[Bug 1830531] Re: .local domain look ups do not trigger name publication

[Trent Lloyd]

The most likely cause for this is that you have packets outbound on port
5353 firewalled either locally or on your network device. When another
host pings the address, the responses are sent via multicast and Avahi
caches that response, and so can then use it without having to transmit
a packet.

Until someone else looks it up, the cache is empty and the query packet
is blocked, so no resolution happens.

To confirm this, other than checking and clearing both iptables and
nftables, you could try run tcpdump on your host and then on another
host to see if you can see the packet generated locally, and then if it
actually arrives on the network.


Note that once avahi has the address in its cache, when it queries the network for it, it includes that address in the packet as  "Known Answer" and the other host won't respond. So when testing this you are likely best to restart the local avahi daemon to clear it's cache before each test. You can see those "Known Answers" in the tcpdump though.

Best viewed with wireshark as it makes decoding the DNS part easy.

As a secondary test, I would suggest trying a different network adapter
(possibly wired instead of wireless, or vica-versa) - you can also get
these problems from weird drivers in some cases. Though usually broken
drivers prevent you from RECEIVING multicast, and so manifests that this
never works, so that seems unlikely in your case, but perhaps not
impossible.

As a third test try 'avahi-resolve-host-name' instead of ping, to
isolate if "avahi" / multicast is the issue, as opposed to the nss-mdns
layer.


Going to mark this Invalid for now, however, if you can show from the packet dumps that the query packets are really not being sent at all even locally feel free to set the status back to New for further investigation. 

** Changed in: avahi (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1830531

Title:
  .local domain look ups do not trigger name publication

Status in avahi package in Ubuntu:
  Incomplete

Bug description:
  On my local network I find that with 18.04 network name lookups using
  .local domains no not work unless stimulated by a non-18.04 machine
  first. This is observed for ssh, http, https and ping, but probably
  not limited to those.

  To demonstrate this here is a ping example.

  ~ $ ping pi.local
  ping: pi.local: Name or service not known
  ~ $ ping pi.local
  ping: pi.local: Name or service not known

  # At this point head to another machine running 16.04.6 and execute ping pi.local.
  # This is immediately successful. Then head back to the 18.04 machine.

  ~ $ ping pi.local
  PING pi.local (192.168.108.28) 56(84) bytes of data.
  64 bytes from pi.this.domain (192.168.108.28): icmp_seq=1 ttl=64 time=4.43 ms
  64 bytes from pi.this.domain (192.168.108.28): icmp_seq=2 ttl=64 time=5.64 ms
  64 bytes from pi.this.domain (192.168.108.28): icmp_seq=3 ttl=64 time=5.98 ms
  64 bytes from pi.this.domain (192.168.108.28): icmp_seq=4 ttl=64 time=5.84 ms
  ^C
  --- pi.local ping statistics ---
  4 packets transmitted, 4 received, 0% packet loss, time 7018ms
  rtt min/avg/max/mdev = 4.435/5.476/5.986/0.613 ms

  After a couple of minutes, the name resolution fails again, but can be
  brought back again by following the procedure above.

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: avahi-daemon 0.7-3.1ubuntu1.2
  ProcVersionSignature: Ubuntu 4.18.0-20.21~18.04.1-generic 4.18.20
  Uname: Linux 4.18.0-20-generic x86_64
  NonfreeKernelModules: nvidia_modeset nvidia
  ApportVersion: 2.20.9-0ubuntu7.6
  Architecture: amd64
  CurrentDesktop: ubuntu:GNOME
  Date: Sun May 26 20:04:58 2019
  InstallationDate: Installed on 2019-05-22 (4 days ago)
  InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
  SourcePackage: avahi
  UpgradeStatus: No upgrade log present (probably fresh install)

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