Multicast source address in recvfrom()

[Derek Tattersall]

In order to become familiar with multicast implementation using FreeBSD,
I found via Google a pair of test programs which multicast sent a simple
text message and received the text message.  I added some code to report
the source address, because none of the references that I looked at
specified the source IP address in the frame.

I ran the sender on A -current system, AMD64 vintage last week.  The
receiver was on a -current system I386 vintage last week.  TCPDUMP shows
the source IP address in the frame as (correctly) 192.168.0.15.  The
receiver reports the source IP address as 200.231.191.191.  I have also
run the same test with an OpenBSD 4.4 Release I386 system as the
receiver.  The openBSD system reports the sender as 192.168.0.15.  A
Fedora 10 system reported the source IP address as 0.0.0.0. 

Googling the RFCs and other information and referring to Comer's and
Stevens' books on TCPIP I can't determine what should be reported.  Does
anybody have clue for me?
-- 
Best regards,
Derek Tattersall
dlt at mebtel.net		dlt666 at yahoo.com		 dtatters at gmail.com