[Bug 447442] Re: avahi-daemon reports "Received response with invalid source port # on interface 'eth0.0'" all the time

[Kevin Stone]

In my case:

- Running several VMs under libvirt.
- Host and VMs have avahi and mDNS setup.
- VMs are in NAT'd network (192.168.122.0/24)
- /var/log/syslog contains

avahi-daemon[17165]: Received response from host 192.168.122.1 with
invalid source port 1049 on interface 'virbr0.0'

What's happening here is NAT translation.  This is because the
destination address for mDNS is 224.0.0.251 and the default iptables
setup is:

# iptables -t nat  -L POSTROUTING -n
Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
MASQUERADE  tcp  --  192.168.122.0/24    !192.168.122.0/24     masq ports: 1024-65535
MASQUERADE  udp  --  192.168.122.0/24    !192.168.122.0/24     masq ports: 1024-65535
MASQUERADE  all  --  192.168.122.0/24    !192.168.122.0/24    

One solution is to not masquerade mDNS packets:

iptables -t nat -I POSTROUTING 1 -m udp -p udp --sport 5353 --dport 5353
-j ACCEPT

A more general fix for multicast and broadcast would probably be better.

Here's tcpdump output from the virbr0 interface showing a mDNS request /
response:

13:19:55.618332 IP 192.168.122.114.5353 > 224.0.0.251.5353: 0 A (QM)? test.local. (32)
13:19:55.619205 IP 192.168.122.6.5353 > 224.0.0.251.5353: 0*- [0q] 1/0/0 (Cache flush) A 192.168.122.6 (42)

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https://bugs.launchpad.net/bugs/447442

Title:
  avahi-daemon reports "Received response with invalid source port # on
  interface 'eth0.0'" all the time

Status in “avahi” package in Ubuntu:
  Expired

Bug description:
  Both in my syslog and in daemon.log these messages are repeated again
  and again:

  Received response with invalid source port 21604 on interface 'eth0.0'
  Invalid response packet.
  Invalid legacy unicast query packet.

  The number of the port changes but the messages don't stop.

  Description:    Ubuntu 9.04
  Release:        9.04

  avahi-daemon:

    Installed: 0.6.23-4ubuntu4
    Candidate: 0.6.23-4ubuntu4
    version table:
   *** 0.6.23-4ubuntu4 0
          500 http://us.archive.ubuntu.com jaunty/main Packages
          100 /var/lib/dpkg/status

  ProblemType: Bug
  Architecture: amd64
  DistroRelease: Ubuntu 9.04
  NonfreeKernelModules: nvidia
  Package: avahi-daemon 0.6.23-4ubuntu4
  ProcEnviron:
   LANGUAGE=
   LANG=ca_ES.UTF-8
   SHELL=/bin/bash
  SourcePackage: avahi
  Uname: Linux 2.6.28-15-generic x86_64

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