Re: Multicast IP packet routed between 2 ports nic on the same host

[Eric Dumazet <eric.dumazet@gmail.com>]

Le lundi 06 juin 2011 à 13:40 +0000, BONNEAU Guy a écrit :
> I am trying to receive multicast data packets from a multicast router
> to my Linux Ubuntu Desktop Workstation using kernel 2.6.35. The Linux
> Desktop has an Intel 82576 dual NIC adapter. Each NIC is configured to
> receive IP data from 2 different subnet. One is from 172.30.8.xx and
> another one from 10.0.xx.xx. Multicast IP data can only be received
> from 172.30.8.xx since there is no multicast source on subnet
> 10.0.xx.xx and IT that administrates the subnet 10.0.xx.xx disabled
> multicast capability of the switches and routers sitting on that
> subnet. The subnet 172.30.8.xx has multicast source broadcasting on
> multicast group 239.255.200.200:8000. 
> 

Hi

Not clear if eth0 and eth1 are on both networks ?

Please send us

ip link
ip addr
ip ro

Thanks

> I am using the application mreceived (version 2.2) from :
> http://www.cs.virginia.edu/~mngroup/software/ to test the network
> multicast set-up and capability of my Ubuntu Desktop Workstation. 
> 
> I open a first console and I use mreceive to join multicast group
> 239.255.200.200:8000 to receive multicast data from subnet 10.0.xx.xx
> using the console command : ./mreceive -g 239.255.200.200 -p 8000 -i
> 10.0.9.164 to the eth0 adapter of my workstation. The application is
> idle and no multicast data is received. This is the expected
> behaviour.
> 
> I open a second console and I use mreceive to join the same multicast
> group 239.255.200.200:8000 to receive multicast data from subnet
> 172.30.8.xx using the console command : ./mreceive -g 239.255.200.200
> -p 8000 -i 172.30.8.31 to the eth1 adapter of my workstation. The
> application starts to receive multicast data and advertises the data
> received. This is also the expected behaviour.
> 
> Now this is where the problem begins. As soon as the multicast data
> begin to be received on the eth1 adapter the first console begins to
> advertise multicast data received on eth0 adapter. I am well aware
> that the Linux kernel implements a multicast level 2 routing
> capability. Thus at first glance this seems to be the expected
> behaviour. However... I have forwarding disabled as well as
> mc_forwarding disabled and rp_filter is enabled for both adapters.
> Thus I don't expect the kernel to forward the multicast data from eth1
> to eth0. 
> 
> I have recompiled the kernel with IP Multicast Routing disabled and
> got the same behavior. I also tried kernel 2.6.38 and had the same
> issue.
> 
> At this point I am inclined to think that the kernel multicast routing
> might have an issue? I might have missing a network configuration
> setting but at this point I am baffled.  I checked the kernel bugbase
> with the multicast tagging and couldn't find a filled bug regarding
> this matter. The only remaining options for me are to fill a bug and
> trace the kernel code (ipmr.c) to understand what going on. Can
> someone shade light on this? Is this an expected behavior or an issue?
> 
> Thanks
> GB 
>