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

[Denis V. Lunev]

Daniel Lezcano wrote:
> 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 :)

hmm, by the way, will this work with macvlan?

also, I am dumb with multicasts :) who will clone the packet if there 
are more than one namespace listen and there are some listeners behind 
ethernet?

Regards,
	Den
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