netdev - Re: kernel module to list sockets with their multicast group joins and respective processes

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Date:	Mon, 16 Jul 2007 13:18:39 -0700
From:	David Stevens <dlstevens@...ibm.com>
To:	Steffen Maier <smaier@...rs.sourceforge.net>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	netdev-owner@...r.kernel.org,
	Steffen Maier <smaier@...rs.sourceforge.net>
Subject: Re: kernel module to list sockets with their multicast group joins and
 respective processes

> sockets that join different groups receive messages from the respective 
> other group (if they are only bound to the wildcard address). Obviously 
> this is handled differently in Linux for IPv4, where the socket matching 

> for incoming message is done solely on the 4-tuple of addresses and 
ports, 
> and IPv6, where the explicit socket joins are taken into account [1,2]. 

        These are not different in v4 vs v6. Group membership is 
per-interface,
delivery depends on the binding (for both v4 and v6), and this is the same
as BSD behavior since IP multicasting was invented.
        There are two levels of checks, and I think you're confusing them.
inet6_mc_check() is checking that somebody (*anybody*) has joined the
group on the receiving interface, before delivering the packet to IP.
Delivery to a particular socket depends on source filter settings, if
they are in use, and bindings (only). The socket has a list of joined
addresses to track source filters and to check for correct join/leave
(a socket can't leave a group it hasn't joined), but that list does not
determine delivery of a multicast packet to the socket when source 
filtering
is not in use.
 +-DLS



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