netdev - Re: PATCH: Multicast: Filter multicast traffic per socket mc

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Date:	Thu, 16 Apr 2009 15:22:49 -0700
From:	David Stevens <dlstevens@...ibm.com>
To:	Vlad Yasevich <vladislav.yasevich@...com>
Cc:	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	netdev-owner@...r.kernel.org, Neil Horman <nhorman@...driver.com>
Subject: Re: PATCH: Multicast: Filter multicast traffic per socket mc_list

Vlad Yasevich wrote on 04/16/2009 02:19:14 PM:

> What seems to be happening though, is that there is an expectation that
> this behavior would change with advent of IGMPv3, which adds the 
additional
> filtering text.  Now, we could point out that there is no normative text
> that requires this filtering on groups, only on sources, but the 
expectation
> is still there.

        I have no such expectation. :-) The additional filters are 
(already)
applied per-socket, but existing apps not using source filters behave as
they did before IGMPv3. That's what I'd expect.
        The RFC you quoted for SSM applies to only the SSM address space,
mentions this behavior explicitly as the norm for outside of that space,
and Linux doesn't support that RFC. If it did, it would include an
address range check as part of it.

> I wonder how BSD and Solaris got away with it?  They both filter on 
multicast
> groups and source addresses.  This is not meant as rhetorical or 
provocative,
> just genuinely wondering.

        I think in practice, it doesn't come up much. That's why people
seem so surprised to learn it works this way, and not the way they
thought it did after using it, sometimes for years. But the documentation
doesn't say a join limits what you receive on a socket, or that it
has to be the same socket you're doing I/O on; people simply assume it.

                                                                +-DLS

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