On Tue, Mar 03, 2009 at 02:41:38PM -0500, Mario Charest wrote:
> Can't do multicast if a gateway isn't defined.   I don't know about the rules, but looking around on the web it seems 
some stack implementation (FreeBSD) don't need this, while other do.
> 
> May I suggest adding some documentation indicating this behavior.
> 

The behaviour is to use normal routing to determine which interface
to send on if the IP_MULTICAST_IF socket option isn't used. ie a
gateway isn't strictly necessary.  You can have a specific route to
the multicast address and even that isn't necessary if IP_MULTICAST_IF
is used.

-seanb