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From: John Baldwin <jhb@freebsd.org>
To: Tim Kientzle <tim@kientzle.com>
Subject: Re: Testing SIOCADDMULTI?
Date: Fri, 1 Feb 2013 09:52:26 -0500
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On Friday, February 01, 2013 1:23:26 am Tim Kientzle wrote:
> >> Would still appreciate any suggestions for how to test these.
> > 
> > You can write a simple app to listen for UDP packets and have it join a 
> > multicast group and have another machine on the same network write a packet to 
> > the multicast group.
> 
> I tried this first, but  the test program worked fine even
> without ADDMULTI/DELMULTI support.   Watching
> tcpdump -e, it appears that IP4 multicast UDP uses
> broadcast at the Ethernet layer.

Were you running tcpdump?  You have to use tcpdump -p to avoid putting
the chip into promiscuous mode if so (promiscious causes the NIC to
receive all multicast regardless of the filters assuming that your
driver supports it correctly).

-- 
John Baldwin