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Date:	Mon, 16 Jul 2007 13:18:39 -0700
From:	David Stevens <>
To:	Steffen Maier <>
	Steffen Maier <>
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 
> and IPv6, where the explicit socket joins are taken into account [1,2]. 

        These are not different in v4 vs v6. Group membership is 
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 
is not in use.

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