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Date: Sat, 13 Nov 2004 14:19:18 +0200
From: John Hay <jhay@icomtek.csir.co.za>
To: freebsd-net@freebsd.org
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Subject: multicast socket behaviour on IPv4 and IPv6
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Hi Guys,

While debugging a misbehaving program, I found that on FreeBSD, if you
bind() a udp socket to a multicast address, so that you can receive on
it, and you then mistakenly use it to send, the behaviour between IPv4
and IPv6 differ. On IPv6 you get a error EOPNOTSUPP, which is
understandable, but on IPv4 the packet is actually send with the source
address being the multicast address. Is that the expected behaviour?

Looking through the code, I see that in IPv6 there is a lot of sanity
checks in the output routine, but very little to check the source
address in the IPv4 output routine.

John
-- 
John Hay -- John.Hay@icomtek.csir.co.za / jhay@FreeBSD.org