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

[Eric W. Biederman]

Daniel Lezcano <dlezcano at fr.ibm.com> writes:

> 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 :)

Sounds more reasonable.  I didn't see the second patch when I replied
which was part of the reason I was worried.  So at least at first glance
that patchset looks reasonable.

Thanks,
Eric
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