[Xen-users] Multicast message handling in VMs - For Upnp server, client or forward in a VM

[Benoit <benoit@xxxxxxxxxxx>]

Hi,

I am using xen 4.1.4 of the Debian Wheezy distribution, with network in bridge mode.
This is a brand new setup, with default setup options on the network point of view.

When a multicast message (here it was Upnp) is sent from the physical network, it can be seen in the eth1 and xenbr1 interfaces, but not in the interfaces inside the VMs.

I have a wlan0 interface on the physical machine that is bridged and seen as 'eth2' interface on a VM.
The wlan0 interface receives the broadcast messages as seen here:
~# tcpdump -ni wlan0Â net 239.0.0.0/8
tcpdump: WARNING: wlan0: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on wlan0, link-type EN10MB (Ethernet), capture size 65535 bytes
21:04:30.711511 IP 10.6.6.2.44990 > 239.255.255.250.1900: UDP, length 98
21:04:30.711527 IP 10.6.6.2.44990 > 239.255.255.250.1900: UDP, length 98
21:04:30.794978 IP 10.6.6.2.44990 > 239.255.255.250.1900: UDP, length 98
21:04:30.794992 IP 10.6.6.2.44990 > 239.255.255.250.1900: UDP, length 98

I added a rule to increment the ttl of the broadcast packet that is received on the physical interface:
Âiptables -t mangle -A PREROUTINGÂ -d 239.255.255.250/32 -i wlan0 -j TTL --ttl-inc 1

However, nothing is seen inside the VM:
Âtcpdump -ni eth2 net 239.0.0.0/8
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

The next step will be to propagate the packet on the other interfaces, but as soon I got nothing on the original bridged interface,...
In some tests I made a few months ago I got "dropped by interface" packets, but now on this new machine, I get nothing more.

So I am seeking for clues on this subject; I am sure that there should be some parameter to change in order to enable it, but so far I didn't find it...

Greetings all
Benoit

PS: I posted my previous test here: http://www.xenproject.org/help/questions-and-answers/multicast-message-handling-in-vms-for-upnp-server,-client-or-forward-in-a-vm.html and Russell Pavlicek suggest to put the subject on this mailing list.

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