[Devel] Re: [patch 0/2][NETNS49][IPV4][IGMP] activate multicast per namespace

[Daniel Lezcano]

Eric W. Biederman wrote:
> Daniel Lezcano <dlezcano at fr.ibm.com> writes:
> 
>> The following patches activate the multicast sockets for
>> the namespaces. The results is a traffic going through 
>> differents namespaces. So if there are several applications
>> listenning to the same multicast group/port, running in
>> different namespaces, they will receive multicast packets.
> 
> At a first glance this feels wrong.  I don't see any per
> namespace filtering of multicast traffic.  Unless the
> multicast traffic is routed/bridged between namespaces
> it should be possible to send multicast traffic in one
> namespace and listen for that same traffic in another
> namespace and not get it.

The described behavior is the case were the namespaces are communicating 
via veth like:

eth0
  |
  |        ------------- nsA
veth0 <--|--> veth1    |
  |        -------------
  |
  |        -------------nsB
veth2 <--|--> veth3    |
           -------------


If an application is listening in nsA and nsB. And if in nsA, an 
application sends multicast traffic, both will receive the packets 
because they are routed by the pair device.
As you said this is the correct behavior, if we have two machines hostA 
and hostB in the same network and both are listening on the multicast 
address and if an application on hostA send multicast packets, both 
should receive the multicast packets.
If the traffic is not routed, multicast will not pass through the 
namespaces.

The description I gave in the patchset introduction was to describe such 
behavior which is, IMHO, important for inter-container communication.
Perhaps, I should have not gave this description which seems to sow 
confusion in mind, sorry for that.

Anyway, I hope the patchset is ok :)


Regards.

	Daniel




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