mDNS – and it should be listed in the same position (but in this case you can omit dns, though it's common to include it as emergency fallback):

hosts: files resolve
 -or-
hosts: files resolve dns

resolved's mDNS support needs to be enabled either via /etc/systemd/resolved.conf or via individual systemd-networkd connection profiles as the MulticastDNS= option, or via Network­Manager connection profiles as the connection.mdns option. (You don't need to do any of this for Avahi.)

The combination of both Avahi for mDNS and systemd-resolved for regular DNS would look like:

hosts: files mdns_minimal [NOTFOUND=return] resolve
 -or-
hosts: files mdns_minimal [NOTFOUND=return] resolve dns
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  • Thank you for this. The only thing that worked for me was changing the line in /etc/nsswitch.conf to hosts: files mdns_minimal [NOTFOUND=return] dns and doing a reboot. I experimented with resolved also but no joy. I notice now that each ping response takes around 5 seconds, when pinging the hostname. Is there a way to make this faster? Commented Dec 17, 2024 at 10:39
  • That might be avahi being asked to resolve the address back to hostname (i.e. the same kind of problem as I mentioned systemd-resolved having) and waiting the whole 5 seconds for a reply that never arrives. Does mdns4_minimal work any better? If not, then fire up Wireshark and see what kind of requests it's sending... Commented Dec 17, 2024 at 10:45
  • Ah yes, mdns4_minimal does ion fact work much better. Now i'm confused though as mdns4_minimal was the default setting which didn't work initially, but now does. However, I did disable IPV6 in /etc/avahi/avahi-daemon.conf Commented Dec 17, 2024 at 11:14
  • I tried this and I also disabled IPv6, but it did not work. See also Commented Mar 13 at 20:51
  • Also see this question Commented Mar 13 at 22:34

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