[avahi] avahi-daemon uses wrong IP address for P2P tun interface on Debian < Stretch

[Trent Lloyd]

Hi Alexander,

This was a known bug that we fixed in 0.6.32

Relevant commit is here:
https://github.com/lathiat/avahi/commit/8b3f8e4a63f09d9c9f86dfaddb0681cc612a79eb#diff-8433b64538fa06175a391bc55285b287

I'm not sure if there's a Debian process to get these fixes pushed into 
the older releases or not, perhaps if there is you can check the process 
and perhaps file a bug for that?

- Trent

On 13/07/17 00:49, Alexander Rössler wrote:
> I have discovered a problem with avahi-daemon and the peer to peer interfaces
> tun0 created by OpenVPN. I tested on Debian Wheezy, Jessie and Stretch
> and can confirm that the problem exists at least on Wheezy and Jessie.
>
> $ ip a
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
>      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>      inet 127.0.0.1/8 scope host lo
>      inet6 ::1/128 scope host
>         valid_lft forever preferred_lft forever
> 2: eth0: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
>      link/ether 78:a5:04:cc:90:ee brd ff:ff:ff:ff:ff:ff
>      inet 10.0.0.5/24 brd 10.0.0.255 scope global eth0
>      inet6 fe80::7aa5:4ff:fecc:90ee/64 scope link
>         valid_lft forever preferred_lft forever
> 9: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
>      link/none
>      inet 10.10.10.161 peer 10.10.10.162/32 scope global tun0
>
> $ sudo service avahi-daemon status
> ● avahi-daemon.service - Avahi mDNS/DNS-SD Stack
>     Loaded: loaded (/lib/systemd/system/avahi-daemon.service; enabled; vendor preset: enabled)
>     Active: active (running) since Wed 2017-07-12 16:22:35 UTC; 21min ago
>   Main PID: 9623 (avahi-daemon)
>     Status: "avahi-daemon 0.6.31 starting up."
>     CGroup: /system.slice/avahi-daemon.service
>             ├─9623 avahi-daemon: running [beaglebone.local
>             └─9624 avahi-daemon: chroot helpe
>
> Jul 12 16:28:28 beaglebone avahi-daemon[9623]: Joining mDNS multicast group on interface tun0.IPv4 with address 10.10.10.158.
> Jul 12 16:28:28 beaglebone avahi-daemon[9623]: New relevant interface tun0.IPv4 for mDNS.
> Jul 12 16:28:28 beaglebone avahi-daemon[9623]: Registering new address record for 10.10.10.158 on tun0.IPv4.
> Jul 12 16:28:38 beaglebone avahi-daemon[9623]: Withdrawing address record for 10.10.10.158 on tun0.
> Jul 12 16:28:38 beaglebone avahi-daemon[9623]: Leaving mDNS multicast group on interface tun0.IPv4 with address 10.10.10.158.
> Jul 12 16:28:38 beaglebone avahi-daemon[9623]: Interface tun0.IPv4 no longer relevant for mDNS.
> Jul 12 16:28:38 beaglebone avahi-daemon[9623]: Withdrawing workstation service for tun0.
> Jul 12 16:43:46 beaglebone avahi-daemon[9623]: Joining mDNS multicast group on interface tun0.IPv4 with address 10.10.10.162.
> Jul 12 16:43:46 beaglebone avahi-daemon[9623]: New relevant interface tun0.IPv4 for mDNS.
> Jul 12 16:43:46 beaglebone avahi-daemon[9623]: Registering new address record for 10.10.10.162 on tun0.IPv4.
>
> As you can see avahi-daemon registers to the peer address instead of the
> local address of the tun0 interfaces. Therefore, service discovery using
> unicast DNS packages does not work. The same setup works fine with
> Debian Stretch. I also tried the latest master on Debian Jessie and got
> the same results.
>
> Is there a way to force the IP address avahi-daemon uses for a given
> interface? Or does someone know another way to "unconfuse" avahi-daemon
> with this kind of setup?
>
> Btw. on wheezy I noticed that avahi first joins the correct mutlicast
> group with the IP address 10.10.10.161 and then disconnects and joins
> the wrong multicast address with IP address 10.10.10.162.
>
> Thanks and best regards,
> Alexander
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