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

Discussion:

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

Alexander Rössler

2017-07-12 16:49:25 UTC

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

Trent Lloyd

2017-07-22 07:57:40 UTC

Permalink

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

Post by Alexander RÃ¶ssler
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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Alexander Rössler

2017-07-24 07:27:16 UTC

Permalink

Hello Trent,

I have also built avahi 0.6.32 and 0.7 from sources and got the same
results on Debian Jessie. For me this looks like it has more to do with
the network stack and/or Linux kernel rather than Avahi itself. However,
I might be wrong here.

I will stick with the solution right now, to use Debian Stretch where
possible. For the other case I will use an additional device (e.g. a RPi
with PiVPN) for the OpenVPN connection.

--
Alexander

Post by Trent Lloyd
Hi Alexander,
This was a known bug that we fixed in 0.6.32
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