netdev - Re: [PATCH] IPv4 Multicast: prevent reception of mcast frames from unjoined groups

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Date:	Fri, 11 Jul 2008 10:53:01 -0700
From:	David Stevens <dlstevens@...ibm.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	davem@...emloft.net, jmorris@...ei.org, kaber@...sh.net,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	netdev@...r.kernel.org, pekkas@...core.fi, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH] IPv4 Multicast: prevent reception of mcast frames from	unjoined
 groups

> currently in ip_mc_sf_allow we assume that we need to allow the frame if 
no
> match is found, but that has the affect of causing frames to be received 
for
> groups a socket hasn't joined.  I asked david aobut this specifically.

        You asked me about this? Or the other David? :-) I don't remember
seeing anything on this-- at least not recently.

        But in the sentence above, I think you missed the point of the
mail I sent before. Joining a group or not on a particular socket has
nothing at all to do with delivery of multicasts to the socket.

        Multicast addresses, like unicast addresses, are for the entire
machine, not just the socket that does the join. If anyone on the
machine has joined the group and your binding matches the packet, you
will receive a copy. That's intentional. If you don't join any groups
at all, but bind to INADDR_ANY, you will receive packets for the port
and protocol and any local unicast or multicast address (including
groups joined by any other process on the machine).

 +-DLS

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