multicast socket behaviour on IPv4 and IPv6

[John Hay]

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 at icomtek.csir.co.za / jhay at FreeBSD.org