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I have a VirtualBox with Debian 3.2.51 guest (vcube) on Ubuntu 13.10 host (ring) with a bridged network adapter. vcube has an Avahi service configured with a vcube.local name.

I can see/ping/access vcube.local by Bonjour name, but cannot see it from other hosts on the (wireless) network. At the same time, there's a lot of wire- and wirelessly connected hosts on the network that we happily see in avahi-discover or other Zeroconf clients.

I have no access to our router and cannot know if it's blocking mDNS or not.

In iptables -vnL output, there are no entries, policies are ACCEPT and byte counts are 0 both on vcube and ring.

The same discovery problem happens for a copy of vcube VirtualBox on a totally different network.

Sometimes it just starts working - we suspect this happens when we start ANOTHER copy of vcube on a different host.

How do I diagnose or fix this problem?

Victor Sergienko
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  • Are you able to ping the guest Debian OS by ip address from one of wireless devices? – Tim Jan 01 '14 at 02:22
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    Something is blocking multicast UDP. You should run a packet dump (I suggest `tshark`, but `tcpdump` will do) in various places: 1. inside vcube on (`-i`) its virtual network adapter; 2. on ring, on the virtual adapter bridged to vcube; 3. on ring, on the physical network adapter (eth0 or such); 4. on another host on the network. You are looking for the mDNS packets, to see where they are blocked. To recap: `sudo tcpdump -i eth0 'host 224.0.0.251 and port 5353'` replacing eth0 as appropriate. – Tobia Jan 02 '14 at 18:31
  • @Tim, yes, it responds to IP address, but not to avahi name. – Victor Sergienko Jan 04 '14 at 09:28
  • Thanks @Tobia, will try it tomorrow. I believe this must be the answer. – Victor Sergienko Jan 04 '14 at 09:29

2 Answers2

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I am not sure I understood your problem very well but I know bridge interfaces and UDP multicasst/boradcast can trigger some eratics behaviours. To work it around you may want to disable multicast snooping on the bridge interface:

echo 0 > /sys/devices/virtual/net/$IFACE/bridge/multicast_snooping

Though I don't know virtualbox well enough to to be sure it uses proper linux bridge utils to setup bridge adpaters...

alxgomz
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  • Looks like this indeed is a problam with multicast (IGMP) snooping in Linux (http://troglobit.com/blog/2013/07/09/multicast-howto/). I wasn't able to fix it with this recipe http://shlrm.org/blog/2013/04/18/multicast-snooping-is-bad/ , because I don't have a `bridge` dir in my `/sys/devices/virtual/net/vboxnet0/` on Linux 3.11.0-15. Stuck again, but at least now I know what it is. – Victor Sergienko Jan 06 '14 at 16:24
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I could NOT get to work these two guys:

  • avahi-daemon - The Avahi mDNS/DNS-SD daemon
  • iptables — administration tool for IPv4 packet filtering and NAT

I even followed following: Well known TCP and UDP ports used by Apple software products. MAYBE you'll have better luck then me)

alexus
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  • It used t work for me, without `iptables` though. Just stopped at some point. Reproduced twice in a totally different environments, only Virtualbox image was the same. – Victor Sergienko Jan 04 '14 at 09:24