Subject: Re: More sockets and link-local multicast questions
To: Andrew White <>
From: Nick Amato <>
List: tech-net
Date: 10/11/2001 12:27:56
On Thu, Oct 11, 2001 at 12:48:46PM +1000, Andrew White wrote:
> Nick Amato wrote:
> > Shouldn't you be using:
> > 
> >         setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,
> >             &mreq, sizeof(mreq));
> > 
> > after using bind(2) to attach to port 9001?
> Yep.  That (deep down) is how I implement this step:
> >> Socket sock_en0 joins mcast group on en0.  sock_en1 does
> >> the same on en1.
> It works as expected for a single socket joining a group on one or more
> interfaces.  The quirk is that if two different sockets join the same group
> on two different interfaces, they BOTH get the packets from either
> interface.  Which leads me to suspect a feature, but I can't tell whether it
> is in the implementation or my understanding.

I may be wrong, but you seem to be binding to instead
of simply port 9001, which is what you want.