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I have three systems running Fedora, named: dragon, wyvern and griffin. I am seeing strange mdns behaviour:

  • From dragon, I can ping and ssh to all of dragon.local, wyvern.local and griffin.local
  • From griffin , I can ping griffin.local only , both wyvern.local and dragon.local give me a DNS error ("name or service not known")
  • From wyvern, all three hostnames (including itself) give me "name or service not known"

All three boxes report a running avahi-daemon along these lines:

● avahi-daemon.service - Avahi mDNS/DNS-SD Stack
   Loaded: loaded (/usr/lib/systemd/system/avahi-daemon.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2018-06-20 20:33:34 AEST; 10min ago
 Main PID: 23500 (avahi-daemon)
   Status: "avahi-daemon 0.7 starting up."
    Tasks: 2 (limit: 4915)
   Memory: 1.4M
   CGroup: /system.slice/avahi-daemon.service
       ├─23500 avahi-daemon: running [dragon.local]
       └─23502 avahi-daemon: chroot helper

Jun 20 20:33:34 dragon avahi-daemon[23500]: New relevant interface virbr0.IPv4 for mDNS.
Jun 20 20:33:34 dragon avahi-daemon[23500]: Joining mDNS multicast group on interface wlp2s0.IPv6 with address fe80::cc1b:70dd:7f3:8ec1.
Jun 20 20:33:34 dragon avahi-daemon[23500]: New relevant interface wlp2s0.IPv6 for mDNS.
Jun 20 20:33:34 dragon avahi-daemon[23500]: Joining mDNS multicast group on interface wlp2s0.IPv4 with address 192.168.1.101.
Jun 20 20:33:34 dragon avahi-daemon[23500]: New relevant interface wlp2s0.IPv4 for mDNS.
Jun 20 20:33:34 dragon avahi-daemon[23500]: Network interface enumeration completed.
Jun 20 20:33:34 dragon avahi-daemon[23500]: Registering new address record for 192.168.124.1 on virbr0.IPv4.
Jun 20 20:33:34 dragon avahi-daemon[23500]: Registering new address record for fe80::cc1b:70dd:7f3:8ec1 on wlp2s0.*.
Jun 20 20:33:34 dragon avahi-daemon[23500]: Registering new address record for 192.168.1.101 on wlp2s0.IPv4.
Jun 20 20:33:35 dragon avahi-daemon[23500]: Server startup complete. Host name is dragon.local. Local service cookie is 1419905038.

I have restarted avahi-daemon on all three machines and seen no change in behaviour. All three have identical /etc/avahi/avahi-daemon.conf, as reported by diff, and which I haven't edited from Fedora default. It looks like this:

# This file is part of avahi.
#
# avahi is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as
# published by the Free Software Foundation; either version 2 of the
# License, or (at your option) any later version.
#
# 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
#add-service-cookie=no
#publish-addresses=yes
publish-hinfo=no
publish-workstation=no
#publish-domain=yes
#publish-dns-servers=192.168.50.1, 192.168.50.2
#publish-resolv-conf-dns-servers=yes
#publish-aaaa-on-ipv4=yes
#publish-a-on-ipv6=no

[reflector]
#enable-reflector=no
#reflect-ipv=no

[rlimits]
#rlimit-as=
#rlimit-core=0
#rlimit-data=8388608
#rlimit-fsize=0
#rlimit-nofile=768
#rlimit-stack=8388608
#rlimit-nproc=3

How can I get all three machines seeing each other, instead of these different combinations of working-ness?

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I've encountered Avahi behaviour like this on occasion, and in general restarting nscd and avahi-daemon on the host(s) having the issue is sufficient to restore mDNS name resolution.

service nscd restart
service avahi-daemon restart

Also, check that mDNS traffic (port 5353) isn't being blocked via a firewall on affected hosts.

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